Showing papers on "Contrast (vision) published in 1974"

Depth perception in disparity gratings

Abstract: OBSERVATION of sinusoidal spatial modulation of luminance has proved a valuable tool in the study of visual processing of luminance distributions on the retina. Information on the limits of processing capability has been gained in such diverse fields as the optics of the eye1, neurophysiology of the retina2, movement3,4 and orientation5,6 sensitivity and cortical processing of spatial frequency7,8. In the field of stereoscopic vision, Blakemore9 and Fiorentini and Maffei10 have found that when luminance gratings of slightly different spatial frequencies were presented ,to each eye, an apparently tilted grating was perceived even if one monocular grating was moving quickly relative to the other. Furthermore, tilt is perceived from gratings of the same spatial frequency but differing in contrast by 50% or more. These phenomena are not easy to explain on the basis of disparities at corresponding retinal points, but seem to require more global processing of the whole image.

Opponent-colour cells in different layers of foveal striate cortex

Abstract: 1. The majority of cells in layer 4B have opponent-colour properties indicating that colour opponency plays an important role in the early stages of visual processing in foveal striate cortex. In contrast to cells in the lateral geniculate nucleus many of these cells receive centre—surround antagonism from the same cone mechanism. Some cells show this spatial antagonism at threshold; others require suprathreshold stimuli for its demonstration. 2. The majority of cells in layer 4B do not show orientation or directional selectivity. The proportion of cells with orientation and directional selectivity increases and the proportion of opponent-colour cells decreases with increasing distance above and below layer 4B so that the majority of cells in the outer layers exhibit considerable spatial selectivity without apparent colour opponency. These changing proportions suggest that the latter cells may be receiving their inputs from different types of opponent-colour cells making them sensitive to different types of colour contrast but not to colour per se. 3. More opponent-colour cells receive inputs from the red- and green- sensitive cone mechanisms than from the blue-sensitive one. This difference is more marked in layer 4B than 3B suggesting that the latter cortical layer may be more involved in colour vision than the former.

Lateral interaction between neural channels sensitive to velocity in the human visual system

Abstract: MACKAY1 has made use of the phenomenon of simultaneous contrast to provide evidence for the existence in the human visual system of neural channels that are sensitive to the density of visual texture. Using the same phenomenon, we have provided comparable evidence for the existence of lateral interaction between channels sensitive to velocity. That such channels do exist is suggested by the preliminary psychophysical observations of Pantle and Sekuler2, who demonstrated a luminance threshold elevation for moving contours that is limited to a range of values around the velocity of the adapting contour.

Color television setup apparatus and method

Abstract: Patterns indicative of the characteristics of contrast, brightness, color and tint are displayed on the picture tube of the television receiver. A plurality of photocells develop corresponding electrical signals responsive to the patterns. The signals drive peak detectors, the outputs of which are sampled at a regular rate. A neutral density filter is between the brightness pattern and its photocell, and when the sampled contrast and brightness outputs are subtracted in a subtractor, a null is obtained at the desired ratio. Color filters are interposed between the tint and color patterns and photocells and at the desired settings, subtraction of their outputs in a subtractor yields zero. A plurality of bi-directional motors are engageable with the receiver contrast, tint, brightness and color level adjustable elements. The contrast and tint adjustment elements are driven from the respective subtractor outputs, whereas the brightness adjustable element is controlled by the brightness peak detector output directly and the color level adjustable element is controlled by the sum of the color and tint peak detector outputs. The motors are stopped when all patterns correspond to desired settings. The method of automatically setting up a color television receiver is also described.

Effects of Spatial Coherence on Fourier Imaging of a Periodic Object

Abstract: The formation and the contrast of Fourier images of a periodic object, especially a sinusoidally transparent object, are investigated under partially coherent illumination. It becomes apparent that the spatial coherence of light affects seriously the contrast of Fourier images and the positions of the Fourier image planes.

Automatic contrast control utilizing three control signals

Abstract: An automatic contrast control circuit in a color television receiver for stabilizing the average DC level of the luminance information at a desired level and preventing focus blooming. The control circuitry, which is suitable for fabrication as a monolithic integrated circuit, contemplates the provision of a gain-controlled luminance amplifier stage for driving an image reproducer with luminance information having a stabilized black level. An average detector coupled to the amplifier stage output develops a control signal representative of the average DC level of the luminance information and applies it to the amplifier stage, varying its gain inversely with changes in the average luminance level. A peak limiter circuit is also provided for modifying the control signal to reduce the amplifier stage''s gain whenever an AC brightness component comprising the luminance information exceeds a defined threshold level, regardless of the average DC level of the luminance information.

Pulse width luminance modulation system for a DC gas discharge display panel

Abstract: A pulse width luminance modulation system for driving a gas discharge panel in line at a time. The driving circuit for the discharge cell comprises a CR time constant element in order to enlarge the contrast range of the picture to be displayed. The discharge cell is caused to produce glow discharge when the pulse width of the pulse width modulation driving pulse is wider than a certain value depending on the CR time constant to produce normal pulse width luminance modulation of the glow discharge, and the discharge cell is caused to produce instantaneous irradiation of which the intensity is dependent on a stored charge in the capacitive element C of the CR element when the driving pulse width is narrower than the certain value so as to widen the low luminance range and by suitably selecting the value of the CR element for obtaining continuity of the two luminance characteristics, and further the input signal for making luminance modulation is applied with a correction in order to make the γ value of the luminance characteristic of the discharge cell a close approximation to that of a cathode ray tube after converting the input signal to a pulse code modulated signal for obtaining an easy γ correction in the low luminance range.

Contrast Orientation in Daphnia Magna and Its Significance for Vertical Plane Orientation in the Pelagic Biotope in General

Abstract: 1. Optical orientation to light-dark boundaries in the cladoceran Daphnia is called contrast orientation. 2. It is suggested that vertical plane orientation in planktonic crustaceans in general is optical orientation and that contrast orientation is possible in the pelagic biotope. 3. Results of experiments clarifying the mechanism of contrast orientation in Daphnia magna are discussed. 4. These results lead to the proposition of an orientation area consisting of 3 median pairs of ommatidia and 2 lateral pairs situated dorsally from the eye axis. 5. Several modes of orientation can be distinguished and it is argued that in a particular case different pairs of ommatidia might have the orientation function. 6. A general model of the mechanism of contrast orientation in Daphnia magna is presented.

Effects of simultaneous contrast on temporal brightness enhancement

Abstract: &NA; Brightness vs. duration curves were measured for targets of constant luminance flashed against various steady background luminances. Increasingly intense backgrounds shifted the curves downward, and systematically reduced the amount of brightness enhancement. This suggests that brightness enhancement is determined by target brightness and cannot be due to refractoriness in spatially independent neural channels.

Apparatus for exposing a light-sensitive layer

Abstract: An apparatus for exposing a light-sensitive layer employed for the manufacture of reproductions of black-and-white or colored patterns, wherein the image of the pattern which has been projected onto a support is taken or scanned by means of an electronic camera and stored on a recording carrier. The light-sensitive layer initially is purely optically exposed with the image of the pattern. The light-sensitive layer is also additionally exposed with the stored image for correction of contrast and/or color shade.

Effects of Radiopaque Contrast Media on the Dynamic Characteristics of Ureteral Function

Abstract: The ureteral peristaltic rate response to radiopaque contrast media was investigated using electrophysiological techniques. The modification caused by these agents in the characteristics of ureteral p

SEEKVAL Project IA1: Effects of Color and Brightness Contrast on Target Acquisition

Abstract: : The report covers an experiment to determine the effects of target color and brightness contrast on visual detection performance by means of the unaided human eye. The data consist mainly of elapsed times between search initiation and correct detection of tank targets at a simulated slant range of about 1 mile. Statistical methods are employed to assess the effects of color with three levels of contrast factor on detection performance. Under the experimental conditions, effects due to color and brightness contrast were each statistically rated, with the observation that interaction effects between these two factors were not statistically significant. The effect of color tended to account for more variance than the effect of brightness contrast.

Dependence of incoherent system response on object contrast.

Abstract: A relationship between the image contrast and the object contrast for a general periodic or a truncated periodic object is derived. The result is illustrated for a periodic object of rectangular wave profile. It has been shown that for a truncated sine wave object the image contrast bears a nonlinear relationship to the object contrast. The contrast dependence of the measured or the apparent transfer function defined as the ratio of the image contrast to object contrast has been investigated.

Application of the Nonlinear Filtering to the Contrast Enhancement of the Image of the Dislocation Observed by an Electron Microscope

Abstract: Nonlinear filtering is one of the useful methods used to achieve contrast enhancement of the image having a wide dynamic range. This paper describes the application of this technique to the contrast enhancement of the image of the dislocation observed by an electron microscope. It is found that this technique is more effective than the familiar linear high pass filtering. Also it is shown mathematically that the contrast reversion (such as dark field image) appearing sometimes during the linear filtering, can be avoided in the nonlinear filtering.

Prediction of Target Detection Thresholds on the Basis of Physiological Considerations

Abstract: This paper presents a physiological math model which predicts the liminal contrast required to detect a target as a function of target size, background brightness and exposure time. The model is based on the premise that target detection occurs when the difference in response of cells across a target/background brightness contour is greater than some threshold. This premise is supported by recent physiological and psycho-physical measurements. A logical "wiring diagram" for the retina is conceived which resembles the actual anatomy of the retina. The photo-receptor cells, bipolar cells and ganglion cells in the model are given simple mathematical response functions. The target detection requirement for a minimum threshold response difference across a contour is used to develop a mathematical expression of threshold target brightness as a function of background brightness. There are two major parameters in the expression for threshold target brightness: 1) Photo-receptor sensitivity to incident luminance, 2) The threshold response difference required for target detection. The expression for threshold target brightness fits the experimental data well. The model is expanded to explain the variation of the sensitivity and threshold parameters with target size and exposure time. The resulting model is self-consistent and closely agrees with the experimental data for background luminance levels of less than one foot lambert and exposure times less than .1 sec. The results presented in this paper indicate that a coupling of psycho-physical measurements with physiological and anatomical findings leads to both a greater understanding of the physiological processes involved and a more powerful formulation of the psycho-physical results.

A Two IC Pal Chrominance/Luminance System

Abstract: The devices to be described perform in two 14 pin packages the necessary chrominance and luminance functions for the PAL system prior to chrominance demodulation. One device provides the necessary chrominance processing functions, while the other device combines luminance functions with manual chrominance control. Specifically, the chrominance IC contains the functions of sub-carrier regeneration, automatic chrominance control, H/ 2 generation and identification, color killer, and burst gating. The luminance IC provides DC operation of the contrast, saturation, and brightness controls, and the functions of beam current limiting and black level clamp.