Effect
Pixelate
Coarsen resolution into blocky pixels with adjustable size.
Pixelation coarsens resolution into visible blocks, once a limit of early digital cameras and game hardware, later a censorship and style device. Mosaic blur in news broadcasts made the chunky grid familiar to everyone.
Block size is the lever between subtle sampling and full retro game read.

Properties
Cells
cells across the shorter side
Softness
blend between neighbouring cells
Command line
Requires Rethings Pro. Install the tool from Rethings → Install Command Line Tool…
rethings apply --effect pixelate --set cells=48 --set softness=0 -i input.jpg -o output.png