Quote:
Originally Posted by dorian
Same thing. The problem is PGS subtitles are gamma (SDR) encoded images that being ST 2084 (HDR) decoded by the display. Code values that ordinarily map to a reasonable light level in SDR get mapped to ridiculous light levels in HDR. As less than 1% of the frame exceeds 1000 nits, the subtitles will almost certainly hit display max too.
[Show spoiler]
It's the anti-aliasing on the text that clips and produces the 10,000 nit reading:
[Show spoiler]
The body of the text has code value 235 (in 8-bit). If we assign gamma a nominal peak luminance of 100 nits, we can see the crazy disparity in light output.
Column 1: code value. Column 2: gamma light output. Column 3: ST 2084 light output.
[Show spoiler] |
Thanks a lot for your clear analysis and explanation. Much appreciated.
From your post, the body of the text has code value 235 (in 8-bit). From the luminance table, that means 82.20 nits in SDR, but 4773 nits in HDR.
Now if one would like to correct the subtitles to use a code value suitable for HDR, what should the code value 235 be replaced with on 4K BDs? And does it differ depending on whether the disc has been mastered using 4,000 or 10,000 nits as max brightness?