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Code Releases Activity

image/png: support encoding of paletted images with alpha channel.

Browse Source 
Encoder now writes tRNS chunk for non-opaque paletted images.
CL includes new test images (basn3a08-trns.[ps]ng).

R=nigeltao, rsc, r
CC=golang-dev
https://golang.org/cl/4432078
This commit is contained in:
Dmitry Chestnykh 2011-05-04 20:46:27 -07:00 committed by Nigel Tao
parent bcf3bfe2fe
commit 737e96c7f3
5 changed files with 339 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
src/pkg/image/png/reader_test.go
View File

@ -28,6 +28,7 @@ var filenames = []string{
"basn3p02", "basn3p02",
"basn3p04", "basn3p04",
"basn3p08", "basn3p08",
"basn3p08-trns",
"basn4a08", "basn4a08",
"basn4a16", "basn4a16",
"basn6a08", "basn6a08",
@ -98,17 +99,30 @@ func sng(w io.WriteCloser, filename string, png image.Image) {
// (the PNG spec section 11.3 says "Ancillary chunks may be ignored by a decoder"). // (the PNG spec section 11.3 says "Ancillary chunks may be ignored by a decoder").
io.WriteString(w, "gAMA {1.0000}\n") io.WriteString(w, "gAMA {1.0000}\n")
// Write the PLTE (if applicable). // Write the PLTE and tRNS (if applicable).
if cpm != nil { if cpm != nil {
lastAlpha := -1
io.WriteString(w, "PLTE {\n") io.WriteString(w, "PLTE {\n")
for i := 0; i < len(cpm); i++ { for i, c := range cpm {
r, g, b, _ := cpm[i].RGBA() r, g, b, a := c.RGBA()
if a != 0xffff {
lastAlpha = i
}
r >>= 8 r >>= 8
g >>= 8 g >>= 8
b >>= 8 b >>= 8
fmt.Fprintf(w, " (%3d,%3d,%3d) # rgb = (0x%02x,0x%02x,0x%02x)\n", r, g, b, r, g, b) fmt.Fprintf(w, " (%3d,%3d,%3d) # rgb = (0x%02x,0x%02x,0x%02x)\n", r, g, b, r, g, b)
} }
io.WriteString(w, "}\n") io.WriteString(w, "}\n")
if lastAlpha != -1 {
io.WriteString(w, "tRNS {\n")
for i := 0; i <= lastAlpha; i++ {
_, _, _, a := cpm[i].RGBA()
a >>= 8
fmt.Fprintf(w, " %d", a)
}
io.WriteString(w, "}\n")
}
} }
// Write the IMAGE. // Write the IMAGE.

3
src/pkg/image/png/testdata/pngsuite/README vendored
View File

@ -10,6 +10,9 @@ The files basn0g01-30.png, basn0g02-29.png and basn0g04-31.png are in fact
not part of pngsuite but were created from files in pngsuite. Their non-power- not part of pngsuite but were created from files in pngsuite. Their non-power-
of-two sizes makes them useful for testing bit-depths smaller than a byte. of-two sizes makes them useful for testing bit-depths smaller than a byte.
basn3a08.png was generated from basn6a08.png using the pngnq tool, which
converted it to the 8-bit paletted image with alpha values in tRNS chunk.
The *.sng files in this directory were generated from the *.png files The *.sng files in this directory were generated from the *.png files
by the sng command-line tool and some hand editing. The files by the sng command-line tool and some hand editing. The files
basn0g0{1,2,4}.sng were actually generated by first converting the PNG basn0g0{1,2,4}.sng were actually generated by first converting the PNG

BIN
src/pkg/image/png/testdata/pngsuite/basn3p08-trns.png vendored Normal file
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Binary file not shown.
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After

Width:  |  Height:  |  Size: 1.5 KiB

301
src/pkg/image/png/testdata/pngsuite/basn3p08-trns.sng vendored Normal file
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@ -0,0 +1,301 @@
#SNG: from basn3p08-trns.png
IHDR {
width: 32; height: 32; bitdepth: 8;
using color palette;
}
gAMA {1.0000}
PLTE {
(255, 3, 7) # rgb = (0xff,0x03,0x07)
(255, 4, 7) # rgb = (0xff,0x04,0x07)
(255, 9, 7) # rgb = (0xff,0x09,0x07)
(217, 14, 7) # rgb = (0xd9,0x0e,0x07)
(255, 14, 7) # rgb = (0xff,0x0e,0x07)
( 2, 22, 19) # rgb = (0x02,0x16,0x13)
(255, 26, 7) # rgb = (0xff,0x1a,0x07)
(255, 31, 7) # rgb = (0xff,0x1f,0x07)
( 10, 37, 14) # rgb = (0x0a,0x25,0x0e)
(179, 37, 6) # rgb = (0xb3,0x25,0x06)
(254, 42, 7) # rgb = (0xfe,0x2a,0x07)
(255, 45, 7) # rgb = (0xff,0x2d,0x07)
( 25, 46, 9) # rgb = (0x19,0x2e,0x09)
( 0, 48,254) # rgb = (0x00,0x30,0xfe)
( 0, 48,255) # rgb = (0x00,0x30,0xff)
( 0, 49,255) # rgb = (0x00,0x31,0xff)
( 0, 51,254) # rgb = (0x00,0x33,0xfe)
( 0, 52,255) # rgb = (0x00,0x34,0xff)
(255, 53, 7) # rgb = (0xff,0x35,0x07)
( 0, 54,252) # rgb = (0x00,0x36,0xfc)
(254, 57, 7) # rgb = (0xfe,0x39,0x07)
(251, 57, 7) # rgb = (0xfb,0x39,0x07)
(247, 59, 7) # rgb = (0xf7,0x3b,0x07)
( 0, 59, 61) # rgb = (0x00,0x3b,0x3d)
( 0, 62,255) # rgb = (0x00,0x3e,0xff)
(142, 63, 5) # rgb = (0x8e,0x3f,0x05)
( 0, 63,250) # rgb = (0x00,0x3f,0xfa)
(255, 63, 7) # rgb = (0xff,0x3f,0x07)
(253, 68, 7) # rgb = (0xfd,0x44,0x07)
( 0, 73,255) # rgb = (0x00,0x49,0xff)
( 0, 73,246) # rgb = (0x00,0x49,0xf6)
(255, 75, 7) # rgb = (0xff,0x4b,0x07)
( 82, 85, 9) # rgb = (0x52,0x55,0x09)
(255, 85, 7) # rgb = (0xff,0x55,0x07)
( 0, 89,255) # rgb = (0x00,0x59,0xff)
( 0, 91,237) # rgb = (0x00,0x5b,0xed)
(255, 94, 7) # rgb = (0xff,0x5e,0x07)
(241,100, 7) # rgb = (0xf1,0x64,0x07)
( 0,101,255) # rgb = (0x00,0x65,0xff)
(253,105, 7) # rgb = (0xfd,0x69,0x07)
( 0,107,223) # rgb = (0x00,0x6b,0xdf)
(255,106, 7) # rgb = (0xff,0x6a,0x07)
( 1,110, 95) # rgb = (0x01,0x6e,0x5f)
(255,115, 7) # rgb = (0xff,0x73,0x07)
( 0,117,255) # rgb = (0x00,0x75,0xff)
(255,124, 7) # rgb = (0xff,0x7c,0x07)
(118,126, 10) # rgb = (0x76,0x7e,0x0a)
( 0,130,250) # rgb = (0x00,0x82,0xfa)
( 0,132,255) # rgb = (0x00,0x84,0xff)
( 0,134,207) # rgb = (0x00,0x86,0xcf)
(255,134, 7) # rgb = (0xff,0x86,0x07)
( 0,136,249) # rgb = (0x00,0x88,0xf9)
(219,140, 6) # rgb = (0xdb,0x8c,0x06)
( 0,140,252) # rgb = (0x00,0x8c,0xfc)
( 0,140,255) # rgb = (0x00,0x8c,0xff)
( 1,142,136) # rgb = (0x01,0x8e,0x88)
(255,143, 7) # rgb = (0xff,0x8f,0x07)
(243,150, 7) # rgb = (0xf3,0x96,0x07)
(198,152, 7) # rgb = (0xc6,0x98,0x07)
(165,153, 7) # rgb = (0xa5,0x99,0x07)
( 0,157,255) # rgb = (0x00,0x9d,0xff)
(255,158, 7) # rgb = (0xff,0x9e,0x07)
( 70,159, 4) # rgb = (0x46,0x9f,0x04)
( 0,160,251) # rgb = (0x00,0xa0,0xfb)
(203,163, 6) # rgb = (0xcb,0xa3,0x06)
( 0,163,239) # rgb = (0x00,0xa3,0xef)
( 1,164,178) # rgb = (0x01,0xa4,0xb2)
(255,166, 7) # rgb = (0xff,0xa6,0x07)
( 1,169,165) # rgb = (0x01,0xa9,0xa5)
( 1,170,255) # rgb = (0x01,0xaa,0xff)
(232,172, 6) # rgb = (0xe8,0xac,0x06)
(255,175, 7) # rgb = (0xff,0xaf,0x07)
(185,176,131) # rgb = (0xb9,0xb0,0x83)
( 1,179,225) # rgb = (0x01,0xb3,0xe1)
(188,179,118) # rgb = (0xbc,0xb3,0x76)
(199,180, 6) # rgb = (0xc7,0xb4,0x06)
( 1,182,255) # rgb = (0x01,0xb6,0xff)
( 1,184,249) # rgb = (0x01,0xb8,0xf9)
(255,184, 7) # rgb = (0xff,0xb8,0x07)
(207,186, 71) # rgb = (0xcf,0xba,0x47)
(193,187, 6) # rgb = (0xc1,0xbb,0x06)
(253,191, 7) # rgb = (0xfd,0xbf,0x07)
(218,193, 48) # rgb = (0xda,0xc1,0x30)
( 1,193,157) # rgb = (0x01,0xc1,0x9d)
( 1,196,244) # rgb = (0x01,0xc4,0xf4)
( 1,196,254) # rgb = (0x01,0xc4,0xfe)
( 48,199, 3) # rgb = (0x30,0xc7,0x03)
(164,199, 5) # rgb = (0xa4,0xc7,0x05)
(220,202, 6) # rgb = (0xdc,0xca,0x06)
(253,203, 7) # rgb = (0xfd,0xcb,0x07)
( 1,204,204) # rgb = (0x01,0xcc,0xcc)
(251,209, 7) # rgb = (0xfb,0xd1,0x07)
(231,208, 24) # rgb = (0xe7,0xd0,0x18)
( 1,210,254) # rgb = (0x01,0xd2,0xfe)
( 2,211,146) # rgb = (0x02,0xd3,0x92)
( 1,212,156) # rgb = (0x01,0xd4,0x9c)
( 1,213,252) # rgb = (0x01,0xd5,0xfc)
(237,219, 15) # rgb = (0xed,0xdb,0x0f)
( 1,218,240) # rgb = (0x01,0xda,0xf0)
(165,220, 5) # rgb = (0xa5,0xdc,0x05)
( 1,221,250) # rgb = (0x01,0xdd,0xfa)
(249,221, 6) # rgb = (0xf9,0xdd,0x06)
(146,222, 4) # rgb = (0x92,0xde,0x04)
( 1,224,184) # rgb = (0x01,0xe0,0xb8)
( 2,224,155) # rgb = (0x02,0xe0,0x9b)
(244,225, 10) # rgb = (0xf4,0xe1,0x0a)
(249,227, 7) # rgb = (0xf9,0xe3,0x07)
( 2,229,133) # rgb = (0x02,0xe5,0x85)
(192,228, 6) # rgb = (0xc0,0xe4,0x06)
( 37,230, 3) # rgb = (0x25,0xe6,0x03)
(246,230, 7) # rgb = (0xf6,0xe6,0x07)
(143,232, 4) # rgb = (0x8f,0xe8,0x04)
(244,233, 8) # rgb = (0xf4,0xe9,0x08)
( 2,236,139) # rgb = (0x02,0xec,0x8b)
( 1,236,227) # rgb = (0x01,0xec,0xe3)
( 1,238,238) # rgb = (0x01,0xee,0xee)
(101,241, 4) # rgb = (0x65,0xf1,0x04)
( 1,241,218) # rgb = (0x01,0xf1,0xda)
( 1,240,232) # rgb = (0x01,0xf0,0xe8)
(167,240, 5) # rgb = (0xa7,0xf0,0x05)
( 27,243, 2) # rgb = (0x1b,0xf3,0x02)
(126,243, 4) # rgb = (0x7e,0xf3,0x04)
( 2,246,113) # rgb = (0x02,0xf6,0x71)
(133,248, 5) # rgb = (0x85,0xf8,0x05)
( 22,250, 1) # rgb = (0x16,0xfa,0x01)
( 2,249,219) # rgb = (0x02,0xf9,0xdb)
(148,250, 5) # rgb = (0x94,0xfa,0x05)
( 2,250,199) # rgb = (0x02,0xfa,0xc7)
(183,252, 5) # rgb = (0xb7,0xfc,0x05)
(176,252, 5) # rgb = (0xb0,0xfc,0x05)
( 2,252,211) # rgb = (0x02,0xfc,0xd3)
( 2,252,190) # rgb = (0x02,0xfc,0xbe)
(164,251, 5) # rgb = (0xa4,0xfb,0x05)
( 12,254,128) # rgb = (0x0c,0xfe,0x80)
(192,253, 5) # rgb = (0xc0,0xfd,0x05)
(164,253, 5) # rgb = (0xa4,0xfd,0x05)
( 26,254, 85) # rgb = (0x1a,0xfe,0x55)
( 14,254, 1) # rgb = (0x0e,0xfe,0x01)
(133,253, 5) # rgb = (0x85,0xfd,0x05)
( 4,253,180) # rgb = (0x04,0xfd,0xb4)
(196,253, 5) # rgb = (0xc4,0xfd,0x05)
( 2,253,198) # rgb = (0x02,0xfd,0xc6)
( 3,255, 91) # rgb = (0x03,0xff,0x5b)
( 3,255, 80) # rgb = (0x03,0xff,0x50)
(186,255, 5) # rgb = (0xba,0xff,0x05)
( 9,255, 2) # rgb = (0x09,0xff,0x02)
( 3,255,118) # rgb = (0x03,0xff,0x76)
( 9,255, 3) # rgb = (0x09,0xff,0x03)
( 10,255, 1) # rgb = (0x0a,0xff,0x01)
( 3,255, 76) # rgb = (0x03,0xff,0x4c)
( 3,255, 86) # rgb = (0x03,0xff,0x56)
( 3,255, 82) # rgb = (0x03,0xff,0x52)
( 13,255, 1) # rgb = (0x0d,0xff,0x01)
( 3,255, 49) # rgb = (0x03,0xff,0x31)
( 3,255,101) # rgb = (0x03,0xff,0x65)
( 61,255, 32) # rgb = (0x3d,0xff,0x20)
(129,255, 5) # rgb = (0x81,0xff,0x05)
(177,255, 5) # rgb = (0xb1,0xff,0x05)
( 3,255, 37) # rgb = (0x03,0xff,0x25)
(149,255, 5) # rgb = (0x95,0xff,0x05)
( 7,255, 6) # rgb = (0x07,0xff,0x06)
(192,255, 5) # rgb = (0xc0,0xff,0x05)
( 2,255,131) # rgb = (0x02,0xff,0x83)
( 3,255, 98) # rgb = (0x03,0xff,0x62)
( 85,255, 11) # rgb = (0x55,0xff,0x0b)
( 2,255,163) # rgb = (0x02,0xff,0xa3)
( 2,255,149) # rgb = (0x02,0xff,0x95)
( 4,255, 23) # rgb = (0x04,0xff,0x17)
( 6,255, 12) # rgb = (0x06,0xff,0x0c)
( 3,255, 67) # rgb = (0x03,0xff,0x43)
(160,255, 5) # rgb = (0xa0,0xff,0x05)
(119,255, 6) # rgb = (0x77,0xff,0x06)
(102,255, 8) # rgb = (0x66,0xff,0x08)
(255,255,255) # rgb = (0xff,0xff,0xff)
(254,254,254) # rgb = (0xfe,0xfe,0xfe)
(254,254,254) # rgb = (0xfe,0xfe,0xfe)
(252,252,252) # rgb = (0xfc,0xfc,0xfc)
(252,252,252) # rgb = (0xfc,0xfc,0xfc)
(250,250,250) # rgb = (0xfa,0xfa,0xfa)
(250,250,250) # rgb = (0xfa,0xfa,0xfa)
(248,248,248) # rgb = (0xf8,0xf8,0xf8)
(248,248,248) # rgb = (0xf8,0xf8,0xf8)
(247,247,247) # rgb = (0xf7,0xf7,0xf7)
(245,245,245) # rgb = (0xf5,0xf5,0xf5)
(245,245,245) # rgb = (0xf5,0xf5,0xf5)
(243,243,243) # rgb = (0xf3,0xf3,0xf3)
(243,243,243) # rgb = (0xf3,0xf3,0xf3)
(241,241,241) # rgb = (0xf1,0xf1,0xf1)
(241,241,241) # rgb = (0xf1,0xf1,0xf1)
(239,239,239) # rgb = (0xef,0xef,0xef)
(238,238,238) # rgb = (0xee,0xee,0xee)
(238,238,238) # rgb = (0xee,0xee,0xee)
(236,236,236) # rgb = (0xec,0xec,0xec)
(236,236,236) # rgb = (0xec,0xec,0xec)
(234,234,234) # rgb = (0xea,0xea,0xea)
(234,234,234) # rgb = (0xea,0xea,0xea)
(232,232,232) # rgb = (0xe8,0xe8,0xe8)
(231,231,231) # rgb = (0xe7,0xe7,0xe7)
(231,231,231) # rgb = (0xe7,0xe7,0xe7)
(229,229,229) # rgb = (0xe5,0xe5,0xe5)
(229,229,229) # rgb = (0xe5,0xe5,0xe5)
(227,227,227) # rgb = (0xe3,0xe3,0xe3)
(226,226,226) # rgb = (0xe2,0xe2,0xe2)
(226,226,226) # rgb = (0xe2,0xe2,0xe2)
(224,224,224) # rgb = (0xe0,0xe0,0xe0)
(224,224,224) # rgb = (0xe0,0xe0,0xe0)
(222,222,222) # rgb = (0xde,0xde,0xde)
(222,222,222) # rgb = (0xde,0xde,0xde)
(220,220,220) # rgb = (0xdc,0xdc,0xdc)
(219,219,219) # rgb = (0xdb,0xdb,0xdb)
(219,219,219) # rgb = (0xdb,0xdb,0xdb)
(217,217,217) # rgb = (0xd9,0xd9,0xd9)
(217,217,217) # rgb = (0xd9,0xd9,0xd9)
(215,215,215) # rgb = (0xd7,0xd7,0xd7)
(214,214,214) # rgb = (0xd6,0xd6,0xd6)
(214,214,214) # rgb = (0xd6,0xd6,0xd6)
(212,212,212) # rgb = (0xd4,0xd4,0xd4)
(212,212,212) # rgb = (0xd4,0xd4,0xd4)
(210,210,210) # rgb = (0xd2,0xd2,0xd2)
(209,209,209) # rgb = (0xd1,0xd1,0xd1)
(209,209,209) # rgb = (0xd1,0xd1,0xd1)
(207,207,207) # rgb = (0xcf,0xcf,0xcf)
(205,205,205) # rgb = (0xcd,0xcd,0xcd)
(205,205,205) # rgb = (0xcd,0xcd,0xcd)
(204,204,204) # rgb = (0xcc,0xcc,0xcc)
(204,204,204) # rgb = (0xcc,0xcc,0xcc)
(202,202,202) # rgb = (0xca,0xca,0xca)
(201,201,201) # rgb = (0xc9,0xc9,0xc9)
(201,201,201) # rgb = (0xc9,0xc9,0xc9)
(199,199,199) # rgb = (0xc7,0xc7,0xc7)
(199,199,199) # rgb = (0xc7,0xc7,0xc7)
(197,197,197) # rgb = (0xc5,0xc5,0xc5)
(196,196,196) # rgb = (0xc4,0xc4,0xc4)
(196,196,196) # rgb = (0xc4,0xc4,0xc4)
(194,194,194) # rgb = (0xc2,0xc2,0xc2)
(193,193,193) # rgb = (0xc1,0xc1,0xc1)
(193,193,193) # rgb = (0xc1,0xc1,0xc1)
(191,191,191) # rgb = (0xbf,0xbf,0xbf)
(191,191,191) # rgb = (0xbf,0xbf,0xbf)
(189,189,189) # rgb = (0xbd,0xbd,0xbd)
(188,188,188) # rgb = (0xbc,0xbc,0xbc)
(188,188,188) # rgb = (0xbc,0xbc,0xbc)
(186,186,186) # rgb = (0xba,0xba,0xba)
(185,185,185) # rgb = (0xb9,0xb9,0xb9)
(185,185,185) # rgb = (0xb9,0xb9,0xb9)
(183,183,183) # rgb = (0xb7,0xb7,0xb7)
(182,182,182) # rgb = (0xb6,0xb6,0xb6)
(182,182,182) # rgb = (0xb6,0xb6,0xb6)
(180,180,180) # rgb = (0xb4,0xb4,0xb4)
(178,178,178) # rgb = (0xb2,0xb2,0xb2)
(178,178,178) # rgb = (0xb2,0xb2,0xb2)
(177,177,177) # rgb = (0xb1,0xb1,0xb1)
(177,177,177) # rgb = (0xb1,0xb1,0xb1)
(175,175,175) # rgb = (0xaf,0xaf,0xaf)
(174,174,174) # rgb = (0xae,0xae,0xae)
(174,174,174) # rgb = (0xae,0xae,0xae)
}
tRNS {
197 187 190 194 186 4 186 189 4 195 84 191 5 193 175 163 205 150 191 213 88 75 67 8 147 191 220 203 95 151 223 199 8 207 156 227 199 65 163 98 226 204 12 202 167 201 11 65 178 228 205 74 59 87 178 19 201 99 18 14 184 204 184 96 22 61 227 199 22 193 97 197 254 59 253 28 192 102 199 247 58 198 244 30 109 202 188 32 96 196 60 203 239 202 230 41 207 237 119 53 213 209 37 55 45 230 214 233 92 185 223 50 230 57 124 217 43 133 221 95 198 47 233 99 194 221 107 138 152 144 226 140 133 220 172 125 218 196 118 225 161 223 235 238 200 155 147 146 172 236 236 151 183 150 234 216 217 211 151 219 132 185 145 147 217 138 144 137 142 151 217 217 213}
IMAGE {
pixels hex
0520201616160a0a0a0a0a0a0a0a010101010101010101000000000000000000
053a3a161616160a0a0a0a0a0a0a0a0a0a06060606060607070707070707071b
053a3a3a161616161615151c1c1c1c1c1c1c12121212121b1b1b1b1b1b1b1b1b
053a3a3a3a252525252527272727272727272724242424242424212121212121
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}

24
src/pkg/image/png/writer.go
View File

@ -130,12 +130,8 @@ func (e *encoder) writePLTE(p image.PalettedColorModel) {
e.err = FormatError("bad palette length: " + strconv.Itoa(len(p))) e.err = FormatError("bad palette length: " + strconv.Itoa(len(p)))
return return
} }
for i := 0; i < len(p); i++ { for i, c := range p {
r, g, b, a := p[i].RGBA() r, g, b, _ := c.RGBA()
if a != 0xffff {
e.err = UnsupportedError("non-opaque palette color")
return
}
e.tmp[3*i+0] = uint8(r >> 8) e.tmp[3*i+0] = uint8(r >> 8)
e.tmp[3*i+1] = uint8(g >> 8) e.tmp[3*i+1] = uint8(g >> 8)
e.tmp[3*i+2] = uint8(b >> 8) e.tmp[3*i+2] = uint8(b >> 8)
@ -143,6 +139,21 @@ func (e *encoder) writePLTE(p image.PalettedColorModel) {
e.writeChunk(e.tmp[0:3*len(p)], "PLTE") e.writeChunk(e.tmp[0:3*len(p)], "PLTE")
} }
func (e *encoder) maybeWritetRNS(p image.PalettedColorModel) {
last := -1
for i, c := range p {
_, _, _, a := c.RGBA()
if a != 0xffff {
last = i
}
e.tmp[i] = uint8(a >> 8)
}
if last == -1 {
return
}
e.writeChunk(e.tmp[:last+1], "tRNS")
}
// An encoder is an io.Writer that satisfies writes by writing PNG IDAT chunks, // An encoder is an io.Writer that satisfies writes by writing PNG IDAT chunks,
// including an 8-byte header and 4-byte CRC checksum per Write call. Such calls // including an 8-byte header and 4-byte CRC checksum per Write call. Such calls
// should be relatively infrequent, since writeIDATs uses a bufio.Writer. // should be relatively infrequent, since writeIDATs uses a bufio.Writer.
@ -447,6 +458,7 @@ func Encode(w io.Writer, m image.Image) os.Error {
e.writeIHDR() e.writeIHDR()
if pal != nil { if pal != nil {
e.writePLTE(pal.Palette) e.writePLTE(pal.Palette)
e.maybeWritetRNS(pal.Palette)
} }
e.writeIDATs() e.writeIDATs()
e.writeIEND() e.writeIEND()