refactor(色彩管理): 统一色彩与四色保真

internal/codec/pdf/color.go

@@ -76,11 +76,7 @@ func (c *TransferCache) Resolve(reader *pdfgo.Reader, style pdfgo.Style, model p
 // 入参: space 合成空间, values 非预乘分量
 // 返回: [3]float64 显示颜色, error 校准颜色转换错误
 func OutputColor(space *pdfgo.ColorSpace, values [4]float64) ([3]float64, error) {
-	if space.Model == "DeviceCMYK" && !space.Calibrated() {
-		black := 1 - values[3]
-		return [3]float64{(1 - values[0]) * black, (1 - values[1]) * black, (1 - values[2]) * black}, nil
-	}
-	return space.RGB(values[:space.Components()], "RelativeColorimetric")
+	return space.SRGB(values[:space.Components()], "RelativeColorimetric")
 }
 
 // NormalBlend 判断混合模式是否为普通覆盖

internal/codec/pdf/image.go

@@ -15,6 +15,11 @@
 package pdf
 
 import (
+	"bytes"
+	"compress/zlib"
+	"context"
+	"encoding/binary"
+	"fmt"
 	"image"
 	"image/color"
 	"math"
@@ -23,6 +28,121 @@ import (
 	"github.com/xiaoqidun/pdfgo"
 )
 
+// EncodeCMYKTIFF 将直接四色图像保存为十六位无损TIFF，不经过显示颜色转换
+// 入参: ctx 取消上下文, source PDF源图像
+// 返回: []byte 含ICC和非预乘透明度的TIFF，非四色图像为nil, error 解码或编码错误
+func EncodeCMYKTIFF(ctx context.Context, source *pdfgo.Image) ([]byte, error) {
+	if ctx == nil || source == nil {
+		return nil, fmt.Errorf("missing CMYK image context or source")
+	}
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	if source.ImageMask {
+		return nil, nil
+	}
+	family, err := source.ColorSpaceFamily()
+	if err != nil || family != "DeviceCMYK" && family != "ICCBased" {
+		return nil, err
+	}
+	if family == "ICCBased" {
+		count, err := source.ColorSpaceComponents()
+		if err != nil || count != 4 {
+			return nil, err
+		}
+	}
+	components, err := source.DecodeComponentsViewContext(ctx)
+	if err != nil {
+		return nil, err
+	}
+	if components.Space == nil || components.Space.Model != "DeviceCMYK" || components.Space.Components() != 4 || components.ColorantSpace != nil {
+		return nil, nil
+	}
+	bounds := components.Rect
+	width, height := bounds.Dx(), bounds.Dy()
+	if width <= 0 || height <= 0 || width > int(^uint(0)>>1)/10 || uint64(width) > uint64(^uint32(0))/10 || uint64(height) > uint64(^uint32(0)) {
+		return nil, fmt.Errorf("invalid CMYK TIFF dimensions")
+	}
+	profile := components.Space.ICCProfile(source.Intent)
+	count := 12
+	if len(profile) != 0 {
+		count++
+	}
+	bitsOffset := uint64(8 + 2 + count*12 + 4)
+	profileOffset := bitsOffset + 10
+	stripOffset := (profileOffset + uint64(len(profile)) + 1) &^ uint64(1)
+	if stripOffset > uint64(^uint32(0)) {
+		return nil, fmt.Errorf("CMYK TIFF profile exceeds size limit")
+	}
+	var compressed bytes.Buffer
+	writer := zlib.NewWriter(&compressed)
+	row := make([]byte, width*10)
+	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+		for x := bounds.Min.X; x < bounds.Max.X; x++ {
+			if (x-bounds.Min.X)%1024 == 0 {
+				if err := ctx.Err(); err != nil {
+					writer.Close()
+					return nil, err
+				}
+			}
+			values, alpha := components.ValuesAt(x, y)
+			pixel := row[(x-bounds.Min.X)*10:]
+			for channel, value := range [5]float64{values[0], values[1], values[2], values[3], alpha} {
+				if math.IsNaN(value) || math.IsInf(value, 0) || value < 0 || value > 1 {
+					writer.Close()
+					return nil, fmt.Errorf("invalid CMYK TIFF component")
+				}
+				binary.LittleEndian.PutUint16(pixel[channel*2:], uint16(math.Round(value*65535)))
+			}
+		}
+		if _, err := writer.Write(row); err != nil {
+			writer.Close()
+			return nil, err
+		}
+		if stripOffset+uint64(compressed.Len()) > uint64(^uint32(0)) {
+			writer.Close()
+			return nil, fmt.Errorf("CMYK TIFF exceeds size limit")
+		}
+	}
+	if err := writer.Close(); err != nil {
+		return nil, err
+	}
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	total := stripOffset + uint64(compressed.Len())
+	if total > uint64(^uint32(0)) || total > uint64(int(^uint(0)>>1)) {
+		return nil, fmt.Errorf("CMYK TIFF exceeds size limit")
+	}
+	data := make([]byte, int(total))
+	copy(data, "II")
+	binary.LittleEndian.PutUint16(data[2:], 42)
+	binary.LittleEndian.PutUint32(data[4:], 8)
+	binary.LittleEndian.PutUint16(data[8:], uint16(count))
+	entries := [][4]uint32{
+		{256, 4, 1, uint32(width)}, {257, 4, 1, uint32(height)},
+		{258, 3, 5, uint32(bitsOffset)}, {259, 3, 1, 8}, {262, 3, 1, 5},
+		{273, 4, 1, uint32(stripOffset)}, {277, 3, 1, 5}, {278, 4, 1, uint32(height)},
+		{279, 4, 1, uint32(compressed.Len())}, {284, 3, 1, 1}, {332, 3, 1, 1}, {338, 3, 1, 2},
+	}
+	if len(profile) != 0 {
+		entries = append(entries, [4]uint32{34675, 7, uint32(len(profile)), uint32(profileOffset)})
+	}
+	for i, entry := range entries {
+		p := data[10+i*12:]
+		binary.LittleEndian.PutUint16(p, uint16(entry[0]))
+		binary.LittleEndian.PutUint16(p[2:], uint16(entry[1]))
+		binary.LittleEndian.PutUint32(p[4:], entry[2])
+		binary.LittleEndian.PutUint32(p[8:], entry[3])
+	}
+	for i := range 5 {
+		binary.LittleEndian.PutUint16(data[int(bitsOffset)+2*i:], 16)
+	}
+	copy(data[int(profileOffset):], profile)
+	copy(data[int(stripOffset):], compressed.Bytes())
+	return data, nil
+}
+
 // StencilImage 按当前填充色读取模板图像，不分配整幅彩色样本
 type StencilImage struct {
 	Source image.Image