Re: My misunderstanding of Postscript printing
- From: Ian Gregory <foo@xxxxxxxxxxx>
- Date: 22 Jun 2007 23:45:07 GMT
On 2007-06-22, paintedjazz@xxxxxxxxx <paintedjazz@xxxxxxxxx> wrote:
Yet when it comes down to it, doesn't the laser printer have to take
that postscript from the ROM chip and still use rasterization to get
the toner powder on to the paper via the fuser roller? So the
Postscript ROM chip interprets the Postscript code in order to just
create a rasterized image anyway?
A postscript printer conatains a postscript interpreter which
interprets the postscript program that you send to it. In
interpreting that program it may create actual printed pages
containing the marks described in the program but it doesn't
have to. It could do some complex calculation and send the
result back to the computer written in a return code or
message. If it does print a page then that is created as
a raster image and sent to the engine (perhaps sent multiple
times if the postscript asked for multiple copies of that page).
Another mystery is printing e.g. a JPEG. Being a rasterized image
already, why would the JPEG even be touched by the printer driver/PPD
except to send it along? Surely, it wouldn't convert it to Postscript
only to be later re-interpreted back to a rasterized image for final
submission.
It might. Postscript contains its own construct to represent
a raster image. Here I am out of my depth though - with some
versions of postscript you might be able to "include" jpegs
directly and the interpreter might then effectively call a
jpeg routine to get the image included on the final raster
image that is sent to the engine. Otherwise the computer would
have to decode the jpeg, do any necessary transformations
and then encode the data as a postscript raster image within
the resulting postscript file - which would then be sent to
the printer for interpreting.
Cheap printers that do not have a postscript interpreter built
in work by getting the computer to run a postscript interpreter
to build the correct sized raster image for sending directly
to the engine.
My favorite postscript program was one I wrote to draw
fractal snowflake patterns. It employed recursion with
a configurable recursion depth. It was only a few short
lines and so was a very small file, but if I set a high
recursion level the interpreter in the printer could
take hours to form a raster image representing millions
of line segments.
Ian
--
Ian Gregory
http://www.zenatode.org.uk/ian/
.
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