Video Synchronization 815the egg causes stimulation in both the long wavelength RED process and the medium-
wavelength GREEN process ( Figure 28.3 ). Because human beings possess three separate
color vision processes we are classifi ed as trichromats. People affl icted with color
blindness usually lack one of the three chemical responses in the normal eye; they are
known as dichromats, although a few rare individuals are true monochromats. What
has not yet been discovered, among people or other animals, is a more-than-three color
perception system. This is fortunate for the engineers who developed color television!
The fact that our cone cells only contain three chemicals is why we may be fooled into
experiencing the whole gamut of colors with the combination of only three so-called
primary colors. The television primaries of red, green, and blue were chosen because
each stimulates only one of the photosensitive chemicals found in the cone cells. The
great television swindle is that we can, for instance, be duped into believing we are seeing
yellow by activating both the red and green tube elements simultaneously—just as would a
pure yellow source. Similarly we may be hoodwinked into seeing light blue cyan with the
simultaneous activation of green and blue. We can also be made to experience paradoxical
colors such as magenta by combining red and blue, a feat that no pure light source could
ever do! This last fact demonstrates that our color perception system effectively “ wraps
around, ” mapping the linear spectrum of electromagnetic frequencies into a color circle,
or a color space. And it is in this way that we usually view the science of color perception:
we can regard all visual sense as taking place within a color three space. A television
studio vectorscope allows us to view color three space end on, so it looks like a hexagon
[ Figure 28.4(a) ]. Note that each color appears at a different angle, like the numbers on a
Yellow light Cyan lightRed Green BlueChemical responseFigure 28.3 : Mechanism of color vision.