Comment by dperfect | Hacker News Reader

Comment by dperfect | Hacker News Reader

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It's hard to boil it down to a simple thesis because the problem is complicated. He admits this in the presentation and points to it being part of the problem itself; there are so many technical details that have been met with marketing confusion and misunderstanding that it's almost impossible to adequately explain the problem in a concise way. Here's my takeaway:

- It was clearly a mistake to define HDR transfer functions using absolute luminance values. That mistake has created a cascade of additional problems

- HDR is not what it was marketed to be: it's not superior in many of the ways people think it is, and in some ways (like efficiency) it's actually worse than SDR

- The fundamental problems with HDR formats have resulted in more problems: proprietary formats like Dolby Vision attempting to patch over some of the issues (while being more closed and expensive, yet failing to fully solve the problem), consumer devices that are forced to render things worse than they might be in SDR due to the fact that it's literally impossible to implement the spec 100% (they have to make assumptions that can be very wrong), endless issues with format conversions leading to inaccurate color representation and/or color banding, and lower quality streaming at given bit rates due to HDR's reliance on higher bit depths to achieve the same tonal gradation as SDR

- Not only is this a problem for content delivery, but it's also challenging in the content creation phase as filmmakers and studios sometimes misunderstand the technology, changing their process for HDR in a way that makes the situation worse

Being somewhat of a film nerd myself and dealing with a lot of this first-hand, I completely agree with the overall sentiment and really hope it can get sorted out in the future with a more pragmatic solution that gives filmmakers the freedom to use modern displays more effectively, while not pretending that they should have control over things like the absolute brightness of a person's TV (when they have no idea what environment it might be in).

While HDR has the problems described by you, in practice, whenever possible, I choose the HDR version of a movie over its SDR version.

The reason is not HDR itself, but the fact that the HDR movies normally use the BT.2020 color space, while the SDR movies normally use the BT.709 color space.

The color spaces based on the limitations of the first color CRT tubes, which are no longer relevant today, i.e. sRGB, BT.709 and the like, are really unacceptable from my point of view, because they cannot reproduce many of the more saturated colors in the red-orange region, which are frequently encountered in nature and in manufactured objects, and which are also located in a region of the color space where human vision is most sensitive.

While no cheap monitor can reproduce the full BT.2020, many cheap monitors can reproduce the full DCI-P3 color space, which provides adequate improvements in the red-orange corner over sRGB/BT.709.

I assume you've watched the "Wider Gamut Misinformation" portion of the video. You're correct in saying that HDR normally uses Rec. 2020 (because Rec. 2100 points to Rec. 2020's color primaries), but Steve points out that Rec. 2020 is an SDR color space which doesn't technically require HDR.

It's true that, given the options available today, the two usually go hand-in-hand (wider color gamut and HDR). However, one of the arguments Steve makes is that a majority of content (and a vast majority of the pixels in that content) doesn't use colors outside Rec. 1886's gamut. Illuminated objects (natural or manmade) almost never go outside that, so you're usually only talking about a few pixels from intensely-saturated light sources in the shot (like LEDs) that might use those colors. Even then, not a lot of filmmakers feel the need to go there, so their movies will look the same in narrow and wide gamuts.

I don't think the video is arguing against wider gamut or even higher dynamic range as options; modern displays are more capable than older ones, so we need tools to allow content creators to use that capability if they desire. The problem is that all of these things (color space, bit depth, transfer function, absolute luminance values, etc) have been lumped together under one label, "HDR", and some of the implementation details are actually worse than what we had with SDR. If you skip to the "Checklist Recap" portion of the video, you'll see that there are actually quite a few downsides to HDR in its current form, but since most of the standards are tightly coupled, we're kind of stuck unless we move to something better.

I also personally choose HDR versions when watching movies, but that's because UHD content is usually also HDR. What I really want is the higher resolution. I've never felt like I'd be missing out if it didn't have HDR because I've compared the two a lot - they're really mostly the same for the movies I watch with a properly calibrated screen. To each their own :)

I disagree about "Illuminated objects (natural or manmade) almost never go outside that".

There are plenty of frequently seen purple-red-orange-yellow objects, like flowers and fruits or clothes which look very noticeably washed out when seen on an sRGB monitor in comparison with being seen on a DCI-P3 monitor, where they look pretty much like in the original (assuming adequate software configuration for managing the color spaces).

While for commercial movies I cannot verify the fidelity of the color reproduction, because I do not have access to the original images, for photographs that I am taking myself there can be no doubt that the color gamut of sRGB or Rec. BT.1886 cannot reproduce satisfactorily a lot of commonly used things.

The primary red of sRGB/Rec. BT.1886 is really a very bad red, very far from a monochromatic red, because the red phosphors of the early CRT tubes could have either good saturation or good luminosity, but not both, so they have chosen a low-saturation red that was bright enough to match the green and blue phosphors.

>> GP: I prefer the larger colorspace and to get it choose HDR, even if it's not really HDR; the reason is not HDR itself.

> P: But that larger colorspace doesn't require HDR, HDR sucks. I prefer UHD and to get it also choose HDR, even though that's not really HDR; the reason is not HDR itself.

To each their own, indeed.

I should have worded it like this: I prefer to watch movies in UHD, even though they're usually also HDR.

I don't think anyone is saying HDR isn't really HDR. It obviously does support higher dynamic range, but it's kind of like giving someone directions in a language they don't speak. Technically, the spec does what it claims to do, but it adds unnecessary requirements on the display side that undermine a lot of the benefit. As a result, you have filmmakers forced to pick an arbitrary level of "scene white", which in turn means that displays aren't using their full range of brightness as effectively as they could. It also means that most TVs and projectors have to implement their own version of "tone mapping", some of which are pretty terrible to be honest. Not just terrible for HDR, but worse than SDR.

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