EP-4738326-A2 - LED THERMAL CHARACTERIZATION AND CALIBRATION FOR AN OPTICAL DISPLAY

EP4738326A2EP 4738326 A2EP4738326 A2EP 4738326A2EP-4738326-A2

Abstract

Techniques are disclosed for calibrating display devices, such as head-mounted augmented reality (AR) devices. One technique includes obtaining, for each of a set of primary color light sources disposed in a unit, measurement points including chromaticity and luminance values as a function of temperature of the unit and drive currents of the primary color light sources. The technique further includes converting the measurement points to an XYZ color space to produce XYZ values. The technique further includes, for each of a set of target luminances and a set of discrete temperatures, calculating primary luminances for each of the primary color light sources, and interpolating or extrapolating the drive currents and the XYZ values for each of the primary luminances to obtain calculated currents. The technique further includes storing the calculated currents indexed by the target luminances and the discrete temperatures.

Inventors

CAPPS, MARSHALL CHARLES

Assignees

Magic Leap, Inc.

Dates

Publication Date: 20260506
Application Date: 20190802

Claims (13)

A method (700) of calibrating a display device (100) including a set of primary color light sources disposed in a unit (106), the method comprising: obtaining, for a characterized primary light source of the set of primary color light sources, measurement points including chromaticity and luminance values, the obtaining comprising: receiving a target temperature for the unit (410); controlling, using a proportional-integral-derivative, PID, controller (132) in conjunction with an LED current controller (122), drive currents for one or more non-characterized primary color light sources of the set to drive the temperature of the unit to the target temperature by: repeatedly receiving a measured temperature of the unit (418); comparing the measured temperature to the target temperature (420); and based on the comparison, iteratively adjusting the drive currents for the one or more non-characterized primary color light sources (422, 424, 432, 434); once the temperature of the unit is at the target temperature, setting a drive current for the characterized primary light source to a target drive current (416) while the drive currents for the non-characterized primary color light sources are set to zero; and measuring the chromaticity and luminance values of light from the characterized primary light source (440); converting (704) the measurement points to an XYZ color space to produce XYZ values; for each of a set of target luminances and a set of discrete temperatures: calculating (710) primary luminances for each of the set of primary color light sources; and interpolating or extrapolating (712) the drive currents and the XYZ values for each of the primary luminances to obtain calculated currents; and storing (714) the calculated currents indexed by the set of target luminances and the discrete temperatures.
The method of claim 1, further comprising: interpolating or extrapolating (706) the measurement points to provide modified measurement points as a function of the discrete temperatures and the drive currents.
The method of claim 2, further comprising: for each of the discrete temperatures, sorting (708) the modified measurement points by the luminance values.
The method of claim 1, wherein calculating (710) the primary luminances and interpolating or extrapolating (712) the drive currents and the XYZ values are performed over multiple iterations.
The method of claim 1, wherein the calculated currents are stored in a lookup table.
A non-transitory computer-readable medium comprising instructions that, when executed by one or more processors, cause the one or more processors to control a calibration system to perform a method of calibrating a display device (100) including a set of primary color light sources disposed in a unit (106), the method comprising: obtaining, for a characterized primary light source of the set of primary color light sources, measurement points including chromaticity and luminance values, the obtaining comprising: receiving a target temperature for the unit (410); controlling drive currents for one or more non-characterized primary color light sources of the set to drive the temperature of the unit to the target temperature by performing operations of: repeatedly receiving a measured temperature of the unit (418); comparing the measured temperature to the target temperature (420); and based on the comparison, determining iterative adjustments for the drive currents for the one or more non-characterized primary color light sources and causing an LED current controller (122) to apply the adjusted drive currents (422, 424, 432, 434); once the temperature of the unit is at the target temperature, causing the LED current controller (122) to set a drive current for the characterized primary light source to a target drive current (416) while the drive currents for the non-characterized primary color light sources are set to zero; and receiving measurement data corresponding to the chromaticity and luminance values of light from the characterized primary light source (440); converting (704) the measurement points to an XYZ color space to produce XYZ values; for each of a set of target luminances and a set of discrete temperatures: calculating (710) primary luminances for each of the set of primary color light sources; and interpolating or extrapolating (712) the drive currents and the XYZ values for each of the primary luminances to obtain calculated currents; and storing (714) the calculated currents indexed by the set of target luminances and the discrete temperatures.
The non-transitory computer-readable medium of claim 6, wherein the operations further comprise: interpolating or extrapolating (706) the measurement points to provide modified measurement points as a function of the discrete temperatures and the drive currents, and for each of the discrete temperatures, sorting (708) the modified measurement points by the luminance values.
The non-transitory computer-readable medium of claim 6, wherein the set of primary color light sources are light-emitting diodes, LEDs.
The non-transitory computer-readable medium of claim 6, wherein the unit comprises a compound parabolic concentrator, CPC.
The non-transitory computer-readable medium of claim 6, wherein measuring the chromaticity and luminance values comprises receiving light transmitted through an eyepiece of the display device (100).
The non-transitory computer-readable medium of claim 6, wherein calculating (710) the primary luminances and interpolating or extrapolating (712) the drive currents and the XYZ values are performed over multiple iterations.
The non-transitory computer-readable medium of claim 6, wherein the calculated currents are stored in a lookup table.
A system for calibrating a display device (100) including a set of primary color light sources disposed in a unit (106), the system comprising: one or more processors (1310); and a non-transitory computer-readable medium according to any one of claims 6 to 12.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Patent Application No. 62/714,503, filed August 3, 2018, entitled "LED THERMAL CHARACTERIZATION AND CALIBRATION FOR AN OPTICAL DISPLAY," the contents of which is herein incorporated in its entirety. BACKGROUND OF THE INVENTION Modern computing and display technologies have facilitated the development of systems for so called "virtual reality" or "augmented reality" experiences, wherein digitally reproduced images or portions thereof are presented to a user in a manner wherein they seem to be, or may be perceived as, real. A virtual reality, or "VR," scenario typically involves presentation of digital or virtual image information without transparency to other actual real-world visual input; an augmented reality, or "AR," scenario typically involves presentation of digital or virtual image information as an augmentation to visualization of the actual world around the user. Despite the progress made in these display technologies, there is a need in the art for improved methods, systems, and devices related to augmented reality systems, particularly, display systems. SUMMARY OF THE INVENTION The present disclosure relates generally to techniques for calibrating display devices. More particularly, embodiments of the present disclosure provide systems and methods for performing a thermal characterization and calibration of one or more light-emitting diodes (LEDs) in an augmented reality (AR) device. Although portions of the present disclosure are described in reference to an AR device, the disclosure is applicable to a variety of applications in image display systems. In accordance with a first aspect of the present invention, a method of calibrating a display device including a set of primary color light sources disposed in a unit is provided. The method may include obtaining, for each of the primary color light sources, measurement points including chromaticity and luminance values as a function of temperature of the unit and drive currents of the primary color light sources. The method may also include converting the measurement points to an XYZ color space to produce XYZ values. The method may further include, for each of a set of target luminances and a set of discrete temperatures, calculating primary luminances for each of the primary color light sources and interpolating or extrapolating the drive currents and the XYZ values for each of the primary luminances to obtain calculated currents. The method may further include storing the calculated currents indexed by the target luminances and the discrete temperatures. In some embodiments, the method further includes interpolating or extrapolating the measurement points to provide modified measurement points as a function of the discrete temperatures and the drive currents. In some embodiments, the method further includes, for each of the discrete temperatures, sorting the modified measurement points by the luminance values. In some embodiments, the primary color light sources are LEDs. In some embodiments, the unit comprises a compound parabolic concentrator (CPC). In some embodiments, measuring the chromaticity and luminance values comprises receiving light transmitted through an eyepiece of the display device. In some embodiments, calculating the primary luminances and interpolating or extrapolating the drive currents and the XYZ values are performed over multiple iterations. In some embodiments, the calculated currents are stored in a lookup table. In accordance with a second aspect of the present invention, a system for calibrating a display device including a set of primary color light sources disposed in a unit is provided. The system may include one or more processors. The system may also include a computer-readable medium comprising instructions that, when executed by the one or more processors, cause the one or more processors to perform operations. The operations may include obtaining, for each of the primary color light sources, measurement points including chromaticity and luminance values as a function of temperature of the unit and drive currents of the primary color light sources. The operations may also include converting the measurement points to an XYZ color space to produce XYZ values. The operations may further include, for each of a set of target luminances and a set of discrete temperatures, calculating primary luminances for each of the primary color light sources and interpolating or extrapolating the drive currents and the XYZ values for each of the primary luminances to obtain calculated currents. The operations may further include storing the calculated currents indexed by the target luminances and the discrete temperatures. In some embodiments, the operations further include interpolating or extrapolating the measurement points to provide modified measurement points as a function of the discrete temperatures and the drive cu