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Have you ever came across a book that you were really
interested in but didn't really have the time to read? What did you do?
If you're like most people (me included) you read only the first and the
last pages. Sure you miss most of the story, but hey, you also find out
the 'who done it' or the 'what did he eat next' (i.e. Hannibal).
For those of you who can relate to this, here's the meat
of this article: The printing industy and the Government Printing Office
prefer TIFF and EPS graphics for all of your professional printing needs.
Supply any other format and you can expect time and/or money problems
and modifications.
(Click here to view a chart that
illustrates file conversion recommendations.)
For the remaining readers who haven't bailed by this point
who like to pick up on all of the dirty details, please read on.
Graphic file formats, while not as confusing as the U.S.
election process, can leave you buffaloed, stymied. Let's fight through
this right here, right now. Let's throw down.
Just as there are musketeers, square meals, stooges, wisemen,
Charlie's Angels, dog nights and tenors there are three basic graphic
file formats. One of which we'd like you to avoid like DC rush hour.
Bitmap files store pictures as matrices (rows and columns) of squares
known as pixels, with each pixel having a particular gray or color value.
Bitmap files are typically created by image-editing programs such as Adobe
Photoshop, or by the software you use to run your scanner. TIFF (tag image
file format), BMP (Windows bitmap), MacPaint, and PCX (PC Paintbrush)
are all examples of bitmap-format graphics files. Your best bet for successful
file output is, without a doubt, TIFF.
Vector files contain sets of instructions for drawing objects--typically
geometric shapes such as lines, ellipses, polygons, rectangles, and arcs.
The drawing instructions say, "Start this line at this point and draw
to that point over there" or "This is a polygon made up of these line
segments." Vector files are typically created by drawing/illustration
programs such as Illustrator, CorelDraw and Freehand or CAD programs such
as Autocad and ArcInfo. PostScript paths and type, such as those you'd
find in an Illustrator EPS (encapsulated PostScript) file, are other examples
of vector elements.
And lastly, MetaFiles, a format GPO recommends that you try to
avoid. MetaFiles can contain both vector and bitmap graphics, but they
don't have to have both--sometimes you'll find metafiles that contain
only an image, for instance. Macintosh PICT, CGM (computer graphics MetaFile),
EMF (enhanced MetaFile) and WMF (Windows MetaFile) formats are all examples
of MetaFiles. MetaFiles are not intended for high-end printing.
The biggest problem with many graphic file formats is that they make too
many assumptions about the system they'll be viewed on, or printed from.
We say such formats are device-specific because they're tied to some feature
of a particular video-display system or printer. Most of these formats
assume that the files stay on the computer system they were created on--not
always a reasonable assumption to make for anyone doing any kind of publishing.
On the other hand, PostScript files (including EPS graphics) are practically
the definition of a device-independent file format--they don't make many
assumptions about the devices on which they'll be used.
Many bitmap formats incorrectly assume that the color palette of the system
they're on will remain the same. This is particularly true of bitmap-only
PICT files, but it's also true for some varieties of indexed-color TIFF's.
Because of this, such graphics can shift or lose colors when you move
them from computer to computer. The same shift or lose of color can happen
when you convert files from one format to another. For example, if you
convert a WMF to a TIFF you can expect some sort of color shift to enter
into the equation
.
In addition, (this should be very interesting to all of our government
designers) most MetaFile and vector formats--except EPS--assume that the
font list of the system they're created on will remain the same, and refer
to fonts by their numbers (as they appear in the list of fonts at the
time the file was created) rather than by their name. This causes problems
when you move to another system, or send your job into GPO, or even when
you install a new font.
If you are going to use a device-specific file format, you should use
it with the devices it's designed for. WMF, for instance, is a file format
that uses commands written in the language of the Windows Graphic Device
Interface (or GDI), which is the core system Windows uses to draw objects
on screen or print to non-PostScript printers. PICT is based on QuickDraw,
the native drawing language of the Macintosh. So if you've got a WMF or
PICT and you use it exclusively on its native platform Windows for WMF
or the Mac for PICT) for on-screen display and non-PostScript printing,
you should fare reasonably well since the majority of all commercial output
devices are PostScript. Although, if you're reading this you're, most
likely, planning on doing high-end, professional, offset printing therefore,
these two formats should be avoided like punch to your gut.
It all comes down to using the formats with the devices they were designed
for. BMP files were intended to be viewed on screen, in Windows, not printed.
EPS and TIFF, the formats GPO recommends for printing, were designed to
work well on high-resolution PostScript printers. And GIF (graphics interchange
format) ans JPEG (Joint Photographics Expert Group) were designed to carry
a great deal of image information in the smallest possible package, which
makes them ideal for online publishing. In addition, and very important,
EPS, TIFF, JPEG, and GIF were designed for interchange between different
computing environments and platforms--something you can't say of WMF (Windows-only)
and PICT (Macintosh-only).
There you have it! Now let me break down this entire article into one
concise, time saving paragraph. If you have WMF, PICT, BMP files it
would be best to convert them into EPS or TIFF format (TIFF for photos
or scans and EPS for vector art) for high-end printing; if you are
publishing something to paper, you'll save yourself time, trouble, and
cold, hard tax-payers cash by doing so.
Click here to view
a chart illustrating file conversion recommendations.
x excerpted in part from an article by Olav Martin Kvern
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