Lightbrush allows you to process an entire image or a selected portion of it. Either may be useful, depending upon the application. Processing a portion of the image generally both speeds computation time and reduces the amount of user input required.
The Mask Tool enables the user to select structured or arbitrary image regions for processing. It contains four selection tools: rectangle, lasso, polygon, and magic wand. For all of the selection tools, holding down the shift key while selecting a region adds it to the area to process (foreground). Holding down the option key while selecting a region adds it to the masked area that will not be processed (background). Figure (B) shows an image with a rectangular region selected and the resulting separation.
When using the polygon tool, clicking on the image creates the next vertex in the polygon. Double-clicking creates the final vertex and closes the polygon by connecting the final vertex to the first vertex.
Other than Bright/Dark Pairs, information provided by the user that is outside of the foreground region is not considered when processing the image. Any pixel under the mask during processing will have the same value in the reflectance map as it does in the original image. Feathering the boundary of the mask can help smoothly integrate the foreground and background.
The tool options panel allows the user to select which tool to use and controls the amount of feathering around the boundary of the mask.