Showing papers on "Contrast (vision) published in 1969"

Depth adjacency in simultaneous contrast

Abstract: The Gelb phenomenon, as an example of whiteness contrast, was investigated with three amounts of separation in depth between the test and induction disc. The cue of binocular disparity was used to vary the perceived depth between the discs. It was found that the magnitude of the contrast effect decreased with an increase in the perceived depth between the two discs. This change was regarded as an instance of the adjacency principle. The problem of whether the binocular disparity cue per se or perceived depth was the significant variable was discussed. The consequences of the results were considered with respect to the relation between whiteness constancy and whiteness contrast and the problem of neural localization of the contrast effect.

Fourier Analysis and Color Discrimination

Abstract: The contrast thresholds of equiluminous chromaticity-modulated gratings are measured for various waveforms (sine-, square-, and triangular-wave gratings). The expectation is expressed that only the fundamental Fourier component is of significance in the threshold visibility of colored gratings. In addition, the Fourier transformation is applied to the chromatic spatial-sensitivity curves. The transformed functions illustrate clearly the spatial organization of the contrast mechanisms. For 160 trolands, the summation area of the red-green chromatic activity extends over 10′, whereas the yellow–blue activity integrates over about 25′. A comparison of the Fourier transforms of a luminance- and chromatic-threshold contrast curve shows (1) inhibitory qualities and (2) the greater spatial sensitivity of the luminous function. The assumption is made that the visual resolution for differences of brightness, as well as chromaticity, is limited by the diffraction of light by the pupil. The visual acuity for differences of hue as a function of the background wavelength is thus predicted for a 30-cpd grating and compared with an empirical function. There is good agreement.

Microvascular effects of topically applied contrast media.

Abstract: The toxicology of roentgen contrast media has received much attention in recent years and has been the subject of several investigations. Side effects such as nausea, vomiting and urticaria are not uncommon after the intravenous and intraarterial injection of contrast media; the latter often also produce a more or less severe local burning sensation. Clinical observations have even indicated more serious effects. Coronary angiography is sometimes followed by electrocardiographic abnormalities (Ross 1963, JACOBSSON & PAULIN 1967). Circulatory changes such as alterations in the minute volume, blood pressure, hematocrit and plasma volume and osmolality have been reported (BROWN et colI. 1965, FODA et colI. 1965, and ISERI et coIl. 1965). In the presence of reduced renal function damage to the kidneys, as reflected in an increased NPN, has been demonstrated after nephroangiography (BAUDISCH & BAUMANN 1964). Albuminuria following urography has been described (KIRKLAND & HASLOCK 1961). INGVAR (1957) and GREITZ & WEISS (1959) during cerebral angiography with moderate amounts of contrast medium registered only a few changes in the EEG, whereas LUNDERVOLD & ENGESET (1967), using larger doses of medium, frequently observed such changes.

Visibility of a Stabilized Target as a Function of Frequency and Amplitude of Luminance Variation

Abstract: A luminous bar of 4 min of arc was superimposed on an evenly illuminated 1°-of-arc circular field of 3, 30, or 300 mL, and the whole target was stabilized with respect to the retina. The bar luminance was varied sinusoidally at frequencies between 2.5 and 40 Hz, and the amplitude of variation yielded time-average contrast values between 0.06 and 6. Subjects indicated the length of time the edges of the bar stayed visible within a 20-sec viewing period. Judgments were also made at 0 Hz for each of the average contrast values. When the target is steady, visibility of the bar is a monotonically increasing function of contrast. Visibility of a target of any contrast can be enhanced to a value above the level obtained at 0 Hz, when its luminance is varied around its average contrast with frequencies between 2.5 and 15 Hz. Within this range, visibility is a decreasing function of frequency, and is found to be independent of contrast. Frequencies higher than 15 Hz are ineffective in lengthening the time during which the stabilized target stays clearly visible, and target visibility at frequencies above 15 Hz becomes once more a function of time-average contrast. At frequencies between 5 and 30 Hz, perception of flicker persists after the edges of the bar target have disappeared.

Holographic method of dimensional inspection

Abstract: To dimensionally compare one contour surface with another, one surface is provided with a contrast pattern and a hologram is made of that surface. Then the hologram is reconstructed and the image of the contrast pattern is superposed on the other surface. The contrast pattern will register with the other surface only to the extent that the two surfaces are alike. Where the surfaces are not alike, the amount of the difference is determined by moving the second surface through a measured distance until the pattern is registered with the surface.

Contour fitting pictorial tracking gate

Abstract: The tracker tracks on a center of contrast on a selected target while trang gates are adjusted automatically to fit the target contrast area's shape and size. The appropriate bright or dark contrast detector is adjusted to allow discrimination of the target contrast from its background, thus allowing a tracking window to encompass the selected contrast area. Orthogonal error signals are provided for servoing a vidicon camera to maintain the viewed field centered on the target.

An electron-optical lens effect as a possible source of contrast in biological preparations.

Abstract: SUMMARY Heavy-metal stain aggregates on the surface of thin sections of biological material have higher contrast than those embedded within the sections and both have greater contrast than can be accounted for by the amplitude image. Disturbances of the incident illumination by a specimen in both light- and electron-optical systems and their possible contribution to image contrast are considered. The hypothesis is proposed that a lens effect produced by the stain aggregates may account for their contrast in the electron microscope in a similar manner to the contrast of glass beads in the light microscope with a low numerical aperture.

TRANSITION FROM ROD TO CONE VISION: II. Successive contrast

Abstract: Stabell, U. & Stabell, B. Transition from rod to cone vision. III. Successive contrast anew. Scand. J. Psychol., 1969, 10, 140–144—The relation between the specific threshold level and the upper limit of the scotopic contrast color was investigated. The achromatic interval between the scotopic and the photopic component increased when time in darkness increased, and when pre-stimulation was reduced as regards intensity, duration, or cone/rod ratio. The results are interpreted on the basis of the opponent theory of color vision.

Threshold contrast as a function of target complexity.

Abstract: ABSTRACT Contrast‐luminance relationships were obtained for 13 test targets, presented for 0.2 second in the center of an extensive uniform field, and having various degrees of complexity. They always were brighter than the background, the luminance of which could be set at predetermined values from 1 to 500 footlamberts. The contrast‐luminance relationships were a function of the target characteristics, differences becoming more marked for background luminances greater than about 10 footlamberts. A comparison with the results obtained by previous investigators with three of the targets indicates that the functional relationships are not significantly affected by experimental procedures or observers. Target complexity appears to be only one of several factors which influence the form of the contrast‐luminance relationships. Considerable differences in the absolute values of threshold contrast were found for targets having approximately the same size of critical detail.

PSYCHOPHYSICAL INVARIANTS OF ACHROMATIC COLOUR VISION: IV. Depth adjacency and simultaneous contrast

Abstract: Lie, I. Psychophysical invariants of achromatic colour vision. IV. Depth adjacency and simultaneous contrast. Scand. J. Psychol., 1969, 10, 282–286.— Achromatic colour contrast as a function of adjacent subareas was investigated by a stereoscopic depth technique. The degree of colour contrast was found to be independent of stereoscopic depth.

Factors in highway sign visibility

Abstract: SIMULATED SIGNS UNDER LABORATORY CONDITIONS WERE USED TO CONTROL MANY OF THE VARIABLES AFFECTING HIGHWAY SIGN VISIBILITY AND ATTENTION VALUE. BY CONTROLLING THESE VARIABLES, IT WAS POSSIBLE TO OBTAIN AN INDEX OF THE FACTORS MOST IMPORTANT IN DETERMINING WHICH SIGNS WERE "SEEN FIRST AND BEST." THE RECORDED SUBJECTIVE IMPRESSION OF THE SUBJECTS PROVED TO BE A BETTER INDEX THAN SEARCH AND RESPONSE-TIME METHODS. THESE INDOOR LABORATORY RESULTS WERE COMPARED WITH A NUMBER OF MATHEMATICAL MODELS. ONE BASED ON BRIGHTNESS RATIOS GAVE THE BEST FIT AND ANOTHER BASED ON PER CENT BRIGHTNESS CONTRAST THE NEXT BEST FIT TO THE EXPERIMENTAL RESULTS. THE LATTER WAS MORE EASILY APPLIED TO ESTIMATE VISIBILITY OF FULL SCALE TEST SIGNS. USING THE PERCENT CONTRAST EQUATION REASONABLY GOOD CALCULATED ESTIMATES WERE OBTAINED OF THE ACTUAL DISTANCES AT WHICH SIGNS WERE SEEN BY TWO GROUPS OF EXPERIMENTAL SUBJECTS UNDER DAY AND NIGHT CONDITIONS. THE NIGHT ESTIMATES WERE SOMEWHAT BETTER THAN THE DAY ESTIMATES PROBABLY AS A RESULT OF MORE VARIABILITY OF DAY VIEWING CONDITIONS. THE EXPERIMENTS INDICATED THAT SIGNS LOCATED OVER THE HIGHWAY WERE MORE LIKELY TO BE SEEN FIRST THAN THOSE TO EITHER SIDE. THE MOST EFFECTIVE FACTORS WERE BRIGHTNESS CONTRAST OF LETTERS-TO-SIGN AND SIGN-TO- BACKGROUND. INDICATED AS AN ADDED FACTOR IN SOME CASES WAS CHROMATIC OR HUE CONTRAST. TO MEASURE ALL OF THE FACTORS WHICH MAY HAVE SOME INTERRELATED INFLUENCE ON SIGN VISIBILITY A GREAT DEAL MORE WORK IS NEEDED. IN THE MEANTIME, HOWEVER, THE BRIGHTNESS RATIO AND PERCENT CONTRAST EQUATIONS MAY BE USED FOR ESTIMATION OF RELATIVE VISIBILITY OF GIVEN TYPES OF SIGN INSTALLATIONS. IN ADDITION, OF COURSE, ADEQUATE LEGIBILITY DISTANCES MUST BE PROVIDED. A METHOD IS SUGGESTED FOR MAKING THE NECESSARY ESTIMATES. ESTIMATES BASED ON BRIGHTNESS CONTRAST FACTORS SHOULD BE APPLIED WITH DUE CONSIDERATION OF THE WIDE RANGE OF BACKGROUNDS AGAINST WHICH HIGHWAY SIGNS ARE SEEN AS SHOWN IN OUR STUDY AND ALSO IN A STUDY BY HANSON AND WOLTMAN DIFFERENCES IN DIFFERENT SEASONS OF THE YEAR AS WELL AS FROM CHANGING VIEWPOINT OF THE DRIVER MUST BE CONSIDERED. /AUTHOR/

Theoretical model for lateral inhibitory interaction in the human retina.

Abstract: Stlmmary.-Several models for lateral inhibitory interaction are available in the literature; however, these models are deficient in providing a systematic account of simultaneous brightness contrast for one or several of the following reasons: (1 ) no rational basis is presented for phenomenal black; ( 2 ) the mediation of lateral inhibitory interaction is generally attributed to the horizontal cells of the human retina, but there is no neuroanatomical evidence that the horizontal cell is present in the central-most fovea, although there is psychophysical evidence that lateral inhibitory interaction occurs in the central-most fovea; ( 3 ) the response characteristics of the receptive field have nor been conceptually integrated into the models despite general theoretical agreement that the receptive field organization is meaningful for simultaneous brightness contrast. These deficiencies have prompted the development of the theoretical model presented here. In addition to integrating the foregoing empirical aspects of simultaneous brightness contrast, the model predicts that the magnitude of perceived brightness contrast will be greater at a corner than along an edge. Empirical data consistent with this prediction are presented. A further prediction that the perceived magnitude of brightness contrast will increase as the angular size of the corner decreases is tested. In a theoretical analysis, an approximation to the experimental results is obtained when contrast effects due both to the predicted effect of angle size and the well known effect of inducing-field area are considered.

TRANSITION FROM ROD TO CONE VISION I. Simultaneous contrast

Abstract: Stabell, B. Transition from rod to cone vision. I. Simultaneous contrast. Scand. J. Psychol., 1969, 10, 61–64.—Above the specific threshold, color quality depended on the test filter, while at lower intensities the same color was observed irrespectively of the test filter used, confirming the assumption that colors within the photochromatic interval are triggered by rod activity. The lawful relation between rise of specific threshold and increase of rod sensitivity was not found under the condition of simultaneous contrast.

Effect of Image Contrast and Resolution on Photointerpreter Target Detection and Identification

Abstract: A psychophysical study was performed to determine the effects of image contrast and resolution on the extraction of information by a photointerpreter from images of Minuteman missile sites. Sixteen target films were selected, each containing a photograph of a different missile site. Sixteen degraded images of each site were processed, representing a 4×4 matrix of resolution and contrast combinations. Both of these image-quality variables were defined in terms of normalized MTF curves. Contrast was measured as the degree of exposure modulation at low spatial frequencies relative to that on the original images. Resolution was measured as the highest spatial frequency at which exposure modulation drops to that just perceivable by eye (about 0.022). The limiting ranges of these variables were preselected to extend from a relatively low (25%) to a relatively high (75%) probability of correct target-component identification. Each of 256 images was then shown to 16 experienced image interpreters. Accuracy and completeness of both target detection and identification was scored. The results indicate (a) that relationships between either contrast or resolution and either detection or identification completeness are roughly logarithmic over the ranges covered in this study; (b) that there is no regular relationship between accuracy and image quality; (c) that the effect of either image-quality variable (contrast or resolution) is diminished at the two higher levels of the other image-quality variable.

The Visibility of Rate of Change of Luminance in the Presence or Absence of a Boundary

Abstract: Luminance change visibility of a Ganzfeld and circular target subtending 15° at the eye was measured for 12 subjects. Visibility of change increased from about 50 per cent at rate of change of 0·03 Log units/sec to 80 per cent at 0·17 Log units/sec. Visibility of change for any one rate and target was identical irrespective of the sign of luminance change. Visibility of luminance change in the Ganzfeld was generally 15 per cent lower than in the 15° target. The luminance change detecting mechanism must therefore depend less upon area signal than on contrast information.

Visual acuity under water without a face mask

Abstract: : Visual acuity was measured under water for subjects without face masks and was compared with their acuity in air. The loss of acuity was around 90 percent for the entire group, but there were marked differences for the various sub-groups. Emmetropes suffered the greatest loss in the water; they required targets more than 20 times as big as those they could see in air. Myopes suffered the least loss; they required an increase in target-size by a factor of only seven. There was no correlation between emmetropic acuity in air and in water. Acuity was also measured at various luminances in air while the subjects wore negative lenses of various powers to induce the same type of out- of-focus vision found under water. High and low contrast targets were used. Calculations were made of the approximate target sizes which can be seen under water at various light levels and at the two levels of contrast.

Improvement of Signal-to-Noise Ratio of Image Converters with S-1 Photocathodes

Abstract: Publisher Summary This chapter discusses the improvement of signal-to-noise ratio of image converters with S-1 photocathodes Image converters with the cathodes give a distinct output from the fluorescent screen, even when no light is falling on the cathode An image resulting from a faint illumination of the cathode would, therefore, disappear in the background or would have so little contrast that the information content of the picture would be seriously diminished It is shown that in the case of the eye, the difference in the numbers of visual events caused by the emitted electrons must be about five times higher than the average fluctuation The upper limit of resolution is given either by the maximum resolution of the eye itself at the luminance of the output screen, or by the fluctuations in the number of electrons leaving the photocathode of the first stage of the tube The limits of resolution as well as the resolving power of the eye in conjunction with an image converter are presented It is found that the resolution of the eye was increased both by reducing the thermal emission, and by increasing the picture brightness