Protanopia and Deuteranopia


There are various types of color "blindness." In most cases, the person can see some colors while other colors appear as a shade of gray. Thus, the more appropriate term is "color vision deficiency." A few people are color blind -- they see the world only in shades of gray.

Color vision deficiencies arise either because the person is missing one of their three types of cones or because the spectral sensitivity function of one type of cone is anomalous -- it is shifted in position to a slightly shorter or slightly longer wavelength than what is considered normal. True color blindness arises when a person is missing two (cone monochromacy) or all three (rod monochromacy) types of cones.

A person missing a single type of cone has a dichromacy. There are three types of dichromacy -- protanopia (missing the L-cone), deuteranopia (missing the M-cone) and tritanopia (missing the S-cone.) Protanopia and deuteranopia are much more common than tritanopia. Mutations of the X chromosome are often the cause of protanopia and deuteranopia and this implies that males are much more likely than females to have these types of dichromacy.

The Activity:

In this activity, you can load a photograph of your choosing (make it a colorful one!) and then see a simulation of how that photograph might appear to a person with protanopia or deuteranopia.

The simulated photographs are only approximate. The algorithm (Viénot, Brettel, & Mollon, 1999) assumes that the observer is an "ideal observer." An ideal observer is based on the average shape of the spectral sensitivity functions of normal people. Most people are close to an ideal observer, but few are probably exactly an ideal observer. Thus, there will likely be slight differences between how you perceive color and how the ideal observer perceives color. The simulated photographs also assume that the monitor is perfectly calibrated to a standard monitor. That is, it is assumed that your monitor displays colors exactly the same way that a standard monitor does. Again, while your monitor is likely close to the standard, unless it has been calibrated, it likely will have some subtle (or not so subtle) differences. These will affect the veridicality of the simulated photographs.

Pick the photograph to process:

Simulated Protanopia:

Simulated Deuteranopia:


Viénot, F., Brettel, H. & Mollon, J. D. (1999). Digital video colourmaps for checking the legibility of displays by dichromats. Color Research & Application, 24, 243-252.<243::aid-col5>;2-v