Normalizing Log to Rec709

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Marko Garafulic

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Normalizing Log to Rec709

PostSat Sep 02, 2017 3:00 am

Hello everyone,

As I'm learning how to work with Resolve to grade footage from my BMCC, I've been practicing how to use Resolve's Log controls to grade log footage and have also been testing LUTs that are designed to normalize log footage.

Several of these LUTs appear to be specifically designed to normalize the footage to Rec709 (e.g. Blackmagic Cinema Camera Film to Rec709).

My understanding is that:
- Video mode in the BMCC records in Rec709.
- Shooting in Film mode (i.e. log) yields higher dynamic range than shooting in Video mode

Does applying a "film-to-Rec709" LUT to log footage essentially negate the increased dynamic range that one might've gained from shooting in Film mode to begin with? In other words, is the result similar to having shot the footage in Video mode to begin with?

Or does log footage with a "film-to-Rec709" normalizing LUT still retain detail / dynamic range that might not have been captured if the footage had been shot in Video mode?

Thank you,
Marko
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Dmytro Shijan

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Re: Normalizing Log to Rec709

PostSat Sep 02, 2017 1:53 pm

Here is my current workflow which describe earlier in different places.
Generate custom 1DLUT in LUTCalc https://cameramanben.github.io/LUTCalc/LUTCalc/index.html
As Out Gamma use Amira709 because for my subjective opinion it it gives best result. (You can also try Alexa-X-2 and LC709/A made by Sony as well)
For color gamut transformation i use native Color Space Transform node in Resolve. In Resolve 14 beta they add New Saturation mapping to Color Space Transform node. This is great feature that finally helps to remove hard saturation clipping in extreme values. So i generated 3DLUT in beta 14 and use it in older version of Resolve. To generate those LUT you need to use trim_lut0.dpx (search on youtube how to use it)

So i set my input to BMDfilmBMDfilm, set timeline for example to Rec2020 with Cineon gamma.
Apply Cineon to Amira709 1DLUT, next apply color space transform LUT.
Do all my grade in log gamma and in wide color space BEFORE transformation luts, but see final result in realtime in Rec709.
AFTER transformation LUT you can apply regular film emulation LUT and add luma sharpen. As a film emulation LUTs i use free GMIC Film Emulation collection converted from original HaldCLUT to .cube format to use in Resolve.


If someone interested here is folder with luts
https://www.dropbox.com/sh/5sugnzr3sx21 ... 9Ysba?dl=0

And it is better to understand all global LOG concept, this is more complicated than just use tutorial.
In chain "log-to linear -> expose -> linear to log" gain wheel acts exact same as exposure(iso) slider in raw. Sometimes it may be useful even when work with ProRes source.
In addition i can only suggest uncheck "Use S-Curve for Contrast" in Resolve project color settings when work in LOG. Just because thats how contrast works in LOG.

P.S. all tools became different in log timeline. There are a lot of tutorial videos explain in details how to use tools in log timeline. For example tutorials about working in Sony Vegas and ACEScc log.
Actually in Resolve with LUTs and color space transform tools you can exact same workflow as with ACES.
BMMCC/BMMSC Rigs Collection https://bmmccrigs.tumblr.com
My custom made accessories for BMMCC/BMMSC https://lavky.com/radioproektor/
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Andrew Kolakowski

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Re: Normalizing Log to Rec709

PostSat Sep 02, 2017 4:00 pm

Marko Garafulic wrote:Does applying a "film-to-Rec709" LUT to log footage essentially negate the increased dynamic range that one might've gained from shooting in Film mode to begin with? In other words, is the result similar to having shot the footage in Video mode to begin with?



Yes, it does, but because Log footage holds more usable data is allows you easier pick what you want for final Rec.709 look. You can't always get perfect shot (exposure etc), so in case of Rec.709 recording you have way less headroom to play with.

There is also now HDR which allows you to use your recordings in more optimal way.
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Marko Garafulic

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Re: Normalizing Log to Rec709

PostSun Sep 03, 2017 1:32 am

Thank you Dmitry and Andrew.

Andrew: I think you're saying that there is an advantage to shooting in Film mode even if you use a normalizing LUT to convert the log footage to Rec 709, correct?
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Andrew Kolakowski

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Re: Normalizing Log to Rec709

PostSun Sep 03, 2017 3:46 pm

Yes and this is a common practice and one of the reasons why pro Rec.709 masters looks so good. They were done from Log (quite often RAW) sources which had tons of useful data so colourist could make a best possible Rec.709 master.
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Marc Wielage

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Re: Normalizing Log to Rec709

PostMon Oct 02, 2017 5:44 am

You can do it completely without LUTs if you simply take the Log image and then in one node, use a custom curve in an S-shape to bring the blacks down, bring the mids down, and adjust the whites back up. I generally will use some Offset control as well (sometimes in a second node) along with a saturation boost in order to normalize the signal. The advantage of doing it all by hand is that you can compensate for exposure and color temperature issues, particularly in sub-optimal conditions.

You can compare the results using Versions in Resolve and just drop in the normal Blackmagic Rec709 LUT to compare the overall effects. It helps to shoot camera color charts so you can more precisely see where everything winds up on the vectorscope.

The basic tutorials available from MixingLight.com, RippleTraining, and FXPHD all go over this stuff in great detail.
marc wielage, csi • VP/color & workflow • chroma | hollywood

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