Compositing Elements in After Effects

[giancarlo_007]

Hi,

Wondered if anyone could help me with some compositing problems I'm having. The first image is the actual render from the vfb window.

Im having great difficulty matching the seperate passes to create the final render in AE. I've read alot of the threads on this site and have used this method in AE with the corresponding exr files.

raw gi x diffuse filter = gi (2nd Image)
raw lighting x diffuse filter = lighting (3rd Image)
Raw reflection x reflection filter = reflection (4th Image)
raw refraction x refraction filter = refraction (not present in scene)

With all the above corresponding files above I used the 'multiply' blending command. i then used the 'add' blending mode with the resulting files to try create a replica of the final render (5th Image), but its coming out with alot of noise on the light solution and the gamma settings seem out. I've rendered the scene with linear multiply colour mapping and no gamma set and clamp colour and sub-pixel off.

Any suggestions as to where im going wrong?

many thanks in advance

[DanielBrew]

You could probably reduce the noise a lot by setting the gamma in color mapping to 2.2 and checking 'don't affect colors'.

The gamma in the last image looks right to me.

[giancarlo_007]

thanks for the response daniel. I've basically figured out that it has something to do with the exr file I'm saving. I've attached the two images of the raw GI, one is saved as a tiff, the other as an exr. As you can see the exr comes up with much lighter exposure, with different gamma settings and i'm playing around with the options of the exr at the moment to match.

Does anyone have any idea what can stop this irregularity?

cheers

[sv]

exr is a linear format, so only save linear data to it.

[pdimov]

Your problem is likely to be gamma-related (sRGB vs linear). I suspect that (in your case) you need to somehow tell AE to treat the EXR images as sRGB.

You may try to use the GI/Lighting/Reflection/Refraction render elements directly instead of reconstructing them in AE as Raw*Filter, because the multiplication may introduce errors unless you're using linear workflow.

If you have Pdplayer (the trial version should be enough) there is a sample composition on

http://www.pdplayer.com/support_and_downloads.html

called "V-Ray Render Elements" that may help.

[pdimov]

The attachment shows what I was able to achieve using your images. I had to set the gamma of the elements to 0.45 to undo the linear to sRGB conversion that (I suspect) AE has applied on load. The color difference in the saturated areas is likely caused by the Raw*Filter multiplication done in the wrong color space.

[giancarlo_007]

thanks pdimov, it looks like you're spot on. only problem now is finding out how to turn off that filter in AE or simply just adjusting the gamma of the images. will have a play and see how it goes. Many thanks for all your help

[rivoli]

Does anyone have any idea what can stop this irregularity?

there's nothing wrong with how AE handles EXRs (apart from the fact that it only reads RGBA). as steve says, EXR it's a linear format, and so it gets interpreted by AE. and when compositing elements it's correct to work linearly, it's the only way to have the mat done correctly when blending layers.

[sv]

there's nothing wrong with how AE handles EXRs (apart from the fact that it only reads RGBA). as steve says, EXR it's a linear format, and so it gets interpreted by AE. and when compositing elements it's correct to work linearly, it's the only way to have the mat done correctly when blending layers.

just to add to what rivoli says, he's right in that you won't be able to correctly re-composite elements in anything other than linear. If colours are displayed in sRGB it's a different thing than having them stored in sRGB.

I'm not sure about afx, but in Nuke it's like this: (this is a single layered EXR, but in AFX's case it would be the different passes as separate files - will be the same thing)

[pdimov]

You're right that the physically correct way to render and combine the layers is in linear color space. That is, one needs to use linear workflow in V-Ray and then use Nuke to add the render elements. Nuke works in linear color space; its Read node converts the image to linear, the math is done on the linear values, and then the viewer node converts to sRGB for display.

As a simplistic example, if we have two EXR render elements A and B, we need A+B to obtain the final render. Nuke does to_linear(A)+to_linear(B), which yields A+B for EXR files because to_linear is a no-op; EXRs are already assumed to be linear and no conversion is done on read.

Things change if the compositing package uses sRGB as its working color space though, as After Effects does (at least by default; I've no idea if it's possible to change that). (So does Pdplayer, for speed reasons.)

In this case, the math is to_sRGB(A)+to_sRGB(B). In order for the final result to be our desired A+B, we somehow need to either ensure that the to_sRGB conversions are no-ops (by telling the compositor that the input is already sRGB), or to undo this conversion by using the equivalent of from_sRGB on the result, such as using a gamma of 0.454545.

So... that's why when not using linear workflow in V-Ray and then blending in AE, one has to use a format that is assumed sRGB, or set the gamma of the EXR layers to 0.454545. (When blending in Pdplayer it's enough to set the color space of the EXR layers to sRGB.)

Hope this helps someone.

--
Peter Dimov
Asynthetic

[rivoli]

Things change if the compositing package uses sRGB as its working color space though, as After Effects does (at least by default; I've no idea if it's possible to change that).

well yes, you can manage colour spaces. even though colour management is off by default.