Display with compressed calibration data

1. A display device comprising:

a projector for providing image light carrying an image in angular domain for displaying by the display device;

a pupil expander operably coupled to the projector for relaying the image light to an eyebox of the display device, wherein optical throughput of the pupil expander has a first dependence on a beam angle and a beam coordinate at the eyebox; and

a controller operably coupled to the projector and configured to:

obtain basis vectors and reconstruction coefficients representing a compressed approximation of the first dependence;

determine calibration data from the basis vectors and the reconstruction coefficients, for applying to the image to at least partially offset the first dependence; and

apply the calibration data to the image.

2. The display device of claim 1 , wherein the controller is configured to multiply basis vectors with the reconstruction coefficients for determining the calibration data.

3. The display device of claim 1 , wherein the first dependence is defined by a plurality of calibration coefficients at grid points of the image, wherein the controller is configured to:

obtain a plurality of restored coefficients at the grid points from the basis vectors and the reconstruction coefficients, the plurality of restored coefficients corresponding to the plurality of calibration coefficients; and

determine the calibration data by interpolating the restored coefficients between the grid points.

4. The display device of claim 1 , further comprising an eye tracking system operably coupled to the controller for determining a particular eye pupil position at the eyebox, wherein the first dependence is defined by a plurality of calibration coefficients at grid points of eye pupil positions at the eyebox, wherein the controller is configured to:

determine interpolated reconstruction coefficients for the particular eye pupil position, by interpolating the reconstruction coefficients between the grid points; and

determine the calibration data by multiplying the basis vectors with the interpolated reconstruction coefficients.

5. The display device of claim 1 , wherein the first dependence is defined by a plurality of brightness coefficients, each brightness coefficient corresponding to a point of a brightness grid of points of the image, and a plurality of color coefficients, two color coefficients corresponding to a point of a color grid of points of the image, wherein the controller is configured to:

obtain a plurality of restored brightness coefficients at the brightness grid points from the basis vectors and the reconstruction coefficients; and

obtain a plurality of restored color coordinate coefficients at the color grid points from the basis vectors and the reconstruction coefficients;

wherein the color grid of points has less points than the brightness grid of points.

6. The display device of claim 5 , wherein the first dependence is defined in YCbCr color space, wherein the brightness coefficients correspond to a luma component of the YCbCr color space, and the color coefficients correspond to blue-difference and red-difference chroma components of the YCbCr color space.

7. The display device of claim 1 , wherein the basis vectors are eigenvectors of a plurality of calibration coefficients at grid points of the image.

8. The display device of claim 1 , wherein the controller is configured to determine reconstructed coefficients using the basis vectors and the reconstruction coefficients, the reconstructed coefficients having a variation greater than or equal to a variation of the first dependence.

9. A calibration system for calibrating a display device comprising a projector for providing image light carrying an image in angular domain, and a pupil expander operably coupled to the projector for relaying the image light to an eyebox of the display device, the calibration system comprising:

a test camera for receiving the image light from the pupil expander, wherein at least one of the pupil expander or the test camera is movable to change a position of the test camera at the eyebox; and

a test controller operably coupled to the test camera and the display device and configured to:

cause the display device to display a calibration frame;

determine a first dependence of optical throughput of the pupil expander on a beam angle and a beam coordinate at the eyebox, by obtaining at least one image of the calibration frame with the test camera;

determine basis vectors and reconstruction coefficients representing a compressed approximation of the first dependence; and

store the basis vectors and the reconstruction coefficients for subsequent access by the display device.

10. The calibration system of claim 9 , wherein the test controller is configured to determine the reconstruction coefficients by projecting test data representing the first dependence onto the basis vectors.

11. The calibration system of claim 10 , wherein the test controller is configured to determine eigenvectors of a covariance matrix of the test data for determining the basis vectors.

12. The calibration system of claim 9 , wherein the first dependence is defined by a plurality of brightness coefficients, each brightness coefficient corresponding to a point of a brightness grid of points of the image, and a plurality of color coefficients, two color coefficients corresponding to a point of a color grid of points of the image, wherein the test controller is configured to:

determine basis vectors and reconstruction coefficients representing a compressed approximation of the plurality of brightness coefficients; and

determine basis vectors and reconstruction coefficients representing a compressed approximation of the plurality of color coefficients;

wherein the color grid of points has less points than the brightness grid of points.

13. The calibration system of claim 12 , wherein the first dependence is defined in YCbCr color space, wherein the brightness coefficients correspond to luma component of the YCbCr color space, and the color coefficients correspond to blue-difference and red-difference chroma components of the YCbCr color space.

14. The calibration system of claim 9 , wherein the basis vectors are eigenvectors of a plurality of calibration coefficients at grid points of the image.

15. A method in a display device comprising a projector for providing image light carrying an image in angular domain, and a pupil expander operably coupled to the projector for relaying the image light to an eyebox of the display device, the method comprising:

obtaining basis vectors and reconstruction coefficients representing a compressed approximation of a first dependence of optical throughput of the pupil expander on a beam angle and a beam coordinate at the eyebox;

obtaining calibration data from the basis vectors and reconstruction coefficients, for applying to the image to at least partially offset the first dependence; and

applying the calibration data to the image.

16. The method of claim 15 , wherein obtaining the basis vectors and the reconstruction coefficients comprises:

using a calibration system to cause the display device to display a calibration frame;

determining the first dependence of optical throughput of the pupil expander on a beam angle and a beam coordinate at the eyebox, by obtaining at least one image of the calibration frame with a test camera of the calibration system;

obtaining the basis vectors using a covariance matrix of test data representing the first dependence;

obtaining the reconstruction coefficients by projecting the test data onto the basis vectors; and

storing the basis vectors and the reconstruction coefficients for subsequent access by the display device.

17. The method of claim 15 , wherein the first dependence is defined by a plurality of calibration coefficients at grid points of the image, the method further comprising:

obtaining a plurality of restored coefficients at the grid points from the basis vectors and the reconstruction coefficients, the plurality of restored coefficients corresponding to the plurality of calibration coefficients; and

obtaining the calibration data by interpolation the restored coefficients between the grid points.

18. The method of claim 15 , wherein the first dependence is defined by a plurality of calibration coefficients at a grid of locations at the eyebox, the method further comprising:

obtaining a plurality of restored coefficients at the grid of locations from the basis vectors and the reconstruction coefficients, the plurality of restored coefficients corresponding to the plurality of calibration coefficients; and

obtaining the calibration data by interpolation the restored coefficients between locations of the grid of locations.

19. The method of claim 15 , wherein the first dependence is defined by a plurality of calibration coefficients at grid points of eye pupil positions at the eyebox, the method further comprising:

determine interpolated reconstruction coefficients for a particular eye pupil position, by interpolating the reconstruction coefficients between the grid points; and,

determine the calibration data by multiplying the basis vectors with the interpolated reconstruction coefficients.

20. The method of claim 15 , wherein the basis vectors are eigenvectors of a plurality of calibration coefficients at grid points of the image, and wherein the calibration data has a variation greater than or equal to a variation of the first dependence.