Time average

Time average is one effect which has many uses besides creating trail patterns of moving objects (figure 10.65). The main use is reducing noise in still images (or in the motionless parts of a video). Merely point a video camera at a stationary subject for 30 frames, capture the frames, and average them using time average and you will have a high quality print. In floating point color models, time average can increase the dynamic range of low quality cameras.

Inside the time average effect is an accumulation buffer and a divisor. A number of frames are accumulated in the accumulation buffer and divided by the divisor to get the average (for 10 accumulated frames the divisor is 10). Because the time average can consume large amounts of memory, it is best applied by first disabling playback for the track, dropping the time average in it, configuring time average for the desired number of frames, and re-enabling playback for the track.

Figure 10.65: GUI for Time Average

Frames count

this determines the number of frames to be accumulated in the accumulation buffer. Ranges from 1to1024 frames.

Accumulate

this outputs the accumulation buffer without dividing it.

Average

this causes the accumulation buffer to be divided before being output. This results is the average of all the frames. The result is similar to Selective Temporal Averaging, but not configurable.

Replace

(Threshold, Border): causes the accumulation buffer to be replaced by any pixels which are not transparent. In combination with motion tracking it allows entire sequences to be combined to form panoramas.

Restart for every frames

if an effect before the time average is adjusted the time average normally does not reread the accumulation buffer to get the change. This forces it to reread the accumulation buffer when other effects change.

Don’t buffer frames

in order to represent the accumulation of only the specified number of frames, the time average retains all the previous frames in memory and subtracts them out as it plays forward. It would run out of memory if it had to accumulate thousands of frames. By disabling subtraction the previous frames are not stored in memory and only the average function is affected by the frame count.