We have measured how color appearance of squarewave bars varies with stimulus strength and spatial frequency. Observer's adjusted the color of an uniform patch to match the color appearance of the bars in squarewave patterns. We used low to moderate squarewave patterns, from one to eight cycles per degree (cpd). The matches are not photoreceptor matches, but rather are established at more central neural sites. The signals at the putative central sites obey several simple regularities. The cone contrast of the uniform patch is proportional to squarewave stimulus strength (color-homogeneity) and additive with respect to the superposition of equal frequency squarewaves containing different colors (color-superposition). We use the asymmetric matches to derive, from first principles, three patterncolor separable appearance pathways. The matches are explained by two spectrally opponent, spatially lowpass mechanisms and one spectrally positive, spatially bandpass mechanism. The spectr...

Lossy compression algorithms used in digital video systems produce artifacts whose visibility strongly depends on the actual image content. Simple error measures such as RMSE or PSNR, albeit popular, ignore this important fact and are only a mediocre predictor of perceived quality. Many applications require more reliable assessment methods. This paper discusses issues in vision modeling for perceptual video quality assessment (PVQA). Its purpose is not to describe a particular model or system, but rather to summarize and to provide pointers to up-to-date knowledge of important characteristics of the human visual system, to explain how these characteristics may be incorporated in vision models for PVQA, to give a brief overview of the state-of-the-art and current efforts in this field, and to outline directions for future research.

In this paper, we propose a new technique for halftoning color images. Our technique parallels recent work in modell, etscd halftoning fm both monochrome and color image, we iucorpurat, c t hunion visual model t, liat account, for the difference in the responses of the hnman viewer to lnminance and chrominance information. Thus, the RGB color space must be transformed to a hlminartce/chrominance based color space. The color transformation we use is a linearization of/.he uniIbrm color space L*a'/' which alo alecouples change between the lnminance and chrominance colnponents. After deriving a tractable expression for total-squared perceived error, we then apply the method of Iterated Conditional Modes (ICM) to iteratively toggle halftone values and exploit several degrees of freedom in reducing the perceived error as predicted by the model.

Color image quality depends on many factors, such as the initial capture system and its color image processing, compression, transmission, the output device, media and associated viewing conditions. In this paper, we are primarily concerned with color image quality in relation to compression and transmission. We review the typical visual artifacts that occur due to high compression ratios and/or transmission errors. We discuss color image quality metrics and present no-reference artifact metrics for blockiness, blurriness, and colorfulness. We show that these metrics are highly correlated with experimental data collected through subjective experiments. We use them for no-reference video quality assessment in di#erent compression and transmission scenarios and again obtain very good results. We conclude by discussing the important e#ects viewing conditions can have on image quality.

Image halftoning converts a high-resolution image to a low-resolution image, e.g. a 24-bit color image to a three-bit color image, for printing and display. Vector error di#usion captures correlation among color planes by using an error #lter with matrix-valued coe#cients. In optimizing vector error #lters, Damera-Venkata and Evans transform the error image into an opponent color space where Euclidean distance has perceptual meaning. This paper evaluates color spaces for vector error #lter optimization. In order of increasing quality, the color spaces are YIQ, YUV, opponent#byPoirson and Wandell#, and linearized CIELab #by Flohr, Kolpatzik, Balasubramanian, Carrara, Bouman, and Allebach#.

AbstractÐIn this paper, we consider accelerated rendering of high quality walkthrough animation sequences along predefined paths. To improve rendering performance, we use a combination of a hybrid ray tracing and Image-Based Rendering (IBR) technique and a novel perception-based antialiasing technique. In our rendering solution, we derive as many pixels as possible using inexpensive IBR techniques without affecting the animation quality. A perception-based spatiotemporal Animation Quality Metric (AQM) is used to automatically guide such a hybrid rendering. The Image Flow (IF) obtained as a byproduct of the IBR computation is an integral part of the AQM. The final animation quality is enhanced by an efficient spatiotemporal antialiasing which utilizes the IF to perform a motioncompensated filtering. The filter parameters have been tuned using the AQM predictions of animation quality as perceived by the human observer. These parameters adapt locally to the visual pattern velocity. Index TermsÐWalkthrough animation, human perception, video quality metrics, motion-compensated filtering. æ 1

several psychophysical studies in apparent motion (AM) have established that the perception of motion is significantly impaired at equiluminance. Still debated, however, is whether color alone can resolve ambiguities in AM. We report here on several psychophysical experiments, the quantitative results of which indicate that color does play a substantial role in AM. These findings seem to support recently proposed neurophysiological frameworks according to which there exist significant interactions among the neuronal pathways mediating the perception of basic visual attributes such as color, motion, form and depth. Color Luminance Apparent motion Equiluminance

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f q A method is described for reducing the visibility of artifacts arising in the display o uantized color images on CRT displays. The method is based on the differential spatial senv sitivity of the human visual system to chromatic and achromatic modulations. Because the isual system has the highest spatial and temporal acuity for the luminance component of an - i image, we seek a technique which will reduce luminance artifacts at the expense of introduc ng high-frequency chromatic errors. In this paper we explore a method based on controlling - n the correlations between the quantization errors in the individual phosphor images. The lumi ance component is greatest when the phosphor errors are positively correlated, and is minimi ized when the phosphor errors are negatively correlated. The greatest effect of the correlation s obtained when the intensity quantization step sizes of the individual phosphors have equal y s luminances. For the ordered dither algorithm, a version of the method can be implemented b imply inverting the matrix of thresholds for one of the color components. H 1.

Conventional grayscale error di#usion halftoning produces worms and other objectionable artifacts. Tone dependent error di#usion #Li and Allebach# reduces these artifacts by controlling the di#usion of quantization errors based on the input graylevel. Li and Allebach optimize error #lter weights and thresholds for each #input # graylevel based on a human visual system model. This paper extends tone dependent error di#usion to color. In color error di#usion, what color to render becomes a major concern in addition to #nding optimal dot patterns. We present a visually optimum design approach for input level #tone# dependent error #lters #for each color plane#. The resulting halftones reduce traditional error di#usion artifacts and achieve greater accuracy in color rendition.