How to render unmultiplied RGBA?

[Dmerc]

I am looking for the middle result:



Appearantly the non-alpha background does not contribute to the semitranlucent pixel. So compositing them with alpha should work brilliant.

Any possibilities to do so in Vray?

Best regards, Peter

[rivoli]

I'm not sure I get the non alpha bg not contributing to semi translucent pixels, but tga supports non premultiplied outputs. rendering against black should give you correct results even with premultiplied images though.

I forgot, rpf saves non premultiplied images too. and you can output to 32 bit, unlike tga.

[3DMK]

.exr can also do non-premultiplied images

[Dmerc]

RGB-Output should be different, no ?

I am aware that some fileformats support that alpha-options. But as far as I understand, the rendered image output should be different as well, so to say the rendered result.



Looking at the sample images, the middle image has pretty sharp edges, the object-color extents all the way to the border. I never got that in Vray so far. Against backdrops like the vray-sky the output even creates some strange overbright edges, that became also visible when alpha was applied.

Any suggestions?

Best regards, P

[rivoli]

it doesn't have to do with vra, it's the way different file formats save the rgb image. if you save to a format that lets you choose between straight and premultiplied output, then you can get what is shown in the middle image.

[Dmerc]

Couldn't quite replicate it yet. Thanx anyway!

[tricky]

I am looking at this issue now.

If I render a tree to the vray frame buffer, can I then save it out (direct from the frame buffer) to a file format which seperates the RGB from the background properly? I'm not exactly sure of the terminology yet, but I think it does have something to do with being 'pre-multiplied' or 'straight'. I guess what I want is a straight output so that when I comp on a new background in after effects, I don't get edge pixel problems.