FS700 + 07Q Accurate Color Processing

J

jcs

Veteran
I have an FS700 + Nanoflash (undecided re:O7Q) and have been working with 5D3 RAW in Resolve and ACR. I've been reading and watching FS700+07Q videos and see that there are issues with color calibration, purple fringing, etc.
From working with 5D3 RAW, my understanding is that Resolve takes the linear data and converts to a colorspace and gamma as a first step. I was able to get the most accurate results by using Rec 709 colorspace and gamma and manually setting white balance and tint by eye to match known lights and scene colors. Even when matched somewhat closely this way, adjusting the luma curve, for example causes incorrect color shifts. Adjusting luma should only affect luma- colors shouldn't shift (much), right? I wrote a custom interactive 3D color corrector a few years ago, allowing direct manipulation of an XYZ RGB colorcube*. What this issue reminds me of is instead of the cube being properly aligned/rotated with respect to RGB colors, it's off, so that when going in the direction of increased color intensity (luma/brightness), the direction is off, and instead of all colors going up as expected the colors shift incorrectly. This is worse if the effective color cube is warped. So minimally it looks like a matrix (linear transform, not lossy) is needed and possibly a 3D LUT (non-linear transform, possibly lossy; don't need both).

Reading the docs here: http://www.convergent-design.com/Portals/0/Odyssey/docs/FS700Raw_PostWorkflow.pdf I see BMD Film is recommended as the colorspace. My understanding is BMD Film takes the linear raw data and converts to a log like, but not actual log color space ( http://www.bmcuser.com/showthread.php?2306-Cineform-Raw-BMD-Film-Curve ).
The next step is to use one of the supplied 3D LUTs:
FS700_Linear_SLOG_2
FS700_Linear_709​
The names seem to imply a linear starting point, however BMD Film isn't linear- it's 'almost log'. I understand this is a new product, and things are still being refined- is that why these are called "simulated log/Rec709"? It would appear you'd want to start with actual linear data before applying a 3D LUT to a calibrated colorspace? Canon raw looks really good processed in ACR- if there's a way to get FS700 footage looking like that with little effort (especially skintones), that would be a win (one way would be with a calibrated 3D LUT).


* similar idea as this app, which looks very cool: https://www.facebook.com/groups/3dlutcreator/
 
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There is a bit of confusion right now what the best method is, i think we're all finding our feet with DNGs, I've spent a lot of downtime looking and i'm still not there yet.

You'll see from the release notes that the recommended workflow is to set the decode to CinemaDNG which generates a linear result and then either grade from that or use that as a basis to convert to whatever you want. CinemaDNG for the most part just 'works'

However there is a bit of a question right now as to how to move on from that step - the supplied LUTS appear to have some colour issues.

Two routes worth investigating

If the CinemaDNG output is true linear then you could use the other LUTs that resolve has to move colourspaces - in the VFX menu there is an accurate Linear to Slog2, however the ranges that expects aren't quite the same, so you'd need to experiment with adjusting exposure first. Resolve seems a bit odd when bringing in files, even Linear, in that you have to range down the super brights. Resolve is a grading app, not a technical utility.

You could also try running Resolve in ACES mode and then use the cinemaDNG input transformation. Eyeballing this seems to produce more natural and accurate colours but again the overall dynamic range looks a little off.

I'm not sure any of these issues are down to the files the O7Q produces, it's much more about navigating the wild west of DNG processing.

You are right in that if you process the DNGs via BMD Film, then that is producing a log output - you can take that and grade from there but you cannot pop a linear to anything LUT on it and get correct results.

Also it's worth remembering that a lot of LUTs will clip. The SLog2 is technically a curve but i don't believe Resolve uses curves in this way, i don't think you can enter an expression for the curve. If you want the full details of the curve then OpenColourIO holds the best references (OCIO)

cheers
Paul
 
Hey JCS,
I was just about to start a new thread, but then saw this one... so I'll add what I was going to post to yours, as they are on a very similar path aiming for a calibrated 3D LUT of some sort (albeit you are much more technical than I am)!


So, I could very likely be missing a single simple step, but I have checked over everything, and can't seem to find an error. I've dealt with .R3D raw before, but not as much with Resolve or Linear raw files.

Importing any 7Q/FS700 raw files, they are super dark. Now I know this: "Note that FS700 Raw files are Linear, thus the files need a Gamma 2.2 correction in order to look correct, as you may notice when you first import your files, they may appear very dark before being corrected." Following the recommended FS700 Davinci Resolve Import Settings (copy/pasted below), I get a totally crushed image that isn't worth trying to save.

My question: is there a way to correct the gamma without using the CD FS700_Raw_Slog LUT? Is there a way to give the needed Gamma 2.2 correction from Linear all by itself? I find using the previously recommended "BMD Film" Colour Space & Gamma settings with the exposure set to +3.00 looks perfect for starting a grade without any LUTs, but the big exposure boost really brings out a lot of noise and grain. Alternatively using the Gamma adjustment in resolve works sometimes, but it seems to wreck havoc on the footage (makes it look just like 8-bit compressed and colours get awful).

The CD FS700_Raw_Slog LUT works OK, but I find it much too log-like for the majority of my shots, and end up squashing it back more towards where it came from originally.

CD's reccommended FS700 Davinci Resolve Import Settings (that don't seem to work at all??)
1. Right click on the file and select “Edit Cinema DNG Codec Settings”
2. Then under the CAMERA RAW select be sure CinemaDNG is selected from the drop down
menu.
3. Set the Decode using method to CinemaDNG Default* (Also be sure your project is setup
correctly)
4. Set the White Balance to As Shot
5. Set the Color Space to Rec709
6. Set the Gamma to Rec709
7. Leave Highlight Recovery off
8. Click Apply


Anyone have a workflow/settings/Gamma Correction LUTs/etc that work well as a baseline? Or can anyone point me in the right direction? I feel like I must be missing a single step, as no one else has really commented on this so far. (*Unless this is at all related to the discussion I read about possibly shooting at 2000ISO but lighting/exposing for 640iso, to get the cleanest image possible?)
 
Dbatch

Are you just trying to grade the files in Resolve or convert them?

The CinemaDNG should give you a linear image to start from. I don't think there's a button that will set a 2.2 gamma as default but the gamma controls would achieve the same thing by eye. You can just grade using the primary controls and all should be well in the world. Grading from Linear is absolutely fine.

There is a separate question about shadows and noise from the FS700, a LUT isn't going to do anything magical that the normal controls in Resolve won't handle.

There is a difference of opinion about exposure and i'm trying to answer those questions for myself.

But from an image perspective going from linear and grading should give you good results?

cheers
Paul
 
Paul- I linked PDF from CD's site- isn't that the latest?
FS700 Davinci Resolve Import Settings

Once you have imported files into the media pool be sure to check the following Settings:

1. Right click on the file and select “Edit Cinema DNG Codec Settings”.
2. Then under the CAMERA RAW be sure CinemaDNG is selected from the drop down menu.
3. Set the Decode using method to Project (also be sure your project is setup correctly) .
4. Set the Color Space to BMD FILM.
5. Set the White Balance to As Shot.
6. Select Highlight Recovery.
7. Click Apply.

For your convenience, Convergent Design has generated several example LUTs that can be applied to your RAW
footage. Keep in mind these LUTs are general approximations, and may need adjusting depending on your
application.​

I see Dbatch posted another example from CD which used Rec709, etc...

I don't see a way for Resolve to provide linear output from those raw settings, unless perhaps using CinemaDNG for Decode Using. One area of confusion is that when CinemaDNG is selected for Decode Using, then all the other options are grayed out (can't do steps 4-6). So, if they meant to use CinemaDNG for Decode Using + their 3D LUT (either log or Rec 709), and not BMD Film for colorspace, that would make sense (provided they are starting from linear colorspace).

I was able to get decent results with 5D3 RAW using Decode Using: Clip, then setting White Balance to Custom, Color Space & Gamma to Rec 709, then adjusting Color Temp, Tint, and Exposure by eye. This should work with FS700 footage, but it won't be calibrated, and is a bit of unnecessary work. Ideally, Decode Using CinemaDNG default and a 3D LUT should be all that's needed for correct results (again, provided CinemaDNG is outputting linear). Does CD (or anyone) plan to create a calibrated Rec 709 vs. simulated?

Dbatch- I believe the reason the colors get awful is the wrong colorspace is being used (and/or a calibration issue). That's why it's important to have a calibrated Rec 709 path if possible. Once we know that we can get a good Rec 709 (because we can compare to the scene/color chart shot), making a log conversion for export makes sense (ideally with a custom 3D LUT vs. another Rec 709 to log 3D LUT).
 
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jcs said:
Paul- I linked PDF from CD's site- isn't that the latest?
FS700 Davinci Resolve Import Settings

Once you have imported files into the media pool be sure to check the following Settings:

1. Right click on the file and select “Edit Cinema DNG Codec Settings”.
2. Then under the CAMERA RAW be sure CinemaDNG is selected from the drop down menu.
3. Set the Decode using method to Project (also be sure your project is setup correctly) .
4. Set the Color Space to BMD FILM.
5. Set the White Balance to As Shot.
6. Select Highlight Recovery.
7. Click Apply.​
Click to expand...


it's from the previous Firmware. see at the bottom of the page: 14- Nov-2013
C-D should fix this quite soon!

Have a look in the set up guide which is in the folder your downloaded with the FW

page 10:

FS700 DAVINCI RESOLVE IMpORT SETTINGS
1. Right click on the file and select “Edit Cinema DNG Codec Settings”
2. Then under the CAMERA RAW select be sure CinemaDNG is selected from the drop down menu.
3. Set the Decode using method to CinemaDNG Default* (Also be sure your project is setup correctly)
4. Set the White Balance to As Shot
5. Set the Color Space to Rec709
6. Set the Gamma to Rec709
7. Leave Highlight Recovery off
8. Click Apply


​
 
Clermond- when CinemaDNG Default is used, steps 4-7 aren't available. If you do step 3 and use the CD Linear to Rec 709 LUT, does it look correct?
 
If you switch to CinemaDNG then the ColorSpace and Gamma are overridden. It is confusing (Resolves fault)
If you set CinemaDNG up in your project settings then you can just Use Project and everything is greyed out.

If you need to manually adjust whitebalance then you have to set it to clip and the gamma options are un greyed but they do not do anything. Only the white balance does.

Highlight recovery does not need to be ticked either. I never understood why that checkbox exists, i asked BMD but nothing was forthcoming. I have noticed some debayer artefacts i the highlights in resolve though.

hope this helps
Paul
 
jcs said:
Clermond- when CinemaDNG Default is used, steps 4-7 aren't available. If you do step 3 and use the CD Linear to Rec 709 LUT, does it look correct?
Click to expand...

off course it is.
3. Set the Decode using method to CinemaDNG Default* (Also be sure your project is setup correctly)
Click to expand...
Either in project settings "camera RAW" or switch to clip and do it there.
 
paulcurtis said:
You could also try running Resolve in ACES mode and then use the cinemaDNG input transformation. Eyeballing this seems to produce more natural and accurate colours but again the overall dynamic range looks a little off.
Click to expand...

I think the ACES route is a non-starter for the RAW footage. I had a look and everything came out slightly too red - indicating the IDT is wrong for the footage, which sort of defeats the point of ACES. It does seem to work quite well for the 4K to HD footage though, using the Slog2 IDT gives quite a nice result, certainly better than the 1D LUT supplied by Resolve, or the Sony LUTs (probably because they assume footage shot on the F55 in SGammut)

Currently the best results I've had so far are using DaVinci RGB and applying the CD Linear_709 LUT. I'm not sure what's up with the 'latest' LUT they provided, but it is simply awful - the original Linear_slog2 LUT works a hell of a lot better (if you're making Slog2 proxies).

You can see this clearly by applying the CD 3D LUTs to each clip then adding Slog2toRec709 1D LUT on top at a node - the 'updated' LUTs are way off what they should be it seems.

Ideally Sony and/or CD will develop a proper ACES IDT for the DNGs from the O7Q (like Sony have for the Sony Raw files) that way we know we're getting the very best out of this camera. Although I honestly have no idea how you'd go about doing that.

However I suspect CD are a touch busy at the 'mo gearing up for NAB.
 
Can any of you guys supply some daylight CinemaDNGs for me to check out/suss out in R10? I might be able to help.
 
Dbatch said:
Kholi, has anyone sent you a few frames yet? If not, I can run out a shoot a few daylight frames for you.
Click to expand...

Not yet. That would be great. I've been dealing with this workflow for a while in various forms, and finish CDNG often. Have spotted a lot of problems on various cameras, been able to get them into an ACES workflow without an existing transform.

It may not happen here, but I'm down to try. The images I've been seeing are encouraging.

kholi dot hicks at gmail dot com

Skin, red, and blue = good to assess
 
paulcurtis said:
If you switch to CinemaDNG then the ColorSpace and Gamma are overridden. It is confusing (Resolves fault)
If you set CinemaDNG up in your project settings then you can just Use Project and everything is greyed out.

If you need to manually adjust whitebalance then you have to set it to clip and the gamma options are un greyed but they do not do anything. Only the white balance does.

Highlight recovery does not need to be ticked either. I never understood why that checkbox exists, i asked BMD but nothing was forthcoming. I have noticed some debayer artefacts i the highlights in resolve though.

hope this helps
Paul
Click to expand...

Re Highlight Recovery box:

It works, however, only best when there's an even "clip". If green goes too fast, you get pink artifacts.

I still believe LR4 handles the top end of a very harshly exposed frame better than Resolve, but it can be fixed.
 
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