Showing papers on "Line segment published in 1977"

An Application of Relaxation Labeling to Line and Curve Enhancement

Abstract: A relaxation process is described and is applied to the detection of smooth lines and curves in noisy, real world images. There are nine labels associated with each image point, eight labels indicating line segments at various orientations and one indicating the no-line case. Attached to each label is a probability. In the relaxation process, interaction takes place among the probabilities at neighboring points. This permits line segments in compatible orientations to strengthen one another, and incompatible segments to weaken one another. Similarly, no-line labels are reinforced by neighboring no-line labels and weakened by appropriately oriented line labels. This process converges, in only a few iterations, to a condition in which points lying on long curves have achieved high line probabilities, while other points have high no-line probabilities, There is some tendency, under this process, for curves to thicken; however, a thinning procedure can be incorporated to counteract this. The process is effective even for curves of low contrast, and even when many curves lie close to one another.

On triangulations of a set of points in the plane

Abstract: A set, V, of points in the plane is triangulated by a subset T, of the straight-line segments whose endpoints are in V, if T is a maximal subset such that the line segments in T intersect only at their endpoints. The weight of any triangulation is the sum of the Euclidean lengths of the line segments in the triangulation. We examine two problems involving triangulations. We discuss the problem of finding a minimum weight triangulation among all triangulations of a set of points and give counterexamples to two published solutions to this problem. Secondly, we show that the problem of determining the existence of a triangulation, in a given subset of the line segments whose endpoints are in V, is NP-Complete.

The detection of line segments.

Abstract: Many simple cells of the visual cortex have long narrow receptive fields, which are strongly excited by lines oriented along their long axis. In the present psychophysical analysis, we assume that there are similar independent ‘subunits’ which contribute, by probability summation, to the detection of a line. If a line segment is shorter than the subunit length, then extending the line length will increase the sensitivity of all the subunits affected by the line, and a relatively large increase in visual sensitivity will occur, corresponding to this ‘physiological summation’ within subunits. However, for a line segment which is much longer than the subunit length, the main effect of extending line length is to stimulate more subunits, resulting in a relatively small increase in sensitivity owing to probability summation. Thus a study of sensitivity (reciprocal threshold) as a function of line length may be used to test the subunit model and to estimate the subunit length. Here we use a quantitative model t...

Color bar generator

Abstract: The invention provides an apparatus for producing video frequency color value signals which correspond to a desired arrangement of vertical or horizontal color bars on a television screen. In the case of vertical color bars the apparatus derives during each line period an identical series of pulses having a multiple of the line frequency. Each series of pulses is applied to a binary counter which provides as output a sequence of sets of binary signals. This sequence of sets of binary signals is translated by a pre-programmed store into a further sequence of sets of binary signals, these latter sets of signals being applied to a digital-to-analogue converter adapted to derive therefrom corresponding sets of color value signals. Each set of color value signals defines a differently colored line segment. The effect of this operation over a plurality of successive line periods is to build up a number of vertical color bars each composed of vertically adjacent line segments of the same color derived from identical sets of color value signals occurring in successive line periods. In the case of horizontal color bars the apparatus operates in a similar manner except that the series of pulses initially produced is at a fraction of the line frequency and is derived once for each field period rather than once for each line period.

Visual extrapolation of a line segment to the point of its intersection with a straight line. I.

Abstract: A study is made of the capacity of fifty subjects to estimate the position of the point of intersection between a straight line and the visually extrapolated extension of a line segment at three different angles between the line and the segment: 30 degrees, 60 degrees and 90 degrees. The results show systematic deviations in the estimation of acute angles. The point of intersection of the straight line and the segment is misperceived to be shifted inwards in the angle between them. It is also shown that the set of imaginary extensions of a line segment with a given length, until its intersection with the given straight line, is determined only by the angle between the straight line and the segment and does not depend on the distance between them. Various possible mechanisms which could determine the solution of the task facing the subjects are discussed.

Visual extrapolation of two converging nonintersecting line segments.

Abstract: Fifty subjects were tested to determine the point of intersection between two converging line segments. The angle between the two nonintersecting line segments was 30 degrees. The orientation of the display as well as the distance between the line segments and the point of their intersection was varied. Two-dimensional normal distributions can be accepted to describe the results - the 50 estimates of the point of intersection for each of the five displays presented. The parameters of these distributions are influenced mainly by two factors characterizing the test line segments: (1) proximity to one of the main axes - vertical and horizontal, and (2) distance to the actual point of intersection. The possible mechanisms that might be involved in the estimation of the point of intersection between two converging line segments are discussed.