A7SII, LUTS and Colour Space

[Alex Moreán]

Hi guys

I've had this camera for some months now, and after lots of tinkering, a couple of disasters and some successful tests, I'm starting to feel confident. I come from a D5300 so this is my first time having to actually chose color spaces/gamuts, and the options are almost endless.

As for the LUT work, I'm kind of confused. I've been reading a lot, so I'm not starting from zero here, but one thing I don't seem to understand is why some people use LUTS as just looks and others use them as a starting point for personal grading. From what I've learned, we record in whatever gamut we chose (cine, video, pro, sgamut, sgamutcine, blahblah) then we translate it to 709 (which is the gamut most of our monitors can display) and then we grade/create looks/whatever we like. Is this the common workflow? because after reading millions of posts I have the feeling that some people just slap a looks LUT  directly to the footage and everything ends up looking teal-orangey, or maybe people use two different LUTS in each clip? Im lost

So far the best results I've gotten have been using the S.Gamut3.Cine which is parallell to the 709 gamut but wider, so supposedly you get rid of the color casts and ofsets... Kind of. But I haven't found what de "pro" "cine" " video" etc gamuts do... Is there any guide?

Cheers 

[DayRaven]

Regarding Luts, they were designed for you to take properly graded footage and adjust it so you could print it to film. Say you had shot a scene and put it on your computer to grade it, but you were delivering on film. As we know, film can be wildly different and what you see on your monitor is not what you will see on the film once printed. So you would get it looking right on your monitor then before delivery, apply the lut, which would make it look horrible on your monitor, but right in the final delivered product.

Of course, that doesn't mean you can't use them creatively, but as with using anything for a purpose it wasn't designed for, proceed with understanding and caution.

[Alex Moreán]

But then, what would be to "proper way" of translating one recording gamut to a working gamut?

[Don Kotlos]

31 minutes ago, Alex Moreán said:

But then, what would be to "proper way" of translating one recording gamut to a working gamut?

There is no "proper way". You can do it anyway you want. 

You can think of LUTs as the easy way of translating color information. 

So you can shoot sgamut3 and have an LUT that gets you to sgamut3.cine space or an LUT that gets you from sgamut3.cine to rec709. You can add another LUT on top of the previous to add secondary looks, or you can have just one that combines all the LUTs together. Or you can do all these things manually with color and contrast manipulation but spend a significant amount of time doing it. 

I agree that people tend to misuse LUTs, but then again color grading is not a trivial task. I find that people misuse/overuse more the slog/sgamut than LUTs... 

While shooting a wider gamut allows more control of the final image since you can do more translations of color (match very different clips), it can lead to bad & unbalanced results easily and with 8bit codecs things can get messy (banding, plastic looking colors, etc..) very fast. That is why wider gamuts  such as sgamut3.cine or log profiles are not always advised. 

For my type of shooting (documentary run&gun style), Cine4/Cine2 gammas with Cinema/Pro/rec709 gamut with rec709 LUTs added in post, give me the best balance between gradability and quality.

[Alex Moreán]

Great!

Now I understand better, thank you. As for the difference between all the color spaces in the A7SII, have you found any graphic or explanation? I know some of them are wider than others, but I cant find an exact bit of information...

 

Thanks!

[Don Kotlos]

1 hour ago, Alex Moreán said:

As for the difference between all the color spaces in the A7SII, have you found any graphic or explanation? I know some of them are wider than others, but I cant find an exact bit of information...

There is no graph that shows this info for all the color profiles unfortunately. My simpliplic generalisation is Cinema for less saturated colors, Pro for more saturation in low contrast scenes, rec709 for extreme light conditions with different light sources or very very low contrast (low light with cloudy sky for instance).

There are some tests on color accuracy with A7s profiles like this one:

http://similaar.com/foto/flaat-a7s/technical-tests.html#color

And there are some useful general info on the color information of sony cameras:

http://www.xdcam-user.com/2014/05/what-is-a-gamut-or-color-space-and-why-do-i-need-to-know-about-it/

http://www.dvinfo.net/article/acquisition/sonyxdcam/my-cinegear-presentation-on-the-sony-f55-part-1.html

Also here is the place to get more info on the Sony color profiles and how to tune them as you wish (very helpful):

https://docs.sony.com/release/Help_C198100111.pdf

[jax_rox]

Just think of LUTs as what they are: They're a way of taking one set of values (the input) and translating it into another of values (the output). What's contained within that can be simple, or it can be complex, but it is no more than a translation of values - and is not tied to film in any particular way, at least not moreso than digital.

[Alex Moreán]

Thanks guys, that was very helpful

I also have seen that in some profiles, this camera tends to cyans and yellows/oranges which is kind of a premade cine look. I guess this is due to the offset of the gamut triangle compared to the ITU 709 standard, right? Not really an issue, but knowing this saves me from unintentional horrible results in post.

Cheers!