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How to apply grayscale filter to image using EaselJS (CreateJS)

Searching the Google for grayscale easeljs leads to some obscure StackOverflow Q&A from 2011. which has a working example. However, it uses a generic filter matrix so you would need to know how grayscale effect actually works on pixel level to understand what it does.

It's much easier to use Easel's built-in functions. However, those are not easy to discover using a search engine. You have to dig into docs. Here's an easy way to do it, adapted from Easel docs. Assuming you have a Bitmap, Container, Shape in variable myDisplayObject:

var matrix = new createjs.ColorMatrix().adjustSaturation(-100);
myDisplayObject.filters = [new createjs.ColorMatrixFilter(matrix)];
myDisplayObject.cache();
        

Make sure you call cache() at the end, because filters are only applied during caching. If you wish to use different filters for different objects in a container, you need to cache() each one separately before adding to container.

Now, you might run this example, and get the error message createjs.ColorMatrix() is not a constructor because createjs.ColorMatrix is undefined. The reason for this is that current version of minified files does not include filters, so you need to include ColorMatrixFilter.js script in your page separately. Lanny says it will be included in one of future versions. I'm not sure that's a good idea though. I doubt many users use filters. I almost built the entire game without it, and only want to include it for Medusa's petrifying effects.

Milan Babuškov, 2013-06-18
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