Methods and systems for anti shading correction in image sensors

An image processing system for dynamically correcting shading effects in pixel outputs in the image sensor based upon radial pixel location performed prior to demosaicing processing, comprising:

• an image sensor, wherein the image sensor comprises at least a pixel array, an array of micro-lenses, and an array of color filters, and wherein
• the image sensor is optically coupled to a lens;
• the array of color filters comprises at least a plurality of first color filters, a plurality of second color filters and a plurality of third color filters;
• the plurality of first color filters, the plurality of second color filters and the plurality of third color filters are arranged in a mosaic pattern;
• and
• each pixel in the pixel array is associated with a one of the color filters;
• means for scanning an analog output from a pixel on the pixel array, wherein the image scanning means is configured to obtain outputs from each pixel in the pixel array;
• means for converting the analog output from the scanned pixel to a digital output;
• means for processing a radial location for the scanned pixel, wherein the radial location is determined relative to a reference location on the pixel array;
• means for calculating a correction factor for the shading effect for the scanned pixel, wherein
• the calculating means calculates the correction factor by applying the radial location to a correction function;
• and
• the correction function is a function of an elliptical-type equation that varies radially;
• and means for correcting the digital output with the correction factor, wherein
• the radial location is described in two-dimensional cartesian coordinates comprising an x-coordinate measured on an x-axis from the reference location and a y-coordinate measured on a y-axis from the reference location,
• the correction function comprises a function of a square root of a square of the x-coordinate summed with a square of the y-coordinate multiplied by a multiplication factor,
• the multiplication factor is calculated from at least a first and a second constant, and
• the first and the second constants are dependent upon wavelength transmissibility of the color filter associated with the scanned pixel and dimensions of the pixel array.

A system for digitally correcting shading effects at a Bayer domain in an image sensor using radial pixel location, comprising:

• a lens;
• a CMOS image sensor optically coupled to the lens, wherein the CMOS image sensor comprises at least,
• an array of color filters positioned underneath the lens, wherein the array of color filters comprises a plurality of red filters, a plurality of blue filters and a plurality of green filters arranged in a Bayer pattern, and
• a pixel array comprising a plurality of pixels positioned beneath the color filters and configured to receive light that passes through the lens and the array of color filters;
• a control unit in communication with the pixel array and configured to select an analog output from a pixel in the pixel array, wherein
• the control unit is configured to scan outputs from each of the plurality of pixels, and
• the pixel is associated with a one of the color filters;
• an analog to digital converter configured to receive the analog output from the selected pixel and to convert the analog output to a digital output;
• a processor in communication with the analog to digital converter and configured to receive the digital output and to correct the digital output for the shading effects, wherein
• the processor is configured to process a relative radial location of the pixel on the pixel array relative to a reference point on the pixel array,
• the processor is configured to calculate a shading correction factor for the pixel by applying a correction function to the relative radial location,
• the correction function is a function of a one of a circular-type equation that varies radially and an elliptical-type equation that varies radially and the correction function including a multiplication factor, the multiplication factor being calculated from at least a first and a second constant, the first and second constants being dependent upon wavelength transmissibility of the color filter associated with the scanned pixel and dimensions of the pixel array, and
• the processor is configured to calculate a corrected digital output by applying the shading correction factor to the digital output.

A method for digitally correcting shading effects at a Bayer domain in a CMOS image sensor using radial pixel location, comprising:

• providing a lens;
• providing said CMOS image sensor, wherein said CMOS image sensor is optically coupled to said lens and comprises at least,
• an array of color filters located underneath the lens, wherein the array of color filters comprises at least a plurality of first color filters, a plurality of second color filters and a plurality of third color filters and wherein the plurality of the first color filters, the plurality of the second color filters and the plurality of the third color filters are arranged in a mosaic pattern, and
• an array of photo-sensitive elements located underneath the array of color filters and configured to receive light passing through the lens and the array of color filters, wherein the array of photo-sensitive elements comprises at least a plurality of first photo-sensitive elements each associated with each of said first color filters, a plurality of second photo-sensitive elements each associated with each of said second color filters and a plurality of third photo-sensitive elements each associated with each of said third color filters;
• identifying a center point of the array of the photo-sensitive elements;
• determining first radial locations for each of the plurality of the first photo-sensitive elements relative to the center point;
• calculating first correction factors for each of the plurality of the first photo-sensitive elements, wherein the first correction factors are based on a multiplication factor and are calculated from the first radial locations, the multiplication factor being calculated from at least a first and a second constant, the first and second constants being dependent upon wavelength transmissibility of the first color filter associated with the photo-sensitive element and dimensions of the array of photo-sensitive elements;
• and
• using the first correction factors to correct digitally converted outputs from each of the plurality of the first photo-sensitive elements at the Bayer domain.

A method for dynamically correcting shading effects in a CMOS image sensor using radial pixel location performed prior to demosaicing processing, comprising:

• providing said CMOS image sensor, wherein said CMOS image sensor is optically coupled to a lens and comprises at least
• an array of color filters located underneath the lens, wherein the array of color filters comprises at least a plurality of first color filters, a plurality of second color filters and a plurality of third color filters and wherein the plurality of the first color filters, the plurality of the second color filters and the plurality of the third color filters are arranged in a mosaic pattern, and
• an array of photo-sensitive elements located underneath the array of color filters and configured to receive light passing through the lens and the array of color filters, wherein the array of photo-sensitive elements comprises at least a plurality of first photo-sensitive elements each associated with each of said first color filters, a plurality of second photo-sensitive elements each associated with each of said second color filters and a plurality of third photo-sensitive elements each associated with each of said third color filters;
• identifying a reference location on the array of photo-sensitive elements;
• using a first processor to calculate initial values for the reference location, wherein
• the initial values are calculated from components of a radial correction function using location information of the reference location, and
• the radial correction function is a function of one of a circular-type equation and an elliptical-type equation, the radial correction function including a multiplication factor, the multiplication factor being calculated from at least a first and a second constant, the first and second constants being dependent upon wavelength transmissibility of the color filter associated with a scanned photo-sensitive element and dimensions of the array of photo-sensitive elements;
• storing the initial values in a memory;
• scanning from the reference location across the array of the photo-sensitive elements to a first photo-sensitive element and retrieving first location information and a first digitally converted output from the first photo-sensitive element, wherein
• the first digitally converted output corresponds to illumination incident upon the first photo-sensitive element, and
• the first location information identifies a first location of the first photo-sensitive element relative to the reference location;
• using a second processor to iteratively calculate a first correction factor for the first photo-sensitive element from the radial correction function, wherein the iterative calculation is calculated from the initial values and the first location information;
• and
• using the first correction factors to digitally correct the first digitally converted output.