Stairs: Testing Stereo Matching Algorithms at Occluding Boundaries

Abstract

When occluding contour and texture discontinuity coincide, area-based matching algorithms give wrong disparity estimates near the contour. The contour `leaks' into one of the regions neighboring it. (Usually, the strong-textured region leaks to the weaker-textured region.) We have developed a method for ranking area-based matching algorithms according to the relative area of the artifacts. Evaluation method is described and results on some algorithms are presented. Our data and ground-truth are available from this page.

The Test Target

Test target: side view Test target: front view Test target: back view
side view front view back view

The staircase-like target (left) is designed to combine all possible texture contrast changes across left or right occlusion boundary (center) or across no depth change (right). All textures are random binary Gaussian noise of different mean gray-value and contrast. The texture pattern is the same on the target's flat back so that the influence on the matching algorithm of the texture boundaries alone can be studied in a control experiment.

PostScript textures for the three panels are available: front, middle, rear.

Rectified Images

Images were taken by calibrated Sony XC-77CE TV cameras, were rectified and sub-sampled to 256×256 pixels.

left rectified image right rectified image
front: left image front: right image
download: [ GIF, PM, PGM] download: [ GIF, PM, PGM]
left rectified image right rectified image
back: left image back: right image
download: [ GIF, PM, PGM] download: [ GIF, PM, PGM]

Ground-Truth Data

Ground-truth disparity map and occlusion maps were obtained from a disparity map recovered by NCC area-based matching with sub-pixel accuracy. Occlusion boundaries were identified manually with pixel precision. Within each flat region of the disparity map a plane was fit to the map, the fit was sampled (see below, left) and occluded regions were automatically identified (see below, right).

disparity map occlusion map
disparity map (pseudocolors) left occlusion map
download: [ASCII] download: [ASCII]
disparity map
download: [ASCII]

Both datafiles are plain ASCII files with 256 rows of 256 IEEE-format double integers. You may download them directly to your Matlab using load. Ground-truth sub-pixel disparity map pixels are NaNs where the disparity is not defined (the corresponding matrix entry is `NaN'). Ground-truth left occlusion map pixels are 1's in areas that are occluded in the right image and 0's elsewhere. The disparity and the occlusion maps are not defined on the background since the background is not considered a part of the ground-truth.

Contour Artifacts Evaluation Method

References

  1. R. Sara and R. Bajcsy. On Occluding Contour Artifacts in Stereo Vision Proc. IEEE Conf. CVPR '97, pp. 852-857. [PostScript, 600kB, gnu-zipped]
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Radim Sara
Last modified: Fri May 7 15:34:00 MET DST 1999