US 4,415,921 A · Automatic calibration system for video displays in vision testing

Abstract

A calibration circuit and method for instructing an instrument operator on how to adjust the brightness and contrast controls of a video display in order to achieve a precise display intensity directly proportional to the video drive signal input to the video display. A photometer detects the display intensity as the video drive is modulated and a differential amplifier compares the video drive to the photometer output signal thereby generating an analog offset signal highly representative of brightness and contrast offsets. The analog offset signal is converted to numerical offset values from which independent brightness and contrast offsets are computed. For raster-scanned video displays only a one-bit analog-to-digital converter, a comparator, is required and a multi-bit numerical value of the video offset may be obtained from the comparator output by the method of counting the number of scan lines in each frame giving a positive comparator output.

Claims17

Dependent claims

A calibration circuit for indicating the error in intensity adjustment of a video display driven by video drive signal comprising, in combination:

light sensor means generating a photometer signal in response to illumination from the video display;
comparator means comparing the photometer signal to the video drive signal for generating an error signal indicative of the error in intensity adjustment of the video display, said comparator means comprising differential amplifier means having an output signal proportional to a difference between the video drive signal and the photometer signal;
digital to analog converter means having a digital control signal input and an analog output generating the video drive signal in response to the logic states on the digital control signal input, and having a response time at least as short as the low frequency response time of the video display to the video drive signal;
and
digital sampling means for intermittently sampling and storing a digital representation of the comparator means output signal, and having a sampling response time at least as short as the low-frequency response time of the video display to the video drive signal,
so that the difference between sampled and stored comparator output signals in response to alternating logic states on the digital control signal input indicates the error in the contrast adjustment of the video display, and the sum of the sampled and stored comparator output signals in response to alternating logic states on the digital control signal input indicates the error in the brightness adjustment of the video display.

3 more elements

A circuit for numerically measuring the light intensity of a raster-scan display having a line sync output and a frame sync output indicating the occurrence of a line scan and a frame scan respectively, comprising, in combination:

(a) a light sensor generating a photometer signal indicating the light transmitted by the display to a localized area in front of the display, and
(b) a comparator having an input receiving the photometer signal and a logic output indicating whether the photometer signal exceeds a preset threshold level, and
(c) a counter having a counter input receiving the line sync signal and an enable input receiving the comparator logic output signal, the counter being responsive to logic transitions on the counter input if a logic state is asserted on the enable input between logic transitions on the counter input, and
(d) indicating means for indicating the counter value after the occurrence of a frame sync pulse,
so that the number of scan lines having an observed light intensity at a localized area in front of the display exceeding a preset threshold is indicated, thus providing a numeric value of the light intensity of the display.

2 more elements

Dependencies are inferred from the claim text.

Automatic calibration system for video displays in vision testing

Life of this patent

Automatic calibration system for video displays in vision testing

Life of this patent

Abstract

Claims17