through a lens far from its center. The rays do not focus on a point inside the
camera, but instead create a cone of light, which looks like a comet tail.The RGB Color Space
All digital cameras rely on a color space definition to capture color. This definition,
which is part of a processing algorithm, forces light values captured by the camera
sensor into a defined color space. Essentially, the camera can only capture specific
colors, not the entire spectrum of color. Generally, this is not significant because the
human eye cannot really discern colors accurately.
There are several color space definitions in use today. Each has its advantages and
disadvantages:
■ RGB—Within the color model RGB are a number of color spaces, such as
Apple RGB, Adobe RGB (1998), and sRGB. Each RGB color space defines color
through three axes (R, G, and B), but differ in gamut and other characteris-
tics. RGB can be thought of as three grayscale images (usually referred to as
channels) representing the light values of red, green, and blue. Combining
these three channels of light produces a wide range of visible colors. The
three colors combined generate white, unlike the CMYK color space, which
generates black. For this reason, the RGB color space is called an additive
color space.
■ sRGB—sRGB is currently the standard color space for cameras and computer
monitors. This standard was created by Microsoft and HP in 1996 as a stan-
dard for computer monitors and software. The sRGB standard includes three
important areas: colorimetric RGB definition, the equivalent gamma value of
2.2, and a set of well defined viewing conditions. This results in a color space
that is equal among all devices, from the digital camera to the printer. The
only problem is that standardization means much fewer colors are possible.
■ YUV—A television standard used in Europe that enables backward compati-
bility with black-and-white televisions. A variant called YIQ is used in North
American television systems. In addition, all DVDs rely on the YUV/YIQ color
space.
The engineers who invented the YUV color space needed a way to make color
television broadcasts backward-compatible with black-and-white TVs. The
color signal they came up with also needed to conserve bandwidth because
three channels of RGB data would not fit into the limited broadcast signal
space. The YUV color space uses RGB information, but it creates a black-and-
white image (luminance) from the full color image and then subtracts theCHAPTER 2 ADVANTAGES AND DISADVANTAGES OF DIGITAL CAMERAS 15