Colors of the Rainbow
Color Properties / Terminology
The Color Wheel
Color Space and Gamut
The process of color vision unveils several interesting facts about color and our perception. For one that perceived brightness (luminance) is the predominant visual information we rely on for orientation and to identify objects. We also learn why all individuals perceive color a little different, or no color at all. Furthermore we get hints that might explain why certain techniques of combining colors in compositions have certain effects.
Light is the Origin
Color perception is a result of achromatic and
chromatic signals derived from light stimuli.
Chromatic signals (~ hue) are mostly derived from the light's wavelength.
Light Stimulates Our Photoreceptor Cells
The eye has photoreceptor cells, called cones, which
we divide into three types.
S-Cones are sensitive to
Each type of cone is less or more stimulated by a light beam and passes on its stimulus value.
The next step is to transform these values into values of three opponent-colors systems. The luma system
(~ range from black to white, or dark to fully illuminated respectively), the blue/yellow system and the red/green system.
Finally the values of the three opponent-colors systems are put together and make up our color perception. Of course, we absorb multiple light beams at once from different angles and therefore can form an image of a scene. The grayscale images on the right show how much visual information is
contained in each channel.
An interesting aspect of cones is their different
sensitivity in regards to wavelength. The
exemplary illustration on the right shows the
sensitivity curves for each type of cone.
We see that cones react to a wide range of wavelength and how their curves overlap. We can also see that sensitivity-peaks are not evenly spaced.
This demonstrates that for most wavelengths we need the input of all three types of cones to distinguish changes in wavelength and/or intensity (number of photons).
Furthermore, the illustration provides evidence that the medium- and long-wavelength cones contribute the most to our brightness perception, if we consider the formula of the luma system from the above: L = B + (R + G).
Individual Color Perception
The physiological prerequisites for color vision allow
drawing the conclusion that there is no
uniformity in color perception among
individuals. Several physiological deviations
can cause a shift in color perception.
For individuals with "normal" vision these shifts can be hardly measured. Less fortunate individuals suffer from significant shifts in color perception, called color vision deficiency or "color blindness". Most of the times this is caused by cones which are defect, absent, or altered in their spectral sensitivity.