Method and apparatus for determining and correcting for illumination variations in a digital projector

A display device, comprising:

• a) a light source;
• b) a light modulator;
• c) drive electronics for driving the light modulator with an input signal;
• d) correction electronics for correcting the input signal on an individual pixel-by-pixel basis for intensity offset;
• e) a memory for storing a defect map of pixel intensity offsets for the display;
• f) means for modulating a pixel in the display at a predetermined rate at a predetermined intensity;
• g) a photosensor for sensing the display to generate a sensed signal;
• h) a synchronous demodulator for demodulating the sensed signal at the predetermined rate to produce a demodulated sensed signal representing a sensed intensity;
• and
• i) means employing the sensed intensity and the predetermined intensity for generating the intensity offset.

A improved method of correcting pixel by pixel variations in a display, including the steps of creating a defect map of pixel intensity offsets for the display;

• correcting an input signal according to the defect map;
• and displaying the corrected input signal on the display, wherein the improvement comprises:
• creating the offset defect map by:
• a) driving all pixels to black or a predetermined intensity level except for a single cluster of pixels that are observed for defects;
• b) modulating the single cluster of pixels in the display at a predetermined rate at a predetermined intensity;
• c) sensing the display with a photosensor to generate a sensed signal;
• d) demodulating the sensed signal with a synchronous demodulator at the predetermined rate to produce a demodulated sensed signal representing a sensed intensity;
• e) employing the sensed intensity and the predetermined intensity to generate a correction offset;
• and
• f) repeating above steps for individual clusters of pixels until pixel-by-pixel variations in the display are corrected.