Usability of Digital Cameras for Verifying Physically Based ...

(a) (b)
Figure 21: Chromaticity diagrams showing the primaries and the white point of
(a) sRGB [srg06] and (b) Adobe RGB [ado06].
3.1.4 RGB Color Spaces
RGB color spaces are commonly used in computer graphics and digital photo-
graphy. They form subspaces of the CIE XYZ color space and therefore do not
contain all visible colors. RGB spaces are specified by defining a white point and
three primary colors. RGB values itself do not identify absolute colors unless they
are assigned to a certain RGB color space.
Common RGB color spaces that have been standardized are sRGB and Adobe
RGB. The location of the primaries and the white point of these RGB color spaces
are shown in figure 21. It can be seen that Adobe RGB has a significantly larger
gamut than sRGB, improving primarily in cyan-greens. The CIE xy chromaticity
coordinates for sRGB are (0.64, 0.33) for red, (0.30, 0.60) for green and (0.15,
0.06) for blue. The red and green vertices for Adobe RGB are very similar, but
the values of the green vertex differ significantly. Red is at (0.64, 0.34), green is
at (0.21, 0.71) and blue is at (0.15, 0.06) [GM02]. The Adobe RGB color space
nonetheless encompasses only roughly 50% of all visible colors.
37