Cell block noise filter and other effects

[Ofnuts]

Another method:

• Start with a small image (you will blow it up by the size of your squares to if you need 16x16 squares in a 800x800 image, start with a 50x50 image/layer).
  
• Fill 50% gray HSV=0,0,50% or RGB=127,127,127
  
• Filter>Noise>HSV noise: Hue=0, Saturation=0, Value=128, Holdness=1. If you have all of this right, Windows>Dockable dialog>Histogram should show a horizontal (but jagged) line, indicating an equal spread of the grays.
  
• Image>Scale image (or Layer>Scale layer): Size=1600%, interpolation=None