The No-Analysis tool enables you to locally reduce the complexity of the analysis performed by Lightbrush. The effect of the No-Analysis tool is to move attributes of the illumination map into the reflectance map.
In general, the No-Analysis tool is useful for marking up areas of the illumination map where there are features that have been incorrectly identified as illumination changes. Within areas of smoothly changing or constant illumination you can use large brush strokes with little regard for precision. However, take care not to cross actual illumination boundaries or they are likely to become blurred.
Image (A) is an example where the No-Analysis tool helps to clean up subtle features in the illumination map.
A single Bright/Dark Pair provides a good reflectance map (B) and illumination map (C). However, the illumination map shows some edges from the pattern on the tablecloth, particularly the branch crossing the middle of the image. This is not surprising, as the branch is drawn in such a way as to appear sunlit, with shadows along the bottom edge.
Image (D) shows a set of No-Analysis scribbles that covers the affected areas. Note that none of the scribbles crosses the strong illumination boundary.
After reprocessing, the illumination map (E) is free of the artifacts caused by the tablecloth pattern. Image (F) shows the final reflectance map, which contains all of the original contrast and color change of the tablecloth, but without the illumination variation.