Re: Help with HLG profile

I anyone available who could present the ICC v4 solution to the Color on
the Web CG at TPAC on Thursday afternoon next week ?

I read back over the very illuminating HLG / PQ discussions from earlier in
the year. Thanks to everyone who posted detailed comments back then. Very
helpful!

At the risk of oversimplifying, what I understand from the discussion is
that distribution of a "scene-referred" signal, S, presumes (1) (in
practice) the existence of a function R( S, C, E ), where S is the signal,
C is the display capabilities and E is the environment, where the output of
R is a display-referred signal which is "correct" for that display in that
environment. A "display-referred" signal, D, is just the exact luminance
that should be output by a display with defined capabilities (C1) in a
defined environment (E1). Distribution of a display-referred signal
presumes (2) (in practice) the existence of a function R'( D, C1, E2, C2,
E2 ) that will convert to a "display-referred" signal that is "correct" for
a display with capabilities C2 in environment E2.

It seems to me most of the differences of opinion boil down to differences
in confidence about the presumptions (1) and (2) and the definition (or
indeed importance of, in some cases) of "correct".

It does seem to me, though, that we could say R'( D, C1, E2, C2, E2 ) = R(
R^-1( D, C1, E1), C2, E2 ) and render the two scenarios somewhat equivalent.

Is the root of the problem that "correct" is not sufficiently well-defined
or agreed upon to determine R ?

Again, apologies for the over-simplification!

...Mark









On Mon, Oct 15, 2018 at 3:32 AM Nigel Megitt <nigel.megitt@bbc.co.uk> wrote:

> The TTWG's solution was borne out of expediency; I can check with the TTWG
> but from my perspective it would be great if we could define a reliably
> better way to do this.
>
> Kind regards,
>
> Nigel
>
>
> From: Chris Lilley <chris@w3.org>
> Date: Monday, 15 October 2018 at 11:28
> To: Simon Thompson-NM <Simon.Thompson2@bbc.co.uk>, Lars Borg <
> borg@adobe.com>, Leonard Rosenthol <lrosenth@adobe.com>, Max Derhak <
> max.derhak@onyxgfx.com>, "public-colorweb@w3.org" <public-colorweb@w3.org>
> Subject: Re: Help with HLG profile
> Resent-From: <public-colorweb@w3.org>
> Resent-Date: Monday, 15 October 2018 at 11:28
>
>
> On 15-Oct-18 12:06, Simon Thompson-NM wrote:
>
>  We believe that the best solution for HDR graphics would be to have the
> ability to have correct, working ICC profiles embedded in the image file
> (rather than using an incorrect profile with the ICC profile name as a key
> to induce specific behaviour in the decoding software, as proposed in the
> TTML group).
>
> Yes, undoubtedly. And as you say, the question is whether a v4 profile can
> be constructed, or whether this really needs ICC Max.
>
> I was very unhappy with the TTML solution, although I did get them to be
> clearer about exactly what they were doing (for example, that applying the
> embedded profile would give the incorrect result).
>
> --
> Chris Lilley
> @svgeesus
> Technical Director @ W3C
> W3C Strategy Team, Core Web Design
> W3C Architecture & Technology Team, Core Web & Media
>
>
>
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