Laser Projection White Balance Tracking

Abstract

The radiance of a laser diode is a function of laser diode drive current. The radiance is also a function of other factors, such as age and temperature. A laser projection device includes laser diodes to generate light in response to a commanded radiance, and also includes photodetectors to provide a measured radiance. The commanded radiance and measured radiance are compared, and drive currents for the laser diodes are adjusted to provide luminance and color balance tracking.

1 . An apparatus comprising:
 image processing circuitry to command a radiance value;   a mapping component to convert the radiance value to a drive current value;   a digital to analog converter to convert the drive current value to a drive current;   a first laser diode to emit light in response to the drive current;   a detector to detect light emitted from the first laser diode; and   a loop circuit coupled to update the mapping component in response to the detector.   
     
     
         2 . The apparatus of  claim 1  wherein the loop circuit comprises:
 a digital filter to receive the radiance value from the image processing circuitry, the digital filter having a response to approximate a response of the digital to analog converter; and   an error calculator coupled to receive information from the digital filter and the detector, and further coupled to provide update information to the mapping component.   
     
     
         3 . The apparatus of  claim 2  further comprising a second laser diode and a third laser diode. 
     
     
         4 . The apparatus of  claim 3  wherein the first laser diode is a green laser diode. 
     
     
         5 . The apparatus of  claim 4  wherein the update information provided to the mapping component is provided to calibrate luminance of the green laser diode. 
     
     
         6 . The apparatus of  claim 5  wherein the update information provided to the mapping component is further provided to calibrate the red laser diode and green laser diode for color balance. 
     
     
         7 . A circuit comprising:
 a laser diode to emit light;   a look up table to map normalized luminance values to drive current values for the laser diode;   a multiplier component to scale data in response to a gain value, and to supply scaled data to the look up table;   a radiance measurement apparatus to detect light emitted from the laser diode;   a radiance prediction apparatus to determine an expected amount of light; and   a comparator to modify the gain value in response to the measurement apparatus and the light prediction apparatus.   
     
     
         8 . The circuit of  claim 7  wherein the radiance measurement apparatus comprises a photodetector, a transimpedance amplifier, and an analog integrator. 
     
     
         9 . The circuit of  claim 8  wherein the radiance measurement apparatus further comprises an analog-to-digital converter and a digital accumulator. 
     
     
         10 . The circuit of  claim 9  wherein the radiance measurement apparatus further comprises a 3×3 spectral response inverse matrix. 
     
     
         11 . The circuit of  claim 9  wherein the analog integrator integrates over a scan line in a video image, and the digital accumulator accumulates over a video frame. 
     
     
         12 . An apparatus comprising:
 image processing circuitry to command radiance values for three different colors;   three mapping components to convert the radiance values to drive current values for the three different colors;   three digital to analog converters to convert the drive current values to drive currents;   three laser diodes to emit different color light in response to the drive currents;   at least one photodetector to detect a measured radiance of the three laser diodes; and   means to modify the three mapping components in response to the measured radiance.   
     
     
         13 . The apparatus of  claim 12  wherein the means to modify the three mapping components includes an error calculation circuit to determine mapping component corrections for luminance variations in the three laser diodes. 
     
     
         14 . The apparatus of  claim 12  wherein the three laser diodes include a red laser diode, a green laser diode, and a blue laser diode. 
     
     
         15 . The apparatus of  claim 14  wherein the means to modify the three mapping components includes an error calculation circuit to determine a mapping component correction for luminance variation in only the green laser diode. 
     
     
         16 . The apparatus of  claim 15  wherein the error calculation circuit further determines mapping component corrections for the red laser diode and the blue laser diode to maintain a color balance. 
     
     
         17 . The apparatus of  claim 15  wherein the error calculation circuit further determines mapping component corrections for the red laser diode and the blue laser diode to maintain a D 65  white. 
     
     
         18 . A color projector comprising:
 at least one laser light source to project a color image;   a circuit coupled to determine an expected radiance of the at least one laser light source;   at least one photo detector to detect a measured radiance of the at least one laser light source; and   a feedback circuit coupled to calibrate the laser light source in response to the expected radiance and the measured radiance.   
     
     
         19 . The color projector of  claim 18  wherein the circuit coupled to determine an expected radiance includes a digital filter to model a response of drive electronics that drive the at least one laser light source. 
     
     
         20 . The color projector of  claim 18  wherein the at least one laser light source comprises a red laser diode, a green laser diode, and a blue laser diode. 
     
     
         21 . The color projector of  claim 18  further comprising a mapping component to map desired radiance values to drive current values for the at least one laser light source. 
     
     
         22 . The color projector of  claim 21  wherein the feedback loop is coupled to modify the mapping component. 
     
     
         23 . A mobile device comprising:
 a laser projector to project an image, the laser projector including a laser diode subject to heating based on video content, the laser projector further including at least one photodetector to detect light emitted from the laser diode, the laser projector further including a mapping component to map desired radiance values to a drive current value for the laser diode, and the laser projector further including a feedback loop to adjust the mapping component in response to the photodetector.   
     
     
         24 . The mobile device of  claim 23  further comprising a memory card slot. 
     
     
         25 . The mobile device of  claim 23  further comprising a communications receiver.