This PDF file contains the front matter associated with SPIE Proceedings Volume 7241, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Visual experiments, if performed in a traditional way, require asking participants to go to a laboratory, where displays are calibrated and illumination conditions are set in a convenient way. In recent years there has been an increasing interest in performing the experiments "out of the lab", with the aim of reducing costs, increasing the number of participants, and differentiating the population. The equivalence of the response of visual experiments performed in controlled and uncontrolled contexts is an open question which calls for research. In this work we aim at analyzing more deeply the equivalence between "controlled" and "uncontrolled" that we found in a previous study of the authors on the comparison of visual preferences for printed images. In particular, we are interested in understanding if, and to what degree, the uncontrolled experiments require actually more participants in order to average out the effects of the many uncontrolled parameters which may affects the response. In addition we aim at exploring the relationship, if any, between our previous conclusions and the difference in the attributes of the images for which the observers were asked to express their preference.

Huge number of historical materials and cultural properties in museums are investigated based on scientific and chemical analysis techniques, however these techniques require specific equipments with difficult operations. In this research, a practical investigation system is developed to provide convenient way for investigating color information in variety of materials as the first step of the investigation process. The system consists of a data projector and a digital camera, and the system is examined to detect metameric color area as an example of investigation purposes. In this research, the data projector has a role of illuminator to yield illuminant metamerism, and the camera takes sequential images under different illumination colors created by the projector. In the experiment, seven colors of illumination are created by the projector, then images are taken under each colored illumination. The Euclid distance in the RGB space between a predetermined reference pixel and test pixels is calculated in each of taken images. These distances are compared with thresholds determined by using a metamerism test chart. The proposed system was examined for the test charts and Japanese authentic wooden prints, and the experimental results showed that the system could offer convenience as the first investigation of the materials.

Recently, tone reproduction is widely used in the field of image enhancement and HDR imaging. This method is especially used to provide the proper luminance so that captured images give the same sensation as the scene. As a result, we can get high contrast and naturalness of colors. There is ample literature on the topic of tone reproduction that has the objective of reproducing natural looking color in digital images. In recent papers, IMSR (Integrated multi-scale Retinex) shows great naturalness in the result images. Most methods, including IMSR, work in RGB or quasi-RGB color spaces, although some method adopted the use of luminance. This raises hue distortion from the point of the human visual system, that is, hue distortion in CIELAB color space. Accordingly, this paper proposes an enhanced IMSR method in a device-independent color space, CIELAB, to preserve hue and obtain high contrast and naturalness. In order to achieve the devised objectives, a captured sRGB image is transformed to the CIELAB color space. IMSR is then applied to only L* values, thus the balance of colors components are preserved. This process causes unnatural saturation, therefore saturation adjustment is performed by applying the ratio of chroma variation at the sRGB gamut boundary according to the corrected luminance. Finally, the adjusted CIELAB values are transformed to sRGB using the inverse transform function. In the result images of the proposed method, containing both high and low luminance regions, visibility in dark shadow and bright regions was improved and color distortion was reduced.

Color constancy is a feature of the human color perception system which ensures that the perceived color of objects remains relatively constant under varying illumination conditions, and therefore closer to the physical reflectance. This perceptual effect, discovered by Helmholtz, was formalized by Land and McCann in 1971, who formulated the Retinex theory. Several theories have ever since been developed, known as Retinex or color constancy algorithms. In particular an important historic variant was proposed by Horn in 1974 and another by Blake in 1985. These algorithms modify the RGB values at each pixel in an attempt to give an estimate of the physical color. Land's original algorithm is both complex and not fully specified. It computes at each pixel a stochastic integral on an unspecified set of paths on the image. For this reason, Land's algorithm has received many recent interpretations and implementations that attempt to tune down the excessive complexity. In this paper, a fast and exact FFT implementation of Land's, Horn and Blake theories is described. It permits for the first time a rigorous comparison of these algorithms. A slight variant of these three algorithms will be proposed, that makes them into contrast enhancing algorithms. Several comparative experiments on color images illustrate the superiority of Land's model to manipulate image contrast.

This paper proposes a computer vision system for improving the image quality around a steady gaze point on a display device. We assume that one observes a localized small area of the displayed image, rather than the whole image, because of a limited visual angle. The computer vision system consists of two subsystems which are an eyegaze detection subsystem and an image quality improvement subsystem. The eyegaze detection subsystem tracks a human gaze point on the display. A tracking algorithm is developed for capturing a human face from a single monocular camera without using any special devices. The image quality improvement subsystem performs a localized Retinex algorithm. Although the conventional algorithms contain a large number of complex computations, the localized algorithm is devised for performing the Retinex computation in high speed for only a localized part within the whole image. The combined system is developed so that the image quality is improved in real time within just local region around the detected gaze point. We make an experimental system consisting of an off-the-shelf digital video camera and a personal computer. The whole performance of the computer vision system is examined experimentally on subjective assessment and processing time.

With the development of fast liquid crystal cells and with advent of backlight units with separate red, green and blue light emitting diodes also first commercial color sequential display emerge. Another technique in commercial application proposes implementing more than three subpixels and thus enhanced color gamut by using multiple color primaries. Also the combination of both color mixture techniques is possible. It is thus desirable to have a simulation workbench at hand that is flexible enough to adapt to the various possibilities of subpixel design and color sequences in display design to evaluate the displayed image in advance. The combination of a multiprimary display model, which can emulate a multiprimary display on a standard RGB LC display, and a spatio-temporal model, that describes LC pixel behavior to arbitrary input signals over time, provides means for simulating the perceived image of a color-sequential display behavior. This article describes the combined model and gives also simulation results that compare advanced displays to conventional vertical stripe RGB LC display.

Displays tends to expand its color gamut, such as multi-primary color display, Adobe RGB and so on. Therefore displays got possible to display high chroma colors. However sometimes, we feel unnatural some for the image which only expanded chroma. Appropriate gamut mapping method to expand color gamut is not proposed very much. We are attempting preferred expanded color reproduction on wide color gamut display utilizing high chroma colors effectively. As a first step, we have conducted an experiment to investigate the psychological effect of color schemes including highly saturated colors. We used the six-primary-color projector that we have developed for the presentation of test colors. The six-primary-color projector's gamut volume in CIELAB space is about 1.8 times larger than the normal RGB projector. We conducted a subjective evaluation experiment using the SD (Semantic Differential) technique to find the quantitative psychological effect of high chroma colors.

Instead of colorimetirc color reproduction, preferred color correction is applied for digital TVs to improve subjective image quality. First step of the preferred color correction is to survey the preferred color coordinates of memory colors. This can be achieved by the off-line human visual tests. Next step is to extract pixels of memory colors representing skin, grass and sky. For the detected pixels, colors are shifted towards the desired coordinates identified in advance. This correction process may result in undesirable contours on the boundaries between the corrected and un-corrected areas. For digital TV applications, the process of extraction and correction should be applied in every frame of the moving images. This paper presents a preferred color correction method in LCH color space. Values of chroma and hue are corrected independently. Undesirable contours on the boundaries of correction are minimized. The proposed method change the coordinates of memory color pixels towards the target color coordinates. Amount of correction is determined based on the averaged coordinate of the extracted pixels. The proposed method maintains the relative color difference within memory color areas. Performance of the proposed method is evaluated using the paired comparison. Results of experiments indicate that the proposed method can reproduce perceptually pleasing images to viewers.

Large-scale, direct view TV screens, in particular those based on liquid crystal technology, are beginning to use LED (Light Emitting Diode) backlight technology. Conservative estimates show that LED-LCD TVs additional cost will be compensated by reduced power consumption over average operational lifetime. Local dimming not only promises power savings but also improving additional features such as overall image contrast and color gamut. Based on a simplified human visual model with regard to content dependent color discrimination and local adaptation possible tradeoffs with regard to color uniformity, viewing angle, local contrast, and brightness variations are being discussed. Comparing an 'ideal reference' (input to elaborated model) with the output of a tunable model enabled estimating a threshold of artifact visibility for still images as well as video clips that were considered relevant. Overall image quality with regard to dynamic contrast as well as dynamic color gamut, spatially and temporally, was optimized after having obtained visibility thresholds. Finally, some cost functions are proposed that enable optimizing most important color quality parameters.

Nowadays, multi-domain vertical alignment (MVA) LCD technology is becoming the mainstream approach for LCTV industry due to its high contrast ratio and wide viewing angle property. However, like many other types of LCD devices, MVA still has the problem of color shift, namely color washout, between normal and oblique viewing angle. In particular, MVA shows an evident gamma curve distortion at large oblique viewing angle. This paper formulates the MVA LCTV color performance in two stages. First, an in-depth LCD characterization was performed on an MVA LCTV with consideration of spectral characteristic, backlight leakage, sub-pixel crosstalk, primary shift. Also, micrograph based sub-pixel analysis was employed and suggested that the off-axis color shift problem of MVA can be improved by using dual sub-pixel technology. Next, a generic LCD color model was proposed to relate the RGB input with the output tristimulus value in XYZ. Sub-pixel based image rendering was performed and the results show the feasibility of LCD color prediction with high colorimetric accuracy both at on-axis and off-axis viewing condition by using the proposed generic color model.

Gray level reproduction in dark areas is one of the major image quality issues of PDP(Plasma Display Panels) that represents gray levels with pulse count modulation. Error diffusion and dithering have been frequently utilized for smooth tone reproduction in dark areas. However, they may result in side effects such as the visibility of minor pixels, flickers and/or motion artifacts. This paper presents a framework to evaluate the performance of gray level reproduction algorithms for PDPs. Various factors affecting the quality of gray level reproduction in dark areas are introduced. Spatiotemporal luminance variations are proposed to measure the performance of the gray level reproduction. Experimental results indicate that the proposed method faithfully represents the performance of gray level reproduction capability of PDPs.

In this paper the performance of screen compensation based on previous work by Nayar et al. and Ashdown et al. and five different camera characterization methods are evaluated. Traditionally, colorimetric characterization of cameras consists of two steps; a linearization and a polynomial regression. In this research, two different methods of linearization as well as the use of polynomial regression up to fourth order have been investigated, based both on the standard deviation and the average of color differences. The experiment consists of applying the different methods 100 times on training sets of 11 different sizes and to measure the color differences. Both CIELAB and CIEXYZ are used for regression space. The use of no linearization and CIELAB is also investigated. The conclusion is that the methods that use linearization as part of the model are more dependent on the size of the training set, while the method that directly convert to CIELAB seems to be more dependent on the order of polynomial used for regression. We also noted that linearization methods resulting in low error in the CIEXYZ color space do not necessarily lead to good results in the CIELAB space. CIELAB space gave overall better result than CIEXYZ; more stabile and better results. Finally, the camera characterization with the best result was combined into a complete screen compensation algorithm. Using CIELAB as a regression space the compensation achieved results between 50 an 70 percents more similar to the same color projected on a white screen than using CIEXYZ (as measured by a spectrophotometer, comparing absolute color difference in CIELAB) in our experimental setup.

Subjective image quality is one of the most important performance indicators for digital TVs. In order to improve subjective image quality, preferred color correction is often employed. More specifically, areas of memory colors such as skin, grass, and sky are modified to generate pleasing impression to viewers. Before applying the preferred color correction, tendency of preference for memory colors should be identified. It is often accomplished by off-line human visual tests. Areas containing the memory colors should be extracted then color correction is applied to the extracted areas. These processes should be performed on-line. This paper presents a new method for area extraction of three types of memory colors. Performance of the proposed method is evaluated by calculating the correct and false detection ratios. Experimental results indicate that proposed method outperform previous methods proposed for the memory color extraction.

A series of psychophysical experiments using categorical judgment method was carried out to develop a colour naturalness metric (CNM) for evaluating image quality of mobile displays. These experiments included colour naturalness judgment and image-quality difference judgment. Through the former one, CNMs were trained and the latter experiment tested the metrics. Two types of CNMs were newly proposed: nonlinearly decaying CNM and linearly decaying CNM. In the CNMs, it was assumed that one familiar object in an image played a critical role to judge the colour naturalness of the whole image. Through a performance comparison between objects' models, one critical object in a scene was selected and with the critical object's model, the whole scene's colour naturalness was predicted.

Our projects are founded on the principles of Color Universal Design (CUD), the objective of which is to promote public information systems, such as train maps, which feature colors recognizable to all color vision types1). In this paper, we were looking for a red which would be clearly distinguishable protan-vision people who see some tone of red as a dark color and consequently confuse it with black. These potentially kinds of red were represented on the Yokohama City Subway map, which we were presented with. We at the CUD believe it is possible to establish color design which is easily distinguishable to people of all color-vision types in order to facilitate excellent visual communication.

Humans can put different colors together and categorize them as "red", "yellow", or "orange" etc. This is called categorical color perception. We applied this property of human color vision to area segmentation for road images in order to compensate color tone change of road images depending on light condition on a road. Basic map of categorical colors is constructed in the L*a*b* space based on the color naming experiment. Area segmentation was done by assigning one of the 14 categorical colors to each pixel. Results were successful, even without any noise reduction technique, A shifted database of categorical colors for images with orangish tone is also prepared by trial and error. Pseudo-color-constancy is successfully obtained for the images of orangish tones using the shifted database. To deal with the lightness change depending on the change of sunlight along the time of day, an appropriate value was added to the lightness of each pixel of the original image. Satisfiable area segmentation was obtained in this case, too. This method indicates the possibility of implementation of color constancy property for color image processing of road scene.

In this paper, we have clarified the relationship between ambient illumination and psychological factors in viewing of display images. Psychological factors were obtained by the factor analysis with the results of the semantic differential (SD) method. In the psychological experiments, subjects evaluated the impressions of displayed images with changing ambient illuminating conditions. The illumination conditions were controlled by a fluorescent ceiling light and a color LED illumination which was located behind the display. We experimented under two kinds of conditions. One was the experiment with changing brightness of the ambient illumination. The other was the experiment with changing the colors of the background illumination. In the results of the experiment, two factors "realistic sensation, dynamism" and "comfortable," were extracted under different brightness of the ambient illumination of the display surroundings. It was shown that the "comfortable" was improved by the brightness of display surroundings. On the other hand, when the illumination color of surroundings was changed, three factors "comfortable," "realistic sensation, dynamism" and "activity" were extracted. It was also shown that the value of "comfortable" and "realistic sensation, dynamism" increased when the display surroundings were illuminated by the average color of the image contents.

The conventional understanding of opponent colors has red and green as one axis and yellow and blue on a second axis. This perceptual opponency is a result of the trichromatic nature of human color vision in combination with subsequent processing in the visual system. This red-green and yellow-blue opponency is fundamental to many different color spaces. CIELAB, CIELUV, CIECAM02, IPT, YCC and more all incorporate this concept of chromatic opponency. In most cases the yellow and blue opponent axes are reasonable. However for the red-green axis it is more like a purplegreen axis due to a consistent, significant bending of the red-green axis. Is dark purple the opposite of green? This paper summarizes the result of analyzing a wide range of color spaces based on their actual opponency. The consistent limitation of a shared matrix formulation for opponency is discussed and finally a simple, invertible color space is considered. The angular differences between quadrants and computed antonyms is shown to be significantly more consistent using this hypothetical alternative color space.

We are currently researching a next-generation broadcasting system named "Super Hi-Vision", which provides images with much higher resolution and quality than a high definition television, and are developing displays for this system. We have developed a projector which can display the high-resolution images of Super Hi-Vision (7680x4320 pixels) and has a high dynamic range of 1.1 million to 1. This projector features a serial combination of two modulation blocks: the first block for chrominance modulation and the second block for luminance modulation. While a conventional projector has one modulation block that contains three devices to modulate red, green, and blue light, our projector has another modulation block that contains a device for luminance to further modulate the combined RGB modulated light. This configuration enables the projector to output high-resolution color images by combining three low-resolution devices for chrominance modulation and one high-resolution device for luminance modulation. As a high-resolution device, we have newly developed a 1.75-inch liquid crystal on silicon device with 8192x4320 pixels. In addition, the dynamic range is dramatically improved because this dual modulation scheme minimizes the black levels in projected images. We demonstrated that our projector displays Super Hi-Vision color images and that it has an extremely high dynamic range of 1.1 million to 1 and a fine 10-bit tone reproduction.

In order to gain a deeper understanding of the appearance of coloured objects in a three-dimensional scene, the research introduces a multidisciplinary experimental approach. The experiment employed two identical 3-D Mondrians, which were viewed and compared side by side. Each scene was subjected to different lighting conditions. First, we used an illumination cube to diffuse the light and illuminate all the objects from each direction. This produced a low-dynamicrange (LDR) image of the 3-D Mondrian scene. Second, in order to make a high-dynamic range (HDR) image of the same objects, we used a directional 150W spotlight and an array of WLEDs assembled in a flashlight. The scenes were significant as each contained exactly the same three-dimensional painted colour blocks that were arranged in the same position in the still life. The blocks comprised 6 hue colours and 5 tones from white to black. Participants from the CREATE project were asked to consider the change in the appearance of a selection of colours according to lightness, hue, and chroma, and to rate how the change in illumination affected appearance. We measured the light coming to the eye from still-life surfaces with a colorimeter (Yxy). We captured the scene radiance using multiple exposures with a number of different cameras. We have begun a programme of digital image processing of these scene capture methods. This multi-disciplinary programme continues until 2010, so this paper is an interim report on the initial phases and a description of the ongoing project.

Field sequential color (FSC) LCD without color filters has been proposed to enhance light efficiency and color gamut. However, a well-known intrinsic visual artifact, color breakup, is perceived when a relative velocity exists between the object on the screen and the observer's eyes. A Stencil-FSC method therefore was proposed recently which cumulates major color information to the first color sub-frame and therefore suppresses the color breakup. However, the display luminance is lower than that of conventional LCDs. To solve this problem, we extend the Stencil-FSC method to display high dynamic range (HDR) images. Its first step is to scale HDR RGB signals to baseline RGB dynamic range. Afterward, performs the original Stencil-FSC method to initialize all setting. Third, checks each backlight color zone of the R, G, B sub-frames to see if they are free for changing their original primaries to RGB mixing primaries. Forth, determines the color-mixing state of the 'free' primaries based on the extra HDR RGB signals. Finally, calculates the LC signals of the new color-mixing primaries. This algorithm would upgrade a FSC LCD as HDR display.

Dynamic range of natural scenes that we see in daily life ranges up to 120dB. Unfortunately, typical imaging devices only cover about 50dB without any special circuit technique. To overcome this dynamic range problem, many algorithms and devices have been developed and commercialized. However, commercialization in the field where image quality is emphasized is not as active as in the filed where the image information is emphasized. This is because there are still some limitations in capturing and displaying high dynamic range (HDR) image without loss of image information (color, edge and contrast, etc.) In displaying HDR image, some losses of image information during tone reproduction are inevitable, since the HDR image have to be processed with some kind of tone reproduction method to compress the dynamic range fit to the low dynamic range (LDR) display devices. Also there is a report that the tone reproduced LDR image on LDR display device is viewed better than HDR image on HDR display according to Oh ^[1]. For this reason, we propose a new method which can tonally reproduce HDR image into a natural LDR image as auto exposed (AE) one with minimum loss of image information.

We propose a system for display of large format images such that natural scenes can be approximated in a laboratory setting, both spectrally and in dynamic range. The system uses a large area (48"x36") high intensity light box constructed using multiple xenon arc lamps with diffusers to maximize surface uniformity. This source is used as a back light for multiple transparency layers mounted on a rigid plexiglass substrate, where images are printed on the transparency layers using a wide format inkjet printer. A detailed transparency printer model for this system is described, where the spectral transmittance can be predicted with a high degree of accuracy for any given combination of input digital ink values (CMYKRGB). This spectral printer model, in conjunction with knowledge of the spectral characteristics of the back light, can be used to approximate the spectral radiance of a target scene. On a per-pixel level, nonlinear constrained optimization is used to solve for the combination of printer inks that produces the best estimate to the spectrum of the target scene. With this system, it is then possible to create realistic static images with a large dynamic range that can be used to benchmark camera systems in a controlled laboratory setting.

Image blur due to handshake is a significant problem for cell-phone cameras. A set of new handshake characteristics are established using a high-frame-rate image capture and processing system. Based on these newly established handshake characteristics, an efficient, effective and inexpensive method for minimizing image blur due to handshake is proposed. The results of applying the proposed method under different scene conditions are presented.

A method is proposed for estimating the spectral reflectance function of an object surface by using a six-color scanner. The scanner is regarded as a six-band spectral imaging system, since it captures six color channels in total from two separate scans using two difference lamps. First, we describe the basic characteristics of the imaging systems for a HP color scanner and a multiband camera used for comparison. Second, we describe a computational method for recovering surface-spectral reflectances from the noisy sensor outputs. A LMMSE estimator is presented as an optimal estimator. We discuss the reflectance estimation for non-flat surfaces with shading effect. A solution method is presented for the reliable reflectance estimation. Finally, the performance of the proposed method is examined in detail on experiments using the Macbeth Color Checker and non-flat objects.

With the development of digital printing technologies, increasing number of primaries are adopted in colour reproduction systems aiming to improve the quality of the print, in particular, to achieve larger colour gamut, better colour constancy, and smoother colour transition. This introduces a huge challenge to the existing device characterisation techniques, e.g. for the task of calculating the colour gamut of an 11-ink printer alone, things may become mission impossible according to literature.¹ This paper aims to address the issue from an artist's point of view, which reveals the fundamentals of the colour gamut of a given medium. The solution is interestingly simple that the empirical method of measuring printed colours for colour gamut calculation remains to be practical and efficient for N-ink printing system characterisation.

We present a new method to estimate color gamut from primary color spectra only. By using this method, the number of prints and measurements for printer characterization is greatly reduced, which is of particular importance if there are many ink candidates to be combined. The method consists in building a mapping between primary color spectra and their combinations, based on a training set. The mapping is data-driven, without relying on assumptions based on classic theoretical models. Furthermore, we study the effects of smoothing this mapping and its consequences in color estimation accuracy. We tested the method on recently released Latex-based ink-jet ink, for different pigment and latex loads. The mean simulation accuracy error, optimizing the smoothing parameter, was below 1.5 dE, and gamut estimation error below 2% error. For pigment kinds, mean accuracy was below 4 dE, and gamut estimation error about 5%. In all cases, this new method outperforms other overprint estimation methods, such as Kubelka-Munk.

Optical bandpass filters play a decisive role in multispectral imaging. Various multispectral cameras use this type of color filter for the sequential acquisition of different spectral bands. Practically unavoidable, small tilt angles of the filters with respect to the optical axis influence the imaging process: First, by tilting the filter, the center wavelength of the filter is shifted, causing color variations. Second, due to refractions of the filter, the image is distorted geometrically depending on the tilt angle. Third, reflections between sensor and filter glass may cause ghosting, i.e., a weak and shifted copy of the image, which also depends on the filter angle. A method to measure the filter position parameters from multispectral color components is thus highly desirable. We propose a method to determine the angle and position of an optical filter brought into the optical path in, e.g., filter-wheel multispectral cameras, with respect to the camera coordinate system. We determine the position and angle of the filter by presenting a calibration chart to the camera, which is always partly reflected by the highly reflective optical bandpass filter. The extrinsic parameters of the original and mirrored chart can then be estimated. We derive the angle and position of the filter from the coordinates of the charts. We compare the results of the angle measurements to a ground truth obtained from the settings of a high-precision rotation table and thus validate our measurement method. Furthermore, we simulate the refraction effect of the optical filter and show that the results match quite well with the reality, thus also confirming our method.

As the number of consumer digital images escalates by tens of billions each year, an increasing proportion of these images are being acquired using the latest generations of sophisticated mobile devices. The characteristics of the cameras embedded in these devices now yield image-quality outcomes that approach those of the parallel generations of conventional digital cameras, and all aspects of the management and optimization of these vast new image-populations become of utmost importance in providing ultimate consumer satisfaction. However this satisfaction is still limited by the fact that a substantial proportion of all images are perceived to have inadequate image quality, and a lesser proportion of these to be completely unacceptable (for sharing, archiving, printing, etc). In past years at this same conference, the author has described various aspects of a consumer digital-image interface based entirely on an intuitive image-choice-only operation. Demonstrations have been given of this facility in operation, essentially allowing criticalpath navigation through approximately a million possible image-quality states within a matter of seconds. This was made possible by the definition of a set of orthogonal image vectors, and defining all excursions in terms of a fixed linear visual-pixel model, independent of the image attribute. During recent months this methodology has been extended to yield specific user-interactive image-quality solutions in the form of custom software, which at less than 100kb is readily embedded in the latest generations of unlocked portable devices. This has also necessitated the design of new user-interfaces and controls, as well as streamlined and more intuitive versions of the user quality-choice hierarchy. The technical challenges and details will be described for these modified versions of the enhancement methodology, and initial practical experience with typical images will be described.

We present a color correction algorithm for histogram equalized images captured by a digital camera. Current color correction methods are based on human color perception of luminance and hue. However, these techniques do not consider nonlinear camera characteristics, therefore the resulting color images show color distortions where brightness modification is severe. We propose a new effective color correction method that depends on the camera brightness and color curve. It utilizes the relationship of luminance and color variation of a camera used for image capture. We can predict chrominance variation after luminance change by tracing the brightness-chrominance curve of the camera model. Therefore the resulting image shows color that would have been obtained at different exposure using the same camera. We verify that the processed images have natural color and that they are similar to images taken at different exposure conditions. Moreover it is possible to apply the proposed method to software bracketing; we can change the exposure condition of an image at post processing stage. All test results demonstrate that our method is accurate and useful in the enhancement of a color of digital images.

Most of high-contrast images are common with dark and bright area. It is difficult to present the detail on both dark and high light areas on display devices. In order to resolve this problem, we proposed a method of image enhancement to improve this image quality and used bilateral filter to keep the detail. In paper, we applied an appropriate algorithm to process images. At first, we use bilateral filter to separate image. One is large scale image and the other is detail image. Second, we made large scale image which was translated into histogram. In order to make the images divided into three stairs, such as lightness, middle-tone and darkness region. We decided two optimal threshold parameters. Finally, according to three images we use different tone-mapping method to process each stair. The tone-mapping method includes adaptive s-curve and gamma curve algorithms. The experiment results of this study revealed image detail and enhancement. To avoid contour phenomenon is in lightness region.

In this paper, we propose a contrast stretching which reflects the visibility of human visual system (HVS) as well as the histogram of a target image. In the proposed method, a target image is contrast-stretched by the auto gain/offset with visibility-based clipping, where the clipping thresholds are decided to maximize the averaged visibility of the contraststretched image. The visibility function is defined by a spatial JND (just noticeable difference), which is the threshold below which any change of a given pixel from its textured neighbors is not perceived by the HVS. Experimental results show that the proposed method efficiently stretch the contrast of target images to be more pleasing to the HVS than some conventional methods.

The mixed content compression (MCC) algorithm developed in this research provides a hardware efficient solution for compression of scanned compound document images. MCC allows for an easy implementation in imaging pipeline hardware by using only an 8 row buffer of pixels. MCC uses the JPEG encoder to effectively compress the background and picture content of a document image. The remaining text and line graphics in the image, which require high spatial resolution, but can tolerate low color resolution, are compressed using a JBIG1 encoder and color quantization. To separate the text and graphics from the image, MCC uses a simple mean square error (MSE) block classification algorithm to allow a hardware efficient implementation. Results show that for our comprehensive training suite, the compression ratio average achieved by MCC was 60:1, but JPEG only achieved 35:1. In particular, MCC compression ratios become very high on average (82:1 versus 44:1) for mono text documents, which are very common documents being copied and scanned with all-in-ones. In addition, MCC has an edge sharpening side-effect that is very desirable for the target application.

In this paper, subpixel shift estimation method using phase correlation with local region is proposed for registration of noisy images. Commonly, phase correlation based on the Fourier shift property is used to estimate the shift between images. Subpixel shift of images can be estimated by the analysis for the phase correlation of downsampled images. However, in case of images with noise or aliasing artifacts, the error in estimation is increased. Thus, we consider a small region in a corner of an image instead of the whole, because flat regions with noise and regions with aliasing induce the error of estimation. In addition, to improve accuracy, the local regions are inversely shifted by varying the subpixel shift values, and obtaining the peak value of phase correlation between the images. Then, the subpixel shift value corresponding to the maximum of the peak values is selected. Real-time implementation of this process is possible because only a local region is used, thereby reducing the process time. In experiments, the proposed method is compared with conventional methods using several fitting functions, and it is applied for the task of super resolution imaging. The proposed method shows higher accuracy in registration than other methods, also, edge-sharpness in superresolved images is improved.

Gamut mapping algorithms are currently being developed to take advantage of the spatial information in an image to improve the utilization of the destination gamut. These algorithms try to preserve the spatial information between neighboring pixels in the image, such as edges and gradients, without sacrificing global contrast. Experiments have shown that such algorithms can result in significantly improved reproduction of some images compared with non-spatial methods. However, due to the spatial processing of images, they introduce unwanted artifacts when used on certain types of images. In this paper we perform basic image analysis to predict whether a spatial algorithm is likely to perform better or worse than a good, non-spatial algorithm. Our approach starts by detecting the relative amount of areas in the image that are made up of uniformly colored pixels, as well as the amount of areas that contain details in out-of-gamut areas. A weighted difference is computed from these numbers, and we show that the result has a high correlation with the observed performance of the spatial algorithm in a previously conducted psychophysical experiment.

Traditionally, the AToB0 tag of an ICC printer profile, containing the perceptual transform from device specific to PCS Lab or XYZ values, has been generated directly from measurement data without considering the color re-rendering included in the PCS to device-specific transform found in the corresponding BToA0 tag. In this case, the AToB0 color conversion will often not be the inverse of the color conversion in the BToA0 tag. However, with ICC version 4, the AToBn and BToAn transforms are in general supposed to be inverses of each other, to the extent possible. This feature supports the re-purposing of color data within an ICC color management workflow. This inversion is a challenge for profile generation due to issues with either directly inverting 3-D interpolations or inverting every step applied in generating the BToA0 tag. Directly inverting a 3-D LUT may not be feasible because the forward mapping is usually not a one-to-one mapping. Mathematically, inverting every operation for generating a BToA0 tag may also be extremely difficult if not impossible. Consequently, a closed-loop method has been developed which iteratively adjusts AToBn tags to improve the invertibility of ICC profile transforms. The test results are very encouraging.

In principal, color reproduction on specific devices can be divided into transformation of color coordinates and the adaptation of colors to a device, called gamut mapping. The well established ICC color management neglects the latter aspect. This paper presents a practical implementation addressing both an eficient color transformation and a sophisticated gamut mapping.

Premilary experiments have shown that the quality of printed images depends on the capacity of the printing system to accurately reproduce details.¹ We propose to improve the quality of printed images by compensating for the Modulation Transfer Function (MTF) of the printing system. The MTF of the printing system is measured using the method proposed by Jang and Allebach,² in which test pages consisting of series of patches with different 1D sinusoidal modulations (modified to improve the accuracy of the results³) are printed, scanned and analyzed. Then the MTF is adaptively compensated in the Fourier domain, depending both on frequency and local mean values. Results of a category judgment experiment show significant improvement as the printed MTF compensated images obtain the best scores.

This work presents a model for dotgain prediction using repetitive patterns based on the characterization of neighboring and clustering effects of a specific printing device. Estimating dotgain is done nowadays by measuring patches of color patterns realized by a specific printing device. Current models use the information about adjacent dots to predict dotgain. However, research has shown that dotgain is influenced by the neighborhood of a dot which in general is bigger than one dot-size, in particular in connection with laser printers. The presented method predicts the dotgain of a dot considering a larger surrounding based on the observation of two main parameters affecting the luminance of a pattern which can be fitted using linear regression.

The Yule-Nielsen modified spectral Neugebauer model enhanced for accounting for ink spreading in the different ink superposition conditions (EYNSN) requires measuring the reflectances of halftone calibration patches in order to compute the ink spreading curves mapping nominal ink surface coverages to effective ink surface coverages. Spectral measurements of dozens of halftone patch reflectance spectra for each considered halftoning method, screen shape or screen frequency variant is cumbersome and time consuming. As an alternative, we compute automatically the reflectance of the calibration patches necessary to establish the ink spreading curves by making use of the two-by-two dot centering model (abbreviated "2-by-2"). The two-bytwo dot centering model requires its own set of calibration patches, among which a very small subset is necessary for predicting the reflectance of the EYNSN calibration patches. For a given combination of printer, paper and inks, using only 68 two-by-two calibration patches for the three CMY inks, respectively 118 two- by-two calibration patches for the four CMYK inks, we are able to predict the reflection spectra of most classical halftone screens and at many different frequencies. We compare the results of predictions where the EYNSN model calibration patches are measured or are predicted with the two-by-two dot centering model. For 125 (CMY) and 625 (CMYK) uniformly distributed patches printed with an ink-jet printer at three different screen frequencies (75lpi, 100lpi and 125lpi), the mean reflectance prediction accuracy is similar, i.e. the decrease in accuracy due to the two-by-two prediction of EYNSN calibration patch reflectance is less than ΔE₉₄=0.4.

For quite some time now, the printing business has been under heavy pressure because of overcapacity, dropping prices and the delocalization of the production to low income countries. To survive in this competitive world, printers have to invest in tools that, on one hand, reduce the production costs and, on the other hand, create additional value for their customers (print buyers). The creation of customer portals on top of prepress production systems allowing print buyers to upload their content, approve the uploaded pages based on soft proofs (rendered by the underlying production system) and further follow-up the generation of the printed material, has been illustrative in this respect. These developments resulted in both automation for the printer and added value for the print buyer. Many traditional customer portals assume that the printed products have been identified before they are presented to the print buyer in the portal environment. The products are, in this case, typically entered by the printing organization in a so-called MISⁱ system after the official purchase order has been received from the print buyer. Afterwards, the MIS system then submits the product to the customer portal. Some portals, however, also support the initiation of printed products by the print buyer directly. This workflow creates additional flexibility but also makes things much more complex. We here have to distinguish between special products that are defined ad-hoc by the print buyer and standardized products that are typically selected out of catalogs. Special products are most of the time defined once and the level of detail required in terms of production parameters is quite high. Systems that support such products typically have a built-in estimation module, or, at least, a direct connection to an MIS system that calculates the prices and adds a specific mark-up to calculate a quote. Often, the markup is added by an account manager on a customer by customer basis; in this case, the ordering process is, of course, not fully automated. Standardized products, on the other hand, are easily identified and the cost charged to the print buyer can be retrieved from predefined price lists. Typically, higher volumes will result in more attractive prices. An additional advantage of this type of products is that they are often defined such that they can be produced in bulk using conventional printing techniques. If one wants to automate the ganging, a connection must be established between the on-line ordering and the production planning system. (For digital printing, there typically is no need to gang products since they can be produced more effectively separately.) Many of the on-line print solutions support additional features also available in general purpose e-commerce sites. We here think of the availability of virtual shopping baskets, the connectivity with payment gateways and the support of special facilities for interfacing with courier services (bar codes, connectivity to courier web sites for tracking shipments etc.). Supporting these features also assumes an intimate link with the print production system. Another development that goes beyond the on-line ordering of printed material and the submission of full pages and/or documents, is the interactive, on-line definition of the content itself. Typical applications in this respect are, e.g., the creation of business cards, leaflets, letter heads etc. On a more professional level, we also see that more and more publishing organizations start using on-line publishing platforms to organize their work. These professional platforms can also be connected directly to printing portals and thus enable extra automation. In this paper, we will discuss for each of the different applications presented above (traditional Print Portals, Web2Print applications and professional, on-line publishing platforms) how they interact with prepress and print production systems and how they contribute to the improvement of the overall operations of a printing organization.

Today's color imaging systems are powerful and complex entities that enable users to replicate lifelike colors. However when a color issue arises, it is very difficult to diagnose and solve. Therefore, it is beneficial to complement a color imaging system with sophisticated and user-friendly tools that help users to self-solve color issues. This paper discusses the assessment of a color printing workflow (CPW) for personal computers and the development of a web-based self-service customer support tool for color printing issues that may arise with electrophotographic color printers. We study the stages in the CPW where the colors of a document may change. From this evaluation, we find the system configuration that may have caused the change. This study provides the foundation for the development of our web-based tool, named the Color Printing Workflow Troubleshooting (CPWT) Tool. This comprehensive assessment of the CPW helps us to determine a troubleshooting strategy for our web-based tool. The set of color issues considered are those that arise when one attempts to reproduce a Pantone spot color.

Four color printing is the common way to render a color image to paper. This four color printing has certain side effects, among them the metameric representation of colors. This means that a single visual color can be generated through multiple different four color combinations. This is normally considered a problem, however, the problem description can be inverted and information can be embedded in a printed color image that is perceptually invisible under normal illumination, but revealed to an infrared imaging system. This means that certain security aspects can now produced in an essentially cost-neutral way.

Gamut mapping is a critical process in the output color management of a printer. In systems consisting of two or more marking engines, these engines could in general have different output color gamuts. In special cases these gamuts can be drastically different. When applying gamut mapping to a multi-engine printing system, which gamut to use is not obvious. In the default case, i.e., if the multi-engine system is treated as a single engine with a single gamut, poor image quality could result. In this paper, we propose gamut mapping strategies for multiple engine printing, which depend on the relative importance of "color rendition" and "page-to-page color consistency" within a given document. In particular, we propose a content-based gamut mapping, wherein the trade-offs between color rendition and page-to-page color consistency can be automatically and dynamically made by segmenting the document and applying gamut mapping according to the needs of the segmented components.

For artists wishing to print onto heavy weight coated and uncoated papers, the opportunity to improve colour density and saturation is always desirable. The paper presents research into methods for mixing and printing colours using the latest multi-primary inkjet printing system. The objective is to investigate the colour printability of the system printing on a fine art paper. The cellular Yule-Nielsen modified spectral Neugebauer model is employed to characterise the printing process. And the preliminary experiment result shows the effectiveness of the proposed method.

A monochromatic binary printer model at the cluster level defined by the halftone frequencies is presented in this paper. The halftone process using a cluster halftone screen creates halftone structures with aligned clusters within halftone cells tiled to fill the image plane. Each halftone cell, or each tile, can be treated as a "primary color", which can be calibrated, or macroscopically measured, from a corresponding halftone pattern. The cluster-based printer model estimates the average color of a halftone pattern containing different halftone cells using a modified Neugebauer spectral (colorimetric) color mixing model incorporating the Yule-Nielsen effect. A method based on the proposed clusterbased printer model for quickly and accurately characterizing the complete tone reproduction curve (TRC) for multicenter halftone screens is also described with the experiment result.

Through the analysis of the light scattering within the ink and paper. we provide the fact of the total incident flux that contains both the collimated flux and the diffuse flux which were caused by the specular reflection and diffuse reflection on the air-ink interface in the process of color reproduction. Considering the phenomenon of the energy of these two parts of the flux are changing constantly, the four-flux kubelka-munk model based on the radiative transfer equation is given. Also, a new four-flux model for calculation of the reflectance of print with rough substrate is established with the Beckmann-Spizzichino model which describe the reflectance of the incident flux with arbitrary rough substrate.

The color prediction of fluorescent ink security printing is a very concerned issus in the field of security printing quality control. This paper first analyzed the light transmission of solid fluorescent ink prints.We make the assumption that the absorption of ink layer and the the radiation of fluorescence are all occur on a very thin layer in the middle of ink layer.And the produced fluorescence are only in upward and downward direction. Under such assumption we analyze the light spreading in fluorescent ink layer of the absorption, scattering and fluorescence of radiation, respectively. So we divide the incidence into three parts. The first is the light reflecting by the air-ink interface.The second part is the upward and downward fluorescence which radiating by the thin fluorescence layer. The third part is the remanent incidence after the absorption of thin fluorescence layer.Through researching the three transmission beams in the dissemination of the dynamics of the ink layer we can calculate the light the reflectance and transmission of fluorescent ink layer using the iterative algorithm.Then using the Murray-Davies model which reflecting the light propagating in halftone ink layer we establish the new reflection Murray-Davies model of halftone fluorescent ink prints.

It developped the Kubelka-Munk model and established a prediction model of fluorescence prints.Based on this,it was developped to the halftone prints and we introduced the scattering probability function which was calculated by the experience probability model. So we can establish an complete prediction model of halftone fluorescence prints.

In 1931, Kubelka and Munk introduced two-flux Kubelka-Munk model based on radiative transfer theory[1]. But the model has lots of strict conditions. In 1942, Saunderson introduced revised method, for there would occur multiple inside reflection in the interface of print, and it would induce density increase in the ink layer, and influenced prediction precision. Dot gain is always the difficult problem in print, it includes physics gain and optical gain. Kubelka-Munk model didn't consider dot gain's effect, especially optical gain. There are many methods to calculate dot gain. Many of them are based on point spread function principle[5]. Recently, Yang Li corrects the scattering coefficient S and absorption coefficient K in the Kubelka-Munk model based on statistical physics theory[2][3][4]. This makes the model has more widely applications. This article, taking into account of oil layer, oil penetration layer and paper layer respectively, thinking over multiple reflection and optical dot gain, builds a new halftone color prediction model.

Colorization is a computer-aided process of adding color to a grayscale image or video. The task of colorizing a grayscale image involves assigning three dimensional (RGB) pixel values to an image which varies along only one dimension (luminance or intensity). Since different colors may have the same luminance value but vary in hue or saturation, mapping between intensity and color is not unique, and colorization is ambiguous in nature, requiring some amount of human interaction or external information. In this paper we propose a semi-automatic process for colorization where the user indicates how each region should be colored by putting the desired color marker in the interior of the region. The algorithm based on the position and color of the markers, segments the image and colors it. In order to colorize videos, few reference frames are chosen manually from a set of automatically generated key frames and colorized using the above marker approach and their chrominance information is then transferred to the other frames in the video using a color transfer technique making use of motion estimation. The colorization results obtained are visually very good. In addition the amount of manual intervention is reduced since the user only has to apply color markers on few selected reference frames and the proposed algorithm colors the entire video sequence.