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Browse Prior Art Database

Photography of Color Cathode Ray Tube Displays

IP.com Disclosure Number: IPCOM000052428D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

O'Rourke, R: AUTHOR

Abstract

In cathode ray tubes the purity margin at the screen edges is improved by progressively reducing the phosphor dot area from the center to the corners of the screen. This reduction in spot area follows a parabolic curve, the area of the spots at the corners being about 40% of that at the center.

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This is the abbreviated version, containing approximately 100% of the total text.

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Photography of Color Cathode Ray Tube Displays

In cathode ray tubes the purity margin at the screen edges is improved by progressively reducing the phosphor dot area from the center to the corners of the screen. This reduction in spot area follows a parabolic curve, the area of the spots at the corners being about 40% of that at the center.

The reduction in spot area results in a progressive reduction of the brightness of the screen towards the edges. This is not normally significant to the eye, but is significant when color or black and white photography is used to record the images displayed on the screen. (A 40% reduction is approximately a one f stop.) Even poorer results are obtained if the camera or lens suffers from any vignetting.

The progressive reduction in brightness can be compensated for by modulating the beam current to increase the intensity of the emission from the phosphor dots at the edges or reducing the emission at the center. The modulation of the beam current should be of parabolic form synchronized with the line scan and having amplitude to give the required correction.

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