Light field display metrology
Examples of a light field metrology system for use with a display are disclosed. The light field metrology may capture images of a projected light field, and determine focus depths (or lateral focus positions) for various regions of the light field using the captured images. The determined focus depths (or lateral positions) may then be compared with intended focus depths (or lateral positions), to quantify the imperfections of the display. Based on the measured imperfections, an appropriate error correction may be performed on the light field to correct for the measured imperfections. The display can be an optical display element in a head mounted display, for example, an optical display element capable of generating multiple depth planes or a light field display.
1. An optical metrology system for measuring imperfections in a light field generated by a display, the optical metrology system comprising:
a display configured to project a target light field comprising a virtual object having an intended focus position;
a camera configured to obtain images of the target light field;
a hardware processor programmed with executable instructions to:
access one or more images corresponding to a portion of the light field;
apply a display-to-camera pixel mapping to transfer pixel values of the display to pixel values of the camera, wherein the display-to-camera pixel mapping comprises:
a first gamma correction that maps color levels of the display to a first intermediate color representation;
a pixel-dependent coupling function that maps the first intermediate color representation to a second intermediate color representation; and
a second gamma correction that maps the second intermediate color representation to color levels registered by the camera;
analyze the one or more images to identify a measured focus position corresponding to a position at which the virtual object is in focus; and
determine imperfections in the light field based at least in part on a comparison of the measured focus position and the intended focus position.
2. The optical metrology system of claim 1 , wherein the display comprises a stack of waveguides configured to output light to project the virtual object to at least one depth plane.
3. The optical metrology system of claim 1 , wherein the camera comprises a digital camera having a small depth of focus.
4. The optical metrology system of claim 3 , wherein the camera has a focus, and the system is configured to sweep the focus of the camera over a range of focuses to obtain the one or more images.
5. The optical metrology system of claim 1 , wherein the camera comprises a light field camera.
6. The optical metrology system of claim 1 , wherein the virtual object comprises a checkerboard pattern, a geometric pattern, or a stochastic pattern.
7. The optical metrology system of claim 1 , wherein the display comprises a plurality of pixels, and the target light field corresponds to a subset of less than all of the plurality of pixels being illuminated.
8. The optical metrology system of claim 1 , wherein the measured focus position includes a depth of focus.
9. The optical metrology system of claim 8 , wherein the measured focus position further includes a lateral focus position.
10. The optical metrology system of claim 1 , wherein the determined imperfections are based at least in part on an error vector between the intended focus position and the measured focus position.
11. The optical metrology system of claim 1 , wherein the hardware processor is further programmed to determine an error correction for the display based at least in part on the determined imperfections.
12. The optical metrology system of claim 1 , wherein the determined imperfections comprise a spatial imperfection.
13. The optical metrology system of claim 12 , wherein the spatial imperfection comprises one or more of an in-plane translation, rotation, scaling, or warping error or an out-of-plane or focal depth error.
14. The optical metrology system of claim 1 , wherein the determined imperfections comprise a chromatic imperfection.
15. The optical metrology system of claim 14 , wherein the chromatic imperfection comprises one or more of a luminance flatness or a chromatic uniformity error associated with a color displayable by the display.