Blackmagic Forum

Hello there,

Sorry if this has been asked already!
My question regards this:

I have Open EXR sequence files exported from Nuke. 16 bit, linear workflow.
When I load the these files into AE, they look the same as in Nuke.
When I load the files into Resolve 8 or 9, they look way too dark.

And this is some reply:

¨After a lot of LUT testing we essentially gave up. Even when we were able to create a LUT workflow that matched the initial frames pretty closely, when we did any grading it simply fell apart - blacks would be grey mush when pushed up and highlights would have casts/banding. We also found that adjusting anything lacked the fine control feel of grading any other type of file in DaVinci.
Failing to find any definitive reason for the problem in the end I assumed the OpenEXR support was a bit premature and we transcoded everything to 16-Bit TIFFs, which worked beautifully.¨

Is there a fix for this?

Thank you very much!

Is there a fix for this?

It is called: Color Space Management.

In Nuke it looks "right" because you have the Color space setup as "linear/RAW"EXR and your monitor environment as "sRGB" hence the Nuke will so a implicit color space transformation.

For more info read:

http://forum.blackmagicdesign.com/viewtopic.php?f=3&t=7546

So, do I have to apply a LUT?

errr.... yes.

you need a 1D lut that map the photometric linear light of your material to the Gamma of the color space you wish to finish ( either rec709/BT1886 or an intermediate color space like Slog ) as your first input LUT in the first node...

If you want to go back to NUKE after color you also want the opposite LUT for re-export.

This is and example of the nodes you might build (top is input bottom is output) (no LUT applied in this case for the visualization)

[resolve shot from the SAN]
[node 1, input LUT: from_linear_light_to_sRGB]
[still in node 1: color as you like]
[ add as many node as you want ]

and you are monitoring in [sRGB] without [display LUT]

when ready to export the shot back to NUKE, make a global LUT for output only that will do
[from sRGB to linear_light]
and export the shot/shots you need.

The [from_linear_light_to_sRGB] and [from sRGB to linear_light] can be generate in NUKE and with a bit of Xcell massage load them in Resolve.

This will color the shot in sRGB color space, not in linear_light.

If you have correct ACES IDT/ODT, that is another viable path, but you have to build IDT and ODT that match the linear-to-sRGB of NUKE to be able to color in a similar linear light AND viewing correctly.

and BTW, i would like someone from BM to show us how to do that... so I can replicate here

Thank you very much for your reply.

I´ve just did some similar workflow:

I´ve exported a LUT drom Nuke (linear to sRGB) and applied it in Davinci.

Here´s some example:

http://forums.creativecow.net/thread/277/15766

Yep, that works.

I'm checking to see if a linear-to-ACES LUT is build-able and usable because the ACES color space will retain the highlight much better that the one mentioned in a roundtrip case...

Let see if we can empirically improve the ACES workflow.

The EXR linear that you have are images that either are created from scratch (CGI) or they are camera capture file that has been converted. I'm curious to understand which ones they are.

I started with doing some internet research and I talked with Joseph Slomka (our Color Science guru and one of the ACES minds behind it) and this is the summaries of what we came out with:

Giving that ACES is a very wide triplet of XYZ values that can encompass all the color you can possibly see (and more outside of the boundaries ) and that the representation in the ACES EXR is in substance a photometric linear light, given that the image is from EXR in NUKE, is already photometric linear in substance as well, the main differences are:

-tonal range mapping
-RGB gamut mapping.

The former is tricky, the latter is more trivial: make a 3x3x3 matrice that map the RGB(Yxy) of your current color space (sRGB/rec709/P3DCI/ any) to the ACET triplet using the method described in the SMPTE RP177 (you can find the triplet here: http://www.oscars.org/science-technology/council/projects/pdf/ACESOverview.pdf).

Ig you can give me some more info on your starting gamut (Yxy coordinates of RGB and W point) I can probably help you to build a 3x3x3 matrice

The tonal range is an evolving representation on the output of the image (I had a brain fart when he was explaining to me) HOWEVER for the practical purposes of your workflow, you CAN safetly assume that is a 1:1 representation.

so,

if you load the EXR as is in the resolve, setup teh ACES workflow and chose the display color space as rec709 (assuming that you have rec709 display) the density/tone of your signal should be ok, the color will be desaturated/whacked. (Unless Nuke 7 can map ACES directly)

Your next task is to make your IDT/ODT as simple as build a 65x65x65 LUT where the math inside is the 3x3x3 matrice above mentioned and it's inverse to map the gamut of your current color space to ACES and viceversa. This LUT is your implicit IDT and the second is your implicit ODT that you will have to apply as 3D lut in input (select in resolve the shots and apply input lut) and 3D lut in output (export with the ODT lut "baked in"). You can definitely build the LUTs in Nuke. The method is displayed in the SMPTE RP177 color space transformations: you need excell to build the math and you will have the 3x3x3 at the end...
\


Tell me where I lost you...

Walter,
You're no longer exclusive to Quantel User Group! Glad I can seek your enlightenment here as well.

cmart400 wrote:Walter,
You're no longer exclusive to Quantel User Group! Glad I can seek your enlightenment here as well.

Hi Chris!!!

Yes, I b****h wherever I go...

Hi Walter thanks for the insight into this workflow, one question further.

What I'm doing is my client sent me 16 bit .exr files from Nuke, im using liner to srgb lut to compensate for the gamma curve , I do My corrections and I want to send a lut of my work back to the nuke vfx editor to match back, the issue is my luts I export do not match when imported to nuke.

Do you know the workflow on this.

thanks in advance.

Greg White wrote:Hi Walter thanks for the insight into this workflow, one question further.

What I'm doing is my client sent me 16 bit .exr files from Nuke, im using liner to srgb lut to compensate for the gamma curve , I do My corrections and I want to send a lut of my work back to the nuke vfx editor to match back, the issue is my luts I export do not match when imported to nuke.

Do you know the workflow on this.

thanks in advance.

Lots off things can go wrong, but for sure a 3d lut is not dense enough to describe whay you want. There is too much change in the gamma to be precise.

waltervolpatto wrote:for sure a 3d lut is not dense enough to describe whay you want.

I tend to agree, the step-density of most LUTs is not enough to cover this bit-depth. You really are looking at a color management approach using a calculated transform. Probably ACES and pick a camera linearization mode (IDT: ie 709(Camera) or even Rec2020(Camera)). If you are exchanging EXR, there may be a problem with value ranging RGB / Linear, so check that out first... that you are not erroneously re-mapping "0-1023" as "64-940." Or vice-versa...

jPo, CSI

It's so complicated for nothing.

How come a color grading software can't interpret exr in linear?

Wouldn't it be more simple to just add this simple feature in Davinci ?

Almost all VFX house are working in flat linear exr, but it seems that most people outside vfx house doesn't know that for some reason ?..?..?

There are few explanations on it too.

I've tried every forums and supposed solutions, but nothing worked. There's still a difference from nuke to davinci.
This problem is still a thing after 8 years !! How come nobody fixed this ?

It's so strange.

I think it's time for someone to write a manual on how VFX house work and operate.

MD

Maxime Desforges wrote:It's so complicated for nothing.
How come a color grading software can't interpret exr in linear?

First thing is to understand what is happening to image data in specific software, then you can figure out how to emulate one software in another. What kind of color management system are you using in Resolve and with what settings? How are you interpreting the exrs in Resolve? What is (if there is) the problem with using 1D linear > sRGB LUT?

Color management in Resolve is a bit different from Nuke, whether it makes more sense or less depends on which side you look at it from.

Maxime Desforges wrote:It's so complicated for nothing.

How come a color grading software can't interpret exr in linear?

Wouldn't it be more simple to just add this simple feature in Davinci ?

Almost all VFX house are working in flat linear exr, but it seems that most people outside vfx house doesn't know that for some reason ?..?..?

There are few explanations on it too.

I've tried every forums and supposed solutions, but nothing worked. There's still a difference from nuke to davinci.
This problem is still a thing after 8 years !! How come nobody fixed this ?

It's so strange.

I think it's time for someone to write a manual on how VFX house work and operate.

MD

It can, wet have DCTL that match the white paper of a given camera and convert mathematically to and from linear light ti e log.