Modifying IDT Gamut / Slog2 IDT choices


(Caleb Barrett) #1

I’m not really knowledgeable enough to know even if this is possible, but I figured I’d ask away and get educated.

My situation is that I’m shooting in Slog2, and I would like to also use sgamut3.cine. Now, obviously there isn’t a manufacturer-supplied IDT to cover that scenario. Is this something I can mess with, like I would have used LUTcalc to do with a LUT?

Speaking of Sony’s IDTs, I have a few choices and it’s confusing me. https://github.com/ampas/aces-dev/tree/master/transforms/ctl/idt/vendorSupplied/sony

For Slog2, what good will a daylight vs tungsten version of the transform do me if I’m manually white balancing in-camera? Should I just be using the daylight option in that case? There are also 10i and 12i versions; what is the difference here?

I’m sorry if these are really basic questions, but I will feel a lot better about which choices I make in-camera if I can finally get my color where I feel like I have a handle on it.


(Scott Dyer) #2

Well, you could theoretically combine the S-Log2 linearization function w/ the S-Gamut3.cine to AP0 matrix, thus creating a hybrid transform from the two existing CTLs. However, as you yourself note, this is not manufacturer recommended and as such will not be available as a built in transform in any color correction tools (e.g. Resolve, Filmlight, etc). However, support for S-Log2 or S-Log3/S-Gamut3Cine are built in. So I would really question why you feel you must use S-Log2 with S-Gamut3cine?

The differences are in the white balance scale factors and the illuminant used to optimize the color conversion matrix. I would recommend choosing the option that is closest to your capture environment. If daylight is closest, go with that.

10-bit and 12-bit integer. Most implementations beyond the camera are floating point so you shouldn’t really even see this choice in color correctors, etc.


(Caleb Barrett) #3

Thanks very much for taking the time to reply.

From my tests the s-gamut3.cine gives a more subdued colour that I prefer. I’m also recording to a 4:2:0 8bit format, so I was thinking that recording in a smaller gamut would be better? I’m extemporizing here; it might not matter one way or the other? Either way, if I want to use Slog2, my hands appear to be tied. No worries.

Sorry, I’m not sure I understand. All other things being equal, recording under an incandescent source vs a daylight source, the camera has been balanced so that the source is neutral; are there still recorded differences that have to be accounted for?

And that explains why I don’t see a choice between the two in Resolve. Thanks very much.