I have a few questions that are not directly related to ACES, but I don’t know a better place than this amazing community where I could get answers. I hope this is not completely off-topic here and really appreciate any answers. And also please feel free to correct my statements. Probably my questions only exist because I have misunderstood something (or everything).
I would like to know more about the exact numbers in Rec709 encoding curve formula and displays’ gamma. Rec709 formula has a linear segment below 0.018, and 0.45 gamma above 0.018.
0.45 is ~1/2.22. But Rec709 encoding was made for CRT displays with gamma 2.4. Is this correct that it was done for compensation of different subjective contrast in real life vs contrast on a display which is surrounded by a dim environment? When something surrounded by darker colors looks less contrasty compared to a bright surround (or to our 360 degree reality). If this is true, then:
a) Why is this compensation needed if there is a linear segment near black, that also makes an image darker? So this 1/2.22 encoding gamma for 2.4 gamma display makes no sense. Because we already get the image darker after a linear segment near black. Is there just a historical reason? For example, at first they decided to encode with 1/2.2 and then to add a linear segment near black to avoid multiplying noise to infinity (is this the reason for a linear segment?).
b) Did CRT displays actually have 2.4? I’ve read that their “gamma was a power law gamma, and at that time thought to be 2.2 (but later found to be closer to 2.4)”. If this is true, then what I wrote above at “a)” makes no sense.
Rec709 encoded video should be displayed on gamma 2.4 display in a dim environment. Consumer displays have gamma 2.2 which is also ok, as they are usually used in bright environments. And the projector gamma is 2.6, because its environment is dark. But all Rec709 to P3 transforms compensate for this by converting from 1/2.4 gamma to 1/2.6 gamma, so 2.6 gamma of the projector is compensated and we get the final image that should be displayed in a dim environment, but is displayed in a dark environment. So, what’s the point of compensating for different decoding gamma if it is different because of the different environment?