The only required input for Lightbrush is an indication of the general character of the illumination field. You will use the Bright/Dark Pair Tool to provide this information.
The Bright/Dark Pair Tool consists of two squares connected by a link. You can click and drag on either end and resize the squares using the control panel sliders or keyboard shortcuts. Each end can be resized separately.
To indicate the general character of the illumination field, place one square on a lit area of a single material or fine texture and the other square on a shadowed area of the same material or fine texture. The tool will automatically detect which end is lit and which end is shadowed, indicating its decision by coloring the lit end yellow and the shadowed end blue.
It is important that both squares cover the same material or fine texture and that the illumination level is the only difference between the two areas. The materials under each square must be the same. In general, larger squares will provide more accurate information to Lightbrush, so long as the squares are covering only a single material or fine texture.
In the example to the right, the user has selected a Bright/Dark Pair on the building, which is a fine texture. The two squares are large relative to the texture of the bricks. Since this pair includes the primary shadow in the image, it provides a useful estimate of the general character of the illumination in the scene.
Once you have placed the Bright/Dark Pair Tool, process the image by either selecting Process Image from the Image menu or using the keyboard shortcut ⌘G.
The only required input for Lightbrush to produce the illumination and reflectance maps is a single Bright/Dark Pair. However, it is sometimes advantageous to use multiple Bright/Dark Pairs in a single image.
When the image consists primarily of a single surface, as in the image of shingles shown in (A), then a single Bright/Dark Pair should suffice.
When the image consists of surfaces at several orientations, as in the image of a brick wall and patio shown in (B), then a Bright/Dark Pair on each surface may produce a better result. For example, placing a Bright/Dark Pair on the brick wall and two other pairs on the patio surface produces a better separation than a single Bright/Dark Pair.
The tool options panel allows you to create a new Bright/Dark Pair and change the sizes of the bright and dark patches.