[scribus] Colour Profiles - make colour matching worse!

[John Beardmore]

Hal V. Engel wrote:
> On Monday 27 July 2009 02:21:20 pm John Beardmore wrote:
>> Peter Nermander wrote:
>>>> OK, but that might be small price to pay if it made CMS accessible to
>>>> more users. At the moment, complexity makes it less than worthwhile for
>>>> most people.
>>> It wouldn't make it easier, because you would still need a profile for
>>> each output device.
>> Yes, but presumably at the moment, for each input device you need a
>> profile for each supported internal representation, 
> 
> The device only has one representation and the device profile describes how 
> that device representation relates to a device independent color space such as 
> CIELab or CIEXYZ.

Yes -  I suppose my point is that if you can standardise on one or the 
other out of CIELab or CIEXYZ, fewer profiles need to be written which 
should simplify things ?


>> or if there isn't an
>> internal representation, each intended output device ?
> 
> No you are not understanding this.  There are two basic types of profiles.  
> Those for input devices and those for output devices.  Those for input devices 
> are only required to have the information to go from the device color space 
> (like say the RGB values of a camera or scanner) to the PCS and output device 
> profiles have the information to go from the PCS to the output device color 
> space (the RGB values of a monitor or the CMYK values of a printer).  Profiles 
> can also have tables that go in the other direction but this is not required.  
> You need two profiles to do a meaningful transform and the PCS is an 
> intermediary between the input device and the output device color spaces.  I 
> think you are making it more complicated than it actually is.

No -  I understand your para above, but it does seem unfortunate that 
there are two PCSs in common use. Is either one better for any 
particular purpose ?


>>> All colors in CIELAB can't be shown on a monitor, and all colors in
>>> CIELAB can't be printed. Some of the colors in CIELAB can be shown on
>>> a minitor but not printed, and some colors in CIELAB can be printed
>>> but now shown on a monitor.
>>>
>>> Also, a color that can be shown on one monitor might not be possible
>>> to show on another, as well as some printers won't be able to print
>>> colors that other printers can print.
>> Understood.
>>
>>> This is where the rendering intent come into place (and this is the
>>> reason Pantone and similar "color indexes" exists).
>> Possibly, but presumably these describe a specific colour, but you still
>> can't represent them on every output device. Maybe you just buy a bottle
>> of the right ink ?
> 
> The real purpose of the Pantone system is to sell these bottles of ink.

:)


>>> There als also colors that can not be reproduced in i digital image.
>>> Gold and silver are two.
>> Not sure that gold is a colour. Reflectivity is perhaps more of a
>> surface property ?
> 
> Gold is most certainly a color

With my science head on I'd always taking it to be a reflection with 
some bands of wavelengths missing ?

Yes -  OK, there is a shade of yellow that some people call gold which I 
can imagine could fall within many colour spaces, but it has little 
similarity to the appearance of polished edge connector which I doubt 
coulour spaces can describe well as the metal surface transforms the 
light / virtual image that impinges on it.


> and the Pantone system has color patches that 
> are gold and silver and variations on these.  You can also purchase inks for 
> these colors to use as spot colors.

Yes -  but I assume that these metal colloids along with varnishes and 
textures fall outside colour gamuts. I'm not sure that I'd regard them 
as colours even if they are marketed as such. Maybe I should have done 
arts instead of science !


Cheers, J/.
-- 
John Beardmore, MSc EDM (Open), B.A. Chem (Oxon), CMIOSH, AIEMA, MEI
Managing Director, T4 Sustainability Limited. http://www.T4sLtd.co.uk/
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