case cbP8:
e.tmp[8] = 8
e.tmp[9] = ctPaletted
+ case cbP4:
+ e.tmp[8] = 4
+ e.tmp[9] = ctPaletted
+ case cbP2:
+ e.tmp[8] = 2
+ e.tmp[9] = ctPaletted
+ case cbP1:
+ e.tmp[8] = 1
+ e.tmp[9] = ctPaletted
case cbTCA8:
e.tmp[8] = 8
e.tmp[9] = ctTrueColorAlpha
}
defer e.zw.Close()
- bpp := 0 // Bytes per pixel.
+ bitsPerPixel := 0
switch cb {
case cbG8:
- bpp = 1
+ bitsPerPixel = 8
case cbTC8:
- bpp = 3
+ bitsPerPixel = 24
case cbP8:
- bpp = 1
+ bitsPerPixel = 8
+ case cbP4:
+ bitsPerPixel = 4
+ case cbP2:
+ bitsPerPixel = 2
+ case cbP1:
+ bitsPerPixel = 1
case cbTCA8:
- bpp = 4
+ bitsPerPixel = 32
case cbTC16:
- bpp = 6
+ bitsPerPixel = 48
case cbTCA16:
- bpp = 8
+ bitsPerPixel = 64
case cbG16:
- bpp = 2
+ bitsPerPixel = 16
}
+
// cr[*] and pr are the bytes for the current and previous row.
// cr[0] is unfiltered (or equivalently, filtered with the ftNone filter).
// cr[ft], for non-zero filter types ft, are buffers for transforming cr[0] under the
// other PNG filter types. These buffers are allocated once and re-used for each row.
// The +1 is for the per-row filter type, which is at cr[*][0].
b := m.Bounds()
- sz := 1 + bpp*b.Dx()
+ sz := 1 + (bitsPerPixel*b.Dx()+7)/8
for i := range e.cr {
if cap(e.cr[i]) < sz {
e.cr[i] = make([]uint8, sz)
i += 1
}
}
+
+ case cbP4, cbP2, cbP1:
+ pi := m.(image.PalettedImage)
+
+ var a uint8
+ var c int
+ for x := b.Min.X; x < b.Max.X; x++ {
+ a = a<<uint(bitsPerPixel) | pi.ColorIndexAt(x, y)
+ c++
+ if c == 8/bitsPerPixel {
+ cr[0][i] = a
+ i += 1
+ a = 0
+ c = 0
+ }
+ }
+ if c != 0 {
+ for c != 8/bitsPerPixel {
+ a = a << uint(bitsPerPixel)
+ c++
+ }
+ cr[0][i] = a
+ }
+
case cbTCA8:
if nrgba != nil {
offset := (y - b.Min.Y) * nrgba.Stride
// "filters are rarely useful on palette images" and will result
// in larger files (see http://www.libpng.org/pub/png/book/chapter09.html).
f := ftNone
- if level != zlib.NoCompression && cb != cbP8 {
+ if level != zlib.NoCompression && cb != cbP8 && cb != cbP4 && cb != cbP2 && cb != cbP1 {
+ // Since we skip paletted images we don't have to worry about
+ // bitsPerPixel not being a multiple of 8
+ bpp := bitsPerPixel / 8
f = filter(&cr, pr, bpp)
}
pal, _ = m.ColorModel().(color.Palette)
}
if pal != nil {
- e.cb = cbP8
+ if len(pal) <= 2 {
+ e.cb = cbP1
+ } else if len(pal) <= 4 {
+ e.cb = cbP2
+ } else if len(pal) <= 16 {
+ e.cb = cbP4
+ } else {
+ e.cb = cbP8
+ }
} else {
switch m.ColorModel() {
case color.GrayModel:
import (
"bytes"
+ "compress/zlib"
+ "encoding/binary"
"fmt"
"image"
"image/color"
+ "io"
"io/ioutil"
"testing"
)
}
}
+func TestWriterPaletted(t *testing.T) {
+ const width, height = 32, 16
+
+ testCases := []struct {
+ plen int
+ bitdepth uint8
+ datalen int
+ }{
+
+ {
+ plen: 256,
+ bitdepth: 8,
+ datalen: (1 + width) * height,
+ },
+
+ {
+ plen: 128,
+ bitdepth: 8,
+ datalen: (1 + width) * height,
+ },
+
+ {
+ plen: 16,
+ bitdepth: 4,
+ datalen: (1 + width/2) * height,
+ },
+
+ {
+ plen: 4,
+ bitdepth: 2,
+ datalen: (1 + width/4) * height,
+ },
+
+ {
+ plen: 2,
+ bitdepth: 1,
+ datalen: (1 + width/8) * height,
+ },
+ }
+
+ for _, tc := range testCases {
+ t.Run(fmt.Sprintf("plen-%d", tc.plen), func(t *testing.T) {
+ // Create a paletted image with the correct palette length
+ palette := make(color.Palette, tc.plen)
+ for i := range palette {
+ palette[i] = color.NRGBA{
+ R: uint8(i),
+ G: uint8(i),
+ B: uint8(i),
+ A: 255,
+ }
+ }
+ m0 := image.NewPaletted(image.Rect(0, 0, width, height), palette)
+
+ i := 0
+ for y := 0; y < height; y++ {
+ for x := 0; x < width; x++ {
+ m0.SetColorIndex(x, y, uint8(i%tc.plen))
+ i++
+ }
+ }
+
+ // Encode the image
+ var b bytes.Buffer
+ if err := Encode(&b, m0); err != nil {
+ t.Error(err)
+ return
+ }
+ const chunkFieldsLength = 12 // 4 bytes for length, name and crc
+ data := b.Bytes()
+ i = len(pngHeader)
+
+ for i < len(data)-chunkFieldsLength {
+ length := binary.BigEndian.Uint32(data[i : i+4])
+ name := string(data[i+4 : i+8])
+
+ switch name {
+ case "IHDR":
+ bitdepth := data[i+8+8]
+ if bitdepth != tc.bitdepth {
+ t.Errorf("got bitdepth %d, want %d", bitdepth, tc.bitdepth)
+ }
+ case "IDAT":
+ // Uncompress the image data
+ r, err := zlib.NewReader(bytes.NewReader(data[i+8 : i+8+int(length)]))
+ if err != nil {
+ t.Error(err)
+ return
+ }
+ n, err := io.Copy(ioutil.Discard, r)
+ if err != nil {
+ t.Errorf("got error while reading image data: %v", err)
+ }
+ if n != int64(tc.datalen) {
+ t.Errorf("got uncompressed data length %d, want %d", n, tc.datalen)
+ }
+ }
+
+ i += chunkFieldsLength + int(length)
+ }
+ })
+
+ }
+}
+
func TestWriterLevels(t *testing.T) {
m := image.NewNRGBA(image.Rect(0, 0, 100, 100))