W3C home > Mailing lists > Public > www-style@w3.org > September 2013

Re: [css-gcpm][css-color] device-cmyk() interaction with RGB-space colors.

From: Dirk Schulze <dschulze@adobe.com>
Date: Tue, 24 Sep 2013 23:27:10 -0700
To: Rik Cabanier <cabanier@gmail.com>
CC: "Tab Atkins Jr." <jackalmage@gmail.com>, Simon Sapin <simon.sapin@exyr.org>, www-style list <www-style@w3.org>
Message-ID: <523BF5D9-0F8A-42C7-8BA0-53E66DF4301D@adobe.com>

On Sep 25, 2013, at 7:50 AM, Rik Cabanier <cabanier@gmail.com> wrote:

> 
> 
> 
> On Tue, Sep 24, 2013 at 10:29 PM, Dirk Schulze <dschulze@adobe.com> wrote:
> 
> On Sep 25, 2013, at 7:20 AM, Rik Cabanier <cabanier@gmail.com> wrote:
> 
> >
> >
> >
> > On Tue, Sep 24, 2013 at 10:15 PM, Dirk Schulze <dschulze@adobe.com> wrote:
> >
> > On Sep 25, 2013, at 12:43 AM, Rik Cabanier <cabanier@gmail.com> wrote:
> >
> > > On Tue, Sep 24, 2013 at 3:25 PM, Tab Atkins Jr. <jackalmage@gmail.com> wrote:
> > > On Tue, Sep 24, 2013 at 3:14 PM, Rik Cabanier <cabanier@gmail.com> wrote:
> > > > On Tue, Sep 24, 2013 at 2:58 PM, Tab Atkins Jr. <jackalmage@gmail.com>
> > > > wrote:
> > > >> On Tue, Sep 24, 2013 at 2:31 PM, Rik Cabanier <cabanier@gmail.com> wrote:
> > > >> > The compositing/blending spec doesn't talk about converting colors [1]
> > > >> > All
> > > >> > the formulas (except for 4 special ones) work on individual color
> > > >> > channels,
> > > >> > regardless of what they represent.
> > > >>
> > > >> Those channels appear to be assumed to be RGB.
> > > >
> > > > Can you point out where that is so I can update the spec?
> > >
> > > Hmm, I guess it actually doesn't.  The few examples that give explicit
> > > color numbers are all written with RGB, but there's nothing outside
> > > the examples that actually talks about the color value.
> > >
> > > Great. I made a not to add CMYK (and spot?) examples for the next version.
> >
> > We already have CMYK so the note would make sense in this level already, wouldn't it?
> >
> > Is there any support for CMYK as an output color space?
> >
> > Even though WebKit does not preserve CMYK (and transforms it into RGB) for CSS, it has proper CMYK handling in Canvas (in Safari). And CSS Compositing addresses Canvas as well.
> >
> > Really? Canvas is always RGBA; how would you create a CMYK canvas?
> 
> You can specify CMYK colors for drawing and WebKit/Safari does exactly that. It draws with the specified CMYK colors.
> 
> Sure, but you won't draw CMYK pixels. The color is somehow converted to RGB and then the operation draws with the converted color. 

The stroke operation for example is done with:

CGContextSetCMYKStrokeColor();

Greetings,
Dirk
Received on Wednesday, 25 September 2013 06:27:59 UTC

This archive was generated by hypermail 2.4.0 : Friday, 25 March 2022 10:08:34 UTC