Browse Prior Art Database

Video Stretching for Pel Shape Correction

IP.com Disclosure Number: IPCOM000049237D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Chase, BO: AUTHOR

Abstract

It is well known that the self-converging yoke of a CRT results in spot distortion in the corners of the screen. Proposed methods of correction involve pre-distorting the beam to form a vertical ellipse at the screen center so that a more acceptable spot shape is achieved when deflected to the screen extremities. The degree to which the beam can be predistorted is limited by the need to maintain legibility of characters at the tube center. The problem is overcome by using standard delay techniques to stretch the trailing edges of the display pulses applied to the video amplifier and thus elongate the pel (picture element) horizontally by different predetermined amounts depending upon the position of the beam on the screen.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 71% of the total text.

Page 1 of 1

Video Stretching for Pel Shape Correction

It is well known that the self-converging yoke of a CRT results in spot distortion in the corners of the screen. Proposed methods of correction involve pre-distorting the beam to form a vertical ellipse at the screen center so that a more acceptable spot shape is achieved when deflected to the screen extremities. The degree to which the beam can be predistorted is limited by the need to maintain legibility of characters at the tube center. The problem is overcome by using standard delay techniques to stretch the trailing edges of the display pulses applied to the video amplifier and thus elongate the pel (picture element) horizontally by different predetermined amounts depending upon the position of the beam on the screen.

One method of implementing the technique is to notionally divide the viewing area of the display screen into a number of zones and assign a predetermined value to each zone representing the amount by which pels in that zone should be stretched to compensate for the shape distortion. The selected values will range in discrete steps from zero for pels in the corner zones to a maximum for pels in central zones where vertical pre-distortion is at its greatest. Thereafter, in operation, the position of the scanning beam is continuously monitored, and as it passes from one zone to another, the appropriate value by which the pels in that zone are to be stretched is read, for example, from a read-only store. Th...