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 performing image correction on a display, the system comprising:
a camera configured to capture an image projected by a display;
a hardware processor programmed with executable instructions to:
generate a vector field based at least partly on the image captured by the camera, the vector field comprising vectors corresponding to deviations between projected positions and expected positions of points of the display; and
calculate, based at least partly on the vector field, at least one of: a centration correction, an aggregate rotation correction, an aggregate scaling correction, or a spatial mapping, for the display;
calculate, based at least partly upon the image captured by the camera, values associated with the luminance of a plurality of points on the display; and
calculate, based at least partly on said determined values, a luminance flattening correction or a chromatic balancing correction, for the display.
2. The optical metrology system of claim 1 , wherein the display comprises a plurality of display layers, at least one display layer of the display comprising a color layer or a depth layer.
3. The optical metrology system of claim 1 , wherein the camera comprises a light field camera or a digital camera having a small depth of focus.
4. The optical metrology system of claim 1 , wherein to calculate the centration correction, the hardware processor is programmed to determine a translation vector corresponding to a translation error between an identified point of the image projected by the display and an expected point position.
5. The optical metrology system of claim 1 , wherein to calculate the aggregate rotation correction, the hardware processor is programmed to determine a rotational amount corresponding to a rotation of the projected display image projected by the display about a point, such that a pixel error amount between the projected positions and the expected positioned is reduced or minimized.
6. The optical metrology system of claim 1 , wherein to calculate the aggregate rotation correction, the hardware processor is programmed to calculate a curl of the vector field.
7. The optical metrology system of claim 1 , wherein to calculate the aggregate scaling correction, the hardware processor is programmed to determine a scaling amount corresponding to a scaling of the image projected by the display about a point, such that a pixel error amount between the projected positions and the expected positioned is reduced or minimized.
8. The optical metrology system of claim 1 , wherein to calculate the aggregate scaling correction, the hardware processor is programmed to calculate a divergence of the vector field.
9. The optical metrology system of claim 1 , wherein to calculate the spatial mapping, the hardware processor is programmed to determine a non-linear transformation to align the projected positions of the image with the expected positions.
10. The optical metrology system of claim 1 , wherein to calculate the luminance flattening correction, the hardware processor is programmed to:
determine a threshold value; and
calculate an amount that lowers different values associated with luminance greater than the threshold value to the threshold value.
11. The optical metrology system of claim 1 , wherein the display comprises a plurality of display layers, and wherein to calculate the chromatic balancing correction, the hardware processor is programmed to:
identify a color cluster associated with at least one of the plurality of display layers, the color cluster comprising at least one additional display layer;
for different points of the at least one display layer, compare the value associated with luminance corresponding to the point on the at least one display layer with a value associated with luminance corresponding to the point on the at least one additional display layer; and
calculate an amount that lowers different values associated with luminance of the at least one display layer to a lower value associated with its corresponding point of the at least one additional layer.
12. The optical metrology system of claim 1 , wherein the display comprises a stack of waveguides configured to output light to project a virtual object to at least one depth plane.
13. The optical metrology system of claim 12 , wherein the virtual object comprises a checkerboard pattern, a geometric pattern, or a stochastic pattern.
14. The optical metrology system of claim 12 , wherein the hardware processor is further programmed to identify a measured focus position corresponding to a position at which the virtual object is in focus.