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# Gamma Correction of a Display

IP.com Disclosure Number: IPCOM000060148D
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 32K

IBM

## Related People

Talkington, CM: AUTHOR

## Abstract

A system is illustrated in Fig. 1 to make the light output of the display substantially proportional to the input voltage. Normally, the typical cathode ray tube (CRT) has a light output which is a function of the drive voltage characterized by the equation

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Gamma Correction of a Display

A system is illustrated in Fig. 1 to make the light output of the display substantially proportional to the input voltage. Normally, the typical cathode ray tube (CRT) has a light output which is a function of the drive voltage characterized by the equation

Light = KVolts3.2 It would be more desirable if the light output were proportional to the input voltage, or more nearly so. Compensation of the voltage to achieve this is referred to as gamma correction. This means to apply gamma correction shown in Fig. 1 is to use the reference voltage input to the Digital-to-analog (D/A) converter 11 to apply some voltage which is controlled by converter a digital word. A second D/A converter 12 is employed which is as fast as the first D/A converter 11 but does not have as severe a slew rate requirement. The output of converter 11 follows a curve proportional to the cube root of the input digital word (DW), so the light output is nearly linear.

Light N[ (K * DW) 1/3]3.2 = K1.1 *DW1.1 To generate this output from 11, the output of 12 is: V2 = (K * DW)-2/3 Such a function is easily implemented by applying a constant output at and above the four level and a voltage corresponding to the slope of line A below the four input level, as shown in the graph of Fig. 2. This slope is generated by applying the complement of the two least significant bits to D/A -2 (Fig. 1) for counts 0, 1, 2, and 3.

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