To view and refine the results:
| 1. | To view the generated motion vector fields, click the channels dropdown menu on top of the Viewer and select: |
• motion - to view both forward and backward motion vectors.
• forward - to view the forward motion vectors.
• backward - to view the backward motion vectors.
| 2. | If the calculated motion vector fields do not produce the results you’re after when used with other nodes (such as Kronos and MotionBlur), try adjusting Vector Detail in the VectorGenerator properties. |
This determines the resolution of the vector field. The larger vector detail is, the greater the processing time, but the more detailed the vectors should be. A value of 1.0 generates a vector at each pixel. A value of 0.5 generates a vector at every other pixel. For some sequences, a high vector detail near 1.0 generates too much unwanted local motion detail, and often a low value is more appropriate.
| 3. | Vector fields usually have two important qualities: they should accurately match similar pixels in one image to another and they should be smooth rather than noisy. Often, it is necessary to trade one of these qualities off against the other. A high Smoothness means the output vector fields are less detailed, but is less likely to provide you with the odd spurious vector (think of it as if the vectors were combed until they are smooth with respect to their neighbors). A low Smoothness concentrates on detail matching, even if the resulting field is jagged. The default value of 0.5 should work well for most sequences. |
| 4. | If there are variations in luminance and overall flickering in your Source sequence, enable Flicker Compensation to avoid problems with your output. |
Examples of variable luminance include highlights on metal surfaces, like vehicle bodies, or bodies of water within a layer that reflects light in unpredictable ways.
Note that using Flicker Compensation increases rendering time.
| 5. | By default, VectorGenerator analyzes motion based on the brightness of the image. Specifically this is the mean of the red, green, and blue channels. However, you can bias this using the Weight Red, Weight Green, and Weight Blue controls under Tolerances. For example, if you set the Weight Red and Weight Green parameters to zero, VectorGenerator only looks for motion in the blue channel. |
| 6. | Once you’re happy with the results, we recommend that you insert a Write node after VectorGenerator to render the original images and the vector channels as an .exr file. This format allows for the storage of an image with multiple layers embedded in it. Later, whenever you use the same image sequence, the motion vector fields are loaded into Nuke together with the sequence. |