Human Visual Properties Research Articles

Adaptive image coding with perceptual distortion control

This paper presents a discrete cosine transform (DCT)-based locally adaptive perceptual image coder, which discriminates between image components based on their perceptual relevance for achieving increased performance in terms of quality and bit rate. The new coder uses a locally adaptive perceptual quantization scheme based on a tractable perceptual distortion metric. Our strategy is to exploit human visual masking properties by deriving visual masking thresholds in a locally adaptive fashion. The derived masking thresholds are used in controlling the quantization stage by adapting the quantizer reconstruction levels in order to meet the desired target perceptual distortion. The proposed coding scheme is flexible in that it can be easily extended to work with any subband-based decomposition in addition to block-based transform methods. Compared to existing perceptual coding methods, the proposed perceptual coding method exhibits superior performance in terms of bit rate and distortion control. Coding results are presented to illustrate the performance of the presented coding scheme.

Design and Evaluation of an Entirely Psychovisual-Based Coding Scheme

In this paper a new psychovisual-based coding scheme is proposed. The analysis and the quantization stages, the two main functions which determine the performances of a coding scheme, are based on the human visual system properties. In the first stage, a filter bank decomposes images into subimages of perceptual significance when a contrast transformation is applied. Analytic cortex filters have been used because they provide an accurate modelization of visual receptive fields. The choice of subbands lies on psychovisual experiments led in the laboratory. It was found that visual information is processed through 17 channels. In the second stage the use of the local band-limited contrast yields very interesting properties concerning the quantization. A scalar and vector quantization have been considered. In this latter case the vector's construction methodology preserves the main properties of the human visual system about perception of quantization impairments and takes into account the masking effect due to interaction between subbands with the same radial frequency but with different orientations. The vector's components are the local band limited contrasts Cij (m, n) defined as the ratio between the luminance Lij at the point (m, n), which belongs to the radial subband i and angular sector j and the average luminance at this location. Hence the vector's dimension depends on the orientation selectivity of the chosen decomposition. The low pass subband, which is nondirectional is scalar quantized. A methodology for automatic subsampling matrix design was also developed. The performance have been evaluated on a set of images in terms of peak SNR, true bit rates, and visual quality. For the latter, no impairments are visible at a distance of four times the height of the used high quality TV monitor. The SNRs are about 6 to 8 dB under the ones of classical subband image coding schemes when producing the same visual quality. Another particularity of this approach, due to the use of the local band limited contrast, lies in the structure of the reconstruction image error which is found to be highly correlated to the structure of the original image.

Red–green and blue–yellow mechanisms are matched in sensitivity for temporal and spatial modulation

The spatial and temporal properties of human colour vision are examined using isoluminant, red–green and blue–yellow tritanopic gratings. Chromatic sensitivity is found to be low-pass as a function of both spatial and temporal frequency along all the chromatic axes investigated, including the tritanopic confusion lines employed to examine the properties of the S-cone driven mechanism. Comparison of sensitivity to on-off and contrast reversing stimuli indicates that transient mechanisms contribute to the detection of red–green patterns but that the detection of S-cone specific patterns is governed by sustained mechanisms. By compensating for transient contributions to red–green sensitivity, it is shown that sensitivity of chromatic mechanisms dominated by L- and M-cone input are closely matched to those with S-cone input.

Generalized filtering operations for hue images

The hue saturation intensity (HSI) color model resembles the color sensing properties of human vision. Thus, it is more suitable to color image analysis than other color models. However, the hue (H) component is a periodic angular signal, to which the conventional signal processing algorithms cannot be applied without producing artifacts. We have developed an algorithm of generalized filtering operations on the angular signals, such as hue images. The developed method divides the input angular data into four groups according to the sign of filter coeffi- cients and the range of angular signals. Each group is processed sepa- rately, and the results from the four groups are combined together. In order to verify our algorithm, we have applied it to the spatial smoothing and gradient processing of hue images. © 2001 Society of Photo-Optical Instru- mentation Engineers. (DOI: 10.1117/1.1334605)

Color schemes to represent the orientation of anisotropic tissues from diffusion tensor data: application to white matter fiber tract mapping in the human brain

This paper investigates the use of color to represent the directional information contained in the diffusion tensor. Ideally, one wants to take into account both the properties of human color vision and of the given display hardware to produce a representation in which differences in the orientation of anisotropic structures are proportional to the perceived differences in color. It is argued here that such a goal cannot be achieved in general and therefore, empirical or heuristic schemes, which avoid some of the common artifacts of previously proposed approaches, are implemented. Directionally encoded color (DEC) maps of the human brain obtained using these schemes clearly show the main association, projection, and commissural white matter pathways. In the brainstem, motor and sensory pathways are easily identified and can be differentiated from the transverse pontine fibers and the cerebellar peduncles. DEC maps obtained from diffusion tensor imaging data provide a simple and effective way to visualize fiber direction, useful for investigating the structural anatomy of different organs. Magn Reson Med 42:526-540, 1999.

Locally adaptive perceptual image coding

Most existing efforts in image and video compression have focused on developing methods to minimize not perceptual but rather mathematically tractable, easy to measure, distortion metrics. While nonperceptual distortion measures were found to be reasonably reliable for higher bit rates (high-quality applications), they do not correlate well with the perceived quality at lower bit rates and they fail to guarantee preservation of important perceptual qualities in the reconstructed images despite the potential for a good signal-to-noise ratio (SNR). This paper presents a perceptual-based image coder, which discriminates between image components based on their perceptual relevance for achieving increased performance in terms of quality and bit rate. The new coder is based on a locally adaptive perceptual quantization scheme for compressing the visual data. Our strategy is to exploit human visual masking properties by deriving visual masking thresholds in a locally adaptive fashion based on a subband decomposition. The derived masking thresholds are used in controlling the quantization stage by adapting the quantizer reconstruction levels to the local amount of masking present at the level of each subband transform coefficient. Compared to the existing non-locally adaptive perceptual quantization methods, the new locally adaptive algorithm exhibits superior performance and does not require additional side information. This is accomplished by estimating the amount of available masking from the already quantized data and linear prediction of the coefficient under consideration. By virtue of the local adaptation, the proposed quantization scheme is able to remove a large amount of perceptually redundant information. Since the algorithm does not require additional side information, it yields a low entropy representation of the image and is well suited for perceptually lossless image compression.

Color schemes to represent the orientation of anisotropic tissues from diffusion tensor data: Application to white matter fiber tract mapping in the human brain

This paper investigates the use of color to represent the directional information contained in the diffusion tensor. Ideally, one wants to take into account both the properties of human color vision and of the given display hardware to produce a representation in which differences in the orientation of anisotropic structures are proportional to the perceived differences in color. It is argued here that such a goal cannot be achieved in general and therefore, empirical or heuristic schemes, which avoid some of the common artifacts of previously proposed approaches, are implemented. Directionally encoded color (DEC) maps of the human brain obtained using these schemes clearly show the main association, projection, and commissural white matter pathways. In the brainstem, motor and sensory pathways are easily identified and can be differentiated from the transverse pontine fibers and the cerebellar peduncles. DEC maps obtained from diffusion tensor imaging data provide a simple and effective way to visualize fiber direction, useful for investigating the structural anatomy of different organs. Magn Reson Med 42:526-540, 1999.

Color schemes to represent the orientation of anisotropic tissues from diffusion tensor data: Application to white matter fiber tract mapping in the human brain

This paper investigates the use of color to represent the directional information contained in the diffusion tensor. Ideally, one wants to take into account both the properties of human color vision and of the given display hardware to produce a representation in which differences in the orientation of anisotropic structures are proportional to the perceived differences in color. It is argued here that such a goal cannot be achieved in general and therefore, empirical or heuristic schemes, which avoid some of the common artifacts of previously proposed approaches, are implemented. Directionally encoded color (DEC) maps of the human brain obtained using these schemes clearly show the main association, projection, and commissural white matter pathways. In the brainstem, motor and sensory pathways are easily identified and can be differentiated from the transverse pontine fibers and the cerebellar peduncles. DEC maps obtained from diffusion tensor imaging data provide a simple and effective way to visualize fiber direction, useful for investigating the structural anatomy of different organs. Magn Reson Med 42:526–540, 1999. © 1999 Wiley-Liss, Inc.

Simplified Human Visual MTF Measurements.

This investigation concerns the measurement method of the human visual MTF properties using a computer display. In this paper, simplified visual MTF measurement was discussed. This paper compares the simplified measurement with the more precise measurement which has been known as general measurement. The test pattern used in the simplified measurement was a grating which had horizontally varied spatial frequencies and vertically varied contrast values. The sensitivity obtained by the simplified measurement is extremely low and the curvature is tranquil compared with the results measured by the precise measurement. This result suggests the pattern must be improved because the lower contrast area is too narrow to obtain an accurate value on the pattern. Latter evidence suggests the subject observed several different spatial frequency gratings simultaneously in his one glance. Taking these into account, the improved pattern was developed. After the MTF properties measurement by the improved simplified MTF pattern, the original MTF properties (precise measurement MTF properties) were estimated.

Feature extraction and simple three-dimensional object shape recognition in real time

A system for shape recognition of simple objects (a cube, a plate, a rod) falling in the field of vision by extracting their image contours is proposed. Recognition is carried out from three projections. The mini- mal time of image processing is 1 ms. The idea of the simultaneous extraction of an image contour and the parameters characterizing its shape is proposed based on the properties of human vision. The sensor is an optoelectronic functional converter representing a system for searching and extracting an image contour by the radius-vector scan with a dissector as a photodetector. It realizes the fastest method of object image analysis to recognize image shape because of the linear functional connection between an electronic parameter (a brightness level as an argument) and a geometric parameter (for example, a radius as a function) of an image in the process of following its contour with a photodetector aperture. As a result, the instantaneous video signal am- plitude (which is proportional to the brightness level at the point of the aperture location) corresponds to the current length of the image radius, and its variation during the tracing of the contour adequately character- izes the image shape, including such features as the extreme dimen- sions and the angles. Simultaneously the coordinates of the contour points of the image and its center of gravity are extracted. The highly informative nature of the video signal also enables us to determine the perimeter, the area, the orientation of the image, and the coordinates of its brightness extremum. The radius-vector scan is the only sensor cur- rently available whose signals carry direct information concerning the image shape in real time. © 1998 Society of Photo-Optical Instrumentation Engi- neers. (S0091-3286(98)00310-9)

人間の視覚・聴覚情報 目の順応特性に基づいた車載ディスプレイの表示方式

With the increasing number of on-board visual displays, it is important to develop displays that are easy to see in various driving environments, such as a snow-covered road. In this paper, we propose a new displaying method that is based on luminance adaptation, one of the human vision properties which is associated with luminance changes that occur while driving. In this method, the level of adaptation by the driver is estimated to the luminance outside the vehicle. Then the luminance and the chromatic saturation of the display is determined by using the adaptation luminance in order to perceive the constant brightness of the display in different environmental luminances. Experimental results of subjective and objective evaluation that compare the conventional display and our new one indicate the effectiveness of the method.

The role of visual field position in pattern-discrimination learning.

Invariance of object recognition to translation in the visual field is a fundamental property of human pattern vision. In three experiments we investigated this capability by training subjects to distinguish between random checkerboard stimuli. We show that the improvement of discrimination performance does not transfer across the visual field if learning is restricted to a particular location in the retinal image. Accuracy after retinal translation shows no sign of decay over time and remains at the same level it had at the beginning of the training. It is suggested that in two-dimensional translation invariance-as in three-dimensional rotation invariance-the human visual system is relying on memory-intensive rather than computation-intensive processes. Multiple position- and stimulus-specific learning events may be required before recognition is independent of retinal location.

Comparison of Laparoscopic Imaging Systems and Conditions Using a Knot-Tying Task

Pilot experiments to determine the important factors in the engineering of laparoscopic (videoscopic) imaging systems are described in this paper. In the first set of experiments, three videoscopic systems were compared by using a knot-tying task: monoscopic, monoscopic with digital contrast enhancement, and stereoscopic. Direct viewing was used as a control. In both experienced and novice subject groups, no difference was found in completion time or errors between the videoscopic conditions. Performance with direct viewing was significantly better, however, indicating that there are factors in videoscopic imaging that degrade perception or distort the relationship between vision and motor response. In the second set of experiments, the effects of contrast and spatial resolution were examined by varying working distance and camera exposure while experienced subjects tied knots on high-and low-contrast surfaces. Good contrast was found to be most important at longer working distances. This result shows that performance of knot tying, a complex task, is affected by contrast sensitivity, which is a fundamental property of human vision.

Comparison of laparoscopic imaging systems and conditions using a knot-tying task

Pilot experiments to determine the important factors in the engineering of laparoscopic (videoscopic) imaging systems are described in this paper. In the first set of experiments, three videoscopic systems were compared by using a knot-tying task: monoscopic, monoscopic with digital contrast enhancement, and stereoscopic. Direct viewing was used as a control. In both experienced and novice subject groups, no difference was found in completion time or errors between the videoscopic conditions. Performance with direct viewing was significantly better, however, indicating that there are factors in videoscopic imaging that degrade perception or distort the relationship between vision and motor response. In the second set of experiments, the effects of contrast and spatial resolution were examined by varying working distance and camera exposure while experienced subjects tied knots on high- and low-contrast surfaces. Good contrast was found to be most important at longer working distances. This result shows that performance of knot tying, a complex task, is affected by contrast sensitivity, which is a fundamental property of human vision.

Ｐｈａｓｅ‐ｏｎｌｙ ｓｙｎｔｈｅｓｉｓを利用した画像の適応的エッジシャープニング

An efficient edge sharpening technique for digital images is proposed. The resulting image has natural smoothness in its gray levels. The technique includes a Laplacian operator (a traditional technique for image enhancement) and the phase-only synthesis in Fourier analysis. The adaptive weighted functions are the S-function and π-function, often used in fuzzy theory. Furthermore, a human visual property is also introduced to attain effective results for human eyes. The processed image results were evaluated using the cross section of the gray levels of the image. Simulation examples indicate that the proposed technique is more effective than the traditional one.

Method for Shape Recovery from Monocular Image Considering Shading.

A human vision model is formulated in this paper, considering that line drawings are not limited to projection only from a polyhedron. To select a line drawing which can serve as an elementary picture for human stereo vision, we performed a psychological experiment. The model was proposed based on the experimental data to describe a property of human vision. Several examples were solved to validate the proposed model. The image-irradiate equation given by the Poisson equation is solved to reconstruct a face. Numerical simulation demonstrates that faces can be recovered precisely by considering the shading on the picture. This successful procedure involves solving the Dirichlet problem of the Poisson equation, specifying the boundary condition which is produced by the reconstructed edges. Numerical examples involve a drawing comprised only of lines, and a line drawing with shading.

Psychophysical RMS Granularity for the Evaluation of Radiographic Mottle

AbstractThe psychophysical RMS (root mean square) granularity ap is proposed for the evaluation of radiographic mottle, i.e., the granularity appearing in a radiograph made with an X-ray screen-film system. The value of is calculated from the Wiener spectrum of the radiographic mottle and the frequency dependence of the minimum perceptible contrast, which expresses a psychophysical property of human vision. Examples are presen ted for three typical X-ray films. The density dependence of a,, is in close agreement with the results of subjective rating that (V the most perceptible density is 1.0 and (2) the perceptibility at density 2.5 is much worse than that at 0.6. Whereas the Selwyn granularity coefficient, which relates to the physical RMS granularity, does not correlate with the results of subjective rating.

Adaptive image contrast enhancement based on human visual properties

Existing methods for image contrast enhancement focus mainly on the properties of the image to be processed while excluding any consideration of the observer characteristics. In several applications, particularly in the medical imaging area, effective contrast enhancement for diagnostic purposes can be achieved by including certain basic human visual properties. Here the authors present a novel adaptive algorithm that tailors the required amount of contrast enhancement based on the local contrast of the image and the observer's Just-Noticeable-Difference (JND). This algorithm always produces adequate contrast in the output image, and results in almost no ringing artifacts even around sharp transition regions, which is often seen in images processed by conventional contrast enhancement techniques. By separating smooth and detail areas of an image and considering the dependence of noise visibility on the spatial activity of the image, the algorithm treats them differently and thus avoids excessive enhancement of noise, which is another common problem for many existing contrast enhancement techniques. The present JND-Guided Adaptive Contrast Enhancement (JGACE) technique is very general and can be applied to a variety of images. In particular, it offers considerable benefits in digital radiography applications where the objective is to increase the diagnostic utility of images. A detailed performance evaluation together with a comparison with the existing techniques is given to demonstrate the strong features of JGACE.

Considerations on the possibility to exchange temporal against spatial resolution in image coding

In order to transmit high definition television signals economically some kind of data compression has to be utilized. We investigate the question how spatio-temporal properties of human vision can be exploited for data reduction. By means of pyramid coding we implement coding schemes which transmit spatial detail information with reduced temporal resolution. In moving areas with correlated motion we introduce motion-compensated interpolation. In the case of uncorrelated motion, where motion estimation often fails and the eye cannot follow the movement, high spatial frequencies are suppressed. The different systems are rated by means of subjective tests. Furthermore motion-compensated interpolation of the highpass signals of a subband codec using quadrature mirror filters will be analysed.

Constant volume operators and lateral inhibition

Constant volume (CV) operators are nonlinear image processing operators in which the area covered by the pointspread function around each point in the input image varies inversely with the light intensity at that point. This operation is designed to make spatial resolution increase with retinal illuminance, but it proves to have unexpected side-effects that mimic other important properties of human spatial vision, including Mach bands and Weber's law. Mach bands are usually attributed to lateral inhibition in the retina, and when retinal image processing is modeled by a linear operator they imply such inhibition, since they cannot be produced by a nonnegative impulse response. CV operators demonstrate that Mach bands and other high-pass filter effects can be created by purely positive pointspread functions, i.e., without inhibition. This paper shows in addition that if one attempts to combine lateral inhibition with a CV operation, the results are dramatically wrong: the edge response always contains Mach bands that bulge in the wrong direction. Thus within the nonlinear theoretical framework provided by CV operators, lateral inhibition is neither necessary nor sufficient for modeling Mach bands and other high-pass filter properties of spatial vision.