Modern production and distribution workflows have allowed for high dynamic range (HDR) imagery to become widespread. It has made a positive impact in the creative industry and improved image quality on consumer devices. Akin to the dynamics of loudness in audio, it is predicted that the increased luminance range allowed by HDR ecosystems could introduce unintended, high-magnitude changes. These luminance changes could occur at program transitions, advertisement insertions, and channel change operations. In this article, we present findings from a psychophysical experiment conducted to evaluate three components of HDR luminance changes: the magnitude of the change, the direction of the change (darker or brighter), and the adaptation time. Results confirm that all three components exert significant influence. We find that increasing either the magnitude of the luminance or the adaptation time results in more discomfort at the unintended transition. We find that transitioning from brighter to darker stimuli has a non-linear relationship with adaptation time, falling off steeply with very short durations.
The critical flicker fusion (CFF) is the frequency of changes at which a temporally periodic light will begin to appear completely steady to an observer. This value is affected by several visual factors, such as the luminance of the stimulus or its location on the retina. With new high dynamic range (HDR) displays, operating at higher luminance levels, and virtual reality (VR) displays, presenting at wide fields-of-view, the effective CFF may change significantly from values expected for traditional presentation. In this work we use a prototype HDR VR display capable of luminances up to 20,000 cd/m^2 to gather a novel set of CFF measurements for never before examined levels of luminance, eccentricity, and size. Our data is useful to study the temporal behavior of the visual system at high luminance levels, as well as setting useful thresholds for display engineering.
We investigated how perceived achromatic and chromatic contrast changes with luminance. The experiment consisted of test and reference displays viewed haploscopically, where each eye sees one of the displays. Test stimuli presented on the test display on a background of varying luminance levels (0.02, 2,20,200,2000 cd/m²) were matched in perceived contrast to reference stimuli presented on a background at a fixed 200 cd/m² luminance level. We found that approximate contrast constancy holds at photopic luminance levels (20 cd/m² and above), that is, test stimuli presented at these luminance backgrounds matched when their physical contrasts were the same magnitude as the reference stimulus for most conditions. For lower background luminances, covering an extensive range of 5 log units, much higher physical contrast was required to achieve a match with the reference. This deviation from constancy was larger for lower spatial frequencies and lower pedestal suprathreshold contrasts. Our data provides the basis for new contrast retargeting models for matching appearances across luminance levels.