I know you can pixelate with Filer / Pixelate / Mosaic, but for some reason images I put through this filter don't look like old 80's/90's video game graphics. Not sure if it's the pixelating itself, or - more likely - the number of colors being used.
Is there a plugin out there specifically designed to make an image look like it came straight out of an old video game?
You might try Image>Mode>Indexed Color
Something like this:
What I don't understand in your "how to" is that after the guy downsizes and then upsizes his image dimensions, those pixels remain perfectly square and sharp. When I do it, there is (of course) anti-aliasing doing its best to smooth all of that.
How does one reach the result of having a 1000x1000 image made up of 25 (gigantic) square "pixels" of 40 pixels each (for example)? Downsizing and upsizing doesn't give me that, but the pixelating tool does.
With his downsizing (and resampling turned on) he is throwing away 98 percent of the pixels. By enlarging image the remaining pixels have to make up the larger image so they are streatched across the image. Each square you see is a pixel.