Re: Default colors vs. gamma

[Quentin Mathé]

Le 1 nov. 04, à 12:03, Fred Kiefer a écrit :

> Looks like my mail was still unclear in what I propose. Sorry for 
> that. I suggest that we don't implement the gamma correction when 
> defining the system colours (I hope this part was clear)

yes, it was clear.

> , but instead implement it as a conversion between calibrate colour 
> spaces and device colour spaces. you see, whenever we want to set a 
> calibrated colour in a device it should be converted to the device 
> colour space. I hope I did put in a comment on this, when I rewrote 
> the colour classes.

ok
I'm not a color expert but here is what I understand : system colors 
should depend when possible on a CIE color space (XYZ, Lab etc.), then 
when the output is done to the screen or the printer, the CMS 
translates the color by using the screen and the printer profiles.

> I think it would be best to have a full CMS impelemented here for the 
> conversions. If you think this is hard remember that the original 
> cairo backend had colour management implemented and that one of the 
> drawing applications, I think it was Cenon, comes with colour 
> management build in.

What is this original cairo backend ? How is it different from the 
cairo backend included in GNUstep since this summer ?
If Cenon has a nice CMS, may be it should included in GNUstep or we can 
improve it in order to create a CMS which fits our needs. ?

> Even if we don't use a CMS library here this conversion is the place 
> where gamma correction should be put. Of course this will require a 
> few more extensions, devices should know about their colour space and 
> that information should be used here and so one, but by using this we 
> would imporve display on the monitor, while not losing (perhaps even 
> gaining) in PS and printer output.

Sure.
Well you haven't replied to my questions on how Mac OS (before 
ColorSync), KDE and GNOME are displaying their colors on screen with a 
gamma which is equal to 1.6 or 1.8 (for Mac OS). But I deduce they are 
probably relying on a light CMS which supports only gamma conversion… 
you propose the same thing if I understand correctly, I think it's the 
right solution and it should be relatively easy to develop a such 
system before to have a full CMS system in the future.
Well but I must say I don't understand why you are saying "this will 
require few more extensions" like devices with a color space specified, 
in my opinion if for the initially we do only gamma conversion, we just 
need to use the gamma set by the user for this screen or the default 
fallback gamma probably 1..6 or 1.8 to transform the system colors 
(probably using a 1.0 gamma) for a relatively right output on the 
screen without consideration of the screen color space.

Nb : I don't know if it would be useful for the printers to have the 
possiblity to specify a gamma.

> If this mail is still unclear, I'll give up and start to code it. 
> Words are so complicated, Objective-C is so easy...

hehe :-) Objective-C : the only C derived language which is easier than 
C itself.

Thanks for your reply Fred, I understand the things better now.

Quentin.

--
Quentin Mathé
qmathe@club-internet.fr