// readImagePass reads a single image pass, sized according to the pass number.
func (d *decoder) readImagePass(r io.Reader, pass int, allocateOnly bool) (image.Image, error) {
var bitsPerPixel int = 0
pixOffset := 0
var (
gray *image.Gray
rgba *image.RGBA
paletted *image.Paletted
nrgba *image.NRGBA
gray16 *image.Gray16
rgba64 *image.RGBA64
nrgba64 *image.NRGBA64
img image.Image
)
width, height := d.width, d.height
if d.interlace == itAdam7 && !allocateOnly {
p := interlacing[pass]
// Add the multiplication factor and subtract one, effectively rounding up.
width = (width - p.xOffset + p.xFactor - 1) / p.xFactor
height = (height - p.yOffset + p.yFactor - 1) / p.yFactor
// A PNG image can't have zero width or height, but for an interlaced
// image, an individual pass might have zero width or height. If so, we
// shouldn't even read a per-row filter type byte, so return early.
if width == 0 || height == 0 {
return nil, nil
}
}
switch d.cb {
case cbG1, cbG2, cbG4, cbG8:
bitsPerPixel = d.depth
gray = image.NewGray(image.Rect(0, 0, width, height))
img = gray
case cbGA8:
bitsPerPixel = 16
nrgba = image.NewNRGBA(image.Rect(0, 0, width, height))
img = nrgba
case cbTC8:
bitsPerPixel = 24
rgba = image.NewRGBA(image.Rect(0, 0, width, height))
img = rgba
case cbP1, cbP2, cbP4, cbP8:
bitsPerPixel = d.depth
paletted = image.NewPaletted(image.Rect(0, 0, width, height), d.palette)
img = paletted
case cbTCA8:
bitsPerPixel = 32
nrgba = image.NewNRGBA(image.Rect(0, 0, width, height))
img = nrgba
case cbG16:
bitsPerPixel = 16
gray16 = image.NewGray16(image.Rect(0, 0, width, height))
img = gray16
case cbGA16:
bitsPerPixel = 32
nrgba64 = image.NewNRGBA64(image.Rect(0, 0, width, height))
img = nrgba64
case cbTC16:
bitsPerPixel = 48
rgba64 = image.NewRGBA64(image.Rect(0, 0, width, height))
img = rgba64
case cbTCA16:
bitsPerPixel = 64
nrgba64 = image.NewNRGBA64(image.Rect(0, 0, width, height))
img = nrgba64
}
if allocateOnly {
return img, nil
}
bytesPerPixel := (bitsPerPixel + 7) / 8
// The +1 is for the per-row filter type, which is at cr[0].
rowSize := 1 + (bitsPerPixel*width+7)/8
// cr and pr are the bytes for the current and previous row.
cr := make([]uint8, rowSize)
pr := make([]uint8, rowSize)
for y := 0; y < height; y++ {
// Read the decompressed bytes.
_, err := io.ReadFull(r, cr)
if err != nil {
if err == io.EOF || err == io.ErrUnexpectedEOF {
return nil, FormatError("not enough pixel data")
}
return nil, err
}
// Apply the filter.
cdat := cr[1:]
pdat := pr[1:]
switch cr[0] {
case ftNone:
// No-op.
case ftSub:
for i := bytesPerPixel; i < len(cdat); i++ {
cdat[i] += cdat[i-bytesPerPixel]
}
case ftUp:
for i, p := range pdat {
cdat[i] += p
}
case ftAverage:
// The first column has no column to the left of it, so it is a
// special case. We know that the first column exists because we
// check above that width != 0, and so len(cdat) != 0.
for i := 0; i < bytesPerPixel; i++ {
cdat[i] += pdat[i] / 2
}
for i := bytesPerPixel; i < len(cdat); i++ {
cdat[i] += uint8((int(cdat[i-bytesPerPixel]) + int(pdat[i])) / 2)
}
case ftPaeth:
filterPaeth(cdat, pdat, bytesPerPixel)
default:
return nil, FormatError("bad filter type")
}
// Convert from bytes to colors.
switch d.cb {
case cbG1:
for x := 0; x < width; x += 8 {
b := cdat[x/8]
for x2 := 0; x2 < 8 && x+x2 < width; x2++ {
gray.SetGray(x+x2, y, color.Gray{(b >> 7) * 0xff})
b <<= 1
}
}
case cbG2:
for x := 0; x < width; x += 4 {
b := cdat[x/4]
for x2 := 0; x2 < 4 && x+x2 < width; x2++ {
gray.SetGray(x+x2, y, color.Gray{(b >> 6) * 0x55})
b <<= 2
}
}
case cbG4:
for x := 0; x < width; x += 2 {
b := cdat[x/2]
for x2 := 0; x2 < 2 && x+x2 < width; x2++ {
gray.SetGray(x+x2, y, color.Gray{(b >> 4) * 0x11})
b <<= 4
}
}
case cbG8:
copy(gray.Pix[pixOffset:], cdat)
pixOffset += gray.Stride
case cbGA8:
for x := 0; x < width; x++ {
ycol := cdat[2*x+0]
nrgba.SetNRGBA(x, y, color.NRGBA{ycol, ycol, ycol, cdat[2*x+1]})
}
case cbTC8:
pix, i, j := rgba.Pix, pixOffset, 0
for x := 0; x < width; x++ {
pix[i+0] = cdat[j+0]
pix[i+1] = cdat[j+1]
pix[i+2] = cdat[j+2]
pix[i+3] = 0xff
i += 4
j += 3
}
pixOffset += rgba.Stride
case cbP1:
for x := 0; x < width; x += 8 {
b := cdat[x/8]
for x2 := 0; x2 < 8 && x+x2 < width; x2++ {
idx := b >> 7
if len(paletted.Palette) <= int(idx) {
paletted.Palette = paletted.Palette[:int(idx)+1]
}
paletted.SetColorIndex(x+x2, y, idx)
b <<= 1
}
}
case cbP2:
for x := 0; x < width; x += 4 {
b := cdat[x/4]
for x2 := 0; x2 < 4 && x+x2 < width; x2++ {
idx := b >> 6
if len(paletted.Palette) <= int(idx) {
paletted.Palette = paletted.Palette[:int(idx)+1]
}
paletted.SetColorIndex(x+x2, y, idx)
b <<= 2
}
}
case cbP4:
for x := 0; x < width; x += 2 {
b := cdat[x/2]
for x2 := 0; x2 < 2 && x+x2 < width; x2++ {
idx := b >> 4
if len(paletted.Palette) <= int(idx) {
paletted.Palette = paletted.Palette[:int(idx)+1]
}
paletted.SetColorIndex(x+x2, y, idx)
b <<= 4
}
}
case cbP8:
if len(paletted.Palette) != 255 {
for x := 0; x < width; x++ {
if len(paletted.Palette) <= int(cdat[x]) {
paletted.Palette = paletted.Palette[:int(cdat[x])+1]
}
}
}
copy(paletted.Pix[pixOffset:], cdat)
pixOffset += paletted.Stride
case cbTCA8:
copy(nrgba.Pix[pixOffset:], cdat)
pixOffset += nrgba.Stride
case cbG16:
for x := 0; x < width; x++ {
ycol := uint16(cdat[2*x+0])<<8 | uint16(cdat[2*x+1])
gray16.SetGray16(x, y, color.Gray16{ycol})
}
case cbGA16:
for x := 0; x < width; x++ {
ycol := uint16(cdat[4*x+0])<<8 | uint16(cdat[4*x+1])
acol := uint16(cdat[4*x+2])<<8 | uint16(cdat[4*x+3])
nrgba64.SetNRGBA64(x, y, color.NRGBA64{ycol, ycol, ycol, acol})
}
case cbTC16:
for x := 0; x < width; x++ {
rcol := uint16(cdat[6*x+0])<<8 | uint16(cdat[6*x+1])
gcol := uint16(cdat[6*x+2])<<8 | uint16(cdat[6*x+3])
bcol := uint16(cdat[6*x+4])<<8 | uint16(cdat[6*x+5])
rgba64.SetRGBA64(x, y, color.RGBA64{rcol, gcol, bcol, 0xffff})
}
case cbTCA16:
for x := 0; x < width; x++ {
rcol := uint16(cdat[8*x+0])<<8 | uint16(cdat[8*x+1])
gcol := uint16(cdat[8*x+2])<<8 | uint16(cdat[8*x+3])
bcol := uint16(cdat[8*x+4])<<8 | uint16(cdat[8*x+5])
acol := uint16(cdat[8*x+6])<<8 | uint16(cdat[8*x+7])
nrgba64.SetNRGBA64(x, y, color.NRGBA64{rcol, gcol, bcol, acol})
}
}
// The current row for y is the previous row for y+1.
pr, cr = cr, pr
}
return img, nil
}
// decode decodes the IDAT data into an image.
func (d *decoder) decode() (image.Image, error) {
r, err := zlib.NewReader(d)
if err != nil {
return nil, err
}
defer r.Close()
bitsPerPixel := 0
pixOffset := 0
var (
gray *image.Gray
rgba *image.RGBA
paletted *image.Paletted
nrgba *image.NRGBA
gray16 *image.Gray16
rgba64 *image.RGBA64
nrgba64 *image.NRGBA64
img image.Image
)
switch d.cb {
case cbG1, cbG2, cbG4, cbG8:
bitsPerPixel = d.depth
gray = image.NewGray(image.Rect(0, 0, d.width, d.height))
img = gray
case cbGA8:
bitsPerPixel = 16
nrgba = image.NewNRGBA(image.Rect(0, 0, d.width, d.height))
img = nrgba
case cbTC8:
bitsPerPixel = 24
rgba = image.NewRGBA(image.Rect(0, 0, d.width, d.height))
img = rgba
case cbP1, cbP2, cbP4, cbP8:
bitsPerPixel = d.depth
paletted = image.NewPaletted(image.Rect(0, 0, d.width, d.height), d.palette)
img = paletted
case cbTCA8:
bitsPerPixel = 32
nrgba = image.NewNRGBA(image.Rect(0, 0, d.width, d.height))
img = nrgba
case cbG16:
bitsPerPixel = 16
gray16 = image.NewGray16(image.Rect(0, 0, d.width, d.height))
img = gray16
case cbGA16:
bitsPerPixel = 32
nrgba64 = image.NewNRGBA64(image.Rect(0, 0, d.width, d.height))
img = nrgba64
case cbTC16:
bitsPerPixel = 48
rgba64 = image.NewRGBA64(image.Rect(0, 0, d.width, d.height))
img = rgba64
case cbTCA16:
bitsPerPixel = 64
nrgba64 = image.NewNRGBA64(image.Rect(0, 0, d.width, d.height))
img = nrgba64
}
bytesPerPixel := (bitsPerPixel + 7) / 8
// cr and pr are the bytes for the current and previous row.
// The +1 is for the per-row filter type, which is at cr[0].
cr := make([]uint8, 1+(bitsPerPixel*d.width+7)/8)
pr := make([]uint8, 1+(bitsPerPixel*d.width+7)/8)
for y := 0; y < d.height; y++ {
// Read the decompressed bytes.
_, err := io.ReadFull(r, cr)
if err != nil {
return nil, err
}
// Apply the filter.
cdat := cr[1:]
pdat := pr[1:]
switch cr[0] {
case ftNone:
// No-op.
case ftSub:
for i := bytesPerPixel; i < len(cdat); i++ {
cdat[i] += cdat[i-bytesPerPixel]
}
case ftUp:
for i, p := range pdat {
cdat[i] += p
}
case ftAverage:
for i := 0; i < bytesPerPixel; i++ {
cdat[i] += pdat[i] / 2
}
for i := bytesPerPixel; i < len(cdat); i++ {
cdat[i] += uint8((int(cdat[i-bytesPerPixel]) + int(pdat[i])) / 2)
}
case ftPaeth:
filterPaeth(cdat, pdat, bytesPerPixel)
default:
return nil, FormatError("bad filter type")
}
// Convert from bytes to colors.
switch d.cb {
case cbG1:
for x := 0; x < d.width; x += 8 {
b := cdat[x/8]
for x2 := 0; x2 < 8 && x+x2 < d.width; x2++ {
gray.SetGray(x+x2, y, color.Gray{(b >> 7) * 0xff})
b <<= 1
}
}
case cbG2:
for x := 0; x < d.width; x += 4 {
b := cdat[x/4]
for x2 := 0; x2 < 4 && x+x2 < d.width; x2++ {
gray.SetGray(x+x2, y, color.Gray{(b >> 6) * 0x55})
b <<= 2
}
}
case cbG4:
for x := 0; x < d.width; x += 2 {
b := cdat[x/2]
for x2 := 0; x2 < 2 && x+x2 < d.width; x2++ {
gray.SetGray(x+x2, y, color.Gray{(b >> 4) * 0x11})
b <<= 4
}
}
case cbG8:
copy(gray.Pix[pixOffset:], cdat)
pixOffset += gray.Stride
case cbGA8:
for x := 0; x < d.width; x++ {
ycol := cdat[2*x+0]
nrgba.SetNRGBA(x, y, color.NRGBA{ycol, ycol, ycol, cdat[2*x+1]})
}
case cbTC8:
pix, i, j := rgba.Pix, pixOffset, 0
for x := 0; x < d.width; x++ {
pix[i+0] = cdat[j+0]
pix[i+1] = cdat[j+1]
pix[i+2] = cdat[j+2]
pix[i+3] = 0xff
i += 4
j += 3
}
pixOffset += rgba.Stride
case cbP1:
for x := 0; x < d.width; x += 8 {
b := cdat[x/8]
for x2 := 0; x2 < 8 && x+x2 < d.width; x2++ {
idx := b >> 7
if len(paletted.Palette) <= int(idx) {
paletted.Palette = paletted.Palette[:int(idx)+1]
}
paletted.SetColorIndex(x+x2, y, idx)
b <<= 1
}
}
case cbP2:
for x := 0; x < d.width; x += 4 {
b := cdat[x/4]
for x2 := 0; x2 < 4 && x+x2 < d.width; x2++ {
idx := b >> 6
if len(paletted.Palette) <= int(idx) {
paletted.Palette = paletted.Palette[:int(idx)+1]
}
paletted.SetColorIndex(x+x2, y, idx)
b <<= 2
}
}
case cbP4:
for x := 0; x < d.width; x += 2 {
b := cdat[x/2]
for x2 := 0; x2 < 2 && x+x2 < d.width; x2++ {
idx := b >> 4
if len(paletted.Palette) <= int(idx) {
paletted.Palette = paletted.Palette[:int(idx)+1]
}
paletted.SetColorIndex(x+x2, y, idx)
b <<= 4
}
}
case cbP8:
if len(paletted.Palette) != 255 {
for x := 0; x < d.width; x++ {
if len(paletted.Palette) <= int(cdat[x]) {
paletted.Palette = paletted.Palette[:int(cdat[x])+1]
}
}
}
copy(paletted.Pix[pixOffset:], cdat)
pixOffset += paletted.Stride
case cbTCA8:
copy(nrgba.Pix[pixOffset:], cdat)
pixOffset += nrgba.Stride
case cbG16:
for x := 0; x < d.width; x++ {
ycol := uint16(cdat[2*x+0])<<8 | uint16(cdat[2*x+1])
gray16.SetGray16(x, y, color.Gray16{ycol})
}
case cbGA16:
for x := 0; x < d.width; x++ {
ycol := uint16(cdat[4*x+0])<<8 | uint16(cdat[4*x+1])
acol := uint16(cdat[4*x+2])<<8 | uint16(cdat[4*x+3])
nrgba64.SetNRGBA64(x, y, color.NRGBA64{ycol, ycol, ycol, acol})
}
case cbTC16:
for x := 0; x < d.width; x++ {
rcol := uint16(cdat[6*x+0])<<8 | uint16(cdat[6*x+1])
gcol := uint16(cdat[6*x+2])<<8 | uint16(cdat[6*x+3])
bcol := uint16(cdat[6*x+4])<<8 | uint16(cdat[6*x+5])
rgba64.SetRGBA64(x, y, color.RGBA64{rcol, gcol, bcol, 0xffff})
}
case cbTCA16:
for x := 0; x < d.width; x++ {
rcol := uint16(cdat[8*x+0])<<8 | uint16(cdat[8*x+1])
gcol := uint16(cdat[8*x+2])<<8 | uint16(cdat[8*x+3])
bcol := uint16(cdat[8*x+4])<<8 | uint16(cdat[8*x+5])
acol := uint16(cdat[8*x+6])<<8 | uint16(cdat[8*x+7])
nrgba64.SetNRGBA64(x, y, color.NRGBA64{rcol, gcol, bcol, acol})
}
}
// The current row for y is the previous row for y+1.
pr, cr = cr, pr
}
// Check for EOF, to verify the zlib checksum.
n, err := r.Read(pr[:1])
if err != io.EOF {
return nil, FormatError(err.Error())
}
if n != 0 || d.idatLength != 0 {
return nil, FormatError("too much pixel data")
}
return img, nil
}
func (d *decoder) idatReader(idat io.Reader) (image.Image, os.Error) {
r, err := zlib.NewReader(idat)
if err != nil {
return nil, err
}
defer r.Close()
bitsPerPixel := 0
maxPalette := uint8(0)
var (
gray *image.Gray
rgba *image.RGBA
paletted *image.Paletted
nrgba *image.NRGBA
gray16 *image.Gray16
rgba64 *image.RGBA64
nrgba64 *image.NRGBA64
img image.Image
)
switch d.cb {
case cbG1, cbG2, cbG4, cbG8:
bitsPerPixel = d.depth
gray = image.NewGray(d.width, d.height)
img = gray
case cbGA8:
bitsPerPixel = 16
nrgba = image.NewNRGBA(d.width, d.height)
img = nrgba
case cbTC8:
bitsPerPixel = 24
rgba = image.NewRGBA(d.width, d.height)
img = rgba
case cbP1, cbP2, cbP4, cbP8:
bitsPerPixel = d.depth
paletted = image.NewPaletted(d.width, d.height, d.palette)
img = paletted
maxPalette = uint8(len(d.palette) - 1)
case cbTCA8:
bitsPerPixel = 32
nrgba = image.NewNRGBA(d.width, d.height)
img = nrgba
case cbG16:
bitsPerPixel = 16
gray16 = image.NewGray16(d.width, d.height)
img = gray16
case cbGA16:
bitsPerPixel = 32
nrgba64 = image.NewNRGBA64(d.width, d.height)
img = nrgba64
case cbTC16:
bitsPerPixel = 48
rgba64 = image.NewRGBA64(d.width, d.height)
img = rgba64
case cbTCA16:
bitsPerPixel = 64
nrgba64 = image.NewNRGBA64(d.width, d.height)
img = nrgba64
}
bytesPerPixel := (bitsPerPixel + 7) / 8
// cr and pr are the bytes for the current and previous row.
// The +1 is for the per-row filter type, which is at cr[0].
cr := make([]uint8, 1+(bitsPerPixel*d.width+7)/8)
pr := make([]uint8, 1+(bitsPerPixel*d.width+7)/8)
for y := 0; y < d.height; y++ {
// Read the decompressed bytes.
_, err := io.ReadFull(r, cr)
if err != nil {
return nil, err
}
// Apply the filter.
cdat := cr[1:]
pdat := pr[1:]
switch cr[0] {
case ftNone:
// No-op.
case ftSub:
for i := bytesPerPixel; i < len(cdat); i++ {
cdat[i] += cdat[i-bytesPerPixel]
}
case ftUp:
for i := 0; i < len(cdat); i++ {
cdat[i] += pdat[i]
}
case ftAverage:
for i := 0; i < bytesPerPixel; i++ {
cdat[i] += pdat[i] / 2
}
for i := bytesPerPixel; i < len(cdat); i++ {
cdat[i] += uint8((int(cdat[i-bytesPerPixel]) + int(pdat[i])) / 2)
}
case ftPaeth:
for i := 0; i < bytesPerPixel; i++ {
cdat[i] += paeth(0, pdat[i], 0)
}
for i := bytesPerPixel; i < len(cdat); i++ {
cdat[i] += paeth(cdat[i-bytesPerPixel], pdat[i], pdat[i-bytesPerPixel])
}
default:
return nil, FormatError("bad filter type")
}
// Convert from bytes to colors.
switch d.cb {
case cbG1:
for x := 0; x < d.width; x += 8 {
b := cdat[x/8]
for x2 := 0; x2 < 8 && x+x2 < d.width; x2++ {
gray.SetGray(x+x2, y, image.GrayColor{(b >> 7) * 0xff})
b <<= 1
}
}
case cbG2:
for x := 0; x < d.width; x += 4 {
b := cdat[x/4]
for x2 := 0; x2 < 4 && x+x2 < d.width; x2++ {
gray.SetGray(x+x2, y, image.GrayColor{(b >> 6) * 0x55})
b <<= 2
}
}
case cbG4:
for x := 0; x < d.width; x += 2 {
b := cdat[x/2]
for x2 := 0; x2 < 2 && x+x2 < d.width; x2++ {
gray.SetGray(x+x2, y, image.GrayColor{(b >> 4) * 0x11})
b <<= 4
}
}
case cbG8:
for x := 0; x < d.width; x++ {
gray.SetGray(x, y, image.GrayColor{cdat[x]})
}
case cbGA8:
for x := 0; x < d.width; x++ {
ycol := cdat[2*x+0]
nrgba.SetNRGBA(x, y, image.NRGBAColor{ycol, ycol, ycol, cdat[2*x+1]})
}
case cbTC8:
for x := 0; x < d.width; x++ {
rgba.SetRGBA(x, y, image.RGBAColor{cdat[3*x+0], cdat[3*x+1], cdat[3*x+2], 0xff})
}
case cbP1:
for x := 0; x < d.width; x += 8 {
b := cdat[x/8]
for x2 := 0; x2 < 8 && x+x2 < d.width; x2++ {
idx := b >> 7
if idx > maxPalette {
return nil, FormatError("palette index out of range")
}
paletted.SetColorIndex(x+x2, y, idx)
b <<= 1
}
}
case cbP2:
for x := 0; x < d.width; x += 4 {
b := cdat[x/4]
for x2 := 0; x2 < 4 && x+x2 < d.width; x2++ {
idx := b >> 6
if idx > maxPalette {
return nil, FormatError("palette index out of range")
}
paletted.SetColorIndex(x+x2, y, idx)
b <<= 2
}
}
case cbP4:
for x := 0; x < d.width; x += 2 {
b := cdat[x/2]
for x2 := 0; x2 < 2 && x+x2 < d.width; x2++ {
idx := b >> 4
if idx > maxPalette {
return nil, FormatError("palette index out of range")
}
paletted.SetColorIndex(x+x2, y, idx)
b <<= 4
}
}
case cbP8:
for x := 0; x < d.width; x++ {
if cdat[x] > maxPalette {
return nil, FormatError("palette index out of range")
}
paletted.SetColorIndex(x, y, cdat[x])
}
case cbTCA8:
for x := 0; x < d.width; x++ {
nrgba.SetNRGBA(x, y, image.NRGBAColor{cdat[4*x+0], cdat[4*x+1], cdat[4*x+2], cdat[4*x+3]})
}
case cbG16:
for x := 0; x < d.width; x++ {
ycol := uint16(cdat[2*x+0])<<8 | uint16(cdat[2*x+1])
gray16.SetGray16(x, y, image.Gray16Color{ycol})
}
case cbGA16:
for x := 0; x < d.width; x++ {
ycol := uint16(cdat[4*x+0])<<8 | uint16(cdat[4*x+1])
acol := uint16(cdat[4*x+2])<<8 | uint16(cdat[4*x+3])
nrgba64.SetNRGBA64(x, y, image.NRGBA64Color{ycol, ycol, ycol, acol})
}
case cbTC16:
for x := 0; x < d.width; x++ {
rcol := uint16(cdat[6*x+0])<<8 | uint16(cdat[6*x+1])
gcol := uint16(cdat[6*x+2])<<8 | uint16(cdat[6*x+3])
bcol := uint16(cdat[6*x+4])<<8 | uint16(cdat[6*x+5])
rgba64.SetRGBA64(x, y, image.RGBA64Color{rcol, gcol, bcol, 0xffff})
}
case cbTCA16:
for x := 0; x < d.width; x++ {
rcol := uint16(cdat[8*x+0])<<8 | uint16(cdat[8*x+1])
gcol := uint16(cdat[8*x+2])<<8 | uint16(cdat[8*x+3])
bcol := uint16(cdat[8*x+4])<<8 | uint16(cdat[8*x+5])
acol := uint16(cdat[8*x+6])<<8 | uint16(cdat[8*x+7])
nrgba64.SetNRGBA64(x, y, image.NRGBA64Color{rcol, gcol, bcol, acol})
}
}
// The current row for y is the previous row for y+1.
pr, cr = cr, pr
}
return img, nil
}