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ColorSync

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ColorSync is Apple’s system-level software to help you manage the color of your documents and devices. Mac OS users can streamline their publishing process using a control panel, AppleScripts and profiles. The result is powerful control over color matching at every step of the workflow process.

Introduction

ColorSync is the industry-standard tool for managing color across input, display, and output devices. This system-level software developed by Apple Computer works with scanners, digital cameras, monitors, printers, copiers, proofers, and presses. ColorSync is also supported in all leading image-editing and page-layout applications.

Anyone responsible for creating print or electronic materials knows how important accurate color can be in conveying information and creating desired responses. They also know how difficult it has been to manage color. A shift in color can seriously damage the effectiveness and accuracy of a product photo or design. Incorrect colors can cause lost sales; mail-order customers often return items because they don’t match the colors in the catalog or on the web site.

ColorSync saves time and money by enabling you to accurately capture, edit, preview, and output color documents. It gives you powerful control over color matching at every step of the workflow process by using unique "profiles" to describe the difference in color performance between what an input or output device does and what we know it should do. These profiles are usually stored as part of an image file (in the file’s header or "table of contents") and provide a description of how this image was captured, what its color space is, and more.

ColorSync calls upon the computational power of "CMMs" (color matching modules) which convert images from one color space to another—for example, from RGB to CMYK—and simultaneously apply the information in the profile to correctly render the image.

In each step of the workflow, ColorSync compensates for any deviations in the image-capturing systems of scanners, the display anomalies of monitors, and the color imaging components of printers and output devices. The CMMs from such highly respected color partners as Heidelberg Prepress, Kodak, and Agfa are packaged in each version of ColorSync along with a unique CMM from Apple Computer.

ColorSync also includes a powerful but easy-to-use monitor calibration system which corrects any irregularities in the monitor’s age, phosphor set, ambient light, white point, or monitor type. ColorSync lets you calibrate your computer’s monitor so that the colors of a displayed image correspond to the original photograph or digital capture. You can even view an image as it would appear on different paper stock or output devices (called a "soft proof"). And, when you use ColorSync to simulate a specific printing press or film recorder, the proof prints you make on a color desktop printer can be amazingly close to the color of the final output.

ColorSync is not "all or nothing." You can choose to only calibrate your monitor, or only calibrate your scanner, or you can implement an entire ColorSync workflow. Each incremental step means time savings, reduction of waste, and added profits.

With ColorSync software, anyone who works with color content can maintain quality throughout a wide array of output media including newspaper photographs, magazines, catalogs, books, web pages, videos, QuickTime movies, photo transparencies, and more. Because ColorSync works directly with the Mac OS and has an open architecture, hardware and software manufacturers have been able to add ColorSync support to their products easily. In fact, more than 100 products ranging from inexpensive scanners to top-of-the-line printing presses now take advantage of the powerful ColorSync color management capabilities. With ColorSync, any color-aware application or device can communicate with any other. With so many products for Mac OS systems now supporting ColorSync, you can finally achieve consistent color at every step of your workflow, from input and output.

The Basics of Color Systems and Color Management

Traditional printing professionals will most likely tell you that they have been doing color management for years. They’ll say they’ve been getting customer-correct color off their printing presses and scanners, that they’ve been proofed accurately by a highly experienced press operator.

Traditionally, designers have sent their color projects to the printer. What did the printer do with these projects? They reworked and translated the designer’s intended colors into the capabilities of their printing facility. Color management has been a sort of imprecise magic.

Enter ColorSync: ColorSync puts the color control back in the hands of the designer, while offering an unprecedented level of color fidelity across media.

Rotating ColorSync ColorSync is system-level "digital glue" which allows peripheral devices, the operating system and applications to communicate. ColorSync acts as a common interpreter of color—from scanner to display to application to printer.

To accomplish this requires system-level knowledge of the color characteristics of each device. These characteristics are described in the device's profile. Profiles are used to show, for example, how a monitor displays a particular color, and this information can be used by a proofing device or printing press to reproduce that same color.

Scanner operators no longer need to stand in front of a large, expensive device, tweaking buttons to get as close as possible to the proper color. Now you can buy off-the-shelf, affordable products that’ll create the profiles needed by ColorSync to produce correct color.

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ColorSync is system software that provides a comprehensive framework for exchanging and matching color information between input devices, displays, applications and output devices, all of which have quite different methods for representing color information.

To truly understand this process, it is necessary to have a basic knowledge of color.

The Evolution of Color

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In 1984, desktop publishing started a revolution in the production of artwork for printing.

As creative people began adopting the Macintosh, their artistic abilities blossomed. They used more images and better type fonts; they added graphics and illustrations to their documents to make everyday work look dramatically better. As quality work could be achieved more easily than ever before, the business of design flourished.

Where a document would have been typed in 1984, it was typeset in 1985, illustrated with compelling graphics in 1986, had photos added in 1989 and was printed in full color in 1991.

Color commands attention and gets better results. Color is very much a part of the fabric of commerce. Yet color alone is not satisfactory. We want quality color, color that matches the original, color that is reliable, color that is affordable.

When you add ColorSync to your production methods, you are turning the management of color into a new business. With this new business, you’ll meet new customers and be able to do more work for your existing customers.

Managed color makes for work that is more profitable, more repeatable, and much easier to achieve than ever before.

A Brief Overview of Color

Color is created through the interaction of light, an object, and the eye. There must be a light to illuminate the object. White light contains many different colors of light. This can be seen by observing how sunlight is broken into its components when passed through a prism. The resulting rainbow represents the "visible spectrum" consisting of the colors that can be seen by the eye. Each color of light has a particular wavelength. An object appears to be a certain color because it has pigments that absorb some of the wavelengths of the light that illuminates it while reflecting others back to the eye.

In other words, the color of the "green" butterfly or the "blue" sweater "happens in our mind" after our visual sensory system responds to the wavelengths of light.

Color Perception

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Our eyes contain sensors which respond to different wavelengths of light. The human visual system works quickly to respond to all the potential wavelength information. It efficiently breaks down the visible spectrum into the three primary regions of red, green, and blue. The eye contains three types of cone receptors. Each receptor is sensitive to about one-third of the visible spectrum. These are red light, green light, and blue light.

The color the eyes see in an object depends on how much red, green and blue light is reflected to the eye. Black is perceived when no light is reflected to the eye. When red, green, and blue lights are reflected to the eye in equal amounts, then white is perceived.

What you see is not always what's there! Many factors can affect our perception of color. For example, about 10% of all men are color blind and about 1% of all women are color blind. A person who looks at color for a long period of time is going to experience retinal fatigue and the colors are not going to be perceived accurately any longer. We need a standard specification system to know exactly what the color is. Lightbox

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The conditions in which color is viewed greatly affect the perception of color. For accurate viewing the light source and environment must be standardized. People in the graphic arts industry, for example, avoid fluorescent and tungsten lighting, use a standard light source, and proof against a neutral gray surface. A viewing booth, such as the Soft-View from GTI, is the easiest way to achieve standard viewing conditions.

The illustration below depicts the same photograph viewed under three different light sources. The leftmost picture is 6500 degrees Kelvin which is equivalent to department store fluorescent lighting. The middle picture is 5000 degrees Kelvin, the industry standard as far as proper viewing standards are concerned. The far right picture is 2500 degrees Kelvin (incandescent).

Color images frequently contain hundreds of distinctly different colors. To reproduce such images on a color peripheral device would be impractical. However, a very broad range of colors can be visually matched by a mixture of three "primary" lights. This allows colors to be reproduced on a display by a mixture of red, green, and blue lights or on a printer by a mixture of cyan, magenta and yellow inks or pigments.

Color Wheel Cyan absorbs red, magenta absorbs green, and yellow absorbs blue. Black is printed to increase contrast and make up for the deficiency of the inks. The illustration at the right helps us to visualize how colors of opposite hues interact.

The use of only three colors to reproduce thousands of colors is possible because the eyes are basically responsive to these three broad sections of the spectrum. The three color values constitute the specification for the matching properties of a color.

The visual sensation of color is very subjective. Each person experiences the sensation of color differently because many variables influence our color perception. Even if we did all see color the same way, we would still interpret and describe it differently based upon our individual life experience. That is one of the reasons for the development of color communication standards and easy-to-use color measurement instruments.

Hue, Saturation, and Brightness

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Color is described as having three dimensions. These dimensions are:

Hue - The name of the color.

Saturation - The degree of hue in a color, or a color's strength. A neutral gray is considered to have zero saturation. An example of color saturation is demonstrated in the red color of the butterfly wings.

Brightness - The term used to describe differences in the intensity of light reflected from or transmitted by a color image. The hue of an object may be blue, but the terms light and dark distinguish the brightness of one object from another.

Additive Versus Subtractive Color

There are only two basic methods to reproduce color - additive and subtractive. Both processes are based on the theory of using three primary colors to create all colors.

Understanding the principles of these two systems is the foundation for understanding the many aspects of the color reproduction process in printing.

Additive Color

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The additive color process begins with black, or the absence of light, and therefore no color. It involves transmitted light before it is reflected by a substrate. With transmitted light, all the colors of the rainbow can be produced by mixing the three primary wavelengths of light (red, green, and blue) in different combinations. Any two of the primary colors mixed together produces another color called a secondary color. Red and green projected together produce yellow, red and blue produce magenta, and blue and green produce cyan. Adding the three primary colors in equal amounts produces white.

Monitors, scanners, and television screens emit light. Therefore they use the additive color system. They can directly add red, green, and blue light to darkness.

A monitor blends varying intensities of red, green, and blue light at each of its pixels. These pixels are so small and close together that the eye is fooled into the perception of many different colors when there are really only three.

Let's use something you might be familiar with to illustrate the additive nature of RGB:

On-Your-Own Exercise: Use the Mac OS 8 Appearance Manager to set a new highlight color using the RGB Picker.

  1. Choose the Appearance Control Panel and select the Color icon to display the Accent Color menu.
  2. Click on the Highlight Color pop-down menu and choose Other.
  3. Select the RGB Picker and set the values to 100% red, 100 % green, and 100% blue. They produce white, illustrating the additive nature of RGB!

Subtractive Color

The subtractive color process is based on light reflected from an object which has passed through pigments or dyes that absorb or "subtract" certain wavelengths, allowing others to be reflected.

The primary subtractive colors - cyan, magenta, and yellow - can be combined to form red, green, and blue as secondary colors. Combining the ideal subtractive primaries in equal amounts produces black.

Printing is based on the subtractive color process. A printer renders color on paper or other substrates, so it must work with reflected light. To do this, printers use the opposing subtractive primaries of cyan, magenta, and yellow. When cyan, magenta, and yellow pigments are deposited on white reflective paper, each component absorbs - or subtracts - its opposing counterpart from the oncoming white light. The printing process uses cyan, magenta and yellow inks to control the amount of red, green, and blue light that is reflected from white paper. These colors are printed on paper as layers of halftone dots in varying sizes and angles to create the illusion of different colors. The effect of varying dot sizes is similar to varying intensities of a monitor's red, green and blue phosphors.

Paper itself has a significant effect on color reproduction. Since paper reflects unabsorbed light back to the viewer, the more reflective the surface, as in coated paper, the wider the range of colors that can be produced.

Let's use something you might be familiar with to illustrate the subtractive nature of CMYK:

On-Your-Own Exercise: Use the Mac OS 8 Appearance Manager to set a new highlight color using the CMYK Picker..

  1. Choose the Appearance Control Panel and select the Color icon to display the Accent Color menu.
  2. Click on the Highlight Color pop-down menu and choose Other.
  3. Select the CMYK Picker and set the values to 100% cyan, 100% magenta, and 100% yellow. They produce black, illustrating the subtractive nature of CMYK!

Color Spaces

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A color space is a model for representing color in terms of intensity values. A color space specifies how color information is represented. It defines a one, two, three, or four dimensional space whose dimensions, or components, represent intensity values. Visually, these spaces are often represented by various solid shapes, such as cubes, cones or polyhedra.

ColorSync supports several different color spaces to give users the convenience of working in whatever kind of color data most suits their needs. For example, RGB space is a three-dimensional color space whose components are the red, green, and blue intensities that make up a given color.

The ColorSync color spaces fall into several groups or base families. An additional color space, Hi-Fi color space, is primarily used in new printing processes involving the use of gold plate and silver, and also for spot coloring.

Gray Spaces

Gray spaces typically have a single component, ranging from black to white. Gray spaces are used for black-and-white and grayscale display and printing.

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RGB-Based Color Spaces

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The RGB space is a three-dimensional color space whose components are the red, green and blue intensities that make up a given color. For example, scanners read the amounts of red, green, and blue light that are reflected from an image and then convert those amounts into digital values. Displays receive the digital values and convert them intro red, green, and blue light seen on screen. RGB color spaces are additive.

RGB-based color spaces are the most commonly used color spaces in computer graphics, primarily because they are directly supported by most color displays. Because the colors produced by RGB specifications vary from device to device they are called device-dependent color spaces. Device-dependent color spaces enable the specification of color values that are directly related to their representation on a particular device.

The groups of color spaces within the RGB base family include RGB spaces, HSV spaces and HLS spaces:

RGB Spaces - any color expressed in RGB space is some mixture of three primary colors: red, green, and blue.

HSV and HLS Spaces - transformations of RGB space that allow colors to be described in terms more natural to an artist. The name HSV stands for hue, saturation, and value. HLS stands for hue, lightness, and saturation.

CMY-Based Color Spaces

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CMY-based color spaces are most commonly used in color printing systems. They are device dependent and subtractive in nature. The groups of color spaces within the CMY family include:

CMY - not very common except on low-end color printers.

CMYK - models the way inks or dyes are applied to paper in printing. The name CMYK refers to cyan, magenta, yellow, and black. Cyan, magenta, and yellow are the three primary colors in this color space. Red, green and blue are the secondaries. Theoretically black is not needed. However, when full-saturation cyan, magenta, and yellow inks are mixed equally on paper, the result is usually a dark brown, rather than black. Therefore, black ink is overprinted in darker areas to give a better appearance.

CMYK colors vary with printer, ink, and paper characteristics. In addition, different devices have different gamuts, or ranges of colors that they can produce. Because the colors produced by both RGB and CMYK specifications vary from device to device, they are called device-dependent color spaces.

Conversion from an RGB color space to a CMYK color space involves a number of variables. It involves device-specific, ink-specific, and even paper-specific calculations of the amount of black to add in dark areas and the amount of other ink to remove where black is to be printed. ColorSync performs these calculations for the user when converting among color spaces.

Device-Independent Color Spaces

Device-Independent color spaces are used mainly for color models and by the system for translating between RGB & CMYK models.

Every color monitor has its own range (or gamut) of colors that it can generate using its RGB phosphors - even monitors made in the same year by the same manufacturer. The same is true for printers and their CMYK colorants, which in general have a more limited gamut than most monitors. Because the colors produced by both RGB and CMYK specifications vary from device to device, they are called device-dependent color spaces.

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Some color spaces allow color to be expressed in a device-independent way - colors that are not dependent on any particular device. Device-independent colors, are meant to be true representations of colors as perceived by the human eye. These color representations, called device-independent color spaces, result from work carried out in 1931 by the Commission Internationale d'Eclairage (CIE) and for that reason are called CIE-based color spaces.

The goal of the CIE was to create a repeatable system of color communication standards for manufacturers of paints, inks, dyes, and other colorants.

These standard's most important function is to provide a universal framework for color matching. Device-independent color spaces are used for the interchange of color data from the native color space of one device to the native color space of another device. They represent the entire range of visible colors as translation spaces. This means that any color that is selected on a display is in the gamut of this neutral color space.

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CIE L*a*b* is a three dimensional color space that is based upon human perception of color. It is the most widely used of the CIE color spaces. L*a*b* color space is based on the theory that a color cannot be both green and red at the same time, nor blue and yellow at the same time. As a result single values can be used to describe the red/green and yellow/blue attributes.

CIE L*a*b* space represents color relative to a reference white point, which is a specific definition of what is considered white light, usually based on the whitest light that can be generated by a given device.

The CIE color spaces form the foundation of device-independent color for color management.

The Elements of Color Management

Color management can easily save time and money for color users by reducing the amount of time and materials it takes to complete color production tasks.

A color management system gives the user the ability to match colors on different input and output devices, to see in advance what colors cannot be accurately reproduced on a specific device and to simulate the range of colors of one device on another.

To achieve accurate, repeatable color reproduction involves the use of software and hardware to calibrate and profile the input and output devices.

A Little History

In the late 1980's, a number of leading color technology companies developed systems for color desktop publishing applications. These were commonly known as color management systems, or CMSs. The first CMSs promised to solve the problem of unmatched colors across desktop color devices. These pioneers took the first step in creating a solution. However, these systems lacked key features, which resulted in poor acceptance by users.

One of the fundamental problems that prevented widespread adoption of early color management systems was the fact that each was implemented using a different architecture. In order to perform color-matching functions, an application manufacturer would have to make specific calls to it. Because there was no common color management framework for applications to use, each application had to align themselves with hardware vendors and of course, new improved CMSs were introduced regularly, with no compatibility between profiles and no consistency among the results.

Apple Computer has the first and best system-wide implementation of a digital color management system because it makes working with color relatively simple, fast, reliable, and repeatable for both users and developers alike.

ColorSync is system software that provides a comprehensive framework for exchanging and matching color information between input devices, displays, applications and output devices.

The API (Applications Programming Interface) is an architecture that allows applications and drivers to request functions from a specific program or system extension. Apple developed the ColorSync APIs to enable applications and drivers to request color matching functions from the Color Matching Module (CMM). As with many other Apple software services, software developers can take full advantage of ColorSync's open architecture without extensive development or collaboration. When a developer such as Adobe wants to implement ColorSync in their applications, they write the code to reference the APIs, which in turn makes color matching requests to the CMM.

The development of measurement instruments has paralleled the development of systems for color desktop publishing applications, or color management systems.

These measuring instruments are an enabling technology for color management. Until measurement instruments, color was adjusted and controlled on printing presses primarily by the human eye which is subject to many frailties.

Three types of instruments can be used to measure color in the graphic arts production workflow:

Densitometer - a photo-electric device that measures and computes how much of a known amount of light is reflected from or transmitted through an object. A densitometer is a simple instrument used primarily in printing, pre-press and photographic applications to determine the strength of a measured color.

Colorimeter - measures light, breaking it down into its RGB components in a manner similar to the human eye. It then determines the color's numeric value using a CIE color space. These measurements are visually interpreted in a color space graph.

Spectrophotometer - measures the amount of light energy reflected from an object at several intervals along the visible spectrum. The result is a complex data set of reflectance values visually interpreted in the form of a spectral curve.

The spectrophotometer is the most accurate, useful and flexible instrument because it gathers complete color information which can be translated into colorimeteric or densitometric data with a few calculations.

Calibration

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Device calibration is an important first step in the desktop color management process as monitor and output device (printers and scanners) performance capabilities can change over time. Calibration ensures that all devices conform to an established state or condition, often specified by the manufacturer.

Calibration really makes a big difference in monitors. Calibrating a monitor adjusts and corrects the monitor's gamma, white and black points, and color balance. Calibration software is used with hardware to send a series of colors to the screen, and the instrument reports back the value of the colors that actually arrive there. Profiling software then builds a corrective profile that is used by ColorSync to drive the monitor.

Monitors should be calibrated on a regular basis.

When calibrating a monitor for color-managed computer processing, it is a good idea to eliminate as many variables from the monitor's environment as possible. Room glare and natural light from windows and skylights can be as much a problem as an uncalibrated monitor. Dimmer switches on lights should be replaced with traditional on-off switches.

Characterization (Profiling)

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Characterization provides a way of deriving the color gamut and reproduction characteristics of a device in a calibrated state. It is a way of determining how an input device captures color or an output device records color when it is calibrated. Characterization data provides the input to profile creation.

In order to accurately render colors from one device's color space to another, some resource must exist that describes each device's color capabilities. Today's digital color management systems use profiles. Profiles describe various color characteristics. They provide ColorSync with information necessary to convert color between device-dependent color spaces and device-independent color spaces.

To manage color, essentially what you have to do is profile the various devices that are used in your workflow, then implement these profiles in the workflow through the applications that you utilize:

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The process of creating a profile depends largely upon the type of device. Scanners, displays, printers, and printing processes all differ significantly, and require different processes. Today's profile creation packages typically include tools for all types of devices.

Profiling a printer, for example, involves creating a testform document, printing it on a proof printer or printing press, then reading the color patches with an instrument, such as a spectrophotometer.

A spectrophotometer is a highly sensitive measuring device which essentially looks at color just as a physicist looks at color. It looks at color based upon the wavelength that is being evaluated.

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The resulting measurements are input to a custom software package that uses several complex algorithms, the result of which is a profile. This process is known as device characterization.

In a color-managed environment, the quality of the results is highly dependent upon the quality and accuracy of the device profiles being used. Quality profiles produce quality results.

ColorSync provides a built-in framework for implementing and managing these device profiles. ColorSync profiles follow the International Color Consortium (ICC) profile format. This format provides a single cross-platform standard for translating color data across devices and across operating systems. A profile created for a particular device is usable on systems running different operating systems.

It is important to recognize that a device profile represents the device in its factory condition. In reality, devices of the same type will deviate, resulting in inconsistencies, and require device calibration. Device calibration should be performed on a regular basis to ensure accuracy.

Color Conversion

Color conversion is the process of translating colors from one color space to another.

Different imaging devices (scanners, displays, printers) work in different color spaces, and each can have a different gamut, or range of colors that can be generated. For example, color displays from different manufacturers all use RGB colors but may have different RGB gamuts. Printers that work in CMYK space vary drastically in their gamuts, especially if they use different printing technologies. Even a single printer's gamut can vary significantly with the ink or type of paper it uses.

Color matching is the process of adjusting converted colors to achieve maximum similarity from the gamut of one color space to the other.

It's easy to see that conversion from RGB colors on an individual display to CMYK colors on an individual printer using a particular paper type can lead to unpredictable results!

When an image is output to a monitor or printer, the device displays only those colors that are within its gamut. Likewise, when an image is created by scanning, only those colors within the scanner's gamut are saved. Devices with different gamuts cannot reproduce each other's colors exactly, but careful shifting of the colors used on one device can improve the visual match when the image is displayed on another.

Since it is not possible to have perfect color matches between devices due to the differences in each device's gamut the Color Matching Module (CMM) performs gamut mapping, a process by which the next closest reproducible color is selected.

ColorSync profiles are used by the CMM, or color transformation engine, in ColorSync-savvy applications. The CMM translates data from one device's colors to another, via an independent color space. The CMM receives the necessary information from the profiles , so that it can accurately transform a color from one device to another. The result is color that is consistent from device to device.

For example, if you want to simulate press conditions on a proofer and visualize that on your screen, you use a software application that takes your screen profile, your proofer profile and your press profile, loads them into the CMM, compares them and sends back the necessary information to the screen. All of this is done transparently to the end-user because the CMM is built into the OS, and the ColorSync APIs are controlling the application requests to the CMM.

Apple's default Color Matching Module is supplied by Apple and LinoType-Hell, a recognized leader in color technology. ColorSync gives the user the flexibility to choose a preferred CMM from any CMMs that are present. The Kodak Color Matching Module is available as an install option with ColorSync 2.5.1. Cross-platform applications that work with the Kodak CMM on the Windows platform can use this CMM to ensure consistent output.

See Also