transparency chunk

src/pixie/fileformats/png.nim

@@ -7,7 +7,7 @@ const
 
 type
   ChunkCounts = object
-    PLTE, IDAT: uint8
+    PLTE, IDAT, tRNS: uint8
 
   PngHeader = object
     width, height: int
@@ -146,7 +146,9 @@ proc unfilter(
       result[unfiteredIdx(x, y)] = value
 
 proc parseImageData(
-  header: PngHeader, palette: seq[array[3, uint8]], data: seq[uint8]
+  header: PngHeader,
+  palette: seq[array[3, uint8]],
+  transparency, data: seq[uint8]
 ): seq[ColorRGBA] =
   result.setLen(header.width * header.height)
 
@@ -178,6 +180,7 @@ proc parseImageData(
 
   case header.colorType:
   of 0:
+    let special = if transparency.len == 2: transparency[1].int else: -1
     var bytePos, bitPos: int
     for y in 0 ..< header.height:
       for x in 0 ..< header.width:
@@ -204,8 +207,9 @@ proc parseImageData(
           inc bytePos
           bitPos = 0
 
+        let alpha = if value.int == special: 0 else: 255
         result[x + y * header.width] = ColorRGBA(
-          r: value, g: value, b: value, a: 255
+          r: value, g: value, b: value, a: alpha.uint8
         )
 
       # If we move to a new row, skip to the next full byte
@@ -213,13 +217,21 @@ proc parseImageData(
         inc bytePos
         bitPos = 0
   of 2:
+    let special =
+      if transparency.len == 6:
+        ColorRGBA(
+          r: transparency[1], g: transparency[3], b: transparency[5], a: 255
+        )
+      else:
+        ColorRGBA()
     var bytePos: int
     for y in 0 ..< header.height:
       for x in 0 ..< header.width:
         let rgb = cast[ptr array[3, uint8]](unfiltered[bytePos].unsafeAddr)[]
-        result[x + y * header.width] = ColorRGBA(
+        var rgba = ColorRGBA(r: rgb[0], g: rgb[1], b: rgb[2], a: 255)
-          r: rgb[0], g: rgb[1], b: rgb[2], a: 255
+        if rgba == special:
-        )
+          rgba.a = 0
+        result[x + y * header.width] = rgba
         bytePos += 3
   of 3:
     var bytePos, bitPos: int
@@ -247,9 +259,15 @@ proc parseImageData(
         if value.int >= palette.len:
           failInvalid()
 
-        let rgb = palette[value]
+        let
+          rgb = palette[value]
+          transparency =
+            if transparency.len > value.int:
+              transparency[value]
+            else:
+              255
         result[x + y * header.width] = ColorRGBA(
-          r: rgb[0], g: rgb[1], b: rgb[2], a: 255
+          r: rgb[0], g: rgb[1], b: rgb[2], a: transparency
         )
 
       # If we move to a new row, skip to the next full byte
@@ -297,7 +315,7 @@ proc decodePng*(data: seq[uint8]): Image =
     counts = ChunkCounts()
     header: PngHeader
     palette: seq[array[3, uint8]]
-    imageData: seq[uint8]
+    transparency, imageData: seq[uint8]
     prevChunkType: string
 
   # First chunk must be IHDR
@@ -333,9 +351,26 @@ proc decodePng*(data: seq[uint8]): Image =
       failInvalid()
     of "PLTE":
       inc counts.PLTE
-      if counts.PLTE > 1 or counts.IDAT > 0:
+      if counts.PLTE > 1 or counts.IDAT > 0 or counts.tRNS > 0:
         failInvalid()
       palette = parsePalette(data[pos ..< pos + chunkLen])
+    of "tRNS":
+      inc counts.tRNS
+      if counts.tRNS > 1 or counts.IDAT > 0:
+        failInvalid()
+      transparency = data[pos ..< pos + chunkLen]
+      case header.colorType:
+      of 0:
+        if transparency.len != 2:
+          failInvalid()
+      of 2:
+        if transparency.len != 6:
+          failInvalid()
+      of 3:
+        if transparency.len > palette.len:
+          failInvalid()
+      else:
+        failInvalid()
     of "IDAT":
       inc counts.IDAT
       if counts.IDAT > 1 and prevChunkType != "IDAT":
@@ -372,7 +407,7 @@ proc decodePng*(data: seq[uint8]): Image =
   result = Image()
   result.width = header.width
   result.height = header.height
-  result.data = parseImageData(header, palette, imageData)
+  result.data = parseImageData(header, palette, transparency, imageData)
 
 proc decodePng*(data: string): Image {.inline.} =
   decodePng(cast[seq[uint8]](data))

tests/pngsuite.nim

@@ -73,6 +73,109 @@ const
     "s39n3p04", # 39x39 paletted file, no interlacing
     # "s40i3p04", # 40x40 paletted file, interlaced
     "s40n3p04", # 40x40 paletted file, no interlacing
+
+    # "bgai4a08", # 8 bit grayscale, alpha, no background chunk, interlaced
+    # "bgai4a16", # 16 bit grayscale, alpha, no background chunk, interlaced
+    "bgan6a08", # 3x8 bits rgb color, alpha, no background chunk
+    # "bgan6a16", # 3x16 bits rgb color, alpha, no background chunk
+    "bgbn4a08", # 8 bit grayscale, alpha, black background chunk
+    # "bggn4a16", # 16 bit grayscale, alpha, gray background chunk
+    "bgwn6a08", # 3x8 bits rgb color, alpha, white background chunk
+    # "bgyn6a16", # 3x16 bits rgb color, alpha, yellow background chunk
+
+    # "tbbn0g04", # transparent, black background chunk
+    # # "tbbn2c16", # transparent, blue background chunk
+    "tbbn3p08", # transparent, black background chunk
+    # # "tbgn2c16", # transparent, green background chunk
+    "tbgn3p08", # transparent, light-gray background chunk
+    "tbrn2c08", # transparent, red background chunk
+    # # "tbwn0g16", # transparent, white background chunk
+    "tbwn3p08", # transparent, white background chunk
+    "tbyn3p08", # transparent, yellow background chunk
+    "tp0n0g08", # not transparent for reference (logo on gray)
+    "tp0n2c08", # not transparent for reference (logo on gray)
+    "tp0n3p08", # not transparent for reference (logo on gray)
+    "tp1n3p08", # transparent, but no background chunk
+    "tm3n3p02", # multiple levels of transparency, 3 entries
+
+    # "g03n0g16", # grayscale, file-gamma = 0.35
+    "g03n2c08", # color, file-gamma = 0.35
+    "g03n3p04", # paletted, file-gamma = 0.35
+    # "g04n0g16", # grayscale, file-gamma = 0.45
+    "g04n2c08", # color, file-gamma = 0.45
+    "g04n3p04", # paletted, file-gamma = 0.45
+    # "g05n0g16", # grayscale, file-gamma = 0.55
+    "g05n2c08", # color, file-gamma = 0.55
+    "g05n3p04", # paletted, file-gamma = 0.55
+    # "g07n0g16", # grayscale, file-gamma = 0.70
+    "g07n2c08", # color, file-gamma = 0.70
+    "g07n3p04", # paletted, file-gamma = 0.70
+    # "g10n0g16", # grayscale, file-gamma = 1.00
+    "g10n2c08", # color, file-gamma = 1.00
+    "g10n3p04", # paletted, file-gamma = 1.00
+    # "g25n0g16", # grayscale, file-gamma = 2.50
+    "g25n2c08", # color, file-gamma = 2.50
+    "g25n3p04", # paletted, file-gamma = 2.50
+
+    "f00n0g08", # grayscale, no interlacing, filter-type 0
+    "f00n2c08", # color, no interlacing, filter-type 0
+    "f01n0g08", # grayscale, no interlacing, filter-type 1
+    "f01n2c08", # color, no interlacing, filter-type 1
+    "f02n0g08", # grayscale, no interlacing, filter-type 2
+    "f02n2c08", # color, no interlacing, filter-type 2
+    "f03n0g08", # grayscale, no interlacing, filter-type 3
+    "f03n2c08", # color, no interlacing, filter-type 3
+    "f04n0g08", # grayscale, no interlacing, filter-type 4
+    "f04n2c08", # color, no interlacing, filter-type 4
+    "f99n0g04", # bit-depth 4, filter changing per scanline
+
+    # "pp0n2c16", # six-cube palette-chunk in true-color image
+    "pp0n6a08", # six-cube palette-chunk in true-color+alpha image
+    "ps1n0g08", # six-cube suggested palette (1 byte) in grayscale image
+    # "ps1n2c16", # six-cube suggested palette (1 byte) in true-color image
+    "ps2n0g08", # six-cube suggested palette (2 bytes) in grayscale image
+    # "ps2n2c16", # six-cube suggested palette (2 bytes) in true-color image
+
+    "ccwn2c08", # chroma chunk w:0.3127,0.3290 r:0.64,0.33 g:0.30,0.60 b:0.15,0.06
+    "ccwn3p08", # chroma chunk w:0.3127,0.3290 r:0.64,0.33 g:0.30,0.60 b:0.15,0.06
+    "cdfn2c08", # physical pixel dimensions, 8x32 flat pixels
+    "cdhn2c08", # physical pixel dimensions, 32x8 high pixels
+    "cdsn2c08", # physical pixel dimensions, 8x8 square pixels
+    "cdun2c08", # physical pixel dimensions, 1000 pixels per 1 meter
+    "ch1n3p04", # histogram 15 colors
+    "ch2n3p08", # histogram 256 colors
+    "cm0n0g04", # modification time, 01-jan-2000 12:34:56
+    "cm7n0g04", # modification time, 01-jan-1970 00:00:00
+    "cm9n0g04", # modification time, 31-dec-1999 23:59:59
+    # "cs3n2c16", # color, 13 significant bits
+    "cs3n3p08", # paletted, 3 significant bits
+    "cs5n2c08", # color, 5 significant bits
+    "cs5n3p08", # paletted, 5 significant bits
+    "cs8n2c08", # color, 8 significant bits (reference)
+    "cs8n3p08", # paletted, 8 significant bits (reference)
+    "ct0n0g04", # no textual data
+    "ct1n0g04", # with textual data
+    "ctzn0g04", # with compressed textual data
+    "cten0g04", # international UTF-8, english
+    "ctfn0g04", # international UTF-8, finnish
+    "ctgn0g04", # international UTF-8, greek
+    "cthn0g04", # international UTF-8, hindi
+    "ctjn0g04", # international UTF-8, japanese
+    "exif2c08", # chunk with jpeg exif data
+
+    # "oi1n0g16", # grayscale mother image with 1 idat-chunk
+    # "oi1n2c16", # color mother image with 1 idat-chunk
+    # "oi2n0g16", # grayscale image with 2 idat-chunks
+    # "oi2n2c16", # color image with 2 idat-chunks
+    # "oi4n0g16", # grayscale image with 4 unequal sized idat-chunks
+    # "oi4n2c16", # color image with 4 unequal sized idat-chunks
+    # "oi9n0g16", # grayscale image with all idat-chunks length one
+    # "oi9n2c16", # color image with all idat-chunks length one
+
+    "z00n2c08", # color, no interlacing, compression level 0 (none)
+    "z03n2c08", # color, no interlacing, compression level 3
+    "z06n2c08", # color, no interlacing, compression level 6 (default)
+    "z09n2c08", # color, no interlacing, compression level 9 (maximum)
   ]
 
   pngSuiteCorruptedFiles* = [