Cryptomatte issue in VRED 2021

[florian.dyck]

Hi,

I am using VRED 2021 and have encountered a strange issue with the cryptomatte passes. There seems to be a "double" image in each layer, material and object cryptomatte, see attached file. Though it is more or less easy to correct, it is a pain to do it for hundreds of objects and materials. And I suppose it is not intended to be like that. Anyone knows where this could come from? I will try to reproduce it and post a file. I was editing the image with Photoshop via the EXR-IO plugin.

thanks

[richardlevene]

Hmm can you preproduce that with a simple scene?

No issue on my end with a simple scene. Using EXR-IO 2.02.00

Richard

[michael_nikelsky · Accepted solution]

Haven´t seen this issue either. Are you rendering to 16 bit EXR or 32 Bit EXR? Seeing these sort of doubled images is something I encountered when the exr was incorrectly read as the wrong format, like a 32bit exr was interpreted to be a 16bit exr with from the file reader.

If you can post your original EXR we can take a look at it, a jpeg isn´t really that helpful in this case.

[richardlevene · Accepted solution]

I am now encountering this issue with 2021.0

It seems to be related to the size of the image. We are rendering at 16500px square.

It is not a plugin issue as the render looks this way in both Photoshop and Nuke

If I do a test render of it at only 1000px square it renders correctly.

@florian.dyckwhat resolution were you trying to render at?

Did you manage to resolve it?

I am going to try rendering stepping down resolution size to see when the issue occurs and will let you know.

Richard

[michael_nikelsky · Accepted solution]

I am currently looking into the issue and there might be a workaround but that requires a lot of memory.

When you are rendering locally (cluster is a different story) there is a memory limit set for the framebuffer that VRED should target. By default that is about 2 GByte which is not enough for high resolutions. If the memory is exceeded VRED splits the image into subtiles for rendering and just combines them in the end. This seems to be broken for Cryptomatte though and the same region is copied to all tiles.

So one thing you might try is to go to the Preferences->Rendersettings and set the  Framebuffer Memory Limit to something really high, 32 or even 64 GByte. This should prevent the splitting but of course can consume a lot of memory, so I recommend at least 128GByte in you system if you want to render high resolutions. On the upside this might also render faster, especially when motion blur is involved.

I will check how to fix the split case though, this of course should work as well.

Kind regards

Michael

[richardlevene · Accepted solution]

Thanks Michael for looking into this. Good to know.

The issues does not happen the older version of Vred that we use (2020.1) so it was obviously a bug that was introduced in newer versions. When rendered on that it writes and extracts the cryptomattes without this issue. But obviously we can't use 2020 for crytomattes due to the issue with the edges (which was fixed in 2021)

We will give the memory workaround a try in 2021 and see how much additional memory it uses for our scene and if it will be an issue for us. We have 128GB to play with but they are big scenes with big many vehicles so take up some memory already plus the very high pixel resolution.

Best,

Richard

[michael_nikelsky · Accepted solution]

Considering all the things that were broken before the 2021 fix with Cryptomatte I would rather guess it was a lucky accident it produced correct results with previous versions. There are a couple of things that disable the memory limit and render the full image all the time, glow/glare for example or cluster rendering in general. So I rather guess you luckily ran into one of these special cases.

However, I found the issue and added a fix for one of the next versions.

Kind regards

Michael

[richardlevene · Accepted solution]

Ha. Great thanks Michael.

Best,

Richard

[florian.dyck · Accepted solution]

If I remember correctly, I rendered at 4096 x 2160 resolution and did not try other size. Anyway, will try to increase the framebuffer as descibed. Thanks!

[florian.dyck]

Hi,

thanks, I will try to reproduce because I switched companies and don't have access to those files anymore.

regards

Florian