Common shadow image problems
Shadows produced from shadow casting
Problem: Shadows produced from shadow casting have jagged shadow boundaries.
Shadow map resolution is low.
Do one of the following:
- Narrow the spread of the spot light so that it just barely covers the region you want lit. This provides a higher accuracy to the shadow map to work from. If you see banding artifacts, try increasing the Min Depth in the Self Shadow Correction section of the light’s Control Window for the light's shadow.
- Increase the resolution of the shadow map as a final resort. Remember, keeping large shadow maps increases memory usage.
Shadows from light fog
Problem: Shadows from light fog may appear incorrect for very thin objects, or Light fog shadows shift over an animation.
See Fog samples in Render > Multi-lister 
.
Increase the Fog samples for the spot light.
Soft shadows produced by raytracing
Problem: Soft shadows produced by raytracing are noisy.
Do one of the following:
See Use Shadow Map in Render > Multi-lister .
For spot lights, toggle Use Shadow MapON so that the raycast shadows are used.
See Shadow Samples in Render > Multi-lister
.Increase Shadow Samples.
Moire pattern on surface when raycasting
Problem: A dark moire pattern on a surface when raycasting, or Incorrect shadows on a surface when raycasting.
The renderer incorrectly believes that a surface is behind its shadow map.
Do one of the following:
Set Min Depth (in the Self Shadow Correction parameters) to a small positive number (in Alias grid units), for example 0.01, for shadow casting spot lights. This temporarily moves the surface (by the Min Depth value) when the renderer is calculating shadows. If Min Depth is too small, the surface will still be behind the shadow map. If Min Depth is too large, other surfaces that should be in the shadow may be moved in front of the shadow map. Perform a test render, and adjust Min Depth until shadows appear correct.
See Min Depth in Render > Create Lights > Spot
.Instead of using Min Depth (as above), use Blend Offset. This variable scales the amount it moves each point on the surface based on the shadow map samples.
See Blend Offset in Render > Create Lights > Spot
.
Moving objects with motion blur
Problem: Incorrect shadows for moving objects with motion blur.
Shadows are not motion blurred. The renderer calculates an object’s shadow map when the camera shutter is at midpoint. When the object moves, it may move behind its own shadow map.
Do one of the following:
See Shadows in Render > Editors > Render Stats 
.
- If the object has a separate surface facing the shadow casting spot light, set Shadows off for that surface (under Render Stats).
- Increase Min Depth or Blend Offset (in the Self Shadow Correction parameters) for shadow casting spot lights.