| Summary: | 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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