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

On Thu, Sep 12, 2013 at 5:31 PM, Tab Atkins Jr. <jackalmage@gmail.com>wrote:

> On Thu, Sep 12, 2013 at 3:29 PM, Rik Cabanier <cabanier@gmail.com> wrote:
> > On Thu, Sep 12, 2013 at 2:55 PM, Tab Atkins Jr. <jackalmage@gmail.com>
> > wrote:
> >> On Thu, Sep 12, 2013 at 1:37 PM, Rik Cabanier <cabanier@gmail.com>
> wrote:
> >> > On Thu, Sep 12, 2013 at 12:54 PM, Simon Sapin <simon.sapin@exyr.org>
> >> > wrote:
> >> >> Maybe, but that’s different from the feature specified in GCPM (and
> >> >> that
> >> >> we just decided to move into Color) which does *device* CMYK, where
> the
> >> >> profile is intentionally unspecified.
> >> >
> >> > Sure, but if you're showing it on screen, you have to convert it to
> RGB
> >> > as
> >> > some point.
> >> > What is the profile for that conversion?
> >>
> >> An unspecified, device-dependent profile.
> >
> > ok, in that case it might be best to do the simple conversion to RGB:
> >
> > red = 1.0 - min(1.0, cyan + black)
> > green = 1.0 - min(1.0, magenta + black)
> > blue = 1.0 - min(1.0, yellow + black)
> >
> >
> > Doing the reverse during printing, you know both profiles so you can do
> an
> > ICC conversion. We probably want to special case rgb(0,0,0) though since
> > everyone wants that to be 100% black.
>
> That would be a device-independent profile, which obviously goes
> against the apparent point of the function
>

Not sure if I follow. When you print, you will use the profile of the
device.
The CMYK values will be used as-is since they are assumed to be in the
colorspace of the device (hence *device*-cmyk).

RGB is always in sRGB so you will go from sRGB to device dependent CMYK