goimagehash/hashcompute.go

// 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"
	"image/draw"

	"gitea.narnian.us/lordwelch/goimagehash/etcs"
	"gitea.narnian.us/lordwelch/goimagehash/transforms"
	"github.com/anthonynsimon/bild/transform"
)

func ToGray(img image.Image) *image.Gray {
	gray := image.NewGray(image.Rect(0, 0, img.Bounds().Dx(), img.Bounds().Dy()))
	gray.Pix = transforms.Rgb2Gray(img)
	return gray
}

func resize(img image.Image, w, h int) *image.Gray {
	resized := transform.Resize(img, w, h, transform.Lanczos)
	r_gray := image.NewGray(image.Rect(0, 0, resized.Bounds().Dx(), resized.Bounds().Dy()))
	draw.Draw(r_gray, resized.Bounds(), resized, resized.Bounds().Min, draw.Src)
	return r_gray
}

// AverageHash function 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")
	}

	ahash := NewImageHash(0, AHash)

	gray := resize(ToGray(img), 8, 8)
	avg := etcs.MeanOfPixels(gray.Pix)

	for idx, p := range gray.Pix {
		if p > avg {
			ahash.leftShiftSet(len(gray.Pix) - 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)

	gray := resize(ToGray(img), 9, 8)

	idx := 0
	for y := 0; y < gray.Bounds().Dy(); y++ {
		for x := 0; x < gray.Bounds().Dx()-1; x++ {
			if gray.Pix[gray.PixOffset(x, y)] < gray.Pix[gray.PixOffset(x+1, y)] {
				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)
	gray := resize(ToGray(img), 32, 32)
	gray32 := make([]float64, len(gray.Pix))
	for i, p := range gray.Pix {
		gray32[i] = float64(p)
	}
	flattens := transforms.DCT2DFast32(&gray32)

	median := etcs.MedianOfPixelsFast64(flattens[:])

	for idx, p := range flattens {
		if p > median {
			phash.leftShiftSet(64 - idx - 1) // leftShiftSet
		}
	}

	return phash, nil
}

// 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
}

// 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 a power of 2
func ExtPerceptionHash(img image.Image, hash_size, freq int) (*ExtImageHash, error) {
	imgSize := hash_size * freq
	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
	// gray := resize(ToGray(img), imgSize, imgSize)
	// gray32 := make([][]float64, imgSize)
	// for i := range gray32 {
	// 	gray32[i] = make([]float64, imgSize)
	// 	for x := range gray32[i] {
	// 		gray32[i][x] = float64(gray.Pix[(gray.PixOffset(x, i))])
	// 	}
	// }

	// pixels := transforms.DCT2D(gray32, hash_size, hash_size)
	// flattens := FlattenPixels(pixels, hash_size, hash_size)
	// median := etcs.MedianOfPixels(flattens)
	// print(hash_size, "x", freq, " pix:", len(gray.Pix), " h:", imgSize, " flatten:", len(flattens), "\n")

	// lenOfUnit := 64
	// if (hash_size*hash_size)%lenOfUnit == 0 {
	// 	phash = make([]uint64, (hash_size*hash_size)/lenOfUnit)
	// } else {
	// 	phash = make([]uint64, (hash_size*hash_size)/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

	gray := resize(ToGray(img), width, height)
	avg := etcs.MeanOfPixels(gray.Pix)

	lenOfUnit := 64
	if imgSize%lenOfUnit == 0 {
		ahash = make([]uint64, imgSize/lenOfUnit)
	} else {
		ahash = make([]uint64, imgSize/lenOfUnit+1)
	}
	for idx, p := range gray.Pix {
		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

	gray := resize(ToGray(img), width+1, height)

	lenOfUnit := 64
	if imgSize%lenOfUnit == 0 {
		dhash = make([]uint64, imgSize/lenOfUnit)
	} else {
		dhash = make([]uint64, imgSize/lenOfUnit+1)
	}
	idx := 0
	for y := 0; y < gray.Bounds().Dy(); y++ {
		for x := 0; x < gray.Bounds().Dx()-1; x++ {
			if gray.Pix[gray.PixOffset(x, y)] < gray.Pix[gray.PixOffset(x+1, y)] {
				indexOfArray := idx / lenOfUnit
				indexOfBit := lenOfUnit - idx%lenOfUnit - 1
				dhash[indexOfArray] |= 1 << uint(indexOfBit)
			}
			idx++
		}
	}
	return NewExtImageHash(dhash, DHash, imgSize), nil
}