ASCII
The layer redrawn as a density ramp of glyphs
The layer redrawn as a grid of glyphs, dense characters where the picture is bright and open ones where it is dark. The font travels inside the shader, so it runs with no assets at all. Colorize slides between pure phosphor and the source's own colour pushed through the glyphs; scan adds the monitor the font implies.
Rendering cost: light. A few samples per pixel: fine fullscreen at full pixel ratio, including on integrated graphics. How to tune it
Take ASCII with you.
ASCII is free. Sign in and it is yours — the background itself, with your settings already saved in, ready to drop into your site. The account is only somewhere to put the files. No card now, and no card later.
The other 61 come with a licence, $9.99 once.
$0forever
Your preset is in the URL. It survives the trip.