[Bf-cycles] Alpha pass independent from transparent option

[Bassam Kurdali]

>         
>         This will be added, but not in the way it's done for blender
>         internal.
>         This should be a feature of the image saving and dependent on
>         the
>         image file format.
>         
I have a question about this (possible future scenario):

Step 1- create a blend file, with some 3d layers to render. do comp
based on render, saving to a format that only allows key alpha. Do some
compositing.

Step 2- make your comp based on ... what? now we don't know what the
alpha is for the renderlayers, because for instance, I don't know the
specifics of the file format... ok, lets say we find out and comp.

Step 3- switch the file to my 'final' rendering format, that say only
allows premul alpha. my comp is now broken, but I only find out after I
render?

So I would make the following suggestion to avoid the ambiguity:

1- do as you said and switch key/premul based on output format (with a a
choice if the format allows both) in the output file settings.

2- allow switching key/premul in renderlayers regardless of output
format , and make them a sane and consistent default (regardless of
output format chosen, maybe something suitable for openexr).

cheers
Bassam