Crazy Saturation Converting SLog2 to Rec709

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DCooper7

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Crazy Saturation Converting SLog2 to Rec709

PostTue Nov 29, 2022 7:46 pm

Hi,
I am a newbie to color management. Any help would be appreciated please

I am using Davinci Resolve free and I am working on a Macbook Pro.
I shot a couple of test clips in SLog 2 on my Sony A7RIII and I followed a video to go into Project Settings and select the input and output, to covert the footage to Rec 709. After saving the settings Davinci changed the clip color to insane levels of saturation.

I messed around with the settings a little, but it made no difference.

Can anyone please tell me where I am going wrong?

I enclose an image of the settings and the color converted clip.

Thank you.
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shebbe

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Re: Crazy Saturation Converting SLog2 to Rec709

PostTue Nov 29, 2022 9:38 pm

Hey,

Can you tell the exact settings that were used on the A7RIII? SLog2 is only the transfer function (gamma). Without knowing what the accompanying primaries were you can't do accurate conversions. It may not be SGamut?

You probably also want to use DaVinci as both the Input and Output DRT instead of Luminance mapping and Saturation Perserving. It will give bright colored lights a more 'natural' sensation of brightness with desaturation towards white the brighter they are, which we are also accustomed to with film.

I would also suggest in general to immediately develop an understanding of color management w.r.t. grading scene-referred. It's virtually impossible to for example adjust exposure in a photographic manner if you are grading display referred, or as Resolve calls it "SDR".
I don't know a good definitive video that explains this properly but what I mean is grading in DaVinci Wide Gamut/Intermediate for example.
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Steve Alexander

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Re: Crazy Saturation Converting SLog2 to Rec709

PostTue Nov 29, 2022 10:15 pm

Have a look at Cullen Kelly's tutorial series (I'll link part 1 of 3, below). He discusses how he uses a color managed workflow in Resolve:

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John Paines

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Re: Crazy Saturation Converting SLog2 to Rec709

PostTue Nov 29, 2022 10:58 pm

Go into the media pool, select all the slog2 clips, right-click any one of them, select "input color space" and make sure slog2 is selected (checked) rather than (for example) rec. 709.

If the value is incorrectly set in the media pool, it will override the setting in the color management page.
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Re: Crazy Saturation Converting SLog2 to Rec709

PostTue Nov 29, 2022 11:02 pm

Try right clicking the clips in the color page and selecting 'Bypass color management.'
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DCooper7

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Re: Crazy Saturation Converting SLog2 to Rec709

PostWed Nov 30, 2022 10:50 am

Thank you everybody for your tips, much appreciated.

@ shebbe I think you were right, thank you... I changed the color mode from ITU709 to S Gamut and filmed another clip and the oversaturation wasn't an issue when I set up the colour management this time.

Would you know why ITU709 causes this problem?

@ Steve Alexander Thank you for the video link!
Last edited by DCooper7 on Wed Nov 30, 2022 11:51 am, edited 2 times in total.
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Uli Plank

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Re: Crazy Saturation Converting SLog2 to Rec709

PostWed Nov 30, 2022 10:55 am

Yes. If you want log, it’s absolutely wrong.
Don’t approach DR with your preconceptions from another NLE.
Many features are better, some worse, most are different.


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shebbe

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Re: Crazy Saturation Converting SLog2 to Rec709

PostWed Nov 30, 2022 1:32 pm

DCooper7 wrote:Thank you everybody for your tips, much appreciated.

@ shebbe I think you were right, thank you... I changed the color mode from ITU709 to S Gamut and filmed another clip and the oversaturation wasn't an issue when I set up the colour management this time.

Would you know why ITU709 causes this problem?

@ Steve Alexander Thank you for the video link!
ITU709 means that you're recording with Rec.709 primaries. So whilst you'll have a "flat" image because of the log gamma the colors will be already converted to Rec.709. If you let management do this again by assuming it is SGamut it will result in a mismatch. Because SGamut is larger the result is oversaturation.

Typically it's assumed that when recorded in SLog2, SGamut is the accompanying primaries which is why they are paired as a choice within Resolve Color Management. I would always shoot in this color space so there's less chance of clipping. The best combination for Sony camera's is SLog3/SGamut3.cine but SLog3 is only practical if you are capable of capturing in 10bit which the A7RIII can't I believe.
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DCooper7

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Re: Crazy Saturation Converting SLog2 to Rec709

PostWed Nov 30, 2022 2:22 pm

Thank you for your reply and this information. This really helps with my work and projects.
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Uli Plank

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Re: Crazy Saturation Converting SLog2 to Rec709

PostThu Dec 01, 2022 2:22 am

I'd avoid Slog2 on Sony's consumer devices as much as you can. 8 bit is simply not enough for it, since for most scenes you'll need to expand it a lot. Only use it for very contrasty situations. Apart from that Slog2 is difficult to grade from any source.
Rather try one of the Cine profiles (I like Cine4 in particular, but that's a matter of taste).

Slog3 from a camera which can record in 10 bit 4:2:2 at decent data rates is a whole different story. It's a shame that they denied it to their customers for so long, only to protect their high-end market. Those recordings grade pretty well.
Don’t approach DR with your preconceptions from another NLE.
Many features are better, some worse, most are different.


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Marc Wielage

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Re: Crazy Saturation Converting SLog2 to Rec709

PostThu Dec 01, 2022 9:08 am

Uli Plank wrote:I'd avoid Slog2 on Sony's consumer devices as much as you can. 8 bit is simply not enough for it, since for most scenes you'll need to expand it a lot. Only use it for very contrasty situations. Apart from that Slog2 is difficult to grade from any source.

I agree: dealing with 8-bit for final color from those little cameras is a nightmare.
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shebbe

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Re: Crazy Saturation Converting SLog2 to Rec709

PostThu Dec 01, 2022 1:25 pm

Uli Plank wrote:I'd avoid Slog2 on Sony's consumer devices as much as you can. 8 bit is simply not enough for it, since for most scenes you'll need to expand it a lot.
I thought that was the case with SLog3 but much less so with SLog2 as it stores less dynamic range. As some extra info for the OP. If you decide to use some of the more "friendly" formats that get you closer to Rec.709 already like Cine4, you can't color manage this in the same way you'd do with "true" log profiles like SLog2/3 as there are no conversion options for these. They are intended to be used as is or receive 'simple' grading in a display referred Rec.709 environment.

Back when we were still using the A7s2 we used the profiling Andrew Reid suggested and sold as a product with some LUTs on his EOSHD website.
https://www.eoshd.com/pro-log/

The profile is SLog2/SGamut3.cine based but works really well compared to stock settings. It may be of interest to you. Being forced to shoot 8bit still sucks of course, but I think shooting wider range and gamut far outweighs the compromise you'd make for the compression and limited bit size for most projects in my opinion. The only thing that is recipe for disaster is pulling keys for chromakeying or color grading but that pretty much goes for any 8bit 4:2:0 footage.

There is also Pro Color which is modified normalized profiles instead of SLog based which will get you a better image straight out of the camera without sacrificing too much dynamic range and color.
https://www.eoshd.com/eoshd-pro-color-5/
Maybe that's also of interest to you.
Just know that I'm talking from experience using the A7s2 which colors and sensor I dislike. I don't know the image quality and out of the box imagery the A7RIII produces.
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