How to change the opacity (alpha, transparency) of an element in a canvas element after it has been drawn?

Question

Using the HTML5 element, I would like to load an image file (PNG, JPEG, etc.), draw it to the canvas completely transparently, and then fade it i

Answer 1

You can't. It's immediate mode graphics. But you can sort of simulate it by drawing a rectangle over it in the background color with an opacity.

If the image is over something other than a constant color, then it gets quite a bit trickier. You should be able to use the pixel manipulation methods in this case. Just save the area before drawing the image, and then blend that back on top with an opacity afterwards.