VFB LUT Export doesn't work

[JonasNöll]

Hi,

I am having following issue, and maybe I am doing something wrong, but pls clarify:

- I export all the CC adjustments in the VFB as a .cube LUT file via the "Save all CC as LUT" function in the VFB
- Open the 32 Bit EXR in Photoshop
- Load the previously exported LUT
- Colors now match for the most parts but the highlights get greyish and clamped

What is the correct workflow to replicate the colors in Photoshop? The issue also exists with PDPlayer and result looks equally wrong like in Photoshop.
Basically the desired workflow is to add all renderelements (lighting, gi, spec, etc.) in Photoshop and then in the end should have a LUT so that it looks identical to the rendering in the VFB.

Attached 2 images to demonstrate the issue. Notice in Photoshop all highlights turn greyish and seem clamped.

Thanks

[JonasNöll]

Here is another example:

[olly]

Hey Jonas,

Are you using the filmic tonemap in your layer tree?
We have found that this layer does not translate as expected within a LUT.

Not sure if it is a bug that Chaos can fix or a limitation of Photoshop.

Cheers
Olly

[JonasNöll]

Hi,

thanks for your reply. Indeed I am using filmic tonemap, but I just tried to just put only an exposure and curve cc adjustment instead and I am having the same issue.
The colors always seem to match but as soon as something reaches a certain brightness it always clamps to grey.
As said same issue in Photoshop or PDPlayer (which is from Chaos), so I assume it's not a Photoshop problem but rather something that wrong with the exported LUT or my workflow
So you can generate a LUT an get identical results in Photoshop as in VFB even in the bright parts?

[olly]

Yes, we routinely save the LUT and apply it in Photoshop for identical results, both with V-Ray Next & V-Ray 5.

I have attached a zip containing a VFBL and the exported LUT so you can test at your end.
Let me know if the results match on your environment.

[JonasNöll]

Hi, thanks for your files. I tested and I initially get identical results with your CC settings and the provided LUT.
The problem is that as soon as I put the highlight burn value in the exposure slider below roughly 0,5 I will get these grey clamped highlights again when I export a LUT, while it looks fine in the VFB.

So it seems to me that if one is trying to compress the dynamic range either with:
- dicreasing the highlight burn value in the exposure CC and/or
- using the filmic tonemap

then those adjustments are not correctly transferred into the LUT and the hightlights are getting clamped. I think the procedure to compress the dynamic range is essential during the tonemapping procedure to get photographic results.

Is there any way to prevent this from happening?

[olly]

Thanks for reporting back.

Could you attach your VFBL so I can take a look here?
DM me if you would rather not make it public.

[JonasNöll]

Hi,

sure, attached you can find:

- Exported linear EXR without any colorcorrections
- PSD that uses this file with the created LUT file
- JPG as how the image should look like according to the VFB
- LUT and VFBL

Edit: Seems can not upload it to the forum: DIRECT DOWNLOAD LINK

Let me know if you have the same issues

[olly]

I get the same discrepancy as you with your example files.

Can you expand on the theory for setting the highlight burn to 0 - is that a normal production setting for you?

[JonasNöll]

Hi, so for propper tonemapping this step is quite essential:

Basically you are reducing the dynamic range of the linear image to something that can be displayed on your monitor. There are various ways to do this but the minimum tonemapping prodcedure would be to reduce the highlight burn (with 0 being for images with an extreme dynamic range, other images might be fine with much higher highlight burn values). This step will bring the colors/intensities in something that can be correctly viewed on your monitor. Since reducing the highlight burn value will naturally also flatten out your contrast the next step would be to bring the contrast back by using for example a curve correction or a lookup table.
So from my perspective there is hardly any project where I would not touch the highlight burn value, or use the filmic tonemap (which does this internally).

All of this works flawless in the VFB but somehow the transformations are falsified when saving out the LUT file from VFB.

[piotrus3333]

Photoshop can not access anything above 1.0 with color lookup adjustment layer.

[piotrus3333]

If Highlight Burn is your starting point for tone mapping it's easy:

[JonasNöll]

@piotrus3333: Awesome, I think with the approach in your video it seems to eliminate those issues.
The requirement would be that the highlight burn is at the very bottom of the stack. Then, in order to save out the LUT from VFB you would need to disable it and then in Photoshop recreate it by using your ChannelMixer approach. Then load the previously exported LUT on top of it!
Do I see this correctly? From the test I did so far seems it works!

So far so good! But how if using Filmic Tonemap, I think in this case there would be no such easy fix for that or?

[piotrus3333]

you can check Reinhard2Filmic luts I posted in that thread.

try with Filmic with white point 1.0 on top of Highlight Burn

or just use curves on Highlight Burn. you will get the same result.

[kosso_olli]

Do I see this correctly? From the test I did so far seems it works!

Although this trick is working, I'd rather have it fixed by the developers.