Data for S-log correction

[Ron Aerts]

I'm using a Transvideo CineMonitor Evolution SBL8 monitor, Really great tool!
The screen has a tool which provides curves for log C, log F and Panalog. I asked Transvideo to provide S-log correction for viewable (rec 709ish) in these presets. They are very helpful and are willing to implement this. I was asked if I have the 'S-log description'. Does anybody know what this is? I assume some values to work out in a gamma formula.
Can some provide the correct data or a place where I can find this? In the attachment what the manual says about curves.
Maybe Allister?

Thanks a lot

[Nate Weaver]

Sony has a white paper they released a little while back:

The formula describing the slope is in there for sure.

http://pro.sony.com/bbsccms/assets/f...log_manual.pdf

While they're at it, they should do S-Log 2 as well, but I haven't seen a white paper for that yet.

[Ron Aerts]

thanks Nate, I forwarded it to Transvideo. I hope it works out.

[Douglas Villalba]

Originally Posted by Nate Weaver

Sony has a white paper they released a little while back:

The formula describing the slope is in there for sure.

http://pro.sony.com/bbsccms/assets/f...log_manual.pdf

While they're at it, they should do S-Log 2 as well, but I haven't seen a white paper for that yet.

They never published one for the F3 that I know about. The one that Nate posted is for the F35.

[Alister Chapman]

Doesn't matter whether it's for the F3, F35, F55 etc. It's the same curve for all cameras, so the same corrections would be applied. Arri Log C is so close to Sony S-log that for general monitoring and viewing applications Log C would work fine.

[Bill Thomas]

To Allister's point. I just recently loaded some "de-logging" LUT's in to Resolve Lite that Andy Shipsides posted on the Abel blog. He had made replica 3D luts for S-Log like the ones that come in the camera (after upgrade). Most had a very subtle look/change except for the SLog to 709 LUT that instantly clipped highlights. Not Andy's fault, that LUT in camera does the same thing. For the fun of it I tried the Arri Log-C to 709 LUT and it was very close to perfect. Had to increase exposure and de-saturate a little but it gave me a great starting point. I've never done it but for rough monitoring on set I'd assume the Log-C lut with a little monitor adjustment would work ok.

[Alister Chapman]

There is a big difference between a viewing LUT that converts S-log to 709 or similar to having the correct gamma curve in the monitor. A viewing LUT takes the full log range and converts it to a different range such as 709 or another gamma compatible with most conventional monitors (which if they are HD will most likely be Rec-709). As 709 can not correctly display the full tonal range of S-Log, then something has to go. Often highlights are clipped or crushed or contrast is reduced. So the LUT adjusted video will never truly represent what the camera is shooting. If you have a monitor with alternative gammas, then the monitor can skip the Rec-709 gamma curve altogether and directly convert the S-Log input to the on screen view. This is much better and more accurate than having to go in to the monitor via a restricted range gamma like 709. However for the very best results you need an OLED monitor to show the full dynamic range of the camera.

[Richard Crook]

Originally Posted by Alister Chapman

Doesn't matter whether it's for the F3, F35, F55 etc. It's the same curve for all cameras, so the same corrections would be applied. Arri Log C is so close to Sony S-log that for general monitoring and viewing applications Log C would work fine.

No its not all the same curve. The new F's have S-Log 2, which is different from S-Log. The S-Log2 Gamma Curve was designed specifically for the extended dynamic range to support full Sony F65 latitude at 1300%, and now they expanded to the F5 and F55.

[Alister Chapman]

S-Log2 is a different curve, but S-Log is S-Log no matter which camera and the curve data for S-Log will be the same for all cameras and what the OP is after is the curve data for S-Log, not S-Log2. Admittedly I shouldn't have included the F55 in may camera list, although it is possible that you will have the option for both S-Log and S-log2.

[Ron Aerts]

Originally Posted by Alister Chapman

If you have a monitor with alternative gammas, then the monitor can skip the Rec-709 gamma curve altogether and directly convert the S-Log input to the on screen view. This is much better and more accurate than having to go in to the monitor via a restricted range gamma like 709. However for the very best results you need an OLED monitor to show the full dynamic range of the camera.

Am I right here?:
The Transvideo monitor has a great measuring tool for exposure. I think it is important not to use the SDI mon output as it can show the converted lut and therefore give inaccurate information. I use the SDI through on the outboard recorder connected to the A and/or B output of the F3, Then I know for sure to measure exposure on the right levels.
I use the measuring tool on the F3 a lot. Is the measuring still correct when one of the LUT's is chosen? I didn't experiment on that yet

[David C. Williams]

Middle grey in Slog is 38%, Slog2 it's 32.3%. A different LUT is needed.

[Alister Chapman]

The F3 centre spot meter or histogram etc is only correct when no LUT is selected. The Transvideo tools should remain accurate when you use the Log C gamma curve as the monitor is measuring the input level, provided you are measuring the cameras clean output, ie no LUT applied in camera.

[Ron Aerts]

Maybe it would be better to let the spotmeter/histogram always measure the sensor value when S-log is on...

[Alister Chapman]

I agree that it would be better for the center spot meter to read sensor values as opposed to post gamma correction values. If you are using the HG LUTs then the last two digits of the LUT name tells you where mid grey should be. So if you select HG8009G40 you should have middle grey at 40 when using the centre spot meter while the LUT is enabled.

[Leonard Levy]

"So if you select HG8009G40 you should have middle grey at 40 when using the centre spot meter while the LUT is enabled."

That is extremely close to 38% is it not? Pretty much as close as I ever get with that center meter anyway. Am I guessing right that other levels like flesh tone would be further off the mark.