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

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

From: Rik Cabanier <cabanier@gmail.com>
Date: Sat, 28 Sep 2013 19:59:43 -0700
Message-ID: <CAGN7qDBxH4LszhmM_6RpjYm7uN81EvoTj3A4tUAafbzBjoesQA@mail.gmail.com>
To: Alan Gresley <alan@css-class.com>
Cc: Dirk Schulze <dschulze@adobe.com>, "Tab Atkins Jr." <jackalmage@gmail.com>, Simon Sapin <simon.sapin@exyr.org>, www-style list <www-style@w3.org>
I can't find how it's done in the Core Graphics documentation.
For going to display, most likely the color are mapped immediately from
CMYK to RGB using the rendering intent and the 'generic' CMYK and RGB
profiles. You can find these profiles in the ColorSync utility.

When 'drawing' to PDF, the CMYK value is preserved.
(This is pretty much the workflow I proposed.)


On Fri, Sep 27, 2013 at 11:17 PM, Alan Gresley <alan@css-class.com> wrote:

> On 25/09/2013 4:27 PM, Dirk Schulze wrote:
>
>>
>> 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
>>
>
> Ok, stroke operation for example is done with
> CGContextSetCMYKStrokeColor() but a typical display device has RGB pixels.
> There must be a conversion somehow from CMYK pixels to RGB pixels or does
> CGContextSetCMYKStrokeColor() only work with printing?
>
>
> Alan
>
> --
> Alan Gresley
> http://css-3d.org/
> http://css-class.com/
>
Received on Sunday, 29 September 2013 03:00:10 UTC

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