The Edit Phase of Lightbrush enables independent or linked manipulation of the illumination and reflectance fields. As noted in the overview, the Factor phase of Lightbrush does not add or subtract any information from the original image: it separates the image into its component parts. Pixel-wise multiplication of the illumination and reflectance fields generated by the factor phase creates a product image that is identical to the original. In the Combined view of the main window, the Product image is located on the lower right.
In the Edit Phase, the user can modify the illumination or reflectance map independently. Independent manipulation of either one modifies the product image, enabling shadow editing or material editing without the conflation of the two types of information in the original image.
The Edit Phase tools also allow linked manipulation. Linked manipulation allows the user to edit one field, but the inverse of the edit is applied to the other field. Therefore, the product image is preserved, and it remains the same before and after the edit. For example, an edit to the illumination field to make an area brighter would make the reflectance field proportionally darker in the same location. Linked manipulation is useful for touching-up a separation prior to other uses.
The example to the right demonstrates independent manipulation of the illumination and reflectance fields. The edit to the reflectance field consists of modifying the color of the subject’s sleeve. Note that the shading and shadows from the original image are preserved, even though the original shirt color is a textured red.
There are two edits to the illumination field. First, the shadow on the subject’s shoulder has been shaved back to reveal more of the vest. Second, the illumination field on the subject’s face and neck have been gamma-compressed significantly (2.5), without modifying the contrast of the reflectance or the rest of the image. This also has the effect of reducing the apparent strength of the highlights on his nose and chest. The combination of the two edits appears to add fill light to the scene and soften the lighting.