graphics - enhancing resolution?

graphics - enhancing resolution?


Author: Axel Petzold
Email: a.petzold@ion.ucl.ac.uk

System Architecture: Intel
RedHat Release: RHL 5.2
FAQ Category: Printing and Printers
Modification Date: Feb 15, 1999

Question:

A common problem is that printers provide 300 dpi or more, however for
graphics (e.g. scanned greyscale/color pictures) the maximal resolution
seems to be 75 dpi, sometimes 150 dpi.  How can the resolution for
graphics be enhanced?  

Answer:

 
Laserprinters use a feature called dithering. They have a fixed matrix of
dots, normally 75 dpi and vary the radius of these dots. So from a
distance one perceives dark grey as dark grey and light grey as light grey
(colour printers plot theses points of different colors over each other -
like the pixels on a TV). Now if you observe the picture closely you will
distinguish the points. You can even use a lineal and meassure their
distance. This distance remains the same whatever you do with your printer
and is by no means close to the 300 dpi you'd thought you'd get.

People who use GIMP can manipulate the language their computer talks to
the printer.  The GIMP offers in it's print function a feature where you
can choose between postscript level 1 and level 2 (what is to be
recommended) or multiple other options. Best results are obtained with
postscript level 2.  Poscript level 3 hasn't been implemented yet. If your
printer is not a postscript printer, you can find in this FAQ "Updating
printtool to work with GhostScript 5.50" a hint howto use GhostScript.

If you really want a photolike image you still need to send your picture
to a company which has the appropiate hardware for such quality. - Until
someone has an idea how to overcome this and push an ordinary laserprinter
to do thatjob... However there is good news - you don't need to scan your
images with more than 150 dpi. This will save you a lot of space on your
harddisk...

References:

None specified.