Re: 24-bit-per-pixel limit to Gdk RGB ?

[TORRI Vincent <Vincent Torri math u-bordeaux fr>]

On Tue, 18 Feb 2003, Thomas Cameron wrote:

> Roland Smith wrote:
>
> > On Tue, 18 Feb 2003 17:16:33 -0300
> > individual <individual mi cl> wrote:
> >
> >  
> >
> > > That's interesting. I was always under the imprsesion that we have left 
> > > 24bpp displays far behind. Here's what my system says:
> > >
> > > Resolution        Video Memory
> > >                                    8MB
> > >                              (SGRAM)
> > >
> > > 640 x 480               32-bit
> > > 800 x 600             32-bit
> > > 1024 x 768          32-bit
> > >    
> >
> > I _think_ that those 8 extra bits are for alpha blending (transparency). 
> >
> >  
> >
> > > Eek.... I was hoping for greater bit depth, but I'm getting more and 
> > > more convinced that it's pointless to try and render a 48 bpp image at 
> > > 48 bpp screen depth when screens are at most 24bpp deep.
> > >    
> >
> > It's not pointless. You won't lose much quality. Consider: on a 1024*768 monitor
> > you can only display 786432 different colors (if every pixel has a different
> > color, which is quite rare, unless you've got some very psychedelic images)
> >
> > To be able to display all the colors in an 24bpp gamut, you'll need 16777216
> > ((2^8)^3) pixels, which is something like 4729*3547 in traditional 4:3 ratio. If
> > you come across a cheap display that can handle this, let me know. :-)
> >
> > Roland
> >  
> The format is this:
>
> 32 bit display: 8-bits RED, 8-bits GREEN, 8-bits BLUE, 8-bits ALPHA
> 16 bit display: 8-bits RED, 8-bits GREEN, 8-bits BLUE

8+8+8=24 not 16. When they are coded with 16 bits, there is 65536 colors 
(2^16). I have read that, in that case (16 bit display) , red and blue was 
both coded with 5 bits and green with 6 bits. It surprised me and I don't 
know at all if this is the case (if there is an additional bit for the 
green color). If someone has a comment...


> This is for computer monitor displays, of course.  Personally, I have 
> never heard of a 48bpp display, and I am quite certain that the human 
> eye could not distinguish such a small degree of difference.  Of course, 
> if you are a quality-phile, like me, you would render in 48bpp anyway.  ;-)

The eye can distinguish 2000000 of colors, a display of 24 bits gives a 
number of colors far beyond what we can see.

Vincent TORRI

> Good luck,
> Tom Cameron
>
>
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-- 
TORRI Vincent
Mathematiques Appliquees Bordeaux                                                
Institut de Mathematiques                                                       
Universite Bordeaux 1                                                           
351 cours de la liberation                                                      
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