
In perceptually uniform colour spaces, the perceptual differences in colour pairs are approximately the same as the Euclidean distance between them. Uniformity is of great importance in applications such as gamut mapping where the perceptual difference between original and mapped colour needs to be minimised. Ideally, in a perceptually uniform colour space, the locus of constant Just Noticeable Difference (JND) around different colour samples should be the unit sphere. While several perceptually uniform colour spaces for Standard Dynamic Range (SDR) and High Dynamic Range (HDR) have been proposed, there is not a standardized uniformity metric with respect to which we might judge whether one space is more uniform than another. In this paper, we propose and develop such a uniformity metric. Importantly, our approach takes into account changes in all three directions of a colour space including luminance and this is in contradistinction to prior art that focuses mainly on the colour signal (separate from luminance). The proposed metric can be based on any perceptual colour difference metric that models JNDs.

Spatial and temporal contrast sensitivity is typically measured using different stimuli. Gabor patterns are used to measure spatial contrast sensitivity and flickering discs are used for temporal contrast sensitivity. The data from both types of studies is difficult to compare as there is no well-established relationship between the sensitivity to disc and Gabor patterns. The goal of this work is to propose a model that can predict the contrast sensitivity of a disc using the more commonly available data and models for Gabors. To that end, we measured the contrast sensitivity for discs of different sizes, shown at different luminance levels, and for both achromatic and chromatic (isoluminant) contrast. We used this data to compare 6 different models, each of which tested a different hypothesis on the detection and integration mechanisms of disc contrast. The results indicate that multiple detectors contribute to the perception of disc stimuli, and each can be modelled either using an energy model, or the peak spatial frequency of the contrast sensitivity function.

Some astronauts have suffered degradation of vision during long-duration space flight, suffering from a condition that has come to be known as Spaceflight Associated Neuro-ocular Syndrome (SANS). While related morphological changes can be observed with imaging technologies such as optical coherence tomography (OCT), it may be useful to have a rapid method for functional vision assessment. In this paper, we compare three tablet-based methods for rapid assessment of contrast sensitivity. First, a relatively novel method developed expressly for touch screens, in which the subject “swipes” a frequency/contrast sweep grating to indicate the boundary between visible and invisible patterns; second, a method-of-adjustment task in which the subject adjusts the contrast of a grating patch up and down to bracket the visual threshold; and third, a traditional temporal two-alternative forced choice (2AFC) task, in which the subject is presented with a near-threshold stimulus in one of two intervals, and must report the interval containing the stimulus. The swipe method shows variability comparable to the 2AFC method, and shows good agreement in estimates of the spatial frequency of peak sensitivity. The absolute sensitivity estimated with the swipe method is higher than that of the other methods, perhaps because subjects are biased to trace outside of the visible pattern region, or perhaps due to stimulus differences.