Re: [gtk-list] Re: how to convert windows RGB color to GdkColor

[Rick L Vinyard Jr <vinyard zianet com>]

"Timothy M. Shead" wrote:
> 
> >    This is not enough.  You then need to add the original value.  I.e.
> >
> >          new_value = (old_value << 8) + old_value;
> >
> >    Assuming old_value is in [0, 255].
> >
> > I thought I understood gdkcolors until now.  I have always been under
> > the impression that a gdkcolor simply uses a 16-bit value for each of
> > red, green, and blue, and that it was converted for whatever hardware
> > you were to run on by dividing (so, to run on something with 8-bit
> > DACs, you'd right-shift by (16-8) == 8).
> 
> Right-shifting to convert from 16bpp to 8bpp works fine:
> 
>         0xFFFF (full-bright) becomes 0xFF (full-bright).
> 
> But left-shifting doesn't:
> 
>         0xFF (full-bright) becomes 0xFF00 (less-than-full-bright).
> 
> Adding in the old value is a fast way to scale the values properly, so 0xFF
> becomes 0xFFFF.  You can multiply by 257.0 if you prefer :)
> 

Well stated. And by gradually shifting through the range, you end up
with a more balanced spectrum of intensities, rather than shifting to a
brighter intensity like I stated earlier. I had forgotten about that
when I replied earlier, and was too focused on data structures.

-- 

Rick L. Vinyard, Jr.