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The short answer is that there is no excuse for your screen shots for
looking anything less than perfect when prepared for offset printing, even
when the images are reduced by 60 percent. I would have a discussion with
your design firm (or change design firms).
You can think of a screen capture (or any other type of bitmapped image) as
a picture made up of individual puzzle pieces. All of the puzzle pieces
(pixels) are the same size. If you try to reduce the size of a puzzle by
pushing in on the edges, some of the pieces will fall out and the picture
will look fuzzy. The only way to make the puzzle smaller would be to reduce
the size of the individual pieces. Programs such as Adobe Photoshop allow
you to reduce bitmapped images by reducing the size of the pixels. When you
reduce the size of the image by 60 percent, the resolution of the image will
increase. If the resolution of the image does not increase, you are "down
sampling" the image--in effect throwing away pieces of the puzzle.
Once you have resized the screen captures in Photoshop by increasing their
resolution, you can import them into your page layout program.
Another parameter that is crucially important in offset printing is the
screen frequency. The prepress software used by your printing company will
render your screen shots as halftones. A halftone is an image composed of
dots (usually circles) of varying diameter with equidistant centers. The
number of dot center points per inch is the screen frequency. Images in
newspapers are usually printed with screen frequencies ranging between 60
and 80. When offset printing on high-quality paper you should be able to go
with a screen frequency as high as 120. A 120 line screen will produce
magazine quality results. If you are printing in color the concept is the
same except you have four halftones per image: one each for the CMYK primary
colors (cyan, magenta, yellow, and black).
There is a relationship between the resolution of your bitmapped images
(screen captures and photographs) and the screen frequency used to produce
the halftones for offset printing. Basically the resolution of your
bitmapped images should be no more than 2.5 times the screen frequency.
Bitmapped resolutions higher than 2.5 times the screen frequency will not
result in improved image quality because you are ultimately constrained by
the resolution of the screen. This means that you could reduce your 72 dpi
screen shots by scaling them to a maximum resolution of 300 dpi for a 120
line screen. If you are using a lower resolution screen, then you can't
reduce the screen shots as much. Screen resolution is limited by the
porosity of the paper and the speed of the printing press, among other
factors.
Your printing company will send the pages, complete with halftones, to an
image setter which prints on photo-sensitive paper or negatives. When
printing to photo-sensitive paper you can expect a resolution of 1200 dpi.
When printing to photographic film you can expect resolutions of 2400 dpi.
Some image setters operate at resolutions as high as 10,000 dpi. In short,
offset printing is serious overkill for screenshots. Think of the quality of
the photographs you seen printed in magazines. This should give you an idea
of the quality you can expect from the offset printing process.
Hope this helps,
Martin R. Smith
-----Original Message-----
From: Dawson McKnight [mailto:dawsonmcknight123 -at- yahoo -dot- com]
Sent: Wednesday, August 20, 2003 11:43 AM
To: TECHWR-L
Subject: Print-ready Graphics Problem
All,
My team has written a document that an outside design
firm is laying out for us and sending out for offset
printing. The problem is this: Now that the firm has
laid out the document, the screenshots are almost
illegible. On screen and in print, the screenshots are
pixilated and "fuzzy"-looking to the point of being
worthless. The document hasn't gone to the printer
yet, so there is still a little time to fix the
problem.
The design firm requested that we send all of our
screenshots to them as TIFs (CMYK, 24-bit, and
"uncompressed"). The resolution of the screenshots is
92 DPI. The firm had to reduce the size of the
screenshots to about 60% of their original size to fit
them into the document. They are laying out the
document in Quark.
So the question is this: How do you produce
screenshots that are "print-ready?" How can I ensure
that the screenshots I am delivering to the design
firm have the adequate resolution to look good in
offset printing? I have seen many examples of
offset-printed manuals with crystal-clear graphics (no
matter how small).
The firm says that they cannot improve the appearance
of the graphics because of the limitations of
screenshots in general, and they can offer no solution
to the problem. That is why I am turning to you for
your collective expertise. I couldn't find anything in
the archives or on the web, believe it or not. I don't
know how to advise them, but I can't release a
document with this low level of quality in its
screenshots.
I am perplexed because I can take the same
screenshots, insert them into a Word or FrameMaker
document, and reduce them to 60% of their original
size, and they look crystal clear when I laser print
them. What could we be doing wrong to make the
graphics look so bad in Quark?
I really appreciate any insights you may have. You
guys are great!
