Spatiotemporal variation of chromatic and achromatic contrast thresholds

Abstract

Moving the retinal image of a sinusoidal grating at a constant velocity (compensated for eye movements) provides controlled spatial and temporal frequencies at every point in the stimulus field. Using this controlled-velocity technique, we have measured the detection threshold for isoluminance, red/green gratings as a function of their spatial and temporal frequencies. The chromatic contrast-threshold surface obtained in this way is analogous to the achromatic contrast-threshold surface measured previously, but the results are quite different. For very low temporal frequencies (below 0.2 Hz), the chromatic sensitivity decreases steadily with decreasing temporal frequency. Below 0.01 Hz, chromatic patterns disappear completely even at maximum contrast (although achromatic or homochromatic patterns do not). In the region above 0.2 Hz, both achromatic and chromatic thresholds can be explained by the same receptive-field-like model. When the center and the surround components of this model are additively combined, they form the chromatic threshold surface; when the sign of either component is reversed, they form the achromatic one.

Detecting and discriminating the direction of motion of luminance and colour gratings

“…2 have the same general form as detection sensitivity functions (Kelly, 1983) and the peak sensitivities are very high, which makes it interesting to see how detection sensitivity compares with directiondiscrimination sensitivity under these conditions. The subjective impressions of our observers in the direction discrimination task led us to expect the two tasks to give very similar sensitivities: observers felt they were unable to see any gratings whose direction of motion they could not discriminate.…”

Spatial and spectral quaternionic approaches for colour images

“…Perceptuals methods [6,9,23,17] are based on the human visual system (HVS) characteristics. For example, in [2], Carron used a marginal gradient method but based on a weight factor : the hue coefficient of each pixel, more relevant than saturation or intensity to split colours.…”

Perception-based fast rendering and antialiasing of walkthrough sequences

“…Usually three separable pattern-color visual mechanisms are considered [11], [39], [44], [36] and the spatiotemporal filters are applied independently to each mechanism, which can effectively triple computational efforts. To reduce computation in the temporal domain, usually only the low pass channel is considered [11], [44] since the temporal sensitivity drops very quickly for chrominance [19]. Some computation savings can be made in spatial processing as well [11] since the spatial sensitivity for chrominance is very low at above eight cpd (cycles per degree) [19].…”

“…To reduce computation in the temporal domain, usually only the low pass channel is considered [11], [44] since the temporal sensitivity drops very quickly for chrominance [19]. Some computation savings can be made in spatial processing as well [11] since the spatial sensitivity for chrominance is very low at above eight cpd (cycles per degree) [19]. Color considerations, although still very costly, are an important part of a quality metric, especially in digital video applications in which lossy-compression of pattern-color components is performed independently.…”

“…In our application, which involves IBR techniques, the pattern-color information is never separated and always undergoes the same processing (i.e., image warping and resampling). Taking into account much poorer acuity of color vision than pattern vision [19], we believe that, in our application, most of the animation impairments can be captured by achromatic processing. In this research, we ignore color processing for efficiency reasons and we leave for future work a more rigorous performance comparison of chromatic and achromatic video quality metrics in our application involving the perception-based guiding of in-between frame computation.…”