Isadora Manual v1.3 - TroikaTronix

To accomplish this, you connect the Video In Watcher actor to the Difference
actor’s video in input, and then connect the difference actor’s video output to the
video in input of the Calc Brightness actor.
For instance, if the camera is looking at a hand, and the hand was moving slightly,
the output of the Difference actor would look something like this.
When there is movement, the Difference actor makes more white pixels. When
there is no movement, the output of the Difference actor is almost black. Thus, the
more movement there is, the higher the value of the brightness output of Calc
Brightness.
But even when there is a lot of movement using this technique, the output value will
never reach 100 – as that would require a completely white frame. To help get a full
range of output, you can use the auto scaling feature of Calc Brightness.
Set the auto frames input to the number of frames you want to analyze (e.g., 150
frames is five seconds of 30fps NTSC video.) Then trigger the auto measure input,
and have the person or object seen in the video feed move both very slowly and
very fast. The auto measure function keeps track of the lowest and highest
brightness values measured, and once the measurement is complete, will start
automatically scaling its measurements so that the output should go from 0 to
100%.
Input Properties
• video in: The source video stream.
• auto frames: Specifies how many frames to examine when using the auto
measure function (see below)
• auto measure: when triggered, measures the brightness of the next n frames
of video (with n being specified by the auto frames input.) The minimum and
maximum brightness measured is then used to automatically scale the
brightness output for subsequent frames.
Output Properties
brightness: The brightness of the current frame of video, with a black frame
yielding a brightness of 0, a white frame yielding a brightness of 100, etc.
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