Using an HLSL compute shader and [numthreads(90, 1, 1)] the GPU spawns 90 parralel threads which are calculating the average color for every LED simaultaneously.

As only picking one pixel at each led would be pretty inaccurate, we are taking zones and use the average color of ever zone.

(For now the average of every zone is picked, if I am testing it in real
life, we might change it - maybe the outer pixels are doubled for a more accurate color that looks better at the end).

I had an issue where some LEDs were using the wrong part of the screen because of incorrect index calculation. I fixed it by correcting the LED and screen coordinates:

(in the picture)