I think Todd is irritated by the fact that, while all he wanted to do is use a Rec.709 conversion with a 'custom' gamma of 2.4, DCP-o-matic upon that point switched to the BT.1886 preset automatically. As if he wasn't allowed to do what he wanted, or as if he was stuck with BT.1886 instead of what he wanted to do.
Why DCP-o-matic reacts in that specific way, Carl needs to answer this. But all conversion parameters of the preset conversions are not changeable, and if you compare those of Rec.709 and BT.1886, you will notice that they are all the same, except for the difference in Gamma.
So, what DCP-o-matic did seems to be some sort of a pattern matching, if the parameters chosen for a custom conversion matches those of a preset, the preset is used.
You can try that if you start with rec709 and then step up the gamma value one by one - some of them result in a 'real' custom preset (like 2.3 or 2.5), while 2.4 will lock to the BT.1886.
So, if he actually graded in Rec.709 with Gamma 2.4, he actually graded in BT.1886. And if he dials in a gamma of 2.4 with Rec.709, he will actually use BT.1886 for the conversion. So, he should be fine...
Now, 2.2 and 2.4 are just simple numbers, while in fact these gamma functions in reality are more complex.
Carl, did you ever take on the more complex gamma functions behind these? I know the visible differences may be small, but, in order to be able to make a clear statement...?
- Carsten
Am 08.08.2017 um 18:34 schrieb cjflynn--- via DCPomatic:
SpectraCal has a nice white paper on this topic:
C J Flynn
Hi Carl,
I have color graded a project in Resolve 12.5, color management is set to Rec.709 gamma 2.4, monitored the same on a Flanders. Taking it in to DCP-O-matic and I see the Rec.709 preset is locked at 2.2. If I change the gamma it changes the preset to BT1886. Is it safe to say this would be correct? I have seen debate as to whether BT1886 is the same as Rec709, but with a 2.4 gamma spec. I'm not an expert on this.
Thanks in advance and thank you for the work you do on this software.
Thanks
Todd Gilpin
Sent from my iPhone
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