update toBuffer function, support RAW data

README.md

@@ -641,6 +641,7 @@ encoded data as a NodeJS Buffer object.
   - `"jpg"`
   - `"png"`
   - `"gif"`
+  - `"raw"`
 0. `params {Object}`: **Optional** Format-specific parameters (See below).
 0. `callback {Function(err, buffer)}`
 
@@ -685,6 +686,16 @@ The `params` object should have the following fields:
   channel of the pixel is above this threshold, this pixel will be considered
   as opaque; otherwise it will be transparent.
 
+##### RAW
+
+No `params` object is supported. The raw image returns an object which contains
+the following fields:
+
+ - `buffer {Buffer}`: Pixeldata
+ - `width {Integer}`: Image width
+ - `height {Integer}`: Image height
+
+
 #### Write to file
 
 Write encoded binary image data directly to a file.

lib/ImagePrototypeInit.js

@@ -587,6 +587,13 @@
                             params.threshold,
                             encoderCb
                         );
+                    } else if (type === 'raw') {
+                        var rawImg = {
+                            buffer: that.__lwip.buffer(),
+                            width: that.__lwip.width(),
+                            height: that.__lwip.height()
+                        };
+                        encoderCb(null, rawImg);
                     } else throw Error('Unknown type \'' + type + '\'');
 
                     function encoderCb(err, buffer) {