Rendering How do I > Correct self shadows
Add and edit lights
Learn how lighting a scene is an important part of the rendering workflow.Create a light
Lighting creates mood, focus, and drama.You can create a light using the Create light tools or using the Multi-lister. You can use the light options to set properties for any new light you create.
By default, lights are named sequentially as you create them: Light, Light#2, and so on. To avoid confusion, however, you should name all lights as you create them. If you let the system assign default names and later combine two or more files, all lights are renumbered to avoid duplicate names. It may then become difficult to distinguish lights by name.
Light#1 is not used explicitly as a name; the first light with a given name is implicitly numbered 1.
To create a light using the Light tools
- Select a tool from the Render > Create lights cascading menu, or click one of these icons on the Create shelf:
.
- Place the light by clicking in the modeling window, or by typing a set of coordinates in the prompt line.
A new light swatch appears in the Multi-lister, and a new light icon appears in the modeling window. Each type of light has a unique modeling window icon and Multi-lister swatch.
In addition, light manipulators are displayed in the modeling window.
(To display the manipulators for an existing light, select the Pick > Object
tool, select the light, and select a Light tool.)
Most lights have one manipulator that controls the light's position. Spot lights have two manipulators: one manipulator controls the light's position, the other manipulator controls its direction (look-at point). Each manipulator consists of a square icon at its center, and three colored arrow icons radiating from the center in the X, Y, and Z directions.
By dragging a square icon you can move the light or the light's look-at point across the view plane (in orthographic windows) or parallel to the ground plane (in perspective windows). By holding the
key while you drag a square icon you can snap the light to grid points.
By dragging an arrow icon you can move the light or the light's look-at point in the X, Y, or Z direction.
To create a light using the Multi-lister
- In the Multi-lister (Render > Multi-lister
> Lights
), select Edit > New Light. A new point light swatch appears in the Multi-lister, and a new point light icon appears in the modeling windows at 0,0,0. Double-clicking the icon opens up the Control Window that allows you to change the light type and other parameters.
To display the light options box
Related topics
Display light icons
You can control whether light icons are displayed in the modeling windows.
To toggle the display of lights on or off
- Select WindowDisplay > Toggles > Lights
.
To open the Toggle Lights Options
- Select WindowDisplay > Toggles > Lights
.
Animate lights
There are different ways of picking lights for animation, depending on which parameters you want to animate.
To animate a light's transformations (translation, rotation, scale) or visibility, pick the light in a modeling window or pick the appropriate light DAG node in the SBD window.
To animate any other light parameter, such as color, intensity, or glow, pick the light in the Multi-lister window. When animating a light through the Multi-lister, the light should not be active in the modeling window unless its transformations or visibility are also to be animated.
To copy all light animation from one light to another, select the root node of one light, and use Animation > Edit > Duplicate animation channels
Correct self shadows
The Self Shadow Correction parameters let you correct self-shadowing problems that can occur with shadow casting spot lights during raycasting.
A spot light uses a shadow map (or depth map) to calculate the shadows cast by surfaces. If a surface is illuminated by a spot light, then the shadow map will begin at the illuminated surface and extend away from the light. Any surface that lies within this shadow map will be in shadow.
A problem may occur on illuminated, shadow casting surfaces. Because the shadow map has a fixed resolution, it may not be smooth enough to describe a surface. The shadow map may actually intersect the surface. This means that the illuminated surface will be partially within its own shadow. The result is a dark moire pattern on the surface.
To solve this problem you can set the Min Depth parameter to a small value. The renderer will then temporarily move the shadow casting surface toward the light, before calculating the shadow map, so the surface will no longer be within its own shadow.
The problem with using Min Depth is that it may be difficult to know what is too small a value and what is too large a value. If the Min Depth value is too small, the surface will still be partially within its own shadow. If the Min Depth value is too large, other surfaces which should be in shadow may no longer be in shadow. Another problem is that the Min Depth value is in world space units, so the magnitude of the value will depend on the scale of your scene. Using Min Depth can also interfere with motion blur.
Using Blend Offset is a better method of solving self-shadowing problems. Whereas Min Depth moves the entire shadow casting surface an equal amount, Blend Offset moves different surface points different amounts, based on the probability that the original point on the shadow map was correct.
Self-shadowing can be even more of a problem with motion-blurred objects. The renderer calculates motion blur by simulating the shutter and exposure time of a real camera. The motion blurred object is rendered several times between the shutter's open and close times for each frame. The shadow map, however, is only calculated at the shutter mid-point. If the object is moving very fast away from the spot light, then it may appear to be entirely within its own shadow for part of the motion blur.
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