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Overlay details: Motion vectors: Colour wheel | Overlay details: Global motion vectors
Representing motion vectors as arrows results in a fixed resolution display with a single arrow representing the mean of a group of motion vectors. An arrow block is 16x16 pixels in size and the number of motion vectors it represents depends on the size of motion vector blocks in a picture sequence. Figure 3 uses the ‘BBC comp’ sequence frame 26 again to illustrate this.
Figure 3. 'BBC comp' sequence frame 26 with overlay of (a) motion vector arrows (b) motion vector arrows with colour indicating size
The colour is calculated using the resultant of the combined motion vector components. By default, motion vectors with a larger displacement than 25 1/8th pixels are clipped in order to keep a consistent colour scale. This threshold may be adjusted using the -clip n command-line parameter.