Whether scanning or printing at high resolutions, much
more data is involved. Table 5.3 illustrates the amount
of data and memory involved to print an 8-by-It-inch graphic.
Memory Requirements To Print a Graphic |
Printer |
Megabytes required |
9-pin dot
150-dpi laser
24-pin dot-matrix
300-dpi laser
400-dpi laser
1270-dpi laser
1690-dpi laser
2540-dpi laser |
0.18
0.24
0.68
0.94
1.67
3.78
16.92
29.96
67.68 |
The first interesting fact that you can observe from this
table is that the 300-dpi laser needs 1M of memory. Most
lasers come with 512K. These printers cannot print a full-page
300-dpi graphic unless more memory is added. Only a half-page
300-dpi graphic can be printed. Because the memory in a
printer is used for things other than just the graphic image,
a small amount of additional memory is needed. If fonts
are downloaded, the memory available for printing graphics
decreases. The standard 512K, 300-dpi laser can print at
only 150 dpi. This is less than the resolution of a 24-pin
dot-matrix printer. The reason dot-matrix printers can print
a 180-by-360-dpi graphic with so little memory is that they
print an 8- or 24-bit-wide strip across the page, and thus
have to image only that strip rather than the whole page.
Inkjet printer models can image the whole page like a laser
printer or image part of a page like a dot-matrix printer.
If object capabilities are in the printer, add 2M.
HINT Some lasers that run out of memory when printing a
graphic print half the page, eject the paper, and then print
the other half. You can combine these halves to form a full-page
300 dpi graphic.
Most people complain how slow object printers are when
printing text compared to character-mode printers. If the
same fonts are available for both, character-mode printers
will print the document quicker. But, object printers print
faster when flexibility and creativity are required. Object
printers also print faster than graphics printers. It can
take more than 17 minutes just to transmit the graphic data
to a 300-dpi graphics-mode printer at 9,600 bps. Much less
data has to be transmitted to an object-mode printer. Of
course, after the data arrives, the object-mode printer
has to think about it. The amount of time an object printer
spends thinking about an object depends on the object, how
much memory, and how fast the object printer is.
Look at the 2,540-dpi laser printer. Consider how long
it would take to transmit 67.68M at 9600 baud more than
20 hours. If an electronic form of a graphics page is going
to be transmitted over telephone wires to a publishing house,
this seems almost impossible. However, an object page can
be transmitted easily.
To speed the transfer of graphics data to its printers,
Hewlett-Packard modified the parallel port of its LaserJet
II to work much faster than the parallel port ever has worked
before. This causes intermittent compatibility problems
with many PC printer interfaces; the printer acts "dead."
If the parallel interface works, data can be transmitted
up to 10 times quicker 1.7 minutes for a 300-dpi page rather
than 17 minutes.
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