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kenny chang avatar image
kenny chang asked ·

How to create multichannel output in KtoA?

Hello,

I am using the RenderOutputDefine node to combine multiple outputs (AOVs). I've set the following:

  • type: merge
  • mergeOutputs: P, N

However, rendering this I get the following error:

Running command: '\installs\windows\katana\2.6v3\Katana2.6v3\bin\ExrCombine' 'c:\users\kc\appdata\local\temp\aovs\P_pass.exr' P_pass 'c:\users\kc\appdata\local\temp\aovs\normal.exr' normal 'c:\users\kc\appdata\local\temp\aovs\lit.exr'
Render process exited with error code:3
CommandLineRender Error: doRender problem
Reason = Render process exited with error code:3

Debugging with the .ass file, the driver that is suppose to be used for outputting the multichannel exr is missing.

Is is a known bug or can someone shine some light on this? I tried it with the Katana example projects for both Arnold and Renderman, and with Renderman, it is outputting fine.

Cheers,

Kenny

aovskatana
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Mike Farnsworth avatar image
Mike Farnsworth answered ·

Arnold core has supported multi-channel EXRs for quite a long time; all that is needed is to take multiple AOVs and have them use the same output driver node. This worked in Arnold 4.x as well.

Katana makes this a bit harder, in that combining EXR outputs is something Katana does, not KtoA/Arnold, and it's fairly picky about what EXRs it will combine. You need to create ArnoldOutputChannelDefine nodes for your outputs, setting the channel ('P' and 'N') and make sure the output is EXR, and not tiled. Katana cannot combine tiled EXR outputs. If you do that, your merge output should work and have all of your channels in the same EXR file.

With KtoA 2.0+ you can get light breakouts all in the same file by using light path expressions; on the ArnoldOutputChannelDefine node you can set a light path expression, and then set the lightGroups parameter to 'separate AOVs'. Don't forget to set the aov parameter on your lights to the group you want each light to be in, and then each light's contribution will be separated in the EXR file for that AOV/channel. These outputs can be tiled EXRs, so long as you don't need them to go through a merge output later.

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“not tiled” , this is the key, thanks Mike!!

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龙龙 李 avatar image
龙龙 李 answered ·

For a long time, finally seems we got the answer,cheer!!

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rachid Hadj Abderrahmane avatar image
rachid Hadj Abderrahmane answered ·

oh yes

Thank you kenny

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kenny chang avatar image
kenny chang answered ·

@rachid ramane, for your mergeOutput (channels), do you have primary checked on? If so, try unselecting it.

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rachid Hadj Abderrahmane avatar image
rachid Hadj Abderrahmane answered ·

Here is the log file:
Render process exited with error code:255
CommandLineRender Error: doRender problem
Reason = Render process exited with error code:255

Yes, "tiled" was unchecked.

any solutions?

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kenny chang avatar image
kenny chang answered ·

Thanks for the explanation Mike. I got both multi-channel EXRs to work, including light groups.

Looks like my original attempt at merging output failed due to both having tiled checked on as well as trying to merge the primary output. Perhaps this is something to try @rachid ramane?

With MtoA, we are able to output multi-channel EXRs with tiled and append option checked on. Is this a limitation with Katana? From the render log, it looks like Katana is running a post process to merge the AOVs where as Maya's Arnold drivers are combinging the AOVs during rendering time?

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rachid Hadj Abderrahmane avatar image
rachid Hadj Abderrahmane answered ·

Hi Mike

It will be great if you can put a simple test scene, because I never succes to output multichanel exr in katana, I've to manually do the merge with ExrCombine.exe.

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rachid Hadj Abderrahmane avatar image
rachid Hadj Abderrahmane answered ·

I asked for that since version 4 of arnold, no correction until now!

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