Fixed pattern noise compensation method and apparatus
First Claim
1. A method for configuring an imaging system in a setup mode of operation so that in a run mode of operation said imaging system compensates image signals generated by said imaging system for fixed pattern noise, said imaging system having an image sensor including a monochrome two dimensional pixel array and being configured to run a bar code decoding application, said method comprising the steps of:
- exposing said pixel array to a scene having a known radiance;
capturing a predetermined number of image signal frames of said known radiance scene and finding a column white value for each column of said pixel array when said each frame is captured, wherein said finding step includes the step of discarding a predetermined number of pixel values in at least one column based on gray scale values of said pixel values;
averaging said column white values to determine an average column white value for each column of said pixel array;
comparing said each average column white value to a predetermined reference value for each column, and therefrom determining a correction value for each column of said array; and
storing said each correction value into a storage location for retrieval by said imaging system when said imaging system processes image signals from said image sensor in said run mode of operation.
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Abstract
The invention relates to a method and apparatus for configuring an imaging system to compensate for fixed pattern noise, variations in pixel values captured from an image sensor that vary according to a fixed pattern. In a method for configuring an imaging system for compensating an additive term component of fixed pattern noise, a pixel array is exposed to a scene of known radiance and an average white value is determined for each pixel of an array. Each average white value is compared to a predetermined reference value to determine a correction value for each pixel. In a method for configuring an imaging system for compensating both an additive and multiplicative component of fixed pattern noise, a pixel array is exposed to a first scene having a first known radiance, and frames of the scene are captured, and then the array is exposed to a second scene having a second known radiance and frames of the second scene are captured. After first and second average white values are determined for each pixel additive and multiplicative term correction values for each pixel are then determined by solving for a system of equations relating the first and second average white values and first and second scene radiances. Correction values can be utilized to correct pixel values of a frame of image data, and a decoding algorithm for attempting to decode a frame of image data including corrected pixel values can be activated.
115 Citations
13 Claims
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1. A method for configuring an imaging system in a setup mode of operation so that in a run mode of operation said imaging system compensates image signals generated by said imaging system for fixed pattern noise, said imaging system having an image sensor including a monochrome two dimensional pixel array and being configured to run a bar code decoding application, said method comprising the steps of:
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exposing said pixel array to a scene having a known radiance; capturing a predetermined number of image signal frames of said known radiance scene and finding a column white value for each column of said pixel array when said each frame is captured, wherein said finding step includes the step of discarding a predetermined number of pixel values in at least one column based on gray scale values of said pixel values; averaging said column white values to determine an average column white value for each column of said pixel array; comparing said each average column white value to a predetermined reference value for each column, and therefrom determining a correction value for each column of said array; and storing said each correction value into a storage location for retrieval by said imaging system when said imaging system processes image signals from said image sensor in said run mode of operation. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for operating an imaging system, said imaging system having an image sensor including a two dimensional pixel array, said method comprising the steps of:
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determining a plurality of correction values, wherein said determining a plurality of correction values includes determining a correction value for each of a plurality of pixels of said two dimensional pixel array; storing said correction values in a first predetermined memory location; in a run mode of operation, capturing a frame of image data into a second predetermined memory; and correcting a plurality of pixel values of said frame using said correction values stored in said first memory location; and executing a bar code decoding algorithm for attempting to decode for decodable bar code indicia, wherein said executing step includes the step of utilizing said frame of image data having said plurality of pixel values that have been corrected utilizing said correction values. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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Specification