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When doing a scan, you should know where and what will be done with the
final image. Is it to be used for a Wordperfect document, PageMaker, HTML
page, just to view in a personal graphic library? Also, how much color
quality is needed in the file? These will be important in deciding which
format is the most efficient to use. It is also beneficial to know the
types of formats an application supports if you plan to import it into
that program. Ofoto allows
you to save your work in either PICT, TIFF, or EPS format. You can
also use a program called Graphic Converter to convert your scanned image
into the format you want.
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PICT - The PICT format is the general standard graphic type found on Macintoshes.
Almost every application on the Mac that supports graphics, will import
the Mac PICT type. This strength of this format is that it uses an object
oriented approach by saving the objects, such as lines or circles, that
are used in drawing programs. When redisplaying the image it uses the
standard Mac QuickDraw routines. With scan images, though, it is forced to
save it like a bitmap since these graphics were not generated as objects,
but scanned in as pixels. The current standard allows up to 32 bit color
which is probably the most that should ever be needed. Since the PICT
format is a platform specific format, it should only be used if the
graphic is going to be used in a Mac application.
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GIF -
If you are not sure exactly where the graphic will be used, saving it as a
GIF (Graphic Interchange Format) is probably the best choice. Developed by
CompuServe, the GIF is the most common and popular format and almost every
platform has some utility to display GIFs and to convert them into another
form. This format can hold up to 256 colors, and uses the Lempel-Ziv-Welch
(LZW) compression algorithm that is similar to those found in such
utilities such as PKZIP on the PCs. Actual compression achieved is between
2:1 to 4 :1, and using another compression utility on a GIF shouldn't be
used since it will most likely not compress any further. Other compression
attempts may even make the file larger due to the overhead of the
compression information. GIF is best for pictures that are scanned in
grayscale (the scanners in the lab can only scan 8-bit grayscale), and
color images that do not have many colors. Colored photographs of real
life images are better left to other formats if color quality is
essential. While it does have these limitations, it is the most popular
form out there and is the best choice for certain applications such as
inline graphics in HTML documents.
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TIFF -
If the 256 color restriction is too limiting for your needs, the TIFF
(Tagged Image File Format) uses 24-bits allowing up to 16,777,216
different colors. Compression with TIFF is available, but due to the lack
of standardization it is safer to leave it uncompressed to ensure that it
will be compatible between applications and platforms. If you need to have
your graphic in TIFF format and it is too large to transport easily, use a
standard compression utility that you know will work on the destination
platform.
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EPS -
Using EPS (Encapsulated PostScript file), is a good choice if the file is
going to be printed elsewhere on a PostScript printer and is not going to
be used for anything else. An advantage of saving it this way, is that the
computer that you want to print it on only has to be able to send the file
to a PostScript printer for it to be able to print correctly. Saving it as
a graphic format such as GIF or TIFF requires a utility to view and print,
which may not be available at the location the document is going to be
printed. The disadvantage is that once in EPS, it is not as convenient to
convert to other graphic types; therefore a copy of the original format
and the EPS format should both be saved. Also, with intensive color
graphics, the PostScript overhead can considerably increase the size of
the file.
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JPEG -
Another graphic type that is also popular is the JPEG standard created by
the Joint Photographic Experts Group. The actual format that uses this
standard seen in common use is JFIF (JPEG File Interchange Format), but it
normally just called JPEG and has extensions of .JPEG or .JPG. This format
provides a 24-bit color "lossy" compression that can provide compression
superior to other formats without losing much quality. This kind of
compression doesn't provide an exact bit representation of the
uncompressed form, rather it manipulates the image by removing redundant
pixels and changing color shading. This technique creates a smaller file
while the changes made try to be small enough not to be noticed by the
human eye. Images that are color or gray-scale photographs work the best,
and give a compression ratio between 10:1 to 20:1. It is possible to
change the compression ratio to make a rougher image in exchange for a
smaller file if high quality is not needed. For pictures that do not have
a large array of colors or depths of gray, GIF would be a better choice
since the JPEG algorithms are not as effective for these pictures.
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