Ondrej Drbohlav

Learn More
This paper develops new theory for the optimal placement of photometric stereo lighting in the presence of camera noise. We show that for three lights, any triplet of orthogonal light directions minimises the uncertainty in scaled normal computation. The assumptions are that the camera noise is additive and normally distributed, and uncertainty is defined(More)
Helmholtz stereopsis guarantees unbiasedness by BRDF of the search for inter-image correspondences. In a practical setup, calibrated pixel sensitivity and corrected light anisotropy are required for the method to work well. In this paper a simple method for joint light-camera radiometric calibration is proposed. Such calibration is shown to be an ill-posed(More)
Lambertian photometric stereo with unknown light source parameters is ambiguous. Provided that the object imaged constitutes a surface, the ambiguity is represented by the group of generalised bas-relief (GBR) transformations. We show that this ambiguity is resolved when specular reflection is present in two images taken under two different light source(More)
We report results from a new methodology for investigating the visually perceived properties of surface textures. Densely sampled two-dimensional 1/f(beta) noise processes are used to model natural looking surfaces, which are rendered using combined point-source and ambient lighting. Surfaces are shown in motion to provide rich cues to their relief. They(More)
Matching of high-dimensional features using nearest neighbors search is an important part of image matching methods which are based on local invariant features. In this work we highlight effects pertinent to high-dimensional spaces that are significant for matching, yet have not been explicitly accounted for in previous work. In our approach, we require(More)
Photometric stereo with uncalibrated lights determines surface orientations ambiguously up to any regular transformation. If the surface reflectance model is separable with respect to the illumination and viewing directions, its inherent symmetries enable to design two previously unrecognized constraints on normals that reduce this ambiguity. The two(More)
The appearance of a surface texture is highly dependent on illumination. This is why current surface texture classification methods require multiple training images captured under a variety of illumination conditions for each class. We show that a single training image per class can be sufficient if the surfaces are of uniform albedo and smooth and shallow(More)
Helmholtz Stereopsis (HS) has recently been explored as a promising technique for capturing shape of objects with unknown reflectance. So far, it has been widely applied to objects of smooth geometry and piecewise uniform Bidirectional Reflectance Distribution Function (BRDF). Moreover, for nonconvex surfaces the inter-reflect ion effects have been(More)