A7S : All the red's are orange.

Y

yoclay

Veteran
Hi,
I am grading someone else's footage and I have encountered something I have heard of before.
The DP shot with an A7S for a few external shots. SLOG2 into an Atomos Assasin - UHD prores 422
I downconverted to FullHD Prores 444.

In any case whether I use the original footage or the downconverted one, all the red's are orange.
Typically this is for tailights, streetlights, etc.

I can easily pull a secondary, but before I do this, I wondered if anyone had any suggestions about correcting this issue?
I have seen a few things about this before...
 
Was the footage acquired in Sgamut ?

The skewing of reds is because Sgamut is a much larger colour space than rec709. If I recall correctly the A7s doesn't have sgamut3.cine that Sonys newer cameras have.

You may have to do some secondary CC to pull those primary colours back into line for rec709 displays.

I use Colorista and just shift the red hue to get it where it needs to be.
 
I see it as well, especially when doing two camera shoots coupled with my FS700. The A7s' reds lean towards orange and the FS700's reds lean towards magenta. Both are usually fine on their own but getting the reds the same is usually the hardest part of matching the two cameras.
 
Yeah they do seem to go more orange. I tried to compensate for things like that in the rec709ish lut i made a while ago.
Would you mind posting a tiff image of raw and your corrected look?
 
Just use a LUT designed for SLOG2/Sgamut. Sgamut was just designed that way since it's a storage format not a viewing format. Just like how if you looked at SLOG2 and said the blacks look too grey... You "fix" it by applying a proper transform that understands the appropriate input. If you apply Sony's SLOG2to709A LUT then you'll be saying your reds are too red after spending so much time looking at SLOG2/Sgamut :) (I had exactly that happen on a short recently, I ended up having to apply a secondary to make my reds more orange again because I didn't have LUTs on set and got used to thinking my primary red gels looked nice and orange on set)
 
Lutcalc! I had much better luck grading a7s footage after making an Slog2.sgamut to slog2.rec709. The online version is free to use. I bought a chrome version for a couple bucks just because I was so grateful for the free app. The app even figures out exposure compensation for you.

https://cameramanben.github.io/LUTCalc/
 
Basically, I hate LUT's. They always create another problem while they are fixing the one you are dealing with.
I have always found it faster to correct from RAW or SLOG than deal with the funkiness of trying to correct the other shifts caused by LUT's.
Occasionally, the ACES workflow can get me closer.
However, it crushes the blacks (yes, I always change the clip attributes to 0-1023 instead of Auto in Davinci - so it's not that) which means that I have to use it on a separate timeline for only those clips that have the issue and re-export out and there will always be some loss of info in the blacks as well. What a pain.

I'll give Strouty's fix a shot.
 
I'm not a fan of LUTs either (I've tried to use them a few times and I always find image quality issues) but if you're shooting sgamut that seems to be the only way forward (and that's why I don't shoot sgamut).
 
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