Tonal Separation and a Digital Zone System

[ChristopherPerez]

@anon8280290

Back to Zones, here’s a Sigma/Foveon camera response curve (mean Lightness v. Zones).

Taking “middle gray”/7Fhex/127dec as a starting point, in both the Gimp and RawTherapee I increased/decreased by adjacent 1EV exposure values. I did this to try and understand what the software is doing. This became my digital reference as it gives me the 1EV separation values that I apply to an input correction curve. Here’s what I see - https://flic.kr/p/2qdUCj3 It looks remarkably similar to the Sigma curve.

@reffort1

I think it’s probably worth mentioning that Zone IX was defined as pure white until Adams’s last round of revisions, c. 1980, when Zone X was promoted to the Normal scale. There are also curiosities in some of Adams’s illustrations that might suggest his definition of white may have been lower than Zone IX at some point.

I never knew this. It’s likely due to where I started - Minor White’s “Zone System Manual.” I’ll have to think about this a bit.

To confirm for myself the potential value of setting a digital input correction curve to -1EV as Zone 5 and Zone 10 as pure white, I took a look at highlights. Here’s what I found - https://flic.kr/p/2qkTvaj For me, understand higher contrast situations, this looks like a useful gain in highlight tonal separation.