Remove node-png dependency #7

lib/psd/image_exports/png.coffee

 fs = require 'fs'
-{Png} = require 'png'
+{PNG} = require 'pngjs'
 RSVP = require 'rsvp'
 
 module.exports =
   toPng: ->
     new RSVP.Promise (resolve, reject) =>
-      png = new Png(new Buffer(@pixelData), @width(), @height(), 'rgba')
-      png.encode(resolve)
+      png = new PNG(filterType: 4, width: @width(), height: @height())
+
+      png.data[i] = p for p, i in @pixelData
+      resolve(png)
 
   saveAsPng: (output) ->
     new RSVP.Promise (resolve, reject) =>
       @toPng()
         .then (image) ->
-          fs.writeFile output, image.toString('binary'), 'binary', resolve
+          image.pack().pipe(fs.createWriteStream(output))
+          resolve()
           

lib/psd/image_modes/rgb.coffee

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

package.json

@@ -12,7 +12,7 @@
     "coffee-script": "~ 1.7.1",
     "jspack": "~ 0.0.3",
     "coffeescript-module": "~ 0.2.1",
-    "png": "~ 3.0.3",
+    "pngjs": "~ 0.4.0",
     "rsvp": "~ 3.0.6",
     "lodash": "~ 2.4"
   },