Apologize if it was already discussed but I couldn’t find a mail to this topic.

In one of the early drafts of Filter Effects we had filter operation support 
for HTML Canvas. We deferred it and IMO it makes more sense to have it as part 
of the Canvas specification text.

I would suggest a filter attribute that takes a list of filter operations 
similar to the CSS Image filter function[1]. Similar to shadows[2], each 
drawing operation would be filtered. The API looks like this:

partial interface CanvasRenderingContext2D {
    attribute DOMString filter;

A filter DOMString could looks like: “contrast(50%) blur(3px)”

With the combination of grouping in canvas[3] it would be possible to group 
drawing operations and filter them together.

Filter functions include a reference to a <filter> element and a specification 
of SVG filters[4]. I am unsure if a reference do an element within a document 
can cause problems. If it does, we would just not support SVG filter references.


[1] http://dev.w3.org/fxtf/filters/#interpolating-filter-image
[3] http://lists.w3.org/Archives/Public/public-canvas-api/2013AprJun/0009.html
[4] http://dev.w3.org/fxtf/filters/#FilterElement

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