The Experts below are selected from a list of 30084 Experts worldwide ranked by ideXlab platform
Koichiro Deguchi - One of the best experts on this subject based on the ideXlab platform.
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On Uniqueness of Solutions of the Three-Light-Source Photometric Stereo
Computer Vision and Image Understanding, 2001Co-Authors: Takayuki Okatani, Koichiro DeguchiAbstract:This paper is concerned with photometric methods using three Images with different lighting direction to obtain shape information of an object. Such methods are based on the photometric equation that relates the normal of the object surface to the triplet of the Image Brightness. This paper discusses the issue of whether the surface normal and the orientation of the 3-vector formed by the Image Brightness triplet is one-to-one in the equation. Several types of photometric methods require this relation to be one-to-one. We mainly consider the case where the reflectance map is an increasing function of the angle between the surface normal and the illuminant direction. We first point out that even in this simple case, it is possible that the relation is not one-to-one. Then we derive several sufficient conditions on the reflectance as well as the illumination configuration for the one-to-one relation.
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Closed Form Solution of Local Shape from Shading at Critical Points
International Journal of Computer Vision, 2000Co-Authors: Takayuki Okatani, Koichiro DeguchiAbstract:In the theory of shape from shading, behaviours of the local solution around a critical point of the Image play an important role. This paper shows that the second derivatives of the object surface can be locally determined at these Image critical points. Closed form expressions of the surface second derivatives in terms of the second derivatives of the Image Brightness and of the reflectance map are shown. They are derived as follows: By differentiating the Image irradiance equation twice at an Image critical point, a set of polynomial equations is obtained that contains the second derivatives of the surface, of the Image Brightness and of the reflectance map. Regarding these equations as simultaneous equations for unknown surface second derivatives, they are algebraically solved and their explicit expressions are derived. Such a derivation is possible only at Image critical points and is impossible at any other Image point. The applicability of the derived expressions to noisy Images is tested using synthetic Images.
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ICPR - Estimation of illumination distribution using a specular sphere
Proceedings 15th International Conference on Pattern Recognition. ICPR-2000, 1Co-Authors: Takayuki Okatani, Koichiro DeguchiAbstract:A method has been proposed for acquiring an omnidirectional Image of a scene using a specular sphere (namely a mirror ball). The method takes the reflected Image on the specular sphere located at a desired position in a scene by an ordinary camera. This paper discusses the relation between the reflected Image of the scene and the radiance of the scene. Due to the reflection on the sphere, the final Image on the camera has geometric distortion. There are imaging systems covering a wide angle by the lens system itself, e.g., a fish-eye lens. The Image obtained by such lens systems has similar geometrical distortion. However, the effect of the distortion on the Image Brightness is different. We point out that the Image distortion due to the lens system affects the Image Brightness, while that due to the reflection on the specular sphere does not. Most of the discussion can be applied to the methods using a curved mirror to obtain a wide angle Image.
Chang-ying J. Yang - One of the best experts on this subject based on the ideXlab platform.
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Real‐time equalization of region‐of‐interest fluoroscopic Images using binary masks
Medical Physics, 1999Co-Authors: Stephen Rudin, Daniel R. Bednarek, Chang-ying J. YangAbstract:In region-of-interest (ROI) radiologic imaging, the x-ray beam is attenuated peripherally to the region of interest to reduce patient exposure. This attenuation reduces the peripheral Image Brightness which may cause contrast in the periphery to also be reduced due to video chain nonlinearity. For optimal viewing, it is necessary that the Image Brightness and contrast in the periphery be brought back to the levels in the ROI. Previously, digital subtraction angiography roadmapping equipment has been used for this equalization; however, the procedure is not independent of patient and gantry motion. A new motion independent method to achieve this equalization involves dividing the real-time video signal into two digital streams one of which is Brightness and contrast enhanced. A pre-acquired binary mask Image is created by thresholding the Image of a uniform object obtained with the ROI filter in place. This binary mask is used to control the recombination of the two Image streams in a digital pipeline processor in order to select the ROI from the unprocessed stream and the periphery from the enhanced stream. This system provides Image equalization at 30 frame/s for real-time ROI imaging display. Images from this method demonstrate excellent Image quality even for peripheral exposure reduction factors exceeding 10.
Pollefeysmarc - One of the best experts on this subject based on the ideXlab platform.
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Robust Radiometric Calibration and Vignetting Correction
IEEE Transactions on Pattern Analysis and Machine Intelligence, 2008Co-Authors: Kimseon Joo, PollefeysmarcAbstract:In many computer vision systems, it is assumed that the Image Brightness of a point directly reflects the scene radiance of the point. However, the assumption does not hold inmost cases due to nonl...
Negahdaripourshahriar - One of the best experts on this subject based on the ideXlab platform.
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Revised Definition of Optical Flow
IEEE Transactions on Pattern Analysis and Machine Intelligence, 1998Co-Authors: NegahdaripourshahriarAbstract:Optical flow has been commonly defined as the apparent motion of Image Brightness patterns in an Image sequence. In this paper, we propose a revised definition to overcome shortcomings in interpret...
Bernard F. Burke - One of the best experts on this subject based on the ideXlab platform.
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Reconciling the Image Brightness ratios in the gravitational lens system 0957+561
The Astrophysical Journal, 1992Co-Authors: S. R. Conner, Joseph Lehar, Bernard F. BurkeAbstract:The gravitational lens effect is achromatic, yet observations at different wavelengths have yielded different values for the Brightness ratio of the two quasar Images, A and B, in 0957+561. The radio observations can be separated into VLBI core and VLBI jet regions, which have different Brightness ratios. We show that both VLA and VLBI observations show a quasar VLBI core Image flux ratio of about 0.75, consistent with optical flux ratios determined from core emission lines and markedly different from the flux ratio of the VLBI jet Images
