A. Pentland, Shape Information from Shading: A Theory about Human Perception, Second International Conference on Computer Vision, p404-413, 1988  Home/Search   Document Not in Database   Summary   Related Articles   Check

.... unattractive properties of global shape from shading algorithms, local shading analysis under some special circumstance was studied: spherical surfaces were discussed in [24, 18] slanted surfaces, where the angle between the light source and the normal is sufficiently large, were discussed in [23]. Others have studied the behaviors of isophotes (lines of equal brightness) and their relationship to geometrical invariants of surfaces [17, 33, 4] The present paper follows these directions in exploring approximations to shape using easy to compute local shading analysis (see also [10] The ....

A. Pentland. Shape information from shading: a theory about human perception. In Proceedings of the 2nd International Conference on Computer Vision, pages 404--413, Tarpon Springs, FL, 1988. IEEE, Washington, DC.

....points in the image. These methods require a priori information and their performance depends on the accuracy of that information. Finally there are a number of methods that use local information to reconstruct depth. 30] and [22] use a rather restrictive local spherical approximation, while [31] and [39] use linear approximations of the reflectance function. In this paper we will focus on single image methods. Although photometric stereo approaches [41, 1, 12] give in general better reconstructions than single view methods, there can be no motion in the scene and in the camera position ....

.... we will haveanm component constraint vector C = C 1 #C 2 #: #C m ] C is a nonlinear constraint with respect to the model parameters, which in the traditional SFS formulations resulted either in nonlinear first order differential equations (PDE s) or in attempts to linearize the constraint [31, 23, 39]. PDE s require appropriate boundary conditions [17] that are often not available, whereas linearization introduces additional error. Instead, we incorporate the above brightness constraint as a nonlinear holonomic constraintin the deformable model framework, presented in a following section. ....

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A.P.Pentland. Shape information from shading: A theory about human perception. In ICCV88, pages 404--413, 1988.

....or intensity and only its first derivative [18] have been used to estimates the shape information. All local methods suffer from the local spherical assumption which may not be correct in all cases. Another local approach uses linearized approximations of reflectance maps to solve the SFS problem [19]. In this method the reflectance map is formulated in terms of surface gradient and then the Fourier Transform is applied to the linear function and a closed form solution for the height (depth) at each point is obtained. Another method makes use of computing the discrete approximation of the ....

Pentland, A.: Shape information from Shading: A theory about Human Preception. Proc. Intl Conf. Computer Vision (1988), pp. 404-413

....second derivatives. He used the assumption that the surface is locally spherical at each point. Under the same spherical assumption, L R [12] computed the slant and tilt of the surface in the light source coordinate system through the first derivative of the intensity. A later approach by Pentland [18] used the linear approximation of the reflectance function in terms of the surface gradient, and applied a Fourier transform to the linear function to get a closed form solution for the depth at each point. Similar to Pentland s method, T S [21] applied the discrete approximation of the gradient ....

....maps obtained for the real images and some synthetic images, such as Penny or Mozart. The intensity of the real images varies slightly, causing the depth estimation to falter, while the synthetic images yield good depth maps, due to the smooth surfaces. 4. 7 Pentland (P) Pentland s algorithm [18] produces good results on most surfaces that change linearly, even if the surface has a naturally varying surface such as a person s face. However, this algorithm falls apart when the surface changes in a non linear manner; this is clearly observed from the results of Sphere. For real images, the ....

A. Pentland. Shape information from shading: a theory about human perception. In ICCV, pages 404--413, 1988.

....shaded image: global methods and local methods. The global methods, in general, are very complex and slow. Sometimes they (e.g. variational calculus methods) require more than thousands of iterations to converge. A representative method of global approaches is used by Horn [9] The local methods [15, 12], on the other hand, are simple, fast and give accurate local details within each homogeneous area, but are not accurate enough globally. In shape from shading algorithms it is assumed that the surface reflectance map is given, or its form is known. However, surfaces of most objects in the real ....

....or its form is known. However, surfaces of most objects in the real world have mixed reflectance forms, such as Lambertian with Specular, or Lambertian with various albedo values. We will not be able to recover the accurate 3D shape information with the shape from shading method alone. Pentland [15] proposed a local algorithm based on the linearity of the reflectance map in the surface gradient (p; q) which greatly simplifies the shape from shading problem, and is very suitable for our purpose. The reflectance function for the Lambertian surfaces is modeled as follows: E(x; y) R(p; q) ....

Pentland, A. Shape information from shading: a theory about human perception. In Second International Conference on Computer Vision (Tampa, FL, December 5--8, 1988), pp. 404--413, Washington, DC, 1988. Computer Society Press.

....assumptions about the surfaces they work with and use these assumptions to calculate surface gradients based on only a local area of image intensities. Local techniques include two approaches by Pentland; one assumes that the surfaces are locally planar, the other that they are local spherical [47][48] Local methods are the fastest of the three approaches, but give the worst results in most cases because of the restrictive assumptions about the surfaces. To directly instantiate the shape and illumination of the hypotheses, we implemented Bichsel Pentland s SFS algorithm [4] We chose ....

A. P. Pentland, "Shape information from shading: a theory about human perception," in Proceedings of Int'l Conference on Computer Vision, 1988, pp.404-413.

....of global approaches is used by Horn [3] His algorithm simultaneously computes both the depth and the surface gradient. He combines three constraints: the brightness constraint, integrability constraint, and gradient smoothness constraint. The local shape from shading algorithms are by Pentland [8], and Lee and Rosenfeld [4] In shape from shading algorithms it is assumed that the reflectance map is given, or its form is known. Since images of most surfaces in the real world can be approximated by Lambertian reflectance, the majority of shape from shading methods use the Lambertian ....

....patches which can be expressed as a linear combination of a set of nodal basis functions. The depth value was computed by minimizing a quadratic cost functional of brightness error. Their method does not require any integrability constraints or assumptions about boundary conditions. Pentland [8] proposed a local algorithm based on the linearity of the reflectance map in the surface gradient (p; q) which greatly simplifies the shape from shading problem. Later, Pentland [9] presented an extension of his linear model to quadratic surfaces using photometric motion for extracting shape and ....

[Article contains additional citation context not shown here]

A. Pentland. Shape information from shading: a theory about human perception. In Second International Conference on Computer Vision (Tampa, FL, December 5--8, 1988), pages 404--413, Washington, DC, 1988. Computer Society Press.

.... unattractive properties of global shape from shading algorithms, local shading analysis under some special circumstance was studied: spherical surfaces were discussed in [24, 18] slanted surfaces, where the angle between the light source and the normal is sufficiently large, were discussed in [23]. Others have studied the behaviors of isophotes (lines of equal brightness) and their relationship to geometrical invariants of surfaces [17, 33, 4] The present paper follows these directions in exploring approximations to shape using easy to compute local shading analysis (see also [10] The ....

A. Pentland. Shape information from shading: a theory about human perception. In Proceedings of the 2nd International Conference on Computer Vision, pages 404--413, Tarpon Springs, FL, 1988. IEEE, Washington, DC.

....shaded image: global methods and local methods. The global methods, in general, are very complex and slow. Sometimes they (e.g. variational calculus methods) require more than thousands of iterations to converge. A representative method of global approaches is used by Horn [9] The local methods [15, 12], on the other hand, are simple, fast and give accurate local details within each homogeneous area, but are not accurate enough globally. In shape from shading algorithms it is assumed that the surface reflectance map is given, or its form is known. However, surfaces of most objects in the real ....

....or its form is known. However, surfaces of most objects in the real world have mixed reflectance forms, such as Lambertian with Specular, or Lambertian with various albedo values. We will not be able to recover the accurate 3D shape information with the shape from shading method alone. Pentland [15] proposed a local algorithm based on the linearity of the reflectance map in the surface gradient (p; q) which greatly simplifies the shape from shading problem, and is very suitable for our purpose. The reflectance function for the Lambertian surfaces is modeled as follows: E(x; y) R(p; q) 1) ....

Pentland, A. Shape information from shading: a theory about human perception. In Second International Conference on Computer Vision (Tampa, FL, December 5--8, 1988), pp. 404--413, Washington, DC, 1988. Computer Society Press.

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A. Pentland, Shape Information from Shading: A Theory about Human Perception, Second International Conference on Computer Vision, p404-413, 1988

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