The shadow filter attempts to cancel out shadowy artifacts from photographed textures. It is not designed to remove large shadows caused by large objects obstructing light from reaching the photographed surface, but it can be very useful for removing small shadows caused by direct lighting during photography.

Since shadows are to be rendered based on the chosen lighting model and the scene lighting, shadows on a texture are almost certainly perceived as artifacts and thus undesired. This node can only attempt to solve this problem, but will by no means always succeed. The success of the shadow filtering operation depends on so many different factors, that it is near impossible to tell, when it will return good results and when it won’t.

The filter works based on detecting dark areas. That area is then considered the area of effect. If this area is very small, only the darkest spots of the texture will be taken into consideration. Including ever brighter areas of the texture will also increase the area of effect. However the filter is not able to tell whether a dark area is a shadow or simply just the color of the surface in that area. Thus certain surfaces – such as granite – will almost certainly fail with this filter.

Upon detecting the dark areas that the effect should be applied to, these areas are brightened in the HSV color model to keep loss of color information as low as possible.

This node probably requires the most balancing of properties to produce acceptable results.