Shading calibration for radial sensor lenses
In various examples, systems and methods for calibration for sensor lens shading using non-radial correction of residual radial shading error are provided. In some embodiments, a calibration flow includes computation of calibration parameters corresponding to radial lens shading correction, and computation of calibration parameters corresponding to non-radial lens shading correction. A lens shading profile may be computed that defines a gain mapping of lens shading effect appearing in an image frame of calibration sensor data. Parameters for radial lens shading correction may be computed from the lens shading profile, and parameters for non-radial lens shading correction may be computed based a residual shading profile generated from the radial lens shading correction. Calibration parameters for radial and non-radial lens shading correction may be used to calibrate sensor data captured by an image sensor module to correct for lens shading.
1. A system comprising:
one or more processing units to:
determine a lens shading profile using calibration image sensor data;
determine one or more first parameters for a first lens shading correction based at least on the lens shading profile;
remove a symmetrical component of a lens shading effect based at least on the one or more first parameters;
apply a second lens shading correction to a residual shading profile to produce a calibrated image frame;
compute one or more uniformity values according to at least one uniformity metric using the calibrated image frame; and
based at least on the one or more uniformity values, determine an adjustment to one or more of the one or more first parameters and one or more second parameters.
2. The system of claim 1 , the one or more processing units further to:
apply the first lens shading correction to the calibration image sensor data to produce the residual shading profile;
determine the one or more second parameters for a second lens shading correction based at least on the residual shading profile; and
remove a non-symmetrical component of the lens shading effect based at least on the one or more second parameters.
3. The system of claim 2 , the one or more processing units further to:
determine a patch array comprising a grid that includes a plurality of control points;
compute a slope corresponding to a rate of change of lens shading at pixels of the lens shading profile corresponding to the plurality of control points;
determine a surface fitting for the patch array based at least on the plurality of control points and the slope at the plurality of control points; and
determine the one or more second parameters for the second lens shading correction based at least on the surface fitting for the patch array.
4. The system of claim 3 , the one or more processing units further to:
compute a Bezier surface fitting for the patch array based at least on the plurality of control points and the slope at the plurality of control points.
5. The system of claim 1 , wherein the calibration image sensor data comprises a flat-field image.
6. The system of claim 1 , wherein the lens shading profile comprises one or more color channels.
7. The system of claim 1 , the one or more processing units further to:
generate the lens shading profile as a map of pixels corresponding to pixels of the calibration image sensor data, wherein one or more individual pixels of the map of pixels represent a gain of a lens shading affect occurring in a corresponding pixel of the calibration image sensor data.
8. The system of claim 1 , the one or more processing units further to:
determine a plurality of control points on a plurality of radial lines radiating from an optical center of the lens shading profile;
compute a slope corresponding to a rate of change of lens shading at pixels of the lens shading profile corresponding to the plurality of control points;
compute a curve fitting for the plurality of radial lines based at least on the plurality of control points and the slope at the plurality of control points; and
determine the one or more first parameters for the first lens shading correction based at least on the curve fitting for the plurality of radial lines.
9. The system of claim 8 , the one or more processing units further to:
compute the curve fitting for the plurality of radial lines using a cubic Hermite spline.
10. The system of claim 1 , the one or more processing units further to:
perform one or more operations based at least on the one or more first parameters or the one or more second parameters.
11. At least one processor comprising:
one or more processing units to:
determine one or more first parameters for a first lens shading correction based at least on a lens shading profile of a calibration image represented by sensor data;
determine one or more second parameters for a second lens shading correction based at least on a residual shading profile generated based on the first lens shading correction;
perform the first lens shading correction based at least on a plurality of control points on a plurality of radial lines radiating from an optical center of the lens shading profile;
determine a calibrated image frame corresponding to the calibration image based at least on applying the second lens shading correction to the residual shading profile;
compute one or more uniformity values for at least one uniformity metric using the calibrated image frame; and
based at least on the one or more uniformity values, determine an adjustment to one or more of the one or more first parameters and the one or more second parameters.
12. The at least one processor of claim 11 , the one or more processing units further to:
store a set of lens shading calibration parameters associated with a sensor used to capture the sensor data based at least on the one or more first parameters and the one or more second parameters.
13. The at least one processor of claim 11 , the one or more processing units further to:
determine a surface model to perform the second lens shading correction based at least on a plurality of control points on a rectangular patch array applied to the residual shading profile.
14. The at least one processor of claim 11 , the one or more processing units further to:
determine the one or more first parameters for one or more color channels of the lens shading profile; and
determine the one or more second parameters for one or more color channels of the residual shading profile.
15. A method comprising:
applying a radial lens shading correction to calibration image sensor data;
generating a residual shading profile based at least on the application of the radial lens shading correction to the calibration image sensor data;
applying a non-radial lens shading correction to the residual shading profile;
generating a set of lens shading calibration parameters associated with a sensor module based at least on the application of the non-radial lens shading correction to the residual shading profile; and
based at least on one or more uniformity values determined using the calibration image sensor data, determining an adjustment to one or more of the radial lens shading correction or the non-radial lens shading correction.