diff options
Diffstat (limited to 'sixel.go')
| -rw-r--r-- | sixel.go | 101 |
1 files changed, 93 insertions, 8 deletions
@@ -4,33 +4,118 @@ package sixel import ( "bufio" + "cmp" "fmt" "image" "image/color" - "image/color/palette" "image/draw" "io" "maps" "slices" ) -func scale100(c uint32) int { - return int(c) * 100 / 0xffff +func scale100(c int64) int8 { + return int8(c * 100 / 0xff) } -var sixelPalette = append(color.Palette{color.Transparent}, palette.WebSafe...) +func scaleFFFF(c int8) uint32 { + return uint32(c) * 0xffff / 100 +} + +type sixelRGB struct { + r, g, b int8 +} + +func (c sixelRGB) RGBA() (r, g, b, a uint32) { + return scaleFFFF(c.r), scaleFFFF(c.g), scaleFFFF(c.b), 0xffff +} + +func cutOnce(colors []color.RGBA) [2][]color.RGBA { + var minR, maxR, minG, maxG, minB, maxB uint8 + for _, c := range colors { + minR, maxR = min(minR, c.R), max(maxR, c.R) + minG, maxG = min(minG, c.G), max(maxG, c.G) + minB, maxB = min(minB, c.B), max(maxB, c.B) + } + rRange, gRange, bRange := maxR-minR, maxG-minG, maxB-minB + if rRange >= gRange && rRange >= bRange { + slices.SortFunc(colors, func(x, y color.RGBA) int { return cmp.Compare(x.R, y.R) }) + } else if gRange >= rRange && gRange >= bRange { + slices.SortFunc(colors, func(x, y color.RGBA) int { return cmp.Compare(x.G, y.G) }) + } else { + slices.SortFunc(colors, func(x, y color.RGBA) int { return cmp.Compare(x.B, y.B) }) + } + return [...][]color.RGBA{colors[:len(colors)/2], colors[len(colors)/2:]} +} + +func cutDepth(colors []color.RGBA, depth int) [][]color.RGBA { + split := cutOnce(colors) + depth++ + if depth == 8 { + return split[:] + } + return append(cutDepth(split[0], depth), cutDepth(split[1], depth)...) +} + +func colorAvg(colors []color.RGBA) sixelRGB { + var r, g, b int64 + for _, c := range colors { + r += int64(c.R) + g += int64(c.G) + b += int64(c.B) + } + n := int64(len(colors)) + c := sixelRGB{r: scale100(r / n), g: scale100(g / n), b: scale100(b / n)} + return c +} + +func avgPaletteRGB(buckets [][]color.RGBA) []sixelRGB { + paletteRGB := make([]sixelRGB, len(buckets)) + for i, bucket := range buckets { + paletteRGB[i] = colorAvg(bucket) + } + slices.SortFunc(paletteRGB, func(x, y sixelRGB) int { + return cmp.Or(cmp.Compare(x.r, y.r), cmp.Compare(x.g, y.g), cmp.Compare(x.b, y.b)) + }) + return slices.Compact(paletteRGB) +} + +func medianCut(img image.Image) color.Palette { + colors := make([]color.RGBA, 0, img.Bounds().Dx()*img.Bounds().Dy()) + for y := img.Bounds().Min.Y; y < img.Bounds().Max.Y; y++ { + for x := img.Bounds().Min.X; x < img.Bounds().Max.X; x++ { + r, g, b, a := img.At(x, y).RGBA() + colors = append(colors, color.RGBA{R: uint8(r >> 8), G: uint8(g >> 8), B: uint8(b >> 8), A: uint8(a >> 8)}) + } + } + buckets := slices.DeleteFunc(cutDepth(colors, 0), func(c []color.RGBA) bool { return len(c) == 0 }) + paletteRGB := avgPaletteRGB(buckets) + if len(paletteRGB) == 256 { + lastBucket := buckets[len(buckets)-1] + secondLastBucket := buckets[len(buckets)-2] + buckets[len(buckets)-2] = secondLastBucket[:len(secondLastBucket)+len(lastBucket)] + buckets = buckets[:len(buckets)-1] + paletteRGB = avgPaletteRGB(buckets) + } + palette := slices.Grow(color.Palette{color.Transparent}, len(paletteRGB)) + for _, c := range paletteRGB { + palette = append(palette, c) + } + return palette +} // Print renders the given image as a sixel. func Print(w io.Writer, img image.Image) error { - palettized := image.NewPaletted(img.Bounds(), sixelPalette) + palette := medianCut(img) + palettized := image.NewPaletted(img.Bounds(), palette) draw.FloydSteinberg.Draw(palettized, palettized.Bounds(), img, image.Point{}) bw := bufio.NewWriter(w) if _, err := bw.WriteString("\033P7;1q"); err != nil { return err } - for i, c := range sixelPalette[1:] { - r, g, b, _ := c.RGBA() - if _, err := fmt.Fprintf(bw, "#%d;2;%d;%d;%d", i, scale100(r), scale100(g), scale100(b)); err != nil { + for i, c := range palette[1:] { + sc := c.(sixelRGB) + if _, err := fmt.Fprintf(bw, "#%d;2;%d;%d;%d", i, sc.r, sc.g, sc.b); err != nil { return err } } |