S-Log Sample, colored in Davinci

[Leonard Levy]

Originally Posted by Alister Chapman

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The .cube luts are 32 bit floating point 3D LUT's with 128 samples. As the original F3 LUT's are 1D these only perform a 1D transform.

Well.. At risk of exposing my technical inadequacies I have to ask again if that means they're 10 bit. I think 32 bit floating point implies 10 bit doesn't it? but what about 128 samples, is that enough? Do I have any idea what I'm talking about?

[Alister Chapman]

The original 1D sony LUT's give a single in and out value for each bit of RGB data. So for an 8bit file or 8bit environment you need an 8 bit LUT, and 10 bit LUT for a 10 bit file. Taking 10 bit as there are 1023 values for each of R, G and B channels then there a total of 1023 x 3 values in the table = 3069. That's not a big file.

A 3D LUT works differently. As a 3D LUT transforms not only the RGB level values but also the saturation and phase values there are many more values in the table. In addition on the input side it works on RGB triplets, so it' not just looking at say the red input value, but the combined red, green and blue value. So a full 10bit 3D lot would have 1023x1023x1023 input values each input value could give any one of 1023x1023x1023 output values, so the table would be impossibly large.

As a result 3D LUTs only have a much smaller number of samples, in the case of a .cube LUT, there are only 128x128x128 input and output samples. As there are fewer samples than there are bits of data the table no longer refers directly to data bits and instead works on % values. For example when the input value = 2% the output is transformed to 4%. As a result it does not matter whether the material is 10 bit or 8 bit. 32 bit floating point is just a measure of the accuracy of the transformation in terms of the number of decimal places used in the multiplier values in the table.

So a .cube LUT does not care whether the material is 8, 10 12 or even 16 bit. It should work in LUT Buddy and resolve.

[Leonard Levy]

Thanks again Alister, I think I understood that.

With the help of everyone here I've been able to progress a lot further in learning how to grade SLog in Final Cut Pro effectively. The LUT's look way better than what I was able to do with the 3 way. Again, for the time being I want to stay in FCP because I know that's what many of my clients use and I want to be able to give them a clear and easy path to grading SLog.

A number of questions remain for me though. So I'll summarize what I've figured out so far & then ask a couple of questions if anyone is still awake or interested.

Now I'm finding an embarrassment of riches in the choice of LUT's to use.
So far Using LUT Buddy free from Red Giant :
- Alister has provided 4 that are the Sony 1D LUT's ,
- you can download Alexa LUT's also and configure them in few different ways with more or less highlight and shadow roll off,
- There is a technicolor LUT designed for the Canon's that works with LUT Buddy ( seems very dark though)
- and you can make your own using LUT Buddy and Colorista free in AE then import the LUT into FCP.

Additionally you can download Natress "Curves and Levels" for $50 and make your own though it only allows you to change the curve at 5 points 0 , 25%, 50%, 75% and 100% on the X axis of exposure.

Some of them (I think) are 3D LUT's that seem to add back some Chroma ( I think the Alexa and the Technicolor) and some like Alister's are 1D and don't, but even the 3D LUT's seem to me to still need a little chroma boost or manipulation.

None of these LUT's are perfect out of the box for every shot of course and because FCP doesn't provide a curves tool of its own, they all seem to need the help of additional filters, especially additional highlight compression and shadow control to get the most from SLog. So I've been experimenting with 2 free plug ins each called Shadow-Highlight from Lyric and Too Much Too Soon that are very useful. To that i add the FCP 3 way for saturation and color control.

I've started trying to compare the LUT's but its pretty time consuming and so far it looks like at least a few of them can be manipulated back to a similar place pretty easily.

Questions -
- Is there any reason to prefer a 3D LUT like the Alexa 's to the 1D LUT's from Alister if you are going to add saturation back anyway? I know a LUT you actually designed for a specific shot would be preferable but is there any reason to think that say the Alexa LUT's would offer an advantage (like perhaps correcting for too much chroma in the shadows or highlights or something else?)

- How do you correct for exposure differences? If you over or under expose the original Slog wouldn't that make you want to adjust your curve to compensate?
Would you:
- Just de-Log first with the LUT and then use the ordinary 3 way controls to compensate?
- Lift or drop your gamma in the 3 way before applying the LUT?
- actually make separate LUTs for different ISO's ( I have seen those somewhere I think for the Alexa)?
- Decide to use Natress instead of the pre made LUT's because you can easily adjust those curves and raise or lower the mid points to adjust for exposure?

- Any other suggestions for other additional filters to use with LUT Buddy or Natress to affect the highlights or shadows. I'd like to find an easy inexpensive tool to change the saturation in the Gains, Gamma's and Darks.
Anybody use Tonalizer/VFX PRO from Irudis?

Thanks again for making this process begin to work for me. (I know a lot of other people have the same questions within FCP.)

lenny levy

[Nate Weaver]

Originally Posted by Leonard Levy

Some of them (I think) are 3D LUT's that seem to add back some Chroma ( I think the Alexa and the Technicolor) and some like Alister's are 1D and don't, but even the 3D LUT's seem to me to still need a little chroma boost or manipulation.

Agreed. on the 3D LUTs add chroma, disagree on they don't add enough. Think it depends on the shot, really.

Originally Posted by Leonard Levy

- Is there any reason to prefer a 3D LUT like the Alexa 's to the 1D LUT's from Alister if you are going to add saturation back anyway? [...] is there any reason to think that say the Alexa LUT's would offer an advantage (like perhaps correcting for too much chroma in the shadows or highlights or something else?)

I can only go by my eye here. I downloaded Alister's Sony-derived .cube LUTs and made some stills in Resolve. I GREATLY prefer the Alexa LUT, but opinions, armpits, etc etc.

[crud. I uploaded all these stills with descriptive filenames so you could all see what's what, but the filenames are stripped off in posting. Make some guesses, and I'll repost a legend to the stills when I get back. Have to run!]

[Alister Chapman]

A LUT is not meant to replace grading. The primary purpose of a LUT is to allow you to view your 12+ stop footage on a conventional 6 stop monitor without it looking like crud. A secondary benefit is that you can create a LUT that will be a close approximation of what your footage might look like after grading. But the LUT is not meant to be a substitute for grading. Any grading should be done before the LUT is applied so that you grade in the widest possible bit/color/dynamic range. After applying a LUT your dynamic range etc is reduced, so grading after the application of a LUTvwill not give the best results.

A real eye opener for me this week has been doing a lot of work with 16 bit linear footage from an F65. You have to have a LUT to even see the material. The default camera LUT is S-Log2 (regular S-log does not have enough DR). Without a LUT the image is almost entirely black.

[Alister Chapman]

In Nate's examples all the LUTs are discarding the highlights (outside the car window). A proper grade would be able to keep the highlights while giving a similar tonal range to the rest of the image.

[Leonard Levy]

Alister,

Would I be interpreting you correctly if by grading before the LUT, you mean just laying the filters in order so that the LUT is last , but that you will be applying changes while viewing with the LUT in place and working on the image.
I don't imagine you could do any grading on the picture without the LUT in place.

Was that an answer to the question about how to deal with exposure issues? i.e. grade with the 3 way above the LUT in the heirarchy of filters?

I'll try to post a few tests after I get more done with these.

[Nate Weaver]

Originally Posted by Alister Chapman

In Nate's examples all the LUTs are discarding the highlights (outside the car window). A proper grade would be able to keep the highlights while giving a similar tonal range to the rest of the image.

The car BG highlights I'd consider a throwaway anyway though...they compete with her face.

In the casino, the graded still was adjusted to bring back the guy's white shirt after the LUT clipped it by default. In my Resolve session, the LUT is the last step in processing, just like you advise.

Originally Posted by Alister Chapman

A LUT is not meant to replace grading. The primary purpose of a LUT is to allow you to view your 12+ stop footage on a conventional 6 stop monitor without it looking like crud.

Of course. As somebody who colors an awful lot, I'd say that it gives the colorist an important starting point.

I posted some time back that it's possible to get a good image without a LUT and just apply your own contrast or curves + saturation to get started, and it's true, but I've now realized that a good LUT can do things that are ton of work if you just have to do them on your own for each shot. There's a very refined s-curve going on in the Alexa LUT that I'd be hard-pressed to create on my own.