Feature optional JPEG alpha channel

lib/document.coffee

@@ -14,7 +14,7 @@ class PDFDocument extends stream.Readable
     super
 
     # PDF version
-    @version = 1.3
+    @version = 1.4
 
     # Whether streams should be compressed
     @compress = @options.compress ? yes

lib/image.coffee

@@ -8,27 +8,37 @@ Data = require './data'
 JPEG = require './image/jpeg'
 PNG = require './image/png'
 
+toBuffer = (src) ->
+  if Buffer.isBuffer(src)
+    src
+  else if src instanceof ArrayBuffer
+    new Buffer(new Uint8Array(src))
+  else if match = /^data:.+;base64,(.*)$/.exec(src)
+    new Buffer(match[1], 'base64')
+  else
+    fs.readFileSync src
+
 class PDFImage
-  @open: (src, label) ->
-    if Buffer.isBuffer(src)
-      data = src
-    else if src instanceof ArrayBuffer
-      data = new Buffer(new Uint8Array(src))
-    else
-      if match = /^data:.+;base64,(.*)$/.exec(src)
-        data = new Buffer(match[1], 'base64')
+
+  @open: (src, label, alphaSrc) ->
+    data = toBuffer src
+
+    if alphaSrc
+      alphaData = toBuffer alphaSrc
+      if not JPEG.is alphaData
+        throw Error 'Alpha mask must be a gray JPEG image'
+      alpha = new JPEG alphaData
+      if alpha.colorSpace != 'DeviceGray'
+        throw Error 'Alpha mask must be a gray JPEG image'
+
+    if data
+      if JPEG.is(data)
+        return new JPEG(data, label, alpha)
+
+      else if PNG.is(data)
+        return new PNG(data, label, alpha)
 
       else
-        data = fs.readFileSync src
-        return unless data
-
-    if data[0] is 0xff and data[1] is 0xd8
-      return new JPEG(data, label)
-
-    else if data[0] is 0x89 and data.toString('ascii', 1, 4) is 'PNG'
-      return new PNG(data, label)
-
-    else
-      throw new Error 'Unknown image format.'
-
-module.exports = PDFImage
+        throw new Error 'Unknown image format.'
+
+module.exports = PDFImage

lib/image/jpeg.coffee

@@ -1,41 +1,50 @@
 fs = require 'fs'
 
-class JPEG
-  MARKERS = [0xFFC0, 0xFFC1, 0xFFC2, 0xFFC3, 0xFFC5, 0xFFC6, 0xFFC7,
-             0xFFC8, 0xFFC9, 0xFFCA, 0xFFCB, 0xFFCC, 0xFFCD, 0xFFCE, 0xFFCF]
-
-  constructor: (@data, @label) ->
-    if @data.readUInt16BE(0) isnt 0xFFD8
-      throw "SOI not found in JPEG"
-
-    pos = 2
-    while pos < @data.length
-      marker = @data.readUInt16BE(pos)
-      pos += 2
-      break if marker in MARKERS
-      pos += @data.readUInt16BE(pos)
-
-    throw "Invalid JPEG." unless marker in MARKERS
-    pos += 2
+MARKERS = [0xFFC0, 0xFFC1, 0xFFC2, 0xFFC3, 0xFFC5, 0xFFC6, 0xFFC7,
+           0xFFC8, 0xFFC9, 0xFFCA, 0xFFCB, 0xFFCC, 0xFFCD, 0xFFCE, 0xFFCF]
 
-    @bits = @data[pos++]
-    @height = @data.readUInt16BE(pos)
-    pos += 2
+getMetaInfo = (data, result = {}) ->
+  if data.readUInt16BE(0) isnt 0xFFD8
+    throw "SOI not found in JPEG"
 
-    @width = @data.readUInt16BE(pos)
+  pos = 2
+  while pos < data.length
+    marker = data.readUInt16BE(pos)
     pos += 2
+    break if marker in MARKERS
+    pos += data.readUInt16BE(pos)
 
-    channels = @data[pos++]
-    @colorSpace = switch channels
-      when 1 then 'DeviceGray'
-      when 3 then 'DeviceRGB'
-      when 4 then 'DeviceCMYK'
-
+  throw "Invalid JPEG." unless marker in MARKERS
+  pos += 2
+
+  result.bits = data[pos++]
+  result.height = data.readUInt16BE(pos)
+  pos += 2
+
+  result.width = data.readUInt16BE(pos)
+  pos += 2
+
+  channels = data[pos++]
+  result.colorSpace = switch channels
+    when 1 then 'DeviceGray'
+    when 3 then 'DeviceRGB'
+    when 4 then 'DeviceCMYK'
+
+  result
+
+class JPEG
+
+  # Returns true if the given data buffer has a JPEG signature
+  @is: (data) ->
+    data[0] is 0xff and data[1] is 0xd8
+
+  constructor: (@data, @label, @alpha) ->
+    getMetaInfo @data, @
     @obj = null
-      
+
   embed: (document) ->
     return if @obj
-    
+
     @obj = document.ref
       Type: 'XObject'
       Subtype: 'Image'
@@ -44,16 +53,20 @@ class JPEG
       Height: @height
       ColorSpace: @colorSpace
       Filter: 'DCTDecode'
-      
+
     # add extra decode params for CMYK images. By swapping the
     # min and max values from the default, we invert the colors. See
-    # section 4.8.4 of the spec.  
+    # section 4.8.4 of the spec.
     if @colorSpace is 'DeviceCMYK'
       @obj.data['Decode'] = [1.0, 0.0, 1.0, 0.0, 1.0, 0.0, 1.0, 0.0]
+
+    if @alpha
+      @alpha.embed(document)
+      @obj.data['SMask'] = @alpha.obj
 
     @obj.end @data
-    
+
     # free memory
     @data = null
-    
+
 module.exports = JPEG

lib/image/png.coffee

@@ -2,7 +2,12 @@ zlib = require 'zlib'
 PNG = require 'png-js'
 
 class PNGImage
-  constructor: (data, @label) ->
+
+  # Returns true if the given data buffer has a PNG signature
+  @is: (data) ->
+    data[0] is 0x89 and data.toString('ascii', 1, 4) is 'PNG'
+
+  constructor: (data, @label, @alpha) ->
     @image = new PNG(data)
     @width = @image.width
     @height = @image.height
@@ -73,7 +78,10 @@ class PNGImage
       @finalize()
 
   finalize: ->
-    if @alphaChannel
+    if @alpha
+      @alpha.embed(@document)
+      @obj.data['SMask'] = @alpha.obj
+    else if @alphaChannel
       sMask = @document.ref
         Type: 'XObject'
         Subtype: 'Image'

lib/mixins/images.coffee

@@ -4,7 +4,7 @@ module.exports =
   initImages: ->
     @_imageRegistry = {}
     @_imageCount = 0
-    
+
   image: (src, x, y, options = {}) ->
     if typeof x is 'object'
       options = x
@@ -20,7 +20,7 @@ module.exports =
       if src.width and src.height
         image = src
       else
-        image = @openImage src
+        image = @openImage src, options.alpha
 
     unless image.obj
       image.embed this
@@ -77,7 +77,7 @@ module.exports =
       else if options.valign is 'bottom'
         y = y + bh - h
 
-    # Set the current y position to below the image if it is in the document flow      
+    # Set the current y position to below the image if it is in the document flow
     @y += h if @y is y
 
     @save()
@@ -87,12 +87,12 @@ module.exports =
 
     return this
 
-  openImage: (src) ->
+  openImage: (src, alpha) ->
     if typeof src is 'string'
       image = @_imageRegistry[src]
 
     if not image
-      image = PDFImage.open src, 'I' + (++@_imageCount)
+      image = PDFImage.open src, 'I' + (++@_imageCount), alpha
       if typeof src is 'string'
         @_imageRegistry[src] = image