CIE 1960 UCS | Strolls with my Dog

As we have seen in the previous post, knowing the characteristics of light at the scene is critical to be able to determine the color transform that will allow captured raw data to be naturally displayed from an output color space like ubiquitous sRGB.

White Point

The light source Spectral Power Distribution (SPD) corresponds to a unique White Point, namely a set of coordinates in the $XYZ$ color space, obtained by multiplying wavelength-by-wavelength its SPD (the blue curve below) by the response of the retina of a typical viewer, otherwise known as the CIE Color Matching Functions of a Standard Observer ( $\hat{x},\hat{y},\hat{z}$ in the plot)

Figure 1. Spectral Power Distribution of Standard Daylight Illuminant D5300 with a Correlated Color Temperature of 5300 deg. K; and CIE (2012) 2-deg XYZ “physiologically relevant” Color Matching Functions from cvrl.org.

Adding (integrating) the three resulting curves we get three values that represent the illuminant’s coordinates in the $XYZ$ color space. The White Point is obtained by dividing these coordinates by the $Y$ value to normalize it to 1.

For example a Standard Daylight Illuminant with a Correlated Color Temperature of 5300 kelvins has a White Point of^[1]

$XYZn$ = [0.9593 1.0000 0.8833]

assuming CIE (2012) 2-deg XYZ “physiologically relevant” Color Matching Functions from cvrl.org. Continue reading White Point, CCT and Tint →

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