Comment by dcrazy | Hacker News Reader

Comment by dcrazy | Hacker News Reader

I’m 14 minutes into this 2 hour 15 minute presentation that hinges on precision in terminology, and Yedlin is already making oversimplifications that hamper delivery of his point. First of all, he conflates the actual RGB triplets with the colorspace coordinates they represent. He chooses a floating point representation where each value of the triplet corresponds to a coordinate on the normalized axes of the colorspace, but there are other equally valid encodings of the same coordinates. Integers are very common.

Secondly, Rec. 2100 defines more than just a colorspace. A coordinate triple in the Rec. 2100 colorspace does not dictate both luminance and chromaticity. You need to also specify a _transfer function_, of which Rec. 2100 defines two: PQ and HLG. They have different nominal maximum luminance: 10,000 nits for PQ and 1,000 nits for HLG. Without specifying a transfer function, a coordinate triple merely identifies chromaticity. This is true of _all_ color spaces.

On the other hand his feet/meters analogy is excellent and I’m going to steal it next time I need to explain colorspace conversion to someone.

If you watch a little further until about 20 minutes what follows is an explanation of what the primaries represent (described by you as “colorspace coordinates”) along with a reasonable simplification of what a transfer function is, describing it as part of the colorspace. I believe that’s reasonable? He merely explains Rec. 2100 as if using the PQ transfer function is innate. Definitely all seems appropriate and well presented for the target audience.

I wasn’t able to resume watching, but if he never describes HLG I would call that a miss for his stated goal.

I don’t want to criticize too much, though. Like I said I’ve only watched 15 minutes, and IIRC this is also the guy who convinced a lot of cinematographers that digital was finally good enough.

The author has a FAQ related to the video and he expands on "Why don’t you mention HLG in the demo" in it https://www.yedlin.net/HDR_Demo_FAQ.html

Continue watching, his overall points are quite valid.

The presentation could surely be condensed, but also depends on prior knowledge and familiarity with the concepts.

He’s also inaccurate when he states that digital cinema is encoded in the P3 color space. It’s actually encoded in the.XYZ colorspace but in most cases, the code values delivered are limited to those that fall within the P3 color gamut. But the XYZ colorspace that’s delivered can encode any color the human eye can see plus many others.

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