Parallax correction for illumination system and method
An imaging system can automatically measure a distance to an object. A camera, having a field of view that includes the object, can define a camera longitudinal axis that extends to a center of the field of view. An illuminator, defining an illuminator longitudinal axis that is substantially parallel to the camera longitudinal axis and is laterally offset from the camera longitudinal axis, can illuminate the object with an illumination field. The illumination field can have an illumination field central axis that is angularly offset from the illuminator longitudinal axis by an angle that depends at least in part on the measured distance to the object to at least partially compensate for parallax error caused by the lateral offset between the illuminator longitudinal axis and the camera longitudinal axis. The camera can capture an image of the object while the illuminator illuminates the object with the illumination field.
1. An imaging system, comprising:
a camera having a field of view that includes an object, the camera defining a camera longitudinal axis that extends to a center of the field of view; and
an illuminator defining an illuminator longitudinal axis that is substantially parallel to the camera longitudinal axis and is laterally offset from the camera longitudinal axis, the illuminator configured to illuminate the object with an illumination field, the illumination field having an illumination field central axis that is angularly offset from the illuminator longitudinal axis by an angle that depends at least in part on a measured distance to the object to at least partially compensate for parallax error caused by the lateral offset between the illuminator longitudinal axis and the camera longitudinal axis,
the camera configured to capture an image of the object while the illuminator illuminates the object with the illumination field.
2. The imaging system of claim 1 , wherein the illuminator includes an illuminator lens and a light-emitting diode (LED) array disposed at or near a focal plane of the illuminator lens, the illuminator longitudinal axis extending from a center of the LED array through a center of the illuminator lens, the LED array configured to emit light through the illuminator lens to form the illumination field.
3. The imaging system of claim 2 , further comprising:
a controller configured to cause the LED array to be powered such that a specified illumination pattern on the LED array is laterally offset on the LED array by an offset amount that depends at least in part on the measured distance to the object to at least partially compensate for the parallax error.
4. The imaging system of claim 3 , wherein the controller is configured to calculate the offset amount as an offset angle multiplied by a focal length of the illuminator lens.
5. The imaging system of claim 4 , wherein the controller is configured to calculate the offset angle as an arctangent of a ratio, the ratio being a lateral offset between the illuminator longitudinal axis and the camera longitudinal axis divided by the measured distance to the object.
6. The imaging system of claim 4 , wherein the controller is configured to determine the offset amount by selecting one of a plurality of predetermined offset amounts.
7. The imaging system of claim 2 , further comprising:
an actuator configured to translate the illuminator lens; and
a controller configured to cause the actuator to translate the illuminator lens by an offset amount that depends at least in part on the measured distance to the object.
8. The imaging system of claim 7 , wherein the controller is configured to calculate the offset amount as an offset angle multiplied by a focal length of the illuminator lens.
9. The imaging system of claim 8 , wherein the controller is configured to calculate the offset angle as an arctangent of a ratio, the ratio being a lateral offset between the illuminator longitudinal axis and the camera longitudinal axis divided by the measured distance to the object.
10. The imaging system of claim 8 , wherein the controller is configured to determine the offset amount as one of a plurality of predetermined offset amounts.
11. The imaging system of claim 1 , further comprising:
a distance sensor configured to measure a time of flight between the distance sensor and the object to determine the measured distance to the object.
12. The imaging system of claim 1 , further comprising:
a distance sensor configured to form a depth map that includes the object to determine the measured distance to the object.
13. The imaging system of claim 1 , wherein the camera includes an auto-focus mechanism that is configured to determine the measured distance to the object.
14. The imaging system of claim 1 , wherein:
the camera and the illuminator are disposed on or in a housing;
the housing defines a plane; and
the illuminator longitudinal axis and the camera longitudinal axis are substantially orthogonal to the plane.
15. A method for capturing an image, the method comprising:
automatically measuring a distance from a housing to an object;
illuminating, from an illuminator disposed on or in the housing, the object with an illumination field, the illuminator defining an illuminator longitudinal axis;
capturing, with a camera disposed on or in the housing, an image of the object while the illuminator illuminates the object with the illumination field, the camera having a field of view that includes the object, the camera defining a camera longitudinal axis that extends to a center of the field of view, the camera longitudinal axis being parallel to the illuminator longitudinal axis and being laterally offset from the camera longitudinal axis,
the illumination field having an illumination field central axis that is angularly offset from the illuminator longitudinal axis by an angle that depends at least in part on the measured distance to the object to at least partially compensate for parallax error caused by the lateral offset between the illuminator longitudinal axis and the camera longitudinal axis.
16. The method of claim 15 , wherein the illuminator includes an illuminator lens and a light-emitting diode (LED) array disposed at or near a focal plane of the illuminator lens, the illuminator longitudinal axis extending from a center of the LED array through a center of the illuminator lens, the method further comprising:
emitting light, from the LED array, through the illuminator lens to form the illumination field.
17. The method of claim 16 , further comprising:
powering the LED array such that a specified illumination pattern on the LED array is laterally offset on the LED array by an offset amount that depends at least in part on the measured distance to the object to at least partially compensate for the parallax error.
18. An imaging system, comprising:
a housing defining a plane;
a camera disposed in or on the housing, the camera having a field of view that includes an object, the camera defining a camera longitudinal axis that extends to a center of the field of view, the camera longitudinal axis being orthogonal to the plane;
a light-emitting diode (LED) array disposed in the housing and being substantially parallel to the plane, the LED array configured to emit light;
an illuminator lens configured to at least partially focus the emitted light to form an illumination field and direct the illumination field toward the object, the illuminator defining an illuminator longitudinal axis that extends from a center of the LED array through a center of the lens, the illuminator longitudinal axis being orthogonal to the plane and laterally offset from the camera longitudinal axis;
a controller configured to:
determine a lateral offset that depends on a measured distance to the object; and
cause the LED array to be powered in a specified pattern, the specified pattern being laterally offset on the LED array by the determined lateral offset to at least partially compensate for parallax error caused by the lateral offset between the illuminator longitudinal axis and the camera longitudinal axis.
19. The imaging system of claim 18 , further comprising:
a distance sensor configured to measure a time of flight between the distance sensor and the object to determine the measured distance to the object.
20. The imaging system of claim 18 , wherein the camera includes an auto-focus mechanism that is configured to determine the measured distance to the object.