Understanding S-log 2's black Level, black gamma, and knee

[Devon]

Can anyone shed some light where these settings should be? Also, anyone know of any good tutorials that cover these topics? Thanks in advance!

[iaremrsir]

Everything you need to know about S-Log 2 can be found in the technical summary.

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

As for tutorials on the topic, I'd be willing to help here as much as possible. I highly recommend taking a look at Alistair Chapman's articles on S-Log at xdcam-user. 

[Devon]

Thanks iaremrsir! I understand Slog-2 and how the curve squeezes the max dynamic range into the image. Although, I'm wondering how black level, black gamma, and knee affect the profile all together? (And I guess I am looking for a simple definition as to what they are.)

Please correct me when I am wrong in the following:

Black level: Essentially sets the black point at 0 IRE?

Black gamma: confused. Is this a gamma inside a gamma?!?! (gamma inception)

knee: shifts where the "hump" in the log curve sits? Does adjusting the knee raise or lower this "hump?"

 

I realize leaving these settings at default would be easy, but I have this horrible obsession about fully understanding my camera.

Can I alter the settings (black gamma, level, and knee) to squeeze even more dynamic range into the image?

 

Sorry I am further confusing everyone! Thanks again!

[iaremrsir]

Ahh so these are in camera settings rather than the characteristics of the actual curve. The black level is probably like it sounds, it changes where black is recorded. In the case of S-Log, it'd allow you to change the recorded black from 90/1023 to 0, or whatever you like really. The knee is likely the knee that is used in many Rec. 709 profiles that allows it to keep more data in the highlights. It would act at the very top of the range and essentially "bend" the curve down to keep more range or clip at a lower point. This depends on if the knee is applied before or after the signal is already clipped from the gamma transform. The higher the value, the sharper the bend is. Not sure on what the black gamma would be. It'd be best to look up the user manual for the camera these settings are for know if there are exact units they are giving you versus an arbitrary scale.

And I must say, it would be a lot easier to leave the values at default. It would also make it much easier in post to do color transforms when needed. But I do share your desire for understanding everything you possibly can about a camera haha 

[Devon]

Thanks for all your help! That helps clear some things up! I've searched all over, and there isn't much info on what these parameters actually do. Even Sony's documentation is vague. 

I'm also seeing that everyone finds it difficult to grade slog-2? Why is this? I find it rather convenient with the help of Conversion LUTS. 

[Inazuma]

On 09/08/2016 at 7:14 AM, Devon said:

Thanks for all your help! That helps clear some things up! I've searched all over, and there isn't much info on what these parameters actually do. Even Sony's documentation is vague. 

I'm also seeing that everyone finds it difficult to grade slog-2? Why is this? I find it rather convenient with the help of Conversion LUTS. 

Here's everything you need to know http://helpguide.sony.net/di/pp/v1/en/cover/level1_01.html

[Devon]

Thats exactly what i was looking for!! Thank you