4 Measurement Tools Used to Keep Color Controlled in a Graphic Arts Workflow

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Color Management: Current Practice and
The Adoption of a New Standard

Michael Has, FOGRA ,Technical Secretary, International Color Consortium
Todd Newman, Chairman, International Color Consortium

Abstract: Historically, managing colour has been a very fourth dimension consuming and costly procedure in the printing, prepress, and moving picture industries. The video industry has started to notice the need for color direction as well. This has led to several years of intense discussions on color management solutions. In response to these discussions, the International Colour Consortium (ICC) created a standard which attempts to serve as a cantankerous-platform device profile format to exist used to characterize color devices. Afterwards a discussion of current practices in manufacture, this standard is described along with a discussion of the major limitations of colour management today. Finally, examples of current color management workflows and ICC colour management workflows are provided.

Introduction

Historically, managing color has been a very time consuming and costly process in the printing, prepress, and film industries. The video industry has started to notice the need for color management too. This has led to several years of intense discussions on color direction solutions. In response to these discussions, the International Color Consortium (ICC) created a standard which attempts to serve as a cross-platform device profile format to be used to characterize colour devices. After a discussion of electric current practices in industry, this standard is described along with a discussion of the major limitations of color management today. Finally, examples of current color direction workflows and ICC colour direction workflows are provided.

Managing Colour in the Printing Industry

There have been a number of dissimilar approaches to generate reliable color in professional person printing the past. Several attempts accept been fabricated to organize these efforts into mutual industry solutions. A few of these approaches evolved into a general standard in the kickoff printing environment, the BVD/FOGRA standard (1), Large parts of that standard subsequently on became an ISO Standard (ii). This standard defines:

• the process colors (as defined in Euroscale (3))
• the color of the paper (white signal)
• measuring conditions (e.g., blackness backing backside newspaper)
• dot gain in the press process

The U.s. Standard for Web Showtime Press (SWOP) for the process colors in showtime print and the comparable Euroscale standard have recently been unified (4). In guild to bank check the quality of the colour reproduction on the press, standardized control strips have been developed. When measured constantly or on a regular basis, the strips serve as indicators of possible changes in color. The unlike printing printing producers (5,6) have developed methods to interpret these measurement data into control algorithms that automatically adjust the press ductors that crusade the ink flow (7).

Managing Colour in the Prepress Industry

The prepress system PVD (Partner vor dem Druck), a Germany, as information technology was offered until the beginning of this yr, provides a representative case of a current prepress colour management solution. This software/hardware solution is based on Silicon Graphics hardware and its operating organization. The system provides users with a method to simulate the final output on a proofing device. This is feasible considering the proofing device and proofing textile can reproduce a wider range of colors than the printing and paper. The proofing device can thus reproduce the color of both inked and uninked ("white") parts of the epitome as they will appear in product. The operator must starting time calibrate the proofing device based on the characteristics of the individual printing. The vendor presets his software with a calibration bend, which must exist manually improved upon using electric current measurement results from the press.

In order to simulate the output paper, the operator needs the color of the paper equally a CMY value. This is obtained by the post-obit iterative process. First, the operator prints control strips that, upon measurement, provide input on the colour of the paper. Second, the color is varied to some degree and again measured. The comparing of the measured results with the data originally intended to be printed stepwise leads to the colour of the newspaper. After calculation other factors for gradation or dot gain (which correlate the aim density of the color on the proofer with that of the last output device), this trial and error approach is repeated. Note that in this organization black is composed of three colors, and not as a divide ink. Because the proofing material is whiter than the press paper, some blackness dissonance, randomly placed black dots, is added to the proofer's output, in order to simulate the actual paper.

Having obtained the color characteristics of the paper and of the process colors of the proofer separately, the combination must besides exist characterized. To keep the motorcar in constant running status, software is used that adapts gradation, density, and depths (10 values per colour in 10% steps between 10% and 100% of density). To proceed the system operating within parameters, the values must be measured on a daily basis. While reliable, the solutions described above for the printing and the prepress industries are very time-consuming and complex.

Managing Color in Movement Pictures

Equally in the printing industries, the introduction of estimator technology to the moving-picture show manufacture has changed the fashion color is handled. In the pre-estimator industry, color management was primarily a trouble of chemistry and process control. The chemical beliefs of the halides and dyes used in the film stock could be measured and modeled. Dyes, filters, and processing materials were designed to piece of work together so that every bit an ensemble colour allegiance was maintained end-to-finish. The color produced on intermediate stock -- the negatives used -- was unimportant as long equally the final result looked good.

The introduction of computers into film processing has changed that. Computers are used in the product of a picture show, not as a display medium. They are used in ii fundamentally different ways in the movie industry: they can be used to modify live action film, either for affect up or to add together special effects; they can be used to generate entirely synthetic images for 2D or 3D animation.

The Cinesite Digital Picture Centers (14) are a good example of the live action awarding. The centers provide a high-quality movie scanner, digital retouch stations, and a light amplification by stimulated emission of radiation driven motion-picture show recorder. Live activity film is brought to the centre, where it is scanned into the system. The retouch stations can be used to clean up and alter the images. For example, in a scene filmed in a moving car, a 2d camera used to tape the actors from a dissimilar bending was been accidentally captured on film. The retouch station was used to replace the images of the camera with the scenery that should have been visible.

The goal of the colour direction organisation hither was to reproduce the colors of the scanned-in film every bit accurately as possible. A secondary goal is that the colors seen on the retouch station accurately friction match the colors to exist produced on the final moving-picture show. Color management is washed by adjusting the response of all devices to lucifer the response of the moving picture printer (17). The CCDs and illumination system of the film scanner where advisedly designed and tuned with filters to match the spectral response of the recorder's lasers. While the monitor primaries could non be changed, the monitor is specially calibrated and the hardware colour lookup tables are adapted to lucifer the film recorder response as best as possible. The monitor is likewise run at a gamma value, 0.6, the closely approximates the motion-picture show response.

The Digital Blitheness DreamMachine which Silicon Graphics is to build for DreamWorks SKG shows the unlike needs for color management in animation. Except for groundwork fine art work which may be scanned in, all the imagery will exist initially merely on workstation monitors. Today, for most animators the color seen on the output film is a hit or miss affair. Several iterations are required before the last result looks like the original created on the computer screen. One of the reasons that personal computers have been then successful is that they take been able to provide WYSIWYG (What Yous See Is What You Go) behavior for certificate production. The goal of color direction in the DreamWorks projection is to provide the same WYSIWYG behavior for animation production.

Color management for the Dreamworks project volition exist based on the ICC profiles described below. Since it is desirable to exist able to support more than one type of film recorder, it is non reasonable to tune the system's spectral response to any one device. Instead, applications run in whatever device color infinite is advisable, usually that of the monitor on the workstation. Then color adjustment is performed at output fourth dimension to move the data into the device colour space of the output device, which might be film recorder or a video device.

One interesting problem that remains is caused past the fact that flick has a wider gamut and dynamic range than does ink on paper. It is possible to simulate a medium of narrower gamut (such as paper) on a device with a wider gamut (such as a monitor). Simply it is a much more difficult problem to simulate the broad gamut of film on the narrower gamut of the monitor. Either the gamut must be compressed for display, which means that problem in shadow or highlight details may not exist noticed until motion picture is recorded, or only a part of the total gamut can at whatsoever time, which means that it is not possible to view the image as a whole. Neither solution is pleasing.

Managing Colour in Video

Equally with film, the introduction of computers changes the way color management must exist performed for video. The reproduction of color for television receiver is defined by the Social club of Motility Motion picture and Boob tube Engineers in a serial of standards, guidelines, and recommended practices. Equally long as televisions are the only output medium, color management can in theory be handled quite but with electronics and physical components matched to the standards. No digital bespeak processing is required. Of course, habitation goggle box sets are not calibrated and viewing weather are almost never fifty-fifty shut to ideal. Another problem is that the phosphors used for brandish in mod televisions are quite dissimilar from those specified by the Federal Communications Committee in 1953 (15) The practical result, particularly when combined with the fact that chroma is subsampled in NTSC , is that the colour on televisions is notoriously inaccurate and smeared.

Increasingly, video imagery is being displayed not on a television receiver set, just on a reckoner's monitor. This is happening as video imagery is incorporated into multi-media documents and as video and computer technology are combined for teleconferencing. Both boob tube sets and computer screens apply an RGB based image and cathode ray tubes to display the output image. Only many of the details of the display system are very different. Television sets, at least in theory, have a gamma of 2.2. The default gamma numbers used on estimator monitors range anywhere from ane.4 to 2.2. Every bit shipped, SGI workstations have a gamma of 1.seven, simply this tin can be configured by the user to any value between 0.0001 and xix.nine. The white point of a tv set is D65, but most estimator monitors have a white indicate of 9300 degrees. Finally, the tabular array below shows the chromaticities for the 1953 reference monitor, SMPTE "C", and the CCIR 709 monitor and the nominal chromaticities for 2 adequately typical calculator monitors: the Sony Trinitron and a Hitachi 2198:

FCC 1953 Receiver Phosphors           x     y Red   0.674 0.326  Light-green 0.218 0.712  Blueish  0.140 0.080  SMPTE "C": Red   0.630 0.340  Green 0.310 0.595  Bluish  0.155 0.070   CCIR 709:  Ruddy 0.640 0.338  Green 0.300 0.600  Blue 0.150 0.060   Sony Trinitron (all +- 0.03): Reddish   0.621 0.340  Green 0.281 0.606  Blue  0.152 0.067   Hitachi CM2198 (all +- 0.02):  Red   0.624 0.339  Green 0.285 0.604  Blue  0.150 0.065 (xvi)        

The SMPTE "C" Specification requires tolerances of +- 0.005 for x and y. This table then, shows two things. First, information technology shows the change over fourth dimension of phosphors used in television, and how poorly the FCC specification, to which broadcast colour is adapted, matches electric current telly receivers. It likewise shows how much the phosphors in typical estimator monitors differ from those used in goggle box.

What this means is that color management is a necessity to accomplish anything resembling colour allegiance when displaying video imagery on computer monitors. The speed with which an image can be transformed is critically important here. On a printing press, or when recording film output, at that place is no concept of "real time." If takes one tenth of a second more than or less to adapt the colour of an image, user satisfaction will be afflicted, but the organization will be usable either way. Simply a color direction system that delivers anything under sixty frames per second of color corrected video is non usable. Fortunately, the operations required to convert from whatever of the receiver color spaces into a computer monitor'south color space are relatively lightweight, at least compared to what is required for print. So a good colour management organization could adopt a less computationally intensive solution.

The Need for Open Color Direction

As illustrated above, the traditional printing and prepress colour calibration environments can be characterized by systems in which the configurations of devices such as scanner, computer paradigm processing program, monitor, and output devices is abiding. Simply when the organization is beingness ready, or perhaps for testing purposes, is it necessary to coordinate the color characteristics of the selected components with one some other. The color direction problem is thus more contained. Ordinarily, colour conversion moves directly from 1 device color infinite to some other. As described above, color conversion is often advertising hoc and empirically derived.

The prepress, press, picture, and video industries are all seeing the rising of two factors that make this sort of solution less and less feasible. Offset, the rise of open systems, of customers mixing equipment from different vendors and of reconfiguring systems often, has given rise to the need for an open solution to color direction. 2d, the ascension in distributed systems, where the certificate creation and reproduction are happening on systems that may be many miles apart, has given rise for the demand to communicate colour reliably between systems.

A colour management system based on a well-divers neutral coding of the colors, such as the CIE color spaces (8), can solve both these bug. If the device-specific colors from whatever peripheral can exist mapped into a device-independent color space, and if all computer and application vendors tin agree on the estimation of that device-independent color space, then it becomes much easier to combine equipment from different vendors into ane arrangement and maintain the meaning of color specifications. Because they are well-divers and reproducible, the CIE color spaces are an splendid language for communicating color data between distributed systems.

Accordingly, beginning in 1993, several companies decided to work toward a common approach to color management. They formed the International Color Consortium (ICC) in order to solve the users' bug in achieving reliable and reproducible color throughout the unabridged reproduction process. Since its formulation, the ICC standard has been widely accepted (Appendix ane), and there is a loftier probability that this will exist accepted by the industry vendors.

The ICC Approach to Color Management

Ane of the kickoff decisions made past the ICC was that colour space transformations were the responsibleness of the operating arrangement. Putting information technology there meant that it did not have to exist replicated in each application while still being available to the appplications. Device profiles, which comprise data on the colour behavior of the various peripherals, provide the information necessary to perform these transforms.

ICC Software Architecture

Of course, the ICC did not mandate a specific operating system, nor a single operating system architecture. Information technology did, however, provide an overview of one possible architecture. Within the operating system, a "Color Management Framework", is designated. Information technology is responsible for the most important colour management functions of the operating organization (for example, the organization of profiles, giving support to different color spaces, retrieval functions, etc.) The framework provides an interface to the various color direction methods. These are the centre of the color direction system performing the conversion of image information into the special color spaces of the output devices. Both CIEXYZ and CIELAB are supported as standard colour spaces within the color management framework. Other interchange color spaces are likewise offered as office of the standard. Others can exist added, as long equally the specification is well-divers and publicly available. Support is given for device color spaces with different numbers of output channels. Profiles can be made for three channels (RGB, CMY, HSV), four channels (CMYK), or even seven-colour printing.

What's in the ICC Contour Specification ?

The ICC Profile specification (9) begins with a descriptive function in which device profiles, color spaces, profile connection spaces, profile chemical element structure, and embedded profiles are explained. The contents of the device profiles are described in a top-down fashion. The ICC profiles basically consist of a table of contents followed by tagged data. The profile document start defines several types of device profiles and what tags must exist in these profiles. So it describes the divers tags and what type they are. After this is a definition of the underlying types. The document concludes with examples and appendices. One particularly important appendix describes how to embed profiles in Encapsulated PostScript, PICT, and TIFF files. Various contour types are specified in the ICC Contour:

• Input Device
• Display Device
• Output Device
• Colour Infinite Conversion
• Device Linking
• Abstract Profile

For each profile blazon, a set of mandatory tags is defined. Any other defined tag may besides be added to a profile.

Generating an ICC Contour

1 of the outset steps in profile building involves measuring the colorimetry of a set of colors from some imaging media or display. If the imaging media or viewing surroundings differ from the reference, it will exist necessary to adapt the measured colorimetry to that advisable for the contour connection infinite. These adaptations account for such differences as white point chromaticity and luminance relative to an platonic reflector, viewing surround, viewing illuminant, and flare. Currently, it is the responsibility of the profile building software to do this adaptation.

For example, to build a scanner profile, vendors browse in a reference image and compare it with a data file that indicates what the scanned values should be. The colors in the reference paradigm are distributed as evenly every bit possible within the CIE colour space. This comparison between the data supplied by the scanner and the previous information for the same image provides good information on the reproduction backdrop of the scanner. Building a contour for a printer inverts the procedure. Here a set of patches evenly distributed in the output ink colour infinite (CMY or CMYK) are generated and printed. These patches are then measured to provide colorimetric data. The mapping function from CIE color space to device color infinite is much more complicated in that case.

Unlike vendors use a different number of test color patches. Several vendors use the IT7.8 Standard epitome, containing of some 190 color patches, while other vendors use test images with 4500 patches. Given the statistical noise on the output point it appears reasonable to measure out some 15 to 20 samples before averaging the result. It is still subject to discussions how many patches are needed to characterize a device accurately. The practical importance of reaching understanding is still an open up question, equally many of the colour direction systems are evidently not aimed at the printing industry market but at the desktop publishing marketplace. In this market, users do not look to take even 190 measurements themselves, just to be able to acquire pre-built profiles off the shelf. Ane decisive difficulty here might be the matter of creating affordably priced profiles to narrate the devices. Another question is whether those profiles will go useless as devices drift from the manufacturer's original calibration.

Color Space Conversion

The question of how to perform color infinite conversions is, of course, fundamental to color management. This breaks down into two questions. First, what is the best color displayable on the output device to use to stand for the colour from the input device? This is non always a straightforward decision if the input device can display colors that the output device cannot. Second, what are the calculations required to map colors from the input space to the output space.

"Optimum Reproduction"

Equipment used for image capture and for prototype reproduction have unlike properties. The dissimilar color spaces involved are not just of considerably dissimilar sizes (how many colors can be displayed) , but likewise vary in shape (which colors tin can exist displayed). Usually, scanners can correspond a wider gamut of colors and a larger dynamic range of colors than output devices such as printers tin. Due to these differences in shape, the desired objective of "optimum reproduction"; is not ever attained by simply making the larger color space smaller. The mathematical operations involved are not linear; thus diminishing the larger of the ii spaces until it fits into the smaller space may likewise substantially distort that color space.

A selection must be made between 2 unlike conceptions of "optimum reproduction."; The first is called "appearance matching." This approach try to take the eye'southward power into business relationship not simply to consider the color at a indicate nether view but as well the color of the neighboring surround. There are ways to compress the source colour space and however continue the image visually balanced . Success is measured subjectively, by asking if the greys announced grayness and "memory colors" (due east.g., flesh, grass, sky) look acceptable. The other approach is chosen "colorimetric matching." Here the goal is to reproduce as many color from the input device as exactly as possible. Success is measured with an objective device such as a colorimeter. In a colorimetric friction match, some colors from the source image volition non be reproducible exactly and some compromises volition have to exist made. Because the relationship between colors within the image has changed, colorimetrically matched images may not "look right" to human viewers.

Both methods accept advantages . Appearance matching is helpful to create the aforementioned impression in an output that would be created by looking at the original. Colorimetric matching yields measurable data that can be communicated reliably. Information technology can enable remote printing by providing a means of verifying that results are accurate. It will have some time to see which systems will be accepted for which practical circumstances.

The mathematics of color transforms

The most simplistic approach to color space transformation is given by an algorithmic transformation of the one color space into another. This is adequate for device-independent colour spaces. For case, here is the defined CIE 1976 Colour Infinite Transformation from the XYZ color infinite into the 50*a*b* :

L*= 116*f(Y/Yn) - 16 a*= 500*(f(10/Xn)-f(Y/Yn)) b*= 200*(f(Y/Yn)-f(Z/Zn))

In this set (X/Xn)ane/three for (10/Xn) >= 0.008856 f(X/Xn) := 7.787*X/Xn + 16/116 for (X/Xn) <0.008856 with f(Z/Zn) and f(Y/Yn) corresponding.

The Alphabetize north marks the coordinates of the white reference point.

The next step in complication is to use some device-specific data, only once again in a purely formulaic mode. One instance would exist the comparatively unproblematic default mechanism, given in the ICC Specification for converting from an RGB display's color space into CIEXYZ. This approach uses both information from the prototype and data from the device profile. Since the input data is RGB-based, so is the relevant contour data. Among others the Input Profile contains several tags that volition be used:

Tag Name           Full general Clarification  redColorantTag     Cherry-red colorant XYZ relative tristimulus values  greenColorantTag   Green colorant XYZ relative tristimulus values  blueColorantTag    Blue colorant XYZ relative tristimulus values  redTRCTag          Red aqueduct tone reproduction curve  greenTRCTag        Green channel tone reproduction curve  blueTRCTag         Bluish channel tone reproduction curve        

The forward mathematical model implied by this information to be used for the calculation of the XYZ value in the connection space every bit it is given in the specification is :

R is the cherry component of the input pixel, G, the green, and B, the blueish

Lr = redTRC[R]; Lg = greenTRC[G]; Lb = blueTRC[B]  Connexion x   redColorantX greenColorantX blueColorantX   Lr  Connection y = redColorantY greenColorantY blueColorantY * Lg  Connection z   redColorantZ greenColorantZ blueColorantZ   Lb        

This mathematical approach represents a unproblematic linearization followed past a linear mixing model. The three tone reproduction curves linearize the raw values with respect to the luminance (Y). The 3x3 matrix converts these linearized values into XYZ values for the CIEXYZ encoding of the contour connection infinite.

In proprietary CMMs, far more complicated models are used (10) to gain results that attempt either to meet referenced originals as close as possible using colorimetric matching or to meet the way colors in their local environment appear to the eye of an experienced user using advent matching.

Supporting ICC-based Color Management In a Traditional Workflow

In the workflow through a digital process the paradigm data is "tagged" with the device characterizing data profile. When it comes to output the information, the profiles of the input and output device are used to calculate the colors every bit they will exist represented in the output device. Workflow in an ICC-based environs is inverse for three reasons: First, because of the need colour management to be open up to support many different device. Second, because image creation and final reproduction may be distributed geographically. Finally, we wish to be able to support output to unlike media (print, film, video) using the many of the same product tools and processes.

For all these reasons, colors can not be adjusted for final display equally they are scanned. They cannot exist adapted at any point during the creation process. The simply fourth dimension color direction can be washed at output. That is the only time that the final brandish medium and brandish device are adamant. Merely just as the creator of the certificate does not know the color characteristics of the device on which the image volition be displayed, the person doing output does not know the color characteristics of the device on which the image was created.

The solution to this problem is to interruption it into two parts. At creation time, ICC profiles may exist used to map the source device's color space into a well-known color space, past tagging the image file in some way. At output time, the input profile and the output device profile can be used past the operating system to map data from the source colour space into the output color space. The one laissez passer approach may be slightly amend than just passing the source paradigm in a CIE color infinite. First, in existent product environments, the source paradigm is oftentimes processed on the same monitor using several different software tools. Information technology is a waste of time to go along converting in and out of the CIE color infinite. Second, colour space conversions may lose some precision due to circular off errors. It may be possible to build a device to device color space translation that minimizes information manipulation. Unlike the earlier device-to-device translations, however, using the ICC profiles allows whatever devices to be connected and any operating arrangement to perform the translation.

The all-time way to provide the mapping of the source device's color space is to embed the ICC contour into the source image. It is possible to utilize 2 files to contain the data, but information technology is quite likely that they will get separated at some fourth dimension. If the data is function of the prototype, in that location is only one file to manage and much less run a risk of losing the color information . This solution also works for documents that include more than than one paradigm and which may take been created on dissimilar devices. 1 document may reference many images which were created on dissimilar devices, each with its own device dependent colour space. The images should, of course, be color adapted separately. So an overall document colour contour would not be acceptable. But each image can accept its own embedded color information and the color adjustment can be washed on each image.

The changes in workflow required to do the color management using the ICC profiles are minor. Given a setup of devices consisting of scanners, monitors, different output devices and software, a practical work menstruum could be that as follows:

1. - Label of scanners using a profile making tool
2. - Characterization of monitors using a profile making tool
3. - Characterization of output devices using a contour making tool
4. - Scanning and reading of the images into a tool like Photoshop
5. - Match of scan to colour space of monitor or lucifer of scan to colour space of monitor including other output devices
6. - Reading of both images into an other tool i.e. Quark or Pagemaker if required a further match to color space of monitor including other output devices
7. - Output

As can be seen in this scenario, the linking of profiles, meaning the ability of the color direction mathematics to match the color spaces of different possible devices for the output, is essential to the usability of this approach. This becomes more difficult if different output devices, ranging from slide printers to computer-to-press processes, are included, especially when the output device is non known at the time the reproduction is done. Communicating the colour further on into the output device leads to some requirements for the database handed over with the file to be e.one thousand. printed.The system should be able to integrate or to access information that permit:

• Presetting of ink ductors and rollers, where possible
• Controlling of scaling devices for the mixture of inks
• Adding of ink recipes from data on file
• Accessing and creation of statistical information on ink consumption
• Support operator
• Request optimal set of primaries

Results

Evaluation of the early results using the ICC's arroyo to color direction highlights the lack of the required tools in the field. A user would obviously need either generic or customized profiles for the systems in the local environment. Color management systems sold today are equipped with generic profiles for nearly of the devices on the market place. A user wanting to produce a customized contour for a scanner would be adequately pleased. The scanner could measure its own scanned information and the profile generating tool tin compare the input data with measured data describing what the scanner should have detected. Well-defined tools like the IT8 targets are available for that purpose. Then are scanner calibration software packages.Output devices like monitors or printers are somewhat more difficult to be characterized since measurement devices are required. Several vendors take produced tools for monitor characterization. Characterizing the printer turns out to be somewhat more difficult. The user has to be aware of the noise underlying the signal of the printer and, to avoid problems occurring because of the dissonance, to measure a sufficient corporeality of prints to average over the dissonance. At the time this paper, the authors accept not had sufficient experience with the few printing profiling tools available to comment on their success. Thus, the experiences we depict are cases in which profiles were generated by the CMM vendors.

The outset experiences were gained while preparing the demonstrations of the work of the ICC for conferences (FOGRA conference on advances in computer publishing February 1995, Seybold Conference, Boston, March 1995). The devices used of the Seybold demonstration were 2 scanners, six computers using iv different operating systems, one dye sublimation printer, and colour management tools coming from four different vendors. The results produced proved that using dissimilar devices and tools could still atomic number 82 to comparable results. Appearance matching was used and a broad and unscientific sampling of the audience showed that the images were accepted every bit equivalent.

Due to the lack of tools, in that location are not many examples of ICC-based colour management outside of the lab environment. A proficient case of the few cases is occurred to a problem: A large magazine producer unremarkably uses rotogravure to print his products. On one occasion, he wanted to personalize the cover of the magazine which was not possible with the tools available. He decided that print the cover cover using a spider web fed starting time printing device available in another factory. His sheet fed first press had been characterized earlier, at FOGRA under standardized conditions (1) . The web fed offset printing was then set to the standardized atmospheric condition described in (1) and the profile created in for a different press was used. The contour of the proofing device (an IRIS printer) and the start contour were linked to enable the operator to simulate the last effect. The results obtained with that approach met the requirements of the advertiser and the publisher.

So far, results are positive for the ICC arroyo. Withal, changes in the color of the paper have caused some problems. If the color of the paper changes, a new contour is needed. Results signal that indicate (W. Steiger, UGRA/EMPA, St. Gallen, private communication, 1995) that the eye is very sensitive even to pocket-sized changes of the white signal of the newspaper, especially in newspaper printing. Thus, fifty-fifty minor changes in the paper require new profiles which may not be available.

Limitations of Color Management

The success of color management is express for several reasons, only iii factors seem to be most important: the average time needed to evaluate colorimetric differences in images; the statistical deviation an output device undergoes when working under usual atmospheric condition; and the absence of calibration equipment in the desktop surroundings.

The accurateness of the calculations involved have been field of study to frequent discussions. The upper limit to the accuracy appears to be given by the number of patches the system would utilize to calculate profiles for apply throughout the process. Users we approached have a profile adding process (such as in Linocolor or in the learning procedure of the neural net used past the ELTEX organization) lasting for hours after the actual measurement of color patches (which is about an hr in itself). They assumed that if the arroyo serves the business this loss of time would be justified.

The time it takes to generate a new profile appears not to be acceptable the retouching process. If the adaptation of the color data to a new color space uses the front end end for also long, the lack of productivity becomes obvious. Only algorithms that work "on the fly" seem to exist accustomed. The system used in the first ICC compatibility demonstrations met this requirement, but some practice still no have all the functionality needed for a professional use.

On the other manus, every output device undergoes some statistical deviations in the accuracy they are able to reproduce an original, fifty-fifty in typical use. In the offset and in the rotogravure procedure, these values range effectually two - iv delta Due east (11, 6) while desktop printers and proofers undergo larger errors (12, 10). The rate at which equipment drifts depends both on the hardware involved (some devices are more than variable than others), operating weather (such as power cycling), and the operating environment (temperature changes, humidity changes). Users in the field find that recalibration is desirable on a daily or at all-time weekly basis.

A concluding problem is that most desktop users exercise not take any scale tools bachelor. Of the few who do, a large percentage do non use these tool on a regular ground. Given the drift described above, users who desire accurate color reproduction need to accept admission to measurement tools and calibration software.

How Authentic Need Nosotros Exist?

Potential users of colour management need to decide just how precise a color lucifer needs to exist earlier they are statisfied. Improving accurateness costs coin to purchase more accurate measurement tools and it takes time to perform calculations to finer tolerances. Only information technology is not articulate how shut a match needs to exist to be acceptable. For case, statistical fabric evaluated by the advertising industry (18. Die Dialogmethode, equally Verkaufsgespraech per Brief und Antwortkarte, 8. Auflage, S. Voegele, Moderne Industrie, Landsberg, 1995) indicates that advertising images are browsed by a reader for an average of less than three seconds before a decision is made whether to examine the page more closely. This browsing consists of a serial of "fixations" in which the eye looks a different locations in the paradigm for an average fourth dimension of just 200 milliseconds. Unremarkably, there are some 5 to fifteen fixations for an A4 size paged. Although color attracts the eye, the fixation steps will not terminal longer, even when viewing an attractive paradigm for the offset time. It is within these one to iii seconds that the reader decides whether to examine the page closely. In dissimilarity, the person deciding whether to accept the work of the prepress shop spends much more than time -- usually several minutes -- evaluating the quality of the piece of work. Other data (13) signal that there is an inverse correlation between the time an epitome is looked at and the accuracy needed to derive a right impression of the colors used:

Comparison between reproduced re-create and original by an inexperienced user: Delta E   Approximate time to realize that difference from original 15        v Seconds  ten        10 Seconds  5         15 Seconds        

Perhaps the tolerances required for acceptance should exist based on expected viewing times.

The actual measured differences in CIELAB delta E that are needed to distinguish a colorimetric difference is still an agile expanse of enquiry and contend. Some enquiry indicates that a delta E of 1.0 is enough for an heart to differentiate between different colors when looking at colour patches such as the IT8 targets. Other research indicates that in an image taken out of a real earth surroundings values of less than two.5 delta E are non visible to the usual user. Since the color patches subtend unlike fields of vision, these results are not necessarily inconsistent. Nevertheless, they make it difficult to set an objective metric of success for color management.

We have already discussed the fact that all output devices drift out of calibration. There is some merit to the stance that color management methods demand not pursue levels of accurateness effectively than the operating tolerances of the output devices . Even so, this accurateness may be desired in order non to add possible errors due to the different processes involved in the whole color reproduction workflow.

Summary

The need for colour management results from the possibility of producing variable system configurations combining differing individual components produced by unlike manufacturers. The user is non restricted to his own specific facility simply can choose betwixt different products. Open organization concepts at the product phase make it necessary to find new ways of dealing with colour on the calculator. The ICC profile standard provides a viable solution to this problem while requiring few changes to the electric current workflow.

* The specification reported in this newspaper has been created by several engineers of the founding members of the ICC. It`s a pleasure to express cheers to Michael Stokes who intensively worked over preliminary versions of this paper and made us aware of errors and needs for farther caption.

Appendix 1

The founding members of the ICC were Adobe Systems Inc., Agfa-Gevaert Northward.V., Apple tree Computers Inc., FOGRA (honorary), Microsoft Corporation, Eastman Kodak Company, Lord's day Microsystems, Silicon Graphics Inc., Taligent Inc.

A number of computer and software manufacturers have given this problem their attention. To mention just some of the current vendors and their products will provide an overview. Doubtless, many more vendors should exist mentioned:

• Adobe: PostScript Level-ii
• Agfa: FotoFlow
• Apple: ColorSync
• Candela: Candela CMS
• Catechism
• ColorArchitect MatchMaker
• Colour Bullheaded
• Daystar: ColorMatch / ColorMatchPro (KCMS)
• EfI: EFI-Color
• Kodak: KCMS (Precision/Colorsense)
• LightSource: OFOTO, Colortron
• Linotype-Hell: LinoColor 3
• Microsoft ICM (based on KCMS Kodak)
• Pantone: POCE (LightSource)
• Photone: Photone-CMS
• Prepress Techn.: SpectreCal
• Silicon Graphics (based on Kodak CMM)
• Storm: ColorProof (Candela)
• Sun KCMS (based on Kodak KCMS)
• Tektronix: Tekcolor

In other color using industries, such as the textile industry, vendors restricting themselves to the individual market, are besides active.

References

1. BVD/FOGRA, Manual for Standardization of the Offset Press Process, Wiesbaden, 1992.

two. ISO 12647-2.

3. ISO 2846-1

4. Recommended Specifications Web Offset Publications, SWOP, Gravure Clan of America, New York, N.Y.,1988

5. Specification of the CiP3 Impress Production Format, Version 1.0, Darmstadt, 1995 .

6. One thousand. Has, Regeltechnische Characterisierung von Bogenoffsetmaschinen, FOGRA Forschungsbericht Nr. three.279, Muenchen 1993

7. M. Has, Ink command in sheet fed web outset press, Advances in Printing science and Engineering, Vol. 22, p 414 ff

8. CIE Publication 15.2, Colorimetry, Vienna, 1986

nine. International Colour Consortium Profile Format, Version iii.01, Boston, 1995.

10.Ralf Kuron, Norbert Stockhausen, Ermittlung von Parametern zur Umrechnung von PostScriptfarbdateien in den darstellbaren Farbbraum eines Ausgabegeraetes, Foschschungsbericht 6.403, Muenchen 1992

xi. K. Schlaepfer, Farbabweichungen im Tiefdruck und Rollenoffsetdruck, St. Gallen, 1985

12. S. Bruees, Ein Organisation zur Proze- und Qualitaetskontrolle in computerbasierten Publikationssystemen, PhD thesis, Muenchen 1993

thirteen. Joel Maelfeldt, FOGRA Seminar on Color in Cloth Printing, Munich, 1995

14, Cinesite Digital Picture show Center, Documentation, Revision 3.one, Cinesite, Inc.

fifteen. LeRoy DeMarsh, "Boob tube Brandish Phosphors/Primaries -- Some History", SMPTE Journal, December 1993.

xvi. Colorimetry for the boob tube primaries is from DeMarsh, see above. For estimator monitors, reference data were provided by the manufacturers.

17. Glenn Kennel, "Digital Film Scanning and Recording: The Technology and Practice,"SMPTE Journal, March 1994.

18. Die Dialogmethode, Das Verkaufsgespraech per Brief und Antwortkarte, 8. Auflage, Southward. Voegele, Moderne Industrie, Landsberg, 1995

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Source: https://www.color.org/wpaper1.xalter