Originally Posted by JimP
So regardless of selecting either 75% or 100% signal intensity in the options/signal generators/device settings, it doesn't impact using Rec.709 or 75%Rec.709 in the Color Management module?
I am going to spend some time on this, not just to answer your question but because this is an issue that comes up often and obviously requires clarification.
1. The 75% of Rec. 709 option in Color Management refers only to 75% saturation of Rec. 709. That means that the target point is 75% of the distance from the white point to the Rec. 709 gamut boundary--a much reduced gamut. The spec for a Rec. 709 red and a 75% saturated Rec. 709 red have different xy coordinates.
2. The 75% and 100% Intensity selectors in the Signal Generator setup refer only to % of intensity. This has nothing to do with the size of the gamut. It only refers to the level of luminance, which is not represented on the CIE Chart at all. A 75% intensity Rec. 709 red and a 100% intensity Rec. 709 red have exactly the same xy coordinates: x0.640, y0.330. They even have the same Y specification: 0.2126. This is true even though they are different levels of luminance because the reference white changes along with the color, thus the ratio between the color's luminance and the luminance of the reference white point stays the same. What changes is the absolute luminance, measured in cd/m2 or ft-L.
3. As a matter of best practice I always recommend using 75% intensity test patterns for color management. You may or may not choose to use the 75% of Rec. 709 target gamut in color management. It helps with some displays and not with others, and it really makes reporting more difficult. However, the two (intensity selection and target gamut selection) really have nothing to do with one another.