Finish PNG exporting

lib/psd/image.coffee

 {Module}    = require 'coffeescript-module'
+
 ImageFormat = require './image_format.coffee'
 ImageMode   = require './image_mode.coffee'
+Export      = require './image_export.coffee'
 
 module.exports = class Image extends Module
   @includes ImageFormat.RAW
   @includes ImageFormat.RLE
   @includes ImageMode.RGB
+  @includes Export.PNG
   
   COMPRESSIONS = [
     'Raw'

lib/psd/image_export.coffee

+module.exports =
+  PNG: require('./image_exports/png.coffee')
\ No newline at end of file

lib/psd/image_exports/png.coffee

+fs = require 'fs'
+{Png} = require 'png'
+RSVP = require 'rsvp'
+
+module.exports =
+  toPng: ->
+    return @png if @png
+
+    @png = new Png(new Buffer(@pixelData), @width(), @height(), 'rgba')
+
+    new RSVP.Promise (resolve, reject) =>
+      console.log "Encoding!"
+      @png.encode(resolve)
+
+  saveAsPng: (output) ->
+    new RSVP.Promise (resolve, reject) =>
+      @toPng()
+        .then (image) ->
+          console.log "Writing!"
+          fs.writeFile output, image.toString('binary'), 'binary', resolve
+          

lib/psd/image_modes/rgb.coffee

@@ -5,14 +5,13 @@ module.exports =
       .filter (ch) -> ch >= -1
 
     for i in [0...@numPixels]
-      r = g = b = 0
-      a = 255
+      r = g = b = a = 0
 
       for chan, index in rgbChannels
         val = @channelData[i + (@channelLength * index)]
 
         switch chan
-          when -1 then a = val
+          when -1 then a = 255 - val
           when 0 then  r = val
           when 1 then  g = val
           when 2 then  b = val

lib/psd/lazy_execute.coffee

@@ -20,7 +20,7 @@ module.exports = class LazyExecute
     return @
 
   get: ->
-    for own key, val of @obj then do (key, val) =>
+    for key, val of @obj then do (key, val) =>
       return if @[key]?
       Object.defineProperty @, key,
         get: ->

package.json

@@ -4,7 +4,9 @@
   "dependencies": {
     "coffee-script": "~ 1.7.1",
     "jspack": "~ 0.0.3",
-    "coffeescript-module": "~ 0.0.2"
+    "coffeescript-module": "~ 0.0.2",
+    "png": "~ 3.0.3",
+    "rsvp": "~ 3.0.6"
   },
   "devDependencies": {
     "coffeeify": "~ 0.6.0"