Thread: matchmoving
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# 12 23-02-2011 , 04:34 PM
LauriePriest's Avatar
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The plate looks like it needs delensing, 3d software is mathematically perfect meaning you dont get lens distortion (all lines are perfectly straight).

This is not the case with real cameras, since light is bending through glass you will get lens distortion which tracking software won't account for. (newer versions can do something to help with this but its not very nice to work with in a pipeline more often than not).

Its probably easier if you do an un-distort in after-effects or nuke to de-lens the plate, you can do something with out the box tools. A pin cussion distortion is usually enough. Just ramp it up untill the lines appear straighter, you might need to adjust the centre of the effect.

Then output the result as a new jpg image sequence and use that to track with.
It will really help if you know your film back information and have a rough idea of what the focal length should be, its not too tricky with hd cameras to make a guess with a bit of googling if your not sure.

Also you should know what aspect ratio the footage was shot at, the footage your using looks a little squashed so if you know what format its shot it check it out. If you track at an incorrect aspect ratio / film back values you will get very odd results in 3D.

Lens distortion often wont stop you getting a solve in shots with little motion or that are nodal but the 3d renders won't feel like they are sitting perfectly as they move through the plate. In longer shots its crucial to get a decently de-lensed plate as they often won't solve at all.

Once you render your 3D work out with the match move remember to use the same values on your pin cussion or other effect used to de-lens your plate but this time invert it so you end up with a correct result. Hopes that makes some sense.


FX supervisor - double negative