Chromatic aberration calibration and validation system

1 . A system for chromatic aberration and geometry calibration and validation of virtual reality head mounted displays (VR HMDs) comprising:

a left eye display and a right eye display,

a measurement device configured in a way that an HMD to be calibrated or validated is attachable to it in a way as such an HMD would be removably attached to the head of a user;

wherein the measurement device comprises:

a left and a right camera, wherein each camera is intrinsically and extrinsically calibrated, and

a control unit connected to the two cameras as well as configured to deliver control signals to the HMD when removably attached to the measurement device and when a camera inter pupillary distance (IPD) is manually or automatically adjusted to a prechosen HMD IPD,

wherein the control unit is configured to execute steps comprising:

a.) setting a virtual IPD equal to the value of camera IPD,

b.) creating a virtual target object for the displays, the virtual target object having an image center identifying element and a plurality of predetermined points within a field of view (FOV) of the cameras,

c.) calculating and transmitting images of said virtual target object to the displays of the HMD,

d.) taking the images of the displays through the HMD lenses with the cameras,

e.) detecting the virtual object and the image center identifying element within the images,

f.) determining a shift, for each camera, for the plurality of predetermined points of the virtual object in relation to the image center identifying element,

wherein the control unit is further configured for

g.) determining said shift for each color channel of a plurality of color channels, and using the shift between one of the color channels and another for calculating a distortion of the predetermined points within the FOV of the cameras, creating a chromatic aberration heatmap for the HMD based on the shift between the two colors, and determining the chromatic aberration validation or denying the chromatic aberration validation, if a predetermined number of points of the predetermined heatmap is inside or outside a predetermined heatmap threshold of the HMD, respectively; and

h.) determining said shift for the plurality of predetermined points colored black on a white background, or for the plurality of predetermined points colored white on a black background, using the shift for creating a geometry heatmap for the HMD, and determining the geometry validation or denying the geometry validation, if a predetermined number of points of the geometry heatmap is inside or outside a predetermined heatmap threshold of the HMD, respectively,

wherein the virtual target object a black cylinder portion with vertical lines in a color or white to be taken separately by each camera with the image center identifying element being a centrally arranged line for each camera and the virtual camera being arranged on the center axis of the cylinder portion, or a black cylinder portion with horizontal lines in a color or white to be taken separately by each camera with the image center identifying element being a centrally arranged line for each camera and the virtual camera being arranged on the center axis of the cylinder portion.

2 . The system according to claim 1 , wherein the shift of the virtual target object is expressed as a plurality of angle values between a distorted line on the virtual target object in relation to the image center identifying element.

3 . A system for chromatic aberration and geometry calibration and validation of virtual reality head mounted displays (VR HMDs) comprising:

a left eye display and a right eye display,

a measurement device configured in a way that an HMD to be calibrated or validated is attachable to it in a way as such an HMD would be removably attached to the head of a user;

wherein the measurement device comprises:

a left and a right camera, wherein each camera is intrinsically and extrinsically calibrated, and

a control unit connected to the two cameras as well as configured to deliver control signals to the HMD when removably attached to the measurement device and when a camera inter pupillary distance (IPD) is manually or automatically adjusted to a prechosen HMD IPD,

wherein the control unit is configured to execute steps comprising:

a.) setting a virtual IPD equal to the value of camera IPD,

b.) creating a virtual target object for the displays, the virtual target object having an image center identifying element and a plurality of predetermined points within a field of view (FOV) of the cameras,

c.) calculating and transmitting images of said virtual target object to the displays of the HMD,

d.) taking the images of the displays through the HMD lenses with the cameras,

e.) detecting the virtual object and the image center identifying element within the images,

f.) determining a shift, for each camera, for the plurality of predetermined points of the virtual object in relation to the image center identifying element,

wherein the control unit is further configured for

g.) determining said shift for each color channel of a plurality of color channels, and using the shift between one of the color channels and another for calculating a distortion of the predetermined points within the FOV of the cameras, creating a chromatic aberration heatmap for the HMD based on the shift between the two colors, and determining the chromatic aberration validation or denying the chromatic aberration validation, if a predetermined number of points of the predetermined heatmap is inside or outside a predetermined heatmap threshold of the HMD, respectively; and

h.) determining said shift for the plurality of predetermined points colored black on a white background, or for the plurality of predetermined points colored white on a black background, using the shift for creating a geometry heatmap for the HMD, and determining the geometry validation or denying the geometry validation, if a predetermined number of points of the geometry heatmap is inside or outside a predetermined heatmap threshold of the HMD, respectively,

wherein the virtual target object comprises a checkerboard target pattern or curved target pattern with a grid of quadrilaterals in a color to be taken separately by each camera with the image center identifying element being a centrally detectable element for each camera and the virtual camera being arranged in the center of the virtual target object.

4 . The system according to claim 3 , wherein the shift of the virtual target object comprises a plurality of shifts between a corner of the virtual target object pattern and a displayed corner of quadrilaterals.

5 . The system according to claim 3 , wherein the checkerboard target pattern or curved target pattern is recorded with several positions and a displacement of a predetermined fraction of the quadrilateral side length to provide a higher resolution of the points.

6 . The system according to claim 5 , wherein the color channels are three color channels of an RGB color space or four color channels of a CMYK color space.

7 . The system according to claim 6 , wherein the color channels are two pairs of two color channels chosen in the RGB space and are red-and-green and blue-and-green.

8 . The system according to claim 2 , wherein the control unit is further configured for using the shift for creating a heatmap for the HMD comprising the difference between the real and the measured angles of the lines and determining the geometry validation or denying the geometry validation, if a predetermined number of points of the predetermined heatmap is inside or outside a predetermined heatmap threshold of the HMD, respectively.

9 . The system according to claim 4 , wherein the control unit is further configured for using the shift for creating a heatmap for the HMD comprising the shifts between the corners and displayed corners and determining the geometry validation or denying the geometry validation, if a predetermined number of points of the predetermined heatmap is inside or outside a predetermined heatmap threshold of the HMD, respectively.