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
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.
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.
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
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 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.
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. 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.
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).
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
(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 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.
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.
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 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 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 The 21st Century, Watson-Guptill Publications, New York.
James Arno (1991). Graphics Gems II. 49-165. Academic Press, Inc.
Peter Fink (1992). PostScript Screening: Adobe Accurate Screens. 15-87. Adobe Systems Incorporated.
Marc D. Miller and Randy Zaucha (1995) The Color Mac, Second Edition. Hayden Books.
Ira Gold (1993). The Promise of Stochastic Screening, Color Publishing, July/August, 7-8.
Jake WiIdman (1994). Stochastic Screen Test, Publish, June, 35-39.
Anita Dennis (1995). Stochastic Aptitude Test, Publish, June, 55-61.
David Pope (1995). HiFi Color, Color Publishing, March/April, 14-19.
Seybold Publications Division (1993). Frequency-Modulated Screening Technology, Seybold Special Report, Vol.1, No.2, May 19. 8-9.
Donald Carli (1994) High-Fidelity Screening: Making Order Out Of Chaos, Fall 94 XPLORATION, 18-21.
Stochastic Screening: Pre-press Issues for Printing on Uncoated Paper, Monadnock Paper Mills, Bennington, NH 03442. 603-588-3311.
Rudolph E. Burger (1993) Color Management Systems, The Color Resource, First Edition.
Spencer and Associates (1994) Color Hardcopy Quality IV Study Report Fourth Edition, Spencer and Associates Publishing, Ltd.
(c) QMS, Inc. 1996
Modification Date: 15-Feb-96 by JGH