Originally Posted by viperlogic
This is where I'm getting lost, especially in terms of Epson controls, so please bear with me, is the st.2084 curve the white dotted line in the luminance view? When doing a 11 or 21 grayscale sweep it produces a yellow solid line. What Epson controls should be used to "match" the yellow solid line to the white dotted line, contrast or gamma? When you say match do you actually mean match the shape of it not its actual points?
In ST.2084 calibration is absolute, so each code value maps to a specific luminance, e.g., code value 502 (50% stimulus) maps to 92.25 nits. This is the white dotted line in the HCFR luminance view (although currently HCFR uses code value 504 and 94.4 nits, due to the use of 8 bits).
If Epson gamma controls are being used then isnt that tone mapping and hence the two steps are the same thing of adjusting to ST.2084 and tone mapping?
No, as I mentioned in my previous post, ST.2084 is the first column in the spreadsheet and goes all the way to 10,000 nits, whereas the tone mapping curves are the ones in the second and third columns, For masters of 1000 nits and 4000 nits respectively.
If contrast is being used then at what should we set contrast to because for me with contrast at 50 up to level 642 flashes. If I want higher levels to flash then I have to reduce contrast eg contrast level 29 causes upto level 712 to flash.
Since the Epson 5040UB cannot hit the absolute curve with the gamma controls, I suggested boosting the Contrast control as an interim step
to set the basis for calibrating the colours, even though that leads to pre-mature clipping (as long as clipping still occurs beyond code value 502). After that you would re-adjust the contrast to give you the proper clipping point.
Using Dominics steps (and contrast at 50 and near same gamma settings on Epson) as our max nits are nearly the same (141 vs 147), I get the following
At that time, I was only focusing on the EOTF and was not adjusting the colours. In hind sight, what I said was a step in the right direction but I would do it differently now, given what zoyd said regarding CMS calibration.
To hit the actual
values of ST.2084 (not just the "shape"), I would now do the following:
- reduce the projected image size to about 50% in area (or 70% in width and height). This will allow us to bring the luminance to 92.2 nits at code value 502
- adjust the gamma controls to match ST.2084
- adjust the CMS to match to primary and secondary colours
- readjust the Gamma and Contrast controls to match the tone mapping curve (1000 or 4000 nits)
When everything is done, zoom the image back to the size of your choice (ideally fitting the screen). Essentially you will get a dimmer version of the proper calibration, with the correct colours and the "correct shape" of tone mapping (correct in "shape" but scaled down in absolute nits).
The end result will still look like the yellow line above, but hopefully won’t have the “terrible” cololours that you had last time.