Browse Prior Art Database

Color Saturation Control for Cathode Ray Tube Monitors

IP.com Disclosure Number: IPCOM000115612D
Original Publication Date: 1995-May-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 87K

Publishing Venue

IBM

Related People

Maciver, MA: AUTHOR

Abstract

Conventional CRT monitor set-up cannot change the saturation of the primary colors on a CRT faceplate without an unacceptable impact to the background level. Fig. 1 illustrates the basic signal path for a conventional video stage for driving the guns of a CRT. The primary colors of a monitor screen (Red, Green and Blue) are dependent on the phosphor composition on the faceplate. These colors can be de-saturated by injecting a signal into the other video channels, thereby increasing the spectral content of the perceived color.

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Color Saturation Control for Cathode Ray Tube Monitors

      Conventional CRT monitor set-up cannot change the saturation of
the primary colors on a CRT faceplate without an unacceptable impact
to the background level.  Fig. 1 illustrates the basic signal path
for a conventional video stage for driving the guns of a CRT.  The
primary colors of a monitor screen (Red, Green and Blue) are
dependent on the phosphor composition on the faceplate.  These colors
can be de-saturated by injecting a signal into the other video
channels,
thereby increasing the spectral content of the perceived color.

      If the signals were simply added together with their relative
proportions defined by a resistor network, the color point of White
would be difficult to control since the control law of the CRT gun is
non-linear.  Although this non-linearity could be compensated for by
high frequency gamma correction, such compensation is expensive.

      The circuitry shown in Fig. 2, which illustrates saturation
control for one channel (Blue), overcomes this problem by overriding
the injected signals in the presence of a stronger signal at the
channel input.  By way of example, the characteristic curve of Fig. 3
illustrates the influence of the Blue signal on the Green channel
output.  The Table shows an 'analogue logic' truth table for all
eight major primary, secondary and tertiary colors, using the
de-saturation of Blue as an example.

      Fig. 4 shows a practical implem...