How to create a lossless WebP image using toDataURL?
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I'm trying out the WebP image format in Chrome using the canvas element. On MDN I saw that `toDataURL` accepts a second argument representing the quality of the resulting image.

I'd like to generate a lossless WebP image of a canvas element. However, if I pass `1` for quality (meaning 100%), I don't get the exact same pixels back. It looks like it is generating a lossy image.

Here's a test case: http://jsfiddle.net/Nf5ve/1/. When drawing the PNG image, a certain color of a certain pixel has a value of 40. After drawing a 100% quality WebP image of the canvas on itself, the same value has changed to 47. This does not seem lossless to me, even though I passed a quality of 100%.

Is it possible to have `toDataURL` create a lossless WebP image, and if so how?