Bluescreen negative values

Discussions - Using ACES
1

So ive got a shot on alexa, in acesCG I get a lot of negative values across a bluescreen.

I understand why this happens but keyers hate it, so whats the best workaround here?

  1. transform plate back to AWG and key that
  2. Ingest plate as linear/AWG, import as RAW and key that.

Option 1 will give me some “loss” by going back and fourth, eoseically as I want the plate to be 16bit. but Indont need to ingest differently…

Any hints?

2

Hi @Finn_Jager,

I guess it depends where you are doing the key, if, for example, you stay in Nuke, you should only suffer from a minimal quality loss that will not be perceptible. You would basically apply a ColorMatrix node to convert from ACEScg to ALEXA Wide Gamut, perform your key and convert back to ACEScg.

Cheers,

Thomas

3

yea rhats what I thought, practially i then need to make sure I have knowledge about the source primaries of the camera then as well, lot of the times we get EXR turnovers that are aces-2065 allready , but I guess just going to something really large and then back should be fine in any case.

4

Maybe you could lift the image just enought for the negative values to be positive, do your key and move it lift it back down to the original image. That’s what I have done a few times when I got negative values in ACEScg.

5

thx yea thats what people have been doing, I do preffer going back to source primaries but it doesnt really matter for a key I suppose.

6

I always gett better keying-results when I key in ACES. The only problem is the negative values.