Color Reproduction

Welcome to the world of color and color printing. Its an exciting world and one that has enjoyed an
explosion of growth over the last several years. Much of this growth certainly can be attributed to the new
technologies and products that have made color more accessible, usable and affordable to the general
public and business. But, with this growth has come some misconception of how color works, especially in
the areas of color application, color matching and color reproduction. The following paper briefly
discusses some industry terms, color principles, output options and color print engine technologies.

The Basics
Pixels (Picture Elements)

The word pixel is a combination of the two words picture and

element. A pixel is simply the smallest individual unit used to
construct a digital image. Each pixel is unique in regard to color
and/or tone and its location on the x and y axes of the Cartesian
system*. Pixels are placed on a grid called a bitmap. Therefore,
digital images consisting of pixels are called bitmap images.
Another type of computer graphic is the vector graphic such as
line art, circles and squares. These images rely on a language
such as PostScript to designate a formula for the shape
requested. Output devices use an address grid to keep track of
the pixels so they can be addressed for printing.

Binary System

The foundation of digital computing is the binary system. Based upon the number two, this system uses
one or zero to control the on/off state. The simplest pixel has two choices: black or white. (A pixel with
two choices is known as a one-bit image, or two raised to the power of one). Adding more bit information
increases the number of color choices. The number of potential color choices for a pixel is called color bit
depth. For example a four-bit pixel would have 16 color choices while an eight-bit pixel would have 256
color choices.

Color choices increase exponentially as the number of bits per pixel increase.

21 = 1 bit = 2 colors 26 = 6 bit = 64

colors
22 = 2 bit = 4 colors 27 = 7 bit = 128
colors
23 = 3 bit = 8 colors 28 = 8 bit = 256
colors
24 = 4 bit = 16 colors 216 = 16 bit = 32,768 colors
25 = 5 bit = 32 colors 224 = 24 bit = 16,777,216 colors

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Resolution

Resolution is a way of describing images that are composed of pixels. An image appears to be continuous
based upon its number of pixels and its resolution. In order for an image to be continuous, one must not be
able to see the individual pixels that were used to create it. If resolution of an image is less than required
by the output device, individual pixels will appear as jagged edges.

A printed magazine image will look continuous from reading

distance, but when viewed with a magnifying glass will show
the individual dots within the halftone. Therefore, distance
affects the continuous appearance of an image.

Resolution of the output device is tied to the number of

elements per inch it can address to produce a dot. As the
elements per inch increase, more information is available to
produce a better quality dot. The pixels in the example are
shown as squares to represent the address grid. Pixels actually
produced are usually round or oblong.

Meeting resolution requirements of the output device is

critical to the quality of the image. The number of pixels an
image to be rendered needs is directly proportional to its
output. When the resolution of the bitmap image matches the
output resolution correctly you will not see the individual pixels. The way in which the pixels of a bitmap
image relate to the output device is called the sampling ratio. For example, the ratio of bitmap images to
halftone dots is 2:1.

Color Principles

Electromagnetic energy that exists in the form of wavelengths

creates the perception of color. For example, the sun provides light
which shines on an object such as an apple. The apple absorbs
some wavelengths and reflects the others. Some of the reflected
light reaches the retina of the human eye which stimulates the brain
and the brain creates a perception of the color red. The visible
spectrum is the range of light that can be seen with the unaided
eye. Wavelengths above the visible spectrum are infrared (heat).
The wavelengths below the visible spectrum include ultraviolet, x-
rays and gamma rays.

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There is a huge difference between the visible spectrum we can see with our eyes and the colors which can
be reproduced on a computer screen and then printed on a color printer. The total number of colors that a
device can produce is called its color gamut. The visible spectrum is larger than the color gamut of a color
monitor, which in turn is larger than what can be reproduced by a color printer. No system can produce all
the colors we can see with our eyes.

Tone

The most dominant wavelengths of the visible spectrum are red, orange, yellow, green, blue, indigo, and
violet. A good example is a rainbow. Tone is the lightness or darkness value of an image and is subjective
as it relates to other values in the image. Consequently, the tonal range of an image is the transition from
light to dark areas. Color is what we see and tone is what
gives color its depth and form. Tone provides shape and
definition to color objects. Tone would still have depth
without color, as is the case with black and white
photographs. As the tonal range of an imaging system
increases, so does the number of tonal steps as well as
image quality. When an image is moved from one device
to another of lesser tonal range the tonal steps must be compressed. Tonal compression means that the
image has fewer tonal steps and is actually loosing values of tone. A compressed tonal range will work
fine if not compressed too far. Fewer tonal steps simply means less detail in the areas where compression
has occurred. For example, where dark areas are compressed there are fewer tonal steps resulting in less
detail.

Hue, Saturation and Value

All colors and tones have an inherent hue, saturation, and value (HSV). Hue is the color being described,
such as yellow, purple, or green. Saturation, also referred to as chroma, is the intensity or purity of the
color. (For example, 100% red would be vivid red whereas 10% would be light pink.) Value is the relative
lightness or darkness of the color. Value is also used to describe tonal values that contain no hue.

Additive and Subtractive Color

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Additive Principle

The primary colors of additive color reproduction are red, blue, and green. When these three primary
colors of light are projected on one another in equal parts they produce white light. Other colors can be
created by varying the intensities of red, blue, and green. The absence of RGB
colored light results in black. Your computer monitor is based on additive color.
Red, blue, and green phosphor coatings on the screen are hit by electron streams
that emit colored light. Monitors produce transmissive colors, which means
projected light energy is passed through a filter to produce color.

Subtractive Principle

Subtractive colors are produced when white light falls on a colored surface and is partially reflected. The
reflected light reaching the human eye produces the sensation of color. Subtractive color is based on the
three colors cyan, magenta and yellow. Other colors are produced by varying the mixture of these primary
colors. When these three colors are mixed together at 100% they produce black. The absence of CMY
pigments would result in white.

Printing and photography are based on subtractive color reproduction. However, printing adds a fourth
color black which compensates for impurities in the ink. The combination of cyan, magenta, and yellow
ink results in a muddy brown. Black is denoted by the letter K to avoid confusion between blue and black.
Hence the C (cyan), M (magenta), Y (yellow), K (black) abbreviation.

Factors Affecting Color Perception

Paper

Paper affects the color reproduced by the CMYK printing process. Coated stocks will produce a wider
range of colors than uncoated stocks because the rough surface scatters the amount of light that bounces
off the paper back to the viewer.

Viewing Conditions

Different light sources affect the colors that you see. For instance, a color viewed under fluorescent light
will look radically different when viewed under incandescent light. Fluorescent light adds green to colors
while incandescent light adds red. For this reason the printing industry developed a standard viewing
condition known as the D50 (5000 Kelvin) light source in addition to a neutral gray background surround.
This light source replicates daylight with equal parts of red, green, and blue.

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Digital Values For Color

The most common digital color system is a 24-bit color system. A 24-bit continuous tone system offers a
choice of 16.7 million colors. A 24-bit RGB color allocates 8 bits to each color: red, green, and blue.
CMYK color uses 32-bit color, with 8-bits allocated to each color. All color to be printed must be
translated from RGB color to CMYK color.

Color Space

Color space describes and organizes all the available colors on a set of axes so they can be communicated
from one person to another or from one device to another. Color is very subjective, influenced by light
conditions and personal psychology. Therefore we need a way in which to describe color accurately. For
instance, a bright blue sky would be similar to 100% cyan plus 50% magenta. Now color can be
quantified, measured, and translated from a computer to a printer. The translation must be good or the
color will not be what we expect. The two parts of the color reproduction process, monitors and printers,
occupy different color spaces. Monitors are based on RGB color whereas printers are based on CMY(K).
This means it is almost impossible for colors on a monitor to match exactly those colors produced by a
printer.

The Centre Internationale dEclairage (CIE) is an international organization

that establishes methods for measuring color. These color standards for
colormetric measurements are internationally accepted specifications that
define color values mathematically. The first color space model, the CIE
x*y*z, was developed in 1931. CIE defines color as a combination of three
axes: x, y, and z. The two color spaces released in 1978 are CIE L*a*b and
CIE L*u*v. The goal was to provide an accurate and uniform reference of
visual perception. CIE L*u*v is used with color monitors and CIE L*a*b is
used for color print production. CIE color models are considered device
independent because the colors should not differ, theoretically, from one
output device to another if properly calibrated. CIE color helps move color values from one system to
another, but there is no way to produce colors using CIE values alone.

At some point RGB digital images must enter CMYK color space to be printed. There are infinite ways to
translate RGB to CMYK and almost every software program utilizes some type of conversion formula
with vastly different results. Therefore CMYK and RGB color cannot be considered device independent.
Every color printing device uses different color reproduction methods and requires different combinations
of the CMYK formula to produce similar color. The same is true of RGB devices. Converting from RGB
to CMYK color is not an exact process because the color gamut of RGB is larger than CMYK. Colors that
are out of gamut must be mapped to the next closest color.

Color Management

Before desktop publishing emerged as an industry, specialized computer-based systems were used for
color publishing. These systems were integrated and installed by one vendor and were closed-loop
solutions. Closed-Loop means that each device in the system was calibrated and communicated via a
common color language. These solutions were very expensive and required extensive training to maintain.

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The advantage of these systems was high-quality, dependable, consistent color.

Low-cost color computers and color printers have made color available to a vast number of users. In many
cases the monitor, computer, scanner and color printer are purchased from different manufacturers. None
communicating in the same color language. The desktop publishing revolution has taken color out of the
hands of pre-press color experts and brought it into the office where the average user is baffled by the
inherent complexity of color. There is a missing link that has prevented color from fulfilling the
expectations of the end-user. This missing link has been a standard color language that can be used by
scanners, monitors, software packages, and color printers.

There are many variables that exist in complex color science that affect the appearance of a color image.
Color communication is very similar to the problems incurred when translating a foreign language. There
are some words that simply do not exist in another language. This is the problem desktop devices have
communicating with each other.

The most often heard complaint from end-users is, Why do the colors I see on my monitor not match the
colors printed by my printer? Monitors are based on RGB color, whereas color printers are based on CMY
(K). Since monitors and color printers exist in different color spaces, each has a finite number of colors
that it can produce, referred to as its color gamut. The visible spectrum is larger than a 24 bit color monitor
can produce and the monitors color gamut is larger than a color printer can produce. Therefore, color
information sent to the printer must first be converted from RGB to CMYK space via software resident on
the host or printer. Then the colors visible on the monitor that are out of the printers gamut must be
mapped to the nearest available color.

Systems that manage and match color across devices are called color management systems (CMS). The
CIE color spaces, as discussed before, provide the foundation upon which device-independent color and
color management are built. The other pieces that are needed for color management are device profiles,
device calibration, and gamut mapping.

A device profile describes a devices color capabilities including color gamut, color production method, and
device operation modes. Device profiles are created by color imaging scientists using spectrophotometers,
which are instruments that measure the relative intensities of light in different parts of the visible spectrum.
The measurements are then entered into proprietary software programs that use sophisticated algorithms to
produce the device profile.

Each device profile is based upon factory conditions and will change as the device ages. This requires
calibration, which determines what deviations have occurred and what action is required to bring the
device back into adherence with the standard. For example, a scanner will need to be recalibrated over
time as the light source ages.

Device profiles are used by the color management software to translate color data from one device to
another based upon an independent color space. The end result is consistent color travelling from the
scanner, monitor, software packages, and finally to the printed color output. However, it is still impossible
to have perfect color matching due to differences in each devices color gamut. For example, deeply
saturated colors visible on a color monitor can not be recreated by color printers using CMYK ink, toner,
or wax.

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Colors that can not be reproduced from one device to another must rely on gamut mapping, which selects
the closest reproducible color. Good color management systems offer rendering options such as business
graphics and photographic settings. These options are needed because the solid color needed to produce a
business graphic is vastly different from the tonal gradations needed to produce a photograph.

Early color management systems first appeared on the market in the 1980s lacked a common color
architecture to build upon. As a result color profiles for different devices were not compatible. Color
management solutions were proprietary and designed to meet the needs of the desktop pre-press market
alone. Hence the majority of color users were left without a color management solution.

The International Color Consortium (ICC) was formed to address the need for a common color framework.
The ICC has developed a standard device profile that contains information about how various devices
render color. The ICC profile standard was based upon the pioneering work done by Apple Computer and
introduced in ColorSync 1.0 in 1993. ColorSync was the first color management architecture to be placed
at the operating system level. This concept has also been adopted by Microsoft for Windows 95, Sun for
Solaris, and by Silicon Graphics for Irix.

The ICC published the standard profile and it is widely available to hardware and software developers. The
goal of the ICC is to provide true portable color that will work in all hardware and software environments.
There are two parts to the ICC profile. The first part contains information about the profile itself, such as
what device created the profile and when. The second part is colormetric device characterization, which
explains how the device renders color.

Color management is finally available for all color users. Macintosh users should look for products that
contain a ColorSync 2.0 profile. Windows users should look for products that support the Windows 95
implementation of color management. However, one should remember that color management does not
mean all devices will match. The final ingredient needed is a way to make the color space transform only
when the final output device is known. In the interim, users needing accurate color the first time out should
invest in third-party color management software (these software packages build color matching engines for
a specific set of devices).

Digital Output Options

There are two basic methods for achieving output for digital images. One is direct digital imaging, in
which each pixel of an image corresponds directly to an output device element. The other method involves
dithering*, in which the four colors cyan, magenta, yellow and black are composed to give the impression
of continuous tone. Each method attempts to produce the appearance of a continuous tone image but all
printing processes use some sort of element to produce color and tone. (*Dithering is the technique of
arranging pixels in a pattern to reproduce tonal value.)

Dither patterns can be ordered or disordered. Ordered dithering produces a pattern that is predetermined
and specific. Disordered dithering employs a certain degree of controlled randomness in the dither pattern.
The dithering process relies upon the halftone cell. The halftone cell controls the placement of pixels
within the cell which in turn simulate color and tone. Some of the available output options are: halftone
screening, stochastic screening, continuous tone and contone.

Halftone Screening

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(Amplitude Modulation or AM Screening)

For the last 100 years, color printing has been based upon
halftone screening. Halftone screening uses halftone cells
(which are comprised of different sized dots) arranged in a grid
pattern to create the illusion of light and dark areas. This
conventional halftoning technique is referred to as amplitude
modulation because the size or amplitude of a dot is changed or
modulated to create different tonal values. The single dot
within the halftone cell grows larger as the tone value becomes
darker and smaller as the tone value becomes lighter. The
center from one halftone cell to the next is always the same.
The spacing of dot placement is controlled by the line screen
which is referred to as lines per inch (lpi). The higher the line
screen the more continuous an image will appear. For example,
halftone dots will be visible with a 60 line screen and invisible to the naked eye at a 150 line screen.

The four color process screens (cyan, magenta, yellow and black) are usually rotated at different screen
angles. These angle rotations create the traditional rosette pattern which can be seen at low line screens.
Repetitive patterns that occur are normally called artifacts. Line screen and angles sometimes create
unwanted moir patterns. Most often these moir patterns occur with checked or herringbone patterns that
conflict with a screen angle or by screens that are poorly reproduced.

Laser printers use a matrix of imaging elements to create the

halftone dot. To determine the matrix, divide the dots per inch (dpi)
of the laser printer by the intended line screen. For example, a 300-
dpi printer combined with a 100 line screen would use a matrix of 3
x 3 image elements per halftone dot. The number of image elements
per inch that a printer or imagesetter can produce is known as the
device resolution. As the number of imaging elements per inch
increases so does the quality of the halftone dot. The elements per
inch combined with the line screen controls the number of gray
levels that can be achieved with an output device. For example, a
1200 dpi laser printer using a 150 line screen would image 150 dots
per inch and every inch would contain 64 imaging elements.
Therefore each dot is created by a halftone cell that contains 8 x 8
imaging elements. An 8 x 8 cell contains a total of 64 on/off
imaging elements. This 8 x 8 cell can potentially produce 64 levels
of gray.

The pixels per inch required for a bitmap image are dependent on the line screen to be used. The ratio of
the bitmap image resolution to the output device is 2:1. The most simple method for determining pixels per

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inch is simply doubling the line screen. For example, when printing with a 100 line screen, the bitmap
image should contain 200 pixels per inch. Users should be aware that increasing the pixel information
greater than the 2:1 ratio does not increase the output quality and generally wastes file space and increases
RIP (raster image processing) time. Raster Image Processing, also know as RIP or render, refers to the
conversion of digital information into physical printed output.

Rational and Irrational Screen Angles

Rational screen angles contain halftone cells that are always the same size and shape. These halftone cells
address tone uniformly across an entire image. The downside of rational angles is that the number of line
screens and screen angles are limited by the output resolution. This makes it difficult to avoid moir and
artifacts unless large halftone cells are used and printed at low line screens. An example of a rational
screen angle is the traditional rosette screen angle pattern.

An alternative to rational screening is irrational screening. Irrational screening uses non-uniform halftone
cells that are different in shape and size. These non-uniform cells allow any screen angle to be used with
any line screen. To present a consistent response to tonal values, predetermined spot functions are assigned
to different tones.

Stochastic Screening
(Frequency Modulation, FM Screening)

Stochastic or frequency modulated screening uses very small

dots of the same size which are placed at random to create
color and tone. FM (frequency modulation) dots create tonal
value by varying the number or frequency of dots, whereas
AM (amplitude modulation) halftone screening varies the dot
size to create different tones. Hence the terms frequency,
which refers to the number of given dots in an area, and
modulated, which refers to the density of the dots relative to
the tonal value of the input pixels. Stochastic screening has
the ability to adapt to image content. This significantly
increases image detail. Stochastic dots are typically 1% to 2%
of halftone dot size.

The word stochastic was derived from the Greek word stochos meaning to guess and is used to describe
processes in which the state of a variable is determined by random factors. FM screening is based on the
random placement of dots. As a result line screen, halftone grids, rosette and moir patterns of AM
screening disappear. FM screening increases the number of dots to generate dark tones and decreases the
number of dots for light areas. If you remember, AM screening increased the dot size for dark areas and
decreased the dot size for light areas.

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The relationship
between the
bitmap image to
the output
devices FM
screening is 1:1.
The FM dot is
more closely
related to
continuous tone
than to the standard AM halftone dot which requires a 2:1 ratio. The increased detail available with FM
screening carries the added benefit of being able to use bitmap images with as little as a 1:2 ratio when
printing with a 600 dpi device.

A problem of past FM screening has been that some offset presses and proofing systems have trouble
holding this very small stochastic dot. The second generation of FM screening uses a cluster approach
which combines very small micro-spots into large micro-dots. This dot-cluster approach was developed to
minimize the difficulty of plating and holding these tiny FM dots on conventional offset presses. This
approach also reduces graininess in highlight areas.

Continuous Tone
(Direct Digital Imaging, CT, Contone)

Continuous tone is defined as output in which the cell is completely filled with color and tone, leaving no
white in the cell. Continuous tone printers produce the illusion of a smooth continuous image without
using the halftone dot and the primary colors. Continuous tone matches each bitmap pixel with a dot on the
output device at a ratio of 1:1, also called direct digital imaging. If you have a color printer that has a
resolution of 300 dots per inch (dpi) it would output one inch of bitmapped data at 300 dpi. For instance, a
bitmap image at 300 pixels per inch (ppi) that is 1200 x 1500 pixels would print at a size of 4 x 5 inches.
Should the image resolution be changed to150 ppi, pixelization would occur and the image output would
loose its continuous tone appearance. (Pixelization occurs whenever the image resolution is less than the
output devices full resolution.) An example of continuous tone output is that from a dye sublimation
printer.

Continuous tone output can also be achieved without this 1:1 ratio by using line screens to achieve the
additional gray levels. The introduction of high resolution color laser printers has brought the ability to
render multi-bit pixels on laser engines. These engines rely upon screening implementations and very
small dots to achieve a continuous tone simulation. Near photographic quality can be achieved using this
method. FM screening as well as AM screening may be utilized for producing images.

Color Engine Technology

The basic color output devices are: inkjet, thermal, electrostatic and photographic.

Thermal

Thermal transfer devices include thermal wax transfer and dye sublimation. Thermal transfer technologies

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use a 3 (CMY) or 4 (CMYK) color ink coated ribbon and special paper which are moved together across a
thermal head. Wherever the thermal head applies heat, the ink fuses to the paper. This technology requires
3 to 4 passes across the thermal head depending on the use of a 3 or 4 color ribbon of ink. The result of this
process is single-bit dots of the primary colors. The QMS ColorScript 230 is an example of a themal wax
printer. Dye sublimation uses a similar technology, except for the fact that the inks used change to a
gaseous state. This requires the thermal head to deliver a much higher temperature but results in finer
control and smaller dots which can deliver multi-bit color. The gas that carries the color and tone entirely
covers the dot being imaged. If less ink is carried, the dot changes in tone. In contrast, thermal wax would
cover only half the dot area and the rest of the cell would remain white. Fresh consumables used for each
image result in a constant cost per page, regardless of the number of colors used.

Inkjet

Inkjet printers transfer color to a page by squirting ink onto the paper. The different methods of applying
the ink are known as liquid and solid inkjet. Both of these methods apply ink only where it is needed; this
results in a variable cost per page. Liquid inkjet uses liquid ink that drys on the paper through evaporation.
Liquid inkjet consists of two techniques known as pulsed inkjet and thermal inkjet. Pulsed inkjet uses
hydraulic pressure to control the ink sent to the print heads and then to the paper. Thermal inkjet uses a
heating element normally located in the ink nozzle that causes the ink to form bubbles. Once the bubbles
become large enough, they are forced from the nozzle onto the paper. The problems with this technology
are non-uniform spot shape and color density that is lost when ink is absorbed into the paper. Another
shortcoming is that the ink remains water soluble and will smear if exposed to moisture.

Solid inkjet uses ink that is solid and must be melted before it is sprayed onto the paper. This ink solidifies
quickly when exposed to room temperature and results in a better dot than liquid inkjet. The ink is dropped
on the page using a print head which contains nozzles of each color. The ink hardens as soon as it makes
contact with the paper. Once the page has been completely covered, a cold roller applies pressure to flatten
the ink and strengthen its bond to the paper.

Electrostatic

Electrostatic printers use electrical charges transferred to a nonconducting surface that either attract or
repel the toner. There are several types of electrostatic processes: direct electrostatic, color xerography and
ElectroInk.

Direct Electrostatic

Direct Electrostatic printers apply a charge directly to specially coated print media. Liquid toner particles
are then swept across the paper and stick to the charged regions. Repelled toner is removed from the page
before the next color pass. After all colors have been placed, the toner is then fused. This technology can
be easily modified for large format printing. Liquid toner provides the advantage of finer toner particles
that can be used to achieve high resolution output.

Color Xerography

Color xerography uses a pre-charged drum or belt that conducts a charge only when exposed to light. The
scanning laser is used to discharge this belt or drum which creates an invisible image. Toner containing

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small iron particles are magnetically attracted to the appropriate areas of the image and repelled from
others. This image is then transferred to a roller which collects all four colors. The image is then
electrostatically transferred to plain paper where it is fused by heat and pressure. The QMS magicolor
printer line is an example of a color xerography printer.

ElectroInk

ElectroInk is a variation of xerography that uses liquid toner. The liquid toner is charged electrostatically
and brought into contact with the photoconductor where it is either attracted or repelled. The colors are
imaged to an offset blanket from which the composite color image is then transferred to the paper media.
This liquid toner offers the advantage of delivering very small dots that can produce very high resolutions.
The Indigo E-Print 1000 is based upon this technology.

Photographic

Photographic imaging devices use slide or print film to produce an image. Examples of this technology are
digital film recorders and digital offset. Digital film recorders are used largely to create 35 mm slides. Film
recorders use light to expose the photographic film. The additive primaries of red, green and blue are
applied to achieve output, since this technology is based on light.

Commercial offset presses are digital offset devices. The digital image is color separated into its CMYK
values and recorded to print film. These films are then used to create plates for the press. The color image
is transferred to the press by using four plates that image the CMYK values. The resulting four color
process CMYK inks are distributed on cylinders, one for each color. The paper travels past each of these
cylinders through the press to accumulate the color image. There are two main types of presses: sheet-fed
presses which use cut-sheet paper of varying sizes and web presses which use a continuous roll of paper
which is later cut to size.

With the advent of computer technology, CMYK separations can be enhanced by adding additional colors.
The use of more colors increases the color gamut of the press and makes it possible to achieve soft pastels,
brightly saturated colors, fluorescent and metallic colors. Hi-Fi color builds upon the standard CMYK
inks. It takes a highly skilled pressman to print these types of color jobs. Since pre-press proofs are usually
not available, press-checks are necessary to approve the job on press.

In Conclusion

Now you have a better understanding of color, what factors affect it, and how it ultimately makes its way
to hard copy output. Take this knowledge and use the powerful tool of color to greatly enhance your
communication.

QMS, ColorScript, and magicolor are registered trademarks of QMS, Inc. All other trademarks are the property of their respective
companies.

References

Robert C. Durbreck and Sol Sherr (1988). Output Hardcopy Devices. 225-459. Academic Press, Inc. Helene W. Eskstein (1991). Color In
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August, 7-8. Jake WiIdman (1994). Stochastic Screen Test, Publish, June, 35-39. Anita Dennis (1995). Stochastic Aptitude Test, Publish,
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(c) QMS, Inc. 1996

Modification Date: 15-Feb-96 by JGH

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