Quote:
Originally Posted by tp4tissue
What does this mean ?
I have a rec709 3dlut (2.4 gamma)
I turn on pixel shader hdr->sdr
The shader outputs 2.2 gamma, then the rec 709 lut brings it down to 2.4 gamma ?
Or does everything still come out at 2.2 ?
Should I make a rec709 lut for 2.2 gamma ?
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fhoech (Displaycal):
<<For SDR, madVR doesn't alter relative luminance of the original signal at all (unless you enable gamma processing or choose "this display is calibrated to" with a gamma that is not 2.2), so if a calibration 3D LUT is used that really is the only thing (apart from the display itself) that affects the resulting tone response (and if not using a 3D LUT, the display itself is the only thing affecting relative luminance of the decoded signal).
For HDR to SDR, madVR decodes the signal with SMPTE 2084 (PQ), applies BT.2390 roll-off and re-scaling using the chosen target peak nits, and then re-encodes to gamma 2.2, and then feeds it into any SDR calibration 3D LUT. So, in both cases, a gamma 2.4 SDR calibration 3D LUT makes the result darker compared to a gamma 2.2 SDR calibration 3D LUT. For SDR, this may be the desired effect (e.g. BT.1886 on an OLED results in an effective 2.4 pure power curve), but for HDR PQ, which is based on absolute luminance, this effect is undesirable.>>
So you should make an rec709 lut for 2.2 gamma.