32bit EXR from Corona Image Editor

[philryan]

Hi all,

We're having an issue here in the office and I just wanted to double check that we're not doing something wrong.

When saving EXRs from the Corona Image Editor, they seem to be saving as 16bit EXRs instead of full float 32bit that we can get if we save the image directly from Max. Is this the case or are we doing something wrong?

[mike288]

Hi, CIE saves 32-bit EXRs/CXRs

[alias_marks]

It appears that, yes, CIE is saving 32 bit exr's and photoshop reads them as 32 bit exr's however when trying to pull the same information from the file it does not appear to have the same bit depth as it does in original CXR.  Attached image to help illustrate.  I realize this is a bit of an extreme example, as you woudl rarely want to boost exposure 10 stops, but curious to get to the bottom of it.

Here is the workflow:  Do you think this is the correct way to go about it?

1.  Render and save CXR from deadline or farm
2.  Open CXR in CIE, save all passes as exr's
3.  Open exr in phothshop, verify that it is indeed in 32 bit mode
4.  Try to boost or pull back exposure, and do not have the same latitude as in CIE.

Thanks for any pointers :)

[pokoy]

See first answer here:
https://forums.adobe.com/thread/2108467

Also, when converting 32bps to 16bps or 8bps in PS, you'll see that the black levels are going to change quite a lot and will never match a 16bps file from Corona's VFB. It's best to avoid PS when working with 32 bits, AE has way better support and also converts correctly.

[alias_marks]

Thanks for the reply.  I've opened up the same exr (saved from CIE), and have tried to up the exposure in After effects with same clipped result.

Next I tried the exr (originally saved from CIE cxr), loaded the exr back into CIE, then tried to up the exposure.  Still getting same clipped behavior.

In this last case I've taken adobe software completely out of the equation and am still coming up stumped.  Is this an issue anyone else has encountered before?

[Juraj]

You can test this by loading up a full float EXR file, and saving that file as a HDR one.

What the heck...so photoshop clips to half-float on import of exr already ?

If I only knew this before... :- O

[mike288]

...
Next I tried the exr (originally saved from CIE cxr), loaded the exr back into CIE, then tried to up the exposure. Still getting same clipped behavior.
...

In CIE saving to EXR (PNG, JPG) saves tonemapped pixel data. That's intentional. Therefore, if you load the EXR again into CIE, you will do the tonemapping twice. Not sure whether you are aware of it. It may be cause of your issues. Please, can you upload both the CXR and EXR files that you have trouble with. You can use our private uploader for that: https://corona-renderer.com/upload. Thanks.

[alias_marks]

Hey Mike, thanks for the reply.  I'm working on getting a file that I can upload for you to take a look.  In the mean time just wanted to say thanks for helping me think through it all.

Cheers,