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Illumination Compensation
When performing removal effects with time shifts, changes in scene lighting and camera irising during the shot can create very noticeable mismatches that give away the effect. Fortunately, SynthEyes and ViewShift offer the tools to be able to compensate for it very exactly. Although this can take a little more time, the results can be very worth it.
While turning on ViewShift's Compensate Illumination checkbox is an obvious first step, you must make the illumination data available to ViewShift on the illumination track of one or more lights. That data will be based on actual measurements by one or more trackers. For more reference on this topic, see Light Illumination. The general process follows here.
Create a light, ie New Light on the Light panel. Drag it around in 3D to someplace plausible. Note that lighting on your meshes won't affect the ViewShift process.
Create a "probe" tracker on a relatively bright, static, portion of the image—in a shot like the car removal above, it should be on a patch of road that cars do not drive over. The tracker size should be relatively large, because its average interior will be measured and the larger area produces lower noise levels. You can use more than one if there is too much occlusion going on, or if the length of the shot warrants. If so, have overlap between successive trackers for better results. (You can also force the tracker to a set of locations that do not correspond to a fixed feature, but migrate along with whatever you're doing—in this case be sure to make the tracker zero-weighted so it does not affect any subsequent solves.)
Select your probe tracker(s).
Run the Trackers/Set Illumination from Trackers script. Enter the name of your light (typically Light01). Set 3D position to Use 2D only. This sets the light's illumination track as the average of illumination of the trackers.
Don't forget to turn on Compensate Illumination before running your ViewShift.
Note : you can examine and refine the Light's illumination track from the Graph Editor after creating it.
The illumination track on a light is associated with the shot of the trackers used to generate it. ViewShift uses only the light(s) associated with the source and viewing shots. If the source and viewing shot/camera are the same, then there can be only one such light; if they are different there can be at most two, one for the source and one for the viewer. Lights on other shots, or lacking an illumination track, are ignored.
Whether there is one light involved or two, pixels being shifted are normalized (divided) by the illumination on the source frame, then multiplied up to match the illumination of the target frame.
Note : That math assumes that you have linear color with a black level at zero. If that isn't the case, and the illumination levels vary substantially, visual mis- matches may result. You may need to correct the color or do additional tweaks. We could add yet more settings for the black level, but there's enough clutter and they would be difficult to adjust accurately.
If the source and destination shots are different, and only one of the two has a light with an illumination track, that single light will be used to normalize the transferred pixels to match the first frame of the shot. That may not be ideal, but it will give a stable level that facilitates downstream compositing without requiring further frame-by-frame adjustments.
©2024 Boris FX, Inc. — UNOFFICIAL — Converted from original PDF.