Re: Color Model

[Joel Biddier]

C. Ecker wrote:

> > Joel Biddier wrote:
> >    
> [...]
>  
>
> > > - CMYK: would be great to have. AFAIK, it requires to change the internal
> > > representation of the color, because CMYK contains additional information
> > > compared to RGB, i.e. by transforming a color from CMYK to RGB information
> > > is lost. Therefore each color in skencil should be represented internaly
> > > in CMYK-format instead of RGB as it is now.
> > >
> > >      
> [...]
>  
>
> > > Are there any arguments for or against changing the current
> > > implementation
> > > ?
> > >
> > >
> > >      
> > Funny you should say this, for I was thinking about this just
> > yesterday... :-).
> >
> >    
> [...]
>  
>
> > CMYK is a better color model (it is what held back Gimp for years. And
> > Skencil, when it comes to high end printing). I would say that we
> > should  change the color model (which is easy for me to say; given that
> > I am not doing the work at this point ;-) ).
> >
> >    
>
> I did never make use of CMYK myself and wonder whether this is really
> needed.
For most users this is the case. It is not as important as I may put on. 
But it does limit the application to web and visual presentations with 
low quality printing.
As I said earlier, that is what Gimp lacked.  They  (the Gimp 
developers) have now added CMYK - putting Gimp in the professional 
printing realm as well. That is, the application can be used effectively 
by the user on all media (visual and printing) with no guess work on 
colors.

> As I understand it the black component is used to correct for
> deficiencies of the printer. This would mean that the rgb to cmyk
> convertion should be done for the whole document with the same settings
> and probably at the stage of printing. Right ?
>  
Yes, the black corrects the CMY color for black (which is more of a 
muddy brown).
You can change the color scheme, but it's not always that simple - there 
are problems.
Some applications do a good job of this by letting the user know when an 
RGB color they have selected is out of the CMYK gamut.
This is a good proactive way out of the problem. But most users may not 
need this (again it is only for those who indent to print to a 
commercial quality printer).

> If we want CMYK what do we need to change then ? Adding a CMYK to the
> color selection is trivial, but what else would be needed ? What about
> images ?  Color proofs ?
>  

That's my big problem - I don't know. I did not even know that adding 
CMYK to the RGB color scheme was trivial.
I thought it might be really hard to change the color scheme to include 
CMYK.
I only understand the topic at the user level - sorry. But I can learn...

There are options to CMYK (such as ICC ) that can muddy the waters...

> A related question is what the color chooser should look like. I found
> that all programs use different variants and I do not have the background
> to descide that. Options are e.g. values from 0 to 255 or from 0 to 1 or
> in hex, or all of them, mixing of colors, a color wheel as in gtk or
> something else ...
>
> Christof
>
>  

RGB - three 0 - 255 color bars (one, red, green and blue)
CMYK - four 0 % - 100% color bars (one cyan, megenta, yellow and black)

note that the bars really use the same RGB colors on the screen.