[argyllcms] Re: White point or black point adjustment not working

On Friday 17 July 2009 03:08:10 pm Alastair M. Robinson wrote:
> Hi,
>
> George Willegers wrote:
> > A line showing R+ G+ B-- changes into something like R-- G- B+
> > And this keeps going on, even if I do change the monitor settings,
> >
> > Can anyone explain what is happening, and better how it can be stopped?
> > Below is some output of dispcal.
> >
> > Adjust R,G & B offsets to get target x,y. Press space when done.
> >   Target Br 0.34, x 0.3025, y 0.3512
> > / Current Br 0.47, x 0.2950, y 0.3346  DE  8.1  R+  G+  B--
>
> I don't know what settings are available on your particular monitor but
> with many LCDs there's not a lot you can do at the black end of the
> scale.  

This depends on the monitor.  On several Samsung LCD monitors that I have 
played around with the RGB controls where actually per-channel gamma controls 
that had little affect on the white point.  With those monitors using the RGB 
controls to set the black point while using the "native" white point appeared 
to work best.  In the case of the particular monitor the the OP is asking 
about it might very well be the other way around.  My point is that you can't 
make blanket statements about how the controls work on LCD monitors.
   
> If you only have one set of RGB controls, use them to tune the
> white point rather than the black point.  If you have RGB offset
> controls as well, then it's worth playing with the black-point.
>
> The fluctuation you're seeing is just due to your instrument's
> repeatability not being perfect, and isn't the huge problem it might
> appear at first sight.
>
> When tuning the white point, you should find that dispcal displays a
> current colour temperature, a dE value and suggested adjustments.  Your
> goal here is to minimise the dE while achieving the colour temperature
> you want.  If you're lucky you'll be able to get the dE low enough that
> the RGB "suggestions" will read R= G= B=.  With less-than-perfect
> repeatability you might not manage that, but just get the dE as low as
> you can.
>
> Hope this is some help
>
> All the best,
> --
> Alastair M. Robinson

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