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Re: [csswg-drafts] [cssom-1][mediaqueries-5][css-color] Dealing with bi-plane (video/graphics) when reporting values (#4471)

From: chcunningham via GitHub <sysbot+gh@w3.org>
Date: Wed, 30 Oct 2019 19:22:34 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-548073347-1572463353-sysbot+gh@w3.org>
I don't think we want to add transfer function. We considered this earlier: while it is a property of displays, and core to HDR support, we concluded that it falls on the "UA" side of the UA-Screen boundary, which is admittedly a blurry concept for things like smart TVs. We instead added it to mediacapabilities.decodingInfo(), which works well for both the classic desktop/laptops as well as smart TV setups. 

For Screen, I think the important considerations are peak brightness and black levels. For example, the UHD alliance certification offers [two specs](https://www.cnet.com/news/what-is-uhd-alliance-premium-certified/): "A minimum brightness of 1,000 nits, along with a black level of a maximum of 0.05 nits (20,000:1 contrast ratio), or a minimum brightness of 540 nits, along with a black level of a maximum of 0.0005 (1,080,000:1).". I'm definitely NOT saying we should adopt those requirements - just giving an example of how a site author might use attributes like peak brightness and black levels to make the call. 

This is obviously more future proof, and the Media Capabilities spec did originally suggest similar (luminance) properties on Screen. This was discussed across several long threads alongside other topics and other Screen proposals, but here's my distillation: hdrSupported was deemed more privacy preserving[[1](https://github.com/w3c/media-capabilities/issues/118#issuecomment-515103664)] and sufficiently practical[[2](https://github.com/w3c/media-capabilities/issues/118#issuecomment-522176125)]. That is, sites don't really care if you're using a $10K pro display that meets the high end of UHD requirments vs a $2K TV that is "HDR" but not nearly as capable - in both cases, they want to send you their best HDR content. 

**But, that last point about the boolean's practicality seems mostly to consider the various levels of HDR currently available**. While we may be at peace with a bool for the whole of the current spectrum, it is definitely worth asking if this is future looking enough for future display capabilities. Example: say in 2025 the high end displays are now offering a contrast ratio of 10x that from the current UHD specification. It seems possible that this could lead sites to add another tier to their encodings which they would offer to these new displays, while offering HDR displays of 2020 the HDR content that was mastered in 2020. 

@mwatson2

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Received on Wednesday, 30 October 2019 19:22:36 UTC

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