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

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

From: Alan Gresley <alan@css-class.com>
Date: Sat, 28 Sep 2013 16:17:03 +1000
Message-ID: <5246745F.4000207@css-class.com>
To: Dirk Schulze <dschulze@adobe.com>
CC: Rik Cabanier <cabanier@gmail.com>, "Tab Atkins Jr." <jackalmage@gmail.com>, Simon Sapin <simon.sapin@exyr.org>, www-style list <www-style@w3.org>
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 Saturday, 28 September 2013 06:17:33 UTC

This archive was generated by hypermail 2.3.1 : Saturday, 28 September 2013 06:17:38 UTC