Reverse Ishihara

A type of PIP that are visible to the Colorblind, but not Color Normals. This is not because the Colorblind have better hue discrimination for some colors, but because they can see a small change in contrast in a field of flat colors whereas Color Normals see many different colors.

Normally, PIPs are designed where the foreground and background are different colors, but represent Colors of Confusion for a certain type of CVD. In Reverse PIPs, all of the colors used in both foreground and background are along a confusion line. In the left image below, orange yellow and green are used [Hues 20°, 40°, 80°, 100°], but tuned to the correct saturation to make sure they are on a line of confusion, and tuned to the same brightness to ensure there is no brightness gradient. Then the image/foreground is added by selectively increasing the brightness (by a small amount) of some of those dots.

The PIP on the left is very easy to read for the strongly red-green Colorblind. The PIP on the right has undergone a hue shift, which reveals (to the Colorblind) the multitude of different colors that were present in the left PIP, which obfuscate the image/foreground (“NO”).