The Velocity Render Channel is a color or grayscale image that stores velocity information about objects that have moved between the current frame and the next frame.
Overview
The Velocity Render Channel stores surface velocity for moving objects in the scene with different colors representing different velocities. Each moving object is rendered with a flat color or gradient. It is commonly used to create mattes for adding motion blur in a composite.
The shading in the Velocity Render Channel is determined by the degree of motion for each object's pivot point. The object's motion between the current frame and the next frame on the X, Y, and Z axes is mapped to R, G, and B components, with movement along the negative axis as 0 and movement along the positive axis as the maximum value. For example, a white object has moved at the maximum velocity on all three axes in a positive direction, while a black object has moved at the maximum velocity in a negative direction on all three axes. A pale yellow object has moved a great deal on all three axes in the positive direction, but mostly on X and Y, while a dark purple object has moved on the -X and -Z axes. A medium gray color indicates no motion.
Because of the relationship between XYZ motion and RGB colors, the Velocity Render Channel can be easily split into R, G, and B components during the compositing process and each direction can be handled separately or together to add motion blur.
Note: Specific objects can be excluded from this Render Element by disabling the Generate Render Elements option in the VRayObjectProperties node for the selected object(s).
Parameters
The parameters for this render channel appear in the Parameters tab under the out Network and within the render elements node.
Name – The text added to the end of the rendered file, when saved as a separate file (e.g. myrender.Velocity.vrimg).
Clamp Velocity – When enabled, sets the limit for the Max Velocity value to 1 for floating print images, 255 for 8-bit images, or 65535 for 16-bit images. This option is useful only when writing to an 8-bit or 16-bit file format.
Max Velocity – Used to scale the velocity values written to the render element so that they fit within the range specifies by the Clamp Velocity parameter. This is only useful if writing to an 8-bit or 16-bit file format.
Ignore Z – Disregards motion along the Z axis.
Filtering – Applies the image filter to this channel. Image filter settings are in the AA sub-tab of the Sampler tab of the V-Ray Renderer node.
Deep Output – Enables deep output.
Common Uses
The Velocity Render Element is useful for adding motion blur in post production at a composite level, without the need for rendering. See the render before and after compositing.
Notes
- It is recommended to disable this render channel when rendering with Motion Blur. This channel is generated when 3D motion blur is enabled in V-Ray. However, the pass will also be motion blurred along with the rest of the image. This will make the element not usable in compositing.