refactor(色彩管理): 优化图像色彩转换性能

internal/base/image/tiff_profile.go

@@ -78,7 +78,7 @@ func applyTIFFColorProfile(ctx context.Context, source image.Image, profile *pdf
 	return applyImageColorProfile(ctx, source, profile, false)
 }
 
-// applyImageColorProfile 按源配置转换显示像素，缺省传递函数在浮点域解码
+// applyImageColorProfile 按源配置转换显示像素，精确复用连续同色结果
 // 入参: ctx 取消上下文, source 源像素, profile 颜色空间, linearSRGB 是否先解码sRGB传递函数
 // 返回: image.Image 十六位显示图像, error 变换或取消错误
 func applyImageColorProfile(ctx context.Context, source image.Image, profile *pdfgo.ColorSpace, linearSRGB bool) (image.Image, error) {
@@ -100,7 +100,10 @@ func applyImageColorProfile(ctx context.Context, source image.Image, profile *pd
 	premultiplied := model == color.RGBAModel || model == color.RGBA64Model
 	table := newTIFFProfileTable(source)
 	result := image.NewNRGBA64(bounds)
+	var previous [4]float64
+	var previousPixel color.NRGBA64
 	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+		misses := 0
 		for x := bounds.Min.X; x < bounds.Max.X; x++ {
 			if (x-bounds.Min.X)&255 == 0 {
 				if err := ctx.Err(); err != nil {
@@ -151,6 +154,17 @@ func applyImageColorProfile(ctx context.Context, source image.Image, profile *pd
 				alpha = pixel.A
 				values = [4]float64{float64(pixel.R) / 65535, float64(pixel.G) / 65535, float64(pixel.B) / 65535}
 			}
+			if misses < 32 {
+				if previousPixel.A != 0 && values == previous {
+					pixel := previousPixel
+					pixel.A = alpha
+					result.SetNRGBA64(x, y, pixel)
+					misses = 0
+					continue
+				}
+				previous = values
+				misses++
+			}
 			if linearSRGB {
 				for i := range 3 {
 					if values[i] <= 0.04045 {
@@ -168,6 +182,11 @@ func applyImageColorProfile(ctx context.Context, source image.Image, profile *pd
 			for i, value := range rgb {
 				channels[i] = uint16(math.Round(max(0, min(1, value)) * 65535))
 			}
+			if misses < 32 {
+				previousPixel = color.NRGBA64{R: channels[0], G: channels[1], B: channels[2], A: 65535}
+			} else {
+				previousPixel.A = 0
+			}
 			if slot >= 0 {
 				table[slot] = color.NRGBA64{R: channels[0], G: channels[1], B: channels[2], A: 65535}
 			}