I found an amazing JS library for image processing. This is very effective JS but little slower. The specialty is it works in browser as well as with node JS. So you can make an image processing tool for Android/iOS by JS now. You will find more details on their site: http://camanjs.com/ but here I experimented myself for browser. Here is the simplest code example for learning the very basic in couple of minutes. You may love it.
Download from here.