Convert Alpha Channel to Transparency/Opacity: PS

[linxe123]

This problem is really starting to bug me! Whenever I render a scene in Maya into tif and I want to save the transparency, I render with the Alpha channel checked in render preferences. My problem is that i need these to be transparency and not alpha channels (i.e. I want to use Photoshop to make multiple layers and I need the top layer, the picture rendered in Maya, to be transparent in some areas). If you understand what I am talking about and can help, please PM me! If you don't completely understand what im talking about and would like for me to clarifly you can PM as well. Thank you.

[failure]

alpha is transparency

[jdj]

Hi

Have you enabled raytracing? Don't know if that works but anyway.

Best regards
/ Daniel

[linxe123]

I know it is transparency but i think a better way to put it would be: how can i convert an alpha mask to actual Photoshop layer transperency/opacity.

[failure]

By default maya outputs images with premultiplied alpha, meaning RGB values of foreground objects are blended with background color and this pixel values are then stored as rgb channels of the image.
Other option is to store image with straigh alpha. In this case non blended rgba values are stored.

Most compositing software will give you options to choose how to interpret rgb and alpha values in imported footage ( premultiplied or straight ). Photoshop doesn't let you choose and it interprets all images as having premultiplied alpha so you'll have to turn it manually to "straight alpha"

Anyway, this is what you should do:
- render on black background
- open your tiff in photoshop ( must have alpha channel )
- load selection from alpha channel
- copy-paste to bring foreground to separate layer
- deselect
- delete background layer
- select foreground layer in layers palette and go Layer->Mating->Remove black matte ( this will "un-multiply" the rgb values )

If you need to do it a lot - create a photoshop action

[joojaa]

yeah, having that as a photoshop action is nifty.

or tell maya to render out straight alpha by uncheking premultiply under maya renderers render options. Or fior mental rays frame buffer section. (note premultiplied alpha produces slightltly faster results, but thats noissue to modern computers)

[linxe123]

Thanks for the help guys. Really appreciate it!