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

[Peter Finderup Lund <firefly diku dk>]

On Wed, 19 Feb 2003, TORRI Vincent wrote:

> (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...

The eye is more sensitive to greenish/yellowish colours.  Some card/modes
are 15-bit: 5 bits per channel.  The better ones are 16-bit: 6 bits for
the green channel and 5 for each of the others.

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

The eye has much greater sensitivity for intensity differences -- there
are built-in edge detectors in our eyes + we also have higher spatial
sensitivity for intensity than for colours.  If the output medium was of a
higher quality than a normal monitor (be it CRT or LCD) you /could/
benefit from far more than 10 bits per channel.  Unfortunately, both types
are too noisy for us to perceive the difference (for example the fact
that we have to time average the intensity of each pixel as it varies
according to phosphor type, frame rate and initial excitation + the bleed
from neighbouring pixels -- the electron gun(s) doesn't (can't!) switch
cleanly on/off).

-Peter

"Of course, I'm not unbiased, but in my humble opinion, I've
  gotten close to something that I can be really proud of."
 -- Knuth on The Art of Computer Programming.