39 lines
1.1 KiB
Go
39 lines
1.1 KiB
Go
// Copyright 2017 The goimagehash Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package transforms
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import (
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"image"
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"image/color"
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)
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func toGray(r, g, b uint8) uint8 {
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// 19595 + 38470 + 7471 equals 65536.
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return uint8((19595*uint32(r) + 38470*uint32(g) + 7471*uint32(b) + 1<<15) >> 16)
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}
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// Rgb2Gray function converts RGB to a gray scale array.
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func Rgb2Gray(colorImg image.Image) []uint8 {
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colorImg.Bounds().Dx()
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bounds := colorImg.Bounds()
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w, h := bounds.Dx(), bounds.Dy()
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pixels := make([]uint8, h*w)
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for i := range pixels {
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x, y := i%w, i/w
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var R, G, B uint32
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switch v := colorImg.At(x, y).(type) {
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case color.NRGBA: // pillow discards alpha during conversion and provides no way to pre-multiply it
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R, G, B = uint32(v.R)<<8, uint32(v.G)<<8, uint32(v.B)<<8
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default:
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R, G, B, _ = colorImg.At(x, y).RGBA()
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}
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// Pillow only operates on 8bit data, operating on higher bit data produces rounding differences
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pixels[i] = toGray(uint8(R>>8), uint8(G>>8), uint8(B>>8))
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}
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return pixels
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}
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