Because of the variety of geometry and different situations that can arise, normal bump maps sometimes give unexpected results. Usually there is a workaround for the problem, or more than one. This topic describes some situations that can arise, and ways to correct them.
Default cage around high-res cylinder
Indentation is missing from top and bottom of the cylinder's normal bump map.
Projection rays (shown in red) parallel the sides of the indentation.
Raising and scaling the upper end of the projection cage.
With the corrected cage, the upper indentation appears correctly in the normal bump map.
Breaking low-res vertices causes the indentations to render in the normal bump map. However, projection now misses some areas of the geometry, so the cage needs to be adjusted further.
When you use tangent space for your normal bump map, usually the values used for the tangents are consistent between the hardware shader, renderers, and third-party applications. However, sometimes portions of the geometry are flipped, relative to each other, causing discontinuities when you render or use a hardware shader. Tangent space is the default option for normal bump mapping, and it is the method you should use for objects that both move and deform, such as animated characters. This problem does not arise when you use the other coordinate spaces: world, screen, or local.
Flipped seams in rendering of pants
Left: Left side shows a discontinuous red stripe
Right: Right side shows a discontinuous blue stripe
The arrows show how the maps are misaligned.
Uncorrected normal bump map shows blue and red “flares.”
Normal bump maps corrected using Flip Horizontal
Red and blue are more evenly distributed, with blue predominating.
Corrected normal maps render more smoothly, without discontinuity.
The arrows show how the maps are correctly aligned to wrap around the pant legs.
If you use the mental ray renderer to render a normal bump map, and the model has overlapping faces (for example, where the low-resolution and high-resolution objects overlap in space), then the normal bump map can show noise where the faces overlap.
Red areas show noise from overlapping faces
The workaround is to adjust either the high-res or the low-res object so that faces are not coincident. One way to do so is to use a . After you have generated the normal map, you can turn off the Push modifier.
Overlapping UV coordinates can cause rendering errors in Render To Texture. The problem is especially noticeable on objects that have mirrored UVs, or symmetrical mapping. If you are working with a character or other model that has mirrored UVs, we recommend that you follow this procedure: