from
The Free On-line Dictionary of Computing (8 July 2008)
bits per pixel
bpp
colour depth
<hardware, graphics> (bpp) The number of {bits} of information
stored per {pixel} of an {image} or displayed by a {graphics
adapter}. The more bits there are, the more colours can be
represented, but the more memory is required to store or
display the image.
A colour can be described by the intensities of red, green and
blue ({RGB}) components. Allowing 8 {bits} (1 {byte}) per
component (24 bits per pixel) gives 256 levels for each
component and over 16 million different colours - more than
the human eye can distinguish. {Microsoft Windows} [and
others?] calls this {truecolour}. An image of 1024x768 with
24 bpp requires over 2 MB of memory.
"High colour" uses 16 bpp (or 15 bpp), 5 bits for blue, 5 bits
for red and 6 bits for green. This reduced colour precision
gives a slight loss of image quality at a 1/3 saving on
memory.
Standard {VGA} uses a {palette} of 16 colours (4 bpp), each
colour in the palette is 24 bit. Standard {SVGA} uses a
{palette} of 256 colours (8 bpp).
Some graphics hardware and software support 32-bit colour
depths, including an 8-bit "{alpha channel}" for transparency
effects.
(1999-08-01)