- question of the week - color of the week  


Colorblindness, or color deficiency, is the inability to perceive differences between particular colors which other people can distinguish.

The human eye has two different types of photoreceptors: rods and cones. Rods are responsible for night vision, and can not distinguish colors. Cones are responsible for color perception during daylight conditions, and are inactive during night. Cones absorb light (photons) and send electrical signal to the brain. There are three different types of cones which have different spectral sensitivity functions (see Figure 1). L-cones have the most spectral sensitivity in long wavelengths, M-cones in medium wavelengths, and S-cones in short wavelengths. Consequently, light can be perceived as a composition of three numbers: (l, m, s), where l, m, and s represent amount of photons absorbed by L-cones, M-cones, and S-cones, respectively. Thus, we usually say that the normal human vision system is trichromatic.

Colorblindness is caused by the situation when a certain type of a cone is deficient or lacked. If one lacks certain type of cones, he/she is a dichromat, and is called a protanope, a deuteranope, or a tritanope depending on lack of L-cones, M-cones, or S-cones respectively. Typical types of colorblindness are shown on Figure 1.

Figure 1: Typical types of color deficiency.

Figure 2 shows examples of the most common color vision deficiency. A dichromat perceives a color in two dimensional color space. If a color (l, m, s) is perceived by a trichromat, the same color will be perceived as (0, m, s), (l, 0, s), and (l, m, 0) by dichromats of different types, a protanope, a deuteranope, or a tritanope, respectively. Thus, in particular two colors that differ only on one values, for example (l1, m, s) and (l2, m, s)), can confuse protanopes (can be seen as the same color), because they perceive the colors as (0, m, s).

Figure 2: Examples of color vision deficiencies (a) original image, (b) deuteranopic vision simulation, (c) protanopic vision simulation.

The main purpose of the project is to make more friendly images for colorblind people. The process of recoloring the original image should be performed in such a way that as much information as possible will remain visible to colorblind people when viewing by them. Figure 3 is an example of recoloring process perform for deuteranopic vision deficiency by CBA.

Figure 3: Example of SmartRecoloringPlus recoloring scheme (a) original image, (b) deuteranopic vision of the original, (c) recoloring of the original seen by a person with normal vision, (d) recolored image seen by deuteranope.