Most industry analyst seem to agree that the phenomenon known as desktop publishing occurred as the result of a serendipitous emergence of the three "A" companies at the right point in time: Apple, Adobe and Aldus. Apple's user friendly operating system provided a vehicle for the traditional graphic designer to migrate from the prevalent tools of the trade to the emerging electronic medium. Adobe provided a rendering language which could rasterize the file and be interpreted by a high end print device as well as a number of existing desktop solutions such as Photoshop and Illustrator'TM that emitted into the language. Finally Aldus offered the first integrated layout package, PageMaker'. Thus was born desktop design and publishing and the link to the traditional publishing industry with Apple' s Macintosh FX model the platform of choice. It is critical to note that these tools were not the tools of the amateur or occasional user. These were the tools of professional publishers which formed the front end to complete, proprietary publishing systems from companies such as Linotype-Hell, Scitex and Agfa. An industry was in transition from high end publishing in which the graphic artists concepts and builds were constructed into plates by a cadre of professional publishers. The transition was one in which the pathway to direct to press fell more and more in the hands of the designer. Note that on the UNIX platform, Silicon Graphics made significant inroads as a high powered platform for publishing but never was able to head off the lead enjoyed by Apple. Today, of course, SGI is very successful in providing the tools for three dimensional graphics and animation. DOS and Windows never played a major role in the publishing arena, although Microsoft, as is discussed below, is making tremendous inroads into the domain. With this brief background, the focus of this presentation is on the migration of more and more capability for graphic design and layout to the hands of computer users as opposed to the migration of computer tools into the hands of the publishing professional. Today most computer owners are capable of producing the most sophisticated graphic design and publishing solutions: Output which rivals that of professionals only years before. Naturally the quality of such output may not always live to the standards of the graphic design and publishing professional, but the output is often remarkably sophisticated. So what has fostered this transition initiated by the three "A"-Companies 10 years ago and what are the directions that are emerging that will structure the future

The design of a color facsimile machine presents a number of unique challenges. From the technical side it requires a very efficient, seamless integration of algorithms and architectures in image scanning, compression, color processing, communications and printing. From the standardization side, it requires that agreements on the color representation space, negotiation protocols and coding methods must be reached through formal international standardization process. This paper presents an introduction to the overall development of color facsimile. An overview of the recent development of the international Color Facsimile Standard is first presented. The standard enables the transmission of continuous-tone colors and gray-scale images in Group 3 (over conventional telephone lines) and Group 4 (over digital lines) facsimile services, with backwards compatibility to current black and white facsimile. The standard provides specifications on color representation and color image encoding methods as well as extensions to current facsimile protocols to enable the transmission of color images. The technical challenges in implementing the color facsimile standard on existing facsimile machines are described next. The integration of algorithms and architectures in color scanning, compression, color processing, transmission and rendering of received hardcopy facsimile in a color imaging pipeline is described. Lastly, the current status on softcopy color facsimile standardization is reported.

There has been work going forward on the development of a frame of reference for locating and invoking digital information services and objects over communications systems and pathways having computational capabilities. An important concept in this context is the notion of a `digital object' as a set of sequences of bits, including a unique identifier for the object called a `handle.' A digital object may incorporate digital works and other representations of digital information in which copyright, patent, trade secret or other rights or interest are claimed, although this need not always be the case. For commercial enterprise to take full advantage of the global information infrastructure, it is helpful to develop a flexible terminology for thinking about digital information from a copyright perspective; in this regard, the concept of `digital work' will be suggested. Clearance of rights and interests in connection with the contents of digital objects should be treated separately from compliance with procedures for accessing digital objects viewed as entities that incorporate and identify contents. A suggested legal framework will be discussed.

In just 5 years, color ink-jet has become the dominant technology for printing color images and graphics in the office and home markets. In commercial printing, the traditional printing processes are being influenced by new digital techniques. Color ink-jet proofing, and concepts such as computer to film/plate or digital processes are contributing to the evolution of the industry. In industrial color printing, the penetration of digital techniques is just beginning. All widely used conventional contact printing technologies involve mechanical printing forms including plates, screens or engraved cylinders. Such forms, which need to be newly created and set up for each job, increase costs. In our era of fast changing customer demands, growing needs for customization, and increasing use of digital exchange of information, the commercial and industrial printing markets represent an enormous potential for digital printing technologies. The adoption characteristics for the use of color ink-jet in these industries are discussed. Examples of color ink-jet applications in the fields of billboard printing, floor/wall covering decoration, and textile printing are described. The requirements on print quality, productivity, reliability, substrate compatibility, and color lead to the consideration of various types of ink-jet technologies. Key technical enabling factors and directions for future improvements are presented.

Although thermal ink jet printers have gained a high market share there are still open questions left in the understanding of the processes in ink jet firing chambers. The experimental investigation of these processes is difficult due to the extremely short time durations of the different phenomena. For example, the bubble life time amounts to approximately 20 microsecond(s) . A new experimental set-up is presented to record phenomena of very short time duration like the bubble nucleation process and the beginning of droplet ejection. This set-up allows realcinematographic visualization with a local resolution of less than 1 micrometers and a time resolution of 10 ns. This also offers the possibility to investigate transient processes like the droplet ejection at high printing frequencies. The essential part of the set-up is a new high speed camera. With an exact evaluation of the digitized images the locus, velocity, and acceleration distributions of the phase interface from liquid to vapor/air can be measured. In addition the results of a numerical model with realistic geometry of the firing chamber and the nozzle have been compared with the experimental results to draw conclusions for pressure propagation in the vapor bubble.

Hewlett-Packard Company recently introduced a line of thermal ink jet printers which delivers 6 to 8 pages per minute laser parity text throughput with true 600 X 600 dpi resolution. In the development of this technology, we achieved major breakthrough in many key areas in the design of the HP 51645A ink jet print cartridge. In order to print at true 600 dpi resolution, the dot size has to be reduced proportionally from the previous 300 dpi resolution. To increase the print engine throughput to meet customer needs, firing frequency of the drop generator has to be higher than any previous thermal ink jet designs. As a result of the need to improve print quality and throughput, all fluidic dimensions in the vicinity of the ink jet drop generator have to be redesigned and scaled down. This geometric redesigning and scaling poses significant challenges to the capabilities of our manufacturing processes, leading to the redesign of the orifice plate. Major development work in ink formulation has resulted in significant improvements in printer performance as well. The pigmented ink designed for this new generation of ink jet printers provides the highest optical density and media independency to meet customer's print quality needs. The ink formulation also improves dry time so as to meet the pages per minute throughput design objective.

We show a correlation between the surface roughness of tantalum heaters in water with the temperature at which nucleation occurs at a set of fixed sites on the heater surface. The smoothest heater displayed the highest nucleation and vapor sheet formation temperatures. Experiments using degassed water indicate that some of the specific surface sites are due to air entrapped in small crevices in the tantalum. The high temperature (> 272 degree(s)C) for the nucleation indicate that the air entrapment sites are on the order of 1 - 4 nm in diameter.

The fluid flow in the thermal ink jet transducers is highly dynamic in the sense that at no time during its operation the flow reaches a steady state condition. The transient flow is affected by the inertial and viscous effects. These two effects are reflected through the inertance and resistance parameters of the transducer geometry. In this paper we will present a general background on the inertance and resistance parameters, present a method for calculating these parameters for a given 3D geometry, and briefly outline their role in the ink drop ejection process.

Today, dry process and color printers are more and more common in medical applications. The main applications for these printers are in ultrasound, nuclear medicine, medical imaging workstations and endoscopy. Each of these disciplines has its specific application requirements. Image quality and other considerations with regard to medical applications are discussed. Although the emphasis in medical imaging lies within grayscale imaging, the increased use of techniques such as doppler imaging, power doppler in ultrasound and image processing with workstations, intensify the need for high quality color output on hardcopy. For the radiology department, hardcopy must be of diagnostic quality and suitable for light box viewing. The different criteria to meet these requirements such as resolution, noise, density and physical properties are discussed. Also a short description of the implementation in the Agfa DRYSTAR 2000^TM printer and its consumables will be explained. The achieved quality level will be supported by measurements. Starting from specific image processing for grayscale imaging (such as Look Up Tables) and specific imaging processing for color imaging, a new dedicated image processing method for medical dry hard copy will be presented. Both optimal grayscale imaging and color imaging combined are needed in ultrasound. In relation to this item, some non resolved issues will be explained. As a conclusion, a brief presentation of a hospital application test, validating the system for diagnostic purposes is given.

In this paper we review image requirements and the potential use of various printing technologies to record digital diagnostic radiographic information. An analysis of limitations and advantages of alternate imaging systems compared to current laser imager/silver halide film systems will be presented. The future move to digital radiology along with its hard copy requirements will also be discussed. The winning technologies in the market place will be determined by their ability to provide adequate image quality at low cost while meeting productivity, durability, and convenience requirements. The first technology to meet these requirements will have a tremendous advantage in the market place. Medical imaging hard copy is dominated by the use of silver halide media providing monochrome images of diagnostic image quality. As new digital medical imaging modalities have emerged they have opened the door to new hard copy technologies. These new technologies have been born and nurtured outside the medical market by small markets with high image quality requirements or by large markets with lower image quality requirements. The former have tended to provide high cost, high quality solutions and the latter low cost, low quality solutions. Silver halide media still dominates, at least in part, because it provides high image quality at a relatively low cost. Yet, the trend away from wet silver halide is evident. These new hard copy technologies are being tested to determine their applicability to the medical market and are finding niches where they provide value. A clear winner that provides the required image quality at low cost has yet to emerge.

This writing describes a strategy for color registration and motion control for tandem xerography. The strategy is based on an intelligent closed-loop controller which automatically calibrates the machine against repeatable errors and compensates for long term errors due to drift. Registration errors are measured by means of a dedicated sensor. Repeatable steady and periodic, errors are characterized at long intervals and compensated by feedforward techniques. Long term drifting errors are periodically detected and corrected. Feedback control is used to counteract unexpected and uncalibrated disturbances. Measurements taken on an experimental breadboard show that registration of four xerographic engines can be maintained to within 45 microns, and that color and gray banding can be eliminated. This limit of registration accuracy is mostly due to stretch of the intermediate belt under the action of image dependent transfer forces.

We have developed high-speed color copier using electrophotographic process (called CLC1000, announced in September of 1995 in Japan.) In this color copier color image can be created by independently forming four color-images (Y, M, C and Bk) on separate four drums and then by accurately overlaying these images on the same receiver. The key challenge lies on how to correct a shift in each color position caused by environmental changes such as location and temperature and how to keep the registration accuracy. Our technologies for design and production have concentrated for resolving this problem. It has been found that the shift in each color position is caused by the change in relative position between laser-beam and drum due to the fluctuation in driving system and image-writing system. So, a mechanism controlling a laser beam relative position to the drum has been developed. This is called registration servo system. Brief explanation of the registration servo system follows. Separate four color-image patterns specially created by each shifted laser beam are transferred on the belt. The CCD in the registration search unit reads the patterns, calculates a magnitude of the shift and decomposes the magnitude into the components: (1) Magnification (M-Shift), (2) Slope (S-Shift), (3) Horizontal (H-Shift) and (4) Vertical (V-Shift). Each component is fed back to the machine in the manner: for M-shift and S-shift, a relative position of the laser beam to the drum is changed by moving reflecting mirrors, and for V-shift and H-shift, by changing a scanning timing. One laser beam (ex. M) is used as a reference for the other beams. The registration servo system is activated at a short interval when environmental conditions change largely and at a long interval when conditions change gently. In this way, a highly accurate registration is achieved.

Electroreceptors are used in many practical applications as receivers for charge. In laser xerography, the receivers are photo-sensitive. They are precharged on the surface in the dark using corona or some other device, and then selectively exposed by a laser beam to discharge the surface charge. The resulting latent image on the surface of the receiver is developed with toner of the opposite polarity. During discharge, the charge spreads in transit through the receiver thickness due to mutual repulsion of like charges, and results in a wider line width than the optical beam width used in exposure. This effect leads to loss in resolution of the developed image. In this paper we describe a generalized numerical algorithm we have developed to treat interaction between the photoreceptor and incident light for 1D images. This allows us to lay down arbitrary space and time dependent exposure profile on the photoreceptor, and study its interaction with photoreceptor design parameters. In particular, the effects studied include line broadening and solid area structure.

The market for color printers will continue to grow at a steady pace through the end of the decade. INTERQUEST expects unit shipments of color printers to grow at a 25% to 30% annual rate through the end of the decade, in the United States. Ink jet, electrophotography, and dye sublimation thermal transfer printers will enjoy the fastest growth while impact dot matrix and pen plotters will continue to lose ground.

In textile printing there are several color outputs that need to be controlled. Just as important is the color coordination of these outputs. The types of color output are the video display on the textile design system (CATD for Computer Aided Textile Design), the color scanner, the color pattern printer, and the actual pattern printed on the textile substrate. Each of these systems has its own gamut(s) that is partially overlapping of the others and will require mapping and/or truncation to adequately represent the colors of the final print in the other systems. One of the goals of instrumentation systems is to control these devices so that the message of the pattern is the same on all four media. To accomplish this is a significant task that has yet to be completed to meet the rigorous requirements of the textile and apparel industries. Several of the major problems and directions for solving them will be discussed in this paper. These include getting good instrumental measurements, translation of data between systems, and specific problems related to the hard copy output.

Color definition and data exchange continue to be dominant themes in both the US and international graphic arts standards activity. However, there is a growing understanding of the role that metrology and printing process definition play in helping define stable process conditions to which color characterization data can be related. Standards have already been published that define the requirements for color measurement and computation, scanner input characterization targets, four-color output characterization data sets, and graphic arts applications of densitometry. Work continues on standards relating to ink testing and ink color specifications. The numerical specifications of SWOP proof printing have been captured in ANSI standard CGATS.6-1995. Work has been completed, and Technical Report ANSI CGATS TR 001-1995 has been published, that relates the colorimetry of the printed sheet to the CMYK input for press proofing meeting SWOP and CGATS.6 specifications. Work is ongoing to provide similar data for other printing processes. Such color characterization data is key to the development of color profiles for standard printing conditions. Specifications for color profiles, to allow color definitions to be moved between color management systems, are being developed by the International Color Consortium. The existing graphic arts data exchange, process control, and color related standards are summarized and the current status of work in progress is reviewed. In addition, the interaction of the formal standards programs and other industry-driven specification activity is discussed.

A paper presented by the NPIRI Color Measurement Task Force at the 1993 annual TAGA meeting reports that colorimetric measurements made with spectrophotometers manufactured by the same company and with the same geometry can differ by 0.7 to 1 .7 CLab iXE and that values from instruments madeby different manufacturers with the same geometry can differ by 1 .5 to 3 .0 AE'. For the mostpart, we can attribute these measured differences to the instruments since the ink onpaper samples used in this study were prepared using methods which insured minimum differences in the colorimetric and physical characteristics ofthe samples. The causes of these instrument-to-instrument measurement differences can be segregated into two general categories: errors from physical stmcture and adjustment ofthe instrument (e. g. wavelength errors) and errors from interaction ofthe instrument with the samples2. During the past fiveyears, the author has written several papers on one ofthe instrument-sample error mechanisms3'4'5'6. This mechanism was termed translucent blurring error in an investigation that was done by Hsia at NIST (ne NBS)7 and edge loss error in early plastics measurement investigations done by Atkins and Billmeyer8. The author coined the term lateral diffusion error (LDE) about three years ago because he felt that it better described the mechanism of this error: the lateral diffusion of light in the sample to areas not viewed by the instrument detection optics.

The accurate measurement of the colorimetry of a CRT is a challenging task that is affected by many factors. New advances in electronics and computer technology have enabled the development of high quality, low cost, sensing mechanisms. The integration of color management facilities into computer operating systems has led to increased consumer demand for on-line, or embedded, measurement and control capability of individual color displays. The embedded measurement device may be attached either to the monitor directly or to the host computer which drives the monitor. The demand for lower cost measurement does not mean that specifications can be compromised. The techniques for achieving these goals are described in this work.

It is generally believed that the most accurate means of measuring the CIE tristimulus values X, Y, Z or chromaticity coordinates x,y from a display is by using a spectroradiometer. Nevertheless, tristimulus colorimeters employing three or four colored filters find wide use because of their simplicity and lower cost. These devices cannot be calibrated to give accurate results in all situations because the spectral responsivities of their filtered detectors are not exactly the CIE color-matching functions. However, for a display that produces a linear superposition of three primary colored lights of fixed spectra, a tristimulus colorimeter can be correctly calibrated to measure all colors on that display. Signals from all of the filtered detectors are used to compute each of the X, Y, z values. The calibration matrix is computed by data fitting to a reference colorimeter. An improvement to the previously published method is reported, an a numerical example is shown. This technique is more tractable with today's digital instrumentation than it was when it was discovered, yet it remains underused. The American Society for Testing and Materials, through its Committee on Color and Appearance, is revising its standard on display measurements using tristimulus colorimeters to encourage the adoption of the technique.

A methodology has been developed to digitize images from photographic color paper (reflection prints) and store the spectral information as a function of the three dye density basis functions inherent to the paper film type. The result is a highly accurate digitization of the spectral information at each spatial pixel that can be digitally stored with very little additional storage space over conventional RGB-type methodologies.

The digitization of photographs by estimating and recording the dye concentrations of each pixel can be used for the device-independent and highly accurate storage and reproduction of photographs. Previous work on this subject has concerned itself with the color accuracy without regard to spatial considerations. This paper represents a beginning in the study of effects and limitations of the spatial resolution of this process, and more importantly of the subtle relationship between spectral accuracy and spatial resolution. Two such relationships are introduced here: the first is spectral inaccuracy due to the spatial integration over the detection spot; and the second is the effect of multiple light bounces within the gelatin of the photographic paper.

Direct thermal printing is a relatively old technology and has been used in hardcopy printing for many years. In this process, heat from a thermal print head causes a transparency or reflection change on a thermally sesitized film or paper. The modern thermoprinters use contact recording method and forms the image with help of thermal print head -linear array of small heating elements. The resolution and time of output process are limited by the heating element size (2 to 10 per mm) and time delay for heating ofthe thermohead element up to temperature of thermal media modification which leads to change of transparency or reflection.' The problem of resolution and time delay may be effectively solved by application of a focused laser beam as a non-contact heating source. This paper deals with the investigation of standard thermal materials on transparent and reflective substrates as a recording media in the process of laser thermal recording. As usual, such kind of materials are used for hard copies output in the process of direct thermal imaging on thermal printers. The paper describes the results ofthe test records on transparent and reflective thermal media samples on polymer and paper substrates.

Serial storage of the pre-rastered half-tone images by a photothermoplastic media is investigated and the results are discussed. The recorded images are regarded as color-divided components of a polychromatic image, interference rastering serving as an encoding tool for color-divided images. The recorded images are characterized by the diffraction efficiency (DE) of each color-divided component being not less than 3.5%, the maximum background DE being 0.2%. KEYWORDS: electrography, color image recording, photothermoplastic media, rastered images.

Error diffusion is an important technique for digital halftoning. It outperforms many other traditional halftoning methods in terms of gray fidelity and detail rendering. A drawback associated with the original error diffusion using the Floyd and Steinberg coefficients is that correlated patterns, sometimes called `worms', can appear in the shadow and highlight areas. The error spreading process can be represented by a linear filter. Non-symmetric diffusion of errors is the source for worm artifacts. In this paper, a new error diffusion weight set is presented, which has two advantages over the standard weights. First, it propagates the error in a more symmetrical manner, and consequently significantly reduces worm artifacts in shadow and highlight regions. Secondly, the new weights involves multiplication of numbers that are powers of 2. As a result, all the multiplications in calculating the error propagation can be implemented as bit shifting, which simplifies both software and hardware implementation.

In a previous paper, we proposed a multi-level error diffusion method for improvement of image quality in digital halftoning. Those obtained images were evaluated by using the quantization levels. However, this quality criterion was not good parameters for evaluation of images. In this paper, RMS (Root Mean Square) granularity and SNR (Signal to Noise Ratio) were introduced to evaluate the multi-level error diffusion images recorded by color printers with the resolution of 200 DPI and 400 DPI. RMS granularity and SNR of eleven images with different quantization levels produced by the method were calculated. The results shows that both physical values are well correlated to the observer rating values.

The mechanism of stochastic screening and its apparent advantages and disadvantages over conventional halftoning have been frequently discussed. A commonly believed advantage of stochastic screening is that it is more stable on the press. To quantify this, an experiment was conducted to examine its print characteristics under some 27 different paper substrates. The test results indicate that the print characteristics of the stochastic screen exhibits less change than its conventional counterpart under a wide range of paper stocks.

The rapid evolution of the low-cost color printing and image capture markets has precipitated a huge increase in the use of color imagery by casual end users on desktop systems, as opposed to traditional professional color users working with specialized equipment. While the cost of color equipment and software has decreased dramatically, the underlying system-level problems associated with color reproduction have remained the same, and in many cases are more difficult to address in a casual environment than in a professional setting. The proliferation of color imaging technologies so far has resulted in a wide availability of component solutions which work together poorly. A similar situation in the desktop computing market has led to the various `Plug-and-Play' standards, which provide a degree of interoperability between a range of products on disparate computing platforms. This presentation will discuss some of the underlying issues and emerging trends in the desktop and consumer digital color imaging markets.

As we witness the coming to maturity of color management technology, questions still remain: have we really solved the big problem of color use on the computer? Is the current solution in the right solution? What are the real obstacles in making computerized color work productive? Color fidelity between devices has been (still is?) a big problem and much effort and progress has been made towards solving it. Are there other problems with color work on the computer? For most people using color is difficult. Instead of being easier, working with color on the computer is more arduous and complex than when using traditional methods. How can we make working with color less of an effort and more enjoyable for computer users? What are the obstacles preventing computer developers from doing this? How do we really empower computer color users? By transforming the way that color work is done: redefine the place color takes in computer systems, provide real tools to manage color work, and provide tools that make computerized color work natural, creative and satisfying.

A method is proposed for solving the mapping problem from the 3D color space to the 4D CMYK space of printer ink signals by means of neural network. The CIE-L*a*b* color system is used as the color space. The color reproduction problem is considered as the problem of controlling an unknown static system with four inputs and three outputs. A controller finds the CMYK signals necessary to produce the desired L*a*b* values from a printer. Our solution method for this control is based on a two-phase procedure. Validity of our method is shown in an experiment using a dye sublimation printer.

An ideal system of colorimetry should provide measures agreeing to what we see in three respects: color specification, difference and appearance. A successful method to quantify these measures depends upon the reliability of psychophysical experimental data. These data sets have been accumulated and were used to derive the LLAB model. The model includes two parts: a chromatic adaptation transform and a uniform color space. Tristimulus values under a particular set of illuminant/observer conditions are transformed to those of D65/2 degree(s) conditions via a chromatic adaptation transform. A modified version of CIELAB is then used to calculate six perceived attributes: lightness (L_L), redness-greenness (A_L), yellowness-blueness (B_L), colorfulness (C_L), hue angle (h_L) and hue composition (H_L). The model gives similar degree of prediction in comparison with the other state of the art models using the accumulated data sets. The LLAB model demonstrates that it is possible to achieve a system, which provides precise measures to quantify color match, difference and appearance.

The goal of a general purpose color scanner is to determine the color of an object in a device independent color space, such as the CIE XYZ tristimulus space. Raw sensor measurements from scanners rarely correspond to CIE XYZ due to design and realizability constraints. The conversion of data from scanner RGB to a device independent color space introduces errors due to the non-colorimetric nature of the scanner and due to the noise present in measurements. This paper analyzes the relative contributions of these two components to color errors. This analysis allows the designer to determine the most cost effective device meeting required specifications.

A new TTL white balance method is studied to get a good white balance for a wide variety of illumination in digital camera system. Parameters of white balance are decided only by analyzing a single shot of images in this method. A locus of a white point under various illumination is plotted in a certain 2D color space, and the point in the space that is assumed to correspond to a white point in the scene is compared to the locus. Four complementary color filters (cyan, yellow, magenta and green) attached on a CCD imager generate four color signals, which are transformed by a 3 X 4 matrix into three of red, green and blue. The adaptive matrix method corresponding to the color temperature of illumination is compared to the fixed matrix method. Calculating the adaptive matrix is based on the Von Kries Law.

The coding of color images is usually confined to coding the color appearance for the illumination present at acquisition time. However, an exact reconstruction of a coded and transmitted document should produce the same color appearance as the original under variable illuminations. In this work we develop a representation of the necessary information to ensure such a color constancy. The only precondition is the absence of mutual illumination as a small but reasonable restriction to the type of illumination. The proposed image representation is developed to a complete image coder concept. Using this concept a hierarchical image description is achieved introducing a minimal color difference.

A common approach for color image processing is to first transform the RGB image to a new color space (such as LHS and YIQ), do the processing, and then transform back to RGB space. in many applications, only the luminance component is processed, and the hue and saturation are preserved. However, when the processed values in the new color system are transformed back to RGB, the transformed values may lie outside the RGB cube. Some researchers clip the processed luminance values before transformation from the processing color space to RGB space. This can lead to a loss of luminance contrast because many pixels may be clipped to approximately the same luminance value. Instead of clipping the luminance, this paper investigates clipping the saturation component. The gamuts of two color coordinate systems, LHS and YIQ, are studied. The procedures for saturation clipping are presented for both systems. Experimental results of clipping saturation and luminance in histogram equalization are presented in the paper. The results show that the contrast of the processed image is much better when saturation clipping is used. The luminance of the image can utilize the full dynamic range, thereby resulting in improved contrast enhancement.

The gamut mapping procedures transform the colors of the original image into the colors that can be reproduced by another device, according with different reproduction criteria. This paper discusses three gamut mapping procedures: gamut clipping, white shifting technique recently introduced by Konica, and an example of UltraColor technique used by Kodak. A new proposed method that maps the out of gamut colors to the gamut colors based on the morphing technique along the constant angle direction or constant device hue in CIELAB or CIELUV is investigated. The mapping procedures dependent on the content of the image are compared with the procedures based only on the device to device gamut mapping. The image dependent mapping procedures exploit more efficiently the potential of adaptation of the observer eye to the contrast of the image than the device mapping methods and conduct to better results. A 3D rendering procedure is used to illustrate different gamut devices and to compare the effect of mapping procedures. The CIELAB and CIELUV color spaces are compared for optimum performance of mapping of the outside gamut colors from one device to another. The mapping methods dependent on the content of the image are evaluated using the 3D histogram visualization technique simultaneously with the gamut visualization. The techniques are applied for simulation on the CRT of the different reproduction media.

In order to systematically evaluate different gamut mapping algorithms, we have simulated gamut mapping on a CRT using simple rendered images of colored spheres floating in front of a gray background. Using CIELab as our device-independent color space, cut-off values for lightness and chroma, based on the statistics of the images, were chosen to reduce the gamuts for the test images. The gamut mapping algorithms consisted of combination of clipping and linearly mapping the original gamut in piecewise segments. Complete color space compression in RGB and CIELAB was also used. Each of the colored originals (R,G,B,C,M,Y, and Skin) were mapped separately in lightness and chroma. In addition, each algorithm was implemented with saturation (C*/L*) allowed to vary or remain constant. Using a paired-comparison paradigm, pairs of test images with reduced color gamuts were presented to twenty subjects along with the original image. For each pair the subjects chose the test images that better reproduced the original. Rank orders and interval scales of algorithm performance with confidence limits were then derived. Certain algorithms were found to perform best consistently over image color. For chroma mapping, clipping of all out-of-gamut colors while keeping lightness constant was the most preferred method. For lightness mapping at the top of the gamut, a particular piecewise mapping technique while keeping saturation constant was preferred. For lightness mapping at the bottom the results gave an indication of the type of algorithm that might be best while keeping chroma constant. The choice of device-independent color space may also influence the choice of gamut mapping algorithm.

One of the major challenges in the prepress environment consists of controlling the electronic color reproduction process such that a perfect match of any original can be realized. Whether this goal can be reached depends on many factors such as the dynamic range of the input device (scanner, camera), the color gamut of the output device (dye sublimation printer, ink- jet printer, offset), the color management software etc. It is obvious that the reliability or, rather, the reproducibility of a particular device is of extreme importance in order to have a permanently correct color characterization. A technique which is often used to ensure this reliability is to carry out a local 1D calibration. Through this 1D calibration the particular device is brought into a reliable and generic state. Applying 1D calibration curves is not only useful to create reliable devices but can also be used to model devices more accurately, at least, if these calibration curves are carefully selected. In this article, we will discuss the overall suitability of applying 1D precompensation curves before applying colorimetric characterization. More specifically, we address problems related to the reliability of devices and the quality of the color characterization. The use of precompensation curves for calibration purposes is merely restricted to output devices. For input devices, precompensation curves are mainly used for quality purposes. Indeed, the careful selection of so-called input luts (lookup tables) is very important to have good-quality scans. In addition, we discuss how the so-called gamma curves relate to these precompensation curves for both scanners and monitors. This article is organized as follows. In the first section, we discuss the benefits of 1D precompensation curves for modeling output devices. We will cover both topics related to the calibration and the mathematical modeling of output devices. In the second section, we address several issues related to the characterization of input devices. We point out how the choice of suitable input luts (gamma curves) and the dynamic range affect the quality of the scanned image. As a case study, we discuss some results we obtained in applying color corrections on scanned negative originals. In the third section, we discuss how the gamma curves used during scanning relate to the gamma characteristics of the monitor and will try to remove some confusion which currently exists in this area. In the fourth section, we summarize the discussed topics and discuss them from an application's point of view.

Printer characterization and color correction are often complex transformations, and are derived with numerous measurements or printer models. There are many sources of errors in these transforms, including inaccuracies in lookup table approximation, errors in the printer model, noise in the data, and spatial and temporal non-uniformities in the printer. A method is proposed to increase the accuracy of an existing printer transform with a relatively small number of refinement measurements. A weighted linear least-squares regression technique is used to improve the fit of the printer response to the refinement data. The hypothesis is that a locally linear transform can adequately capture the difference between the true printer transform and its approximation. In contrast to existing approaches that only refine the individual C, M, Y, K responses, the proposed method attempts to account for cross-colorant interactions by using mixed colors in the refinement set. Furthermore, the refinement data is not restricted to lying on a regular grid, and can be freely chosen based on any a priori knowledge about the printer. The approach is tested for two related transforms: the characterization transform which maps CMYK to L*a*b*; and its inverse, the color correction transform that maps L*a*b* to CMYK. Results show an improvement in transform accuracy with a relatively small number of measurements.

This paper investigates the development of printer device profiles used in color document printing system environments when devices with intrinsically different gamut capabilities communicate with one another in a common (CIELAB) color space. While the main thrust of this activity focuses on the output printer, namely the Xerox 5760 printer, and its rendition of some device independent image description, characterizations are provided which investigate relative areas of photographic, monitor, and printer gamuts using a visual hue leaf comparison between devices. The printer is modeled using 4th-order polynomial regression which maps the device independent CIELAB image representation into device dependent printer CMYK. This technique results in 1.89 AEEavg over the training data set. Some key properties of the proposed calibration method are as follows: (1) Linearized CMYK tone reproduction curves with respect to AEEpaper to improve the distribution of calibration data in color space. (2) Application of GCR strategy and linearization to the calibration target prior to the regression on the measured CIELAB and original CMY values. Each strategy employs a K addition/No CMY removal method which maximizes printer gamut and relies on the regression to determine the appropriate CMY removal. The following GCR strategies are explored: CMY only (0% K addition), 50% K addition, 100% K addition, and non-linear K addition. A library of image processing algorithms is included, using LabView object oriented programming, which provides a modular approach for key color processing tasks. In the user interface, an image is selected with appropriate GCR strategy, and the program operates on the image. In general, the pictorial image quality is excellent for each GCR strategy with subtle differences between GCR approaches. Quantitative analysis of Q60 color matching performance is included.

The Hexachrome Hi-Fi colorant set has added Orange and Green to the normal Cyan, Magenta and Yellow inks used in the extant printing process. The new inks have been added to expand the gamut of printable colors. This new ink set maximizes the total volume of the printable gamut. Therefore, both lightness and chromaticity bounds were considered in the design of the new Hexachrome ink set. This method of adding extra inks is being explored by others to develop richer reds, greens and blues in other reproduction techniques. These new inking systems require new measurement standards to control ink density, dot gain and ink trap on press. Spectrophotometery is suggested as a new standard to control the complex interaction of these new ink combinations. The use of spectral tags is now possible because of the introduction of low cost spectrophotometers. These new instruments will allow inks to be completely described by their spectral signatures. The establishment of spectral signatures as the new standard instead of density will allow new inks to be used and controls to be specified without having to define yet another set of status filters. Tags are being employed to specify the targeted use of color images in a document. Recently the ability to add a PostScript colorant tag has been made possible with the ColorTron spectrometer and software developed by Light Source Computer Images. These colorant tags can be added to the image files to completely describe the preferred reproduction. These can indude the overprint ink spectra which better specify the interactions of the primary ink sets. The new specification should also include measurement conditions so that the control conditions can be accurately repeated at any location. The world of printing is no longer an isolated community where a single measurement instrument was used to control a press. In this production scenario, the repeatability of the instrument was more important than accuracy. With image files now being distributed widely over electronic networks , the need for accuracy, precision and known measurement method is becoming paramount in the control of printing dependent on the new extra-trinary processes.