Add phash generation and dupe checking (#1158)

vendor/github.com/corona10/goimagehash/.gitignore

@@ -0,0 +1,14 @@
+# Binaries for programs and plugins
+*.exe
+*.dll
+*.so
+*.dylib
+
+# Test binary, build with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+
+# Project-local glide cache, RE: https://github.com/Masterminds/glide/issues/736
+.glide/

vendor/github.com/corona10/goimagehash/AUTHORS.md

@@ -0,0 +1,5 @@
+## AUTHORS
+- [Dominik Honnef](https://github.com/dominikh) dominik@honnef.co
+- [Dong-hee Na](https://github.com/corona10/) donghee.na92@gmail.com
+- [Gustavo Brunoro](https://github.com/brunoro/) git@hitnail.net
+- [Alex Higashino](https://github.com/TokyoWolFrog/) TokyoWolFrog@mayxyou.com

vendor/github.com/corona10/goimagehash/CODEOWNERS

@@ -0,0 +1 @@
+*.go @corona10

vendor/github.com/corona10/goimagehash/Gopkg.lock

@@ -0,0 +1,17 @@
+# This file is autogenerated, do not edit; changes may be undone by the next 'dep ensure'.
+
+
+[[projects]]
+  branch = "master"
+  digest = "1:34534b73e925d20cc72cf202f8b482fdcbe3a1b113e19375f31aadabd0f0f97d"
+  name = "github.com/nfnt/resize"
+  packages = ["."]
+  pruneopts = "UT"
+  revision = "83c6a9932646f83e3267f353373d47347b6036b2"
+
+[solve-meta]
+  analyzer-name = "dep"
+  analyzer-version = 1
+  input-imports = ["github.com/nfnt/resize"]
+  solver-name = "gps-cdcl"
+  solver-version = 1

vendor/github.com/corona10/goimagehash/Gopkg.toml

@@ -0,0 +1,34 @@
+# Gopkg.toml example
+#
+# Refer to https://golang.github.io/dep/docs/Gopkg.toml.html
+# for detailed Gopkg.toml documentation.
+#
+# required = ["github.com/user/thing/cmd/thing"]
+# ignored = ["github.com/user/project/pkgX", "bitbucket.org/user/project/pkgA/pkgY"]
+#
+# [[constraint]]
+#   name = "github.com/user/project"
+#   version = "1.0.0"
+#
+# [[constraint]]
+#   name = "github.com/user/project2"
+#   branch = "dev"
+#   source = "github.com/myfork/project2"
+#
+# [[override]]
+#   name = "github.com/x/y"
+#   version = "2.4.0"
+#
+# [prune]
+#   non-go = false
+#   go-tests = true
+#   unused-packages = true
+
+
+[[constraint]]
+  branch = "master"
+  name = "github.com/nfnt/resize"
+
+[prune]
+  go-tests = true
+  unused-packages = true

vendor/github.com/corona10/goimagehash/LICENSE

@@ -0,0 +1,25 @@
+BSD 2-Clause License
+
+Copyright (c) 2017, Dong-hee Na
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright notice, this
+  list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright notice,
+  this list of conditions and the following disclaimer in the documentation
+  and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

vendor/github.com/corona10/goimagehash/README.md

@@ -0,0 +1,93 @@
+![GitHub Action](https://github.com/corona10/goimagehash/workflows/goimagehash%20workflow/badge.svg)
+[![GoDoc](https://godoc.org/github.com/corona10/goimagehash?status.svg)](https://godoc.org/github.com/corona10/goimagehash)
+[![Go Report Card](https://goreportcard.com/badge/github.com/corona10/goimagehash)](https://goreportcard.com/report/github.com/corona10/goimagehash)
+
+# goimagehash
+> Inspired by [imagehash](https://github.com/JohannesBuchner/imagehash)
+
+A image hashing library written in Go. ImageHash supports:
+* [Average hashing](http://www.hackerfactor.com/blog/index.php?/archives/432-Looks-Like-It.html)
+* [Difference hashing](http://www.hackerfactor.com/blog/index.php?/archives/529-Kind-of-Like-That.html)
+* [Perception hashing](http://www.hackerfactor.com/blog/index.php?/archives/432-Looks-Like-It.html)
+* [Wavelet hashing](https://fullstackml.com/wavelet-image-hash-in-python-3504fdd282b5) [TODO]
+
+## Installation
+```
+go get github.com/corona10/goimagehash
+```
+## Special thanks to
+* [Haeun Kim](https://github.com/haeungun/)
+
+## Usage
+
+``` Go
+func main() {
+        file1, _ := os.Open("sample1.jpg")
+        file2, _ := os.Open("sample2.jpg")
+        defer file1.Close()
+        defer file2.Close()
+
+        img1, _ := jpeg.Decode(file1)
+        img2, _ := jpeg.Decode(file2)
+        hash1, _ := goimagehash.AverageHash(img1)
+        hash2, _ := goimagehash.AverageHash(img2)
+        distance, _ := hash1.Distance(hash2)
+        fmt.Printf("Distance between images: %v\n", distance)
+
+        hash1, _ = goimagehash.DifferenceHash(img1)
+        hash2, _ = goimagehash.DifferenceHash(img2)
+        distance, _ = hash1.Distance(hash2)
+        fmt.Printf("Distance between images: %v\n", distance)
+        width, height := 8, 8
+        hash3, _ = goimagehash.ExtAverageHash(img1, width, height)
+        hash4, _ = goimagehash.ExtAverageHash(img2, width, height)
+        distance, _ = hash3.Distance(hash4)
+        fmt.Printf("Distance between images: %v\n", distance)
+        fmt.Printf("hash3 bit size: %v\n", hash3.Bits())
+        fmt.Printf("hash4 bit size: %v\n", hash4.Bits())
+
+        var b bytes.Buffer
+        foo := bufio.NewWriter(&b)
+        _ = hash4.Dump(foo)
+        foo.Flush()
+        bar := bufio.NewReader(&b)
+        hash5, _ := goimagehash.LoadExtImageHash(bar)
+}
+```
+
+## Release Note
+### v1.0.3
+- Add workflow for GithubAction
+- Fix typo on the GoDoc for LoadImageHash
+
+### v1.0.2
+- go.mod is now used for install goimagehash
+
+### v1.0.1
+- Perception/ExtPerception hash creation times are reduced
+
+### v1.0.0
+**IMPORTANT**
+goimagehash v1.0.0 does not have compatible with the before version for future features
+
+- More flexible extended hash APIs are provided ([ExtAverageHash](https://godoc.org/github.com/corona10/goimagehash#ExtAverageHash), [ExtPerceptionHash](https://godoc.org/github.com/corona10/goimagehash#ExtPerceptionHash), [ExtDifferenceHash](https://godoc.org/github.com/corona10/goimagehash#ExtDifferenceHash))
+- New serialization APIs are provided([ImageHash.Dump](https://godoc.org/github.com/corona10/goimagehash#ImageHash.Dump), [ExtImageHash.Dump](https://godoc.org/github.com/corona10/goimagehash#ExtImageHash.Dump))
+- [ExtImageHashFromString](https://godoc.org/github.com/corona10/goimagehash#ExtImageHashFromString), [ImageHashFromString](https://godoc.org/github.com/corona10/goimagehash#ImageHashFromString) is deprecated and will be removed
+- New deserialization APIs are provided([LoadImageHash](https://godoc.org/github.com/corona10/goimagehash#LoadImageHash), [LoadExtImageHash](https://godoc.org/github.com/corona10/goimagehash#LoadExtImageHash))
+- Bits APIs are provided to measure actual bit size of hash
+
+### v0.3.0
+- Support DifferenceHashExtend.
+- Support AverageHashExtend.
+- Support PerceptionHashExtend by @TokyoWolFrog.
+
+### v0.2.0
+- Perception Hash is updated.
+- Fix a critical bug of finding median value.
+
+### v0.1.0
+- Support Average hashing
+- Support Difference hashing
+- Support Perception hashing
+- Use bits.OnesCount64 for computing Hamming distance by @dominikh
+- Support hex serialization methods to ImageHash by @brunoro

vendor/github.com/corona10/goimagehash/doc.go

@@ -0,0 +1,5 @@
+// Copyright 2017 The goimagehash Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package goimagehash

vendor/github.com/corona10/goimagehash/etcs/doc.go

@@ -0,0 +1,5 @@
+// Copyright 2017 The goimagehash Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package etcs

vendor/github.com/corona10/goimagehash/etcs/utils.go

@@ -0,0 +1,61 @@
+// Copyright 2017 The goimagehash Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package etcs
+
+// MeanOfPixels function returns a mean of pixels.
+func MeanOfPixels(pixels []float64) float64 {
+	m := 0.0
+	lens := len(pixels)
+	if lens == 0 {
+		return 0
+	}
+
+	for _, p := range pixels {
+		m += p
+	}
+
+	return m / float64(lens)
+}
+
+// MedianOfPixels function returns a median value of pixels.
+// It uses quick selection algorithm.
+func MedianOfPixels(pixels []float64) float64 {
+	tmp := make([]float64, len(pixels))
+	copy(tmp, pixels)
+	l := len(tmp)
+	pos := l / 2
+	v := quickSelectMedian(tmp, 0, l-1, pos)
+	return v
+}
+
+func quickSelectMedian(sequence []float64, low int, hi int, k int) float64 {
+	if low == hi {
+		return sequence[k]
+	}
+
+	for low < hi {
+		pivot := low/2 + hi/2
+		pivotValue := sequence[pivot]
+		storeIdx := low
+		sequence[pivot], sequence[hi] = sequence[hi], sequence[pivot]
+		for i := low; i < hi; i++ {
+			if sequence[i] < pivotValue {
+				sequence[storeIdx], sequence[i] = sequence[i], sequence[storeIdx]
+				storeIdx++
+			}
+		}
+		sequence[hi], sequence[storeIdx] = sequence[storeIdx], sequence[hi]
+		if k <= storeIdx {
+			hi = storeIdx
+		} else {
+			low = storeIdx + 1
+		}
+	}
+
+	if len(sequence)%2 == 0 {
+		return sequence[k-1]/2 + sequence[k]/2
+	}
+	return sequence[k]
+}

vendor/github.com/corona10/goimagehash/go.mod

@@ -0,0 +1,3 @@
+module github.com/corona10/goimagehash
+
+require github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646

vendor/github.com/corona10/goimagehash/go.sum

@@ -0,0 +1,2 @@
+github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646 h1:zYyBkD/k9seD2A7fsi6Oo2LfFZAehjjQMERAvZLEDnQ=
+github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646/go.mod h1:jpp1/29i3P1S/RLdc7JQKbRpFeM1dOBd8T9ki5s+AY8=

vendor/github.com/corona10/goimagehash/hashcompute.go

@@ -0,0 +1,183 @@
+// Copyright 2017 The goimagehash Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package goimagehash
+
+import (
+	"errors"
+	"image"
+
+	"github.com/corona10/goimagehash/etcs"
+	"github.com/corona10/goimagehash/transforms"
+	"github.com/nfnt/resize"
+)
+
+// AverageHash fuction returns a hash computation of average hash.
+// Implementation follows
+// http://www.hackerfactor.com/blog/index.php?/archives/432-Looks-Like-It.html
+func AverageHash(img image.Image) (*ImageHash, error) {
+	if img == nil {
+		return nil, errors.New("Image object can not be nil")
+	}
+
+	// Create 64bits hash.
+	ahash := NewImageHash(0, AHash)
+	resized := resize.Resize(8, 8, img, resize.Bilinear)
+	pixels := transforms.Rgb2Gray(resized)
+	flattens := transforms.FlattenPixels(pixels, 8, 8)
+	avg := etcs.MeanOfPixels(flattens)
+
+	for idx, p := range flattens {
+		if p > avg {
+			ahash.leftShiftSet(len(flattens) - idx - 1)
+		}
+	}
+
+	return ahash, nil
+}
+
+// DifferenceHash function returns a hash computation of difference hash.
+// Implementation follows
+// http://www.hackerfactor.com/blog/?/archives/529-Kind-of-Like-That.html
+func DifferenceHash(img image.Image) (*ImageHash, error) {
+	if img == nil {
+		return nil, errors.New("Image object can not be nil")
+	}
+
+	dhash := NewImageHash(0, DHash)
+	resized := resize.Resize(9, 8, img, resize.Bilinear)
+	pixels := transforms.Rgb2Gray(resized)
+	idx := 0
+	for i := 0; i < len(pixels); i++ {
+		for j := 0; j < len(pixels[i])-1; j++ {
+			if pixels[i][j] < pixels[i][j+1] {
+				dhash.leftShiftSet(64 - idx - 1)
+			}
+			idx++
+		}
+	}
+
+	return dhash, nil
+}
+
+// PerceptionHash function returns a hash computation of phash.
+// Implementation follows
+// http://www.hackerfactor.com/blog/index.php?/archives/432-Looks-Like-It.html
+func PerceptionHash(img image.Image) (*ImageHash, error) {
+	if img == nil {
+		return nil, errors.New("Image object can not be nil")
+	}
+
+	phash := NewImageHash(0, PHash)
+	resized := resize.Resize(64, 64, img, resize.Bilinear)
+	pixels := transforms.Rgb2Gray(resized)
+	dct := transforms.DCT2D(pixels, 64, 64)
+	flattens := transforms.FlattenPixels(dct, 8, 8)
+	median := etcs.MedianOfPixels(flattens)
+
+	for idx, p := range flattens {
+		if p > median {
+			phash.leftShiftSet(len(flattens) - idx - 1)
+		}
+	}
+	return phash, nil
+}
+
+// ExtPerceptionHash function returns phash of which the size can be set larger than uint64
+// Some variable name refer to https://github.com/JohannesBuchner/imagehash/blob/master/imagehash/__init__.py
+// Support 64bits phash (width=8, height=8) and 256bits phash (width=16, height=16)
+// Important: width * height should be the power of 2
+func ExtPerceptionHash(img image.Image, width, height int) (*ExtImageHash, error) {
+	imgSize := width * height
+	if img == nil {
+		return nil, errors.New("Image object can not be nil")
+	}
+	if imgSize <= 0 || imgSize&(imgSize-1) != 0 {
+		return nil, errors.New("width * height should be power of 2")
+	}
+	var phash []uint64
+	resized := resize.Resize(uint(imgSize), uint(imgSize), img, resize.Bilinear)
+	pixels := transforms.Rgb2Gray(resized)
+	dct := transforms.DCT2D(pixels, imgSize, imgSize)
+	flattens := transforms.FlattenPixels(dct, width, height)
+	median := etcs.MedianOfPixels(flattens)
+
+	lenOfUnit := 64
+	if imgSize%lenOfUnit == 0 {
+		phash = make([]uint64, imgSize/lenOfUnit)
+	} else {
+		phash = make([]uint64, imgSize/lenOfUnit+1)
+	}
+	for idx, p := range flattens {
+		indexOfArray := idx / lenOfUnit
+		indexOfBit := lenOfUnit - idx%lenOfUnit - 1
+		if p > median {
+			phash[indexOfArray] |= 1 << uint(indexOfBit)
+		}
+	}
+	return NewExtImageHash(phash, PHash, imgSize), nil
+}
+
+// ExtAverageHash function returns ahash of which the size can be set larger than uint64
+// Support 64bits ahash (width=8, height=8) and 256bits ahash (width=16, height=16)
+func ExtAverageHash(img image.Image, width, height int) (*ExtImageHash, error) {
+	if img == nil {
+		return nil, errors.New("Image object can not be nil")
+	}
+	var ahash []uint64
+	imgSize := width * height
+
+	resized := resize.Resize(uint(width), uint(height), img, resize.Bilinear)
+	pixels := transforms.Rgb2Gray(resized)
+	flattens := transforms.FlattenPixels(pixels, width, height)
+	avg := etcs.MeanOfPixels(flattens)
+
+	lenOfUnit := 64
+	if imgSize%lenOfUnit == 0 {
+		ahash = make([]uint64, imgSize/lenOfUnit)
+	} else {
+		ahash = make([]uint64, imgSize/lenOfUnit+1)
+	}
+	for idx, p := range flattens {
+		indexOfArray := idx / lenOfUnit
+		indexOfBit := lenOfUnit - idx%lenOfUnit - 1
+		if p > avg {
+			ahash[indexOfArray] |= 1 << uint(indexOfBit)
+		}
+	}
+	return NewExtImageHash(ahash, AHash, imgSize), nil
+}
+
+// ExtDifferenceHash function returns dhash of which the size can be set larger than uint64
+// Support 64bits dhash (width=8, height=8) and 256bits dhash (width=16, height=16)
+func ExtDifferenceHash(img image.Image, width, height int) (*ExtImageHash, error) {
+	if img == nil {
+		return nil, errors.New("Image object can not be nil")
+	}
+
+	var dhash []uint64
+	imgSize := width * height
+
+	resized := resize.Resize(uint(width)+1, uint(height), img, resize.Bilinear)
+	pixels := transforms.Rgb2Gray(resized)
+
+	lenOfUnit := 64
+	if imgSize%lenOfUnit == 0 {
+		dhash = make([]uint64, imgSize/lenOfUnit)
+	} else {
+		dhash = make([]uint64, imgSize/lenOfUnit+1)
+	}
+	idx := 0
+	for i := 0; i < len(pixels); i++ {
+		for j := 0; j < len(pixels[i])-1; j++ {
+			indexOfArray := idx / lenOfUnit
+			indexOfBit := lenOfUnit - idx%lenOfUnit - 1
+			if pixels[i][j] < pixels[i][j+1] {
+				dhash[indexOfArray] |= 1 << uint(indexOfBit)
+			}
+			idx++
+		}
+	}
+	return NewExtImageHash(dhash, DHash, imgSize), nil
+}

vendor/github.com/corona10/goimagehash/imagehash.go

@@ -0,0 +1,294 @@
+// Copyright 2017 The goimagehash Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package goimagehash
+
+import (
+	"encoding/binary"
+	"encoding/gob"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"io"
+)
+
+// Kind describes the kinds of hash.
+type Kind int
+
+// ImageHash is a struct of hash computation.
+type ImageHash struct {
+	hash uint64
+	kind Kind
+}
+
+// ExtImageHash is a struct of big hash computation.
+type ExtImageHash struct {
+	hash []uint64
+	kind Kind
+	bits int
+}
+
+const (
+	// Unknown is a enum value of the unknown hash.
+	Unknown Kind = iota
+	// AHash is a enum value of the average hash.
+	AHash
+	//PHash is a enum value of the perceptual hash.
+	PHash
+	// DHash is a enum value of the difference hash.
+	DHash
+	// WHash is a enum value of the wavelet hash.
+	WHash
+)
+
+// NewImageHash function creates a new image hash.
+func NewImageHash(hash uint64, kind Kind) *ImageHash {
+	return &ImageHash{hash: hash, kind: kind}
+}
+
+// Bits method returns an actual hash bit size
+func (h *ImageHash) Bits() int {
+	return 64
+}
+
+// Distance method returns a distance between two hashes.
+func (h *ImageHash) Distance(other *ImageHash) (int, error) {
+	if h.GetKind() != other.GetKind() {
+		return -1, errors.New("Image hashes's kind should be identical")
+	}
+
+	lhash := h.GetHash()
+	rhash := other.GetHash()
+
+	hamming := lhash ^ rhash
+	return popcnt(hamming), nil
+}
+
+// GetHash method returns a 64bits hash value.
+func (h *ImageHash) GetHash() uint64 {
+	return h.hash
+}
+
+// GetKind method returns a kind of image hash.
+func (h *ImageHash) GetKind() Kind {
+	return h.kind
+}
+
+func (h *ImageHash) leftShiftSet(idx int) {
+	h.hash |= 1 << uint(idx)
+}
+
+const strFmt = "%1s:%016x"
+
+// Dump method writes a binary serialization into w io.Writer.
+func (h *ImageHash) Dump(w io.Writer) error {
+	type D struct {
+		Hash uint64
+		Kind Kind
+	}
+	enc := gob.NewEncoder(w)
+	err := enc.Encode(D{Hash: h.hash, Kind: h.kind})
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// LoadImageHash method loads a ImageHash from io.Reader.
+func LoadImageHash(b io.Reader) (*ImageHash, error) {
+	type E struct {
+		Hash uint64
+		Kind Kind
+	}
+	var e E
+	dec := gob.NewDecoder(b)
+	err := dec.Decode(&e)
+	if err != nil {
+		return nil, err
+	}
+	return &ImageHash{hash: e.Hash, kind: e.Kind}, nil
+}
+
+// ImageHashFromString returns an image hash from a hex representation
+//
+// Deprecated: Use goimagehash.LoadImageHash instead.
+func ImageHashFromString(s string) (*ImageHash, error) {
+	var kindStr string
+	var hash uint64
+	_, err := fmt.Sscanf(s, strFmt, &kindStr, &hash)
+	if err != nil {
+		return nil, errors.New("Couldn't parse string " + s)
+	}
+
+	kind := Unknown
+	switch kindStr {
+	case "a":
+		kind = AHash
+	case "p":
+		kind = PHash
+	case "d":
+		kind = DHash
+	case "w":
+		kind = WHash
+	}
+	return NewImageHash(hash, kind), nil
+}
+
+// ToString returns a hex representation of the hash
+func (h *ImageHash) ToString() string {
+	kindStr := ""
+	switch h.kind {
+	case AHash:
+		kindStr = "a"
+	case PHash:
+		kindStr = "p"
+	case DHash:
+		kindStr = "d"
+	case WHash:
+		kindStr = "w"
+	}
+	return fmt.Sprintf(strFmt, kindStr, h.hash)
+}
+
+// NewExtImageHash function creates a new big hash
+func NewExtImageHash(hash []uint64, kind Kind, bits int) *ExtImageHash {
+	return &ExtImageHash{hash: hash, kind: kind, bits: bits}
+}
+
+// Bits method returns an actual hash bit size
+func (h *ExtImageHash) Bits() int {
+	return h.bits
+}
+
+// Distance method returns a distance between two big hashes
+func (h *ExtImageHash) Distance(other *ExtImageHash) (int, error) {
+	if h.GetKind() != other.GetKind() {
+		return -1, errors.New("Extended Image hashes's kind should be identical")
+	}
+
+	if h.Bits() != other.Bits() {
+		msg := fmt.Sprintf("Extended image hash should has an identical bit size but got %v vs %v", h.Bits(), other.Bits())
+		return -1, errors.New(msg)
+	}
+
+	lHash := h.GetHash()
+	rHash := other.GetHash()
+	if len(lHash) != len(rHash) {
+		return -1, errors.New("Extended Image hashes's size should be identical")
+	}
+
+	distance := 0
+	for idx, lh := range lHash {
+		rh := rHash[idx]
+		hamming := lh ^ rh
+		distance += popcnt(hamming)
+	}
+	return distance, nil
+}
+
+// GetHash method returns a big hash value
+func (h *ExtImageHash) GetHash() []uint64 {
+	return h.hash
+}
+
+// GetKind method returns a kind of big hash
+func (h *ExtImageHash) GetKind() Kind {
+	return h.kind
+}
+
+// Dump method writes a binary serialization into w io.Writer.
+func (h *ExtImageHash) Dump(w io.Writer) error {
+	type D struct {
+		Hash []uint64
+		Kind Kind
+		Bits int
+	}
+	enc := gob.NewEncoder(w)
+	err := enc.Encode(D{Hash: h.hash, Kind: h.kind, Bits: h.bits})
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// LoadExtImageHash method loads a ExtImageHash from io.Reader.
+func LoadExtImageHash(b io.Reader) (*ExtImageHash, error) {
+	type E struct {
+		Hash []uint64
+		Kind Kind
+		Bits int
+	}
+	var e E
+	dec := gob.NewDecoder(b)
+	err := dec.Decode(&e)
+	if err != nil {
+		return nil, err
+	}
+	return &ExtImageHash{hash: e.Hash, kind: e.Kind, bits: e.Bits}, nil
+}
+
+const extStrFmt = "%1s:%s"
+
+// ExtImageHashFromString returns a big hash from a hex representation
+//
+// Deprecated: Use goimagehash.LoadExtImageHash instead.
+func ExtImageHashFromString(s string) (*ExtImageHash, error) {
+	var kindStr string
+	var hashStr string
+	_, err := fmt.Sscanf(s, extStrFmt, &kindStr, &hashStr)
+	if err != nil {
+		return nil, errors.New("Couldn't parse string " + s)
+	}
+
+	hexBytes, err := hex.DecodeString(hashStr)
+	if err != nil {
+		return nil, err
+	}
+
+	var hash []uint64
+	lenOfByte := 8
+	for i := 0; i < len(hexBytes)/lenOfByte; i++ {
+		startIndex := i * lenOfByte
+		endIndex := startIndex + lenOfByte
+		hashUint64 := binary.BigEndian.Uint64(hexBytes[startIndex:endIndex])
+		hash = append(hash, hashUint64)
+	}
+
+	kind := Unknown
+	switch kindStr {
+	case "a":
+		kind = AHash
+	case "p":
+		kind = PHash
+	case "d":
+		kind = DHash
+	case "w":
+		kind = WHash
+	}
+	return NewExtImageHash(hash, kind, len(hash)*64), nil
+}
+
+// ToString returns a hex representation of big hash
+func (h *ExtImageHash) ToString() string {
+	var hexBytes []byte
+	for _, hash := range h.hash {
+		hashBytes := make([]byte, 8)
+		binary.BigEndian.PutUint64(hashBytes, hash)
+		hexBytes = append(hexBytes, hashBytes...)
+	}
+	hexStr := hex.EncodeToString(hexBytes)
+
+	kindStr := ""
+	switch h.kind {
+	case AHash:
+		kindStr = "a"
+	case PHash:
+		kindStr = "p"
+	case DHash:
+		kindStr = "d"
+	case WHash:
+		kindStr = "w"
+	}
+	return fmt.Sprintf(extStrFmt, kindStr, hexStr)
+}

vendor/github.com/corona10/goimagehash/imagehash18.go

@@ -0,0 +1,13 @@
+// +build !go1.9
+
+package goimagehash
+
+func popcnt(x uint64) int {
+	diff := 0
+	for x != 0 {
+		diff += int(x & 1)
+		x >>= 1
+	}
+
+	return diff
+}

vendor/github.com/corona10/goimagehash/imagehash19.go

@@ -0,0 +1,9 @@
+// +build go1.9
+
+package goimagehash
+
+import (
+	"math/bits"
+)
+
+func popcnt(x uint64) int { return bits.OnesCount64(x) }

vendor/github.com/corona10/goimagehash/transforms/dct.go

@@ -0,0 +1,75 @@
+// Copyright 2017 The goimagehash Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package transforms
+
+import (
+	"math"
+	"sync"
+)
+
+// DCT1D function returns result of DCT-II.
+// DCT type II, unscaled. Algorithm by Byeong Gi Lee, 1984.
+func DCT1D(input []float64) []float64 {
+	temp := make([]float64, len(input))
+	forwardTransform(input, temp, len(input))
+	return input
+}
+
+func forwardTransform(input, temp []float64, Len int) {
+	if Len == 1 {
+		return
+	}
+
+	halfLen := Len / 2
+	for i := 0; i < halfLen; i++ {
+		x, y := input[i], input[Len-1-i]
+		temp[i] = x + y
+		temp[i+halfLen] = (x - y) / (math.Cos((float64(i)+0.5)*math.Pi/float64(Len)) * 2)
+	}
+	forwardTransform(temp, input, halfLen)
+	forwardTransform(temp[halfLen:], input, halfLen)
+	for i := 0; i < halfLen-1; i++ {
+		input[i*2+0] = temp[i]
+		input[i*2+1] = temp[i+halfLen] + temp[i+halfLen+1]
+	}
+	input[Len-2], input[Len-1] = temp[halfLen-1], temp[Len-1]
+}
+
+// DCT2D function returns a  result of DCT2D by using the seperable property.
+func DCT2D(input [][]float64, w int, h int) [][]float64 {
+	output := make([][]float64, h)
+	for i := range output {
+		output[i] = make([]float64, w)
+	}
+
+	wg := new(sync.WaitGroup)
+	for i := 0; i < h; i++ {
+		wg.Add(1)
+		go func(i int) {
+			cols := DCT1D(input[i])
+			output[i] = cols
+			wg.Done()
+		}(i)
+	}
+
+	wg.Wait()
+	for i := 0; i < w; i++ {
+		wg.Add(1)
+		in := make([]float64, h)
+		go func(i int) {
+			for j := 0; j < h; j++ {
+				in[j] = output[j][i]
+			}
+			rows := DCT1D(in)
+			for j := 0; j < len(rows); j++ {
+				output[j][i] = rows[j]
+			}
+			wg.Done()
+		}(i)
+	}
+
+	wg.Wait()
+	return output
+}

vendor/github.com/corona10/goimagehash/transforms/doc.go

@@ -0,0 +1,5 @@
+// Copyright 2017 The goimagehash Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package transforms

vendor/github.com/corona10/goimagehash/transforms/pixels.go

@@ -0,0 +1,39 @@
+// Copyright 2017 The goimagehash Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package transforms
+
+import (
+	"image"
+)
+
+// Rgb2Gray function converts RGB to a gray scale array.
+func Rgb2Gray(colorImg image.Image) [][]float64 {
+	bounds := colorImg.Bounds()
+	w, h := bounds.Max.X-bounds.Min.X, bounds.Max.Y-bounds.Min.Y
+	pixels := make([][]float64, h)
+
+	for i := range pixels {
+		pixels[i] = make([]float64, w)
+		for j := range pixels[i] {
+			color := colorImg.At(j, i)
+			r, g, b, _ := color.RGBA()
+			lum := 0.299*float64(r/257) + 0.587*float64(g/257) + 0.114*float64(b/256)
+			pixels[i][j] = lum
+		}
+	}
+
+	return pixels
+}
+
+// FlattenPixels function flattens 2d array into 1d array.
+func FlattenPixels(pixels [][]float64, x int, y int) []float64 {
+	flattens := make([]float64, x*y)
+	for i := 0; i < y; i++ {
+		for j := 0; j < x; j++ {
+			flattens[y*i+j] = pixels[i][j]
+		}
+	}
+	return flattens
+}

vendor/github.com/nfnt/resize/.travis.yml

@@ -0,0 +1,7 @@
+language: go
+
+go:
+  - "1.x"
+  - "1.1"
+  - "1.4"
+  - "1.10"

vendor/github.com/nfnt/resize/LICENSE

@@ -0,0 +1,13 @@
+Copyright (c) 2012, Jan Schlicht <jan.schlicht@gmail.com>
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.

vendor/github.com/nfnt/resize/README.md

@@ -0,0 +1,151 @@
+# This package is no longer being updated! Please look for alternatives if that bothers you.
+
+Resize
+======
+
+Image resizing for the [Go programming language](http://golang.org) with common interpolation methods.
+
+[![Build Status](https://travis-ci.org/nfnt/resize.svg)](https://travis-ci.org/nfnt/resize)
+
+Installation
+------------
+
+```bash
+$ go get github.com/nfnt/resize
+```
+
+It's that easy!
+
+Usage
+-----
+
+This package needs at least Go 1.1. Import package with
+
+```go
+import "github.com/nfnt/resize"
+```
+
+The resize package provides 2 functions:
+
+* `resize.Resize` creates a scaled image with new dimensions (`width`, `height`) using the interpolation function `interp`.
+  If either `width` or `height` is set to 0, it will be set to an aspect ratio preserving value.
+* `resize.Thumbnail` downscales an image preserving its aspect ratio to the maximum dimensions (`maxWidth`, `maxHeight`).
+  It will return the original image if original sizes are smaller than the provided dimensions.
+
+```go
+resize.Resize(width, height uint, img image.Image, interp resize.InterpolationFunction) image.Image
+resize.Thumbnail(maxWidth, maxHeight uint, img image.Image, interp resize.InterpolationFunction) image.Image
+```
+
+The provided interpolation functions are (from fast to slow execution time)
+
+- `NearestNeighbor`: [Nearest-neighbor interpolation](http://en.wikipedia.org/wiki/Nearest-neighbor_interpolation)
+- `Bilinear`: [Bilinear interpolation](http://en.wikipedia.org/wiki/Bilinear_interpolation)
+- `Bicubic`: [Bicubic interpolation](http://en.wikipedia.org/wiki/Bicubic_interpolation)
+- `MitchellNetravali`: [Mitchell-Netravali interpolation](http://dl.acm.org/citation.cfm?id=378514)
+- `Lanczos2`: [Lanczos resampling](http://en.wikipedia.org/wiki/Lanczos_resampling) with a=2
+- `Lanczos3`: [Lanczos resampling](http://en.wikipedia.org/wiki/Lanczos_resampling) with a=3
+
+Which of these methods gives the best results depends on your use case.
+
+Sample usage:
+
+```go
+package main
+
+import (
+	"github.com/nfnt/resize"
+	"image/jpeg"
+	"log"
+	"os"
+)
+
+func main() {
+	// open "test.jpg"
+	file, err := os.Open("test.jpg")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// decode jpeg into image.Image
+	img, err := jpeg.Decode(file)
+	if err != nil {
+		log.Fatal(err)
+	}
+	file.Close()
+
+	// resize to width 1000 using Lanczos resampling
+	// and preserve aspect ratio
+	m := resize.Resize(1000, 0, img, resize.Lanczos3)
+
+	out, err := os.Create("test_resized.jpg")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer out.Close()
+
+	// write new image to file
+	jpeg.Encode(out, m, nil)
+}
+```
+
+Caveats
+-------
+
+* Optimized access routines are used for `image.RGBA`, `image.NRGBA`, `image.RGBA64`, `image.NRGBA64`, `image.YCbCr`, `image.Gray`, and `image.Gray16` types. All other image types are accessed in a generic way that will result in slow processing speed.
+* JPEG images are stored in `image.YCbCr`. This image format stores data in a way that will decrease processing speed. A resize may be up to 2 times slower than with `image.RGBA`. 
+
+
+Downsizing Samples
+-------
+
+Downsizing is not as simple as it might look like. Images have to be filtered before they are scaled down, otherwise aliasing might occur.
+Filtering is highly subjective: Applying too much will blur the whole image, too little will make aliasing become apparent.
+Resize tries to provide sane defaults that should suffice in most cases.
+
+### Artificial sample
+
+Original image
+![Rings](http://nfnt.github.com/img/rings_lg_orig.png)
+
+<table>
+<tr>
+<th><img src="http://nfnt.github.com/img/rings_300_NearestNeighbor.png" /><br>Nearest-Neighbor</th>
+<th><img src="http://nfnt.github.com/img/rings_300_Bilinear.png" /><br>Bilinear</th>
+</tr>
+<tr>
+<th><img src="http://nfnt.github.com/img/rings_300_Bicubic.png" /><br>Bicubic</th>
+<th><img src="http://nfnt.github.com/img/rings_300_MitchellNetravali.png" /><br>Mitchell-Netravali</th>
+</tr>
+<tr>
+<th><img src="http://nfnt.github.com/img/rings_300_Lanczos2.png" /><br>Lanczos2</th>
+<th><img src="http://nfnt.github.com/img/rings_300_Lanczos3.png" /><br>Lanczos3</th>
+</tr>
+</table>
+
+### Real-Life sample
+
+Original image  
+![Original](http://nfnt.github.com/img/IMG_3694_720.jpg)
+
+<table>
+<tr>
+<th><img src="http://nfnt.github.com/img/IMG_3694_300_NearestNeighbor.png" /><br>Nearest-Neighbor</th>
+<th><img src="http://nfnt.github.com/img/IMG_3694_300_Bilinear.png" /><br>Bilinear</th>
+</tr>
+<tr>
+<th><img src="http://nfnt.github.com/img/IMG_3694_300_Bicubic.png" /><br>Bicubic</th>
+<th><img src="http://nfnt.github.com/img/IMG_3694_300_MitchellNetravali.png" /><br>Mitchell-Netravali</th>
+</tr>
+<tr>
+<th><img src="http://nfnt.github.com/img/IMG_3694_300_Lanczos2.png" /><br>Lanczos2</th>
+<th><img src="http://nfnt.github.com/img/IMG_3694_300_Lanczos3.png" /><br>Lanczos3</th>
+</tr>
+</table>
+
+
+License
+-------
+
+Copyright (c) 2012 Jan Schlicht <janschlicht@gmail.com>
+Resize is released under a MIT style license.

vendor/github.com/nfnt/resize/converter.go

@@ -0,0 +1,438 @@
+/*
+Copyright (c) 2012, Jan Schlicht <jan.schlicht@gmail.com>
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.
+*/
+
+package resize
+
+import "image"
+
+// Keep value in [0,255] range.
+func clampUint8(in int32) uint8 {
+	// casting a negative int to an uint will result in an overflown
+	// large uint. this behavior will be exploited here and in other functions
+	// to achieve a higher performance.
+	if uint32(in) < 256 {
+		return uint8(in)
+	}
+	if in > 255 {
+		return 255
+	}
+	return 0
+}
+
+// Keep value in [0,65535] range.
+func clampUint16(in int64) uint16 {
+	if uint64(in) < 65536 {
+		return uint16(in)
+	}
+	if in > 65535 {
+		return 65535
+	}
+	return 0
+}
+
+func resizeGeneric(in image.Image, out *image.RGBA64, scale float64, coeffs []int32, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var rgba [4]int64
+			var sum int64
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				coeff := coeffs[ci+i]
+				if coeff != 0 {
+					xi := start + i
+					switch {
+					case xi < 0:
+						xi = 0
+					case xi >= maxX:
+						xi = maxX
+					}
+
+					r, g, b, a := in.At(xi+in.Bounds().Min.X, x+in.Bounds().Min.Y).RGBA()
+
+					rgba[0] += int64(coeff) * int64(r)
+					rgba[1] += int64(coeff) * int64(g)
+					rgba[2] += int64(coeff) * int64(b)
+					rgba[3] += int64(coeff) * int64(a)
+					sum += int64(coeff)
+				}
+			}
+
+			offset := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
+
+			value := clampUint16(rgba[0] / sum)
+			out.Pix[offset+0] = uint8(value >> 8)
+			out.Pix[offset+1] = uint8(value)
+			value = clampUint16(rgba[1] / sum)
+			out.Pix[offset+2] = uint8(value >> 8)
+			out.Pix[offset+3] = uint8(value)
+			value = clampUint16(rgba[2] / sum)
+			out.Pix[offset+4] = uint8(value >> 8)
+			out.Pix[offset+5] = uint8(value)
+			value = clampUint16(rgba[3] / sum)
+			out.Pix[offset+6] = uint8(value >> 8)
+			out.Pix[offset+7] = uint8(value)
+		}
+	}
+}
+
+func resizeRGBA(in *image.RGBA, out *image.RGBA, scale float64, coeffs []int16, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[x*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var rgba [4]int32
+			var sum int32
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				coeff := coeffs[ci+i]
+				if coeff != 0 {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(maxX):
+						xi *= 4
+					case xi >= maxX:
+						xi = 4 * maxX
+					default:
+						xi = 0
+					}
+
+					rgba[0] += int32(coeff) * int32(row[xi+0])
+					rgba[1] += int32(coeff) * int32(row[xi+1])
+					rgba[2] += int32(coeff) * int32(row[xi+2])
+					rgba[3] += int32(coeff) * int32(row[xi+3])
+					sum += int32(coeff)
+				}
+			}
+
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*4
+
+			out.Pix[xo+0] = clampUint8(rgba[0] / sum)
+			out.Pix[xo+1] = clampUint8(rgba[1] / sum)
+			out.Pix[xo+2] = clampUint8(rgba[2] / sum)
+			out.Pix[xo+3] = clampUint8(rgba[3] / sum)
+		}
+	}
+}
+
+func resizeNRGBA(in *image.NRGBA, out *image.RGBA, scale float64, coeffs []int16, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[x*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var rgba [4]int32
+			var sum int32
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				coeff := coeffs[ci+i]
+				if coeff != 0 {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(maxX):
+						xi *= 4
+					case xi >= maxX:
+						xi = 4 * maxX
+					default:
+						xi = 0
+					}
+
+					// Forward alpha-premultiplication
+					a := int32(row[xi+3])
+					r := int32(row[xi+0]) * a
+					r /= 0xff
+					g := int32(row[xi+1]) * a
+					g /= 0xff
+					b := int32(row[xi+2]) * a
+					b /= 0xff
+
+					rgba[0] += int32(coeff) * r
+					rgba[1] += int32(coeff) * g
+					rgba[2] += int32(coeff) * b
+					rgba[3] += int32(coeff) * a
+					sum += int32(coeff)
+				}
+			}
+
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*4
+
+			out.Pix[xo+0] = clampUint8(rgba[0] / sum)
+			out.Pix[xo+1] = clampUint8(rgba[1] / sum)
+			out.Pix[xo+2] = clampUint8(rgba[2] / sum)
+			out.Pix[xo+3] = clampUint8(rgba[3] / sum)
+		}
+	}
+}
+
+func resizeRGBA64(in *image.RGBA64, out *image.RGBA64, scale float64, coeffs []int32, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[x*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var rgba [4]int64
+			var sum int64
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				coeff := coeffs[ci+i]
+				if coeff != 0 {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(maxX):
+						xi *= 8
+					case xi >= maxX:
+						xi = 8 * maxX
+					default:
+						xi = 0
+					}
+
+					rgba[0] += int64(coeff) * (int64(row[xi+0])<<8 | int64(row[xi+1]))
+					rgba[1] += int64(coeff) * (int64(row[xi+2])<<8 | int64(row[xi+3]))
+					rgba[2] += int64(coeff) * (int64(row[xi+4])<<8 | int64(row[xi+5]))
+					rgba[3] += int64(coeff) * (int64(row[xi+6])<<8 | int64(row[xi+7]))
+					sum += int64(coeff)
+				}
+			}
+
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
+
+			value := clampUint16(rgba[0] / sum)
+			out.Pix[xo+0] = uint8(value >> 8)
+			out.Pix[xo+1] = uint8(value)
+			value = clampUint16(rgba[1] / sum)
+			out.Pix[xo+2] = uint8(value >> 8)
+			out.Pix[xo+3] = uint8(value)
+			value = clampUint16(rgba[2] / sum)
+			out.Pix[xo+4] = uint8(value >> 8)
+			out.Pix[xo+5] = uint8(value)
+			value = clampUint16(rgba[3] / sum)
+			out.Pix[xo+6] = uint8(value >> 8)
+			out.Pix[xo+7] = uint8(value)
+		}
+	}
+}
+
+func resizeNRGBA64(in *image.NRGBA64, out *image.RGBA64, scale float64, coeffs []int32, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[x*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var rgba [4]int64
+			var sum int64
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				coeff := coeffs[ci+i]
+				if coeff != 0 {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(maxX):
+						xi *= 8
+					case xi >= maxX:
+						xi = 8 * maxX
+					default:
+						xi = 0
+					}
+
+					// Forward alpha-premultiplication
+					a := int64(uint16(row[xi+6])<<8 | uint16(row[xi+7]))
+					r := int64(uint16(row[xi+0])<<8|uint16(row[xi+1])) * a
+					r /= 0xffff
+					g := int64(uint16(row[xi+2])<<8|uint16(row[xi+3])) * a
+					g /= 0xffff
+					b := int64(uint16(row[xi+4])<<8|uint16(row[xi+5])) * a
+					b /= 0xffff
+
+					rgba[0] += int64(coeff) * r
+					rgba[1] += int64(coeff) * g
+					rgba[2] += int64(coeff) * b
+					rgba[3] += int64(coeff) * a
+					sum += int64(coeff)
+				}
+			}
+
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
+
+			value := clampUint16(rgba[0] / sum)
+			out.Pix[xo+0] = uint8(value >> 8)
+			out.Pix[xo+1] = uint8(value)
+			value = clampUint16(rgba[1] / sum)
+			out.Pix[xo+2] = uint8(value >> 8)
+			out.Pix[xo+3] = uint8(value)
+			value = clampUint16(rgba[2] / sum)
+			out.Pix[xo+4] = uint8(value >> 8)
+			out.Pix[xo+5] = uint8(value)
+			value = clampUint16(rgba[3] / sum)
+			out.Pix[xo+6] = uint8(value >> 8)
+			out.Pix[xo+7] = uint8(value)
+		}
+	}
+}
+
+func resizeGray(in *image.Gray, out *image.Gray, scale float64, coeffs []int16, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[(x-newBounds.Min.X)*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var gray int32
+			var sum int32
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				coeff := coeffs[ci+i]
+				if coeff != 0 {
+					xi := start + i
+					switch {
+					case xi < 0:
+						xi = 0
+					case xi >= maxX:
+						xi = maxX
+					}
+					gray += int32(coeff) * int32(row[xi])
+					sum += int32(coeff)
+				}
+			}
+
+			offset := (y-newBounds.Min.Y)*out.Stride + (x - newBounds.Min.X)
+			out.Pix[offset] = clampUint8(gray / sum)
+		}
+	}
+}
+
+func resizeGray16(in *image.Gray16, out *image.Gray16, scale float64, coeffs []int32, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[x*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var gray int64
+			var sum int64
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				coeff := coeffs[ci+i]
+				if coeff != 0 {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(maxX):
+						xi *= 2
+					case xi >= maxX:
+						xi = 2 * maxX
+					default:
+						xi = 0
+					}
+					gray += int64(coeff) * int64(uint16(row[xi+0])<<8|uint16(row[xi+1]))
+					sum += int64(coeff)
+				}
+			}
+
+			offset := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*2
+			value := clampUint16(gray / sum)
+			out.Pix[offset+0] = uint8(value >> 8)
+			out.Pix[offset+1] = uint8(value)
+		}
+	}
+}
+
+func resizeYCbCr(in *ycc, out *ycc, scale float64, coeffs []int16, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[x*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var p [3]int32
+			var sum int32
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				coeff := coeffs[ci+i]
+				if coeff != 0 {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(maxX):
+						xi *= 3
+					case xi >= maxX:
+						xi = 3 * maxX
+					default:
+						xi = 0
+					}
+					p[0] += int32(coeff) * int32(row[xi+0])
+					p[1] += int32(coeff) * int32(row[xi+1])
+					p[2] += int32(coeff) * int32(row[xi+2])
+					sum += int32(coeff)
+				}
+			}
+
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*3
+			out.Pix[xo+0] = clampUint8(p[0] / sum)
+			out.Pix[xo+1] = clampUint8(p[1] / sum)
+			out.Pix[xo+2] = clampUint8(p[2] / sum)
+		}
+	}
+}
+
+func nearestYCbCr(in *ycc, out *ycc, scale float64, coeffs []bool, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[x*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var p [3]float32
+			var sum float32
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				if coeffs[ci+i] {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(maxX):
+						xi *= 3
+					case xi >= maxX:
+						xi = 3 * maxX
+					default:
+						xi = 0
+					}
+					p[0] += float32(row[xi+0])
+					p[1] += float32(row[xi+1])
+					p[2] += float32(row[xi+2])
+					sum++
+				}
+			}
+
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*3
+			out.Pix[xo+0] = floatToUint8(p[0] / sum)
+			out.Pix[xo+1] = floatToUint8(p[1] / sum)
+			out.Pix[xo+2] = floatToUint8(p[2] / sum)
+		}
+	}
+}

vendor/github.com/nfnt/resize/filters.go

@@ -0,0 +1,143 @@
+/*
+Copyright (c) 2012, Jan Schlicht <jan.schlicht@gmail.com>
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.
+*/
+
+package resize
+
+import (
+	"math"
+)
+
+func nearest(in float64) float64 {
+	if in >= -0.5 && in < 0.5 {
+		return 1
+	}
+	return 0
+}
+
+func linear(in float64) float64 {
+	in = math.Abs(in)
+	if in <= 1 {
+		return 1 - in
+	}
+	return 0
+}
+
+func cubic(in float64) float64 {
+	in = math.Abs(in)
+	if in <= 1 {
+		return in*in*(1.5*in-2.5) + 1.0
+	}
+	if in <= 2 {
+		return in*(in*(2.5-0.5*in)-4.0) + 2.0
+	}
+	return 0
+}
+
+func mitchellnetravali(in float64) float64 {
+	in = math.Abs(in)
+	if in <= 1 {
+		return (7.0*in*in*in - 12.0*in*in + 5.33333333333) * 0.16666666666
+	}
+	if in <= 2 {
+		return (-2.33333333333*in*in*in + 12.0*in*in - 20.0*in + 10.6666666667) * 0.16666666666
+	}
+	return 0
+}
+
+func sinc(x float64) float64 {
+	x = math.Abs(x) * math.Pi
+	if x >= 1.220703e-4 {
+		return math.Sin(x) / x
+	}
+	return 1
+}
+
+func lanczos2(in float64) float64 {
+	if in > -2 && in < 2 {
+		return sinc(in) * sinc(in*0.5)
+	}
+	return 0
+}
+
+func lanczos3(in float64) float64 {
+	if in > -3 && in < 3 {
+		return sinc(in) * sinc(in*0.3333333333333333)
+	}
+	return 0
+}
+
+// range [-256,256]
+func createWeights8(dy, filterLength int, blur, scale float64, kernel func(float64) float64) ([]int16, []int, int) {
+	filterLength = filterLength * int(math.Max(math.Ceil(blur*scale), 1))
+	filterFactor := math.Min(1./(blur*scale), 1)
+
+	coeffs := make([]int16, dy*filterLength)
+	start := make([]int, dy)
+	for y := 0; y < dy; y++ {
+		interpX := scale*(float64(y)+0.5) - 0.5
+		start[y] = int(interpX) - filterLength/2 + 1
+		interpX -= float64(start[y])
+		for i := 0; i < filterLength; i++ {
+			in := (interpX - float64(i)) * filterFactor
+			coeffs[y*filterLength+i] = int16(kernel(in) * 256)
+		}
+	}
+
+	return coeffs, start, filterLength
+}
+
+// range [-65536,65536]
+func createWeights16(dy, filterLength int, blur, scale float64, kernel func(float64) float64) ([]int32, []int, int) {
+	filterLength = filterLength * int(math.Max(math.Ceil(blur*scale), 1))
+	filterFactor := math.Min(1./(blur*scale), 1)
+
+	coeffs := make([]int32, dy*filterLength)
+	start := make([]int, dy)
+	for y := 0; y < dy; y++ {
+		interpX := scale*(float64(y)+0.5) - 0.5
+		start[y] = int(interpX) - filterLength/2 + 1
+		interpX -= float64(start[y])
+		for i := 0; i < filterLength; i++ {
+			in := (interpX - float64(i)) * filterFactor
+			coeffs[y*filterLength+i] = int32(kernel(in) * 65536)
+		}
+	}
+
+	return coeffs, start, filterLength
+}
+
+func createWeightsNearest(dy, filterLength int, blur, scale float64) ([]bool, []int, int) {
+	filterLength = filterLength * int(math.Max(math.Ceil(blur*scale), 1))
+	filterFactor := math.Min(1./(blur*scale), 1)
+
+	coeffs := make([]bool, dy*filterLength)
+	start := make([]int, dy)
+	for y := 0; y < dy; y++ {
+		interpX := scale*(float64(y)+0.5) - 0.5
+		start[y] = int(interpX) - filterLength/2 + 1
+		interpX -= float64(start[y])
+		for i := 0; i < filterLength; i++ {
+			in := (interpX - float64(i)) * filterFactor
+			if in >= -0.5 && in < 0.5 {
+				coeffs[y*filterLength+i] = true
+			} else {
+				coeffs[y*filterLength+i] = false
+			}
+		}
+	}
+
+	return coeffs, start, filterLength
+}

vendor/github.com/nfnt/resize/nearest.go

@@ -0,0 +1,318 @@
+/*
+Copyright (c) 2014, Charlie Vieth <charlie.vieth@gmail.com>
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.
+*/
+
+package resize
+
+import "image"
+
+func floatToUint8(x float32) uint8 {
+	// Nearest-neighbor values are always
+	// positive no need to check lower-bound.
+	if x > 0xfe {
+		return 0xff
+	}
+	return uint8(x)
+}
+
+func floatToUint16(x float32) uint16 {
+	if x > 0xfffe {
+		return 0xffff
+	}
+	return uint16(x)
+}
+
+func nearestGeneric(in image.Image, out *image.RGBA64, scale float64, coeffs []bool, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var rgba [4]float32
+			var sum float32
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				if coeffs[ci+i] {
+					xi := start + i
+					switch {
+					case xi < 0:
+						xi = 0
+					case xi >= maxX:
+						xi = maxX
+					}
+					r, g, b, a := in.At(xi+in.Bounds().Min.X, x+in.Bounds().Min.Y).RGBA()
+					rgba[0] += float32(r)
+					rgba[1] += float32(g)
+					rgba[2] += float32(b)
+					rgba[3] += float32(a)
+					sum++
+				}
+			}
+
+			offset := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
+			value := floatToUint16(rgba[0] / sum)
+			out.Pix[offset+0] = uint8(value >> 8)
+			out.Pix[offset+1] = uint8(value)
+			value = floatToUint16(rgba[1] / sum)
+			out.Pix[offset+2] = uint8(value >> 8)
+			out.Pix[offset+3] = uint8(value)
+			value = floatToUint16(rgba[2] / sum)
+			out.Pix[offset+4] = uint8(value >> 8)
+			out.Pix[offset+5] = uint8(value)
+			value = floatToUint16(rgba[3] / sum)
+			out.Pix[offset+6] = uint8(value >> 8)
+			out.Pix[offset+7] = uint8(value)
+		}
+	}
+}
+
+func nearestRGBA(in *image.RGBA, out *image.RGBA, scale float64, coeffs []bool, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[x*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var rgba [4]float32
+			var sum float32
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				if coeffs[ci+i] {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(maxX):
+						xi *= 4
+					case xi >= maxX:
+						xi = 4 * maxX
+					default:
+						xi = 0
+					}
+					rgba[0] += float32(row[xi+0])
+					rgba[1] += float32(row[xi+1])
+					rgba[2] += float32(row[xi+2])
+					rgba[3] += float32(row[xi+3])
+					sum++
+				}
+			}
+
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*4
+			out.Pix[xo+0] = floatToUint8(rgba[0] / sum)
+			out.Pix[xo+1] = floatToUint8(rgba[1] / sum)
+			out.Pix[xo+2] = floatToUint8(rgba[2] / sum)
+			out.Pix[xo+3] = floatToUint8(rgba[3] / sum)
+		}
+	}
+}
+
+func nearestNRGBA(in *image.NRGBA, out *image.NRGBA, scale float64, coeffs []bool, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[x*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var rgba [4]float32
+			var sum float32
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				if coeffs[ci+i] {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(maxX):
+						xi *= 4
+					case xi >= maxX:
+						xi = 4 * maxX
+					default:
+						xi = 0
+					}
+					rgba[0] += float32(row[xi+0])
+					rgba[1] += float32(row[xi+1])
+					rgba[2] += float32(row[xi+2])
+					rgba[3] += float32(row[xi+3])
+					sum++
+				}
+			}
+
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*4
+			out.Pix[xo+0] = floatToUint8(rgba[0] / sum)
+			out.Pix[xo+1] = floatToUint8(rgba[1] / sum)
+			out.Pix[xo+2] = floatToUint8(rgba[2] / sum)
+			out.Pix[xo+3] = floatToUint8(rgba[3] / sum)
+		}
+	}
+}
+
+func nearestRGBA64(in *image.RGBA64, out *image.RGBA64, scale float64, coeffs []bool, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[x*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var rgba [4]float32
+			var sum float32
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				if coeffs[ci+i] {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(maxX):
+						xi *= 8
+					case xi >= maxX:
+						xi = 8 * maxX
+					default:
+						xi = 0
+					}
+					rgba[0] += float32(uint16(row[xi+0])<<8 | uint16(row[xi+1]))
+					rgba[1] += float32(uint16(row[xi+2])<<8 | uint16(row[xi+3]))
+					rgba[2] += float32(uint16(row[xi+4])<<8 | uint16(row[xi+5]))
+					rgba[3] += float32(uint16(row[xi+6])<<8 | uint16(row[xi+7]))
+					sum++
+				}
+			}
+
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
+			value := floatToUint16(rgba[0] / sum)
+			out.Pix[xo+0] = uint8(value >> 8)
+			out.Pix[xo+1] = uint8(value)
+			value = floatToUint16(rgba[1] / sum)
+			out.Pix[xo+2] = uint8(value >> 8)
+			out.Pix[xo+3] = uint8(value)
+			value = floatToUint16(rgba[2] / sum)
+			out.Pix[xo+4] = uint8(value >> 8)
+			out.Pix[xo+5] = uint8(value)
+			value = floatToUint16(rgba[3] / sum)
+			out.Pix[xo+6] = uint8(value >> 8)
+			out.Pix[xo+7] = uint8(value)
+		}
+	}
+}
+
+func nearestNRGBA64(in *image.NRGBA64, out *image.NRGBA64, scale float64, coeffs []bool, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[x*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var rgba [4]float32
+			var sum float32
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				if coeffs[ci+i] {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(maxX):
+						xi *= 8
+					case xi >= maxX:
+						xi = 8 * maxX
+					default:
+						xi = 0
+					}
+					rgba[0] += float32(uint16(row[xi+0])<<8 | uint16(row[xi+1]))
+					rgba[1] += float32(uint16(row[xi+2])<<8 | uint16(row[xi+3]))
+					rgba[2] += float32(uint16(row[xi+4])<<8 | uint16(row[xi+5]))
+					rgba[3] += float32(uint16(row[xi+6])<<8 | uint16(row[xi+7]))
+					sum++
+				}
+			}
+
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
+			value := floatToUint16(rgba[0] / sum)
+			out.Pix[xo+0] = uint8(value >> 8)
+			out.Pix[xo+1] = uint8(value)
+			value = floatToUint16(rgba[1] / sum)
+			out.Pix[xo+2] = uint8(value >> 8)
+			out.Pix[xo+3] = uint8(value)
+			value = floatToUint16(rgba[2] / sum)
+			out.Pix[xo+4] = uint8(value >> 8)
+			out.Pix[xo+5] = uint8(value)
+			value = floatToUint16(rgba[3] / sum)
+			out.Pix[xo+6] = uint8(value >> 8)
+			out.Pix[xo+7] = uint8(value)
+		}
+	}
+}
+
+func nearestGray(in *image.Gray, out *image.Gray, scale float64, coeffs []bool, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[x*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var gray float32
+			var sum float32
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				if coeffs[ci+i] {
+					xi := start + i
+					switch {
+					case xi < 0:
+						xi = 0
+					case xi >= maxX:
+						xi = maxX
+					}
+					gray += float32(row[xi])
+					sum++
+				}
+			}
+
+			offset := (y-newBounds.Min.Y)*out.Stride + (x - newBounds.Min.X)
+			out.Pix[offset] = floatToUint8(gray / sum)
+		}
+	}
+}
+
+func nearestGray16(in *image.Gray16, out *image.Gray16, scale float64, coeffs []bool, offset []int, filterLength int) {
+	newBounds := out.Bounds()
+	maxX := in.Bounds().Dx() - 1
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[x*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var gray float32
+			var sum float32
+			start := offset[y]
+			ci := y * filterLength
+			for i := 0; i < filterLength; i++ {
+				if coeffs[ci+i] {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(maxX):
+						xi *= 2
+					case xi >= maxX:
+						xi = 2 * maxX
+					default:
+						xi = 0
+					}
+					gray += float32(uint16(row[xi+0])<<8 | uint16(row[xi+1]))
+					sum++
+				}
+			}
+
+			offset := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*2
+			value := floatToUint16(gray / sum)
+			out.Pix[offset+0] = uint8(value >> 8)
+			out.Pix[offset+1] = uint8(value)
+		}
+	}
+}

vendor/github.com/nfnt/resize/resize.go

@@ -0,0 +1,620 @@
+/*
+Copyright (c) 2012, Jan Schlicht <jan.schlicht@gmail.com>
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.
+*/
+
+// Package resize implements various image resizing methods.
+//
+// The package works with the Image interface described in the image package.
+// Various interpolation methods are provided and multiple processors may be
+// utilized in the computations.
+//
+// Example:
+//     imgResized := resize.Resize(1000, 0, imgOld, resize.MitchellNetravali)
+package resize
+
+import (
+	"image"
+	"runtime"
+	"sync"
+)
+
+// An InterpolationFunction provides the parameters that describe an
+// interpolation kernel. It returns the number of samples to take
+// and the kernel function to use for sampling.
+type InterpolationFunction int
+
+// InterpolationFunction constants
+const (
+	// Nearest-neighbor interpolation
+	NearestNeighbor InterpolationFunction = iota
+	// Bilinear interpolation
+	Bilinear
+	// Bicubic interpolation (with cubic hermite spline)
+	Bicubic
+	// Mitchell-Netravali interpolation
+	MitchellNetravali
+	// Lanczos interpolation (a=2)
+	Lanczos2
+	// Lanczos interpolation (a=3)
+	Lanczos3
+)
+
+// kernal, returns an InterpolationFunctions taps and kernel.
+func (i InterpolationFunction) kernel() (int, func(float64) float64) {
+	switch i {
+	case Bilinear:
+		return 2, linear
+	case Bicubic:
+		return 4, cubic
+	case MitchellNetravali:
+		return 4, mitchellnetravali
+	case Lanczos2:
+		return 4, lanczos2
+	case Lanczos3:
+		return 6, lanczos3
+	default:
+		// Default to NearestNeighbor.
+		return 2, nearest
+	}
+}
+
+// values <1 will sharpen the image
+var blur = 1.0
+
+// Resize scales an image to new width and height using the interpolation function interp.
+// A new image with the given dimensions will be returned.
+// If one of the parameters width or height is set to 0, its size will be calculated so that
+// the aspect ratio is that of the originating image.
+// The resizing algorithm uses channels for parallel computation.
+// If the input image has width or height of 0, it is returned unchanged.
+func Resize(width, height uint, img image.Image, interp InterpolationFunction) image.Image {
+	scaleX, scaleY := calcFactors(width, height, float64(img.Bounds().Dx()), float64(img.Bounds().Dy()))
+	if width == 0 {
+		width = uint(0.7 + float64(img.Bounds().Dx())/scaleX)
+	}
+	if height == 0 {
+		height = uint(0.7 + float64(img.Bounds().Dy())/scaleY)
+	}
+
+	// Trivial case: return input image
+	if int(width) == img.Bounds().Dx() && int(height) == img.Bounds().Dy() {
+		return img
+	}
+
+	// Input image has no pixels
+	if img.Bounds().Dx() <= 0 || img.Bounds().Dy() <= 0 {
+		return img
+	}
+
+	if interp == NearestNeighbor {
+		return resizeNearest(width, height, scaleX, scaleY, img, interp)
+	}
+
+	taps, kernel := interp.kernel()
+	cpus := runtime.GOMAXPROCS(0)
+	wg := sync.WaitGroup{}
+
+	// Generic access to image.Image is slow in tight loops.
+	// The optimal access has to be determined from the concrete image type.
+	switch input := img.(type) {
+	case *image.RGBA:
+		// 8-bit precision
+		temp := image.NewRGBA(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewRGBA(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeights8(temp.Bounds().Dy(), taps, blur, scaleX, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.RGBA)
+			go func() {
+				defer wg.Done()
+				resizeRGBA(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeights8(result.Bounds().Dy(), taps, blur, scaleY, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.RGBA)
+			go func() {
+				defer wg.Done()
+				resizeRGBA(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	case *image.NRGBA:
+		// 8-bit precision
+		temp := image.NewRGBA(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewRGBA(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeights8(temp.Bounds().Dy(), taps, blur, scaleX, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.RGBA)
+			go func() {
+				defer wg.Done()
+				resizeNRGBA(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeights8(result.Bounds().Dy(), taps, blur, scaleY, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.RGBA)
+			go func() {
+				defer wg.Done()
+				resizeRGBA(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+
+	case *image.YCbCr:
+		// 8-bit precision
+		// accessing the YCbCr arrays in a tight loop is slow.
+		// converting the image to ycc increases performance by 2x.
+		temp := newYCC(image.Rect(0, 0, input.Bounds().Dy(), int(width)), input.SubsampleRatio)
+		result := newYCC(image.Rect(0, 0, int(width), int(height)), image.YCbCrSubsampleRatio444)
+
+		coeffs, offset, filterLength := createWeights8(temp.Bounds().Dy(), taps, blur, scaleX, kernel)
+		in := imageYCbCrToYCC(input)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*ycc)
+			go func() {
+				defer wg.Done()
+				resizeYCbCr(in, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		coeffs, offset, filterLength = createWeights8(result.Bounds().Dy(), taps, blur, scaleY, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*ycc)
+			go func() {
+				defer wg.Done()
+				resizeYCbCr(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result.YCbCr()
+	case *image.RGBA64:
+		// 16-bit precision
+		temp := image.NewRGBA64(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewRGBA64(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeights16(temp.Bounds().Dy(), taps, blur, scaleX, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.RGBA64)
+			go func() {
+				defer wg.Done()
+				resizeRGBA64(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeights16(result.Bounds().Dy(), taps, blur, scaleY, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.RGBA64)
+			go func() {
+				defer wg.Done()
+				resizeRGBA64(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	case *image.NRGBA64:
+		// 16-bit precision
+		temp := image.NewRGBA64(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewRGBA64(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeights16(temp.Bounds().Dy(), taps, blur, scaleX, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.RGBA64)
+			go func() {
+				defer wg.Done()
+				resizeNRGBA64(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeights16(result.Bounds().Dy(), taps, blur, scaleY, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.RGBA64)
+			go func() {
+				defer wg.Done()
+				resizeRGBA64(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	case *image.Gray:
+		// 8-bit precision
+		temp := image.NewGray(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewGray(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeights8(temp.Bounds().Dy(), taps, blur, scaleX, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.Gray)
+			go func() {
+				defer wg.Done()
+				resizeGray(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeights8(result.Bounds().Dy(), taps, blur, scaleY, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.Gray)
+			go func() {
+				defer wg.Done()
+				resizeGray(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	case *image.Gray16:
+		// 16-bit precision
+		temp := image.NewGray16(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewGray16(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeights16(temp.Bounds().Dy(), taps, blur, scaleX, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.Gray16)
+			go func() {
+				defer wg.Done()
+				resizeGray16(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeights16(result.Bounds().Dy(), taps, blur, scaleY, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.Gray16)
+			go func() {
+				defer wg.Done()
+				resizeGray16(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	default:
+		// 16-bit precision
+		temp := image.NewRGBA64(image.Rect(0, 0, img.Bounds().Dy(), int(width)))
+		result := image.NewRGBA64(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeights16(temp.Bounds().Dy(), taps, blur, scaleX, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.RGBA64)
+			go func() {
+				defer wg.Done()
+				resizeGeneric(img, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeights16(result.Bounds().Dy(), taps, blur, scaleY, kernel)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.RGBA64)
+			go func() {
+				defer wg.Done()
+				resizeRGBA64(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	}
+}
+
+func resizeNearest(width, height uint, scaleX, scaleY float64, img image.Image, interp InterpolationFunction) image.Image {
+	taps, _ := interp.kernel()
+	cpus := runtime.GOMAXPROCS(0)
+	wg := sync.WaitGroup{}
+
+	switch input := img.(type) {
+	case *image.RGBA:
+		// 8-bit precision
+		temp := image.NewRGBA(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewRGBA(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeightsNearest(temp.Bounds().Dy(), taps, blur, scaleX)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.RGBA)
+			go func() {
+				defer wg.Done()
+				nearestRGBA(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeightsNearest(result.Bounds().Dy(), taps, blur, scaleY)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.RGBA)
+			go func() {
+				defer wg.Done()
+				nearestRGBA(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	case *image.NRGBA:
+		// 8-bit precision
+		temp := image.NewNRGBA(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewNRGBA(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeightsNearest(temp.Bounds().Dy(), taps, blur, scaleX)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.NRGBA)
+			go func() {
+				defer wg.Done()
+				nearestNRGBA(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeightsNearest(result.Bounds().Dy(), taps, blur, scaleY)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.NRGBA)
+			go func() {
+				defer wg.Done()
+				nearestNRGBA(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	case *image.YCbCr:
+		// 8-bit precision
+		// accessing the YCbCr arrays in a tight loop is slow.
+		// converting the image to ycc increases performance by 2x.
+		temp := newYCC(image.Rect(0, 0, input.Bounds().Dy(), int(width)), input.SubsampleRatio)
+		result := newYCC(image.Rect(0, 0, int(width), int(height)), image.YCbCrSubsampleRatio444)
+
+		coeffs, offset, filterLength := createWeightsNearest(temp.Bounds().Dy(), taps, blur, scaleX)
+		in := imageYCbCrToYCC(input)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*ycc)
+			go func() {
+				defer wg.Done()
+				nearestYCbCr(in, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		coeffs, offset, filterLength = createWeightsNearest(result.Bounds().Dy(), taps, blur, scaleY)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*ycc)
+			go func() {
+				defer wg.Done()
+				nearestYCbCr(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result.YCbCr()
+	case *image.RGBA64:
+		// 16-bit precision
+		temp := image.NewRGBA64(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewRGBA64(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeightsNearest(temp.Bounds().Dy(), taps, blur, scaleX)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.RGBA64)
+			go func() {
+				defer wg.Done()
+				nearestRGBA64(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeightsNearest(result.Bounds().Dy(), taps, blur, scaleY)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.RGBA64)
+			go func() {
+				defer wg.Done()
+				nearestRGBA64(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	case *image.NRGBA64:
+		// 16-bit precision
+		temp := image.NewNRGBA64(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewNRGBA64(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeightsNearest(temp.Bounds().Dy(), taps, blur, scaleX)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.NRGBA64)
+			go func() {
+				defer wg.Done()
+				nearestNRGBA64(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeightsNearest(result.Bounds().Dy(), taps, blur, scaleY)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.NRGBA64)
+			go func() {
+				defer wg.Done()
+				nearestNRGBA64(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	case *image.Gray:
+		// 8-bit precision
+		temp := image.NewGray(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewGray(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeightsNearest(temp.Bounds().Dy(), taps, blur, scaleX)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.Gray)
+			go func() {
+				defer wg.Done()
+				nearestGray(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeightsNearest(result.Bounds().Dy(), taps, blur, scaleY)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.Gray)
+			go func() {
+				defer wg.Done()
+				nearestGray(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	case *image.Gray16:
+		// 16-bit precision
+		temp := image.NewGray16(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewGray16(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeightsNearest(temp.Bounds().Dy(), taps, blur, scaleX)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.Gray16)
+			go func() {
+				defer wg.Done()
+				nearestGray16(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeightsNearest(result.Bounds().Dy(), taps, blur, scaleY)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.Gray16)
+			go func() {
+				defer wg.Done()
+				nearestGray16(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	default:
+		// 16-bit precision
+		temp := image.NewRGBA64(image.Rect(0, 0, img.Bounds().Dy(), int(width)))
+		result := image.NewRGBA64(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeightsNearest(temp.Bounds().Dy(), taps, blur, scaleX)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.RGBA64)
+			go func() {
+				defer wg.Done()
+				nearestGeneric(img, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeightsNearest(result.Bounds().Dy(), taps, blur, scaleY)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.RGBA64)
+			go func() {
+				defer wg.Done()
+				nearestRGBA64(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	}
+
+}
+
+// Calculates scaling factors using old and new image dimensions.
+func calcFactors(width, height uint, oldWidth, oldHeight float64) (scaleX, scaleY float64) {
+	if width == 0 {
+		if height == 0 {
+			scaleX = 1.0
+			scaleY = 1.0
+		} else {
+			scaleY = oldHeight / float64(height)
+			scaleX = scaleY
+		}
+	} else {
+		scaleX = oldWidth / float64(width)
+		if height == 0 {
+			scaleY = scaleX
+		} else {
+			scaleY = oldHeight / float64(height)
+		}
+	}
+	return
+}
+
+type imageWithSubImage interface {
+	image.Image
+	SubImage(image.Rectangle) image.Image
+}
+
+func makeSlice(img imageWithSubImage, i, n int) image.Image {
+	return img.SubImage(image.Rect(img.Bounds().Min.X, img.Bounds().Min.Y+i*img.Bounds().Dy()/n, img.Bounds().Max.X, img.Bounds().Min.Y+(i+1)*img.Bounds().Dy()/n))
+}

vendor/github.com/nfnt/resize/thumbnail.go

@@ -0,0 +1,55 @@
+/*
+Copyright (c) 2012, Jan Schlicht <jan.schlicht@gmail.com>
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.
+*/
+
+package resize
+
+import (
+	"image"
+)
+
+// Thumbnail will downscale provided image to max width and height preserving
+// original aspect ratio and using the interpolation function interp.
+// It will return original image, without processing it, if original sizes
+// are already smaller than provided constraints.
+func Thumbnail(maxWidth, maxHeight uint, img image.Image, interp InterpolationFunction) image.Image {
+	origBounds := img.Bounds()
+	origWidth := uint(origBounds.Dx())
+	origHeight := uint(origBounds.Dy())
+	newWidth, newHeight := origWidth, origHeight
+
+	// Return original image if it have same or smaller size as constraints
+	if maxWidth >= origWidth && maxHeight >= origHeight {
+		return img
+	}
+
+	// Preserve aspect ratio
+	if origWidth > maxWidth {
+		newHeight = uint(origHeight * maxWidth / origWidth)
+		if newHeight < 1 {
+			newHeight = 1
+		}
+		newWidth = maxWidth
+	}
+
+	if newHeight > maxHeight {
+		newWidth = uint(newWidth * maxHeight / newHeight)
+		if newWidth < 1 {
+			newWidth = 1
+		}
+		newHeight = maxHeight
+	}
+	return Resize(newWidth, newHeight, img, interp)
+}

vendor/github.com/nfnt/resize/ycc.go

@@ -0,0 +1,387 @@
+/*
+Copyright (c) 2014, Charlie Vieth <charlie.vieth@gmail.com>
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.
+*/
+
+package resize
+
+import (
+	"image"
+	"image/color"
+)
+
+// ycc is an in memory YCbCr image.  The Y, Cb and Cr samples are held in a
+// single slice to increase resizing performance.
+type ycc struct {
+	// Pix holds the image's pixels, in Y, Cb, Cr order. The pixel at
+	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*3].
+	Pix []uint8
+	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
+	Stride int
+	// Rect is the image's bounds.
+	Rect image.Rectangle
+	// SubsampleRatio is the subsample ratio of the original YCbCr image.
+	SubsampleRatio image.YCbCrSubsampleRatio
+}
+
+// PixOffset returns the index of the first element of Pix that corresponds to
+// the pixel at (x, y).
+func (p *ycc) PixOffset(x, y int) int {
+	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*3
+}
+
+func (p *ycc) Bounds() image.Rectangle {
+	return p.Rect
+}
+
+func (p *ycc) ColorModel() color.Model {
+	return color.YCbCrModel
+}
+
+func (p *ycc) At(x, y int) color.Color {
+	if !(image.Point{x, y}.In(p.Rect)) {
+		return color.YCbCr{}
+	}
+	i := p.PixOffset(x, y)
+	return color.YCbCr{
+		p.Pix[i+0],
+		p.Pix[i+1],
+		p.Pix[i+2],
+	}
+}
+
+func (p *ycc) Opaque() bool {
+	return true
+}
+
+// SubImage returns an image representing the portion of the image p visible
+// through r. The returned value shares pixels with the original image.
+func (p *ycc) SubImage(r image.Rectangle) image.Image {
+	r = r.Intersect(p.Rect)
+	if r.Empty() {
+		return &ycc{SubsampleRatio: p.SubsampleRatio}
+	}
+	i := p.PixOffset(r.Min.X, r.Min.Y)
+	return &ycc{
+		Pix:            p.Pix[i:],
+		Stride:         p.Stride,
+		Rect:           r,
+		SubsampleRatio: p.SubsampleRatio,
+	}
+}
+
+// newYCC returns a new ycc with the given bounds and subsample ratio.
+func newYCC(r image.Rectangle, s image.YCbCrSubsampleRatio) *ycc {
+	w, h := r.Dx(), r.Dy()
+	buf := make([]uint8, 3*w*h)
+	return &ycc{Pix: buf, Stride: 3 * w, Rect: r, SubsampleRatio: s}
+}
+
+// Copy of image.YCbCrSubsampleRatio constants - this allows us to support
+// older versions of Go where these constants are not defined (i.e. Go 1.4)
+const (
+	ycbcrSubsampleRatio444 image.YCbCrSubsampleRatio = iota
+	ycbcrSubsampleRatio422
+	ycbcrSubsampleRatio420
+	ycbcrSubsampleRatio440
+	ycbcrSubsampleRatio411
+	ycbcrSubsampleRatio410
+)
+
+// YCbCr converts ycc to a YCbCr image with the same subsample ratio
+// as the YCbCr image that ycc was generated from.
+func (p *ycc) YCbCr() *image.YCbCr {
+	ycbcr := image.NewYCbCr(p.Rect, p.SubsampleRatio)
+	switch ycbcr.SubsampleRatio {
+	case ycbcrSubsampleRatio422:
+		return p.ycbcr422(ycbcr)
+	case ycbcrSubsampleRatio420:
+		return p.ycbcr420(ycbcr)
+	case ycbcrSubsampleRatio440:
+		return p.ycbcr440(ycbcr)
+	case ycbcrSubsampleRatio444:
+		return p.ycbcr444(ycbcr)
+	case ycbcrSubsampleRatio411:
+		return p.ycbcr411(ycbcr)
+	case ycbcrSubsampleRatio410:
+		return p.ycbcr410(ycbcr)
+	}
+	return ycbcr
+}
+
+// imageYCbCrToYCC converts a YCbCr image to a ycc image for resizing.
+func imageYCbCrToYCC(in *image.YCbCr) *ycc {
+	w, h := in.Rect.Dx(), in.Rect.Dy()
+	p := ycc{
+		Pix:            make([]uint8, 3*w*h),
+		Stride:         3 * w,
+		Rect:           image.Rect(0, 0, w, h),
+		SubsampleRatio: in.SubsampleRatio,
+	}
+	switch in.SubsampleRatio {
+	case ycbcrSubsampleRatio422:
+		return convertToYCC422(in, &p)
+	case ycbcrSubsampleRatio420:
+		return convertToYCC420(in, &p)
+	case ycbcrSubsampleRatio440:
+		return convertToYCC440(in, &p)
+	case ycbcrSubsampleRatio444:
+		return convertToYCC444(in, &p)
+	case ycbcrSubsampleRatio411:
+		return convertToYCC411(in, &p)
+	case ycbcrSubsampleRatio410:
+		return convertToYCC410(in, &p)
+	}
+	return &p
+}
+
+func (p *ycc) ycbcr422(ycbcr *image.YCbCr) *image.YCbCr {
+	var off int
+	Pix := p.Pix
+	Y := ycbcr.Y
+	Cb := ycbcr.Cb
+	Cr := ycbcr.Cr
+	for y := 0; y < ycbcr.Rect.Max.Y-ycbcr.Rect.Min.Y; y++ {
+		yy := y * ycbcr.YStride
+		cy := y * ycbcr.CStride
+		for x := 0; x < ycbcr.Rect.Max.X-ycbcr.Rect.Min.X; x++ {
+			ci := cy + x/2
+			Y[yy+x] = Pix[off+0]
+			Cb[ci] = Pix[off+1]
+			Cr[ci] = Pix[off+2]
+			off += 3
+		}
+	}
+	return ycbcr
+}
+
+func (p *ycc) ycbcr420(ycbcr *image.YCbCr) *image.YCbCr {
+	var off int
+	Pix := p.Pix
+	Y := ycbcr.Y
+	Cb := ycbcr.Cb
+	Cr := ycbcr.Cr
+	for y := 0; y < ycbcr.Rect.Max.Y-ycbcr.Rect.Min.Y; y++ {
+		yy := y * ycbcr.YStride
+		cy := (y / 2) * ycbcr.CStride
+		for x := 0; x < ycbcr.Rect.Max.X-ycbcr.Rect.Min.X; x++ {
+			ci := cy + x/2
+			Y[yy+x] = Pix[off+0]
+			Cb[ci] = Pix[off+1]
+			Cr[ci] = Pix[off+2]
+			off += 3
+		}
+	}
+	return ycbcr
+}
+
+func (p *ycc) ycbcr440(ycbcr *image.YCbCr) *image.YCbCr {
+	var off int
+	Pix := p.Pix
+	Y := ycbcr.Y
+	Cb := ycbcr.Cb
+	Cr := ycbcr.Cr
+	for y := 0; y < ycbcr.Rect.Max.Y-ycbcr.Rect.Min.Y; y++ {
+		yy := y * ycbcr.YStride
+		cy := (y / 2) * ycbcr.CStride
+		for x := 0; x < ycbcr.Rect.Max.X-ycbcr.Rect.Min.X; x++ {
+			ci := cy + x
+			Y[yy+x] = Pix[off+0]
+			Cb[ci] = Pix[off+1]
+			Cr[ci] = Pix[off+2]
+			off += 3
+		}
+	}
+	return ycbcr
+}
+
+func (p *ycc) ycbcr444(ycbcr *image.YCbCr) *image.YCbCr {
+	var off int
+	Pix := p.Pix
+	Y := ycbcr.Y
+	Cb := ycbcr.Cb
+	Cr := ycbcr.Cr
+	for y := 0; y < ycbcr.Rect.Max.Y-ycbcr.Rect.Min.Y; y++ {
+		yy := y * ycbcr.YStride
+		cy := y * ycbcr.CStride
+		for x := 0; x < ycbcr.Rect.Max.X-ycbcr.Rect.Min.X; x++ {
+			ci := cy + x
+			Y[yy+x] = Pix[off+0]
+			Cb[ci] = Pix[off+1]
+			Cr[ci] = Pix[off+2]
+			off += 3
+		}
+	}
+	return ycbcr
+}
+
+func (p *ycc) ycbcr411(ycbcr *image.YCbCr) *image.YCbCr {
+	var off int
+	Pix := p.Pix
+	Y := ycbcr.Y
+	Cb := ycbcr.Cb
+	Cr := ycbcr.Cr
+	for y := 0; y < ycbcr.Rect.Max.Y-ycbcr.Rect.Min.Y; y++ {
+		yy := y * ycbcr.YStride
+		cy := y * ycbcr.CStride
+		for x := 0; x < ycbcr.Rect.Max.X-ycbcr.Rect.Min.X; x++ {
+			ci := cy + x/4
+			Y[yy+x] = Pix[off+0]
+			Cb[ci] = Pix[off+1]
+			Cr[ci] = Pix[off+2]
+			off += 3
+		}
+	}
+	return ycbcr
+}
+
+func (p *ycc) ycbcr410(ycbcr *image.YCbCr) *image.YCbCr {
+	var off int
+	Pix := p.Pix
+	Y := ycbcr.Y
+	Cb := ycbcr.Cb
+	Cr := ycbcr.Cr
+	for y := 0; y < ycbcr.Rect.Max.Y-ycbcr.Rect.Min.Y; y++ {
+		yy := y * ycbcr.YStride
+		cy := (y / 2) * ycbcr.CStride
+		for x := 0; x < ycbcr.Rect.Max.X-ycbcr.Rect.Min.X; x++ {
+			ci := cy + x/4
+			Y[yy+x] = Pix[off+0]
+			Cb[ci] = Pix[off+1]
+			Cr[ci] = Pix[off+2]
+			off += 3
+		}
+	}
+	return ycbcr
+}
+
+func convertToYCC422(in *image.YCbCr, p *ycc) *ycc {
+	var off int
+	Pix := p.Pix
+	Y := in.Y
+	Cb := in.Cb
+	Cr := in.Cr
+	for y := 0; y < in.Rect.Max.Y-in.Rect.Min.Y; y++ {
+		yy := y * in.YStride
+		cy := y * in.CStride
+		for x := 0; x < in.Rect.Max.X-in.Rect.Min.X; x++ {
+			ci := cy + x/2
+			Pix[off+0] = Y[yy+x]
+			Pix[off+1] = Cb[ci]
+			Pix[off+2] = Cr[ci]
+			off += 3
+		}
+	}
+	return p
+}
+
+func convertToYCC420(in *image.YCbCr, p *ycc) *ycc {
+	var off int
+	Pix := p.Pix
+	Y := in.Y
+	Cb := in.Cb
+	Cr := in.Cr
+	for y := 0; y < in.Rect.Max.Y-in.Rect.Min.Y; y++ {
+		yy := y * in.YStride
+		cy := (y / 2) * in.CStride
+		for x := 0; x < in.Rect.Max.X-in.Rect.Min.X; x++ {
+			ci := cy + x/2
+			Pix[off+0] = Y[yy+x]
+			Pix[off+1] = Cb[ci]
+			Pix[off+2] = Cr[ci]
+			off += 3
+		}
+	}
+	return p
+}
+
+func convertToYCC440(in *image.YCbCr, p *ycc) *ycc {
+	var off int
+	Pix := p.Pix
+	Y := in.Y
+	Cb := in.Cb
+	Cr := in.Cr
+	for y := 0; y < in.Rect.Max.Y-in.Rect.Min.Y; y++ {
+		yy := y * in.YStride
+		cy := (y / 2) * in.CStride
+		for x := 0; x < in.Rect.Max.X-in.Rect.Min.X; x++ {
+			ci := cy + x
+			Pix[off+0] = Y[yy+x]
+			Pix[off+1] = Cb[ci]
+			Pix[off+2] = Cr[ci]
+			off += 3
+		}
+	}
+	return p
+}
+
+func convertToYCC444(in *image.YCbCr, p *ycc) *ycc {
+	var off int
+	Pix := p.Pix
+	Y := in.Y
+	Cb := in.Cb
+	Cr := in.Cr
+	for y := 0; y < in.Rect.Max.Y-in.Rect.Min.Y; y++ {
+		yy := y * in.YStride
+		cy := y * in.CStride
+		for x := 0; x < in.Rect.Max.X-in.Rect.Min.X; x++ {
+			ci := cy + x
+			Pix[off+0] = Y[yy+x]
+			Pix[off+1] = Cb[ci]
+			Pix[off+2] = Cr[ci]
+			off += 3
+		}
+	}
+	return p
+}
+
+func convertToYCC411(in *image.YCbCr, p *ycc) *ycc {
+	var off int
+	Pix := p.Pix
+	Y := in.Y
+	Cb := in.Cb
+	Cr := in.Cr
+	for y := 0; y < in.Rect.Max.Y-in.Rect.Min.Y; y++ {
+		yy := y * in.YStride
+		cy := y * in.CStride
+		for x := 0; x < in.Rect.Max.X-in.Rect.Min.X; x++ {
+			ci := cy + x/4
+			Pix[off+0] = Y[yy+x]
+			Pix[off+1] = Cb[ci]
+			Pix[off+2] = Cr[ci]
+			off += 3
+		}
+	}
+	return p
+}
+
+func convertToYCC410(in *image.YCbCr, p *ycc) *ycc {
+	var off int
+	Pix := p.Pix
+	Y := in.Y
+	Cb := in.Cb
+	Cr := in.Cr
+	for y := 0; y < in.Rect.Max.Y-in.Rect.Min.Y; y++ {
+		yy := y * in.YStride
+		cy := (y / 2) * in.CStride
+		for x := 0; x < in.Rect.Max.X-in.Rect.Min.X; x++ {
+			ci := cy + x/4
+			Pix[off+0] = Y[yy+x]
+			Pix[off+1] = Cb[ci]
+			Pix[off+2] = Cr[ci]
+			off += 3
+		}
+	}
+	return p
+}