Added Crop Module (#8)

* ImageThreshold.js and ImageSelect.js bugfixes

* Added Crop Module

* lowercase parameters

* Added usage notes, changed a variable name.

src/modules/Crop.js

@@ -0,0 +1,61 @@
+/*
+ * Image Cropping module
+ * Usage:
+ *    Expected Inputs:
+ *      options.x : x-coordinate of image where the modules starts cropping | default : 0
+ *      options.y : y-coordinate of image where the modules starts cropping | default : 0
+ *      options.w : width of the resulting cropped image | default : 50% of input image width
+ *      options.h : height of the resulting cropped image | default : 50% of input image height
+ *    Output:
+ *      The cropped image, which is essentially a rectangle bounded by the lines:
+ *          x = options.x
+ *          x = options.x + options.w
+ *          y = options.y
+ *          y = options.y + options.h
+ */
+ module.exports = function Crop(options){
+
+   options = options || {};
+   options.title = "Crop Image";
+   options.format = options.format || "png";
+
+   function draw(image) {
+     var getPixels = require("get-pixels"),
+         savePixels = require("save-pixels"),
+         base64 = require('base64-stream');
+
+     getPixels(image.src,function(err,pixels){
+       var newdata = [];
+       var ox = options.x || 0;
+       var oy = options.y || 0;
+       var w = options.w || Math.floor(0.5*pixels.shape[0]);
+       var h = options.h || Math.floor(0.5*pixels.shape[1]);
+       var iw = pixels.shape[0]; //Width of Original Image
+       newarray = new Uint8Array(4*w*h);
+       for (var n = oy; n < oy + h; n++) {
+         newarray.set(pixels.data.slice(n*4*iw + ox, n*4*iw + ox + 4*w),4*w*(n-oy));
+       }
+       pixels.data = newarray;
+       pixels.shape = [w,h,4];
+       pixels.stride[1] = 4*w;
+
+       var buffer = base64.encode();
+       savePixels(pixels, options.format)
+         .on('end', function() {
+
+         var img = new Image();
+
+         img.src = 'data:image/' + options.format + ';base64,' + buffer.read().toString();
+
+         if (options.output) options.output(img);
+
+       }).pipe(buffer);
+
+     });
+   }
+
+   return {
+     options: options,
+     draw: draw
+   }
+ }