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@@ -0,0 +1,207 @@
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// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package ofdgo
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import (
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"context"
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"fmt"
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"image"
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"image/color"
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"math"
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)
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// readTIFFColorProfile 读取主图的ICC配置，校验颜色模型和数据范围
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// 入参: ctx 取消上下文，可为nil, data TIFF编码, layout 主图布局
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// 返回: *colorProfile 颜色配置，未声明时为nil, error 配置或取消错误
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func readTIFFColorProfile(ctx context.Context, data []byte, layout tiffImageLayout) (*colorProfile, error) {
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if ctx == nil {
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ctx = context.Background()
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}
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if err := ctx.Err(); err != nil {
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return nil, err
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}
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if layout.profileSize == 0 {
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return nil, nil
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}
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at, size := uint64(layout.profileOffset), uint64(layout.profileSize)
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if at+size > uint64(len(data)) {
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return nil, fmt.Errorf("truncated TIFF color profile")
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}
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kind := ""
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switch layout.photometric {
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case 0, 1:
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kind = "GRAY"
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case 2, 3:
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kind = "RGB"
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case 5:
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kind = "CMYK"
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default:
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return nil, fmt.Errorf("unsupported TIFF profile color model")
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}
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profile, err := parseColorProfile(kind, data[at:at+size])
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if cancelErr := ctx.Err(); cancelErr != nil {
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return nil, cancelErr
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}
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return profile, err
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}
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// applyTIFFColorProfile 将源颜色转换为十六位sRGB，保留独立透明度和隐藏颜色
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// 入参: ctx 取消上下文，可为nil, source 解码图像, profile 已校验的颜色配置
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// 返回: image.Image 独立透明度图像, error 颜色变换或取消错误
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func applyTIFFColorProfile(ctx context.Context, source image.Image, profile *colorProfile) (image.Image, error) {
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if ctx == nil {
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ctx = context.Background()
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}
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if err := ctx.Err(); err != nil {
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return nil, err
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}
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bounds := source.Bounds()
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if bounds.Dx() <= 0 || bounds.Dy() <= 0 || bounds.Dx() > math.MaxInt/8/bounds.Dy() {
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return nil, fmt.Errorf("TIFF profile image dimensions exceed capacity")
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}
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cmyk, _ := source.(*planarTIFFImage)
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if cmyk != nil && !cmyk.cmyk {
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cmyk = nil
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}
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model := source.ColorModel()
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premultiplied := model == color.RGBAModel || model == color.RGBA64Model
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table := newTIFFProfileTable(source)
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result := image.NewNRGBA64(bounds)
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for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
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for x := bounds.Min.X; x < bounds.Max.X; x++ {
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if (x-bounds.Min.X)&255 == 0 {
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if err := ctx.Err(); err != nil {
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return nil, err
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}
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}
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slot := -1
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if len(table) != 0 {
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index, alpha := tiffProfileSample(source, x, y, len(table))
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slot = index
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if pixel := table[index]; pixel.A != 0 {
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pixel.A = alpha
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result.SetNRGBA64(x, y, pixel)
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continue
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}
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}
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var values [4]float64
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var alpha uint16
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if cmyk != nil {
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ink := cmyk.inksAt(x, y)
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alpha = ink[4]
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if cmyk.alpha == 1 && alpha == 0 {
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continue
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}
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maximum := float64(65535)
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if cmyk.alpha == 1 {
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maximum = float64(alpha)
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}
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for i := range values {
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values[i] = min(1, float64(ink[i])/maximum)
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}
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} else if premultiplied {
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var pixel color.RGBA64
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if native, ok := source.(image.RGBA64Image); ok {
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pixel = native.RGBA64At(x, y)
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} else {
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pixel = color.RGBA64Model.Convert(source.At(x, y)).(color.RGBA64)
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}
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alpha = pixel.A
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if alpha == 0 {
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continue
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}
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for i, value := range [3]uint16{pixel.R, pixel.G, pixel.B} {
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values[i] = min(1, float64(value)/float64(alpha))
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}
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} else {
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pixel := imageNRGBA64At(source, x, y)
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alpha = pixel.A
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values = [4]float64{float64(pixel.R) / 65535, float64(pixel.G) / 65535, float64(pixel.B) / 65535}
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}
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rgb, err := profile.rgb(values)
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if err != nil {
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return nil, err
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}
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var channels [3]uint16
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for i, value := range rgb {
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channels[i] = uint16(math.Round(max(0, min(1, value)) * 65535))
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}
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if slot >= 0 {
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table[slot] = color.NRGBA64{R: channels[0], G: channels[1], B: channels[2], A: 65535}
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}
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result.SetNRGBA64(x, y, color.NRGBA64{R: channels[0], G: channels[1], B: channels[2], A: alpha})
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}
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}
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if err := ctx.Err(); err != nil {
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return nil, err
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}
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return result, nil
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}
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// newTIFFProfileTable 为离散颜色分配查找表，预乘颜色及小图保持逐像素变换
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// 入参: source 已解码且尺寸有效的图像
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// 返回: []color.NRGBA64 颜色表，Alpha非零表示已有结果，不适用时为nil
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func newTIFFProfileTable(source image.Image) []color.NRGBA64 {
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count := 0
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switch source := source.(type) {
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case *image.Gray:
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count = 256
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case *image.Gray16:
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count = 65536
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case *image.Paletted:
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count = len(source.Palette)
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case *planarTIFFImage:
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if source.alpha != 1 {
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if len(source.palette) != 0 {
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count = len(source.palette)
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} else if source.gray {
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count = 256
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if source.packed[0] != 0 {
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count = 1 << source.packed[0]
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} else if _, ok := source.planes[0].(*image.Gray16); ok {
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count = 65536
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}
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}
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}
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}
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if count == 0 || count >= source.Bounds().Dx()*source.Bounds().Dy() {
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return nil
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}
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return make([]color.NRGBA64, count)
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}
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// tiffProfileSample 读取查找表索引与独立透明度，颜色键不包含透明度
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// 入参: source 适用查找表的图像, x 横坐标, y 纵坐标, count 颜色表长度
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// 返回: int 颜色索引, uint16 透明度
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func tiffProfileSample(source image.Image, x, y, count int) (int, uint16) {
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switch source := source.(type) {
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case *image.Gray:
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return int(source.GrayAt(x, y).Y), 65535
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case *image.Gray16:
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return int(source.Gray16At(x, y).Y), 65535
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case *image.Paletted:
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index := source.ColorIndexAt(x, y)
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_, _, _, alpha := source.Palette[index].RGBA()
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return int(index), uint16(alpha)
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case *planarTIFFImage:
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index := int(uint32(source.sampleAt(0, x, y)) * uint32(count-1) / 65535)
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alpha := uint16(65535)
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if source.alpha != 0 {
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alpha = source.sampleAt(1, x, y)
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}
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return index, alpha
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}
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return 0, 0
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}
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