UBC Theses and Dissertations
Aspects of image reshaping Romanzin, Christopher Anthony
Old images are often used in the creation of new images, either to enhance the appearance of the result or to achieve a manual or computational savings. Without ample care this practice can lead to missing or conflicting visual cues in the result, since an old image may exhibit shading artifacts that are inconsistent with the scene it is incorporated into. Therefore there is a need to process a source image so that it is consistent with the way it is to be used. Current methods for altering the shading artifacts found in an image are largely ad hoc , pixel based and are somewhat unintuitive. This work explores methods for enabling a user to manipulate 3D shading artifacts in an image, that is, performing image editing operations that relate to physical processes such as moving and dimming a light source, or changing the reflectance properties of objects in an image-without having full knowledge of the scene properties. We call this goal one of image reshading, and it is closely tied between the disciplines of computer graphics and computational vision as it involves generating images and inferring properties of the scene that give rise to an image. Image reshading is an enormous problem of its own, and this work explores only a few aspects of it. The first is the detection and removal of specular highlights from image data alone. Current techniques are explored and applied to textured images that are commonly used in computer graphics. The second image reshading task examined is to solve for the geometry of a light source illuminating a scene given an image of the scene and the geometry of the visible objects. A series of constraints formed by the shading of Lambertian and Phong reflectors is presented and a strategy for determining the position, orientation, and size of a rectangular source is demonstrated. Finally, given an image, a geometric model of the objects in the image, and the light source distribution, a method for solving for the relative emissive strengths and the reflectance parameters of surfaces in the image is given. This final reshading operation allows a large number of useful image editing operations to be performed.
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