System and method for detecting and correcting defective pixels in an image sensor

An image signal processing circuit comprising:

• an interface configured to receive image data acquired using an image sensor of an imaging device;
• and
• an image processing pipeline configured to perform a set of processing operations on the image data, wherein one of the set of processing operations detects and corrects for defective pixels in the image data, and wherein the image processing pipeline comprises defective pixel detection and correction logic configured to:
• receive an input pixel of the image data;
• determine if the location of the input pixel corresponds to a location entry in a static defect table, identify the input pixel as being a static defect if the location of the input pixel is found in the static defect table, and determine a first replacement value for correcting the input pixel;
• if the input pixel is not identified as a static defect, determine if the input pixel is a dynamic defect, and determine a second replacement value for the input pixel if the input pixel is determined to be a dynamic defect, wherein the input pixel is determined to be a dynamic defect by:
• identifying eight neighboring pixels of the same color as the input pixel;
• calculating pixel-to-pixel gradients with respect to the input pixel for each of the eight neighboring pixels located within a processing region defined within an imaging frame of the image sensor;
• determining a count of the number of the pixel-to-pixel gradients which are less than a dynamic defect threshold value, wherein the dynamic defect threshold value is adjustable based upon a high frequency component of the eight neighboring pixels located within the processing region;
• and
• identifying the input pixel as a dynamic defect if the determined count is less than a maximum count value;
• and
• correct the input pixel using either the first or second replacement value based upon whether the input pixel is determined to be a static defect, or a dynamic defect.

A system, comprising:

• an imaging device comprising an image sensor;
• and
• image processing circuitry configured to process image data acquired using the image sensor, wherein the image processing circuitry comprises:
• defective pixel detection and correction logic configured to:
• determine, for a current image frame of the image data, if the location of an input pixel corresponds to a location entry in a static defect table, identify the input pixel as being a static defect if the location of the input pixel is found in the static defect table, and correct the input pixel using a static defect replacement value;
• and
• if the input pixel is not identified as a static defect, determine if the input pixel is either a dynamic defect or speckled, and correct the input pixel using a non-static defect replacement value if the input pixel is determined to be a dynamic defect or speckled;
• and
• a memory device configured to store the static defect table and the static defect replacement value, wherein the static defect table is configured to be updated intermittently during image processing to store locations corresponding to newly-detected static defects.

One or more non-transitory tangible computer-readable storage media having instructions encoded thereon for execution by a processor, the instructions comprising:

• code to determine if an input pixel in a current frame of image data acquired by an image sensor corresponds to a location entry in a static defect table, and to identify the input pixel as a static defect if the location of the input pixel is found in the static defect table, wherein each location entry in the static defect table is associated with a minimum gradient value;
• code to correct the input pixel using a static defect replacement value determined as the value of a previous pixel of the same color in scanning order;
• code to, if the input pixel is not identified as a static defect, determine whether the input pixel is a dynamic defect by identifying eight neighboring pixels of the same color as the input pixel, calculating pixel-to-pixel gradients with respect to the input pixel for each of the eight neighboring pixels located within a processing region defined within an imaging frame of the image sensor, determining a count of the number of the gradients which are less than a dynamic defect threshold value, and identifying the input pixel as a dynamic defect if the determined count is less than a maximum count value;
• code to calculate a dynamic defect replacement value by calculating directional gradients as the sum of the difference between the input pixel and two neighboring pixels of the eight neighboring pixels in each of a horizontal direction, a vertical direction, an upper-right direction, and an upper-left direction, determining the direction corresponding to the minimum gradient, and interpolating the values of the two neighboring pixels associated with the minimum gradient direction;
• code to correct the input pixel using the dynamic defect replacement value;
• code to determine if the input pixel was identified as a dynamic defect for a particular number of consecutive frames preceding the current frame and, if the input pixel was identified as a dynamic defect for the particular number of consecutive frames, determine a minimum value of the pixel-to-pixel gradients for each of the eight neighboring pixels located within the processing region, and store the location of the input pixel and the minimum gradient value into the static defect table.

An image signal processing circuit comprising:

• an interface configured to receive image data acquired using an image sensor of an imaging device;
• and
• an image processing pipeline configured to perform a set of processing operations on the image data, wherein one of the set of processing operations detects and corrects for defective pixels in the image data, and wherein the image processing pipeline comprises defective pixel detection and correction logic configured to:
• receive an input pixel of the image data;
• determine if the location of the input pixel corresponds to a location entry in a static defect table, identify the input pixel as being a static defect if the location of the input pixel is found in the static defect table, and determine a first replacement value for correcting the input pixel;
• if the input pixel is not identified as a static defect, determine if the input pixel is a speckled and determine a second replacement value for the input pixel if the input pixel is determined to be speckled, wherein the input pixel is determined to be speckled by:
• identifying eight neighboring pixels of the same color as the input pixel;
• calculating pixel-to-pixel gradients with respect to the input pixel for each of the eight neighboring pixels located within a processing region defined within an imaging frame of the image sensor;
• calculating an average gradient value as the difference between the value of the input pixel and an average of the values of the eight neighboring pixels within the processing region;
• and
• identifying the input pixel as being speckled if the average gradient value is greater than a speckle threshold value, wherein the speckle threshold value is adjustable based upon a high frequency component of the eight neighboring pixels located within the processing region;
• and
• correct the input pixel using either the first or second replacement value based upon whether the input pixel is determined to be a static defect or speckled.