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Dot
pitch, quoted as dpi, dots per inch, is the maximum number of dots in a given
inch of print on a printer or for that matter on any display device e.g.
the monitor.
DPI
is important as it is an indicator of the maximum resolution available. The
greater the DPI the more detail can be printed or displayed.
The
DPI refers to both horizontal and vertical planes and these days normally means
that the screen is composed of cells which are squares of say 255 x
255 dots, with each dot being individually displayed in 1 of 16 million colours!
The more dots the greater the Resolution and the larger the Video RAM. Typically
the Video RAM is 1Mb, 2Mb or greater for very high resolution. A large part of
the video RAM holds the colour information but nevertheless there are an awful
lot of bytes holding the basic dots.
In
the past, with black & white screens and block graphics, video RAM was
typically 4Kb for a 64 column 32 row screen and character generators, basically
ROM, held a bit pattern for each displayable character so the resolution was
'fixed' as the character generators held bit patterns in 8 x 16 dot 'cells' and
the DPI was more commonly known as CPI, characters per
inch!
Printers at the time also had their own character generators and printed
characters according to an output byte value, typically 0-127, and the character
set was limited to what was in the character generator although special output
control bytes gave some variants i.e. bold,italic and condensed by changing the
position of consecutive rows of dots or double striking slightly offset et
cetera! At this time there were no True Type Fonts, TTF. Graphics, if available,
were limited to simple blocks within each 'cell' which allowed very basic chunky
graphics of an extremely low resolution!
Today
there are no character generators as such, basic character set bit patterns are
held within the firmware to enable low level operations, i.e. where fonts are
not available e.g. start-up routines. The font library held in the font file is
able to take advantage of the very high resolution of the PC's video to provide
such things as 'real' handwriting which require a very high DPI. Also today's
Printers are able to print a bit image of the entire screen so that enables TTF
to be correctly printed alongside graphics with true circles rather than
ellipses et cetera!
It's
all down to DPI !!!
Well
chief you made me reach back a few years on this one, but it's still in the grey
matter even though I don't ever think about it anymore!!!
Brian
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