Is there a trick to creating an animated gif of tv static that will allow it to be relatively small?

Question

Apologies in advance, but this isn't really a photoshop question. Rather, I'm trying to come up with something that is convincing but exploits the compression and features of the gif format as best as possible to produce the smallest possible file for the animation.

Some constraints:

• It needs to be at least 20 or 30 frames. I've tried with fewer (and since they're largely uncompressable 15 frames is half the size of 30, generally speaking)
• Size needs to be no less than about 256x192
• It doesn't need to be color though, nor even full grayscale. I've seen convincing stills with as few as about 16 grays
• It can have a pattern, but not one that is instantly obvious to the human eye. If someone takes a single frame and after a minute or two can spot the pattern (which makes it compressable?) that's ok
• Frames 2 through n can use quite a bit of alpha, but when I started using big horizontal stripes of alpha, it was instantly noticeable to my eyes. So you don't get to rack up a bunch of RLE with the easy cheat.
• All of the above and still needs to look good at 30-33ms frame speed. No variable speed or relying on anything significantly faster than that.

Also acceptable: an apng that complies with the above constraints. Possibly even mpeg, if you can come up with that (I'm ignorant of how the DCT does its magic).

Ideally I could get something down in the 250kbyte range, but I'd settle for anything significantly smaller than the 9 meg monstrosity I cooked up last week.

Oh, and one last thing: obviously I don't expect anyone to supply the graphic for me. I'm just looking for some trick(s) that will let me get there myself eventually.

Answer 1

This is a very interesting question.

Static (random noise) by its nature is actually highly incompressible. Information theory says that true noise is basically incompressible, and the more patterns something contains the more compressible it becomes (to the point of a solid line of 1's or 0's being perfectly compressible.

The ideal would be to create a true noise generator (just random numbers), but that doesn't help within the constraints of your problem.

The best thing I can think of is storing a number of small tiles of static and displaying them in staggered fashion to prevent the eye catching on to any patterns. Aside from that, you won't have much luck compressing this beyond 256 x 192 x 20 / 2 or about 500 kilobytes ( assuming 20 frames with resolution of 256 x 192, using 4 bit color depth ).

Simply encoding your animated gif in 16 color mode should get you to that point.