Image sensor defect identification using blurring techniques

Abstract

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 . An apparatus, including:
 a defect detector to identify an image sensor array (ISA) element in a imaging system as unusable if, in a blurred image of a scene captured by the imaging system, a contrast ratio between an illuminance indicated by the ISA element and an average illuminance indicated by a set of surrounding ISA elements is greater than a threshold contrast value and if the average illuminance indicated by the set of surrounding ISA elements is greater than a threshold illuminance value; and   a defect location memory coupled to the defect detector to store a location of the ISA element relative to a matrix associated with the ISA if the ISA element is identified as unusable.   
   
   
       2 . The apparatus of  claim 1 , wherein the illuminance indicated by the ISA element corresponds to a magnitude of an illuminance signal from the ISA element and wherein the illuminance indicated by the set of surrounding ISA elements corresponds to an average of a set of illuminance signal magnitudes from the set of surrounding ISA elements. 
   
   
       3 . The apparatus of  claim 2 , further including:
 a sharpness comparator coupled to the defect detector to calculate a contrast ratio associated with the magnitude of the illuminance signal from the ISA element and with the average of the set of illuminance signal magnitudes from the set of surrounding ISA elements and to compare the resulting contrast ratio to the threshold contrast value.   
   
   
       4 . The apparatus of  claim 3 , wherein the contrast ratio comprises a first ratio of the average of the set of illuminance signal magnitudes from the set of surrounding ISA elements to the magnitude of the illuminance signal from the ISA element if the first ratio yields a quotient of greater than or equal to one. 
   
   
       5 . The apparatus of  claim 3 , wherein the contrast ratio comprises 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 if the second ratio yields a quotient greater than one. 
   
   
       6 . The apparatus of  claim 3 , further including:
 a threshold sharpness memory coupled to the sharpness comparator to store a threshold sharpness value derived by a calibration imaging system.   
   
   
       7 . The apparatus of  claim 2 , further including:
 a scene illuminance comparator coupled to the defect detector to compare an illuminance corresponding to the average of the set of illuminance signal magnitudes from the set of surrounding ISA elements to a threshold illuminance value.   
   
   
       8 . The apparatus of  claim 7 , further including:
 a threshold illuminance memory coupled to the scene illuminance comparator to store a threshold illuminance value derived by a calibration imaging system.   
   
   
       9 . The apparatus of  claim 1 , wherein an unusable ISA element comprises at least one of a defective ISA element or an occluded ISA element. 
   
   
       10 . The apparatus of  claim 1 , wherein the imaging system comprises a digital camera. 
   
   
       11 . The apparatus of  claim 2 , further including:
 an analog-to-digital converter (ADC) coupled to the ISA to digitize the illuminance signal from the ISA element.   
   
   
       12 . The apparatus of  claim 11 , further including:
 a digital gain and black level adjustment module coupled to the ADC to perform a black level calibration on a digitized illuminance signal from the ISA element such that the digitized illuminance signal from the ISA element corresponds to a level of zero illuminance when no light is incident to the ISA element.   
   
   
       13 . The apparatus of  claim 10 , further including:
 a white point correction module coupled to the ADC to normalize a digitized illuminance signal from the ISA element by removing a color cast introduced by a non-white scene illumination.   
   
   
       14 . The apparatus of  claim 1 , further including:
 defect correction logic operatively coupled to the defect location memory to adjust a captured image to compensate for an effect of the unusable ISA element on the captured image.   
   
   
       15 . A system, including:
 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; and   a threshold selector coupled to the 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.   
   
   
       16 . The system of  claim 15 , wherein the calibration imaging system comprises a calibration digital camera. 
   
   
       17 . The system of  claim 15 , further including:
 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.   
   
   
       18 . The system of  claim 15 , further including:
 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.   
   
   
       19 . The system of  claim 18 , further including:
 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.   
   
   
       20 . The system of  claim 19 , further including:
 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.   
   
   
       21 . The system of  claim 19 , further including:
 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.   
   
   
       22 . The system of  claim 21 , further including:
 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.   
   
   
       23 . A method, including:
 imaging a scene with an imaging system using an image blurring technique;   identifying an image sensor array (ISA) element 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; and   identifying the ISA element 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.   
   
   
       24 . The method of  claim 23  further comprising:
 configuring the imaging system as a digital camera.   
   
   
       25 . The method of  claim 23 , wherein the image blurring technique comprises at least one of defocusing a lens, increasing an exposure integration time, or moving the imaging system relative to the scene while the scene is being captured by the imaging system. 
   
   
       26 . The method of  claim 23 , further including:
 measuring the magnitude of the illuminance signal from the ISA element;   measuring the set of illuminance signal magnitudes from the set of surrounding ISA elements; and   calculating the average of the set of illuminance signal magnitudes from the set of surrounding ISA elements, wherein the set of surrounding ISA elements surrounds the ISA element.   
   
   
       27 . The method of  claim 26 , further including:
 comparing a surrounding ISA element average illuminance value corresponding to the average of the set of illuminance signal magnitudes from the set of surrounding ISA elements to a threshold illuminance value;   discarding a defect identification if the surrounding ISA element average illuminance value is not greater than the threshold illuminance value; and   storing a record of an identified unusable ISA element in a defect memory if the surrounding ISA element average illuminance value is greater than the threshold illuminance value.   
   
   
       28 . The method of  claim 27 , further including:
 repeatedly imaging a calibration scene with a calibration imaging system using the image blurring technique, wherein at least one known unusable calibration ISA element is present at a known location in a calibration ISA associated with the calibration imaging system; and   determining a combination of the threshold illuminance value and the threshold sharpness value such that the at least one known unusable calibration ISA element is reliably detected.   
   
   
       29 . The method of  claim 28 , further including:
 classifying the at least one known unusable calibration ISA element as at least one of a calibration dark defect element or a calibration bright defect element.   
   
   
       30 . The method of  claim 28 , further including:
 iteratively varying an average calibration illuminance associated with the calibration scene as measured by the calibration imaging system;   for each iteration of the average calibration illuminance associated with the calibration scene, iterating a calibration threshold illuminance variable;   for each iteration of the calibration threshold illuminance variable, iterating a calibration threshold sharpness variable;   for each iteration of the calibration threshold sharpness variable, performing a calibration sharpness test on each calibration ISA element in the calibration ISA associated with the calibration imaging system; and   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;   selecting a smallest candidate threshold illuminance value as the threshold illuminance value; and   selecting a smallest candidate threshold sharpness value as the threshold sharpness value.   
   
   
       31 . The method of  claim 30 , 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. 
   
   
       32 . The method of  claim 30 , 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;   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; and   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.   
   
   
       33 . The method of  claim 32 , wherein the calibration ISA element sharpness ratio comprises a magnitude of a calibration illuminance signal from the each calibration ISA element in the calibration ISA divided by an average of a set of calibration illuminance signal magnitudes from a set of calibration ISA elements surrounding the each calibration ISA element if the resulting calibration ISA element sharpness ratio is greater than one. 
   
   
       34 . The method of  claim 32 , wherein the calibration ISA element sharpness ratio comprises the average of the set of illuminance signal magnitudes from the set of calibration ISA elements surrounding the each calibration ISA element in the calibration ISA divided by the magnitude of the illuminance signal from the each calibration ISA element if the resulting calibration ISA element sharpness ratio is at least one of greater than one or equal to one. 
   
   
       35 . The method of  claim 30 , further including:
 measuring the magnitude of the illuminance signal from the each calibration ISA element.   
   
   
       36 . The method of  claim 30 , further including:
 measuring a magnitude of an illuminance signal from each one of the set of calibration ISA elements surrounding the each calibration ISA element in the calibration ISA; and   calculating the average of the set of calibration illuminance signal magnitudes from the set of calibration ISA elements surrounding the each calibration ISA element in the calibration ISA.