Subject: Image translation program

From: Charles Letner <[email-masked]>
Date: Thu, 28 Jul 1994 12:05:18 -0700 (PDT)

Hello all,
	I am having a little problem that is REALLY starting to annoy me. 
I am trying to output images to a printer.  My printer is capable of 600
dpi postscript output.  I also have access to a color postscript printer. 
I can save my images in any number of formats including postscript (only
91 dpi).  However, 91 dpi is not publication quality.  I'd like to know if
there is a file conversion program that will take my image files (TIFF
would be good, though as I said I can output other formats) and output 600
dpi postscript files?  I would like this to be a unix program (I'm using a
SG Indigo II) and viewing capabilities isn't essential for this utility. 
As I expect I'm not the first to have this little problem I will send a
summary of the responses.
Your help will be appreciated.

Thank you,
Chuck

Charles Letner
Wright State University
Department of Biochemistry
Dayton, OH 45435
e-mail: [email-masked]

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From: [email-masked] (C.S.RAMAN)
Date: Thu, 28 Jul 1994 14:00:44 -0500 (CDT)

> As I expect I'm not the first to have this little problem I will send a

What you want is the PBM translation suite. It comes in three
different flavors:

PBM
PBMPLUS
NETPBM

You can find these at many anon. FTP sites (using ARCHIE).  PBM is
capable of converting images from one format to numerous others and is
extremely useful.

Alternatively, you could also try John Christy's ImageMagik available
at various anon. FTP sites.  You may have to search for some of the
utilities that go with it to accomplish your task.

Cheers
-raman
-- 
C.S.Raman                           
UNIX Programming & Administration   
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---

From: "Omar Stradella" <[email-masked]>
Date: Thu, 28 Jul 1994 16:34:01 -0400

On Jul 28, 12:05pm, Charles Letner wrote:
> Subject: CCL:Image translation program
> Hello all,

Depends on what you mean by 91 dpi, that probably really means cells/inch
instead of pixels/inch, since your PostScript printer will print at
whatever dpi was built or configured for. Let's use as an example
your B/W 600 dpi printer, each dot can be only white or black.
If you are printing a B/W image (that means no grays
at all) such as a molecule represented with circles (balls)
and straight lines (sticks) then you can get the full 600 dpi
resolution. If you want to print an image with gray levels, the conversion
program has to "halftone" the image, halftoning is the process by which
continuous-tone colors are approximated by a pattern of pixels that can
achieve only a limited number of discrete colors. So now the "points"
that form the image are not longer pixels but groups of black and white
pixels that combined produce the correct level of gray. So, if your
image is 91 cells/inch that is 600/91 = 6 pixels per side or 36 pixels per
cell, then 37 levels of gray are possible. Your image looks grainy but
you can appreciate the differences of "color". If you convert a rasterized
image (like a TIFF file) to PostScript, you'll always have to halftone
the image, if you want a finer grain you'll get a smaller range of
gray tones. If you want 600 dpi you will get only black and white, no
grays at all. In that case I would prefer an image created with PostScript
primitives (lines and circles) instead of a rasterized image. Publication
quality rasterized images can only be obtained with "publication
quality printers", that is 1500 dpi or more, since 1500/6 = 250 cells/inch
or 250 gray dots/inch which should look good enough. The same principles
apply to color printers.

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