jQuery plugin for turning image into grayscale

jquery.grayscale.js

(function($){

     /**
     * Renders an image in gray scale using canvas
     * @param {Boolean} toggle - Optional, whether or not to add or remove the grayscale effect
     * @return {jQuery}
     */
    $.fn.grayScale = function(toggle) {
        function _grayscale(src){
            var canvas = document.createElement('canvas');
            var ctx = canvas.getContext('2d');
            var imgObj = new Image();
            imgObj.src = src;
            canvas.width = imgObj.width;
            canvas.height = imgObj.height;
            ctx.drawImage(imgObj, 0, 0);
            var imgPixels = ctx.getImageData(0, 0, canvas.width, canvas.height);
            for(var y = 0; y < imgPixels.height; y++){
                for(var x = 0; x < imgPixels.width; x++){
                    var i = (y * 4) * imgPixels.width + x * 4;
                    var avg = (imgPixels.data[i] + imgPixels.data[i + 1] + imgPixels.data[i + 2]) / 3;
                    imgPixels.data[i] = avg;
                    imgPixels.data[i + 1] = avg;
                    imgPixels.data[i + 2] = avg;
                }
            }
            ctx.putImageData(imgPixels, 0, 0, 0, 0, imgPixels.width, imgPixels.height);
            return canvas.toDataURL();
        }

          return this.each(function() {
               var $img = $(this);
               if(this.nodeName == 'IMG') {
                    if(toggle === false) {
                         var origSrc = $img.attr('data-src');
                         if(origSrc) {
                              this.src = $img.attr('data-src');
                              $img.removeAttr('data-src');
                         }
                    }
                    else if( !$img.attr('data-src') ) {
                         $img.attr('data-src', this.src);
                         this.src = _grayscale(this.src);
                    }
               }
          });
    };

})(jQuery);