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Convergence Measurement of CRT Displays

IP.com Disclosure Number: IPCOM000089163D
Original Publication Date: 1977-Sep-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Brandon, M: AUTHOR

Abstract

Convergence error on a CRT display is the distance by which the primary colors are misregistered. The magnitude of the error changes from point to point over the screen and measurement and subsequent correction is often a time consuming and laborious task. The technique here described enables convergence error to be measured simply and rapidly. The technique assumes that one of the three primary colors is correctly positioned, and, this is used as a reference in order to measure the position error of the other two colors for all points on the display.

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Convergence Measurement of CRT Displays

Convergence error on a CRT display is the distance by which the primary colors are misregistered. The magnitude of the error changes from point to point over the screen and measurement and subsequent correction is often a time consuming and laborious task. The technique here described enables convergence error to be measured simply and rapidly. The technique assumes that one of the three primary colors is correctly positioned, and, this is used as a reference in order to measure the position error of the other two colors for all points on the display.

First, a scaled reference grid pattern 1 of horizontal and vertical lines is drawn in a selected primary color over a portion of the screen, as shown in the figure. Then a similar grid pattern 2 of lines in another primary color is drawn to cross the lines of the grid 1 at shallow angles. In the absence of convergence error, the second lines cross the first lines at known predicted places. With convergence the actual crossing points do not coincide with the predicted points, and the magnitude of the error can be easily read off from the scales. This pattern of crossing lines is repeated on the screen for all areas where convergence is to be measured. The entire procedure is then repeated to measure the convergence of the third primary color.

The technique described is applicable for both directed beam and raster scan CRT displays. In order to alleviate the problem known as sta...