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Is the perception of 3D shape from shading based on assumed reflectance and illumination?

Todd JT, Egan EJ, Phillips F - Iperception (2014)

Bottom Line: A gauge figure adjustment task was used to measure observers' perceptions of local surface orientation on the depicted surfaces, and the probe points included 60 pairs of regions that both had the same orientation.The results show clearly that observers' perceptions of these three types of stimuli were remarkably similar, and that probe regions with similar apparent orientations could have large differences in image intensity.This latter finding is incompatible with any process for computing shape from shading that assumes any plausible reflectance function combined with any possible homogeneous illumination.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, The Ohio State University, Columbus, OH; e-mail: todd.44@osu.edu.

ABSTRACT
The research described in the present article was designed to compare three types of image shading: one generated with a Lambertian BRDF and homogeneous illumination such that image intensity was determined entirely by local surface orientation irrespective of position; one that was textured with a linear intensity gradient, such that image intensity was determined entirely by local surface position irrespective of orientation; and another that was generated with a Lambertian BRDF and inhomogeneous illumination such that image intensity was influenced by both position and orientation. A gauge figure adjustment task was used to measure observers' perceptions of local surface orientation on the depicted surfaces, and the probe points included 60 pairs of regions that both had the same orientation. The results show clearly that observers' perceptions of these three types of stimuli were remarkably similar, and that probe regions with similar apparent orientations could have large differences in image intensity. This latter finding is incompatible with any process for computing shape from shading that assumes any plausible reflectance function combined with any possible homogeneous illumination.

No MeSH data available.


Related in: MedlinePlus

Two images of a deformed sphere (A and B) and their corresponding patterns of isophotes (C and D). The image in Panel A was rendered with a Lambertian BRDF using a collimated light field that was parallel to the viewing direction. The one in Panel B was textured with a linear intensity gradient that was oriented parallel to the viewing direction. The isointensity contour plots are coded so that red bands represent the highest image intensities and the violet bands represent the lowest.
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Figure 1: Two images of a deformed sphere (A and B) and their corresponding patterns of isophotes (C and D). The image in Panel A was rendered with a Lambertian BRDF using a collimated light field that was parallel to the viewing direction. The one in Panel B was textured with a linear intensity gradient that was oriented parallel to the viewing direction. The isointensity contour plots are coded so that red bands represent the highest image intensities and the violet bands represent the lowest.

Mentions: A ramp-shaded image is created by texturing a surface with a planar projection of a linear intensity gradient. This defines the local image intensity for each local surface region based on its position irrespective of its orientation. Note that this is the opposite of an image rendered with a BRDF, which defines the local image intensity for each local surface region based on its orientation irrespective of its position. For surfaces that are approximately spherical, ramp-shaded images can be quite similar to those rendered with a Lambertian BRDF. This is demonstrated in Figure 1, which shows two images of a deformed sphere. The image in Panel A was rendered with a Lambertian BRDF using a collimated light field that was parallel to the viewing direction. The one in Panel B was textured with a linear intensity gradient that was oriented in depth (i.e. it is the equivalent of a range image). Panels C and D show the pattern of isophotes for these images, in which the borders between the colored bands mark points with the same image intensity, and the hue of these bands identifies the magnitudes of image intensity. Note that both images have quite similar patterns of isophotes. It is mainly in the concave crease where they diverge, such that the Lambertian shading in this region is much brighter than in the ramp-shaded version.


Is the perception of 3D shape from shading based on assumed reflectance and illumination?

Todd JT, Egan EJ, Phillips F - Iperception (2014)

Two images of a deformed sphere (A and B) and their corresponding patterns of isophotes (C and D). The image in Panel A was rendered with a Lambertian BRDF using a collimated light field that was parallel to the viewing direction. The one in Panel B was textured with a linear intensity gradient that was oriented parallel to the viewing direction. The isointensity contour plots are coded so that red bands represent the highest image intensities and the violet bands represent the lowest.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4441026&req=5

Figure 1: Two images of a deformed sphere (A and B) and their corresponding patterns of isophotes (C and D). The image in Panel A was rendered with a Lambertian BRDF using a collimated light field that was parallel to the viewing direction. The one in Panel B was textured with a linear intensity gradient that was oriented parallel to the viewing direction. The isointensity contour plots are coded so that red bands represent the highest image intensities and the violet bands represent the lowest.
Mentions: A ramp-shaded image is created by texturing a surface with a planar projection of a linear intensity gradient. This defines the local image intensity for each local surface region based on its position irrespective of its orientation. Note that this is the opposite of an image rendered with a BRDF, which defines the local image intensity for each local surface region based on its orientation irrespective of its position. For surfaces that are approximately spherical, ramp-shaded images can be quite similar to those rendered with a Lambertian BRDF. This is demonstrated in Figure 1, which shows two images of a deformed sphere. The image in Panel A was rendered with a Lambertian BRDF using a collimated light field that was parallel to the viewing direction. The one in Panel B was textured with a linear intensity gradient that was oriented in depth (i.e. it is the equivalent of a range image). Panels C and D show the pattern of isophotes for these images, in which the borders between the colored bands mark points with the same image intensity, and the hue of these bands identifies the magnitudes of image intensity. Note that both images have quite similar patterns of isophotes. It is mainly in the concave crease where they diverge, such that the Lambertian shading in this region is much brighter than in the ramp-shaded version.

Bottom Line: A gauge figure adjustment task was used to measure observers' perceptions of local surface orientation on the depicted surfaces, and the probe points included 60 pairs of regions that both had the same orientation.The results show clearly that observers' perceptions of these three types of stimuli were remarkably similar, and that probe regions with similar apparent orientations could have large differences in image intensity.This latter finding is incompatible with any process for computing shape from shading that assumes any plausible reflectance function combined with any possible homogeneous illumination.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, The Ohio State University, Columbus, OH; e-mail: todd.44@osu.edu.

ABSTRACT
The research described in the present article was designed to compare three types of image shading: one generated with a Lambertian BRDF and homogeneous illumination such that image intensity was determined entirely by local surface orientation irrespective of position; one that was textured with a linear intensity gradient, such that image intensity was determined entirely by local surface position irrespective of orientation; and another that was generated with a Lambertian BRDF and inhomogeneous illumination such that image intensity was influenced by both position and orientation. A gauge figure adjustment task was used to measure observers' perceptions of local surface orientation on the depicted surfaces, and the probe points included 60 pairs of regions that both had the same orientation. The results show clearly that observers' perceptions of these three types of stimuli were remarkably similar, and that probe regions with similar apparent orientations could have large differences in image intensity. This latter finding is incompatible with any process for computing shape from shading that assumes any plausible reflectance function combined with any possible homogeneous illumination.

No MeSH data available.


Related in: MedlinePlus