Showing papers on "Human visual system model published in 1977"

Representing Visual Information

Abstract: : Vision is the construction of efficient symbolic descriptions from images of the world An important aspect of vision is the choice of representations for the different kinds of information in a visual scene In the early stages of the analysis of an image, the representations used depend more on what it is possible to compute from an image than on what is ultimately desirable, but later representations can be more sensitive to the specific needs of recognition This essay surveys recent work in vision at MIT from a perspective in which the representational problems assume a primary importance An overall framework is suggested for visual information processing, in which the analysis proceeds through three representations; (1) the primal sketch, which makes explicit the intensity changes and local two-dimensional geometry of an image, (2) the 2 1/2-D sketch, which is a viewer-centered representation of the depth, orientation and discontinuities of the visible surfaces, and (3) the 3-D model representation, which allows an object-centered description of the three-dimensional structure and organization of a viewed shape Recent results concerning processes for constructing and maintaining these representations are summarized and discussed (Author)

A Nonlinear Model for the Spatial Characteristics of the Human Visual System

Abstract: Several recent papers have presented data from experimental investigations of the human ivsual system (HVS) which support the general hypothesis that the HVS is composed of spatial frequency channels. It has been pointed out, however, that a linear systems analysis of the entire system is not valid. Furthermore, a nonlinear model consisting of a log-bandpass filter produced some experimental results with deviations at high spatial frequencies. A new structure for a nonlinear mathematical model which is easily quantifiable, produces results which compare with experimental data, and has a physiological correlate is presented. The significance of this model is that the bandwidth of the visual system decreases as contrast increases. Thus the system appears to maximize the signal to noise ratio while attempting to maintain a constant " perceptual" spatial-frequency fidelity.

On the Role of the Observer and a Distortion Measure in Image Transmission

Abstract: This paper considers the characteristics of the human visual system as they are related to sensitivity to encoding errors in still achromatic images. The starting point is a discussion in Section I of the role of a numerical measure of distortion in the determination of optimum encoding. Section II then discusses several ways of determining properties of the human observer and discusses the methodology of psychophysical experiments. Section III then discusses the results of a number of pertinent experiments and presents a model based on these experiments for detecting perturbations of an image. Section IV concludes by discussing how this model can be incorporated into a distortion measure and how this distortion measure might be used. Since the model of the human observer is quite complicated, the mathematical model is not tractable analytically, and results in this last section are as yet fragmentary.

Design of Quantizers for DPCM Coding of Picture Signals

Abstract: Visual thresholds play an important role in the process of incorporating properties of the human visual system in encoding picture signals. They tell us how much the picture signal can be perturbed without the perturbations being visible to human observers. We describe psychovisual experiments to determine the amplitude thresholds at a single edge having a given slope and then present methods to incorporate the visual threshold data directly into the design of quantizers for use in Differential Pulse Code Modulation (DPCM) systems. In the first class of methods, quantizer characteristics are obtained such that the quantization error is kept below the visual threshold as determined by the slope at a picture element and either (a) the number of quantizer levels, or (b) the entropy of the quantized output is minimized. In the second class of methods, different measures of the suprathreshold quantization error are minimized for a fixed number of levels, or for a given constraint on the entropy of the quantized signal. We present empirical relationships between the various distortion measures and the subjective quality of the pictures rated on a five point impairment scale. We then discuss the structure of the quantizers obtained by the above mentioned optimization methods, evaluate their performance on real pictures, and compare them with the ones described in the literature.

Constant variance enhancement: a digital processing technique

Abstract: An image enhancement process is one in which the image is manipulated for the purpose of increasing the information extractable by the human visual system. Constant variance enhancement is a technique which employs a high pass filtering to reduce the local average to zero for all regions of the picture and then applies a gain factor equal to the reciprocal of the local standard deviation to produce an output picture in which all local regions have equal variance. An example of a constant variance enhancement is presented with pictures illustrating the various mathematical stages of the processing operations. The concept of differential luminance gain is introduced as a crude measure of enhancement effectiveness and is numerically evaluated for the illustrative processing. The significance of negative differential luminance gain is considered, and ways of dealing with these spurious results are considered.

Processing by the human visual system of the light and dark contrast components of the retinal image

Abstract: The investigation is concerned with the processing of light and dark bar patterns by the human visual system. A response phenomenon, the frequency shift effect, is studied with particular attention being given to the most suitable parametric description. Previous investigations of the effect showed that the perceived spatial frequency of a test grating pattern can be changed, transiently, after a period of adaptation to a grating of different frequency. In the present work it is shown that the perceived width of the bars of one polarity (i.e. light or dark) in the test grating can be changed independently of the width of bars of the opposite polarity both in the test grating and in the adaptation grating. It is shown that there is no simple interpretation of this result in terms of the spatial frequency spectra of the gratings. It is suggested that the human visual system processes positive and negative contrast polarities in independent channels. The results are discussed in relation to the on- and off-centre receptive field characteristics obtained in microelectrode recordings from vertebrate visual systems.

Chromatic Spatial Frequency Characteristics of Human Visual System (Color Difference Discrimination)

Abstract: 色覚機能を明らかにするためにも, カラー画像伝送の基礎としても, 視覚の色度空間周波数特性を知る必要がある.ここでは無彩色を中心とする補色間の正弦波パターンの色差弁別により視覚の色度空間周波数特性を測定した.得られた周波数特性はバンドパスフィルター型であり, 明暗が最も広帯域であり, 色度では赤-緑が広帯域であり, 黄-青の組合せは最も狭帯域であった.画面輝度の影響や空間異方性についても測定した.

Interpolative Picture Coding Using a Subjective Criterion

Abstract: Interpolative picture coding refers to sending coded information about a few picture elements separated in space and interpolating all the rest of the picture elements. In this paper we consider sending coded information about picture elements separated by as large a distance as possible along a scan line. We study the effects of a few twodimensional interpolation strategies and evaluate the usefulness of several different error criteria required to judge the faithfulness of the interpolated signal. The error criteria are motivated by our knowledge of pictorial information processing in the human visual system. Based on the picture quality and entropy of the coded output as the criterion for judging the coding schemes, we find that error measures in which the interpolation error is filtered adaptively and compared to a varying threshold perform the best. The filter is adapted based on the spatial activity of the signal: high-bandwidth filter for low activity areas and low-bandwidth filter for high activity areas. The variation in threshold is based on the spatial masking of the interpolation error and has a high value in high activity areas and a low value in low activity areas. Our computer simulations indicate that, for head-and-head-and-shoulders-type pictures, it is possble, without affecting the picture quality, to reduce the entropy of the coded output by as much as 40 percent over that obtainable from previous element differential pulse code modulation (DPCM) system.

On the classification of visual patterns: Systems analysis using detection experiments

Abstract: Behavioral experiments are indispensable for the analysis of biological systems for cognition and recognition. When these are carried out as detection experiments three types of description can be used for the problem of visual pattern recognition which allow conclusions to be drawn on the operating function of the system. Provided that the signals to be recognized have additive noise superimposed on them, system description is possible: 1. on the basis on the probabilities of recognition and of mix-up,--2. through the analysis of the transformation of distribution densities of the noise,--3. by means of the measurable distances of the patterns from each other in feature space.-The analysis of the distribution densities shows that the human visual system acts like a linear classifier in the classification of six geometrical patterns. The independence of the classification from intensity as well as the human reaction to alteration in the power spectrum of the noise support this result. Simulation experiments on a computer show the efficacy of various biological relevant parameters for the linear classification and suggest that a narrow band and probably feature specific filtering precedes the classification.

Two-Dimensional Spectral Analysis for Image Coding, Processing and Recognition: An Approach Based on Some Properties of the Human Visual System

Abstract: The main purpose of this work is showing the use in the field of digital image processing (such as coding, enhancement and recognition) of what has been learned so far about the functioning of the peripheral visual system in man.

On-line digital image restoration and manipulation using a minicomputer.

Abstract: A digital image processing system using a minicomputer that has the capability to make on-line digital image processing has been developed. By use of this system image restoration of motion blurred images due to uniform linear and rotating motion has been carried out in the space domain with the aid of the idea of man–machine feedback. To restrain extreme noise amplification during the restoration process, the technique of smoothing and differentiation of the data based on a method of least squares has been applied. A new technique to manipulate the low contrast image is also demonstrated by which the processed image is observable with better appearance than that of the unprocessed one. In this manipulation, the human visual system has played an important part in complementing discarded image information.

Halftone Pictorial Encoding

Abstract: This report briefly reviews a new technique for pictorial encoding. Exploiting the characteristics of the human visual system, a halftone screening procedure is utilized to develop a binary-pixel representation of the image. This binary data is then encoded, enabling much less than 1 bit/pixel storage/communications cost. The proposed strategy is simple to implement, primarily digital, and capable of high speeds. Furthermore, the output image is most compatible with binary display and marking engine technologies.

Research on Visual Perception of Complex and Dynamic Imagery.

Abstract: : This report discusses three main research topics, each of which is interpreted in terms of a spatial frequency analysis model of the human visual system. Parameters which affect the perception of clusters of line elements in dynamic, computer-generated displays are investigated. Transitions between perception of the moving cluster as a group and perception of the motion of the individual elements of the cluster are studied as a function of display frame rate, subject dark adaptation, image contrast, spatial orientation and various positional perturbations of elements in the cluster. The effect of spatial frequency components on eye movement in real-life scenes was studied by correlating eye movement patterns obtained from photographic scenes which were spatially high-pass filtered, low-pass filtered or unfiltered. Results indicate that areas of scenes containing strong low spatial frequency components attract attention more than areas containing strong high spatial frequency components. Velocity coding in the human visual system was studied by means of moving sinusoidal gratings. Results with complex moving gratings indicate that velocity perception depends partially on the temporal variation of intensity at each point on the retina due to the moving pattern. A complex pattern containing a fundamental spatial frequency and higher harmonic components appears to be moving faster than a stimulus consisting of only the fundamental component and moving at the same velocity as the complex pattern.

A Modification of the Fourier Transform Model in Visual Perception

Abstract: i As for photographic systems , the human visual system can also be described by an MTF. However, due to the complexity and non-linearity of the visual system, the MTF alone is a poor predictor of response. We have formulated and tested two mathematical models which modify the MTF of the eye. Effectively, an imperfect integrating function (low pass filter) has been proposed to be operating on stimuli which are sent to the brain. The models were tested and found to be better predictors of visual response than the present MTF alome.