The plots below show dependences between lightness, hue, chroma, colorfulness, and saturation after tone mapping and color correction. The dependences are visualized in the CIELAB, CIELUV, CIECAM02 and iCAM color spaces. The lines depict the change of perceptual attributes for six basic colors of different luminance (red, magenta, blue, cyan, green and yellow) when the compression factor c varies from 0 to 2. The initial points (c=1) are marked with black squares. Two images on the left were generated using the color correction formula that does not preserves luminance of the tone-mapped images (Nonlinear, Equation 2 in the paper), and images on the right were generated using the luminance preserving formula (Linear, Equation 3 in the paper). The dotted lines depict tone mapping without color correction (Equation 1 in the paper).
All perceptual correlates change along complex and non-linear trajectories, which do not explain the effect of color correction. CIELUV saturation and CIECAM saturation are the most consistent across contrast changes for the non-linear color correction formula, but they do not explain why much stronger desaturation is necessary for c<0.6
CIELUV CHROMA (Non-linear color correction) | CIELUV CHROMA (Luminance preserving color correction) | ||
CIELUV SATURATION (Non-linear color correction) | CIELUV SATURATION (Luminance preserving color correction) | ||
CIELAB CHROMA (Non-linear color correction) | CIELAB CHROMA (Luminance preserving color correction) | ||
CIELAB SATURATION (Non-linear color correction) | CIELAB SATURATION (Luminance preserving color correction) | ||
CIECAM02 CHROMA (Non-linear color correction) | CIECAM02 CHROMA (Luminance preserving color correction) | ||
CIECAM02 COLORFULNESS (Non-linear color correction) | CIECAM02 COLORFULNESS (Luminance preserving color correction) | ||
CIECAM02 SATURATION (Non-linear color correction) | CIECAM02 SATURATION (Luminance preserving color correction) | ||
iCAM CHROMA (Non-linear color correction) (implementation downloaded from http://www.cis.rit.edu/mcsl/icam/hdr/) | iCAM CHROMA (Luminance preserving color correction) | ||