updated Filter comments

src/filters/Brighten.js

@@ -9,8 +9,11 @@
     var brightness = config.val || 0;
     var data = imageData.data;
     for(var i = 0; i < data.length; i += 4) {
+        // red
         data[i] += brightness;
+        // green
         data[i + 1] += brightness;
+        // blue
         data[i + 2] += brightness;
     }
 };

src/filters/Grayscale.js

@@ -13,6 +13,5 @@ Kinetic.Filters.Grayscale = function(imageData, config) {
         data[i + 1] = brightness;
         // blue
         data[i + 2] = brightness;
-        // i+3 is alpha (the fourth element)
     }
 };