How to aid visualization by reducing number of tones or colors through posterization.
How to Reduce Colors/Tones in GIMP
As in video, except that Posterize is found under Colors on menu.
How to Reduce Colors/Tones in Image J
Under Image > Look Up Tables and then select from list and hope for the best.
You may have to make color images into 8-bit color (Image > Type > 8-bit color) or into 8-bit grayscale (Image > Type > 8-bit) .