Add CMYK image exporting

lib/psd/color.coffee

+Util = require './util.coffee'
+
+module.exports =
+  cmykToRgb: (c, m, y, k) ->
+    r = Util.clamp (65535 - (c * (255 - k) + (k << 8))) >> 8, 0, 255
+    g = Util.clamp (65535 - (m * (255 - k) + (k << 8))) >> 8, 0, 255
+    b = Util.clamp (65535 - (y * (255 - k) + (k << 8))) >> 8, 0, 255
+    [r, g, b]
+
+  # def cmyk_to_rgb(c, m, y, k)
+  #   Hash[{
+  #     r: (65535 - (c * (255 - k) + (k << 8))) >> 8,
+  #     g: (65535 - (m * (255 - k) + (k << 8))) >> 8,
+  #     b: (65535 - (y * (255 - k) + (k << 8))) >> 8
+  #   }.map { |k, v| [k, Util.clamp(v, 0, 255)] }]
+  # end

lib/psd/image.coffee

@@ -7,8 +7,9 @@ Export      = require './image_export.coffee'
 module.exports = class Image extends Module
   @includes ImageFormat.RAW
   @includes ImageFormat.RLE
-  @includes ImageMode.RGB
   @includes ImageMode.Greyscale
+  @includes ImageMode.RGB
+  @includes ImageMode.CMYK
   @includes Export.PNG
   
   COMPRESSIONS = [
@@ -41,6 +42,7 @@ module.exports = class Image extends Module
     switch @mode()
       when 1 then @setGreyscaleChannels()
       when 3 then @setRgbChannels()
+      when 4 then @setCmykChannels()
 
   calculateLength: ->
     @length = switch @depth()

lib/psd/image_mode.coffee

 module.exports =
-  RGB: require('./image_modes/rgb.coffee')
   Greyscale: require('./image_modes/greyscale.coffee')
+  RGB: require('./image_modes/rgb.coffee')
+  CMYK: require('./image_modes/cmyk.coffee')

lib/psd/image_modes/cmyk.coffee

+Color = require '../color.coffee'
+module.exports =
+  setCmykChannels: ->
+    @channelsInfo = [
+      { id: 0 },
+      { id: 1 },
+      { id: 2 },
+      { id: 3 }
+    ]
+
+    @channelsInfo.push { id: -1 } if @channels() is 5
+
+  combineCmykChannel: ->
+    cmykChannels = @channelsInfo
+      .map (ch) -> ch.id
+      .filter (ch) -> ch >= -1
+
+    for i in [0...@numPixels]
+      c = m = y = k = 0
+      a = 255
+
+      for chan, index in cmykChannels
+        val = @channelData[i + (@channelLength * index)]
+
+        switch chan
+          when -1 then a = val
+          when 0 then c = val
+          when 1 then m = val
+          when 2 then y = val
+          when 3 then k = val
+
+      [r, g, b] = Color.cmykToRgb(255 - c, 255 - m, 255 - y, 255 - k)
+      @pixelData.push r, g, b, a

lib/psd/util.coffee

-module.exports = class Util
-  @pad2: (i) -> (i + 1) & ~0x01
-  @pad4: (i) -> ((i + 4) & ~0x03) - 1
-  @getUnicodeCharacter: (cp) ->
+module.exports =
+  pad2: (i) -> (i + 1) & ~0x01
+  pad4: (i) -> ((i + 4) & ~0x03) - 1
+  getUnicodeCharacter: (cp) ->
     if cp >= 0 and cp <= 0xD7FF or cp >= 0xE000 and cp <= 0xFFFF
       return String.fromCharCode(cp)
     else if cp >= 0x10000 and cp <= 0x10FFFF
@@ -18,3 +18,6 @@ module.exports = class Util
       second = (0x3ff & cp) + 0xDC00
 
       String.fromCharCode(first) + String.fromCharCode(second)
+
+  clamp: (num, min, max) ->
+    Math.min(Math.max(num, min), max)