Image sensor defect identification using blurring techniques
View Patent ↗Embodiments described herein may operate to image a scene with an imaging system using an image blurring technique. An image sensor array (ISA) element may be identified as a dark defect element if a first ratio of an average of a set of illuminance signal magnitudes from a set of surrounding ISA elements to a magnitude of an illuminance signal from the ISA element is greater than a threshold sharpness value. The image sensor array element may be identified as a bright defect element if a second ratio of the magnitude of the illuminance signal from the ISA element to the average of the set of illuminance signal magnitudes from the set of surrounding ISA elements is greater than the threshold sharpness value.
1. A system comprising:
a calibration imaging system to capture a plurality of blurred calibration images of a calibration scene, wherein at least one known unusable calibration image sensor array (ISA) element is present at a known location in a calibration ISA associated with the calibration imaging system;
a calibration defect detector operatively coupled to the calibration ISA to identify a calibration ISA element as a candidate unusable element if a calibration contrast ratio calculated from an illuminance indicated by the calibration ISA element and an average illuminance indicated by a set of surrounding calibration ISA elements is greater than a calibration threshold contrast value, and the average illuminance indicated by the set of surrounding ISA elements is greater than a calibration threshold illuminance value;
a threshold selector coupled to the calibration defect detector to select a combination of the calibration threshold illuminance value and the calibration threshold contrast value such that the at least one known unusable calibration ISA element is reliably identified as unusable and no other calibration ISA elements are identified as unusable;
an illuminance controller coupled to the calibration defect detector to iteratively vary an illuminance associated with the calibration scene as ones of the plurality of blurred calibration images are captured;
a threshold illuminance iterator coupled to the threshold selector to iteratively vary the calibration threshold illuminance value across a dynamic range of the calibration ISA for each iteration of the average illuminance associated with the calibration scene as the ones of the plurality of blurred calibration images are captured; and
a threshold sharpness iterator coupled to the threshold selector to vary the calibration threshold contrast value across the dynamic range of the calibration ISA for each iteration of the calibration threshold illuminance value as the ones of the plurality of blurred calibration images are captured.
2. The system of claim 1 , further comprising:
a microcontroller unit (MCU) coupled to the calibration imaging system to perform system management and control operations, wherein the MCU comprises at least one of an application-specific integrated circuit or a digital signal processor.
3. The system of claim 1 , further comprising:
a scene illuminance comparator coupled to the threshold illuminance iterator to determine whether the average illuminance indicated by the set of surrounding calibration ISA elements is greater than the calibration threshold illuminance value.
4. The system of claim 1 , further comprising:
a sharpness comparator coupled to the threshold sharpness iterator to calculate the calibration contrast ratio as the greater of the illuminance indicated by the calibration ISA element to the average illuminance indicated by the set of surrounding calibration ISA elements and the average illuminance indicated by the set of surrounding calibration ISA elements to the illuminance indicated by the calibration ISA element, and to determine whether the calibration contrast ratio is greater than the calibration threshold contrast value.
5. The system of claim 1 , wherein the calibration imaging system comprises a calibration digital camera.
6. The system of claim 1 , further comprising a digital camera coupled to the calibration imaging system.
7. A method comprising:
capturing a plurality of blurred calibration images of a calibration scene, wherein at least one known unusable calibration image sensor array (ISA) element is present at a known location in a calibration ISA associated with the calibration imaging system;
identifying a calibration ISA element as a candidate unusable element if a calibration contrast ratio calculated from an illuminance indicated by the calibration ISA element and an average illuminance indicated by a set of surrounding calibration ISA elements is greater than a calibration threshold contrast value, and the average illuminance indicated by the set of surrounding ISA elements is greater than a calibration threshold illuminance value;
selecting a combination of the calibration threshold illuminance value and the calibration threshold contrast value such that the at least one known unusable calibration ISA element is reliably identified as unusable and no other calibration ISA elements are identified as unusable;
iteratively varying an illuminance associated with the calibration scene as ones of the plurality of blurred calibration images are captured;
iterating a calibration threshold illuminance variable for each iteration of the average calibration illuminance associated with the calibration scene; and
iterating a calibration threshold sharpness variable for each iteration of the calibration threshold illuminance variable.
8. The method of claim 7 , wherein iteratively varying an illuminance associated with the calibration scene includes iteratively varying an average calibration illuminance associated with the calibration scene.
9. The method of claim 7 , further comprising:
performing a calibration sharpness test on each calibration ISA element in the calibration ISA associated with the calibration imaging system for each iteration of the calibration threshold sharpness variable.
10. The method of claim 9 , further comprising:
flagging values of the calibration threshold illuminance variable as candidate threshold illuminance values and flagging values of the calibration threshold sharpness variable as candidate threshold sharpness values if the calibration sharpness test performed on the each calibration ISA element in the calibration ISA identifies the each calibration ISA element as defective and not as mis-identified.
11. The method of claim 10 , further comprising:
selecting a smallest candidate threshold illuminance value as the threshold illuminance value.
12. The method of claim 11 , further comprising:
selecting a smallest candidate threshold sharpness value as the threshold sharpness value.
13. The method of claim 9 , wherein the calibration sharpness test comprises:
calculating a calibration ISA element sharpness ratio;
comparing the calibration ISA element sharpness ratio to the calibration threshold sharpness variable,
comparing the average illuminance associated with the calibration scene to the calibration threshold illuminance variable.
14. The method of claim 13 , further comprising:
identifying the each calibration ISA element in the calibration ISA as defective if the calibration ISA element sharpness ratio is greater than the calibration threshold sharpness variable, if the average illuminance associated with the calibration scene is greater than the calibration threshold illuminance variable, and if the each calibration ISA element in the calibration ISA is the at least one known unusable calibration ISA element.
15. The method of claim 13 , further comprising:
identifying the each calibration ISA element as mis-identified if the calibration ISA element sharpness ratio is greater than the calibration threshold sharpness variable, if the average illuminance associated with the calibration scene is greater than the calibration threshold illuminance variable, and if the each calibration ISA element is not the at least one known unusable calibration ISA element.
16. The method of claim 7 , wherein an iteration range of at least one of the average illuminance associated with the calibration scene, the calibration threshold illuminance variable, or the calibration threshold sharpness variable corresponds to a dynamic range of the calibration ISA.