Reveal a picture piece by piece

Question

I am trying to reveal a picture piece by piece. I found this thread here need ideas to only display some pixels and gray out the remaining pixels, with an excellent answer from

Answer 1

Here's a branch of corsiKa's fiddle with some mods, most significant of which is the way the pixels are removed, allowing a time period to be specified.

The need for the pixels to have ids is also avoided, therefore the HTML is simpler.