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Cut-Off and G2 Set-Up using Gray Levels

IP.com Disclosure Number: IPCOM000114865D
Original Publication Date: 1995-Feb-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 73K

Publishing Venue

IBM

Related People

McKechnie, R: AUTHOR

Abstract

CRT-based displays require G2 and cut-off voltage levels to be correctly set as part of the color balance set up process. Correct setting of these levels ensures that the required numbers of gray levels can be displayed. It also ensures that the display has good color and gray scale tracking with contrast i.e., white looks white throughout the complete contrast range. Spot shape and size and, therefore, focus is also affected by cut-off and G2 setting. The reliability of the electron gun in CRTs can be affected by wrong setting of G2 and cut-off levels and this can reduce tube life.

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Cut-Off and G2 Set-Up using Gray Levels

      CRT-based displays require G2 and cut-off voltage levels to be
correctly set as part of the color balance set up process.  Correct
setting of these levels ensures that the required numbers of gray
levels can be displayed.  It also ensures that the display has good
color and gray scale tracking with contrast i.e., white looks white
throughout the complete contrast range.  Spot shape and size and,
therefore, focus is also affected by cut-off and G2 setting.  The
reliability of the electron gun in CRTs can be affected by wrong
setting of G2 and cut-off levels and this can reduce tube life.

      The traditional method of setting cut-off and G2 levels in
display production is to use a color analyser which can be used to
measure brightness and color point e.g., a Minolta CA-100 color
analyzer.  With no video present G2 and cut-off pots are adjusted
until the analyser registers the required brightness and color point.
These readings correlate to the required G2 and cut-off levels.  This
is a very repeatable method of set up but it has a number of
disadvantages.  One of these is the fact that color analysers are
expensive, so the capital outlay required to kit out a production
line is substantial.  The following outlines a simple and cost saving
method for cut-off and G2 set up using gray levels.

      Gray levels are a function of the display input.  Most video
drivers use DACs on the output stages to provide the correct form of
video signal.  The number of gray levels that can be displayed is
dependent on the resolution of the DACs i.e., a 4 bit can display 16
g...