Autodesk 12812-051462-9011 User Guide 3 - Page 775

Most third-party tools expect the motion vector encoded as colors where red is the X axis and green is the Y axis. To fit into the confines of a color (especially when not using floating point and a color range extends only from black to white), the motion is scaled by a factor (here called Max Displace) and the resulting value range, which is -1 to 1, is mapped to the color channel's 0 to 1 range. The shader also support a couple of different floating point output modes. Interface Max Displace (pixels) Sets the maximum encoded motion vector length. Motion vectors of this number of pixels or above are encoded as the maximum value that is possible to express within the limit of the color (that is, white or black). To maximally utilize the resolution of the chosen image format, it is recommended that you use a Max Displace value of 50.0 (the default) for eight-bit images (which are not really suitable for this purpose) and a value of 2000.0 for 16-bit images. The shader outputs an informational statement of the maximum motion vector encountered in a frame to aid in tuning this parameter. For details, consult the documentation for your third-party motion-blur shader. If Max Displace is 0.0, motion vectors are encoded relative to the image resolution. For example, for an image 600 pixels wide and 400 pixels high, a movement of 600 pixels in positive X is encoded as 1.0 in the red channel, while a movement 600 pixels in negative X is encoded as 0.0. A movement in positive Y of 400 pixels is encoded as 1.0 in the blue channel etc. Blue Channel is Magnitude When on, the blue color channel represents the magnitude of the blur, and the red and green channels encode the 2D direction only. When off, the blue channel is unused and the red and green channels encode both direction and magnitude. Floating Point Format When not set to 0, the shader writes real, floating-point motion vectors into the red and green channels. They are not normalized to 6030 | Chapter 19 Material Editor, Materials, and Maps