Method for dynamically calibrating an image capture device
View Patent ↗A method for dynamically calibrating an image capture device comprises: a) determining a distance (D CRT , D EST ) to an object within a scene; b) determining a first lens actuator setting (DAC INIT ) for the determined distance; c) determining a second lens actuator setting (DAC FOCUS ) providing maximum sharpness for the object in a captured image of the scene; and d) storing the determined distance (D CRT , D EST ) and the first and second lens actuator settings. These steps are repeated at a second determined distance separated from the first determined distance. A calibration correction (ERR NEAR PLP , ERR FAR PLP ) for stored calibrated lens actuator settings (DAC NEAR PLP , DAC FAR PLP ) is determined as a function of at least: respective differences between the second lens actuator setting (DAC FOCUS ) and the first lens actuator setting (DAC INIT ) for each of the first and second determined distances; and the stored calibrated lens actuator settings are adjusted according to the determined calibration corrections.
1. A method for calibrating an image capture device comprising:
a) determining a first lens actuator setting for a first determined distance to an object in a scene to be imaged by an image capture device;
b) determining a second lens actuator setting providing a greater sharpness than the first lens actuator setting;
repeating a) and b) at a second determined distance different than the first determined distance;
determining a calibration correction to obtain a determined calibration correction based at least in part on:
a difference between the first lens actuator setting and the second lens actuator setting for the first determined distance; and
a difference between the first lens actuator setting and the second lens actuator setting for the second determined distance; and
adjusting a stored calibrated lens actuator setting based at least on the determined calibration correction.
2. The method of claim 1 , wherein determining the first lens actuator setting comprises determining the first lens actuator setting as a function of a first calibrated lens actuator setting for a pre-determined near focus distance, a second calibrated lens actuator setting for a pre-determined far focus distance, a focal length of the image capture device, and the first determined distance.
3. The method of claim 2 , further comprising, determining the calibration correction for at least one of the first calibrated lens actuator setting or the second calibrated lens actuator setting as a function of at least one of:
a difference between the first determined distance and the second determined distance and one of the pre-determined near or far focus distances;
a difference between the pre-determined near focus distance and the pre-determined far focus distance; and
a difference between the first determined distance and the second determined distance, and the focal length.
4. The method of claim 1 , further comprising storing the first determined distance, the first lens actuator setting and the second lens actuator setting in memory of the image capture device.
5. The method of claim 1 , further comprising, prior to determining the first lens actuator setting:
adjusting the stored calibrated lens actuator setting as a function of at least one of an operating temperature of the image capture device, or a function of an operating orientation of the image capture device; and
storing the at least one of the operating temperature, or the operating orientation of the image capture device with the first determined distance, the second determined distance, the first lens actuator setting, and the second lens actuator setting in memory of the image capture device.
6. The method of claim 1 , wherein determining the second lens actuator setting comprises beginning a search for a focus position using the first lens actuator setting.
7. The method of claim 1 , further comprising calibrating a camera module of the image capture device based on a linear relationship between the first lens actuator setting or the second lens actuator setting and a lens position that focuses at a given distance.
8. The method of claim 1 , wherein determining the first determined distance and the second determined distance to the object comprises:
estimating a distance to the object to obtain an estimated distance based on an imaged size of the object and an assumed dimension of the object; and
testing whether a potential correction resulting from the estimated distance exceeds a threshold value before at least one of:
storing the first determined distance, the first lens actuator setting, and the second lens actuator setting in memory of the image capture device; or
determining the calibration correction,
wherein the threshold value is a function of an absolute difference between a respective one of the first lens actuator setting or the second lens actuator setting at a far limit of focus and a near limit of focus at a given focus distance.
9. A non-transitory computer readable medium comprising:
computer readable instructions embodied therewith, the computer readable instructions to, when executed by a processor:
a) determine a first lens actuator setting for a first determined distance to an object in a scene to be imaged by an image capture device;
b) determine a second lens actuator setting providing a greater sharpness than the first lens actuator setting;
repeat a) and b) at a second determined distance different than from the first determined distance; and
determine a calibration correction based at least in part on:
a difference between the first lens actuator setting and the second lens actuator setting for the first determined distance; and
a difference between the first lens actuator setting and the second lens actuator setting for the second determined distance.
10. The non-transitory computer readable medium of claim 9 , wherein:
determining the first lens actuator setting comprises determining the first lens actuator setting as a function of a stored calibrated lens actuator setting for a pre-determined near focus distance, a stored calibrated lens actuator setting for a pre-determined far focus distance, a focal length of the image capture device, and the first determined distance; and
determining the second lens actuator setting comprises determining the second lens actuator setting providing a greater sharpness than the first lens actuator setting for the object in a captured image of the scene.
11. The non-transitory computer readable medium of claim 9 , wherein determining the first lens actuator setting is based on the following formula:
DAC
INIT
=
DAC
FAR
PLP
+
(
DAC
NEAR
PLP
-
DAC
FAR
PLP
)
*
(
D
FAR
-
D
CRT
,
EST
)
(
D
FAR
-
D
NEAR
)
*
(
D
NEAR
-
f
)
(
D
CRT
,
EST
-
f
)
where
DAC FAR PLP is a second calibrated lens actuator setting for a pre-determined far focus distance;
DAC NEAR PLP is a first calibrated lens actuator setting for a pre-determined near focus distance;
D FAR is a far focus distance;
D NEAR is a near focus distance;
D CRT,EST is the first determined distance; and
f is a focal length.
12. The non-transitory computer readable medium of claim 9 , wherein the calibration correction for calibrated lens actuator settings, ERR FAR PLP and ERR NEAR PLP , is calculated based on the following formulae:
{
ERR
FAR
PLP
=
∝
D
2
*
ERR
D
1
-
∝
D
1
*
ERR
D
2
∝
D
2
-
∝
D
1
ERR
NEAR
PLP
=
(
1
-
∝
D
2
)
*
ERR
D
1
-
(
1
-
∝
D
1
)
*
ERR
D
2
∝
D
1
-
∝
D
2
where D 1 and D 2 , are the first and second determined distances respectively, ERR D 1 and ERR D 2 are computed using the following formulae:
ERR D 1 =DAC D 1 FOCUS −DAC D 1 INIT [26]
ERR D 2 =DAC D 2 FOCUS −DAC D 2 INIT [26]
and ∝ D 1 and ∝ D 2 are computed using the following formulae:
{
∝
D
1
=
(
D
FAR
-
D
1
)
(
D
FAR
-
D
NEAR
)
*
(
D
NEAR
-
f
)
(
D
1
-
f
)
∝
D
2
=
(
D
FAR
-
D
2
)
(
D
FAR
-
D
NEAR
)
*
(
D
NEAR
-
f
)
(
D
2
-
f
)
.
13. The non-transitory computer readable medium of claim 9 , further comprising adjusting stored calibrated lens actuator settings comprises providing new settings DAC FAR NEW and DAC NEAR NEW based on the formulae:
{
DAC
FAR
NEW
=
DAC
FAR
PLP
+
ERR
FAR
PLP
DAC
NEAR
NEW
=
DAC
NEAR
PLP
+
ERR
NEAR
PLP
.
14. An image capture device comprising:
a lens actuator mechanically coupled a lens to adjust a position of the lens;
a digital-to-analog converter (DAC) electrically coupled to the lens actuator to drive the lens actuator; and
an auto-focus (AF) module electrically coupled to the DAC and the lens actuator to determine a DAC code, the DAC to convert the DAC code into an equivalent analog signal to drive the lens actuator, wherein the AF module:
a) determines a first lens actuator setting as a function of: a stored calibrated lens actuator setting for a pre-determined near focus distance, a stored calibrated lens actuator setting for a pre-determined far focus distance, a focal length of the image capture device, and a first determined distance;
b) determines a second lens actuator setting providing maximum sharpness for an object in a captured image of a scene;
repeats a) and b) at a second determined distance different than the first determined distance; and
determines a calibration correction for a calibrated lens actuator setting to obtain a determined calibration correction as a function of:
a difference between the first lens actuator setting and the second lens actuator setting for the first determined distance; and
a difference between the first lens actuator setting and the second lens actuator setting for the second determined distance; and
adjusts a stored calibrated lens actuator setting based on the determined calibration correction.
15. The image capture device of claim 14 , further comprising a laser device or a stereo camera system to determine the first determined distance and the second determined distance.
16. The image capture device of claim 14 , wherein the first determined distance and the second determined distance are different than one another by depths of field at the first determined distance and the second determined distance.
17. The image capture device of claim 14 , wherein adjusting the stored calibrated lens actuator setting comprises adjusting the stored calibrated lens actuator setting as a function of at least one of an operating temperature of the image capture device, or a function of an operating orientation of the image capture device.
18. The image capture device of claim 17 , further comprising non-volatile memory to store at least one of the first lens actuator setting, the second lens actuator setting, the first determined distance, the second determined distance, the calibration correction, the a pre-determined near focus distance, the pre-determined far focus distance, the focal length, the operating temperature, the operating orientation of the image capture device or the stored calibrated lens actuator setting.
19. The image capture device of claim 17 , wherein the AF module:
estimates a distance to the object to obtain and estimated distance based on an imaged size of the object and an assumed dimension of the object; and
tests whether a potential correction resulting from the estimated distance exceeds a threshold value before at least one of:
storing the first determined distance, the first lens actuator setting, and the second lens actuator setting in memory of the image capture device; or
determining the calibration correction,
wherein the threshold value is a function of an absolute difference between a respective one of the first lens actuator setting or the second lens actuator setting at a far limit of focus and a near limit of focus at a given focus distance.
20. The image capture device of claim 14 , wherein the AF module defines a linear relationship between the lens actuator and a position of the lens to focus at a given distance.