Mark D. Fairchild

A multiscale model of adaptation and spatial vision for realistic image display

In this paper we develop a computational model of adaptation and spatial vision for realistic tone reproduction. The model is based on a multiscale representation of pattern, luminance, and color processing in the human visual system. We incorporate the model into a tone reproduction operator that maps the vast ranges of radiances found in real and synthetic scenes into the small fixed ranges available on conventional display devices such as CRT’s and printers. The model allows the operator to address the two major problems in realistic tone reproduction: wide absolute range and high dynamic range scenes can be displayed; and the displayed images match our perceptions of the scenes at both threshold and suprathreshold levels to the degree possible given a particular display device. Although in this paper we apply our visual model to the tone reproduction problem, the model is general and can be usefully applied to image quality metrics, image compression methods, and perceptually-based image synthesis algorithms. CR Categories: I.3.0 [Computer Graphics]: General;

iCAM06: A refined image appearance model for HDR image rendering

A new image appearance model, designated iCAM06, was developed for High-Dynamic-Range (HDR) image rendering. The model, based on the iCAM framework, incorporates the spatial processing models in the human visual system for contrast enhancement, photoreceptor light adaptation functions that enhance local details in highlights and shadows, and functions that predict a wide range of color appearance phenomena. Evaluation of the model proved iCAM06 to have consistently good HDR rendering performance in both preference and accuracy making iCAM06 a good candidate for a general-purpose tone-mapping operator with further potential applications to a wide-range of image appearance research and practice.

Time course of chromatic adaptation for color-appearance judgments

Observer production of achromatic appearance has previously been used to measure the time course of chromatic adaptation for changes from daylight to incandescent illuminants at constant luminance, indicating an exponential decay of chromatic adaptation with a time constant of the order of 10 s. The work extends previous results in several ways. The psychophysical technique was significantly improved to provide more reliable estimates of color appearance as a function of adaptation duration, and the time course of chromatic adaptation was measured for six chromaticity changes. Three observers tracked achromatic appearance on a computer-controlled CRT display during transitions of 2-min duration between the various chromaticities. The results indicate that observer differences are statistically significant. However, differences in time course for different chromaticity changes are not statistically significant (within observer). Single or piecewise exponential decay functions cannot be fitted to the data. However, sum-of-two-exponentials functions provided accurate descriptions of the data. The results suggest two stages of adaptation: one extremely rapid (a few seconds) and the other somewhat slower (approximately 1 min). Chromatic adaptation at constant luminance was 90% complete after approximately 60 s.

Evaluating HDR rendering algorithms

A series of three experiments has been performed to test both the preference and accuracy of high dynamic-range (HDR) rendering algorithms in digital photography application. The goal was to develop a methodology for testing a wide variety of previously published tone-mapping algorithms for overall preference and rendering accuracy. A number of algorithms were chosen and evaluated first in a paired-comparison experiment for overall image preference. A rating-scale experiment was then designed for further investigation of individual image attributes that make up overall image preference. This was designed to identify the correlations between image attributes and the overall preference results obtained from the first experiments. In a third experiment, three real-world scenes with a diversity of dynamic range and spatial configuration were designed and captured to evaluate seven HDR rendering algorithms for both of their preference and accuracy performance by comparing the appearance of the physical scenes and the corresponding tone-mapped images directly. In this series of experiments, a modified Durand and Dorseys bilateral filter technique consistently performed well for both preference and accuracy, suggesting that it is a good candidate for a common algorithm that could be included in future HDR algorithm testing evaluations. The results of these experiments provide insight for understanding of perceptual HDR image rendering and should aid in design strategies for spatial processing and tone mapping. The results indicate ways to improve and design more robust rendering algorithms for general HDR scenes in the future. Moreover, the purpose of this research was not simply to find out the “best” algorithms, but rather to find a more general psychophysical experiment based methodology to evaluate HDR image-rendering algorithms. This paper provides an overview of the many issues involved in an experimental framework that can be used for these evaluations.

iCAM framework for image appearance, differences, and quality

Traditional color appearance modeling has recently ma- tured to the point that available, internationally recommended mod- els such as CIECAM02 are capable of making a wide range of pre- dictions, to within the observer variability in color matching and color scaling of stimuli, in somewhat simplified viewing conditions. It is proposed that the next significant advances in the field of color ap- pearance modeling and image quality metrics will not come from evolutionary revisions of colorimetric color appearance models alone. Instead, a more revolutionary approach will be required to make appearance and difference predictions for more complex stimuli in a wider array of viewing conditions. Such an approach can be considered image appearance modeling, since it extends the concepts of color appearance modeling to stimuli and viewing envi- ronments that are spatially and temporally at the level of complexity of real natural and man-made scenes, and extends traditional image quality metrics into the color appearance domain. Thus, two previ- ously parallel and evolving research areas are combined in a new way as an attempt to instigate a significant advance. We review the concepts of image appearance modeling, present iCAM as one ex- ample of such a model, and provide a number of examples of the use of iCAM in image reproduction and image quality evaluation.

Precision requirements for digital color reproduction

An environment was established to perform device-independent color reproduction of full-color pictorial images. In order to determine the required precision for this environment, an experiment was performed to psychophysically measure colorimetric tolerances for six images using paired comparison techniques. These images were manipulated using 10 linear and nonlinear functions in the CIELAB dimensions of lightness, chroma, and hue angle. Perceptibility tolerances were determined using probit analysis. From these results, the necessary precision in number of bits per color channel was determined for both the CIELAB and the CRT rgb device color spaces. For both the CIELAB color space and the CRT rgb device space, approximately eight color bits per channel were required for imperceptible color differences for pictorial images, and 10 bits per channel were required for computational precision.

Refinement of the RLAB Color Space

The prediction of color appearance using the RLAB color space has been tested for a variety of viewing conditions and stimulus types. These tests have shown that RLAB performs well for complex stimuli and not-so-well for simple stimuli. This article reviews the various psychophysical results, interprets their differences, and describes evolutionary enhancements to the RLAB model that simplify it and improve its performance.

Psychophysical evaluation of gamut mapping techniques using simple rendered images and artificial gamut boundaries

Using a paired comparison paradigm, various gamut mapping algorithms were evaluated using simple rendered images and artificial gamut boundaries. The test images consisted of simple rendered spheres floating in front of a gray background. Using CIELAB as our device-independent color space, cut-off values for lightness and chroma, based on the statistics of the images, were chosen to reduce the gamuts for the test images. The gamut mapping algorithms consisted of combinations of clipping and mapping the original gamut in linear piecewise segments. Complete color space compression in RGB and CIELAB was also tested. Each of the colored originals (R,G,B,C,M,Y, and Skin) were mapped separately in lightness and chroma. In addition, each algorithm was implemented with saturation (C(*)/L(*)) allowed to vary or retain the same values as in the original image. Pairs of test images with reduced color gamuts were presented to twenty subjects along with the original image. For each pair the subjects chose the test image that better reproduced the original. Rank orders and interval scales of algorithm performance with confidence limits were then derived. Clipping all out-of-gamut colors was the best method for mapping chroma. For lightness mapping at low lightness levels and high lightness levels particular gamut mapping algorithms consistently produced images chosen as most like the original. The choice of device-independent color space may also influence which gamut mapping algorithms are best.

Observer variability in metameric color matches using color reproduction media

Standard color-matching functions are de

Ganglion cell pathways for rod vision

Measurements of the acuity of rod vision made by two different techniques show it to vary only slightly with eccentricity. At eccentricities beyond 15 deg acuity is well predicted from the sampling properties of the mosaic of the P-class of ganglion cells. With decreasing eccentricity acuity falls progressively below the sampling limit of P-cells, but even at the lowest eccentricity examined (5 deg) does not reach the limit imposed by the sampling properties of the mosaic of M-cells. At an eccentricity of 5 deg rod vision could be supported by as few as 20% of P-cells.