A new evaluation of the local structure of sustained spatial channels with local stimuli in peripheral retina employs the
masking sensitivity approach to minimize analytic assumptions. The stimuli were designed to address predominantly the
sustained response system at 5 deg eccentricity. Under these conditions, the lowest spatial-frequency channel peaked at
about 2 cycle/deg, 4 times higher than previous estimates, with a bandwidth of 1.5-2 octaves. The highest spatialfrequency
channel peaked at 5-6 cycle/deg with about a 1 octave bandwidth. The data are consistent with there being
only one channel tuned between these extremes, although they do not exclude a more continuous channel structure. Our
analysis shows that there are no sustained channels tuned below 2 cycle/deg but there may be channels above the
highest-frequency channel measured if tested with more selective stimuli than employed in our study. For local
sustained stimuli, human peripheral spatial processing therefore appears to be based a simpler channel structure than is
often supposed.
The properties of human stereoscopic mechanisms may be derived from dichoptic interaction and masking effects on stereoscopic detection thresholds in any relevant stimulus domain (spatial frequency, temporal frequency, disparity, orientation, etc.). The present study focuses on the spatial properties of mechanisms underlying stereoscopic depth detection. The computational approach is based on the full exploration of plausible model structures to characterize their idiosyncrasies, which often allows exclusion of proposed mechanisms by comparison with data obtained under conditions in which the idiosyncrasies should be expressed. For example, we conducted a detailed analysis of threshold elevation functions (TEFs) under plausible channel shapes, combination rules and masking behavior derived from previous studies. The analysis reveals that TEFs may be much narrower than and differ in shape from the underlying mechanisms. For example, only two discrete channels are required to produce TEFs peaking close to each fixed test frequency, with no relation to channel peaks. We apply this analysis to the stereospatial masking functions collected by Yang and Blake (1991) to determine the likely channel structure underlying the empirical masking performance. The analysis generally supports the two-mechanism model that they propose but shows that the assumptions underlying their estimates of the unmasked sensitivity function are incorrect. The analysis excludes stereospatial channels tuned below 2.5 c/deg, a region in which Schor, Wood, and Ogawa (1984) obtained evidence for many narrowly tuned channels by measuring disparity thresholds for targets with different peak tunings in the two eyes. Our computational model for the latter data is consistent with the lowest tuned channel being at 2.5 c/deg, this channel being narrowly tuned to dichoptic contrast differences, as described by Legge and Gu (1989) and Halpern and Blake (1988). Thus, all such stereo tuning data can be explained in a model in which all stereoscopic channels are tuned above 2.5 c/deg.
A completely linear method for reconstruction of 3D structure from two central projections is proposed. We show that this method for combining such parameters as speed, robustness and generality performs better than all other algorithms.
KEYWORDS: RGB color model, Human vision and color perception, Visualization, Optical filters, Calibration, Image resolution, Binary data, LCDs, Computing systems, Video
The precision of human vision requires displays to be accurate to about 0.2% of the luminance range. We present a technique by which this grey-level precision can be achieved with the use of an 8-bit color monitor. The basic idea is to 'steal' adjacent bits from the color variation for use in increasing the precision of the luminance variation. On a monitor with 8 bits per color gun, the technique can provide 1786 or more grey levels at a cost of one bit of color jitter, with standard D/A hardware. The color variations are invisible under almost all conditions.
KEYWORDS: 3D image processing, Visual system, Stereoscopic displays, Cameras, Image processing, Superposition, Eye, Visualization, 3D vision, Chemical elements
A new method is proposed for extraction of 3-D rigid depth interpretations from pairwise comparisons of weak perspective projections. The method provides a simple criterion to test for the correctness of correspondence for a pair of images; the method also provides a description of a one-parameter family of interpretations for each pair of images that satisfies this criterion. We show that if at least three projections of a volumetric object are known, then a 3-D rigid interpretation can be inferred from pairwise comparisons between any one of these images and other images in the set. The 3-D interpretation is derived from the intersection of corresponding one-parameter families. The method provides a uniform computational basis for different processes of depth perception (for example, depth-from-stereo and depth-from- motion). In fact, a single mechanism for these processes in the human visual system could be sufficient. The proposed method does not require information about relative positions of eye(s) or camera(s) for different projections, but this information can be easily incorporated. This method can be applied for pairwise comparison within a single image. If any non-trivial correspondence is found it means that several views of the same object are present in the same image or that the object with volumetric symmetry is presented within the image. Results of pairwise comparison within a single image may also be considered in the process of depth reconstruction. If the object possesses two or more symmetries, its depth can be reconstructed from single image. Symmetry as a source of structural information is widely used by the visual system.
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