scanning - theory of color
TRANSCRIPT
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ning
T he Creative W orld of Digital D ata
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Introduction
H ello and W elcome!
With t he small book youre now holding, we at
Heidelberg CPS would like to offer and share with
you the knowledge and experience in the field of
scanning which we have acquired in over thirty
years of pre-press development and production.
I t s import ant to r ealize that t his isnt a manual
for your scanner, and so aft er reading this book you
may not be a fully qualified scanning expert.
But youll gain an excell ent i ntroduction into t he
world of scanning and it s vast potential , so that
even as a beginner, youl l easily be able to achieve
scanning results which fulfill high expectations.
To make sure your introduction to scanning is as
excit ing as the topic it self , well only address as
much theory as is absolutely necessary for a basic
but fundamental understanding of the technology.
That way your first priority can be a thorough
famili arization with our useful, practice-oriented
ti ps. (Some of which may be of help to even the
more experienced scanner user.)
Since we have a few surprises waiting for you,
theres no point in dragging out the introduction
any longer.
H ave fun reading, playing, and scanning !! !
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Theory of Color
Bits and Bytes
Opacity and Density Resis
Drum Scanners versus Flatbed Scanners Te
Scanner Handling
System Calibration C
Storage Structure
I mage Assessment
Prior to Scanning
Scan Process From Docum
Scanning Standard Originals
Scanning Heads-Up Originals
Scanning with Image Manipulation
Pixel Retouching
Data M anagement
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But we can see the colors of the visible spectrum
because the electromagnetic radiation in these
areas has a wavelength capable of acting as a
color stimulus for our eyes.
Thus, to perceive color we need
q light
q an object either to reflect or to let the light
through
q the eye and the brain.
Different colors are perceived just as subjec-
t ively as sounds, tastes or smells.
The same color can provoke a number of dif-
ferent reactions in dif ferent people. L ike our
little,blue circle here:
Sometimes these reactions depend not only on a
persons sense of taste but also on his or her color
sensit ivit y.The spectr al sensit ivit y of each persons
eyes varies slightly. That s why two people might
come to different conclusions when judging a
single color. One might call t urquoise green, while
the other might say that its bluish.
Colors are not only perceived subjectively how-
ever, but ar e also infl uenced by external circum-
stances.
One influence might be the kind of light source.
Which one of us hasnt seen a beautif ul colored
sweater in a department store which ended up
looking absolutely terrible in daylight?
At the same time, the size of an object can be
important as well.
I magine that youve had to pick out a fabri c for
your sofa by choosing f rom among small swatches
of fabri c. When you go to pick up the sofa, one
glance and you take a big step back to ask your-
self : is this really the color I picked out? Colors
often prove to be much more intense on large sur-
faces than on smaller ones.
How is it that we see different colors?
To answer t hat question, we have to star t out bytak ing a look at both physics and biology. We pro-
mise, however, to keep it lively and color ful for you.
This graphic shows the whole range of electro-
magneti c waves, of which only very few are visible
to the human eye.
We cant see UV- or i nfr ared rays, for example.
q What a blue! Wow!
q Thats a terribly loud blue!
q A beautiful, glowing blue. I like it!
q and so forth.Theoryof
Color
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Here you see once again our li tt le blue circle, but
this time half of it is on a bright background and
half on a dark background. Clearly, the eff ect of
the color depends on the background against
which it lies.
L ast but not least, you have to t ake the obser-
vers point of view into account.
An objects color can look drastically different
depending on the angle from which youre looking
at i t. The color may look either darker or lighter.
This is especially noticeable among fabrics.
Of equal importance is the objects background.
How does the monitor display colors?
M onitor s and televisions produce color by way
of electromagnetic waves that correspond to red,
green and blue. However, screens arent able to dis-
play the full range of colors which are visible to
the human eye. Their range of color is more limi -
ted.
Any desired color can be produced by adding
the colors of the three color channels (RGB for
Red, Green, and B lue).This is called additive color
mixing. I f t he colors of t wo of the color channels
are mixed in equal propor ti ons, new base color s
are created.
Bl ue and green add up to a bright , light blue cal-
led cyan. M agenta, a bright pink, is made by mix-
ing red and blue. Red and green together make yel-
low.
I f r ed, green, and blue light are mixed equally
together at f ull power, you get white light.
Theoryof
Color
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I magine that a surf ace printed magenta and cyan
is ill uminated by normal daylight. As explained
above, this white daylight can be thought of as
composed of equally bright r ed, green and blue
rays of light. I f t his white light str ikes a colored
sur face, the surf ace absorbs the complementar y
colors from t he light and reflects the rest. Our
surface was printed with equal parts of cyan and
magenta. Cyans complementary color is r ed, while
magenta s complementar y color i s green. Wi th the
subtraction of the absorbed, complementary
colors, all thats left is blue. Blue is reflected, andagain we see our little blue circle.
H ow are colors printed?
Pri nted colors dif fer fr om monit or colors in thattheyre produced by overlaying ink pigments on
paper instead of by combining different wave-
lengths. I f however you were to tr y to print red,
green, and blue on top of one another, you
wouldnt be able to produce very many colors.
You wouldn t be able to make yell ow, for instance.
This is why printing inks work using subtractive
color mixing, which wed like to intr oduce to you
at t his point.
Theoretically, if we were to print a surface wit h
equal par ts of cyan, magenta and yell ow, wed see
black, because all colors would be absorbed and
none reflected.
I n practi ce, however, thi s black looks more li ke amuddy green or brown. That s why four color s are
general ly used in print ing ( you may have heard t he
expression four-color print ). Black is used as
the fourth color in order to achieve a real black.
Thus, a normal four-color print is produced by a
CMYK basis (CMYK stands for Cyan, M agenta,
Y ellow, and Bl ack) .Theoryof
Color
Print ing with Cyan, M agenta Yel low and Black Printing with Red, Green and Blue
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For practi cal purposes, this also means that con-
ventional color printing only tolerates colors that
can be mixed fr om these four base colors. (A ll
other color s have to be speciall y printed.)
The print spectrum is thus smaller than the visi-
ble spectrum and also smaller than the monitor
spectrum.
I f color perception is so very subjective, how can
you make someone understand which color youd
like your new car? How do the scanner and com-
puter make sure that the scanned image is colored
just li ke t he or iginal?
Clearly we need a system that precisely defines
diff erent colors.
For that reason every color has been described
by three base values:
q tone (hue)
q saturation (chroma)
q brightness (luminance)
These three graphics clearly show what the
terms describe.
If you follow the circle of the first illustration,
you can recognize different color tones like green,
yell ow, and red. Looking at t he second il lustrati on,
moving fr om the center outwards, the color satu-
rat ion clearl y increases.The color s become ri cher.
You can see a progression of varying brightness
from the darker bottom to the brighter top in the
third illustration.
All three values of any color can be measured
wit h a special tool call ed a spectr ophotometer. You
can easily alter an image by changing even just oneof t hese values. That s why they oft en appear as
variable parameters in software for image ma-
nipulation.
A number of systems have been developed using
these measurable values. Each of these systems allows
every color to be assigned a clearly defined value.
1 Tone (H ue) 2 Saturation (Chroma) 3 Brightness (Luminance)
Theoryof
Color
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Theoryof
Color
I n thi s coordinate system every color has been
assigned a specifi c point. I nside the space of t his
abstract tr iangle (or shoe sole, or colorf ul what-
ever-it-is) lie all the colors visible to the human
eye. Al ong the x-axis of t he coordinate system you
can see the red colors, while the green colors are
situated along the y-axis. This two-dimensional
illustration shows all colors irrespective of their
brightness. I f you can imagine a thir d axis which
extends perpendicularly through the plane of the
page (and against which youd bump your nose ifyou got too cl ose), the various values of brightness
would li e here. One problem wit h this systems il lu-
stration, though, is that the distances between the
colors dont correspond to our perceptions of color
dif ferences, and that including the thir d dimension,
and thus the brightness, is very dif fi cult .
To avoid confusion, though, wel l only intr oduce
two of them to you:
I n 1931, the Yxy Color model, also called the
Norm Color model was developed by the
Commission I nternationale dEclair age (CI E) . The
CIE defines reliable standards for purposes of
color production and lighting. An ill ustration of
their Norm Color system looks like this:
-bblue
-agreen
+ byellow
+ are d
To address thi s short coming, in 197 6 the com-
mission developed the Lab model in which the
color space was represented three dimensionally.
All colors with equal brightness still lie on a
single plane of the model.
Here you can see how each individual plane
extends along the a-axis from left to right and
along the b-axis from the bottom to the top.
M oving outwar ds fr om the center of the cross,
positive a-axis values increase to the right and
negati ve a-axis values decrease to t he left . Posit ive
b-axis values increase towards the top and negati-
ve b-axis values decrease towards the bottom.
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Posit ive a-values are red, so the redder a color
is, the higher i ts a-value is. Negative a-values are
greenish. I n other words, complementary colors
are aligned opposite to one another. The same istr ue of yell ow and blue. Posit ive b-values are yel-
lowish. Negative b-values are bluish.
Br ightness, meanwhile, increases from t he bot-
tom of the model to the top.
And here we have an illustration of the whole
three dimensional color model for you:
-agreen
+ byellow
+ are d
L
white
black
Theoryof
Color
-bblue
You can name every color exactly by giving its
brightness, L ( for Luminance), and its specific
a- and b-values. I n the real world, though, it might
be a bit troublesome to order a necktie in
L = + 43 .51,
a = + 1 5.4 5,
and b = - 22.85.
So, why are we bothering to explain all this ???Because some scanners and scanner softwares
work within this Lab Color space to ensure an
accurate exchange of data.
Next wed like to explain how these colors are
displayed by the computer on the monitor.
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I f, however, a pixel i s the product of several bi ts,
tones between black and white can also be repre-
sented. That would be li ke a good, old-fashioned
lamp wit h two bulbs and two swit ches, of which
both or neit her or one or the other can be switched
On at any given time. I n this case, there are four(22) dif ferent, possible posit ions.
M ost scanners operate with a bi t depth of 8 bit s.
That means that 8 bits represent each pixel.
Therefore the pixel can take on 256 (2 8) different
posit ions, and the scanner can produce that many
different shades of gray.BitsandB
ytes
On these two pages youll find a number of tech-
nical concepts and defini ti ons. Some of them might
prove to be new to you.
But dont be discouraged, we wont go into too
much detail ! ! !
Wed simply like to pass on to you the funda-
mentals of the technology wit h which your scanner
and computer work because theyre of utmost
importance for the actual scanning.
So lets get down to business.
W hat is a Bit?
When you work wi th a computer, regardless of
whether youre writ ing a text , preparing a picture,
or programming soft ware, calculat ions are being
carri ed out by the computer. I n the process of
these calculations, millions of tiny, electronic
switches are activated. A bi t is one of t hese swit ch-
es. I t only knows two posit ions: On and Off . The
results of computer calculations are therefore
combinations of Ons and Offs.The computer r epre-
sents them in combinations of 1s and 0s. 1 corre-
sponds to On and 0 to Off .
1 Bit
2 Bit
11
1 0
01
00
01
Relationship between bitdepth
and the number of possible shades of gray
All types of digitalized pictures are called bit-
maps. L ike in the second pictur e on the next page,
a bitmap is composed of a lot of tiny squares.
These tiny square picture points are called pixels.
Pixel is formed from the words Picture and
Elements.
Whether a pi xel can take on black, white, gray-
scale or even colored tones depends on the pixels
bit depth. This also sounds much more complicated
than it really is.
When exact ly one bit represents a pixel, depen-
ding on whether the bit is switched to On or Off ,
the pixel wil l be white or black. I magine a lamp
wi th a single bulb and a single power swit ch, a
spotlight for example. I t can be eit her On or Off ,
and not slightly On or slightly Off .
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For this reason its important to note both the
original and the reproduced sizes of the document
when determining the scan resolution.
At the same time, youl l have to consider that a
higher scan resolution always means that youre
working with a larger amount of data.This in turn
slows down your computer. Thus, you shouldnt sel-
ect a higher resolution than is absolutely neces-
sary.
High-quality scanner software automatically
calculates the scan resolution required for the
selected sizing factor.
I f youd like to start scanning right now, and
need information for the calculation of scan reso-lution, turn to the chapter entitl ed Prior to
Scanning . Thats where youll find the exact f or-
mulas. But be careful: you are bound to miss
something in between.
I f color images are being represented, the scan-ner functions with a bit depth of 8 bits for each of
the color channels. That means that RGB-repro-
ductions are produced with 256 x 256 x 256
(2563) different combinations of red, green, and
blue, and that over 16 milli on dif ferent colors can
be represented.
Hi gh end scanners work wi th a bit depth of up to
16 bits.They can thus represent 65536 x 655 36 x
65536 dif ferent colors. Such a huge number i s
really hard to imagine, isnt i t?
Aside fr om the bit depth, bit maps are described
by the scan resolut ion, the dimensions of t he docu-
ment and the selected color model.
The term scan resolution describes the number
of individual samples that the scanner takes over a
specifi c area. I t s measured in dpi ( dots per inch).
Thus the scan resolution is actually pretty
import ant, because the precision of the scan
depends on this resolution.
BitsandB
ytes
I f you scan a document wi th l ow-level resolu-
ti on, the image wil l be made of only a few dots per
inch. I ndividual pi xels will be visible as small
squares in the pict ure. This is most cl early visible
along curves or diagonal lines. They of ten appear
to be fr ayed or stepped, as though someone had
been nibbling on them.
The qualitys dependence on scan resolution
becomes especially obvious when the image is
enlarged for print ing. I f you dont increase the
resolut ion when enlarging an image, the individual
pixels themselves will be enlarged and become
visible. A resolut ion that s applied to a small docu-ment will suffice as long as the picture is to be
reproduced in the same size. I f youd like to
enlar ge the pictur e, however, you should select a
higher scan resolution.
Bitdepth: 1-bit , 2-bit , 8-bit
from black and white to color
The enlargement causes
the individual pixels to become visible
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OpacityandDensity
Opacity
Opacit y (O) r efers to t he color layer s resistance
to letting light through. I n real lif e, this resistance
is never consistent across the whole surface of the
document. M ore light is let t hrough and reflected
by bright areas of the document than by dark
areas. The less light an area of a document l ets
through, the greater it s opacity. Opacit y can bedescribed by a single value the total amount of
light which str ikes the surf ace divided by the amo-
unt of light let through.
For example:
An amount of light equalling 1000 light units
stri kes a slide. The color layer of a bright ar ea on
the slide allows 100 light unit s to pass through.
This area of the slide has an opacity of 10.
The same is true for reflective documents.
I f a secti on of a newspaper clipping reflects 200
of the original 1000 light units , then this sec-
tions opacity is 5.
Theoreti cally, opacit y can have an infinite value,
but in practi ce the value usually li es between 1 and
1000.
I n practice, when light strikes eit her a t rans-
parent original (like a slide) or a reflective original
(l ike a photo or a newspaper cli pping), not all the
light t hat stri kes the original will be let t hrough or
reflected. Some light i s always absorbed. The
strength of this absorpt ion depends on the opacity
and densit y of the original s color layer.
10001000 1000
1000
1000 1000 1000 1000
900
100
101
800 20020 2
Regardle ss of whether its a transparent
or a reflective original,
the darker the surface, the higher
the opacity and density
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OpacityandDensity
Density
I n principle, densit y (D) designates the samething as opacit y: the document s resistance to let-
ting light through.
Density also tends to vary across the document.
Dark surface areas have a higher density and
bright surface areas a lower one.
M athemati cally, densit y refers to t he power t o
which we rai se the opacity value. Therefore it is
general ly a smaller, more user-f ri endly value than
opacity.
That sounds pretty confusing, but in trut h it spretty simple:
Lets take another look at the graphic for our
tr ansparent document. On a relat ively bright ar ea
of the document where 100 light units are let
through, we calculate an opacity of 10. On a dark-
er area of the document where only 10 light units
pass through, the opacit y is 100 or 102. The densi-
ty of this darker area is thus 2.
As you might well imagine, it wouldnt do for a
scanner t o scan only dark ar eas properly, or f or
that matt er, only bright areas. The scanner has towork with a documents entire density range if
its to redisplay the natural contrasts between
the dark and bright areas. We can figure out a
documents density range by looking at the dif-
ference between the area with the highest density
(the image shadow) and the one with the lowest
density (the image highlight).
I f we measure, for example, a highest densit y of
2.4D and a lowest densit y of 0.3D, our document s
density range equals 2.1D.
Reflective originals generally have a density of
2.0D. Transparent originals might have a densit y
of 3 .0D or even more. Your scanner has to be
that much more sensitive if youre hoping to use
it to scan the greater image range of transparent
originals wit h sati sfying result s. The exact sensi-
tivity of your scanner is listed among its other
technical specifi cations.
Image shadow
Image highlight
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DrumScannersversusFlatbedScanners
From Light to Electricity to Digital D ata
The active scanner reads light reflections from
reflective originals (li ke a newspaper clipping) and
picks up the amount of let-through-light when
scanning transparent originals (li ke a slide). The
light source projects a laser-like beam which spi-
rals across the original while the cylinder is rota-
ting.
The reflected (newspaper clipping) or transmit-
ted (slide) light is then picked up and passed along
by the scanner s eye-like sensor unit . The incominglight signal is divided into three color channels
red, green, and blue. A separate photomultiplier
tube (PM T) senses the light f or each color and
transforms it into electric signals.
Once inside a photocathode, these light rays
produce electrical charges. Unfortunately, the
resultant stream of charges is still too weak to be
of much use. But once the stream is passed along
a charge intensifi er , the available charges are
sufficient to produce a strong electric signal.
Because, however, computers arent designed to
work wit h analog, electri c signals, the signals have
to undergo one final tr ansformation: they have to
be digitali zed. This signal tr ansformation takes
place in an analog/digital converter (alias A/D
conver ter), which turns the analog signals into
useful, digit al values.
Drum scanners and flatbed scanners dont just
look diff erent, but are also diff erent in terms of
handling, technology, ...
Drum Scanners
M ounting of Originals
All the documents which you intend to drum
scan must be mounted on the scanners acrylic
glass cylinder. The documents should be thin and
flexible so that they can be laid flat on this drum.
To simpli fy the process, you can r emove the cylin-der from the scanner and attach it to a specially
designed mounting unit . Once the cylinder i s
mounted, it s easier t o posit ion the documents
exactly as youd like them to appear on the screen.
Careful posit ioning is important: the document
image appears on the screen in the same way as
you scanned it , and rotat ing the image angle after
scanning costs not only time but diminishes the
qualit y of your r esults. Ef ficiency can in fact be
fur ther improved by working wit h addit ional cylin-
ders: whil e the fir st set of or iginals is scanning,youll be able to mount other originals on another
drum.
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Drum
ScannersversusFlatbedScanners
P ractical A dvantages and D isadvantages
The full-fledged application of drum scanner tech-
nology offers several advantages:
q high-speed efficiency
q high sensitivity (density resolution of up to
4.2D) , which lets you scan documents that ei-
ther reflect poorly or dont let much light
through
q minimal noise
q optical r esolution of up to 9,600 dpi, which al-
lows 3,000% enlargement ( enough for you to
enlarge a small slide to medium poster size)
The point-by-point scanning guarantees some fur-
ther advantages, li ke:
q diminished interference from stray light
q consistently high resolution across the entire
scan surface (which means absolutely no change
in scan quality)
High-quality drum scanners are universally ap-
plicable, but the mounting of originals requir es
some dexterity.
Drum Scanner Signal Processing
Original
Mirror
M irror
Color F ilter
Light Source
Photomultiplier Tube
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DrumScannersversusFlatbedScanners
F latbed Scanners
M ounting Originals
I n contr ast to drum scanners, documents for
flatbed scanning are laid on a horizontal tray.
Thus, they don t necessaril y have to be thin and
flexible. Some scanners will even allow you to scan
documents of pract ical ly any t hickness (books and
fabrics for example).
From Light to Electricity to Digital D ata:
A New Conversion
Flatbed scanning also requires careful posi-
ti oning of t he originals, but t his is much simpler on
the horizontal tray than it is on the cylinder of a
drum scanner. On most fl atbed scanners, the tr ay is
attached to the scanner it self. What that means
however, is t hat you can t simul taneously scan and
be busy preparing another tr ay with originals. (A t
the time being there are only a few exceptions
which of fer a removable document tr ay.)
As wit h a drum scanner, in a fl atbed scanner
light signals are first transformed into electricalsignals and then into digit al signals. I nternally
however, the fl atbed scanner s technology is quit e
different to that of a drum scanner. A halogen lamp acts as the sole light source.The
lamp shines on a single stri p of the original and the
original is scanned line-by-line.
The light reflected or let through by the original
is picked up by thousands of extremely small
photodiodes. These photodiodes are aligned on a
sili con chip. The selected charges set f ree by the
light are collected for a while and then transmitted
into a CCD (Charge Coupled Device)-line.
From here on, the signal proceeds simil arly to
the way it would in a drum scanner. The charges
are read out from the line and finally turned into
computer-ready digital data by an A /D-conver ter.
I f the CCD in question has a single fil ter for r ed,
green and blue color channels, then all thr ee color
channels can be scanned in a single pass (also
known as the Single Pass Technique).
If however the CCD is working with the help of
ext ernal f il ters, the scanning has to be divided
among a total of three passes (called the Triple
Pass Technique) t o all ow for a fi lt er change before
the star t of each pass. Almost all modern fl atbed
scanners operate with the Single Pass Technique
because it allows the added advantage of higher
efficiency.
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Drum
ScannersversusFlatbedScanners
A Practical Comparison to the Drum Scanner
q most fl atbed scanners aren t as eff icient as drum
scanners
q the optical resolution is determined by the num-
ber of CCD-elements and can only be increased
or diminished by software interpolation
q because it s more sensit ive to str ay light, fl atbed
line-by-line scanning is more likely to produce
images with faults than dot-by-dot drum scan-
ning
q lower density resolution than with a drum scan-
ner
Despi te these disadvantages, a high-end flat bedscanner performs comparably with a drum scanner
when scanning normal originals.The drum scanner
is truly superior only in cases demanding very high
qualit y work. Fur thermore, new CCD technology is
continually being developed and even now the
more moderate price and simpler handling often
make flatbed scanners the preferred choice.
CCD Unit
Original
Light Source
M irror
M irror
Flatbed Scanner Signal Processing
Digital Cameras
I n the fi eld of photography, CCD technology is
also being used to produce computer images of
lar ge and three-dimensional objects. The case of
digital cameras has been outfitted with individual
matrix-shaped CCDs.
The result is that a subject can be captured
directly in digital data without resorting to film.
This technology is primarily used in photography
for catalogues, by journali sts (who send press pho-
tos over modems to their editing offices) and in
advertising for studio photography.
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DrumScannersversusFlatbedScanners
This table gives you an overview of the various
types of scanners, their main applications and
much more.
I n many offi ces nowadays, the scanner is just as
common and as much at home as the computer.
I t s oft en used to r ecord text and for document
archives.
Scanners are becoming increasingly popular at
home as well . When you combine a scanner wit h a
reasonably pri ced computer, you can slowly f ami-
liarize yourself with digital image preparation.You
shouldnt expect professional qualit y result s, but
youll definit ely have a lot of f un with i t.
Flatbed Scanner Drum Scanner
Office DTR Lower M id Range Upper M id Range High-End
Office Applicat ions Office Applicat ions, Pre Press, Pre Press, Pre Press,
( for example, OCR), DTP and Adver t ising DTP and Adver t ising High-End High-EndDiscr iminat ing Agencies Agencies I mage Product ion I mage Product ion
Home Users
Reflect ive Reflect ive or Reflect ive or Reflect ive or Reflect ive orOriginals, Transparent Transparent Transparent Transparent
Originals, Originals, Originals, Originals,flexible or st i f f, flexible or st i f f, flexible or st i f f, flexible or st i f f, flexible,
var ious thicknesses, a lmost any a lmost any 0.4 inch thick thinthi ckness for thi ckness for
Reflect ive Reflect ive
Originals Originals
(3D-Objects) , (3D-Objects) ,b& w and color b& w and color b& w and color b& w and color b& w and color
low average average to high high very high
300 x 300 dpi to 600 x 1200 dpi > 1200 dpi > 3800 dpi > 9600 dpi400 x 400 dpi
< 3,0 D < 3,0 D > 3,0 D > 3,7 D > 4,2 D
The vast majorit y of scans, however, are stilltak ing place in other fi elds: in the high end region,
by which we mean not only professional image pre-
paration but also small companies with their own
DTP departments as well as in advertising agen-
cies for graphic design jobs. These are exact ly the
sorts of places where a scanner can be a helpful
tool for the support of creative assignments.
ScannerOverview
Area ofApplication
SuitableOriginals
Work Ef ficiency
OpticalResolution
Density Range
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ScannerH
andling
I n principle, your scanner i s just as fr iendly or as
fini cky as any other electronic device. That means
that t he scanner doesnt like to be too hot, too
cold, or t oo damp. But when preparing a scanner
work stati on, you should keep the foll owing consid-
erat ions in mind:
Place your scanner on a sturdy surface.
I t s really annoying to have to r emain absolut e-
ly still just because the slightest motion could
cause the table under the scanner to r ock, which in
turn might lead to faulty scan results.
Set up a work station in an area which can be
fair ly well protected against sun light. Reflections
on the monitor can be bothersome even if youre
just wr it ing a text . I n work that invol ves pictures,
reflecti ons can be a real pain. I mage detai ls can
become unrecognizable, and that doesnt make
your work any easier.
Shopping T ips
I f youre establishing a new DTP depart ment in
which several people are to work , you should con-
sider setting up a special station intended exclu-
sively for scanning purposes. On the one handyoull avoid crowding at t he station, and on the
other hand the stat ion can be supplied wit h it s own
specialized equipment.
Youll need a high performance computer with
plenty of memory to process and store the large
amounts of data. And, if you want t o reproduce the
scans yourself , youl l also need an appropriate
print er. Above all however, you should have a real-
ly good, large monit or wit h a suitable 24-bit
graphic card.
Only high-quali ty, well -equipped systems all ow
for truly good work.
A good scanner by itself doesnt amount to a
good scanner workstat ion ! ! !
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H ow does calibration work ?
High-qualit y scanners leave the fact ory properl ycalibrated. I f aft er a while you start to notice
changes in the port rayal of i ndividual originals, you
should recalibrat e your scanner. The simplest way
to test the calibration is to rescan an original that
youve al ready successful ly scanned and saved.You
can then compare the earlier and more recent scan
results side by side on the monitor.
For calibrat ion, youre going to need a calibrati on
set which consists of:
q a calibrati on document (f or instance, a standard
IT8 document)q a disk with the determined Lab values of the
individual color fields of the test document
q calibration software
I n case youve just unpacked and instal led your
new scanner, you should check to see that your
system (which consists of your monitor, scanner,
and printer) i s full y calibrated. By calibrat ion we
mean that the pieces of your system conform to
one another or are in tune with each other.
W hy does the system have to be calibra ted?
A scanner senses red, green and blue (RGB)
light dif ferently than the human eye does. That
means that a scanner, or even a monitor, sees an
original diff erently than our eyes would, and as
a result displays the colors in a dif ferent way. Even
wit h the intr oduction of special color fi lt ers, the
image wont conform 1 00% to our expectations.
A scanner might also need recalibration if you
are install ing a new system component, even if thi s
new component is replacing an old one of the same
make and model. You should always recalibrate
your system when you change scanners, monitor s
or pri nters, or when you replace a part of a com-
ponent.
A certain aging process in the scanners halogenbulb can also bring about changes in scan results.
Once in a while you should give your scanner a
check-up. I f t he need arises, adjust or r epair
trouble spots that have developed.
Such test runs and adjustments are not only
simple but quickly taken care of.SystemC
alibration
T his is what an I T 8 document looks like
(lar ger in real life, though)
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System
Calibration
The actual calibration begins with a scan of the
test document (known as the Calibration Scan).
The values for individual color fields obtained
through this scan are then compared with the
determined Lab values on the disk. From t his com-
parison, the computer can calculate a specific
color profi le for your scanner.
For al l f ur ther scan processes, the scanners
color profile will be assigned to the RGB-data of
the scanned image.
Keep in mind however, that scanner calibration
alone doesnt suff ice.The monitor and printer have
to be calibrated as well . Ei ther your soft ware will
allow you to select the proper monitor and printer
calibration settings so that you can undertake a
similar calibration, or you can request the color
profile of your component including their calibra-
tion settings from the manufacturers.
Only completely calibrated systems will guaran-
tee that the original image on your monitor looks
the same as both the unscanned original and the
original produced by your printer. By the way, an
IT8 document has a gray scale spectrum which is
very well suit ed for the check-up.
A P ractical Tip
For t he calibration check-up, rescan a gray-
scale original in color mode because its changes
are easier to notice than those of a color original.
I f you see a color cast, it s time for a new
calibration.
I T 8 Document
RGB-TIFF Fi leScanner
Calibration File ComputerStored
Lab Values
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Avoid Chaos !!!
Dont be surprised that the question of data
storage arises befor e youve even star ted scanning.
Before you scan the fir st original, you should
definitely review the following:
A I s obvious and easy to expl ain
Youre working with large amounts of data.
M ake sure that you have enough memory at
your disposal before star ti ng work. Especiallywhen several images are being scanned in one
batch. You might not notice until the last
second that theres not enough disk space left
to save the final scans. You shouldnt let
annoying things li ke that happen to you.
B Takes a little longer to explain
Try to establish a definite structure for data
storage before you star t working. Decide
which folders to set up and by which system
the files should be named. I f you dont , youmay end up spending a lot of time searching
for misplaced data. This can be especiall y cri -
tical when several people are preparing the
data and each develops his own system for the
purpose of data storage. Even if you know
which folder to search through, you can stil l
have problems finding the file.StorageS
tructure
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StorageS
tructure
This text (the one youre reading right now)
could for example, be stored under t he fol lowing
file names:
q stostruc, according to the text content. This
system would be fairly conclusive but might be
awkward when working with pictur es.
For pictures you might need a data name like
womanwi thch i l dunderpa lmt ree inga rden in -
fr anceonabeauti fulday, which would probably con-
flict with the softwares restrictons for the number
of permitted characters.
q 072495 , according to the date on which i t was
produced.
That could prove to be tr oublesome, though,
because after a while you probably wouldnt
remember when each file was produced.
q paul5 , because it s the fi ft h fil e on which Paul
worked on a certain day.
not so nice, however, when you pass on your
data to a third party who knows that M r. Smith
gave him the data, but who doesnt know that
M r. Smith s name is Paul, and thus doesnt know
in which stage of t he job M r. Smith worked on the
data.
That sounds trivial, but i t can be a real problem.
Thus, you should establ ish a single system to which
everyone always keeps.
Restructuring a full hard drive after the fact is
much more time consuming than keeping to one
storage str ucture from the star t.
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Because different sorts of originals have to be
scanned in dif ferent ways, you should always begin
the scan process by assessing and classifying your
originals.
I n the fol lowing pages weve prepared a number
of groups and examples which should be of help in
assessment and classification.
First of all we should consider those originalswhich are most easily scanned. I n practi ce, these
Standard Originals make up the vast majority
of al l or iginals. I ncluded in the group of Standard
Originals are:
Color I mages
By color images we mean color slides or photos.
Bilevel Im ages (L ine Ar t I mages)
By bilevel images we dont necessarily mean
images which are split into two sections.
Bilevel images are any originals that consist of
only black and white no gray, no color. A hand-
written text (provided its written on white paper,
using black ink) e.g. is a bilevel image.
ImageAss
essment
Grayscale Images
Grayscale images are what you might generallycall black and whit e. These images are actually
black, white, and gray. I ncluded are slides or pho-
tographs.
Of course these originals are only considered tobe standard if they dont contain particular sub-ject-based featur es, li ke str ong color cast or lowcontrast.
I f t hey did contain such part icular f eatures, or i f
the image had to be scanned in an unusual way,
they would be counted among the Heads-Up
Originals.
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ImageAss
essment
Color Cast Images
Color cast images contain a color imbalance.
When looking at one you have the feeling you are
looking through a color filter (or toned sunglas-
ses). Old yellowed photos are a good example.
Low Key Images
Low key images are low contrast just like high
key images. The dif ference is that l ow key images
are exceptionally dark.
Catchlight Images
Catchlight images contain small very bright
reflections, or catchlights , just like you might
see on windows or chrome metals.
Wi thin the group of Heads-Up Originals you can
find:
H igh Key Im ages
High key images are images which depict a
very bright subject wi th very lit tl e contr ast, like the
picture below. A f urt her example of a high key
image is the famous polar bear in snow .
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U nfocused Original s
Unfocused originals are those originals in which
lines arent clearly defined.The outlines appear hazy.
Not only the subject but also the subject pr esen-
tation can contribute to difficulty in scanning anoriginal. For example we have:
Ar tistic and Computer Ge nerate d Originals
This palett e of various techniques includes, for
example, watercolors or oil paints. But also com-
puter generated images show some particularities
which you have to regard.
I mproperly Li t Originals
These originals are either very bright and over-exposed or very dark and underexposed. I n these
cases brightness or darkness is the product of a
technical mistake and not related to the depicted
subject of the image.
ImageAss
essment
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Negative Originals
These are grayscale or color originals presentedin the form of negatives.
A screen dot which is supposed to be 25% black
(you might al so call i t light gray) i s smaller t han a
50% black screen dot ( which is a bit darker) ,
which is in turn smaller than a 100% black dot. A
single screen dot is always made up of several
image dots which can be either black or whit e.The
dark -er the screen dot is supposed to be, the more
black image dots you have. Just as is the case wi thbit depth, the number of representable color l evels
depends on the number of image dots that form
each screen dot.The minimum number of gray sha-
des required to represent an optically continual
color spectr um is 64.Thus, a screen dot consists of
a matrix of 8 x 8 picture dots.
The width of the print screen is described by the
number of screen lines per unit area. The unit of
measure is lpi, or li nes per i nch.
Screened Originals
Any original, be it grayscale or color, is screened
as soon as it is reproduced in a pr inted format (f or
example, newspaper clippings). The screen repre-
sents different hues with dots of various sizes.
ImageAss
essment
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Dont rush off to start scanning now that you
have assessed the originals ! ! !
Nows the time to ask yourself a fundamental
question:
Do you want t o reproduce your image exact ly as
it is now (same size, poorly li t, etc.) , or should you
alter t he image in one way or another? I f, for
example, you want to change the size of t he image,
you should take this into account in the scan reso-
lution.
Quality scanner software takes over the resolu-
ti on calculat ion for you, as the formulas presented
below are already integrated into t he program. Al l
you have to do is input the desired print-out size
and the screen ruling manually.The soft ware t akes
care of everything else.
For t hose of you however, who would like to
learn the exact formulas, here is all youll need to
calculate the scan resolution for the most used
printout forms.
For printers that can reproduce gray shades
(like a thermosublimation printer)
I n case youll later want t o print t he image wit h
a printer t hat r eproduces gray shades, you can cal-
culate scan resolut ion using the following method:
The sizing fact or is found by dividing the desir ed
size by the original size.
For example: You want to scan an original that s1x1 inches. The original i s too small , so you decide
to enlarge the reproduction to 3x3 inches and
print it with your 300 dpi printer.
The following calculation results:
I f you want to reduce your image, the sizing factor
is accordingly small er than 1. For a r eduction of
the 1x1 i nch image to 0.5 x0.5 inches, the sizing
factor would be 0.5.
The scan resolution depends above all on the
medium wit h which the image is to be repro-
duced later on.
Sizing factor = 3/1 = 3
Scan Resolution = 30 0 dpi x 3 = 90 0 ppi
Scan Resolution =
Resolution of the Printer x Sizing Factor
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Scanning for Screen P rinting
The stor ys the same, whether you want t o scan
a grayscale or a color original. I f you want t o print
the image at some later date (for use as a maga-
zine illustration, for i nstance), use the following
formula to calculate the scan resolution:
I n real li fe it is ext remely rar e that a single pixel
correlates exactly t o a single screen dot. I f the
scan resolution were to correspond to the screenresolut ion, the screen dot could take on an incorrect
color value. This would be especiall y visible at
sharp edges in the image. I n order t o avoid that ,
you have to include the screening factor in the
equation. This fact or increases the scan resolut ion
and lets the output device (for example a printer)
calculate the color value of the screen dot more
precisely.The screening factor should be roughly 2.
Then the color value of each screen dot will be cal-
culated from four pixels (a 2x2 matrix) and thus
be much more precise.So, if we stil l want to enlarge our 1 x 1 inch
image to 3 x 3 inches, but t his time for t he purpose
of printi ng it in a 150 lpi raster for a magazine, we
should calculat e the scan resolut ion li ke this:
Printing with a Screening Printer
Quite a lot of computer printers also work with
print screens.You alr eady have the formula for thiskind of printout. I n principle, it s the same as for
screen prints.
All thats left to calculate is the one value with
which well replace the printout screen ruling.This
value is dependent on the maximum print r esolut ion
of the printer and the number of desired color levels.
Screen Ruling = 15 0 lpi
Screening Factor = 2
Sizing Factor = 3
Scan Resolution = 150 lpi x 2 x 3 = 900 ppi
Scan Resolution = Printouts Screen Ruling x
Screening Factor x Sizing Factor
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Back to a litt le math:
We can calculate the desired value by dividingthe maximum print resolution of the printer by the
square root of the number of desired color shades.
Dont put the book away yet !!!
This is as easy to understand as it is to explain.
Youre once again scanning our now famous
1 x 1 inch image and stil l want to enlarge it to 3 x 3
inches. L ater, youre going to print it on your
600 dpi printer and want to achieve a minimum of
64 diff erent color shades.
Youll want calculate it li ke this:
Therefore, you need the fol lowing scan resolution:
Theres a relationship between the screen ruling
and the number of r epresentable color shades. I f
youre trying to produce higher quality work by
work ing wit h a finer screen, the number of r epre-
sentable shades is r educed accordingly. Color vi-
gnettes in such a case often cant be displayedwi thout obvious gaps.
Unfor tunately, scan resolut ion has technical
limit ations. I t cant be raised to arbitr arily chosen
levels. For l arge-scale image enlargements, you
have to rely on another source of assistance to
ensure a quality printout.
This software-based assistance is called interpo-
lat ion. I nterpolat ion adds new pixels to the original
ones so that these originals dont have to be enlar-
ged as much as they did before.The color values of
the new pixels are determined on the basis of the
surrounding pixels.
6 4 = 8
600 dpi / 8 = 75 lpi
Screening Factor = 2
Sizing Factor = 3
Scan Resolution = 75 lpi x 2 x 3 = 450 ppi
Too much interpolation can blur the individual
pict ure lines, causing the enti re image to appear
fuzzy. Therefore you should never attempt to
increase the scan resolut ion of bilevel originals by
way of int erpolation. The exact scan resolut ion of
bilevel originals is determined using the formula:
Scan Resolution = Printer Resolution x Sizing
Factor. You never want to overstep the maximum
resolution of the output device.
BE CAREFUL
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So, now to the question of whether the images
subject should be depicted just as it appeared in
the original, or i f changes in the tonal range and
gradation should be set up in order to manipulate
the image during the scan. Whats that? We stil l
havent explained what the tonal range of an
image is? No problem. Well clear that up right
now.
Take another look at our standard original for a
grayscale image:
Now take a look at the diagram which accom-
panies this image:
On the diagram you see an axis numbered 0 to
255 which ext ends fr om black to whit e. There are256 ver ti cal bars arranged along this axis. (The
number 256 should be familiar to you from the
Bi ts and Bytes chapter. I t cor responds to t he num-
ber of shades of gray that an 8 bit scanner can
distinguish.)
The height of a bar indicates exactly how many
pixels display that i ndividual shade. Taken coll ec-
ti vely, the bars form the original s histogram.
You can see that the heights of the bars are quite
consistent, as is the distri bution of various shades
of gray on the original. This consistency extendsfrom total ly black to completely whit e.
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canning
For color images, a histogram can eit her indi-
cate the brightness of the entire image or be set
to provide the histograms of each, distinct color
channel.
For the purpose of comparison with the stan-
dard original, take a look at these high key and low
key images along with their histograms:
Clearl y, the dist ri bution of bars and thus the dis-
tribution of the pixels are by no means consistent
along the axis. Rather, the pixels of t he high key
image are bunched in the brighter region while
those of the low key image are gathered in the
darker region. I f youre interested in manipulatingthese images so that you can print them dif ferent-
ly than they originally appeared, you should now
direct your att ention to gradation.
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Take a look at this diagram:
Along the horizontal axis you see the inputvalues for the various shades of gray. The ver t ical
axis displays the corresponding output values. For
the represented gradation curve, this means that
all the values will be expressed in the same shades
in which they were originally entered.
With help of these gradation curves you can
manipulate your original.
Just take a look at our slightly manipulated
standard grayscale original, it s histogram and this
altered gradation curve:
For comparison, heres the original prior t o
manipulation:
M anipulat ing an image by introducing infl uences
to the gradation curves requires some experience.
You should practice by testing the effects of diffe-
rent changes on the images of various originals.
Now t o the actual scanning !! !
You see that we have darkened the dark tones
and brightened the bright t ones. Thus, the tonal
range has been str etched out. The histogram now
depict s holes at a few places. That means that a
few intermediate shades are no longer present.
Detail s are disappearing fr om the image. This
effect is called posterisation. PriortoS
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Next, an automati c tonal range correction is
perf ormed to guarantee an optimi zed data t ransfer
of the RGB image.
Finally, the computer will automatically analyse
the original. I t will basically be repeating the same
analysis which you alr eady went through:
q Is this a standard original with a clearly defined
image shadow and image highlight?
q What does the tonal range look like?
q Does the image have a color cast?
The automatic tonal range correction however,
could cause a high key image to become a lot
darker because the scanner mistook it for an over-
exposed image.
Clearly, that s not our goal. We want the compu-
ter image to look j ust like the original t hat we liked
in t he fir st place.
To that end, before doing the scan you have to
choose the option of either a Standard Original
scan, a Heads-Up Original scan, or a M anipulati on
scan.
Following the scan, these options str eamline
once again into a single path.I f necessary youll retouch the image. Then
youll save the personally quality-controlled image
that youve personally scanned in a personally sel-
ected file of a personally selected data carrier.
But now to the differences of scanning in full
detail ! ! !
The prett y ill ustr ation on the right page shows in
full detail the exact sequence of the scan process.
Never theless, we want t o share a few explanatory
points with you.
Youll begin the scan process by mounting the
originals. You should tr y to ensure that t he
originals and the tray are as dust-free as possible.
M ake sure you lay the originals fl at on t he glass.
Correct folds or waves in the originals as they
arise.
An entire scan process can consist of three indi-
vidual scans.
The first of these scans is the overview scan.
On the overview screen you see the tray with all
the mounted originals. From this overview, youll
select t he area that youd li ke to scan, and enter, as
far as your software allows, the type of original
that is to be scanned (negati ve, reflecti ve, tr anspa-
rent, etc.).
Af ter t he overview scan, you activate the pre
scan. Before your scanner star ts the pre scan, your
software will probably do the following three
things:
Fir st, the computer will alt er the original
gradation so that the monitors RGB image corre-
sponds to the perception of the human eye.
ScanProc
ess
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ScanProc
ess
Tip:
If you try to wipe the dust from the originals
wit h a normal dust rag, you might end up making
the situation worse despite your good intentions.
Rubbing an original brings about a static charge
which att racts even more dust. Cleaning wit h an
anti-static rag isnt a good idea eit her, since theyre
often soaked in an emulsion that can leave streaks
on the original.
The most suitable tool for cleaning the originals
is an anti-stati c brush, like the kind you used to
clean vinyl records wi th. These brushes should be
available in all art and design stores.
Pr e Scan
Pixel Retouching
Overview scan
Scan
I mage M anipulation
Scan
Heads Up Originals
Scan
Standard Originals
M ounting the Original
Data Storage
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Scanning
StandardOrigin
als
This is a quick and easy chapter. Scanning stan-dard originals like this one is a very simple and
almost automatical procedure.
As long as youve thought out the appropriate
resolution in advance by taking all the relevant
points into consideration, and as long as youre not
considering any manipulations of the image, all
that you have to do now is enter the desired reso-lut ion, activate the scan, lean back and wait f or t he
final result.
But before you do that, you should review all the
relevant points one final time.
Are you sure that youre really dealing with a
standard original?
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Scanning
StandardOrigin
als
Have you calculat ed the resolut ion properly?(I f youre scanning for printi ng purposes, pay
attention to the screen ruling.)
Should the original really be scanned without
manipulation?
Have you answered all these questions wit h Yes?
Well t hen, go ahead ! ! ! Scanning can be that simple !!!
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Scanning
Heads-UpOriginals
Weve named these originals Heads-Up Originals
because theyre all unusual in ways that have to be
accounted for when youre scanning. That doesn t
necessarily mean that theyre more dif ficult , only
that they cant be scanned as quickl y or, most
import antly, as automatically as Standard
Originals.
In this chapter youll find the most important
types of Heads-Up Originals, their i ndividual fea-
tures, and ti ps for work ing with them so that j us-
tice is done to their unusual characteristics.
High Key and Low Key Images
The trouble with scanning high key images has
already been briefly mentioned. I f t he automatic
tonal r ange correction was acti vated, the result ant
image might look like this:
because the scanner mistook it for an overexposed
original. The image shadow would be reset to a
lighter area of the image (the value of which is too
high) and the entire image would end up darker
than the original image.
The same is tr ue for l ow key images, except t hat
here the image highlight is reset to a darker area
(wit h a changed highlight value thats too low) and
the enti re image is brightened.This is how i t l ooks:
I n order to avoid such a result , you should foll ow
the directions on the next page:
Original
Original
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Scanning
Heads-UpOriginals
Go through the pre scan using all the available
automatic functions (the correction function should
be set t o normal ). Now take a look at the preview
image on the monitor. Do you like it? Does it look just
li ke the original? Good. Act ivate the scan.
M ore likely, though, you wil l see the eff ect weve
just descr ibed and t he image wi l l have changed, so
that now the high key image looks darker or the
low key image appears bright er. I f this is the case,
you should see if you prefer the result once you
have manually adjusted the image shadow or high-
light.
You can achieve a number of dif ferent eff ects bychanging the image shadow and image highlight.
Try a few different values and see what the preview
images look like. I f you like one of t he sett ings, go
ahead and activate the scan. M anual adjustment
of image shadows and image highlights calls for
some practi ce, but in t he end youl l be able to scan
and reprint your high and low key images so that
they look just like the originals.
Catchlight Images
The earli er pr inciple applies here as well : prescan with all the available automatic functions,
take a look at what comes out of it and then de-
cide what you want to do.
The problem with catchlight images is that the
program can set the image highlight in a catch-
light, resulting in an image thats too dark. I f t he
catchlights are small li ke reflecti ons on water, the
program sometimes recognizes what they are, and
the problem doesnt ari se. Larger catchlights can
become tr oublesome, though, for example, a bright
window.
This effect is very similar to what happens when
youre taking pictures wit h an automatic aper ture
selection. I f you take a picture against the light
and the sun is par t of the picture, the lighting will
be set accordingly. People or t hings in the pict ure
may end up looking like black outlines.
I f you notice that t he preview image is clearly
darker than the original, you should once again
manually set the image highlight to the proper
posit ion. This is the brightest area of the image,
aside from catchlights. But as before, manually
setting the image highlight will definitely take
some practice.
Tip:
I f youre dealing with one large catchlight, you
can select an image section for the original analy-
sis which doesnt include the catchli ght. That way,
the catchlight wont be taken into account in the
analysis, and the above-mentioned problem in
determining the image highlight wont come up.
Original
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Color Cast I mages
Once again, the question i s whether t he compu-ter image is supposed to correspond to the original
or i f it should be alt ered. Should the color cast be
kept or f il tered out? M aybe you want t he yell owed
photo from the Fifties to look the same once its
scanned. I f your soft ware is equipped to correct
color casts, you should deacti vate the function by
sett ing it to uncorrected . You should also deac-
tivate the color cast balancing function if your pro-
gram is unable to recognize that a high-percent-
age color cast is probably intentional. Otherwise,
the red might be filtered out of that excellent sun-
set photo. I f you actually do want t o filt er t he redout of t he sunset, the automat ic color cast correc-
tor (i f you have one) won t suffice. Youll eit her
have to choose the option stronger for t he color
cast corrector manually or alter the saturation of
the red area by hand. That would be a shame for
the sunset, though, wouldnt i t?
Over- or U nderexposed I mages
These recommendations also depend on whether
the later computer image is supposed to actually
look like the original or if you want to correct it.
I f you dont want t o change anything, scan your
underexposed original l ike a Standard Original and
set the correction function to uncorrected so
that it is not acti vated. The scanned image will
then corr espond to your original, and be just as
poorly lit.
Corrected
that has a higher value.The result is that all areas
which are darker t han this one wil l be set to black.
The image will turn darker overall . I n underexpo-
sed images, the image highlight wont be set in t hebrightest ar ea. Al l ar eas brighter t han the image
highlight wi ll be set to white, and the entir e image
will look brighter.
If your software doesnt allow you this option,
following the pre scan youll have to reset the
image highlight or shadow by hand.
However, if you do want to correct t he image,
and your software lets you address the problem as
a poorly exposed image, it s rather simple.
By entering underexposed , you automatically
acti vate a special program which perf orms exact ly
the same job t hat weve just described for high and
low key images (except that there we didnt want
it ). The image will be analyzed and automatically
corr ected. The image shadow of an overexposed
original will be set in a somewhat brighter areaScanning
Heads-UpOriginals
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Scanning
Heads-UpOriginals
U nfocused Original s
M ost scanners offer an aut omati c sharpeningoption. Just like all the other automatic f unctions,
this will also have to be shut off if the computer
image is to remain as unfocused as the original.
Then the original will be possible to be scanned
just li ke a standard original . However, this might
only rarely be the case.
I f you tr y to sharpen the image by activating the
fil ter option, the technical r esult is this:
This graphic shows you the tonal value jump be-
tween darks and brights on one section of the
image. I f t hese were to be a sharp edge in the
image, the transit ion would be very dir ect and the
curve very steep. Here, however, you see the line
climb relat ively slowly. The tr ansit ion is soft .
An even less focused copy will be produced from
the unfocused image. (Sounds illogical? Dont
worry, it ll be clear i n a minute! ) The transit ions
between the individual gray shades in the less fo-
cused copy are smoother and less conspicuous
than in the original.
When the curve of the less focused image is sub-
tracted from the curve of the unfocused original,
thi s curve result s.
I f we now add this mask to the line of the ori-
ginal image, small peaks appear at the points of
tr ansit ion. This means that at t hese posit ions the
dark region turns a litt le darker, and the bright
region a li tt le brighter. The overall contr ast
between dark and bright intensifies at this point.
The resultant image looks more focused.
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Scanning
Heads-UpOriginals
Be careful !!! Too much sharpening can bring
about unpleasant side effects.
Fir st of all , the image may suddenly look very
sharp but also terribly art ifi cial. Something will
look wrong wit h the image, but you wont be able
to pinpoint the exact nature of the problem.
Fur thermore, the image contr ast might be too
drasti c, so that halos form around the bright areas
in t he image.These bright surf aces spread out and
as a resul t f ewer detail s can be seen.This effect is
similar to posterisation.
A related side effect arises when sharpening not
only affects the image subject but also causes the
individual pixels or even fi lm grains to become visi-
ble. Here, eff ects like mott ling or speckli ng can pop
up. M ott ling i s taken to mean the lar ge scale deve-
lopment of dots on the image. Film grains or un-
evenness in the fi lm text ure can be seen. Speckling
refers to the pixel inaccuracy, oft en caused by
noise, in which bright individual pixels appear i n
dark regions.
Speckling
resulting from too much sharpening
Ar tistic and Computer Ge nerate d Originals
A number of different problems can arise when
youre scanning artificial and computer generated
images. Fir st, the colors worked with oft en lie out-
side the range of printable colors and are there-
fore diffi cult t o reproduce. The same is tr ue of
color effects such as neon colors.
The str uctur e of t he image can be another prob-
lem. Oil paintings for instance, often come alive
not just because of the colors but also because of
the visible color layering.This cant be reproduced
in the scan or subsequent print.All you can do here is to try different settings
and see which of them comes closest t o por tr aying
the original.
Negative Originals
Negative originals are truly a topic in themsel-
ves.
Lets take a case in which were dealing with a
negative original with nothing unusual in the sub-
ject, a t rue Standar d Original wi thout anythingpar ticular ( not high key, not l ow key, not poorly
exposed and definitely no color cast) : thi s negative
can be scanned like a regular Standard Original.
Generally your software will let you enter the ori-
ginal as a negati ve. The reversal process proceeds
automatically so that a positive image appears on
the monitor directly after the pre scan.
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Scanning
Heads-UpOriginals
Even speciali sts, however, have to resor t to good
old tr ial and error when dealing with more dif ficult
subjects.
Heres another practical ti p:
Dont wait until youre pressed for time to work
wit h negatives for t he fi rst time, but go ahead and
experiment beforehand to see what effects you can
create.They can be pretty excit ing: for instance, not
just a col or cast but a red cast f or the bright areas
and at the same time a green cast for the dark
areas is possible among many other effects.
As we just said, if youre not pressed for time
and have a full half hour to produce a top quality,
full y normal image, it can be a lot of f un!
Screened Originals
I f you scan screened (printed) originals as you
would Standard Originals, youll oft en end up wit h
the unwanted moir effect (the little stars or
bright lines).
For scanners which can`t descreen, the following
tip:
You can achieve good results if you can make
your scanner think that its had an unfocused ori-
ginal f rom the start . You engage in a lit tl e hard-
ware defocusing, so to speak.
This is achieved by simply laying a glass pane or
a fil m layer over the document t ray. The originals
will be assembled on the pane of glass and thus bebeyond the range of f ocus. A pane of glass is
actual ly better suit ed because film can bring about
stray light eff ects. I t should be about one tenth of
an inch thick and above all have polished edges.
However, be careful: make sure that you dont
scratch the document tray in the scanner!
M oir
How can you avoid this effect so that you canscan and later even re-use a newspaper clipping?
Your soft ware has a descreening function. This
function helps you to artificially defocus the origi-
nal. For t hat, however, you have to know the scre-
en ruli ng with which the image was print ed. Once
again back to the screen counter!
All this assumes that defocusing and later refo-
cusing will effectively deal with the moir effect.
But unfortunately we cant offer you a 100%
guarantee of success.
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Youve already read a lot about image manipu-
lation in the section on scanning Heads-Up
Originals. Every t ime you darken an overexposed
image or filter out the offending shade in a color
cast or iginal, youre perf orming an image manipu-
lat ion. Above and beyond that, though, theres stil l
a lot of room for manipulation ! ! !
1 pict ure says 1000 words, and on these two
pages alone we have 6 pict ures. Here you see
our standard color original as a grayscale ori-
ginal and our usual grayscale original as a bilevel
original.
On the following page weve manipulated ourStandard Original in a number of very different
ways. Aft er the pre scan, all you do is alter the
gradation cur ve of t he image and star t the scan on
the basis of t hese al tered sett ings. Weve depicted
the gradation curve that goes with each of t he ima-
ges in order to show you how we set up the mani-
pulation.
Weve achieved this effect by intentionally mis-leading the scanner. When you enter t he sor t of ori -
ginal youre supposed to be scanning, no ones forc-
ing you to tell the tr uth. Any time that youre
mounting a color original on the document tray,
you can claim t hat i t s a grayscale original. The
scanner automatically sets the conversion into
action.
Scanning
withImageManipulation
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Scanning
withImageManipulation
I f your soft ware has a Sector Correction
menu option, one simple manipulat ion possibi li ty
stands out. Wi th this option you can change the
saturation or even the tone of an individual color
(hue), which quickly and easily allows you to
achieve effects like these:
These pages depict only a small proportion of
the possible manipulat ion eff ects. Experimentat ion
in this area will not only be worth t he effor t, it s
also lots of fun !!!
Variation of all color channels
Variation of cyan channel
Variation of magenta channel
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Technical ly speaking, when retouching youre r e-
placing individual pixels whose color values have
been altered by dust or scratches. I n actual prac-
tice what youre doing is copying a neighboring
pixel. Even though it sounds complicated, this is
very simple if you use the right tool.
Since however the typical image usually doesnt
contain two neighboring pixels with exactly the
same color value, it wont suff ice to simply recolor
all the fault y pixels in the same tone. The re-touching would be just as str ik ing as the imper fec-
tion.
To successful ly remove disruptive fact ors, you
need a tool with which to reconstruct the diverse
arrangement of the individual pixels.
To that end, youl l copy an enti re group of pixels
from a neighboring area with similar colors and
use it to replace the faulty pixels.
This retouched picture will be much less con-spicuous.
If however there are large imperfections across
the entir e image, this practice can be rather time
consuming.Thus its really important that you pro-
tect your originals fr om unwanted fluff, water, and
so on.
Dust, fluf f, scratches, water marks are what you
dont want to see on your originals. But unfor tun-
ately, in t he real world you cant always protect
them from the environmental influences which
bring about these side effects.
Af ter t he pre scan, you can check to see if a bi t
of fluff or dust appears on the digital image on
your screen. These imperf ections wil l be especial ly
clear t o the eye aft er drasti c enlar gements.
You should wait until after the scan to remove
them, though, because then the problem can be
seen in finest detail.
Even though much is entir ely automati c, pixel
retouching still has to be carried out by hand.
PixelReto
uching
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PixelReto
uching
I mperfect pixelsreplaced by one single color
I mperfect pixels
replaced by neighboring pixels
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T his might make the situation clearer:
Your scanner software operates with a specific
color model (CI EL AB, for example). I f you want
to use the data for a number of different applica-
tions you should definitely save the data in a for-
mat that corresponds to this color model (a CIE-
L AB format, in this example). From here, the data
can be reformatted to correspond to further appli-
cations.
If however you save your data in a special for-
mat (like CM YK for offset printing), and then
afterwards have to use it for another application
with a second special format (like RGB data for amult i-media show for instance), youre going to
end up reformatt ing twice. The data will fi rst have
to be converted to match the color model of the
scanner software before it can be changed to the
new format .This double conversion not only wastes
time but also threatens the quality of the end
product.
Here you see that the space requirements from
one piece of data to the next vary depending not
only on the kind of original involved (whether its
a graytone or color image, for example), but also
decisively on the color space ( RGB, CM YK, CI E-
L AB ) . Never thless, you shouldnt simply select
the format for your data which requires the least
amount of memory. When selecti ng a format you
have to consider the datas intended use. I s the
data going to be used only once or over and over
for different purposes?
After the scan and pixel retouching (if neces-
sary) all you have left to think about is saving the
data and handing it over. At thi s stage, there are a
couple of guidelines you should follow to ensure
that everything fl ows as smoothly and eff icientl y as
possible.
Its important that you take time to consider
data and image formatt ing before you star t t o save
your data.This table shows the space requirements
for various originals in different image formats:
DataManagement
I mage ( 6.3 x 7.9 in ) Disk Space RequiredStorage as: TI FF File
without Compression
Bilevel Original, 600 ppi 2,195 KB
Bilevel Original, 1,200 ppi 8,729 KB
Grayscale I mage, 200 ppi 1,984 KB
Grayscale I mage, 300 ppi 4,416 KB
Color I mage saved as RGB or Lab File, 200 ppi 5,856 KB
Color I mage saved as RGB or Lab File, 300 ppi 13,120 KB
Color I mage saved as CM YK F ile, 200 ppi 17,472 KB
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General Tips for D ata Transfer
You should be sure to ask five times over whatkind of data carrier youre supposed to use when
transferring the data.
Diskettes are often inappropriate for the trans-
fer of large amounts of data.
DAT tapes are also problematic because they
can be formatted in various ways.
Magnetic optical disks (MOD) are generally
tr ouble-f ree, as are removable cart ridges for which
the data carriers designation has been standard-
ized. But even here there are a number of di ff erentformats (for example cartridges for 44MB,
105M B, 200M B, etc.). You should therefore ask
about t he hardwar e prerequisites early on.
I n case the data are to be used for pr int ing, be
sure to ask ten times over what data format you
should use. Veri fy w hich printi ng process, paper
and screen ruling have been lined up.This verifica-
tion is without a doubt faster than reworking the
data or scanning the entire original set once again.
(A n especiall y import ant point, since right before a
deadline youre not likely to have a lot of time atyour disposal.) Time lost due to unreadable data
can be a terri ble aggravation.
I t s even more aggravating when fal se or mis-
sing information leads to mistakes in data storage
and transfer, or t o printed work that doesnt at all
look like its supposed to.
M ake sure that you have all the necessary infor -
mation!
DataManagement
The same is true for the image format:
The most common image format is TIFF
(Tagged Image File Format) in which the imagesare saved pixel by pixel. Al l of t he most common
systems support the TIFF format.
So even if youre constantly using different pro-
grams for di ff erent purposes, you can general ly
import all your data as TIFF data into the pro-
gram youre using at the moment and continue
your work worr y-free.
I n practi ce, thi s means that youre always on the
safe side as long as you save your data in t he color
model of your scanner software and in the TIFFformat.
Now, if you know exact ly how you plan t o use the
data and if youre really only going to use it for a
single purpose, you can go ahead and deviat e from
this sure fire practice.
So, you know for example that the originals are
to be used for layout work and wi th a specifi c DTP
program. I t s probably the right choice to save the
data directly in CMYK -EPS format. EPS stands
for Encapsulated Postscript. I f you save a CMY K
image as EPS data, a total of five data pieces willbe produced.They first of all contain a main file in
either TIFF or PICT format that offers a rough
preview of the entir e image. M eanwhile, the fine
data for the image are saved in four different files
arranged by the four, distinct CM YK color chan-
nels.
The rough preview can be of use when posi-
ti oning your l ayout. The small er amount of data in
this image simplifies and speeds up the work in
comparison to the fine data.
I f youre absolut ely sure that the scans are to be
printed and you know the exact printing process,
the exact screen ruling and the sort of paper to be
used in printing and you also know that the scans
wont be used for another printing process some-
time next week then, and only then, you should
save the data in t he corresponding CMYK format.
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Well , that s the fir st step as far as were concerned.
We hope we were able to make this booksdemanding content understandable and even en-
tertaining, despite all the theory.
Now t hat your scanning career s getti ng star ted,
be sure to take time to t r y things out. Experiment!
Play with the possibilities that your scanner and
soft ware off er and see what kinds of eff ects theyl l
let you create.
Youll soon discover that its not only fun but
quickly helps you gain valuable experience.
One la st pra ctical tip
Jot down all the effects that you see while ex-
perimenting and especially note the settings that
you used to create them. I f l ater on you uninten-
tionally produce something similar, it l l be a lot
easier for you to figure out how and why its sud-
denly come up again.
Well , there are only two things left to say in this
book:
Thanks for your interest !!!
And most of a ll, we wish you success
in scanning ! !!
OneFinal
Word
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Publisher
Heidelberg CPSColour Publishing Solutions GmbHDu Pont-Strae 1D-61352 Bad Homburg
Heidelberg CPS Company425 Oser AvenueHauppauge, NY 11788
Heidelberg CPS Ltd.St. James Place, Knapp RoadChelt enham, Gloucestershir e GL5 0 3QR
Al l images are scanned, using TOPAZ orChromagraph 3900 from HeidelbergerDruckmaschinen.
PostScript is a registered trademark of AdobeSystems I nc.T I FF is a registered trademark ofM icrosoft Corporation and A ldus Corporation.Kodak is a registered trademark of Kodak AG.The ill ustrations for the Lab- and theNormcolormodell are published with kind permis-sion of M inolta GmbH, Ahrensburg.
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ning