Why LUTS for S-Log Grading and not your eye?

[MikeOfBonsall]

I don't understand why all the workflows for grading the S-Log footage require a LUTS. Why can't you grade with the scopes and your eyes just like any other video?

[cws]

My opinion only.... I think the choice of using a lut or grading by eye (with scopes) pretty much comes down to whether you understand what an S-log curve (or any other gamma adjustment) you invoke on capture is doing to the image, and whether you want a "technically correct" conversion to undo that curve in your grading system before working the images.

I would imagine that most users of more basic video systems (like the Alpha's) are happy to work by eye to get a pleasing result...  but any result is also going to depend on whether you've got an accurately calibrated monitor/TV to start with...

So if you are used to using scopes/waveforms, RGB parade's whatever... then you probably know what to expect from the image and how to adjust it without a LUT.

 

On the other hand, if you are on a paid project trying to combine images from multiple sources, its usually better technically to invert any capture gamma back to a common point (linear?) before grading.

There's no hard and fast rule.... sometimes its going to depend a lot on the project, your normal workflow, who is paying for a result at the end, what their expectation is and how hard you want it to be to meet that expectation.

 

whatever works best for you...

[nomad]

Specific LUTs make it much easier to work with Slog2, it's pretty difficult to get the colors right by hand, since Slog2 has some non-linearities.

Other log formats are easier, but I'd never recommend Slog3 on a camera with 8 bit only.

[MikeOfBonsall]

Thanks I get this now. But as SONY put S-Log2 on their camera why do they not give an official anti-dope to unravel it? Why do I have to negotiate with a bunch of third parties touting LUTs?

[flord]

Be careful what you wish for...

If you want to know how to unravel it... you can read the official s-log2 technical paper. 

https://pro.sony.com/bbsccms/assets/files/micro/dmpc/training/S-Log2_Technical_PaperV1_0.pdf

 

With the formulas, you can convert from s-log2 to linear and back. But do you know how to handle linear data?

 

If you want to create your own LUT the proper way, you must convert from s-log2 to linear, you convert the gamut from s-gamut to BT.709, you convert back to log, you apply an s-curve (dynamic range compression), you add a gamma for REC.709 display and you bake the whole thing in one 3d lookup table file. 

 

Once you have that file, grading s-log 2 becomes very easy and always produces natural looking images. 

If you don't want to build your own LUT, you can use an OCIO compliant software to grade, and use the official ACES config, which contains the proper settings for all s-log curves and gamuts. 

 

Using a properly built LUT makes a huge difference in grading. 

[MikeOfBonsall]

Flord: Thanks and very interesting, but I  asked why are S-log2 LUTS only available from third parties all of which seem to be different? Why does Sony not offer downloadable generic LUTS to match their log curves as a starting point for grading to the desired style?

 

ALSO I saw a video a few days ago that I can not now find (and YouTube history does not have it?) that reviewed some LUTS for the A7 that were reported to be very good and cost only $10. Does anyone know who they were talking about? ALSO where are the reviews of the FREE LUTS that are available online?

[flord]

Hey Mike, 

Tell me what LUT format you need, I can make you one you will love, based on that paper I sent. 

[cws]

Try the free version of Resolve, it should have what you need to invert s-log.. although there will be a learning curve...

[MikeOfBonsall]

OK guys - thanks- and since asking that silly question I have learnt a lot! Found out I have a Sony2 LUT in my Resolve. Duh!