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Originally Posted by Alexkral
The problem with HDR being too dark is still there though. 100 nits for diffuse white is too low in not ideal conditions (I'd say it's even too low in ideal conditions but that's just my oppinion) compared to where most people is used to see it in SDR. ITU-R BT.2408-0 recommends diffuse white = 203 nits for PQ and HLG production on a 1000 nits peak luminance display. Another study in the same report suggests diffuse white at 140 nits for indoor scenes and 425 nits for outdoor scenes, for PQ with 4000 nits peak luminance. I think I have read somewhere that at least some titles now are being graded with diffuse white at 203 nits. This should be the best way to solve this. We loose 1 stop at highlights but the overall brightness match better with SDR.
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I wouldn't be against raising the value of reference white slightly for PQ HDR content. The problem is all existing HDR displays are tuned to tone map for a reference white of 100 nits, so I don't know how you would get around that without breaking support for all legacy HDR displays. I don't think HDR is too dark when viewed without ambient light in the room.
Displays could at least have a standard brightness slider like video games to make HDR a little brighter during the daytime, even if raised the bottom of the image a little.
Quote:
Originally Posted by Alexkral
If I'm not wrong, both SMPTE ST 2094-10 (Dolby Vision) and SMPTE ST 2094-40 (HDR10+) curves change dynamically the knee point in a similar way that what Soulnight's utility with dynamic target nits is doing now with the BT.2390 EETF.
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The knee point just changes where the tone mapping roll-off begins. The curve always slopes to the right away from the PQ curve, so the image never gets brighter; it only gets darker.
Soulnight's tool increases or decreases the target nits. Increasing the target nits raises the knee point further up the PQ curve to reduce compression, but it also changes the absolute brightness of all values relative to the output display. For example, if the display is 100 nits, selecting 200 nits will lead to a loss of more or less half of the calculated brightness of the tone mapped values because the target display is assumed to be twice as bright as the actual output display. The gamma curve is relative, so the output brightness isn't always that precise, but it is close.
When the target nits is higher, the pixel values are more spread out, but they use more of the lower region of the gamma curve to handle the majority of the pixels 0-100 nits. The pixels that represent the highlights are separated to the brightest end of the gamma curve. So the image has more contrast between bright and dark detail and looks less flat because the pixels are less compressed, but the overall image ends up darker.