Re: [css-color] wider/deeper colors

On Fri, Feb 19, 2016 at 11:05 AM, Chris Lilley <chris@w3.org> wrote:

> Hello Mark,
>
> Thursday, February 18, 2016, 8:19:53 PM, you wrote:
>
>
> Does, or should, this thread consider High Dynamic Range as well as wide
> color gamut and higher bit depth ?
>
> ...Mark
>
> It should consider it, yes, particularly for output on web-enabled TVs,
> home cinemas, and suchlike devices which handle a high dynamic range.
>

​Ok. We may also see laptops / tablets / monitors with high dynamic range
too.

An issue I see with HDR is that for sRGB it is clear how the luminance of
the peak white is determined: the user sets it to whatever is comfortable
for them with the brightness control, possibly modulated by ambient light
sensors.

Since most content will be sRGB, I would expect the same to apply with HDR
displays: the user will set the brightness to whatever makes peak white of
the ​sRGB graphics comfortable for them.

So, then, what luminance should HDR signals be rendered at ? I think if you
rendered the peak white of an HDR video at the same luminance as the peak
of the sRGB then you are going to get a very dim image and are not
exercising the HDR capabilities of the display.

Put another way, there is no canonical mapping of the sRGB color volume
into the color volume of an HDR display. Such a mapping is parameterized at
least by the ratio between peak white in sRGB and peak white of an HDR
signal.

Additionally, when we define a color through RGB codepoint values we now
need to specify the transfer function as well: it is not implicit in a
colorspace definition which defines only the primaries.

...Mark



>
> On a related note, there should be an open issue about black point
> compensation, too.
>
>
>
>
> *-- Best regards, Chris  Lilley Technical Director, W3C Interaction Domain*
>