Three elliptical skin color models are presented for skin color detection. The first one is to model the skin color cluster using a single ellipse ignoring the lightness dependency. It is simple and efficient, and the skin color detection accuracy may be adequate for many applications. In the second model, the skin color ellipse is adapted to different lightness levels to better fit the shape of the skin color cluster. The model is more complex to train, and the computation efficiency is lower, but the skin color detection accuracy is considerably higher. In the third method, an ellipsoid is trained to fit the skin color cluster. It is almost as simple to train as the first model, but the skin color detection accuracy is higher. Having skin color detection accuracy almost as high as the second model, this model is easier to train and may be more efficient in computation.

Color embedding and recovery are investigated using a wavelet transform that enables color information to be hidden in gray images and then retrieved to recover color images. In a wavelet transform, high-frequency subbands are replaced by chrominance information from an image, yet the use of subbands can cause some loss of details and saturation. Therefore, this article proposes color embedding and recovery using a wavelet packet transform with a pseudorandom code to embed saturation information. In the color-to-gray process, the RGB is first converted to YCbCr color space to perform a two-level wavelet packet transform for a Y image. The CbCr color components are then embedded into the two subbands with the minimum amount of energy in the Y image, thereby minimizing the loss of details when compared to using a wavelet transform. In addition, to compensate the color saturation, the maximum and minimum values of the CbCr components from the original image are embedded into the diagonal-diagonal subband in a pseudorandom code form. In the recovery process, the saturation of the recovered image is compensated by applying the ratio of the original CbCr values to the extracted CbCr values. Experimental results show that the proposed method improves the color saturation of the recovered image when comparing the color difference and peak signal-to-noise values.

This article presents a measurement method for integrated three-dimensional shape and multispectral color measurement with the use of a single detector for data acquisition. Its implementation comprises a shape measurement system using structured light projection combined with a custom developed multispectral camera. Both devices are controlled by dedicated software which enables the estimation of spectral reflection in every point registered on the surface of the measured object. The main application of this research is the digitization of cultural heritage objects for storage, visualization, and copying purposes. Examples of measurement results are presented as well as discussion of measurement uncertainty and directions of further research.

To overcome shortcomings of digital images or to reproduce traditional film grains, some photographers add noise to digital image. In an effort to find a factor of preferable noise, the authors analyzed how a professional photographer introduces noise into black-and-white images and found two characteristics: (1) There is more noise in midtones than in highlights and shadows and (2) histograms in highlights are skewed toward shadows, and vice versa, while almost symmetrical in midtones. The authors also found that by approximating the symmetrical histograms by a Gaussian distribution and skewed ones by a chi-squared distribution, the noise could be reproduced to an extent that well satisfies the professional. Comparison of professional's noise to film grain showed that they have the following in common: (1) more noise in midtones but almost none in brightest and darkest region and (2) asymmetrical histograms in highlights and shadows. The authors think that these characteristics might be candidates for "good" noise" that allows simulation of traditional film photography.

In this study, the authors investigated how noise affects sharpness perception. The authors probed the sharpness of black-and-white tree bark images with various noise levels. Overall, the sharpness decreased as the noise amount increased, while some observers seemed to perceive more sharpness. The authors next used one- and two-dimensional unifrequency patterns as stimuli in an attempt to reduce such variability in the judgment. The result showed that sharpness of higher-frequency stimuli decreased with increased noise, while that of lower-frequency stimuli increased at certain levels. From this result, the authors thought that noise reduces the sharpness at edges, but can sharpen the lower-frequency component or texture of the image. To prove this prediction, the authors experimented again with the image used in the first experiment. The perceived sharpness only decreased when noise was added to the edge regions, whereas it improved when noise was applied to texture. The authors consider that the interaction between noise and texture increases the perception of image sharpness.

Differential gloss is the term used to describe the condition where areas of a printed image, especially adjacent areas, appear to reflect light in different ways giving these areas distinctly different gloss appearances. This phenomenon is quite common in dry toner electrophotographic imaging and some ink jet imaging technologies. Differential gloss, while well known, is difficult to quantify in a meaningful way. One of the tasks undertaken by international standards community was to develop an image quality scale for the visual attribute of differential gloss. In an attempt to do this, experimentation was conducted using prints of three scenes. The results of this experimentation showed that the rankings made by the observers were scene dependent, indicating that the single number provided by measuring gloss differences on a patch target would be insufficient to describe the differential gloss perceived in complex images. The experimentation described in this study was undertaken to examine the effect of scene content on the perceptibility of differential gloss. The results indicate that gloss differences are more perceptible when they are central to the scene, are separated by well-defined edges, and of a feature size greater than about 0.5 cm but less than about 10 cm. The experiment also provided evidence that the presence of a human face can increase the perceptibility of differential gloss.

A system using interaction of evanescent light waves with particles in a liquid allows one to observe accumulation, stability, and adhesion of such particles at and in the vicinity of a surface. Accumulation can be due to electrophoresis, sedimentation, or equilibration of the substrate surface with the bulk solution. The observation is sensitive only to particles within 1 μm of the interface, so it can be made with an arbitrary thickness of fluid. Evanescent wave absorption is monitored adjacent to an indium tin oxide coated glass slide affixed to a high index prism. The test fluid can be either constrained by a secondary metal electrode or left as a free fluid film. In the latter case a free charge can be injected into the system from an external charge generator allowing one to separate field- and charge-induced effects. This system is ideal for investigating device life limiting interactions between colorants and substrates in displays.

The dynamics of toner and carrier particles in a two-component development system used in electrophotography were studied to clarify the development characteristics and to reduce the image defects due to the bead-carry-out (BCO) phenomenon. The height of the developed toner line image and the density of carrier particles adhered to the photoreceptor surface after development were measured and the behavior of the toner and carrier particles was observed using a high-speed microscope camera. This study clarifies that development occurs not only in the contact area between the carrier brush and the photoreceptor but also in the pre- and postnip regions where the brush does not make contact with the photoreceptor and that the occurrence of BCO is reduced in the image area rather than in the nonimage area at a low dc development voltage at a high toner concentration and with the development sleeve at a high-speed ratio. The mechanisms of these phenomena are investigated using independent experimental and numerical analysis.