vray Camera moves when using scanline renderer

[invisiblecities]

When rendering alphachannels for different materials in a scene I used to switch to scanline and use a matte shadow material to do the alpha channels . But since I am using the vray physical camera any perspective correction I have done with guess vertical shift on the camera dissapears so the alpha channel s dont line up with the render. Is there a way round this?

[joconnell]

Nope unfortunately - you'd also find problems if you were motion blurring passes between vray and the scanline. Two options are to use vray override materials with a white vray light material and use the vray matte options (the right click vray properties menu) so you can set up matte passes without having to overwrite material assignments, secondly would be to use the vray matte element that dimo has written - you'll find it on the forum.

Using the scanline for mattes is a bit sketchy - blur, camera and anti aliasing issues could lead to trouble but it's often worth taking the risk for speed.