Methods for understanding the fundamental mechanisms of laser photothermal imaging are described and applied to model imaging media. The light response is characterized with a series of Gaussian laser pulses of varying intensities and durations. The results are compared to a reference model, the "local fluence" model, that assumes the likelihood of exposure at a given pulse duration depends solely on the laser fluence received at that location. The mechanisms underlying the material behavior are studied with time-resolved microscopy using a variety of exposure and viewing conditions. The imaging media have in common a silicone rubber (polydimethylsiloxane) coating that can be removed by a single laser pulse to form an imaged spot that attracts ink. They differ in having a thin-film absorber layer, a volume absorber layer, or a combination of volume absorber and energetic underlayer. The thin-film media are the least sensitive with longer duration microsecond pulses but the most sensitive with nanosecond pulses, which is explained using a thermal conduction model. The volume absorbing media show deviations from the local fluence model that indicate the existence of useful dot gain properties which improve sensitivity. Time-resolved microscopy shows that this dot gain results from high-speed mechanical effects caused by hot gas trapped under a silicone rubber balloon.

In this paper we propose a new strategy of watermarking which extends the principle of histogram specification to color histogram. The proposed scheme embeds into a color image a color watermark from either the xy chromatic plane or the xyY color space. The scheme resists to geometric attacks (e.g., rotation, scaling, etc.,) and, within some limits, to JPEG compression. The scheme uses a secret binary pattern, or combines some patterns generated by a secret key to modify the chromatic distribution of an image. By using the inverse pattern, the watermark is detected without knowing the original image. Examples of images and attacks are given to illustrate the relevance of the proposed approach, i.e., its invisibility and the robustness. In the second part of this paper we investigate the usefulness of our watermarking approach for color image authentication. Several experiments are presented to show that our scheme ensures image authentication, detects tampered regions in case of malicious attacks and ensures a certain degree of robustness to common image manipulations like JPEG compression, etc. Compared with other blind authentication schemes, the experiments show that the detection ability, the invisibility, as well as the robustness to some common image processing are improved.

In this paper, we present a new steganographic method based on the pixel value differencing approach. The previous research of pixel value differencing can provide a better visual quality after embedding secret data than the well-known least-significant-bit (LSB) method but the embedding data capacity is much less than LSB method. We propose a new steganographic method by using pixel value differencing that hide secret data only in smooth areas, and this new method can provide much more hiding capacity than the previous research. The experimental results show the proposed method can hide much more data and keep a good visual quality of the stegoimage.

Probably, the most well-known vector filter is the vector median filter (VMF) which is based on the theory of robust statistics and performs good noise suppression in color images. However, the VMF is designed to perform a fixed amount of smoothing. This may lead to too much unnecessary substitutions in the input image and, as a result, blurring and loss of image details. In order to avoid this drawback when dealing with impulsive noise, the switching schemes aim at selecting a set of pixels of the input image to be filtered leaving the rest of the pixels unchanged. In this paper, two switching filters which base the selection of the noisy pixels to be filtered on statistical tests are proposed. The proposed filters present good noise suppression while preserving fine image details appropriately. Comparisons to classical and recently introduced impulsive noise multichannel filters are provided. Moreover, the noisy pixel selection techniques are computationally simple, and the filters significantly reduce the computational complexity of the VMF.

Text-enhanced error diffusion is proposed to sharpen text regions in complex documents, including natural images with a multifunctional printer. To enhance the sharpness of the text regions, the input image is segmented into text and background regions using the maximum gradient difference. Edge-enhanced error diffusion is then applied to the text regions to sharpen the text, while Floyd and Steinberg's error diffusion is applied to the background regions to obtain smooth dot patterns. However, this combination of algorithms can generate two kinds of artifact around the text regions: boundary and dot-elimination artifacts. Boundary artifacts are a series of dots distributed around text blocks, and this propagation error generated below a text line by the edge-enhanced error diffusion is largely diffused forward into the background region. Thus, to gradually decrease these propagation errors, a grayscale dilation operator is processed along the boundary of a text block, thereby creating a gradual dilated transition region. Edge-enhanced error diffusion using different multiplicative parameters is then applied to these regions. Meanwhile, dot-elimination artifacts are dot-disappearing phenomena occurring around high-frequency regions due to the characteristic of the edge-enhanced error diffusion to sharpen edge regions more. Thus, an error scaling factor is inserted in front of the error filter in the architecture of the edge-enhanced error diffusion to scale down the propagation errors. Experiments demonstrate that text readability is improved by increasing the sharpness of the text regions, and a less grainy appearance is simultaneously achieved compared with conventional edge-enhanced error diffusion in the background regions.

The most straightforward way of halftoning a color image is to halftone its cyan, magenta, and yellow channels independently. It has been shown in literature that halftoning the color channels dependently and using dot-off-dot strategy as much as possible will improve the print quality. Since a yellow dot on white substrate is much less visible than the other two colored dots in a number of methods only the C and M channels are halftoned dependently and the Y channel is halftoned independent of the two others. In this paper we will show that preventing the yellow dots from being printed on blue dots will improve the print quality and results in smoother textures. The color reproduction and the ink consumption for the proposed dependent color halftoning are also discussed.

With the popularization of digital photo printing, there is a demand for print image quality that approaches the quality of silver halide photographs. One way to achieve this is through automatic correction of image luminance/tone. The conventional approach based on spatially invariant mapping often causes undesired luminance changes when enhancing contrast; moreover, luminance changes are also accompanied by changes in contrast. This paper proposes a novel algorithm for the enhancement of the contrast and lightness using spatially variant mapping to achieve high-quality printing of images photographed using digital cameras. First, we define a "contrast-gain" function to quantitatively evaluate the visual contrast that results from tone mapping. Based on this function, the proposed tone mapping algorithm enables independent control of the lightness and contrast through spatially variant processing. Next, we formalize a "shadow-up tone curve," which produces an effect similar to auxiliary lighting during photography. Our contrast-gain-based visual tone mapping method, which uses the shadow-up tone curve in the algorithm, has none of the unnaturalness that arises with a conventional single tone curve. Furthermore, it provides an extremely natural effect similar to that in images photographed by a professional photographer using auxiliary light provided by a reflection board.

The concepts and technology for an open loop color management system such as that specified by the International Color Consortium (ICC) have been around for a number of years. The adoption of this workflow by the graphic arts industry has been slow. A major contribution to the lack of popularity is that the quality part of the ICC workflow is unregulated and the average user is unable to independently assess the quality of profiles and profile making software. This paper describes a number of test methods that can be used to evaluate the colorimetric accuracy of ICC scanner, monitor, and printer profiles. ICC profiles are being used in a number of color proofing scenarios. In order to understand the color reproduction abilities of such proofing systems it is necessary to quantify the accuracy of the underlying ICC profiles used in the workflow. A quality metric can be useful to provide feedback on how well a device has been characterized and therefore provide limits on the ability of a color managed system. Further, a universally defined merit figure will allow the comparison of results across manufacturers, allowing the user to make informed choices appropriate for their workflow. If we are able to establish a benchmarking procedure akin to the miles per gallon fuel consumption quoted for motor vehicles this provides a universal quality metric that can help raise the quality of profiling software, assist user choice, and ultimately lead to the greater acceptance of ICC color management in graphic arts and the printing industry. The quality of input profiles is described in terms of a ΔE calculation. Input profiles from ten different profiling packages were evaluated. Profiles were made for a flatbed scanner using Agfa, Fuji, and Kodak IT8.7/2 targets. The average ΔE for input profiles is shown to be in the range of ΔE 0.60–2.46. A procedure is described for evaluating the quality of monitor profiles in terms of measured gamma, white point and the color reproduction of 24 specially chosen colors. Eleven monitor systems were evaluated. Monitor profiles were made for an Apple Cinema HD LCD display and measurements were made to verify the accuracy of these profiles using a telespectroradiometer. It is shown that commercial products were able to reproduce 24 patches of a color checker on a monitor with an average ΔE of 2.92–5.81. A printer profile metric is also described. This research describes three possible metrics for a printer profile–accuracy of the B2A1 tag (PCS to Device), A2B1 tag (Device to PCS), and a round trip test. Data are presented to show that the average accuracy of the output profile colorimetric intent (average of B2A1 and A2B1) for an Epson ink jet printer can be between ΔE 1.72–3.49. The accuracy of the printer profile is useful when considering the use of an ink jet printer in color management proofing workflows. This research proposes a ΔE metric system that can be used to evaluate the quality of commercially created ICC input, display, and output profiles. The data presented here are fundamentally a methodology that can be used to estimate the colorimetric accuracy of profiles. The use of commercial profiling products is only to illustrate how the metrics may be determined in practice. The data, however, do show useful information about the state of color management products today and this analysis can be used to track the improvements and evolution in ICC profiling software.

The color characterization of digital cameras often requires the use of standard charts containing a fixed number of color samples. The exact choice of such characterization charts–how many (and which) known samples to include–is known to affect characterization performance. This study describes methods to select optimum color samples from a set of 1269 Munsell surface colors. The effect of sample selection on characterization performance is evaluated and compared with performance using the standard GretagMacbeth ColorChecker and GretagMacbeth ColorChecker DC colors. The work confirms that the standard charts appear to have been well selected. However, we show that it is possible to select 24 samples from the Munsell set that outperform the GretagMacbeth ColorChecker and that this selection can be efficiently derived using an algorithm called MAXMINC. It is proposed that this algorithm may have general applicability; for example, to the optimal selection of samples constrained to be a subspace Munsell color solid.

We have developed an image eraser for reuse of paper printed on with decolorizable toner, which is composed of leuco dye and developer. The decolorizable toner loses color when heated. The image eraser enables decolorization of a bundle of paper instead of one sheet at a time. Before designing the image eraser, we studied three problems caused by heating, ghost images, sticking, and color change of paper. We have optimized the heating conditions of the image eraser, i.e., the heating temperature is 130–140 °C, and the heating period is 2h.