John Paines wrote:I don't think it makes sense at all, you can't create data where there is none by mapping it beyond its original color space, and I don't believe Dolby thinks so either.
Actually, you
can do an SDR -> HDR conversion, but I would agree that (in general) you can't get a wider color gamut than what's already there. But you can tone-map & trim the highlights to get a brighter image for HDR. A much brighter image, as a matter of fact.
Kevin Shaw has a good tutorial on the process, either going from HDR -> SDR or from going SDR -> HDR. I know of documentaries and other shows that "repurposed" material to get HDR out of it, and when it's done well, it can look very good.
No question, going from HDR to SDR, particularly Dolby Vision to SDR, is a better way to go. Dolby Labs did a good presentation on this technique a few months ago, and they make a good case that it's possible to derive a better SDR out of HDR than you could in just grading an SDR deliverable directly from the same material.