jpg checkpoint

src/pixie.nim

@@ -1,13 +1,14 @@
 ## Public interface to you library.
 
 import pixie/images, pixie/masks, pixie/paths, pixie/common, pixie/blends,
-  pixie/fileformats/bmp, pixie/fileformats/png, flatty/binny, os
+  pixie/fileformats/bmp, pixie/fileformats/png, pixie/fileformats/jpg,
+  flatty/binny, os
 
 export images, masks, paths, PixieError, blends
 
 type
   FileFormat* = enum
-    ffPng, ffBmp
+    ffPng, ffBmp, ffJpg
 
 proc toMask*(image: Image): Mask =
   ## Converts an Image to a Mask.
@@ -23,23 +24,26 @@ proc toImage*(mask: Mask): Image =
 
 proc decodeImage*(data: string | seq[uint8]): Image =
   ## Loads an image from a memory.
-  if data.len > 8 and cast[array[8, uint8]](data.readUint64(0)) == pngSignature:
-    return decodePng(data)
-
-  if data.len > 2 and data.readStr(0, 2) == "BM":
-    return decodeBmp(data)
-
-  raise newException(PixieError, "Unsupported image file format")
+  if data.len > 8 and data.readUint64(0) == cast[uint64](pngSignature):
+    decodePng(data)
+  elif data.len > 2 and data.readUint16(0) == cast[uint16](jpgStartOfImage):
+    decodeJpg(data)
+  elif data.len > 2 and data.readStr(0, 2) == "BM":
+    decodeBmp(data)
+  else:
+    raise newException(PixieError, "Unsupported image file format")
 
 proc readImage*(filePath: string): Image =
   ## Loads an image from a file.
   decodeImage(readFile(filePath))
 
 proc encodeImage*(image: Image, fileFormat: FileFormat): string =
-  ## Encodes an image into a memory.
+  ## Encodes an image into memory.
   case fileFormat:
   of ffPng:
     image.encodePng()
+  of ffJpg:
+    image.encodeJpg()
   of ffBmp:
     image.encodeBmp()
 
@@ -52,5 +56,7 @@ proc writeFile*(image: Image, filePath: string) =
   let fileFormat = case splitFile(filePath).ext:
     of "png": ffPng
     of "bmp": ffBmp
-    else: ffPng
-  writeFile(filePath, image.encodeImage(fileFormat))
+    of "jpg": ffJpg
+    else:
+      raise newException(PixieError, "Unrecognized file extension")
+  image.writeFile(filePath, fileformat)

src/pixie/fileformats/jpg.nim

@@ -0,0 +1,152 @@
+import flatty/binny, pixie/common, pixie/images
+
+# See http://www.vip.sugovica.hu/Sardi/kepnezo/JPEG%20File%20Layout%20and%20Format.htm
+
+const
+  jpgStartOfImage* = [0xFF.uint8, 0xD8]
+
+template failInvalid() =
+  raise newException(PixieError, "Invalid JPG buffer, unable to load")
+
+proc readSegmentLen(data: seq[uint8], pos: int): int =
+  if pos + 2 > data.len:
+    failInvalid()
+
+  let segmentLen = data.readUint16(pos).swap().int
+  if pos + segmentLen > data.len:
+    failInvalid()
+
+  segmentLen
+
+proc skipSegment(data: seq[uint8], pos: var int) {.inline.} =
+  pos += readSegmentLen(data, pos)
+
+proc decodeSOF(data: seq[uint8], pos: var int) =
+  let segmentLen = readSegmentLen(data, pos)
+  pos += 2
+
+  if pos + 6 > data.len:
+    failInvalid()
+
+  let
+    precision = data[pos].int
+    height = data.readUint16(pos + 1).swap().int
+    width = data.readUint16(pos + 3).swap().int
+    components = data[pos + 5].int
+
+  pos += 6
+
+  if precision != 8:
+    raise newException(PixieError, "Unsupported JPG bit depth")
+
+  if components != 3:
+    raise newException(PixieError, "Unsupported JPG channel count")
+
+  debugEcho width, " x ", height
+
+  if 8 + components * 3 != segmentLen:
+    failInvalid()
+
+  for i in 0 ..< 3:
+    discard
+
+  pos += components * 3
+
+proc decodeDHT(data: seq[uint8], pos: var int) =
+  skipSegment(data, pos)
+
+proc decodeDQT(data: seq[uint8], pos: var int) =
+  skipSegment(data, pos)
+
+proc decodeDRI(data: seq[uint8], pos: var int) =
+  skipSegment(data, pos)
+
+proc decodeSOS(data: seq[uint8], pos: var int) =
+  let segmentLen = readSegmentLen(data, pos)
+  pos += 2
+
+  if segmentLen != 12:
+    failInvalid()
+
+  let components = data[pos]
+  if components != 3:
+    raise newException(PixieError, "Unsupported JPG channel count")
+
+  for i in 0 ..< 3:
+    discard
+
+  pos += 10
+  pos += 3 # Skip 3 more bytes
+
+  while true:
+    if pos >= data.len:
+      failInvalid()
+
+    if data[pos] == 0xFF:
+      inc pos
+      if pos == data.len:
+        failInvalid()
+      if data[pos] == 0xD9: # End of Image:
+        inc pos
+        break
+      elif data[pos] == 0x00:
+        discard # Skip this byte
+      else:
+        failInvalid()
+
+    inc pos
+
+proc decodeJpg*(data: seq[uint8]): Image =
+  ## Decodes the JPEG into an Image.
+
+  if data.len < 4:
+    failInvalid()
+
+  if data.readUint16(0) != cast[uint16](jpgStartOfImage):
+    failInvalid()
+
+  var pos: int
+  while true:
+    if pos + 2 > data.len:
+      failInvalid()
+
+    let marker = [data[pos], data[pos + 1]]
+    pos += 2
+
+    if marker[0] != 0xFF:
+      failInvalid()
+
+    case marker[1]:
+    of 0xD8: # Start of Image
+      discard
+    of 0xC0: # Start of Frame
+      decodeSOF(data, pos)
+    of 0xC2: # Start of Frame
+      raise newException(PixieError, "Progressive JPG not supported")
+    of 0xC4: # Define Huffman Tables
+      decodeDHT(data, pos)
+    of 0xDB: # Define Quantanization Table(s)
+      decodeDQT(data, pos)
+    of 0xDD: # Define Restart Interval
+      decodeDRI(data, pos)
+    of 0xDA: # Start of Scan
+      decodeSOS(data, pos)
+      break
+    of 0xFE: # Comment
+      skipSegment(data, pos)
+    of 0xD9: # End of Image
+      failInvalid() # Not expected here
+    else:
+      if (marker[1] and 0xF0) == 0xE0:
+        # Skip APPn segments
+        skipSegment(data, pos)
+      else:
+        raise newException(PixieError, "Unsupported JPG segemnt")
+
+  raise newException(PixieError, "Decoding JPG not supported yet")
+
+proc decodeJpg*(data: string): Image {.inline.} =
+  decodeJpg(cast[seq[uint8]](data))
+
+proc encodeJpg*(image: Image): string =
+  raise newException(PixieError, "Encoding JPG not supported yet")

src/pixie/fileformats/png.nim

@@ -22,7 +22,7 @@ template failInvalid() =
 when defined(release):
   {.push checks: off.}
 
-proc parseHeader(data: seq[uint8]): PngHeader =
+proc decodeHeader(data: seq[uint8]): PngHeader =
   result.width = data.readUint32(0).swap().int
   result.height = data.readUint32(4).swap().int
   result.bitDepth = data[8]
@@ -78,7 +78,7 @@ proc parseHeader(data: seq[uint8]): PngHeader =
   if result.interlaceMethod != 0:
     raise newException(PixieError, "Interlaced PNG not yet supported")
 
-proc parsePalette(data: seq[uint8]): seq[array[3, uint8]] =
+proc decodePalette(data: seq[uint8]): seq[array[3, uint8]] =
   if data.len == 0 or data.len mod 3 != 0:
     failInvalid()
 
@@ -145,7 +145,7 @@ proc unfilter(
 
       result[unfiteredIdx(x, y)] = value
 
-proc parseImageData(
+proc decodeImageData(
   header: PngHeader,
   palette: seq[array[3, uint8]],
   transparency, data: seq[uint8]
@@ -297,10 +297,7 @@ proc parseImageData(
     discard # Not possible, parseHeader validates
 
 proc decodePng*(data: seq[uint8]): Image =
-  ## Decodes the PNG from the parameter buffer. Check png.channels and
-  ## png.bitDepth to see how the png.data is formatted.
-  ## The returned png.data is currently always RGBA (4 channels)
-  ## with bitDepth of 8.
+  ## Decodes the PNG into an Image.
 
   if data.len < (8 + (8 + 13 + 4) + 4): # Magic bytes + IHDR + IEND
     failInvalid()
@@ -323,7 +320,7 @@ proc decodePng*(data: seq[uint8]): Image =
     data.readStr(pos + 4, 4) != "IHDR":
     failInvalid()
   inc(pos, 8)
-  header = parseHeader(data[pos ..< pos + 13])
+  header = decodeHeader(data[pos ..< pos + 13])
   prevChunkType = "IHDR"
   inc(pos, 13)
 
@@ -353,7 +350,7 @@ proc decodePng*(data: seq[uint8]): Image =
       inc counts.PLTE
       if counts.PLTE > 1 or counts.IDAT > 0 or counts.tRNS > 0:
         failInvalid()
-      palette = parsePalette(data[pos ..< pos + chunkLen])
+      palette = decodePalette(data[pos ..< pos + chunkLen])
     of "tRNS":
       inc counts.tRNS
       if counts.tRNS > 1 or counts.IDAT > 0:
@@ -407,7 +404,7 @@ proc decodePng*(data: seq[uint8]): Image =
   result = Image()
   result.width = header.width
   result.height = header.height
-  result.data = parseImageData(header, palette, transparency, imageData)
+  result.data = decodeImageData(header, palette, transparency, imageData)
 
 proc decodePng*(data: string): Image {.inline.} =
   decodePng(cast[seq[uint8]](data))

tests/test_jpg.nim

@@ -0,0 +1,5 @@
+import pixie/fileformats/jpg
+
+let original = readFile("tests/data/jpeg420exif.jpg")
+
+discard decodeJpg(original)