EXR and PNG different result and Cryptomatte issue

[Witt3D]

Hi, I guess this topic has been discussed for a long time.

Just trying to point out my thoughts on it. I know it's a color management problem, but as it works now is not a clean workflow for sure, and the most important thing, our work is slow down.
Working with vray for so long now, we have come out to make finals render in PNG format, cause is the format that seems to match closer with Vray Frame Buffer, not exact but pretty close. The point is that we use to test and modify our scene base on tVray Frame Buffer to get the final image we like.
After that taking your image into Photoshop shows that they are not exactly the same and always you have to post process the image to get it as you would like, as you did before on the Vray Frame Buffer. More work on our side, and what is worse, twice work.
But now we get another problem with PNG. Cryptomatte becomes transparent in Photoshop because Alpha is embedded in the file. Again something that makes our work harder. Perhaps is a technical problem, i dont know, but it would be really easy for us to get a decent PNG CRyptomatte to work with, without any workaround.

So if you choose to render in EXR format for Cryptomatte to work with Photoshop, then the final image is completely different because Ocio color management is not applied. Again everything is harder on our side, and do we need some workaround to make it work.

There are some solutions but not accurate, and also make us work on things we would not like to work. We just want to focus on renders, light, materials, composition, ...
Finally most of us have to render everything twice to get all the files we need, and as close as we would like to Vray Frame Buffer. Or render everything with "resume enabled", so that we later have the vray file to open it in VRay FRame Buffer and save as EXR again, but just Cryptomatte. Again everything is not clean and is always more work on our side.

I`m not really a Colormanagment expert, but it would be great to dsiplay everyting as close as possible with our common image editting tools. And apply internally any colormagment needed on any format so that we get displayed the same result on exr, png, jpg,.. . Also allow to write Cryptomatte on png with no alpha would be great and time saving.
Just two examples in PNG and EXR.


Thank you.

[hermit.crab]

First of all, Cryptomatte works only with multi-channeled image formats by design.

So if you choose to render in EXR format for Cryptomatte to work with Photoshop, then the final image is completely different because Ocio color management is not applied. Again everything is harder on our side, and do we need some workaround to make it work.

Yes, but you can either bake the OCIO in the .exr or set the PS color management to match it.

As for the differences, the .png (image_002) seems to have double gamma applied, hence the whitening. Is your 3ds Max Gamma set to 2.2? Otherwise, you can easily fix the image by adding an Exposure adjustment in PS and setting the Gamma Correction to 0.4545.

EDIT: Just saw we're in the Maya section. Maybe you have Gamma correction enabled in the V-Ray color mapping section? Also, does the image look similar to the VFB when you open it in the ChaosPlayer?

[Witt3D]

Hi, first of all, thank you for you reply.

First of all, Cryptomatte works only with multi-channeled image formats by design.

If think the best way to work with, should be to check if you want it as multi-channeled or not, if not just as a plain interger layer like "Object ID" would work in most of the cases fine, in order not to re-render everything twice. I think is a cleaner solution and should fit better in common workflows.

Yes, but you can either bake the OCIO in the .exr or set the PS color management to match it.

Yes, it's a color management issue, but you should ask users to get the correct Giturb installation, and to know and waste time to install it in common post-processing tools. In our case it was not easy and I think you don't have to deal with these problems when you buy a render engine as Vray. For me, I could be wrong, it should be an out of the box matter.
I think, and generally disagree, that Vray is trying to follow a roadmap where things are really simple to try to get photorealistic results for intermediate or beginner users. You have disabled a lot of important advanced settings in the render settings to try and make it simpler and more user friendly. But then you come up with a final image that finally has all this stuff with color management that's not really clear even to advanced users. It's something that confuses me. You see one thing and then when you press "save" you get another thing. If you want to do it really simple, apply it to everything involve with the render. If not, is something that just mess everything.

As for the differences, the .png (image_002) is saved linearly and does not have a gamma curve applied, hence the whitening. Is your 3ds Max Gamma set to 2.2? Or maybe you're overriding the gamma with 1? Otherwise, you can easily fix the image by adding an Exposure adjustment in PS and setting the Gamma Correction to 0.4545.

Image _002 is EXR format not png. We have try everything, you can download both and try on PSD to get Image_002 as close as you can to image_001. We couldnt on an esay way. For this project we have 18 renders. Is a tremendous work on post, where everything looked perfect on Vray Frame Buffer. Attached image of render setting for color mapping. Inverse color mapping like 0.454545 doesnt work. You can try yourself.

Doesnt try anything with ChaosPlayer. The point again for us, is that Vray Frame Buffer, should work with the same or as close as pòssible Color managment as PSD, Nuke, AFter Effects, Windows preview image, ....(where most of the users look to our renders) . And then if you dont uncheck any cehckbox where you dont want to apply any Color Mangament, as an out of the box tool, if you write in any format you should get the same result. And of course, internally if you choose to render in PNG, JPG, or any other format that doesnt accept multi-channel, Cryptomatte should be written with no alpha as an interger layer.

All of this stuff is code that should run internally and do life easier to users, this is the main difference when you see a solid and good piece of software.

[hermit.crab]

Actually, it may not be a gamma issue, but a color space one. Are you rendering in ACES space? Check this guide for matching EXRs in PS. If the differences persist, I suggest you send the scene (simplified) so we can take a look.