зеркало из https://github.com/golang/image.git
300 строки
8.2 KiB
Go
300 строки
8.2 KiB
Go
// Copyright 2014 The Go 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 vp8l
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// This file deals with image transforms, specified in section 3.
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// nTiles returns the number of tiles needed to cover size pixels, where each
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// tile's side is 1<<bits pixels long.
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func nTiles(size int32, bits uint32) int32 {
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return (size + 1<<bits - 1) >> bits
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}
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const (
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transformTypePredictor = 0
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transformTypeCrossColor = 1
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transformTypeSubtractGreen = 2
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transformTypeColorIndexing = 3
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nTransformTypes = 4
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)
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// transform holds the parameters for an invertible transform.
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type transform struct {
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// transformType is the type of the transform.
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transformType uint32
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// oldWidth is the width of the image before transformation (or
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// equivalently, after inverse transformation). The color-indexing
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// transform can reduce the width. For example, a 50-pixel-wide
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// image that only needs 4 bits (half a byte) per color index can
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// be transformed into a 25-pixel-wide image.
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oldWidth int32
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// bits is the log-2 size of the transform's tiles, for the predictor
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// and cross-color transforms. 8>>bits is the number of bits per
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// color index, for the color-index transform.
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bits uint32
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// pix is the tile values, for the predictor and cross-color
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// transforms, and the color palette, for the color-index transform.
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pix []byte
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}
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var inverseTransforms = [nTransformTypes]func(*transform, []byte, int32) []byte{
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transformTypePredictor: inversePredictor,
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transformTypeCrossColor: inverseCrossColor,
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transformTypeSubtractGreen: inverseSubtractGreen,
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transformTypeColorIndexing: inverseColorIndexing,
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}
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func inversePredictor(t *transform, pix []byte, h int32) []byte {
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if t.oldWidth == 0 || h == 0 {
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return pix
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}
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// The first pixel's predictor is mode 0 (opaque black).
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pix[3] += 0xff
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p, mask := int32(4), int32(1)<<t.bits-1
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for x := int32(1); x < t.oldWidth; x++ {
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// The rest of the first row's predictor is mode 1 (L).
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pix[p+0] += pix[p-4]
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pix[p+1] += pix[p-3]
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pix[p+2] += pix[p-2]
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pix[p+3] += pix[p-1]
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p += 4
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}
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top, tilesPerRow := 0, nTiles(t.oldWidth, t.bits)
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for y := int32(1); y < h; y++ {
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// The first column's predictor is mode 2 (T).
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pix[p+0] += pix[top+0]
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pix[p+1] += pix[top+1]
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pix[p+2] += pix[top+2]
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pix[p+3] += pix[top+3]
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p, top = p+4, top+4
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q := 4 * (y >> t.bits) * tilesPerRow
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predictorMode := t.pix[q+1] & 0x0f
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q += 4
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for x := int32(1); x < t.oldWidth; x++ {
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if x&mask == 0 {
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predictorMode = t.pix[q+1] & 0x0f
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q += 4
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}
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switch predictorMode {
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case 0: // Opaque black.
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pix[p+3] += 0xff
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case 1: // L.
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pix[p+0] += pix[p-4]
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pix[p+1] += pix[p-3]
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pix[p+2] += pix[p-2]
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pix[p+3] += pix[p-1]
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case 2: // T.
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pix[p+0] += pix[top+0]
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pix[p+1] += pix[top+1]
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pix[p+2] += pix[top+2]
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pix[p+3] += pix[top+3]
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case 3: // TR.
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pix[p+0] += pix[top+4]
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pix[p+1] += pix[top+5]
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pix[p+2] += pix[top+6]
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pix[p+3] += pix[top+7]
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case 4: // TL.
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pix[p+0] += pix[top-4]
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pix[p+1] += pix[top-3]
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pix[p+2] += pix[top-2]
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pix[p+3] += pix[top-1]
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case 5: // Average2(Average2(L, TR), T).
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pix[p+0] += avg2(avg2(pix[p-4], pix[top+4]), pix[top+0])
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pix[p+1] += avg2(avg2(pix[p-3], pix[top+5]), pix[top+1])
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pix[p+2] += avg2(avg2(pix[p-2], pix[top+6]), pix[top+2])
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pix[p+3] += avg2(avg2(pix[p-1], pix[top+7]), pix[top+3])
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case 6: // Average2(L, TL).
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pix[p+0] += avg2(pix[p-4], pix[top-4])
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pix[p+1] += avg2(pix[p-3], pix[top-3])
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pix[p+2] += avg2(pix[p-2], pix[top-2])
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pix[p+3] += avg2(pix[p-1], pix[top-1])
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case 7: // Average2(L, T).
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pix[p+0] += avg2(pix[p-4], pix[top+0])
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pix[p+1] += avg2(pix[p-3], pix[top+1])
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pix[p+2] += avg2(pix[p-2], pix[top+2])
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pix[p+3] += avg2(pix[p-1], pix[top+3])
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case 8: // Average2(TL, T).
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pix[p+0] += avg2(pix[top-4], pix[top+0])
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pix[p+1] += avg2(pix[top-3], pix[top+1])
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pix[p+2] += avg2(pix[top-2], pix[top+2])
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pix[p+3] += avg2(pix[top-1], pix[top+3])
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case 9: // Average2(T, TR).
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pix[p+0] += avg2(pix[top+0], pix[top+4])
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pix[p+1] += avg2(pix[top+1], pix[top+5])
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pix[p+2] += avg2(pix[top+2], pix[top+6])
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pix[p+3] += avg2(pix[top+3], pix[top+7])
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case 10: // Average2(Average2(L, TL), Average2(T, TR)).
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pix[p+0] += avg2(avg2(pix[p-4], pix[top-4]), avg2(pix[top+0], pix[top+4]))
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pix[p+1] += avg2(avg2(pix[p-3], pix[top-3]), avg2(pix[top+1], pix[top+5]))
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pix[p+2] += avg2(avg2(pix[p-2], pix[top-2]), avg2(pix[top+2], pix[top+6]))
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pix[p+3] += avg2(avg2(pix[p-1], pix[top-1]), avg2(pix[top+3], pix[top+7]))
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case 11: // Select(L, T, TL).
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l0 := int32(pix[p-4])
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l1 := int32(pix[p-3])
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l2 := int32(pix[p-2])
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l3 := int32(pix[p-1])
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c0 := int32(pix[top-4])
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c1 := int32(pix[top-3])
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c2 := int32(pix[top-2])
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c3 := int32(pix[top-1])
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t0 := int32(pix[top+0])
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t1 := int32(pix[top+1])
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t2 := int32(pix[top+2])
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t3 := int32(pix[top+3])
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l := abs(c0-t0) + abs(c1-t1) + abs(c2-t2) + abs(c3-t3)
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t := abs(c0-l0) + abs(c1-l1) + abs(c2-l2) + abs(c3-l3)
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if l < t {
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pix[p+0] += uint8(l0)
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pix[p+1] += uint8(l1)
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pix[p+2] += uint8(l2)
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pix[p+3] += uint8(l3)
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} else {
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pix[p+0] += uint8(t0)
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pix[p+1] += uint8(t1)
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pix[p+2] += uint8(t2)
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pix[p+3] += uint8(t3)
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}
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case 12: // ClampAddSubtractFull(L, T, TL).
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pix[p+0] += clampAddSubtractFull(pix[p-4], pix[top+0], pix[top-4])
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pix[p+1] += clampAddSubtractFull(pix[p-3], pix[top+1], pix[top-3])
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pix[p+2] += clampAddSubtractFull(pix[p-2], pix[top+2], pix[top-2])
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pix[p+3] += clampAddSubtractFull(pix[p-1], pix[top+3], pix[top-1])
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case 13: // ClampAddSubtractHalf(Average2(L, T), TL).
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pix[p+0] += clampAddSubtractHalf(avg2(pix[p-4], pix[top+0]), pix[top-4])
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pix[p+1] += clampAddSubtractHalf(avg2(pix[p-3], pix[top+1]), pix[top-3])
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pix[p+2] += clampAddSubtractHalf(avg2(pix[p-2], pix[top+2]), pix[top-2])
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pix[p+3] += clampAddSubtractHalf(avg2(pix[p-1], pix[top+3]), pix[top-1])
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}
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p, top = p+4, top+4
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}
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}
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return pix
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}
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func inverseCrossColor(t *transform, pix []byte, h int32) []byte {
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var greenToRed, greenToBlue, redToBlue int32
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p, mask, tilesPerRow := int32(0), int32(1)<<t.bits-1, nTiles(t.oldWidth, t.bits)
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for y := int32(0); y < h; y++ {
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q := 4 * (y >> t.bits) * tilesPerRow
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for x := int32(0); x < t.oldWidth; x++ {
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if x&mask == 0 {
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redToBlue = int32(int8(t.pix[q+0]))
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greenToBlue = int32(int8(t.pix[q+1]))
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greenToRed = int32(int8(t.pix[q+2]))
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q += 4
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}
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red := pix[p+0]
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green := pix[p+1]
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blue := pix[p+2]
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red += uint8(uint32(greenToRed*int32(int8(green))) >> 5)
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blue += uint8(uint32(greenToBlue*int32(int8(green))) >> 5)
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blue += uint8(uint32(redToBlue*int32(int8(red))) >> 5)
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pix[p+0] = red
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pix[p+2] = blue
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p += 4
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}
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}
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return pix
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}
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func inverseSubtractGreen(t *transform, pix []byte, h int32) []byte {
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for p := 0; p < len(pix); p += 4 {
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green := pix[p+1]
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pix[p+0] += green
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pix[p+2] += green
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}
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return pix
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}
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func inverseColorIndexing(t *transform, pix []byte, h int32) []byte {
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if t.bits == 0 {
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for p := 0; p < len(pix); p += 4 {
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i := 4 * uint32(pix[p+1])
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pix[p+0] = t.pix[i+0]
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pix[p+1] = t.pix[i+1]
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pix[p+2] = t.pix[i+2]
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pix[p+3] = t.pix[i+3]
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}
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return pix
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}
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vMask, xMask, bitsPerPixel := uint32(0), int32(0), uint32(8>>t.bits)
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switch t.bits {
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case 1:
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vMask, xMask = 0x0f, 0x01
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case 2:
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vMask, xMask = 0x03, 0x03
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case 3:
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vMask, xMask = 0x01, 0x07
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}
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d, p, v, dst := 0, 0, uint32(0), make([]byte, 4*t.oldWidth*h)
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for y := int32(0); y < h; y++ {
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for x := int32(0); x < t.oldWidth; x++ {
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if x&xMask == 0 {
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v = uint32(pix[p+1])
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p += 4
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}
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i := 4 * (v & vMask)
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dst[d+0] = t.pix[i+0]
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dst[d+1] = t.pix[i+1]
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dst[d+2] = t.pix[i+2]
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dst[d+3] = t.pix[i+3]
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d += 4
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v >>= bitsPerPixel
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}
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}
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return dst
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}
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func abs(x int32) int32 {
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if x < 0 {
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return -x
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}
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return x
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}
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func avg2(a, b uint8) uint8 {
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return uint8((int32(a) + int32(b)) / 2)
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}
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func clampAddSubtractFull(a, b, c uint8) uint8 {
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x := int32(a) + int32(b) - int32(c)
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if x < 0 {
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return 0
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}
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if x > 255 {
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return 255
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}
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return uint8(x)
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}
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func clampAddSubtractHalf(a, b uint8) uint8 {
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x := int32(a) + (int32(a)-int32(b))/2
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if x < 0 {
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return 0
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}
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if x > 255 {
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return 255
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}
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return uint8(x)
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}
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