Re: [css-color] wider/deeper colors

On Tue, Mar 22, 2016 at 10:19 PM, Simon Fraser <smfr@me.com> wrote:

> On Mar 22, 2016, at 6:54 pm, Rik Cabanier <cabanier@gmail.com> wrote:
>
> On Tue, Mar 22, 2016 at 5:49 PM, Simon Fraser <smfr@me.com> wrote:
>
>>
>>
>> The 4k/5k iMac and the new iPad Pro composite in unclipped sRGB, and map
>> to the display colorspace (DCI-P3) at the end. We (WebKit) have no control
>> over the colorspace used for compositing, so we don’t have knobs to tune
>> here.
>
>
> Why can't you use colorsync?
>
> https://developer.apple.com/library/ios/technotes/tn2313/_index.html#//apple_ref/doc/uid/DTS40014694-CH1-FRAMEWORKS_FOR_COLOR_MATCHING_WHEN_RENDERING_TO_THE_DISPLAY
> <https://developer.apple.com/library/ios/technotes/tn2313/_index.html#//apple_ref/doc/uid/DTS40014694-CH1-FRAMEWORKS_FOR_COLOR_MATCHING_WHEN_RENDERING_TO_THE_DISPLAY>
>
>
> ColorSync is about doing color matching, not composting. To be clear, when
> I say “compositing” here I mean what happens when you paint non-opaque
> images and colors on top of each other, and when the GPU composites
> non-opaque textures.
>

Are you sure?
The documentation on your website seems to point out that colorsync is used
to map from input to destination during compositing.

https://developer.apple.com/library/ios/technotes/tn2313/_index.html#//apple_ref/doc/uid/DTS40014694-CH1-FRAMEWORKS_FOR_COLOR_MATCHING_WHEN_RENDERING_TO_THE_DISPLAY
<https://developer.apple.com/library/ios/technotes/tn2313/_index.html#//apple_ref/doc/uid/DTS40014694-CH1-FRAMEWORKS_FOR_COLOR_MATCHING_WHEN_RENDERING_TO_THE_DISPLAY>
This link shows how you tag the input

In the following link:
https://developer.apple.com/library/ios/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_context/dq_context.html#//apple_ref/doc/uid/TP30001066-CH203-SW9
under "Listing 2-5  Creating a bitmap graphics context", it shows how to
create a context with a profile. If you follow the links on the page, it
describes how you can attach name color spaces (such as sRGB and p3).
>
> Also, if you composite in unclipped sRGB, how are you honoring images with
> a high gamut profile such as p3 or AdobeRGB?
>
>
> Because it’s unclipped? Compositing happens in 10-bit or half-float
> textures which may contain < 0 or > 1 values. A P3 image is mapped into
> this unclipped sRGB space for compositing, then the final result is mapped
> into Display-P3 at the end.
>

That's a bit odd :-)
Does this mean there's no gamut mapping from the image profile to the p3
profile? it seems you can't do that because the intermediate space is
unbounded...