Re: Q: Default bpp resolution 32 in Linux?

[Hubert Chan <hackerhue@crosswinds.net>]

Lee Elliott <LeeE@spatial.freeserve.co.uk> writes:

> Hello,
> 
> I don't think that using 32bpp increases the number of colours that can
> be used - 32bpp is generally used as 24bpp (8bpp each for RGB) + 8bpp
> alpha channel.  16bpp is split R=5bpp, G=6bpp & B=5bpp.  I've seen 36bpp
> scanners and they do work with more colours - 12bpp each for RGB.

I've never seen the alpha channel actually being used, but the main advantage
that 32bpp has over 24bpp is that it is/should be faster, since pixel addresses
line up with word boundaries in 32bpp (each pixel is 4 bytes rather than 3
bytes).  And, of course, the disadvantage is that it takes more memory.

It wouldn't make much sense to have more than 16M colours on a screen, since
16M is about the number of colours that a person can see on a screen.
Interestingly, people can see more colours on printed matter than on a screen,
which may be one reason scanners use higher bit depths.

Hubert