Browse Prior Art Database

Automatic CRT Focus Adjustment

IP.com Disclosure Number: IPCOM000041558D
Original Publication Date: 1984-Feb-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Related People

Slager, SL: AUTHOR

Abstract

A method is described that permits rapid evaluation of the optimum focus adjustment in a CRT device. In a manufacturing environment, rapid optimization of CRT focus without human intervention is desirable to achieve a high degree of uniformity, high quality and throughput of finished products. Fig. 1 illustrates the overall block diagram of the focus adjustment scheme. The CRT display 1 will have displayed on its face any arbitrary pattern or characters from the pattern or character generator 2. Ordinary text characters can be employed, and no special format or pattern is required. The face of the CRT display is viewed by a video camera 3 focussed on the image plane for the CRT 1. An interface between the video camera 3 and a computer is shown as interface 4.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 3

Automatic CRT Focus Adjustment

A method is described that permits rapid evaluation of the optimum focus adjustment in a CRT device. In a manufacturing environment, rapid optimization of CRT focus without human intervention is desirable to achieve a high degree of uniformity, high quality and throughput of finished products. Fig. 1 illustrates the overall block diagram of the focus adjustment scheme. The CRT display 1 will have displayed on its face any arbitrary pattern or characters from the pattern or character generator 2. Ordinary text characters can be employed, and no special format or pattern is required. The face of the CRT display is viewed by a video camera 3 focussed on the image plane for the CRT 1. An interface between the video camera 3 and a computer is shown as interface 4. This device captures an image of a single dot or illuminated area on the face of the CRT 1 for processing by the computer 5. The computer executes an algorithm that determines the degree of focus and drives a manipulator interface 6 to adjust a potentiometer 7 for optimum focus of the CRT 1. The manipulator may be simply a stepper motor that is driven incrementally forward or reverse by a certain number of degrees defined as a step for the manipulator. The focus-optimizing algorithm operates on the principles described with reference to Fig. 2. In Fig. 2, a chart of light intensity versus distance from the center of a dot on the face of the CRT display is shown. The dashed line indicates the effect of an out-of-focus dot. It will be observed that at a low threshold of light intensity, light can be observed at a greater distance from the center of the dot when the dot is out-of-focus than when a dot is sharply in focus as illustrated by the solid line. The algorithm works on the basic property of a focussed dot or character edge. A dot or an image in the display screen which is in focus will have fairly crisp and sharp edges while out-of-focus images or dots have a gradual transition from dark to light. The image that is captured in the interface 4 can be of either single or multiple dots or characters and the analysis is first carried out to determine the number of points in a captured image that have a light value above the low threshold. A second analysis is car...