The Same-Reflectance tool enables you to specify that two different areas of the image are the same material. Any differences in the appearance of the two areas in the original image are assigned to the illumination map.
In general, there are two uses for the Same-Reflectance tool:
(1) to link two sides of a shadow by crossing the shadow boundary with a single scribble; or
(2) to link different areas of the same material using groups of separate scribbles.
To specify that two different scribbles cover one material, draw the first scribble, then hold down the shift key and draw the second scribble. Continuing to hold down the shift key while creating more scribbles will add all of the new scribbles to the existing group.
The Same-Reflectance tool is normally used with a small brush size. It is important that all Same-Reflectance scribbles in a group cover only a single material color.
The example images (A-E) show Same-Reflectance scribble usage. Image (A) shows the original image. Image (B) shows several Bright/Dark Pairs and the resulting reflectance map after processing. Note the shadow boundary still visible near the red surface.
Image (C) shows a series of Same-Reflectance scribbles drawn in green across the shadow boundary on the wood. The highlighted scribbles form a single group, since they were all drawn while holding down the shift key. Image (C) also includes five other Same-Reflectance groups: a set on the red gas can, a pair on the black cap, a set on the yellow spout, a pair on the hay, and a pair on the grass. The latter two link the materials on either side of the yellow spout. Except for the first scribble drawn in each group, they were drawn while holding down the shift key.
Note that the reflectance map in (D), displayed without scribbles, shows much less variation on the gas can, and the shadow boundary on the wood is gone. The shadows and highlights on the two surfaces end up in the illumination map, as shown in image (E).