RGB Color Space

The red, green, and blue (RGB) color space is widely used throughout computer graphics. Red, green, and blue are three primary additive colors (individual components are added together to form a desired color) and are represented by a three-dimensional, Cartesian coordinate system (Figure). The indicated diagonal of the cube, with equal amounts of each primary component, represents various gray levels. Table contains the RGB values for 100% amplitude, 100% saturated color bars, a common video test signal.


  - RGB Color cube









The RGB color space is the most prevalent choice for computer graphics because color displays use red, green, and blue to create the desired color. Therefore, the choice of the RGB color space simplifies the architecture and design of the system. Also, a system that is designed using the RGB color space can take advantage of a large number of existing software routines, since this color space has been around for a number of years. However, RGB is not very efficient when dealing with “real-world” images. All three RGB components need to be of equal bandwidth to generate any color within the RGB color cube. The result of this is a frame buffer that has the same pixel depth and display resolution for each RGB component. Also, processing an image in the RGB color space is usually not the most efficient method. For example, to modify the intensity or color of a given pixel, the three RGB values must be read from the frame buf fer, the intensity or color calculated, the desired modifications performed, and the new RGB values calculated and written back to the frame buf fer. If the system had access to an image stored directly in the intensity and color format, some processing steps would be faster. For these and other reasons, many video standards use luma and two color dif ference signals. The most common are the YUV, YIQ, and YCbCr color spaces. Although all are related, there are some differences.