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Re: Wide Color Gamut and High Dynamic Range displays

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Thu, 29 Jan 2015 10:49:26 -0800
Message-ID: <CAAWBYDB+FVUYJDUzidTJreNEFyn8AiLqg83nJ0oAixLW0Qodvg@mail.gmail.com>
To: Rik Cabanier <cabanier@gmail.com>
Cc: Mark Watson <watsonm@netflix.com>, "www-style@w3.org" <www-style@w3.org>
On Wed, Jan 28, 2015 at 9:37 PM, Rik Cabanier <cabanier@gmail.com> wrote:
> On Wed, Jan 28, 2015 at 5:45 PM, Mark Watson <watsonm@netflix.com> wrote:
>> The term VUI refers specifically to information attached to a (H.26x)
>> video stream. I'm not sure exactly what's in the "color profile" you're
>> referring to (would like to know).
>
> I found a place that describes the VUI entry: line 105 in
> http://git.videolan.org/?p=x264.git;a=blob;f=doc/vui.txt
> I believe it is the color profile of the video stream (transfer + matrix
> coefficients)

Yes, VUI seems exactly analogous to the concept of "color profile" in
image decoding.

Mark, fyi, "color profile" defines how to map the bytes of the image
data into colors in a well-defined colorspace, typically one of the
"interconnect" spaces that cover all or most of human vision, like
CIELab.  You can then map from the interconnect space into the
display's gamut using the display's color profile.

> Why so? It looks like if you have the VUI info, you have all the information
> to construct a profile.

The problem isn't the profile, it's that the automatic gamut
correction that has to occur if your source file has a wider gamut
than the display is not high-quality (and realistically can't be - as
David points out, whether you want to emphasize the bright or the dark
parts of a scene when displayed on a screen with low luminance range
is an artistic choice, and no technical solution can adequately handle
that automatically).

It's better to deliver a file version specifically formatted for the
lower-gamut screens, which has those kinds of corrections purposely
done by someone competent, and only send the higher-quality version to
screens that can handle it, or close to it.

>> What I'm wondering is what is the appropriate way to indicate these
>> capabilities ? Should these be additional attributes in CSS OM View ? Or
>> should they be new things to be used with Media Queries ? Are there other
>> options ? What are the design criteria for choosing between options ?
>
> I'm still unsure what you're trying to do. Are you trying to pick a video
> based on the connected display or change CSS attributes?

Pick a video source.  Context is <video><source>, which can take a
media='' attribute and do codec negotiation, and related things using
JS-based video streaming.

~TJ
Received on Thursday, 29 January 2015 18:50:16 UTC

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