Defective pixel filtering for digital imagers

A method for detecting a defective pixel based upon the luminance values generated by the pixel element and its two nearest neighbors comprising:

• determining a first difference value between the luminance value of the pixel and the luminance value of a first neighboring pixel;
• comparing the first difference value to a pre-determined threshold value;
• determining a second difference value between the luminance of the pixel and the luminance value of a second neighboring pixel;
• comparing the second difference value to the pre-determined threshold value;
• detecting whether the luminance value for the pixel falls within an acceptable range defined by the luminance value for the first neighboring pixel and the luminance value for the second neighboring pixel;
• and
• identifying the pixel element as defective if the luminance value for the pixel element does not fall within the acceptable range and neither the first difference value nor the second difference value is less than or equal to the threshold value.

A defective pixel filter comprising:

• a first comparator circuit receiving as input a first pixel value and a second pixel value and outputting a valid logic signal to a first input of an AND circuit and to a first inverter when the first pixel value is greater than the second pixel value;
• a first difference calculator receiving as input said first pixel value and said second pixel value and outputting to a first input of a second comparator circuit a first difference value corresponding to the difference between said first and second pixel values;
• said second comparator circuit also receiving as input a threshold value and outputting a valid logic signal to a first input of an OR circuit when the first difference value is less than or equal to said threshold value;
• a third comparator circuit receiving as input said second pixel value and a third pixel value and outputting a valid logic signal to a second input of said first AND circuit and to a second inverter when the second pixel value is greater than the third pixel value;
• and
• a second difference calculator receiving as input said second pixel value and said third pixel value and outputting a second difference value corresponding to the difference between said second and third pixel values to a first input of a fourth comparator circuit;
• said fourth comparator circuit also receiving as input a threshold value and outputting a valid logic signal to a third input of said OR circuit when the second difference value is less than or equal to said threshold value;
• and
• a second AND circuit coupled to said first and second inverters and having an output coupled to a fourth input of said OR circuit.

A digital imager comprising:

• a lens mechanism;
• a sensor array positioned within a focal plane of said lens mechanism;
• an analog buffer and amplifier coupled to an output of said sensor array;
• and
• imaging logic coupled to said amplifier;
• wherein said imaging logic includes a defective pixel filter comprising:
• means for detecting whether a first pixel is outside an acceptable range defined by luminance values of first and second neighboring pixels;
• means for determining whether said first pixel deviates from said first neighboring pixel by greater than a threshold value and means for determining whether said first pixel deviates from said second neighboring pixel by greater than a threshold value;
• means for calculating a corrected pixel value;
• and
• means for substituting said corrected pixel value for said first pixel if said first pixel is outside said acceptable range and said first pixel deviates from said first neighboring pixel by greater than a threshold value and said first pixel deviates from said second neighboring pixel by greater than a threshold value.