What does the HDR Zones Histogram represent in Resolve 17?

[Asker Mammadov]

I haven't been able to find an answer for the discrepancy between the Scopes Histogram and the HDR Zones Histogram. I've attached 2 pictures below showing the Histogram for a Gray Scale ramp and the settings I'm using(I know they're not HDR. I was just trying to understand what the HDR Histogram is actually showing). I understand the x-axis represents the tonal range(in stops rather than the typical tones in the primaries curve) and I understand why it ends at a 100 nits (The limitation of SDR being a 100 nits) but why is the histogram an exponential curve on the HDR Zones whereas it's a straight bar in scopes as it's supposed to be (all of this is at default settings). On top when I change the Output Color Space to Rec709 2.4 it's still an exponential curve and ends at a 100nits but the Y-axis is only like 1/4th way up.

Basically, what does Y-axis actually represent both for the Histogram and Blue Curve/Line in HDR Zones? Thanks

P.S: I'm not a pro colorist or anything. Just someone who is genuinely interested 

 

 

Output Space sRGB, Timeline Working Luminance: SDR 100

Output Space Rec709 2.4, Timeline Working Luminance: SDR 100

Output Space sRGB/Timeline Working Luminance 4000 HDR(Just another example)

Scopes Histogram(Always stays the same)

Edited September 19, 2021 by Asker Mammadov