Документ взят из кэша поисковой машины. Адрес оригинального документа : http://crydee.sai.msu.ru/ftproot/pub/misc/doc/pm5/scantip2.faq Дата изменения: Fri May 12 10:35:40 1995 Дата индексирования: Mon Dec 24 05:00:59 2007 Кодировка:

Hello Folks!

Here are two more postings that the mastermind Jeff Bone has posted. Both
of them I think are appropriate for inclusion in the archives...

Geof.
(gwp@cs.purdue.edu)


1st Posting (Some newer graphic formats)
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As most of you know I somehow became the self-proclaimed authority on
scanning and bitmap data formats for the LIST. As such, I receive a lot of
direct mail from different "listeners" who have questions regarding this
topic.

One of the most recent topics that became a subject for much discussion
regards the image data file format JPEG and the newer Kodak PhotoCD format.
So for any interested (especially those who requested it), below is a
summary of the information exchanged...


JPEG
- (Joint Photographic Experts Group) is a bitmap file format that was
proposed by this global consortium of vendors/developer/academics/ and
others. It is designed for storing color pixel data in a variety of
different bit-depths 4, 8, 15, 16, 24, 32 (number of colors, respec-
tively 16, 256, 32768, 65536, 16.7M, 4.3B).

- JPEG is a compressed file format. That is all of the original informa-
tion (each pixel that made up the photograph or whatever when it was
created or scanned) is not necessarily present in the saved JPEG file.

- JPEG is known as a LOSSY compressed file format. That means that some
of the original data is discarded (lost) in the interest of making the
file smaller. Maintaining greater quality means a larger file,
smaller file means less quality. While a compressed TIFF file's best
compression ratios can only reach 2 or 3 to 1, JPEG compression ratios
with no appreciable loss of quality can approach 20 or 40 to 1. Even
higher ratios can be achieved with JPEG.

- Essentially JPEG is a very simple file format that requires a very
complex method for reading and writing it. JPEG requires a compressor
to create/write the file and a decompressor to read/view the file.

- PostScript Level 2 printers will be able to perform a decompression
on an embedded JPEG file "on-the-fly." Thus making it possible to use
very high resolution JPEG compressed color images in desktop publishing
documents without the performance penalty associated with using large
un-compressed bitmaps.


PhotoCD
- PhotoCD is a file format that is created by Kodak expressedly for arch-
iving photographs. The most common media for PhotoCD images is a CD-
ROM disk, however it is possible to have PhotoCD images on any media
accessible by your computer. It stores files in one of three bit
depths 8, 15, 24 (and technically provides developers with the ability
to add more in the future).

- The PhotoCD file is actually three or four images in one file.
Whereas JPEG, TIFF, etc., can have virtually any resolution (horizon-
tal and vertical amount of pixels), PhotoCD has specific fixed
resolutions. There is the original high resolution file, a 2x
version which is half the resolution of the high res, a 4x version
which is one fourth the resolution of the high res, and a 16x
version which is one sixteenth the high resolution version (also
known as a thumbnail). It is not necessary for all versions to be
present in the file.

- PhotoCD files are not compressed in any way. Each original pixel is
represented in the file. This can obviously make the file sizes rather
large when dealing with the full res files.

- Currently there is only one way to create a PhotoCD file, through Kodak
or an authorized Kodak PhotoCD production company. Kodak requires the
purchase of a custom series of hardware and software to produce the
PhotoCD file.

There are, however, many ways to read a PhotoCD file, including Photo-
Shop plug-ins, PageMaker import filters, etc.


SO WHICH IS BETTER

- JPEG for some things, PhotoCD for others.

- JPEG has wider support and is a more well developed specification
than is the PhotoCD format.

- PhotoCD is a proprietary format and Kodak wants to keep it that way
at least for a while.

- JPEG files (even ultra high resolution ones) can take up far less
space than even the medium resolution PhotoCD files because of the
lossy compression.

- PhotoCD files maintain all of the fine detail and tonal quality since
none of the original scan is sacrificed for space.

- JPEG files could require longer to open and save on slower machines
because they must be decompressed or compressed first before viewing.


SO WHAT DO YOU USE, OH WISE ONE (as if we care)

- We used compressed TIFF files for temporary and short-term storage, but
then we migrate all our long-term storage image files into a JPEG file
with varying rates of quality (but never below 70%) depending on the
image.

- We see PhotoCD as a resonable format for Photo Stock catalogs on CD-ROM
but we don't see it as a viable format for in-house work until either
high capacity erasable optical (or better storage) gets cheaper and the
license to write PhotoCD becomes affordable.



2nd Posting (About the scanning FAQ)
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For those who have joined recently, quite a few I think, every few months
Geof Peters updates the PageMaker FAQ and distributes it via the LIST and at
about the same time I try to update the Scanning FAQ. Together we innudate
a fair portion of the email systems in the country with enough information
about PageMaker and scanning to keep you busy for the next month trying all
the nifty tricks and techniques that the rest of the list comes up with.
Well it's about that time again for the Scanning FAQ...

But, don't worrying I'm not about to deluge your email system with fifty pages
of Scanning FAQ. What I'm doing instead is a little fishing. I am at work
compiling an update of the Scanning FAQ and some additional information and I
would appreciate it if you could take a few moments and respond to any of the
following questions that you feel compelled to. This will help me to know
how exactly to release the Scanning FAQ and what additional questions/topics
to devote time to.

1) Would you prefer to receive the entire Scanning FAQ and information
updates through your Email system (like last time), or would you
prefer to receive only the updates and have the FAQ maintained in the
FTP site?

2) Do you have access to the FTP site, and have you used it to obtain
a copy of the Scanning FAQ?

3) Would you prefer to have the Scanning FAQ in a more polished booklet
form saved in a PageMaker file so that you could download it and
print it out at your site?

4) What additional scanning related topics would you like to see detailed
in the next update, example:
a. Color Scanning
b. Calibration Techniques
c. File issues (ie - file types, compression schemes, etc.)
d. Control issues (ie - dot gain, pre-screening, masking, etc.)

5) Would you be interested in having access to some sample scan files
that illustrate certain techniques?

6) Anything else, specifically related to scanning and PageMaker?

Remember to please use my direct email address ( jbone@dopig.uab.edu ) so as
not to clog up the LIST and make a lot more people mad at me.

Additionally, you might want to look over the current Scanning FAQ to get
some ideas or make suggestions for the upcoming revision, you can get it via
anonymous FTP from WUARCHIVE.WUSTL.EDU in the subdirectory \doc\misc\pagemakr.

Thanks in advance...