Illumination Decomposition for Material Recoloring with Consistent Interreflections
Robert Carroll, Ravi Ramamoorthi, Maneesh Agrawala
Abstract
Changing the color of an object is a basic image editing operation, but a high quality result must also preserve natural shading. A common approach is to first compute reflectance and illumination intrinsic images. Reflectances can then be edited independently, and recomposed with the illumination. However, manipulating only the reflectance color does not account for diffuse interreflections, and can result in inconsistent shading in the edited image. We propose an approach for further decomposing illumination into direct lighting, and indirect diffuse illumination from each material. This decomposition allows us to change indirect illumination from an individual material independently, so it matches the modified reflectance color. To address the underconstrained problem of decomposing illumination into multiple components, we take advantage of its smooth nature, as well as user-provided constraints. We demonstrate our approach on a number of examples, where we consistently edit material colors and the associated interreflections.
We seek to recolor the input image (a). However, changing the color (reflectance) of the shirt alone, without modifying the illumination, does not account for the correct diffuse reflection on the girl's arm or interreflections in the fine texture of the shirt (b). Indeed, the image in (b) still has bluish reflections on the arm and a purple color shift on the shirt. Our user-assisted decomposition lets us modify indirect illumination to match the modified shirt color (c), leading to a much more consistent and natural looking recoloring.