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 7.2-1). The indicated diagonal of the Due to the many implementations of the RGB color cube, with equal amounts of each primary component, space, the sRGB color space was formalized. The speci- represents various gray levels. Table 7.2-1 contains the fication for sRGB (IEC 61966-2-1) uses BT.709 RGB values for 100% amplitude, 100% saturated color chromaticity, D65 reference white, a display gamma of bars, a common video test signal. 2.2, and linear RGB (8 bits per color). The RGB color space is the most prevalent choice for sRGB values have a normalized range of 0-1, with computer graphics because color displays use red, green, 8-bit digital sRGB values having a range of 0-255 for and blue to create the desired color. Therefore, the black-white. Aversion called "Studio RGB" uses an 8-bit choice of the RGB color space simplifies the architecture range of 16-235 for black-white, enabling compatibility and design of the system. Also, a system that is designed with video applications. using the RGB color space can take advantage of a large One limitation of sRGB is that since the normalized number of existing software routines, since this color values are restricted to the 0-1 range, colors outside the space has been around for a number of years. gamut (the triangle produced by them) cannot be used. However, RGB is not very efficient when dealing with For this reason, the extended RGB color space, "scRGB," real-world images. All three RGB components need to be was developed. Communications Engineering Desk Reference; ISBN: 9780123746481 Copyright © 2007 Elsevier Inc. All rights reserved CHAPTER 7.2 Colour spaces scG = (scG16 / (8192)-0.5 scB = (scB16 / 8192)-0 MAGENTA WHITE if (scR16, scG16, scB16) < 4095 sR's = 0 sG's 0 BLACK GREEN sB's 0 if 4096 < (scR16, scG16, scB16) < 4243 YELLOW sR' 8 = round[4.500 X scR X 255] Figure 7.2-1 The RGB C