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------------- PAGEMAKER/QUARK LISTSERV -----------------
------------- S C A N N I N G F A Q UPDATE 1/22/93 -----------------
Special Thanks...
To Geof Peters, Monte Olsen, Cindy Stone, Gary Hartling, Jeff Needleman,
and the guy who ask for a explanation of the meaning of life that gave
me a deluge of new material to use in updating this FAQ. Many of you will
note your remarks incorporated into this FAQ without the slightest regard
for crediting the source.
Also my thanks to Pete Fink, the president of Peter Fink Communications (the
guy who helped Adobe create Adobe Accurate Screening technology), and
publisher of "Desktop to Press" newsletter for allowing me to use excerpts
from his resource known as the "How to Make Sure What You See Is What You
Get" booklet.
We like it so much that we give it to all of our Service Bureau clients.
Much of this FAQ is drawn from excepts of this resource, and I would like
to give him full credit for allowing me to use his booklet as a springboard
for this FAQ, for reasons of consistency, readability, and because I am
plugging his booklet so thoroughly his office deemed it unnecessary to foot-
note all occurrences of information taken directly from his work. I recom-
mend you contact him for a complete copy:
Peter Fink Communications, Inc.
120 Q Street NE
Washington, DC 200002
(800) 551-5921
Get the booklet ($10.95 US plus shipping and handling, less in quantity),
it goes on to cover Halftones and Dot Gain, Optimum LPI, Fonts, Cropping
and Scaling, Masking and Flatness, Blends and Banding, and more all in a
24 page booklet you can keep by your computer.
----------------------------------------------------------------------------
Scanning artwork can be broken down into four primary catagories:
1) Line Art
2) Halftones
3) Greyscale
4) Color
Each of these catagories have their own unique problems when scanning,
before I continue with some techniques for greyscale scanning, I'd like
to define and discuss these catagories.
Line Art Scanning
-----------------
Line Art scanning is best defined as simply transferring pen and ink
style drawings, clip art, and some pencil sketches into the computer
system. Line Art has no shading nor color other than black. Line Art
scanning is considered 1-bit scanning, that is the computer sees the
image as either black or white.
Line Art scans, since they can only be black or white, do not have the
luxury of anti-aliasing (a technique that makes smooth transitions between
black and white by adding varying steps of grey), and therefore are prone
to having jagged edges around curves when scanned at lower resolutions
than the final output device. Therefore, you should not use Line Art style
scanning to scan photographs or textured art unless you are attempting to
achieve some special (read - often weird) effects.
Line Art should be scanned at as high a resolution as the final output
device to eliminate the "jaggie" effect. In other words if you have original
art that is 5x7 and you're going to output at 5x7 on a 1200 dpi imagesetter,
ideally it should be scanned at 1200dpi to achieve the best possible image.
Note that if your original is larger than the final size, you should adjust
your original scan resolution by the same ratio so as to not have more
resolution than necessary.
On a personal note here, while the goal of matching original scan
resolution with final output resolution is desirable, very few of
your clients will be able to discern any difference between 600dpi scans
and 1200dpi scans, especially when your final output will be printed on
glossy paper stock. However, the difference in imaging time to your printer
or imagesetter will be quite remarkable since you are dealing with 4 times
as much data in a 1200dpi scan.
Geoff Peters adds, One last thing worth mentioning here is tracing.
The majority of line art that he scans are simple cartoon drawings or doodles.
He then uses Corel Trace to convert it to postscript and thus enables him to
increase the image to any size with out the fear of the Jaggies.
Halftone Scanning
-----------------
Halftone scanning evolved because someone discovered that they could
scan photographs from magazines. While I won't get into the legal issues
here, suffice it to say that there will be a legal problem with using any
pre-published images. Assuming that you have the permission to use a
pre-printed piece, don't -- ask for the original photograph instead.
Halftone scanning is essentially treated like a greyscale scan by most
software and the conventional wisdom says to scan the image at a
resolution lower than the original in order to reduce the threat of
moires. Well, about all you can do is reduce the number of moire patterns
that you will have, not reduce the threat. If you scan a halftone, you
will have moires. Without getting too technical, the reason for this is
that all halftones generated by a press have "irrational" screens and
inconsistent angles applied. Irrational screens and inconsistent angles
are used to increase the quality of the printed piece for the type of
press being used, they are called irrational and inconsistent because in
the case of the press, they are adjusted mechanically by the press
operator (If they were generated by a high-end four-color system--Scitex,
Chromacom, etc.--the irrational screens were computed elaborately). To
properly eliminate potential moires your scanner would have to adjust its
resolution, tracking (pickup alignment), and linearity (the range of
grey scales) dynamically across the entire image.
Granted, this may not be a big deal if all you intend is to scan the
cover of SI's swim-suit issue to embarrass your colleague (of course, I
would never advocate this type of blatantly criminal activity), but
assuming your goal is publication quality work, Halftone scanning should
always be used as a last resort if at all.
Halftone Scanning vs. Halftone Screening
----------------------------------------
Halftone scanning should not be confused with halftone screening. Sound
confusing? Halftone scanning is scanning an original from an already screen-
ed source such as a magazine, coffee table book, newspaper, etc. However,
many scanners now come with plug-ins, or custom software that has an option
labeled "Halftone." Check your manual about this, but most of these options
are for creating a custom halftone screen of the image being scanned not for
scanning a pre-screened halftone.
As an example, Microtek's Adobe PhotoShop plug-in has a halftone option
that allows you to screen an image to a number of preset patterns as you scan
the original. This is important because Microtek, and most other scanner
makers, have done their homework on their scanners and know how to generate
a halftone screen that will best take advantage of their machine's capabili-
ties with your chosen output device. Another advantage is that once the scan
is completed, you don't have a large grey scale file, but rather a simple
1-bit black and white file that approximates the grey range of your selected
output device and takes up only a fraction of the space that a grey scale
would.
The disadvantage to this, is that your screened scan is now appropriate
for really only one output device. For instance, If you perform a halftone
scan with the Microtek plug-in set for a "5x5 60 dot #1" pattern (the recom-
mended pattern for the Apple Laserwriter IIf photograde) it will look great
when printed to the Laserwriter, but appear like a strange rippled newspaper
photo when printed at 1200dpi on a Linotronic.
Halftone screening a scan is not entirely without merit, however. Many
manufacturers will give you some screen patterns (such as horizontal or
vertical lines) that can create some very artistic effects regardless of
output device.
Greyscale Scanning
------------------
Greyscale scanning is most often used for original photographs, but can
also be effective for maintaining the "soft" edge of some pencil sketches
that use lots of shading. Most good flatbed desktop greyscale scanners
are now capable of scanning 256 shades of grey. Don't be swayed by a
manufacturers claim of 4096 shades of grey. While this may be true, you
won't be able to use them. The current PostScript specification only
allows for 254 halftone steps (the way a shade of grey is represented in
print, 254 steps with pure white and pure black which makes 256 total).
Principles
Most of us scan at too high a resolution. As we increase scan
resolution, we capture too much detail--and the scan's file can balloon to
outrageous size. The imagesetter [ or laserprinter ] must render all of
that data, using lots of costly RIP time [ RIP - Raster Image Processor,
the specialized computer in your laserprinter or more expensive
imagesetters.
As you work with a scanned image, the computer constantly has to re-
crunch the scan data. Over the course of a project this time really adds
up. Scans with way too much data not only rob your time, they can even
crash the RIP--in which case you don't even get a page.
Take a few moments to calculate what you need rather than scanning at
high detail "just to be on the safe side." Capture just enough detail for
what you need to do.
Production Tips
- Do a little arithmetic before you scan. Planning to reduce the image
to 50%? This doubles the resolution. Reducing to 33% triples the
resolution, and so on.
- For greyscales, a final resolution of 1.5 times the LPI works well in
most cases. For soft subjects you can get away with 1.3 times the
LPI.
(i.e. - Linotronic output at 1200 dpi, 133 lpi your scan resolution
should be no greater than 200 dpi. Final scan resolution
means that you've calculated the change in spatial
resolution when you size your original scan, as
discussed in the above tip)
- Avoid data overkill. Clean up scans in a retouching program before
using them. Adjust their size and resolution before placing them in
a layout program.
Crop the image in a package like PhotoShop or PhotoStyler as closely
as possible to avoid having the RIP compute all that "white space."
Avoid using PageMaker or other layout programs ability to "crop" a
scan, this feature merely masks an area and does not decrease the
data that the RIP must compute.
- Sharpening the image in a retouching program gives a better looking
result than using a high scan resolution. Make the on-screen image
just a little sharper than you think is needed--it softens a bit in
production.
The CCD chip in your scanner that actually reads the greyscale data
is linearily balanced, meaning that the transitions between grey
areas tend to be minimized too much. Sharpening algorithms in
retouching programs like PhotoShop and PhotoStyler adjust for
this. Always run your programs "Sharpen" routine on a scanned
photo to compensate for this.
Another little known tip is to add "noise" to a scan to minimize
the transitional steps between your grey scales. For instance if
you have created a blend in your illustration package that has only
thirty steps, you can export the EPS file into your favourite image
editor and add 1 or 2 units of random "noise" with the noise filter
to take away hard edges and "cheat" your eye. This technique works
well for ultra-high and very low resolution scans too that either
exceed the grey level of your imagesetter or produce very pixelated
images.
Common Mistakes
- Taking a big high resolution scan and shrinking it to tiny size--16
Megabytes for a postage stamp--yow! Reduce resolution by sampling
down in a retouching program or re-scan at a lower resolution.
- Cropping a little piece of a big image in a page layout program--the
RIP has to process that whole big image, then *throw away* what's
outside the cropping window. Crop first in a retouching program, and
bring what you need of the image into the page at the proper size.
- Misuse of the text wrap feature of PageMaker. Be careful not to overlap
your wrap points (ie - create a spider web of an irregular shaped text
wrap where a wrap point is inside another wrap point, this mistake will
crash the RIP because you are allowing PageMaker to define an illegal
object (the object of the text wrap outline and associate it with the
scan object)
- Thinking that white borders don't count--white creates data too.
Crop the borders away while scanning to save the most time, or later
in your image editing software.
- Using a page layout program to rotate big images. The RIP likes its
image data straight. Twisting all those pixels is risky, lengthy
work. Rotate in a retouching program.
- Scanning Line Art as a grey scale because it has fancy stippled
shadow detail. Scan your artwork at a higher Line Art resolution
rather than grey scale. 2x3 inch 150 dpi 8-bit grey scale is 2 Meg
worth of data compared to 600K for a 2x3 inch 400 dpi 1-bit Line
Art scan.
Color Scanning
--------------
First, color scanning _is_ possible on the desktop regardless of what
your stripper may have said. And it would be possible for me to write a
few thousand pages about how to not do it, but in this FAQ, I'm going to
limit our discussion to primarily greyscale scanning. But while I have
your attention I may as well interject my opinion about color scanning.
For most of us, color scanning is needed for color separations for used
in four-color printing. Your Howtek, Microtek, Sharp, or even Nikon color
scanner does a good job if you have a skilled operator and an exacting
output service bureau, but don't assume you are going to save any money or
time. More often, the years of color experience a good four-color shop has
is worth the effort to use traditional methods, and will save you time in
the long run. We have one of the best desktop color systems around
(Quadra's with SuperMac displays, 128 Meg Memory, 2 Gigabyte Hard Drives,
Nikon LS3510 slide scanner, and Optronics Colorgetter Drum Scanner System)
and we choose not to use it for large format and high quality
pieces. We instead send these out to a local Chromacom-based Separator.
If your bent on doing color on your desktop, try a hybrid approach.
Traditional four-color separator scans the art and gives the DTPer a low-
res image for placement. Output is then sent back to the four color shop
where the high res is used. Hybrid methods are growing in popularity as
users realize their "eye" for color and equipment isn't as good as expected.
------------- PAGEMAKER/QUARK LISTSERV -----------------
------------- S C A N N I N G F A Q UPDATE 1/22/93 -----------------
Part 2
Do You Really Need All That Resolution?
It seems even the scanner makers are now caught up in the "more-is-better"
routine. A few years ago 300dpi 16-shade grey was an incredible scanner, to-
day it seems if you don't have a 600dpi 24-bit scanner you'll likely to get
drummed out of the local DTP users club.
But do you really need 600dpi? It is quite possible that, depending on your
application, you could produce some very pleasing and fully professional
results with less investment.
I suppose I should explain my first question now. I won't assume anything,
so don't let me insult your intelligence, just overlook any riduculously
elementary parts.
1.
A flatbed scanner is merely a series of CCDs (charge coupled device = light
sensitive integrated circuit) mounted in a stationary row that light
reflected from a piece of flat art is allowed to pass over. These CCDs
register presence or absence of light (ON/OFF) thus producing a pixel
electronically. Since they are mounted in a single row that is the way the
electronic file is created, row by row. Essentially the CCDs are reflected
one row of the flat art at a time until the image is completely built.
2.
That being the case, resolution or the number of pixels written based on what
is reflected is controlled two ways. The number of pixels horizontally is
controlled by how closely the CCDs are placed next to each other along the
single row. The number of pixels vertically is controlled by how slowly the
light bar and mirror inch along the length of the flat art thus reflecting
onto the CCDs. Therefore, the more CCDs and the smaller the steps of the
advancing light bar the greater the resolution. Currently there are five
major scanner motor manufacturers (many re-packgers) and they all build
their systems essentially the same way. The highest resolution flat bed
scanning system currently is physically limited to 400 dots (pixels) per
linear inch. You may say wait a minute I've seen 600, 800, and 1200 dpi
ratings, but note I stated the physical limit is 400 dpi. This is true,
there currently is a real physical limit as to how many CCD ICs can be placed
side by side in one inch and that limitation is 400 right now.
3.
This 400dpi physical limitation has been breached by what is known as
interpolation. Interpolation is a software/firmware process whereby the
scanner essentially samples two pixels and averages (often times using more
complex formulas) the two pixels together to form an extra pixel (or more) in
the middle. Better scanners now do this in hardware, but some still rely on
their scanning software to do it (often uninvolving the user). But
nevertheless, this higher resolution is only psuedo-data. That is, it is
data being create by averaging and not by actually sampling it from the
original art.
4.
Grey-scale scanners are scanners with CCDs that can differentiate between
levels of light falling on them, rather than just being on or off, the grey
scale scanner can determine if the pixel should be any number of shades of
grey. Most scanner manufacturers have stopped R&D once they acheived 256
shades of grey because the current version of PostScript can only recreate
256 levels of grey, however there are many high-end systems that can produce
much more levels (4096, 32768, etc.)
5.
Color scanners are nothing more than grey scale scanners that have filtration
(most commonly Red, Green, and Blue) and make multiple passes to generate 256
levels of each RGB component. The software then recombines the three passes
to create full color. Higher quality scanners perform all three scans in one
pass at the same time to perserve registration (although this is not usually a
problem in good three pass scanners).
6.
Imagesetters are unable to produce continuous tones, that is that
are unable to make a pixel different shades of grey like the scanner "sees"
them, instead they use a very complicated screening pattern to simulate
shades of grey to the naked eye. At higher magnifications you can easily see
that a photo is not really a photo, but is a series of variable size dots.
This is called "half-toning." Half-toning, therefore, isn't using all of the
pixels to create the dot patterned image, in most cases it's using only half
or less of a high resolution scans original data.
7.
So the question becomes why scan so high if the data won't be used. There is
a formula for this of course. It is, scan at 1.5 times the lines per inch
(LPI) of the final output device. Therefore if you are outputting to a 2400
dpi imagesetter at 150 LPI then the normal maximum resolution you need to
scan at is only 200dpi. So if the un-informed user scanned his photo at
600dpi thinking he needed that high res capability because he was going out
to a high res imagesetter, he would be sending over 9 times too much data to
the imagesetter. This would result in a very long RIP time and possible
crash of the RIP.
8.
Line art scans (black and white) could, of course, be a good candidate for
the high resolution scanner, but more likely if you plan to use a piece of
line art you can scan a large original and reduce it. Or better yet,
autotrace it into your favorite illustration program and forget having to
work with large, slow bitmaps.
9.
High resolution color becomes a different story somewhat. It is possible to
find a continuous tone color output device where it would be nice to output a
"true" continous tone modification that would rival the original (i.e.-
National Enquirer PhotoShop modification of a 35mm slide at high res and then
reoutput to 4x5 negative on a film recorder to produce a retouched print).
However, continuous tone output requires very high resolution to produce
satisfactory results. This requirement pushes the upper envelope of flat bed
scanning (800, 1200dpi) and becomes a job for the slide scanner and drum
scanner. Unfortunately at these ultra high resolutions the personal computer
becomes a liability. Today I have been working on a photo retouch of a 35mm
slide that we intend to re-output to 4x5 on our Solitaire film recorder.
Unfortunately the full resolution file (4800 dpi) was over 250 Megabyte!
This is definitely not a job for PhotoShop.
10.
Finally, I have listed a few scanners in different catagories to show
their relative merits and estimated pricing, they are all units that we
use or have used internally and found them to be very reliable:
300dpi Grey Scale:
Hewlett-Packard ScanJet $ 800
Apple OneScanner 700
400-600dpi Color Flat Bed:
Microtek 300Z (300dpi) 1,200
Microtek 600Z (600dpi) 1,500
XRS 3cx (AutoRads & X-Rays, 600dpi) 4,500
Sharp JS450 (400dpi) 6,500
600-2000dpi Color Flat Bed:
Sharp JS600 (600dpi) 8,000
Imapro XL (1200dpi) 14,500
AGFA Imagemaster (1600dpi) 22,500
Artronic ViewScan (2000dpi transmissive) 35,000
3000dpi Slide Scanners:
Nikon LS3500 7,500
Nikon LS3510 (12-bit) 10,500
Leaf 35 14,000
Leaf 45 (35mm & 4x5 12-bit) 19,000
4000-6000dpi Drum Scanners:
Dangraf DeskDrum (4000dpi, 12-bit) 22,500
Optronics ColorGetter (6000dpi, 16-bit) 85,000
------------- PAGEMAKER/QUARK LISTSERV -----------------
------------- S C A N N I N G F A Q UPDATE 1/22/93 -----------------
Questions and Answers
-- Where can I find information about specific scanning courses?
Systems of Merritt, Inc. (authors of "Inside PostScript"
2551 Old Dobbin Dr. East and original QMS color PS models)
Mobile, AL 36695
(205) 660-1240
Peter Fink Communications, Inc. (publisher of "Desktop to Press"
120 Q Street NE and member of development team for
Washington, DC 20002 Adobe's Accurate Screens technology)
(800) 551-5921
American Newspaper Publishers Association
11600 Sunrise Valley Drive
Reston, VA 22091
(703) 648-1212
TypeWorld/Color Publishing Systems Seminars
Barrie Evans
PennWell Publishing Co.
(800) 225-0556
QuarkXPress Users International
P.O. Box 170
Salem, New Hampshire 03079
(603) 898-2822
Graphic Arts Foundation
4615 Forbes Avenue
Pittsburg, PA 15213
(412) 621-6941
ACM/SIGGRAPH
Conference Management
401 North Michigan Ave
Chicago, IL 60611
(312) 644-6610
-- What are the specific copyright laws, et.al., governing scanning
-- for use in my DTP?
Jeff Needleman provides the following information regarding this:
Use a Scanner, Go to Jail
-------------------------
by Mark H. Anbinder -- TidBITS Contributing Editor
Hewlett-Packard included a bulletin in a recent mailing to dealers
warning them that, when demonstrating the capabilities of HP
scanners, they must avoid scanning money and other "sensitive
documents." Anyone who does scan such documents risks
"Constructive Seizure" of their computer equipment, up to $25,000
in fines, or up to fifteen years imprisonment.
Apparently HP has learned of an incident where U.S. Treasury
agents seized an HP ScanJet IIc scanner, HP DeskJet 500C printer,
and an HP Vectra personal computer. The dealer and HP sales
representative involved spent a considerable amount of time
retrieving the equipment.
HP provides this list of guidelines from the U.S. government.
Unacceptable scanning:
* Money
* Federal Reserve notes
* U.S. postage stamps
* Foreign postage stamps
* Revenue stamps
* Other negotiable valuated articles (for example, checks, bonds,
and securities)
* Identification documents (for example, driver's license and
governmental identification documents
Acceptable scanning:
* Photographs of people, places, or things
* Pictures from magazines, newsletters, and calendars
* Other similar non-sensitive documents
We wish to add that, if you do scan photographs (or even text)
from copyrighted publications, it's important to secure permission
before using that material in any way.
Perhaps the government is concerned that computer input and output
devices are becoming powerful enough that counterfeiting is (or
will soon be) a real concern. We've seen the latest output
technology, though, and we're skeptical that counterfeiting with
multi-million-dollar technology would be cost-effective! Of
course, until output quality catches up with the government's
concerns, we'll be unable to avoid the image of a crook lugging
along a 24-bit color 1152 x 870 monitor, trying to convince
someone that the scanned image on it is legal tender!
[This article is being published simultaneously in TidBITS and
Clicks!, the newsletter of the Ithaca Macintosh Users' Group.]
Copyright 1990-1992 Adam & Tonya Engst. Non-profit, non-commercial
publications may reprint articles if full credit is given.
Until today, I was quite sure that scanning fell under the usual laws
restricting reproduction of U. S. and foreign security obligations. The old
laws were liberalized back in 1958 and again in 1968 to allow reproduction
in some cases. The primary exceptions to the usual prohibitions are given
in Title 18, U. S. Code, Section 504:
"Notwithstanding any other provisions of this chapter, the following are
permitted:
[A-C provisions deal with postage/revenue/other securities of the U. S.]
and
(D) postage stamps, revenue stamps, notes, bonds, and any other obligation
or other security of any foreign government, bank or corporation, for
philatelic, numismatic, educational, historical, or newsworthy purposes in
articles, books, journals, newspapers, or albums (but not for advertising
purposes, except illustrations of stamps, and paper money in philatelic or
numismatic articles, books, journals, newspapers, or albums)."
The section goes on to spell out how the printed illustrations must appear.
All have to be in black and white, except that postage stamps can be
illustrated in color; all must be of a size less than 75% or more than 150%
in linear dimension of each item illustrated (except that US stamps can be
exact size if illustrated in b&w). The negatives and plates used have to be
destroyed "after their final use."
There's another section regarding film, microfilm or slides for projection
upon a screen of such items; they're allowed completely except for
advertising purposes (philatelic advertising is allowed), but you can't
make prints or other reproductions from such films or slides except by
permission of the Secretary of the Treasury.
-- Do I really need to keep the photographs or negatives from a client job
-- since I've already scanned the images and have them saved with the rest
-- of the job files for any future changes?
Maybe not, but I'll answer that question by relating our situation. Our
department handles most of the medical photography for the university and
its various medical research facilities. This generates thousands of
negatives a year for us to archive. We currently have a vault of over 15
years worth of medical photography negatives.
We began to toss around the idea of scanning them to store them digitially
then converting some of our Nikons to the new Kodak digital backs to record
the imagery in digital form from the get go. Problem though is two fold:
(1) No digital storage medium is as permanant as film. Proof is the fact
that we have film stored for over 40 years that is still in good enough
shape to make a print and/or re-archive. Hard drives we bought only five
years ago are now dead or dying, tape backup is about as reliable over
long periods of time as an 8-track tape, and optical storage systems once
thought to be truly permanant have now been shown to begin substrate cor-
ruption after only years service.
(2) Most digital storage medium mechanisms are bound in time technologically.
That is to say, if you standardize on DAT tape whose to say that DAT tape
will not go the way of QIC 20 format or 9 track format. The mechanism
may not be available in the near future let alone the distant future.
So to compensate for this many organizations develop elaborate redunancy
policies regarding digital storage. This means that they get multiple
copies of the image in digital form often on different types of storage
systems. Redunancy and multiple mediums drastically increase the
physical space requirements for image storage. In short, save the
negatives.
-- The question I have is where do they come up with setting the
-- LPI to 53, 83, and 106. Are these magic numbers or what?
Almost! The screen rulings (LPI) are based on a mathematical formula
that takes into consideration, among other things, the occilation frequency
of the video clock generator in the laser control circuit. What? Suffice
it to say that the rulings are practically magical. As a matter of fact
most screen frequencies and angles used in four color separating in more
expensive imagesetters are arrived at with a great deal of secrecy because
these little differences mean the world to those little color rosettes.
-- What exactly is the difference between a PICT and a TIFF file format?
For the most part they contain the same type data when it comes to bitmap
information, that is each pixel in the image. But the PICT file
specification (created by Apple and based on Quickdraw) can also contain
vector data. Vector data is resolution independant. For example, instead
of a series of pixels making up a line across an image in a bitmap, a
vector line would be an x,y coordinate where the line starts and stops
and then a value for its thickness and color.
As you can see the PICT file can be much more complex than a TIFF file and
this is why Aldus along with Microsoft created the TIFF file specification.
They needed a simple yet "rich" file type that could handle greyscale data
from a scanned file and be exchanged between various machines and operating
systems. TIFF is the most widely supported bitmap file format to date. It
is now capable of handling not only greyscale data but color data as well
and even has the ability to store data in a compressed form (LZW and
Packbits in the 5.0 spec, CCITT IV and V, and JPEG/M-JPEG in the 6.0
spec). PICT currently has only one method for compressing a file,
through the use of the Quicktime/Quickpress extension from Apple, this
allows a PICT file to be stored as a JPEG compressed file and read by
any application without conversion first.
-- Which format is best for a specific image (i.e. a simple B&W, a scaled
-- image, a color image, etc.)
It depends entirely on your situation. Remember, that more pleasing it is
-- the more memory and the slower your system will be in manipulating them.
In my opinion TIFF is the best file format for all of these examples
mentioned. The basic TIFF file (5.0) can handle 1-bit, 4-bit, and 8-bit
greyscale data, and can handle 8-bit, 16-bit, and 24-bit color data. The
most common forms however are 1-bit and 8-bit greyscale, and 8-bit and 24-
bit color. With the two basic forms of compression recognized in the
TIFF spec you can successfully compress all of these types of images so
that they take up less space in storage without worrying about using
some secondary compression utility.
-- Why are there so many different DPI scales? What common laser printers
-- use what DPI? What DPI do image-setters use? What DPI can PageMaker
-- handle? MicroSoft Word? Quark? What about an Image Writer or a
-- Stylewriter?
DPI or Dots Per Inch is a clever marketing tool that the early laserprinter
manufacturers came up with that really doesn't mean a whole lot. A few
years ago, imagesetter manufacturers and scanner makers were talking in
the more descriptive SPSI (spots per square inch) and LPI (lines per
inch) measurements. It was very common for imagesetters to produce 1.6
million SPSI at 133 LPI, or 1270dpix1270dpi with 256 grey scales.
Marketing types couldn't compete because the laserprinter seemed paltry
in comparison, 90,000 SPSI at 53 LPI, or 300dpix300dpi with 14 grey
scales.
Anyway DPI has become dominant because laserprinter manufacturers had more
advertising money. Most laserprinters are now showing their DPI uniformly
anyway, so you can simply square the DPI and get an accurate SPSI.
So DPIxDPI = SPSI which is much more useful in determining how much better
one laserprinter is over another one. For instance, the original Apple
Laserwriter is 90,000 spsi (300x300), the NeXT Laserprinter is 160,000 spsi
(400x400) which is 1.7 times better not 1.3 as the 400/300 ratio would
suggest. Where this really gets interesting is with the new crop of 600dpi
lasers. For instance, the new QMS 860 is 360,000 spsi, or 4 times better
not 2 times as the 600/300 ratio would suggest.
Below is a list of some common printers and their SPSI:
Printer SPSI Type
------------------------------------------------------
Epson LX-80 14,400 9-pin Dot Matrix
Apple Imagewriter 20,760 18-pin Dot Matrix
Apple Laserwriter 90,000 Canon CX Laserprinter
HP LaserJet III 90,000 Canon SX Laserprinter
Panasonic KXI1124 129,600 24-pin Dot Matrix
Canon BJ10e 129,600 Canon 36-valve Bubble Jet
NeXT Laserprinter 160,000 Fujitsu Laserprinter
Dataproducts LZ960 160,000 Fujitsu Laserprinter
Compaq PageMarq 20 320,000 Xerox Laserprinter
HP LaserJet IV 360,000 Canon BX Laserprinter
Lasermaster L1000 600,000 Fujitsu Laserprinter
Linotronic 170 1,612,900 Infrared Laser imagesetter
Linotronic 330 11,444,689 Helium Neon Laser imagesetter
AGFA SelectSet 5000 21,622,500 Helium Argon Laser imagesetter
-- What are the best ways (if any) to compress a graphics file once it's
-- been scanned?
The TIFF format provides a Compressed TIFF version -- that is usually
recognized anytime that Uncompressed TIFF is. Other formats can be
manually compressed -- but will need to be manually uncompressed anytime
you need them. Manual compression is used more for archiving the file
for storage and can save a significant amount of space.
Without loosing any of the data, most forms of compression are based on the
LZH (Lempel-Zimpel-Huffman) algorithm, they are:
For the Mac: For the PC: For UNIX Machines;
Stuffit PKZip Unix Compress
CompactPro ARJ Zoo
Disk Doubler Zoo PKZip
ARJ
They are all good and most will compress a file within 5-10% of the other.
-- My Hewlett-Packard ScanJet came with a rudimentary scanning package.
-- Is there better scanning software than DeskScan? What are the main
-- features to look for in scanning software?
Concensus favorite for grey scale scanning is Ofoto. Look especially
for software that gives you the ability to scan and save in all the
common file formats that you will want to use, and your scanning software
should definitely allow you to crop and rotate before or during saving.
If you don't already own an image processing package, check out Photo-
Styler for the PC and PhotoShop for the Mac. These packages won't
require separate scanning software but rather allow for the addition of
a "plug-in" module that will allow scanning from inside these applications.
Finally
-------
If you have any questions or additions to this FAQ, please feel free to
send them directly to me:
Jeff Bone, Electronic Imaging Coordinator
University of Alabama at Birmingham
School of Medicine
933 19th Street South, CHSB-19 Room 320
Birmingham, Alabama 35294-2041
voice (205) 934-4396
fax (205) 934-3749
email jbone@dopig.uab.edu