[Scribus] [SLIGHTLY OFFTOPIC] How do I do color correction

[Hal V. Engel]

On Tuesday 06 March 2007 15:18, jon wrote:
> > sRGB is an approximation of a monitor calibrated to gamma 2.2 and ?
> > D65. ?Not
> > gamma 1.8 which is a now long obsolete Mac standard. ?In addition, ?
> > most CRTs
> > have a native gamma between 2.3 and 2.5 so even sRGB will be ?
> > incorrect for
> > most CRTs.
>
> Sorry to intervene here but I thought gamma 1.8 is a defacto standard ?
> for prepress monitor devices, isn't it?

Almost everyone now uses gamma = 2.2 and this has been considered the standard 
on the Mac for some time now.  The Mac is used a lot for prepress work and 
there was a time when 1.8 gamma was the Mac (and therefore the prepress) 
standard.   What really matters is that your monitor is adjusted and 
calibrated to a known gamma (it could really be almost anything with in 
reason) and then characterized (IE. profiled) at that gamma.  Then no matter 
what your monitors gamma images will be displayed correctly when you use a CM 
aware application like Scribus or CinePaint or Photoshop assuming that you 
have CM setup correctly.   In other words if you have two monitor sitting 
site by site and one has a gamma of 1.8 and the other has a gamma of 2.2 and 
you use the correct profiles to display the same image on both monitors they 
will have the same appearance.

My main point was that using sRGB as your monitor profile if your monitor was 
calibrated to a gamma of 1.8, or any gamma other than 2.2, would give bad 
results since sRGB has a gamma close to 2.2.  The CMS would think your 
monitor had a gamma of 2.2 because of the profile when it really had a gamma 
of 1.8 and not make the right corrections to correctly display the image on 
that monitor.  Your images would end up being much too dark on your display 
in this case.  In other words your monitor gamma needs to be a close match to 
your monitor profiles gamma.

Just a small technical note.  sRGB has gamma = 2.2 over most of it range and 
then deviates from that at the dark end of it's tonal range.  Therefore it is 
not truly a 2.2 gamma but only close it being 2.2.

There are other reasons to use a monitor gamma near 2.2.  Generally most 
non-color managed images are considered to be sRGB.  Having your monitor 
calibrated to gamma = 2.2 will result in things like images on web sites 
being displayed fairly close to the way they should be.

Hal