VFB correction controls

[peteristrate]

Hi guys,

1.
I'm trying to replicate the VFB correction controls(like exposure, gamma, LUT, white balance, etc.) in post, but in order to do that successfully in post, I need to know in which order are these corrections applied in the VFB so I can apply them in post in the same order.
I guess the developers know this for sure.

I tried different orders in post but seems that no matter how I do it, I still can't get the same results as in the VFB.
All I'm using at the moment is:
- highlight burn(under Exposure rollout)
- sRGB(gamma)
- LUT (with Convert to Log space before applying to LUT disabled).

2.
Also, my second question is: what does "Convert to Log space before applying to LUT" means? How can I reproduce this in post?


Thank you.
Regards,
Peter Istrate.

[Fat Tony]

you can save the LUT from VFB if you click on globals in VFB about CC. Only thing you have to skip is highlight clamping as it should be baked in LUT. and also it will not write LUT so the one you are applying you should apply as extra one. Log footage is meant for movie cameras mostly to what i understand, in most cases it should be off but some luts are meant for Log footage, you will see if it is correct or not just switching on/off

[peteristrate]

Hi Tony.

Yes, I know I can save the all corrections as a .cube(or similar) file but that would not be very useful.
I need to break down every single step in post, not just load an .cube file in post.

If I was to just load a .cube file in post, then it would make no sense to do that as I could simply save the image with all corrections on from the VFB.

But the reason I need to break down every single step in post is that I want to make other changes before or in between these steps/corrections: I need to apply masks to different objects on the raw(32 bit image), etc.

[peteristrate]

Hi guys,

Alexander Yolov(QA specialist at ChaosGroup) answered my question and the correct order is as follows, from top(first) to bottom(last):
- levels (first)
- white balance
- exposure
- curves
- HUE saturation
- color balance
- background image
- LUT
- sRGB
- ICC
- OCIO

Then I went on to do some tests, as seen in the image attached.
And I went on comparing the result in the VFB with the result from Fusion(compositing software).

1.First, on the Left: A and B comparison in red color:
And I compared the:
- VFB with exposure(highlight burn) + sRGB applied
vs.
- Fusion:32bit raw image + exposure Corona highlight compression(which is the same with Vray highlight burn) + sRGB.
The results were perfectly identical as seen on the left view when comparing A and B.

2.Second, on the Right: A and B comparison in yellow color:
And I compared the:
- VFB with exposure(highlight burn) + LUT + sRGB applied
vs.
- Fusion:32bit raw image + exposure Corona highlight compression(which is the same with Vray highlight burn) + LUT + sRGB.
The results were NOT identical as seen on the right view when comparing A and B.


I made sure there are no Fusion importing errors/different settings that could affect the imported images and LUT.
Please let me know if the test above makes sense.
Is this a Vray bug in how it saves/displays the image with the LUT on?

P.s.: if you want to test this yourself with a compositing software, then it has to be one that supports 32 bit images like Fusion or Nuke.
You cannot test this with Photoshop as it doesn't support 32 bit images.

[Svetlozar Draganov]

From what I can see the difference comes from the added LUT file right? It looks like Fusion and VFB applies that LUT file differently.
Can you send us output files along fusion comp and LUT file so we could investigate what's going on.

Let us also know if you already did a similar comparison between Nuke and VFB or Nuke and Fusion.

[peteristrate]

Ok, I'll post this on google groups(bug reporting group for Vray GPU).
I haven't tried Nuke as we don't have a license for that.

[yolov]

We'll check in with the devs for more info and get back to you once we have anything useful to share.

[peteristrate]

Cheers, guys!
I hope it's just my silly understanding of the process and that I missed something in the process. But better to be wrong than not to be aware of a potential bug