i am working on a shot of helicopter that i created in 3d and i want to put over a footage. i rendered out the beauty pass and motion vector (velocity) pass according to the workflow faq on the Re:vision website. the vector pass is not antialiased 16bit tiff image with alpha. i even created the overscanned vector image sequence as said on the website (using maxscript)
when i load everything into After Effects CS3 and try to make motion blur there using RSMB vectors, i get all kinds of artefacts... but the biggest problem is that i can not seem to create realistic MB for the rotors of the helicopter using RSMB... is there any kind of tutorial or something like that available for my case? i've been struggling with the scene for far too long and then i had to rerender the beauty pass with native MB applied to it, but it's not a good solution as all of you might agree... i need a solution to make realistic MB in post processing... can you give me any tip?
thank you all in advance...
Unfortunately helicopter blades don't work well for this technique - there is too much difference between frames for a single motion vector value to represent the proper thing (a bit for the same reason that train wheel goes backward in 18 FPS old movies). The helicopter blade friends includes the hummingbird wings and various insects in motion and close-up.
Option 1: Make a copy of the scene and Render that element only with a lot more FPS or frames (slow down the animation) and frame average AFTER with something like SmoothKit Frame Accumulate -- e.g. if you render 5X slower/5X more frames instead of 24, that would be 2 before and 2 after in SK Frame Accumulate and then you posterize time to recover the proper duration.
Option 2: If the camera is static or the blade is easy to isolate. You can sometimes do something with SmoothKit Directional Per-Pixel. Essentially you would need to draw an ellipse with a radial greyscale fill in a precomp that follows the helicopter blade, and use that as the layer the direction is made from and as well use the alpha of that to control where the directional blur is applied (the Length control).