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

From: Chris Lilley <chris@w3.org>
Date: Mon, 30 Sep 2013 13:14:22 +0200
Message-ID: <0389217.20130930131422@w3.org>
To: Alan Gresley <alan@css-class.com>
CC: "Tab Atkins Jr." <jackalmage@gmail.com>, Rik Cabanier <cabanier@gmail.com>, Simon Sapin <simon.sapin@exyr.org>, www-style list <www-style@w3.org>
Hello Alan,

Saturday, September 28, 2013, 8:37:04 AM, you wrote:

> On 25/09/2013 9:23 PM, Chris Lilley wrote:
>> Hello Tab,
>>
>> Wednesday, September 25, 2013, 12:25:28 AM, you 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>
>>>>> I doubt that this "just use the channels" approach is compatible with
>>>>> some other color spaces, like Lab, though.
>>>>
>>>> It is compatible. You can try it in PhotoShop :-)
>>
>> It is compatible because it is an additive colour space.
>>
>>> How does that work, though?  I mean, HSL doesn't work in a "just use
>>> the channels" approach,
>>
>> HSL isn't an additive colour space; its syntactic sugar for RGB and
>> thus you composite the RGB values.
>>
>>>   which is why the HSL blend modes are
>>> non-separable.  Why would Lab work?
>>
>> Because Lab is an additive colourspace with orthogonal channels.

> Can you point me to a display device that shows Lab or is this just 
> theoretical?

Neither. Its not a display device and its not 'just theoretical'.

Tab asked why some colourspaces could perform independent channel by
chanel operations, suspected that it applied to RGB but not Lab; and I
answered why (you can do it with ones that are additive). Lab is an
example of an additive colourspace and can be, and is, used for
compositing.

That doesn't require it to be a native device profile. Its a space for
computation.

-- 
Best regards,
 Chris                            mailto:chris@w3.org
Received on Monday, 30 September 2013 11:14:29 UTC

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