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

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

diff --git a/src/pkg/image/png/reader_test.go b/src/pkg/image/png/reader_test.go
index efa6336d792f979c6f958fa915ee345d453be1ca..bcc1a3db475609e79224372ce2596ab64e909f07 100644 (file)
--- a/src/pkg/image/png/reader_test.go
+++ b/src/pkg/image/png/reader_test.go
@@ -28,6 +28,7 @@ var filenames = []string{
        "basn3p02",
        "basn3p04",
        "basn3p08",
+       "basn3p08-trns",
        "basn4a08",
        "basn4a16",
        "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").
        io.WriteString(w, "gAMA {1.0000}\n")
 
-       // Write the PLTE (if applicable).
+       // Write the PLTE and tRNS (if applicable).
        if cpm != nil {
+               lastAlpha := -1
                io.WriteString(w, "PLTE {\n")
-               for i := 0; i < len(cpm); i++ {
-                       r, g, b, _ := cpm[i].RGBA()
+               for i, c := range cpm {
+                       r, g, b, a := c.RGBA()
+                       if a != 0xffff {
+                               lastAlpha = i
+                       }
                        r >>= 8
                        g >>= 8
                        b >>= 8
                        fmt.Fprintf(w, "    (%3d,%3d,%3d)     # rgb = (0x%02x,0x%02x,0x%02x)\n", r, g, b, r, g, b)
                }
                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.

diff --git a/src/pkg/image/png/testdata/pngsuite/README b/src/pkg/image/png/testdata/pngsuite/README
index abe3ecb201d6c61b2e63c82d236257245c6218cd..c0f78bde87a567bb8ab9017d3ee0b4abc7fc0155 100644 (file)
--- a/src/pkg/image/png/testdata/pngsuite/README
+++ b/src/pkg/image/png/testdata/pngsuite/README
@@ -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-
 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
 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

diff --git a/src/pkg/image/png/testdata/pngsuite/basn3p08-trns.png b/src/pkg/image/png/testdata/pngsuite/basn3p08-trns.png
new file mode 100644 (file)
index 0000000..b0fc0c1
Binary files /dev/null and b/src/pkg/image/png/testdata/pngsuite/basn3p08-trns.png differ

diff --git a/src/pkg/image/png/testdata/pngsuite/basn3p08-trns.sng b/src/pkg/image/png/testdata/pngsuite/basn3p08-trns.sng
new file mode 100644 (file)
index 0000000..78dc367
--- /dev/null
+++ b/src/pkg/image/png/testdata/pngsuite/basn3p08-trns.sng
@@ -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
+053a3a3a4034343425252727272727393939392d2d2d2d2d2d2d323232323232
+053a3a404034343434343939393939393939394747474343433d3d3d3d3d3d3d
+053a404b4b4b50505046464646464646464659595959595151514e5b5b616161
+053a404b4b4b50505058585858585858588c8c8c595959595b656a6e70707070
+053a4b4b4b4b5050506c5858585858588c8c8c8c8c8c5965656a6a6e70707070
+053b4b4b4b636363506c6c6c6c6c6c8781808c8c8c86a1a1a1906e6e70707070
+053b4b5757636363636c6c6c6c7787878181808c8c86a1a190909d9d9d9daa70
+053b576666666f6363777777777e8787848481808086a19090aaaaaaaa9f9f9f
+053b576666797979797b7b7b7b7b8a8a8a8a848480809c9c9c9c9c9c9c9c9c9c
+053b66747474747474747b7b7b7b8a8a8a8a8a8aacacacacacacacacacaca4a4
+052e7474747474747474747b7b7b8a8a8a6d6d6d6d6d6d6da4a4a4a4a4a4a4a4
+052e7474747474747474a0a0a0a0a0a09393936d6d6d6d787878787878787878
+05207474747474a0a0a0a0a0a0a0a0a093939191949494948989898989898989
+052a2a2a7171717171a7a7a7a7a7a7a7a7a79e9e9e9e9e9e9e9e959595959595
+052a53536871717171717171a9a9a9a9a9a9a9a9a9a9a9a99595959595959595
+053753536871717171717171a3a3a3a3a3a3a3a3979797979a9a9a9a8e8e8e8e
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+054453535f68687171717171a5a5a5a5a5a5a6a6a6a6a68b8b8b8b8b8b8b8b6b
+054444535f686767676767677272727f7f8383838383838d8d8d8d8d8d8d8b8b
+054444535f6767675a5a5a627272727275757f7f7f7f5d73737d7d7d82828282
+0544445367675a5a5a5a4d546262727272757575755d5d5d7373737376767676
+054444535349495a5a5a4d4d54626262626275754c5d5d5d5d60646464767676
+054444444949494949494d4d4d5454546262624c4c4c4c4c5555556060646464
+05444444444941414133353f3f3f3f3f3f4d3636363c3c454545454531313131
+05444444442f2f2f2f333535353535352c2c2c2c2c3030303030282828282828
+053744442f2f2f2f2f2f333535351d1d22222222262626262323232323232323
+053737372f2f2f2f2f2f2f331818181818181d1d1d1d1d131a1a1a1a1a1e1e1e
+052a37372f2f2f2f2f2f18111111110f0e0e0e0e0d0d0d0d0d0d0d0d0d0d0d13
+}

diff --git a/src/pkg/image/png/writer.go b/src/pkg/image/png/writer.go
index 2d593f6a7ff18d7dff853a61b0b2eaa92f99a255..a27586f2394e1ff1bb43bacc0cbf93048251483d 100644 (file)
--- a/src/pkg/image/png/writer.go
+++ b/src/pkg/image/png/writer.go
@@ -130,12 +130,8 @@ func (e *encoder) writePLTE(p image.PalettedColorModel) {
                e.err = FormatError("bad palette length: " + strconv.Itoa(len(p)))
                return
        }
-       for i := 0; i < len(p); i++ {
-               r, g, b, a := p[i].RGBA()
-               if a != 0xffff {
-                       e.err = UnsupportedError("non-opaque palette color")
-                       return
-               }
+       for i, c := range p {
+               r, g, b, _ := c.RGBA()
                e.tmp[3*i+0] = uint8(r >> 8)
                e.tmp[3*i+1] = uint8(g >> 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")
 }
 
+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,
 // 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.
@@ -447,6 +458,7 @@ func Encode(w io.Writer, m image.Image) os.Error {
        e.writeIHDR()
        if pal != nil {
                e.writePLTE(pal.Palette)
+               e.maybeWritetRNS(pal.Palette)
        }
        e.writeIDATs()
        e.writeIEND()