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A. H. J. Oomes, J. T. Todd; Shape from texture: seeing cylinders in line and blob patterns. Journal of Vision 2001;1(3):395. doi: https://doi.org/10.1167/1.3.395.
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What are the features that allow observers to perceive three-dimensional shape from a pattern of lines and blobs? We report here on experiments with singly-curved surfaces in which observers judge the shape of deformed cylinders from texture. We showed observers an elliptical cylinder in an upright orientation with the top and bottom occluded from view. The main axis of the cross-section was shown in different orientations so that the closest point of the object could be off center. For the textures we used a variety of patterns with lines, blobs and combinations of them. The patterns were mapped on the cylinders in different orientations with different scaling factors. Viewing distance was varied from close (strong perspective) to far (orthographic projection). The observer's task was to match the shape of a full cue cylinder (shown stereoscopically) with the shape of the target cylinder by adjusting depth and shear. By moving the mouse forward or backward, the depth of the object could be varied, while a left- or rightward motion changed the shear, and consequently the orientation of the cross-section. As expected, observers underestimate the depth of the cylinder but are closer to veridical on the shear. In the case of blob patterns, compression gradient and blob-orientation are the major factors that convey shape, with irregular positioned blobs leading to closer to veridical judgements than regular ones. For line patterns, shape is mostly conveyed by the curvature of lines in the case of orthographic projection. In the case of (strong) perspective, convergence of lines is a major factor, with regularly spaced horizontal lines giving the strongest percept of shape.
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