Black Level Visibility as a Function of Ambient Illumination

摘要

One of the key new attributes of HDR imaging and displays is the ability to present many stops of shadow detail, and with the best systems, a perceptually pure black. Displays perform at their best in a dark room as no ambient illumination impinges on the surface of the display, which would elevate the display's perceived black level. In addition, the viewer sees the most shadow detail when the region surrounding the display is also dark. In addition to applications where a display is viewed in a dark surround environment, there are also many viewing conditions where higher ambient light levels occur. Knowledgeable viewers prevent ambient illumination from reflecting from the display, but even for those viewers, surrounding luminance will be increased. To understand the impact of this surrounding ambient illumination on black level visibility and shadow detail, and to further guide ambient compensation algorithms, we performed a psychophysical study to assess the human visual system's ability to perceive detail when impacted by surround luminance. For the stimuli, we used a Gabor signal to probe the visual system's best capability. For the display, we used a Pulsar display with a large 1.0 neutral density filter placed over the display to enable black levels as low 0.0005 cd/m^2, relevant for OLED and cinema applications. The surround luminance levels ranged from fully dark up to 100 cd/m^ 2, and for each of these, shadow detail thresholds were measured as a function of display mean luminance levels from .001 to 400 cd/m^2. The results are useful for perceptual display performance assessment and tone-mapping applications, and PLUGE design. Further analysis found they are consistent with an existing surround effect visual model, which has basis in the cone photoreceptors.