An Effective EOTF for Showing Gradients on 10 000 Nit Rec. 2020 Displays

ABSTRACT

Electro‐Optical Transfer Function (EOTF) plays a critical role in image encoding, which aims to minimize the number of bit‐depth while preventing visible artifacts of contour banding. Past studies commonly employed Gabor patches (i.e., sine‐wave gratings) as stimuli, but visual experiences suggest that artifacts are commonly observed in images with transitions and gradients. Therefore, we carefully designed, built, and calibrated an HDR/WCG display system, which can cover a wide luminance range (i.e., 0.005–12 000 cd/m ² ) and a color gamut close to Rec. 2020. The stimuli were carefully designed to be gradients/transitions with changes in luminance and simultaneous changes in luminance and chroma, and to have systematically varied luminance, number of bands, and color of stimuli. The experiment results suggested that the achromatic stimuli introduced the lowest threshold of contrast. In particular, the thresholds at the low luminance levels were below those characterized by the Barten curve and the 10‐bit PQ curve, while those at the high luminance levels were above these two curves. The insufficient digital counts at low luminance levels for the 10‐bit PQ curve corroborates the visual experience. Based on the experiment results, an effective 10‐bit EOTF was proposed, which was believed to prevent visible artifacts for showing gradients on 10 000 cd/m ² Rec. 2020 displays.