Video monitor color control system

A method of periodically calibrating a cathode-ray tube display (CRT) to establish a stored relationship between a set of RGB signal values and associated CRT intensity values such that perceptually accurate colors are displayed on the CRT in response to CIE tri-stimulus XYZ color input signal values, comprising the steps of:

• storing a set of measured CRT color data in an SA matrix representing a relationship between the RGB signal values driving the CRT and a set of CIE tri-stimulus color values;
• setting the RGB signals to a maximum value to display a standardized white on the CRT;
• storing a measured peak intensity vector P relating the RGB maximum signal values to a set of corresponding CRT intensity values of the standardized white displayed on the CRT;
• subjecting the CRT display to a period of use likely to cause a measurable change in the standardized white displayed in response to the maximum RGB signal values;
• following the period of use, stepping the RGB signal values through a group of values substantially spanning from a zero RGB signal value to the maximum RGB signal values;
• storing in the lookup table a sensed CRT intensity value corresponding to each stepped RGB signal value;
• finding in the lookup table a set of maximum CRT intensity values associated with the maximum RGB signal values;
• comparing the maximum CRT intensity values with the peak intensity vector P , and generating a correction factor intensity vector Pc ;
• multiplying the SA matrix by the correction factor intensity vector Pc to generate a corrected matrix A relating CIE tri-stimulus XYZ color values to associated CRT intensity values;
• receiving a CIE tri-stimulus XYZ color value signal;
• dividing the XYZ color value signal by A to generate a corresponding CRT intensity value;
• finding in the lookup table the RGB signal value corresponding to the CRT intensity value;
• and
• driving the CRT with the corresponding RGB signal value to display on the CRT the perceptually accurate color in response to the received CIE tri-stimulus XYZ color value signal.

Apparatus for periodically calibrating a cathode-ray tube display (CRT) to establish a stored relationship between a set of RGB signal values and associated CRT intensity values such that perceptually accurate colors are displayed on the CRT in response to color input signal values, comprising:

• a CRT driver causing the CRT to display light intensity levels in response to RGB signal values, a processor generating an initial RGB signal value for displaying a predetermined color on the CRT, and a memory storing a lookup table and a measured phosphor intensity vector associated with the initial RGB signal value;
• the processor generating a group of RGB signal values such that a corresponding group of CRT intensity levels is displayed on the CRT;
• and
• a sensor generating a phosphor intensity vector for each light intensity level sensed on the CRT, the processor storing in the lookup table the phosphor intensity vector associated with each of the group of RGB signal values, finding in the lookup table a current phosphor intensity vector associated with the initial RGB signal value, comparing the current CRT intensity vector with the initial CRT intensity vector to generate a correction factor vector, and altering the color input signal values with the correction factor to generate corrected RGB signal values that are sent to the CRT driver for displaying perceptually accurate colors on the CRT in response to the color input signal values.

Apparatus for periodically calibrating a cathode-ray tube display (CRT) to establish a stored relationship between a set of RGB signal values and associated CRT intensity values such that colorimetrically accurate colors are displayed on the CRT in response to CIE tri-stimulus XYZ color input signal values, comprising:

• a CRT driver causing the CRT to display light intensity levels in response to the RGB signal values, a processor generating a maximum RGB signal value for displaying an initial white color on the CRT, and a memory storing a lookup table, a CRT phosphor intensity vector associated with the initial white color, and an SA matrix representing an initially measured relationship between the RGB signal values driving the CRT and a set of CIE tri-stimulus XYZ color values;
• the processor generating a group of RGB signal values such that a corresponding group of CRT intensity levels is displayed on the CRT;
• and
• a sensor generating a phosphor intensity vector in response to each light intensity level sensed on the CRT, and the processor storing in the lookup table a phosphor intensity vector associated with each value in the group of RGB signal values and inserting computed phosphor intensity vectors associated with any RGB signal values not in the group of RGB signal values, finding in the lookup table a current phosphor intensity vector associated with the maximum RGB signal value, comparing the current CRT intensity vector with the intensity vector associated with the initial white color and generating a correction factor vector, multiplying the SA matrix by the correction factor to generate a corrected A matrix relating the CIE tri-stimulus XYZ color values to associated CRT intensity values, dividing a particular device independent color value by A to generate a particular CRT intensity value, locating in the lookup table a particular RGB signal value corresponding to the particular CRT intensity value, and sending to the CRT driver the particular RGB signal value, thereby displaying on the CRT a colorimetrically accurate color associated with the particular CIE tri-stimulus XYZ color value.