I saw Mariko give a talk about this last week - http://2016.render-conf.com/talks#drawing-on-canvas-a-few-th...

It was absolutely fantastic; really great information about image data & how to process it.

Also - CSS tricks don't work if you're writing command line tools or backend code in JS.

That is true, but grafi.js relies on a browser's canvas API to convert an image to a Uint8ClampedArray of colour values, so it won't work on a command line or backend either. As a way to learn about convolution filters it seems fairly good though.

Good point. https://www.npmjs.com/package/get-pixels can help parse an image to pixels, but it returns a different format than the canvas API's Uint8ClampedArray.

I haven't tested but I think you can convert ndarray to Uint8ClampedArray by doing

    new Uint8ClampedArray(ndarray.data);

Node-canvas provides a compliant Canvas implementation:

https://github.com/Automattic/node-canvas

that is wrong way to do this - write efficient code (simple operations on an array) instead of using huge canvas library to make a library you don't need to use usable