Sat vs Sat curve compared to Hue vs Sat explain please.

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InterrobangMP

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Sat vs Sat curve compared to Hue vs Sat explain please.

PostTue Aug 16, 2022 8:57 pm

I watched a tutorial the other day that made me aware of a curve I had not thought to use previously, and I thought it could solve part of the intense Magenta/red saturation that I get in some shots from the BMPCC4k.
However, in practice, I don't really like the results.
The tutorial used the Sat vs Sat curve to tone down any colour that was over saturated. I quite often get colours in a shot that are way more saturated than the rest of the image. I have a shot here, where the red part of the bike is taking over the image, but I don't want to loose saturation in the skin tones. Previously I've used Hue vs Sat to tone it down, but this always brings the skintones to a muddy dark beige. The bike is clearly more saturated than the skin, so I figure Sat vs Sat would help tone it down, and it does without effecting the skintones too much. But the effect that this curve has on the bike is clearly different to the Hue vs Sat. With Sat vs Sat, the gradation between what is affected and what is not, seems a lot harsher. It creates unnatural bands within the red of the bike. Hue vs Sat looks a lot more natural on the bike, but ruins my skin tones.
I've exaggerated the Sat vs Sat adjustment a little to show what I'm talking about here. You can see the darker parts of the red are heavily contrasting with the lighter parts. This does not happen with Hue vs Sat.

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Screen Shot 2022-08-17 at 8.49.38 AM.jpg
Screen Shot 2022-08-17 at 8.49.38 AM.jpg (379.16 KiB) Viewed 649 times
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Steve Alexander

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Re: Sat vs Sat curve compared to Hue vs Sat explain please.

PostTue Aug 16, 2022 9:25 pm

Is it 8-bit 4:2:0 source video? That would explain the banding, perhaps. Could be the Sat vs Sat can break footage with less color info more easily than Hue vs Sat (I don't know, just guessing).
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InterrobangMP

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Re: Sat vs Sat curve compared to Hue vs Sat explain please.

PostTue Aug 16, 2022 9:30 pm

Steve Alexander wrote:Is it 8-bit 4:2:0 source video? That would explain the banding, perhaps. Could be the Sat vs Sat can break footage with less color info more easily than Hue vs Sat (I don't know, just guessing).

It's BRAW
Thinking about it a bit more I realise that it is the darker areas that hold more saturation, naturally. The Sat vs Sat adjustment is targeting based on saturation levels. The darker areas are more saturated. It's bringing them down more. Hue vs Sat is targeting the hue and bringing all of that hue (light and dark) down.

But I would be interested to hear any ideas for smoothing this banding issue out, the curve does not quite cut it.
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Steve Alexander

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Re: Sat vs Sat curve compared to Hue vs Sat explain please.

PostTue Aug 16, 2022 11:49 pm

I wouldn’t have expected banding with BRAW. Maybe someone else will have a suggestion.
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InterrobangMP

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Re: Sat vs Sat curve compared to Hue vs Sat explain please.

PostWed Aug 17, 2022 2:18 am

Steve Alexander wrote:I wouldn’t have expected banding with BRAW. Maybe someone else will have a suggestion.

Yeah, it's definitely not the old 8 bit banding.
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Hardy-

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Re: Sat vs Sat curve compared to Hue vs Sat explain please.

PostWed Aug 17, 2022 5:05 am

If just the brighter part of that magenta area is oversaturated, I would try to use the Luma vs Sat curve as well, in addition to the other curves. Maybe increase the Sat of the darker stuff and decrease the Sat of the brighter stuff, in addition to the Hue vs Sat fine-tuning.

As there are multiple curve parameters involved here, I would also try the Color Warper instead of the Curves. (Maybe with max amount of warp grid points and with Auto Lock set to 1 or 2 points.)
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Jack Fairley

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Re: Sat vs Sat curve compared to Hue vs Sat explain please.

PostWed Aug 17, 2022 5:20 am

Are you using Gen 4 or Gen 5 color science?
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Hendrik Proosa

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Re: Sat vs Sat curve compared to Hue vs Sat explain please.

PostWed Aug 17, 2022 6:59 am

Convert RGB to HSV or some other model where saturation is separated and look at that channel. It could be pretty far from being smooth.
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InterrobangMP

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Re: Sat vs Sat curve compared to Hue vs Sat explain please.

PostThu Aug 18, 2022 12:52 am

aha, yes, these suggestions make sense, I'll give them a try, thanks
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mattfezz

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Re: Sat vs Sat curve compared to Hue vs Sat explain please.

PostThu Aug 18, 2022 12:58 am

try keeping more of the sat vs sat curve straight across so all the values move down the same amount see if that helps. Not sure if it will but give it a try.

Are you using any colour management systems?

Could always reach for the qualifier if the curves are not working.
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