2D motion blur
In rendering, a fast way to approximate true (3D) motion blur. 2D motion blur is a post process that looks more uniform, and therefore not quite as realistic, as 3D motion blur. 2D motion blur is perfect for medium-to-far-away surfaces, where level of detail is not important.
Also known as fake blur. See also motion blur. Contrast with 3D motion blur.
2D motion blur artifacts can occur when...
2D motion blur can cause artifacts when rendering in scenes with fog, or solid objects in front of transparent ones, or if the background color is not black.
Workaround
There are three possible workarounds:
Take out transparent objects, fog, glow, and background color from the scene. Render the 2D blur and composite those elements back into the scene.
Set the Smooth Value to 0. In the command line, this is -m 0. This solution is to skip the smooth-mask operation. The image may look more aliased as a result.
Turn on Smooth Color. In the command line, this is -r 1. This solution uses a different smoothing algorithm. The image may look more blurry as a result.
2D Motion Blur problems
For Maya software rendering only.
If dark halos display around the objects
Try the following:
Make sure the background color is black
Make sure Smooth Color is turned on if there is fog in the scene.
Moving transparent objects with a background
The background is also blurred in this case even though it should not be. The solution is to blur the transparent object separately and composite with the rest of the scene. This workaround can be difficult for complex scenes with lots of transparency, or for transparent particles.
Detailed background behind moving objects
Some details may be lost because assumptions must be made about the background area occluded by the moving objects. The solution is to blur the moving objects without the background and then composite the results.
Rotating objects
May not look exactly right, because assumptions about what the back sides of these objects should look like must be made. Try using 3D motion blur.
Objects entering from outside the image or leaving the image
The edges of frames may not get the correct detail, because assumptions must be made about the object color that is just outside a frame. The solution is to render a slightly larger image which covers the original image and then crop it to the desired size.
Rendered results from 3D and 2D are quite different
Try not to mix the rendered images from two different kinds of blurring operations.