With this nonlinear relationship, equal steps in encoded luminance correspond roughly to subjectively equal steps in brightness. Ebner and FairchildFritz Ebner and Mark D Fairchild, "Development and testing of a color space (IPT) with improved hue uniformity," Proceedings of IS&T/SID's Sixth Color Imaging Conference, p 8-13 (1998). used an exponent of 0.43 to convert linear intensity into lightness (luma) for neutrals; the reciprocal, approximately 2.33 (quite close to the 2.2 figure cited for a typical display subsystem), was found to provide approximately optimal perceptual encoding of grays.
With this nonlinear relationship, equal steps in encoded luminance correspond roughly to subjectively equal steps in brightness. Ebner and FairchildFritz Ebner and Mark D Fairchild, "Development and testing of a color space (IPT) with improved hue uniformity," Proceedings of IS&T/SID's Sixth Color Imaging Conference, p 8-13 (1998). used an exponent of 0.43 to convert linear intensity into lightness (luma) for neutrals; the reciprocal approximately 2.33 (quite close to the 2.2 figure cited for a typical display subsystem), was found to provide approximately optimal perceptual encoding of grays.