Beyond Grading - Blender Compositing and Post Processing - page 45

The light direction can be modified by left-clicking and dragging on the diffused
sphere thumbnail image provided on the node.
This fake lighting works great when used as secondary light highlights. However,
as seen on the vertical brick in the preceding screenshot, light leaks can be en-
countered as shadowing is not considered. This can often spoil the fun. A quick fix
for this is to use the Ambient Occlusion information to occlude the unwanted areas.
The following screenshot illustrates the workflow of using the Ambient Occlusion
pass along with the normal pass to resolve the light leak issue. The technique is
to multiply the dot output of the Normal node with Ambient Occlusion info from the
rendered image using Mix or Math nodes. As it can be observed in the following
screenshot, the blue light leaks on the inside parts of the vertical brick is minimized
by the Ambient Occlusion information. This solution works as long as relighting is not
the primary lighting for the scene.
Another issue that can be encountered while using the Normal node is negative val-
ues. These values will affect the nonlight areas, leading to an unwanted effect. The
procedure to curb these unwanted values is to clamp them from the Dot output of
the Normal node to zero, before using as a mask input to grade nodes.
The following screenshot illustrates the issue with negative values. All pixels that
have an over-saturated orange color are a result of negative values.