Matchmove distortion

[Da_elf]

Ive been reading a book on matchmoving and was wondering from those who work in film about something. vra has its way of distorting the image to make it look like the distortion you get due to wide angle lens (or to be more technical the inter-relation between the lens and the stop). it says that usually the image is undistorted before matchmove calculations are made. So would this mean that the 3d rendered needs to be undistorted and distortion is added in post to put the 3d and the main image back to normal (obviously the original footage will be used and not the undistored footage being re-distorted)

[instinct]

Usually that´s the way it´s beeing done afaik....At least that´s how we did the few times we did it :P

Thorsten

[Da_elf]

so more or less you dont try to match the camera distortion in the 3d program then. would it be easier or more trouble if you could match the distortion in the 3d program. once the match move is calculated the camera will move exactly the same therefore if you have the same camera distortion in the 3d program then your images will line up (in theory)

[instinct]

Well the problem is that you wont be able to create a camera that is distorting the right way in the matchmoving process. That´s why you remove the distortion prior to tracking in the first place...but i might be wrong there!

Thorsten

[joconnell]

Most of the matchmove apps these days have a lens distortation tool that allow you to draw a calibration line over the background plate you are tracking and then distort the plate until a straight line in it matches your calibration line - the tracker then takes this into account when solving for 3d. Most also have an option to render out the plates with the reverse distortion applied so your 3d lines match up. They also have the ability to apply the distortion to an image sequence so once you've tracked, modeled and rendered your 3d stuff you can apply the same lens distortion to your 3d render before comping it over. There's a lens correct filter in after effects that does this task too.

Definitely do it in the matchmove app though as it'll make a difference to how well an object ties to a surface as it passes by the edge of the lense.