44rh1n said:
WOW, you’re right! I just checked my iTunes copy, and it looks REALLY good! It’s still only HD for me (hopefully it upgrades to 4K for me eventually – iTunes usually does!), but it’s definitely the new master. It looks WAY better than the old green extended Blu-ray master!So I’m curious about something. When you stream the new master from iTunes/Apple TV on an 1080p SDR monitor, what are you actually watching? I get that the 4K would just be downscaled to 1080p, but what about the HDR? Is there some kind of tone mapping being done, or does Apple already have a 1080p SDR version of the new master that automatically streams if they detect you’re using a non-HDR screen?
The simple answer is that the 1080p version is an SDR master that’s been derived from the HDR master. It’s not HDR, but it comes from the same source.
The more complex answer is that this was mastered in Dolby Vision. A lot of people don’t quite understand what Dolby Vision actually is, so let me explain: Dolby Vision is when you take an HDR (Rec.2020/ST.2084) graded master, and use Dolby’s trim analysis tools to perform a shot-for-shot tonemapping of the entire film. Every single shot is analyzed and remapped to fit inside of a Rec.709/Gamma 2.4/100-nit SDR container. After the analysis, Dolby has additional custom trim tools that allow the colorist to fine-tune the SDR version of the film. They can tweak the exposure, the saturation, and the balance/tint. This way, they can make SDR version look as good as possible. Then the same analysis/trim pass is repeated a number of times to accommodate the capabilities of different screens. For example, a brand new analysis and trim pass will be performed for 600-nit TVs, 400-nit TVs, etc. This is why Dolby Vision HDR looks so much better on consumer screens than generic HDR, because its tonemapping is done by the colorist himself rather than just using a TV’s automatic tonemapping. Every version of the film, tailored to your specific screen, was done by the colorist.
So when you’re watching the SDR version, you’re not just watching something that’s been automatically tonemapped. You’re watching the Dolby Vision SDR version that the colorist has actually created, using Dolby’s toolkit, and derived from that original HDR master. That’s what Dolby Vision is – a toolset that allows filmmakers to create an HDR master and then interpolate the color grade all the way down to SDR while preserving the original intent of the grade.
And yes, I would imagine that the new 1080p Blu-rays are going to be from that same Dolby Vision SDR trim. So they will likely look the same as the iTunes 1080p versions, but with a much higher bitrate.
Hope that makes sense.