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Steve,
I can explain better using black and white printers; for color, just add
four times the explanation.
For a monochrome printer, there is a tradeoff between lpi and grayscales. If
you have a 600 dpi printer, and you chose a 600 lpi screen, you have two
grayscales, white and black. Anything you print will look very posterized,
for each pixel has to be black or white. If a part of the image is offwhite
or light gray, it becomes white, if it's dark gray, or medium gray, it
becomes black.
If you decide to change it to 300 lpi, each element of the line is composed
2x2 cells (300 lpi x 2 pixels/per cell = 600 dots). This gives you 5
grayscales, white, 1 pixel dark, 2 dark, 3 dark and 4 dark. You would still
see lots of posterization. It help[s to draw a little 2x2 square.
Typically, most 600 dpi printers use 100 or 106 lpi, to give you about 37
levels of grey, draw a 6x6 square. You may be able to set the printer to use
a lower lpi with a higher numnber of grayscales.
Now, for color, CMYK, you have 4 lpi's to worry about, and screen angles so
that you don't get moires. It gets complicated.
I did a search on lpi vs dpi, and the following link is pretty good,
http://graphicdesign.about.com/library/weekly/aa070998.htm
George
In lugnet.publish, Steve Barile writes:
> I have been pondering this point for years, but don't know much about the
> half toning for CMYK ink mixing algorithms. Is this something you know
> about? Can you share some more info and or links to pages that explain the
> difference between printer advertised resolution, for instance how many
> printer dots make up an image pixel.
> SteveB
>
> In lugnet.publish, Philippe Hurbain writes:
> > What kind of extraordinary printer do you have ??? Even with good inkjet
> > photo printers (with so called 1440 dpi resolution, which is actually dot
> > placement resolution), you can't see improvements above 200 dpi...
> >
> > To be conservative, your image dimension need to be 250 dpi x 8 inches =
> > 2000 dots wide.
> >
> > Philo
> > www.philohome.com
> >
> >
> > In lugnet.publish, Richard Marchetti writes:
> > > Hey Y'all:
> > >
> > > I have a project created in Ldraw/POV-Ray of which I would like to create a
> > > higher (PPI/DPI) resolution image of approximately 8" x 8". I'd like to be
> > > able to achieve something like 600-1200 ppi for the final image printed on
> > > paper.
> > >
> > > I have used Photoshop for mocking up my final designs and it has a tendency
> > > to default to 72 ppi. It can be arbitrarily set to a higher resolution, but
> > > if the original image's resolution isn't likewise higher you just end up
> > > with a blurry, more ppi heavy image. I hope I am making myself understood...(?)
> > >
> > > I have the funny feeling that what I need to know is some arcane POV-Ray
> > > thing that would up the ppi of the images outputted from POV-Ray. Anyway,
> > > that would be one solution.
> > >
> > > Anyway, I'd be grateful for any help in creating images with higher ppi.
> > >
> > > -- Hop-Frog
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