Humans see multicolor complex images with illuminants that have very low amounts of 400 to 580nm light when there is enough long-wave light greater than 590nm. Interactions between rods and long-wave (L) cones generate these colors. They are observed when there is insufficient light for a threshold response from M- and S-cones. This paper measures the spectral emission of a wood fire and a wax candle and it compares these low-color temperature spectral radiant exitances with the sensitivities of rods and long-wave cones. The paper reviews some of the literature on the evolution of human cone pigments and the early use of fire by hominids.

Colour management systems need to be accurate and repeatable, particularly in graphic arts applications such as converting image data to proofing systems and to final print processes. Modelling and computation errors were analyzed for a number of characterization data sets including single press sheet measurements and reference printing conditions based on SWOP and ISO 12647-3. Errors were calculated at double precision and compared with the AToB, BToA and round trip errors found in ICC profiles generated from the same data sets. Data sets which are averaged from measurements of multiple press sheets consistently performed better than transforms built from single-sheet measurements. A significant part of the transform error lies in the limited precision of computation. BToA transform errors averaging 1 ΔE*_ab appear to be a reasonable expectation for well-formed data sets. This needs to be placed in the context of errors arising from measurement uncertainty and the variation in colour reproduction systems, which are considerably larger.

We propose a simple and effective method for the dequantization of color images, effectively interpolating the colors from quantized levels to a continuous range of brightness values. The method is designed to be applied to images that either have undergone a manipulation like image brightness adjustment, or are going to be processed in such a way. Such operations often cause noticeable color bands in the images that can be reduced using the proposed Constrained Diffusion technique. We demonstrate the advantages of our method using synthetic and real life images as examples. We also present quantitative results using 8 bit data that has been obtained from original 12 bit sensor data and obtain substantial gains in PSNR using the proposed method.

A gamut mapping method, spring-primary gamut mapping, was developed for device to device color mapping. Instead of performing gamut mapping point-wisely, it selects a small number of points for gamut mapping and determines the color mapping of other points by interpolation using color similarity information. It incorporates primary adjustment and gamut mapping into a single step. Using the color similarity information of neighbor colors for color mapping, it well preserves the color to color relationship. Applying interpolation instead of gamut mapping for majority of colors, it tremendously increases the speed of gamut mapping process.

We treat image-to-device gamut mapping as a multi-criteria optimization problem. Our approach leads to a parameterized mathematical optimization problem that allows to constrain the degree to which objectives like contrast preservation, hue preservation, saturation preservation and the continuity of the mapping can be violated while maximizing the device gamut exploitation. We demonstrate the feasibility of our approach on several benchmark image- and device gamuts.

This study has three primary aims circumventing current limitations of color reproduction technologies: firstly, to derive base-line image quality factors from both color printer experts and academic research works. Individual factors were verified by systematic experiments, secondly, to develop a perceptual gamut mapping algorithm covering the image quality and preference factors derived, thirdly, to apply the algorithm to printer driver as acting for a vendor specific perceptual intent. Algorithm of this study tried to optimization between control parameters of gamut mapping and color shifting factors of preference, e.g. skin, sky and green grass. Profile builder using this algorithm outperforms, in industrial and academic aspects, existing commercial tool and CIE recommended algorithms.

This paper proposes a method of gamut estimation using data segmentation and 2D surface splines. The device data is first segmented into hue intervals, and then each hue interval is analyzed iteratively to construct a 2D gamut boundary descriptor for that hue interval. The accuracy and smoothness of the gamut boundary estimate can be controlled by the number of hue intervals selected and the sampling within each hue interval.

Color calibration or the use of color measurement processes to characterize the color properties of a device or workflow is often expected or assumed for many color reproduction applications. However it is interesting to consider applications or situations in which color calibration is not as critical. In the first case it is possible to imagine an implicit color calibration resulting from a standardization or convergence of the colorant and substrate spectrum. In the second case it is possible to imagine cases where the device color variability is significantly less than the user color thresholds or expectations for color consistency. There are still general requirements for this form of pragmatic color but they are generally lower than for the higher end of digital color reproduction. Finally it is possible to imagine an implicit calibration that leverages in some way the highly accurate memory color for the hue of common objects. This scenario culminates with a challenge to create a natural capture calibration standard that does not require individual calibration, is spectrally diverse, is inexpensive and is environmentally friendly.

Lightening or darkening an image is a fundamental adjustment used to improve aesthetics or correct exposure. This paper describes new geometrical algorithms for lightness adjustment, implementing fast traversal of colors along lightness-saturation curves, applicable when the data starts naturally in YCC space (JPEG images or MPEG videos). Here, YCC refers generically to color spaces with one luminance and two color difference channels, including linear YCC spaces and CIELAB. Our first solution uses a class of curves that allows closed-form computation. Further assuming that saturation is a separable function of luminance and curve parameter simplifies the computations. This approach reduces clipping and better adjusts lightness together with saturation. Preliminary evaluation with 96 images finds good subjective results, and clipping is reduced to about 5% of a prior approach.

The measurement of gloss is conventionally made by specialised instruments that determine the ratio of reflected to incident illumination at a single fixed angle. This study investigated whether digital photography with flash illumination could be used as an alternative. Multiple exposures were combined by a high dynamic range (HDR) imaging technique to produce a two-dimensional intensity profile of the reflectance around the specular point. The method was tested for six paper samples of varying gloss, and the results were found to correlate well with instrumental measurements. The image gloss profiles, however, provided more information about the distribution of the reflection over a range of angles and also gave an indication of the surface texture.

Image-enhancement technology has been developed from first principles whereby an unskilled user may enhance and optimize the image quality of any digital photograph to personal choice within a matter of seconds. The novel methodology, which by virtue of its simple user-interface, real-time computation, and lack of any appreciable user learning-curve, naturally lends itself to many practical imaging applications in addition to that of a stand-alone application, including digital cameras, printers and photo-kiosks, or provision as an image-processing web-service. The basic imaging philosophy and principles leading to the development of this enhancement technology are discussed.

In this study, we measure the colors used in a Japanese Animations. The result can be seen on CIE-xy color spaces. It clearly shows that the color system is not a natural appearance system but an imagined and artistic appearance system. Color constancy of human vision can tell the difference in skin and hair colors between under moonlight and day light. Human brain generates a match to the memorized color of an object from daylight viewing conditions to the color of the object in different viewing conditions. For example, Japanese people always perceive the color of the Rising Sun in the Japanese flag as red even in a different viewing condition such as under moonlight. Color images captured by a camera cannot present those human perceptions. However, Japanese colorists in Animation succeeded in painting the effects of color constancy not only under moonlight but also added the memory matching colors. They aim to create a greater impact on viewer's perceptions by using the effect of the memory matching colors. In this paper, we propose the Imagined Japanese Animation Color System. This system in art is currently a subject of research in Japan. Its importance is that it could also provide an explanation on how human brain perceives the same color under different viewing conditions.

The number of images taken by digital still cameras (DSC) and camera phones is rising dramatically but the number of digital images being transferred onto paper is not keeping up with that rate of increase. This paper tries to evaluate why this is the case and offers suggestions on how to encourage consumers to print their most valuable memories while using convenient solutions both at home and professionally.

The image processor in digital TV has started to play an important role due to the customers' growing desire for higher quality image. The customers want more vivid and natural images without any visual artifact. Image processing techniques are to meet customers' needs in spite of the physical limitation of the panel. In this paper, developments in image processing techniques for DTV in conjunction with developments in display technologies at Samsung R and D are reviewed. The introduced algorithms cover techniques required to solve the problems caused by the characteristics of the panel itself and techniques for enhancing the image quality of input signals optimized for the panel and human visual characteristics.

This study investigates the color error problems posed by large flat panel displays and proposes a subpixel-rendering algorithm to mitigate the problem. The color error problems are caused by Mach band effect and the convergence error of a pixel on large subpixel structured displays and named a color band error. The proposed method includes three processes; a finding process of areas or pixels generating the error, an estimating process of the error, and a correction process of the error. To correct the color band error, we take an error erosion approach, an error concealment approach, and a hybrid approach of the error erosion and the error concealment. In this paper, we experimented to know the threshold where human vision can detect by a psychophysical method. In addition, we applied our proposed method to a commercial 42" plasma display to confirm the effect. The results show that all observers see the color band error at a sharp edge having above 64-gray difference and the converted test images by our algorithm are preferred to the original test images. Finally, this paper reports that the Mach band effect and the convergence error on large subpixel structured display produce color band errors on images having sharp edge and the proposed method effectively corrects the color band errors.

On a plasma display panel (PDP), luminous elements of red, green, and blue have different time responses. Therefore, a colored trails and edges appear behind and in front of moving objects. In order to reduce the color artifacts, this paper proposes a motion-based discoloring method. Discoloring values are modeled as linear functions of a motion vector to reduce hardware complexity. Experimental results show that the proposed method has effectively removed the colored trails and edges of moving objects. Moreover, the clear image sequences have been observed compared to the conventional ones.

The authors have successfully developed a six-primary-color liquid crystal display using six-color LEDs. More specifically, a prototype of a six-primary-color liquid crystal display having a color gamut of 170% or wider then that of conventional techniques has been constructed. Furthermore, this monitor has a newly developed calibration system using an integrated color sensor, so that it can keep its white point chromaticity stable.

The present paper proposes a nonlinear approach using a neural network for color control of projection displays, including the LCD and DLP types. This approach accepts variations in primary color coordinates and coupling among RGBW channels. We regard a display system as an unknown nonlinear system with RGB signal inputs and XYZ tristimulus outputs. We determine the RGB values so that the projector outputs the desired XYZ values. The neural network is used for estimating adaptively an inverse mapping from the XYZ space to the RGB space. Because of a direct mapping, we can eliminate the need to predict white channel separation. Moreover, we present a method for correcting the emitted luminance, according to the spatial location and the surface color of a screen. The spatial correction is needed because a color image from a computer is not displayed uniformly on the screen. Also the screen color correction is needed because color reproduction is based on the light reflected from the screen. The correction makes it possible to reproduce accurate color images on a colored wall at any location.

This paper proposes an illuminant-adaptive reproduction method using light adaptation and flare conditions for a mobile display. Mobile displays, such as PDAs and cellular phones, are viewed under various lighting conditions. In particular, images displayed in daylight are perceived as quite dark due to the light adaptation of the human visual system, as the luminance of a mobile display is considerably lower than that of an outdoor environment. In addition, flare phenomena decrease the color gamut of a mobile display by increasing the luminance of dark areas and de-saturating the chroma. Therefore, this paper presents an enhancement method composed of lightness enhancement and chroma compensation. First, the ambient light intensity is measured using a lux-sensor, then the flare is calculated based on the reflection ratio of the display device and the ambient light intensity. The relative cone response is nonlinear to the input luminance. This is also changed by the ambient light intensity. Thus, to improve the perceived image, the displayed luminance is enhanced by lightness linearization. In this paper, the image's luminance is transformed by linearization of the response to the input luminance according to the ambient light intensity. Next, the displayed image is compensated according to the physically reduced chroma, resulting from flare phenomena. The reduced chroma value is calculated according to the flare for each intensity. The chroma compensation method to maintain the original image's chroma is applied differently for each hue plane, as the flare affects each hue plane differently. At this time, the enhanced chroma also considers the gamut boundary. Based on experimental observations, the outer luminance-intensity generally ranges from 1,000 lux to 30,000 lux. Thus, in the case of an outdoor environment, i.e. greater than 1,000 lux, this study presents a color reproduction method based on an inverse cone response curve and flare condition. Consequently, the proposed algorithm improves the quality of the perceived image adaptive to an outdoor environment.

The preferred skin color reproduction algorithm is developed for the mobile display especially for a portrait image with one person as a main object occupying most of the screen. According to the developed technique, the skin area in an image is detected using color value of each pixel in YCbCr color space. The skin color boundary is defined as a quadrangle in Cb-Cr plane. The colors of pixels belonging to skin area are shifted toward the preferred colors while there is no color change for the other pixels. The psychophysical experiments are conducted to investigate the optimal model parameters providing the most pleasant image to the users. Then, the performance of developed algorithm is tested using the optimal parameters. The result shows that for more than 95% cases, the observers prefer the images treated with the developed algorithm compared to the original image. It is believed that the developed algorithm can be applied to the mobile application to improve the image quality regardless the input sources.

The color fidelity of displays such as LCD and PDP was commonly estimated by a series of color patches. However, no strong evidence showed that these color patches are well correlated to the real-world image characteristics. To minimize the gap between the color patches and the image characteristics, the present study first accumulated the statistics of different classes of image. Then, we chose several of them as reference images, manipulated their colors intentionally, and finally asked observers to compare the reference images with their color-perturbed counterparts. In the end, based on the classified image statistics, an empirical model was derived to predict the overall results of the visual image differences. In the model, the pixel frequencies (probability) of 125 color clusters summarized by a certain type of images were taken into account for predicting the displays' color fidelity on the type of images. The 125 color clusters were linked in a 5x5x5 cellular structure. If the color manipulation breaks the intera-relationship of the cellular structure, the reproduction would be unnatural. In contrast, if the manipulation shifts the colors without breaking the relationship, the reproduction still looks fine. We called the intera-relationship as Cellular Uniformity and integrated the measurement into our model. It could be an interesting idea for future development on image quality assessment.

The technique of support vector regression (SVR) is applied to the color display calibration problem. Given a set of training data, SVR estimates a continuous-valued function encoding the fundamental interrelation between a given input and its corresponding output. This mapping can then be used to find an output value for a given input value not in the training data set. Here, SVR is applied directly to the display's non-linearized RGB digital input values to predict output CIELAB values. There are several different linear methods for calibrating different display technologies (GOG, Masking and Wyble). An advantage of using SVR for color calibration is that the end-user does not need to apply a different calibration model for each different display technology. We show that the same model can be used to calibrate CRT, LCD and DLP displays accurately. We also show that the accuracy of the model is comparable to that of the optimal linear transformation introduced by Funt et al.

We have developed a method to calibrate a display to a predetermined state and to make an ICC display profile by visual calibration for soft proofing. Our method adjusts a color of display white point to a color of a white object under a viewing illuminant, so our method can calibrate the display white point for any viewing illuminant. In order to calibrate the tone reproduction curve of a display, the brightness and hue of a continuous tone image is adjusted to the brightness and hue of a binary image. In addition, three pairs of images having different values of brightness are used. These methods can calibrate the display which has complex tone reproduction curve like LCD displays. In Electronic Imaging 2005, we reported that these methods can calibrate tone reproduction curves of LCD displays accurately₁. In this paper, we evaluated the matching accuracy between display white point and paper white under various illuminances and color temperatures to bear out the effect of our method under practical illumination. We found from this experiment that the matching accuracy was almost the same in all illumination conditions. Furthermore, all subjects calibrated the chromaticity of display white point more bluish than the chromaticity of paper white in all illumination conditions, and the dispersion of yellow-blue direction was larger than that of red-green direction. This yellow-blue direction was almost the same as the long axis of MacAdam ellipse. We also evaluated the capability of color discrimination between display and paper in various illumination conditions. At 500lx or less, many subjects made judgments that the color of display white point was similar as the color of paper white when color difference between display and paper was small, but the correlation of color difference with judgement was small at 1000lx or more. The cause of these results is the maximum luminance of the display was darker than that of paper at 1000lx or more. These results suggest that ISO 3664:2000 P2 condition is appropriate to compare the image on computer display with that on paper at the same time.

Color data conversion between CMYK and CIEL*a*b* color space is not directly corresponded, that is many CMYK combinations could reproduce the same CIEL*a*b* value. When building a LUT converting from CIEL*a*b* to CMYK for a CMYK color printer, one to one correspondence between CMYK and CIEL*a*b* must be aimed. The proposed method in this paper follows steps: (1) print and measure CIEL*a*b* values of CMYK reference chart, (2) set-up parameters to assign the amount of black extraction, (3) generate gamut boundary descriptors for gamut mapping and for black extraction using CMYK-CIEL*a*b* data under predetermined black extraction parameters, (4) perform gamut mapping for given CIEL*a*b* using the gamut boundary descriptor for gamut mapping, (5) determine K value of the gamut-mapped CIEL*a*b* using the gamut boundary descriptors for black extraction. The suggested method determines K value for given CIEL*a*b* using gamut boundary descriptors in CIEL*a*b color space. As a result, a color printer using this method can make out accurate black amount and reproduces more consistent CMYK images under different black extraction options.

This paper proposes a method of colorimetric characterization based on the color correlation between the distributions of colorant amounts in a CMYKGO printer. In colorimetric characterization beyond three colorants, many color patches with different combinations of colorant amounts can be used to represent the same tri-stimulus value. Therefore, choosing the proper color patches corresponding each tri-stimulus value is important for a CMYKGO printer characterization process. As such, the proposed method estimates the CIELAB value for many color patches, then selects certain color patches while considering high fidelity and the extension of the gamut. The selection method is divided into two steps. First, color patches are selected based on their global correlation, i.e. their relation to seed patches on the gray axis, and become the reference for correlation. However, even though a selected color patch may have a similar overall distribution to the seed patch, if the correlation factor is smaller than the correlation factors for neighboring patches, the color patch needs to be reselected. Therefore, in the second step, the color patch is reselected based on the local correlation with color patches that have a lower correlation factor with the seed patch. Thus, to reselect the color patch, the seed patch is changed to the average distribution of eight neighboring selected color patches, and the new color patch selected considering the new correlation factor. Consequently, the selected color patches have a similar distribution to their neighboring color patches. The selected color patches are then measured for accuracy, and the relation between the digital value and the tristimulus value for the color patches stored in a lookup table. As a result of this characterization, the gamut is extended in the dark regions and the color difference reduced compared to conventional characterization methods.

When time, temperature or an external environment change, a laser electrophotographic printer produces quite different color tones from original ones. To achieve consistent color reproduction, many researchers have tried to characterize printer tone curves and developed methods to correct color tones. Color channel independent methods are most widely used, and there are two approaches in color channel independent method: (1) Instrument-based correction and (2) visual correction. Two approaches provide some trade-offs between cost and accuracy. In this paper we propose a methodology which combines the strengths of these two approaches. We describe how we design a calibration page and how we characterize lightness variation of a reference patch. We then present the procedure of our global tone correction method based on visual appearance match of end-users as well as the predetermined reference lightness model. We simulate tone distortion state by varying hardware parameters, and perform visual appearance match experiments to subjects. Our experimental results show that our method can significantly reduce color difference between the original print and the print at the distortion state. This suggests that we can reliably estimate the distortion parameter, and correct tones close to an original state.

Document imaging and transmission systems (typically MFPs) require both effective and efficient image rendering methods that support standard data formats for a variety of document types, and allow for real time implementation. Since most conventional raster formats (e. g. TIFF, PDF, JPEG) are designed for use with either black and white text, or continuous-tone images, more specialized rendering methods are often required for representing mixed content documents. The baseline TIFF format supports a few binary compression options: PackBits, CCITT G3 and G4. Conventionally, halftoning algorithms, such as error diffusion, can be used to create a binary representation of a document image in the TIFF format. However, PackBits, CCITT G3 and G4 compression generally do not produce desired compression on halftone images. In this paper, we propose an efficient error diffusion algorithm optimized for PackBits compression. This method, which we refer to as POED (PackBits optimized error diffusion), is a form of threshold modulation error diffusion which takes advantage of the byte-oriented run length structure of PackBits compression by encouraging repetition of bytes in the resulting binary image. To maintain the sharpness of text, a binary segmentation algorithm is provided to switch off the adaptive error diffusion procedure and switch on the Floyd Steinberg error diffusion procedure in text regions. The POED method with PackBits compression yields higher compression ratios than the conventional error diffusion method, while maintaining desirable visual quality with low computational and memory requirements. We show experimental results to compare our method with the Floyd Steinberg error diffusion method.

I propose a halftone screen design method based on a human visual system model and the characteristics of the electro-photographic (EP) printer engine. Generally, screen design methods based on human visual models produce dispersed-dot type screens while design methods considering EP printer characteristics generate clustered-dot type screens. In this paper, I propose a cost function balancing the conflicting characteristics of the human visual system and the printer. By minimizing the obtained cost function, I design a model-based clustered-dot screen using a modified direct binary search algorithm. Experimental results demonstrate the superior quality of the model-based clustered-dot screen compared to a conventional clustered-dot screen.

AM-FM hybrid screen represents a clustered dot halftone screen whose dot clusters are aperiodic and dot growth pattern is irregular. Unlike AM ordered screen, AM-FM hybrid screen is free of the inter-screen and subjective moires. However, it results in brightness variation called as stochastic noise. In this paper, a new AM-FM hybrid screen design technique is proposed. In the proposed method, locations of dot cluster centers are determined first by a distance measure based algorithm. They serve as initial patterns to construct AM-FM hybrid screens. Number of dot cluster centers is chosen based on the maximum screen frequency allowed for a given printer. Dot cluster centers should be distributed homogeneously within and between color channels. Also, there should not be noticeable tiling artifacts. Dot orders of highlight area are decided during the construction of initial patterns. For the gray levels darker than that of initial patterns, dot clusters start to be formed. In order to expand dot clusters while maintaining the green noise characteristics with a peak at the principal frequency of cluster centers, an optimum dot growth filter is designed. A set of pixel locations is determined by the proposed dot growth filter. In order to reduce brightness variation and low frequency noise, channel dependent dot growth algorithm is proposed. Among the set of candidates, a pixel location that minimizes brightness variation is selected.

Clustered dots screens are widely used in digital printing. Our research focuses on irregular cluster-dot screens. Irregular screens are appealing since there are many more irregular screens than regular ones. As a result, they provide a larger set of multi-separation screen combinations for avoiding interaction between screening frequencies of concurrent screens. Their down side is that they often have harmonic artifacts. Our design challenge is to reduce these artifacts' visual impact. We present frequency-domain based methods to reduce these artifacts' visual impact. State-of-the-art screens incorporate many, predominantly spatial domain, design considerations which we cannot ignore. Accordingly, the proposed methods are designed to introduce minimal modifications to given screens. The proposed methods eliminate, or reduce the few artifacts visible in a set of irregular screens. This work can be generalized to other printing technologies, and to screen design.

Stochastic screening technique uses a fixed threshold array to generate halftoned images. When this technique is applied to color images, an important problem is how to generate the masks for different color planes. Ideally, a set of plane dependent color masks should have the following characteristics: a) when total ink coverage is less than 100%, no dots in different colors should overlap from each other. b) for each individual mask, dot distribution should be uniform, c) no visual artifact should be visible due to the low frequency patterns. In this paper, we propose a novel color mask generation method in which the optimal dot placement is searched directly in spatial domain. The advantage of using the spatial domain approach is that we can control directly the dot uniformity during the optimization, and we can also cope with the color plane-dependency by introducing some inter-plane constraints. We will show that using this method, we can generate plane dependent color masks with the characteristics mentioned above.

Halftones, or periodic cluster dithers, are point-to-point, contone pixel to halftone dot, conversion processes. This paper describes an approach to achieving accurate halftone reproduction by using the errors caused during the scan conversion process without comparison to the source pixels and maintaining the point-to-point scan conversion paradigm. Two types of density errors encountered in the halftoning process are considered. 1. An error describing the difference between the input pixel value and the halftone threshold value. 2. An error describing the difference between the density level of the output data and the reflection density of the ink or toner on the page.

We present an analysis and model for evaluation of color shifts in halftone printing caused by inter-separation misregistration for periodic clustered dot halftones. Using a lattice framework, we present intuitive analysis that demonstrates conditions under which the average color is asymptotically invariant under inter-separation misregistration. Combining the framework with an analytic representation for the halftone dots, we develop a hybrid analytical-numerical model for quantitatively estimating color shifts as a function of inter-separation misregistration. The model is compared against experimental data for a xerographic printer.

As vector error filters are capable of passing errors generated in one color component to other color components, it provides more flexibility in shaping the halftone texture. As a result, it may potentially produce halftones with better image quality. In this paper, we analyze color error diffusion with vector error filters. In particular, we will discuss its halftone spectrum features and its stability conditions with respect to the filter coefficients. For spectrum analysis, we will derive the high-pass and average color preservation conditions, which ensure decent image quality. Since error diffusion is a feedback system, the vector error filters may cause instability, if it is not properly designed. This may potentially generate ever-increasing quantization error that masks the input and produces unacceptable output images. The stability conditions we will discuss provide guidelines for designing stable systems.

There are two main families among the halftoning methods: halftoning by masking (i.e. blue noise masking) and error diffusion halftoning. The first family produces neither "worms" nor defects related to stationary regimes but has a limited spatial bandwidth. The error diffusion halftoning method is characterized by a very broad spatial bandwidth allowing good rendition of very thin lines and patterns but this method presents sometimes unpleasant worms or stationary regimes. These methods are complementary with respect to quality. In this paper we propose a halftoning algorithm in black and white, derived from the error diffusion of Floyd Steinberg. By using a new threshold modulation, our new method combines the advantages of both masking and error diffusion algorithms. In order to evaluate our algorithm we defined a set of test images allowing the evaluation of the critical points of quality for the technical imagery: graininess, patterning and spatial bandwidth. The rendering of the presented algorithm has low graininess, no unpleasant patterning and broad spatial bandwidth.

This paper presents a generalization of dispersed-dot dithering. While existing methods such as Bayer's assume that color dots are arranged in a square matrix, this method works with arbitrarily-placed color points. To create a good dither pattern for arbitrarily-placed points, they must be ordered so that consecutive pairs are maximally separated. In this paper, the ordering is obtained by hierarchically coloring the vertices of the points' adjacency graph. Each level in the coloring hierarchy adds a color digit to each graph vertex's label, and sorting the resulting multi-digit labels produces the desired consecutive-point separation. The method can reproduce Bayer's dispersed-dot dither matrices, but can also produce many similar matrices. Multiple matrices can be used to minimize repetitive artifacts that plague Bayer dither, while retaining its parallelizability. The method can also be applied to artistic dithering: given a repeatable motif image, its pixels can be grouped into subsets, one for each gray level, and each subset ordered. Concatenating the subsets yields a dither matrix that reproduces a motif while displaying an overall image. Unlike in previous artistic dither methods, the motif image can be arbitrary, and need not be specially constructed.

Halftoning approaches to image rendering on binary devices have traditionally relied on rectangular grids for dot placement. This practice has been followed mainly due to restrictions on printer hardware technology. However, recent advances on printing devices coupled with the availability of efficient interpolation and resampling algorithms are making the implementation of halftone prints over alternate dot placement tessellations feasible. This is of particular interest since blue noise dithering principles indicate that the visual artifacts at several tone densities, which appear in rectangular-grid halftones, can be overcome through the use of hexagonal tessellations. While the spectral analysis of blue noise dithering provides the desired spectral characteristics one must attain, it does not provide the dithering structures needed to achieve these. In this paper, these optimal dithering mechanisms are developed through modifications of the Direct Binary Search (DBS) algorithm extensively used for rectangular grids. Special attention is given to the effects of the new geometry on the Human Visual System (HVS) models and on the efficient implementation of the hexagonal-grid DBS. This algorithm provides the best possible output at the expense of high computational complexity, and while the DBS algorithm is not practical in most applications, it provides a performance benchmark for other more practical algorithms. Finally, a tone-dependent, hexagonal-grid, error-diffusion algorithm is developed, where the DBS algorithm is used to optimize the underlying filter weights. The characteristics of the HVS are thus implicitly used in the optimization. Extensive simulations show that hexagonal grids do indeed reduce disturbing artifacts, providing smoother halftone textures over the entire gray-scale region. Results also show that tone-dependent error-diffusion can provide comparable results to that of the DBS algorithms but at a significantly lower computational complexity.

In this paper we illustrate an application that displays high-resolution images on Multi-Projector Tiled High Resolution Display Wall. Our goal is to enable the users to view high-resolution image data, such as photos from satellites and microscopes. Panoramas can also be played circularly. Users pan across the image, scale the image, and play panoramas interactively. Our prototype is implemented over a local area network with a PC cluster and a monitor. Image data are initially stored in the monitor PC. The critical issues emphasized in this paper are: using dynamically-selected multi-resolution texture hierarchy to overcome the limit of texture size, using binary-tree transferring structure to reduce the latency from O(N) to O(log₂ N)(N is the number of Displayer PCs), and using parallel Macro-Micro clocks for system synchronization to eliminate accumulated displacement while achieving a high frame-rate.

It is difficult to segment and detect the boundary of cloud images because of the complicated and various shapes and blurry edges of cloud. In this paper, we present an idea and a set of realizable design about self-adaptive segmentation by means of mathematical morphology firstly. Then, we proposed a boundary detection method base on wavelet transform. Some practices show that the segmentation models are self-adaptive, the whole processing system is general and the algorithm is high efficient in the processing of infrared satellite cloud image.

The principle of electrical capacitance tomography (ECT) is introduced and the simulation based on the finite element method (FEM) about the sensitivity distribution of 12-electrode capacitance transducers for oil and water two-phase flow system is discussed. The optimal function is presented based on sensitivity distribution which plays an important role in image reconstruction. The influence which the structural parameters of transducers impose on the performance of ECT is studied and the parameter optimizing is achieved by employment orthogonal design method combined with FEM.

An analytic method of embedding color watermarks into the color images is proposed. The original image is color image of size 480X640, and the watermark image is 24-bit-gray scale image of size 120X160. The quality variations of the embedded image and extracted watermark are analyzed. From the experimental results they appear that the quality of embedded image varies with the quantization index (QI). They also show that the quality of extracted watermark is dependent on the gray-level of the original image. The relationship between the gray-level and the noise of embedded image has been quantitatively analyzed. The digital quantization method is also important to decrease the noise of embedding image and the error of extracting watermark.

The image quality cannot be easily applied to a color management system because the quality cannot be quantified by objective methods in general. In this paper, two subjective experiments are performed to quantify the relation between the printed image quality and the color-change of the images. In these experiments, observers are requested to estimate the color-changed images that are caused by the saturation decrease of three primary colors. The results of the experiment show that decreasing color saturation of the primary colors affects the quality of printed images. In addition, the decreasing saturation of B on image quality is significantly larger than the effects of decreasing saturation of other primary colors.