Processing Data From A CCD And CCD Imaging Apparatus To Correct Smearing Artifacts

Abstract

A method of processing data from a CCD 1 having a line of light sensitive CCD elements is provided. The method comprises the steps of receiving measured illumination data readout from the CCD corresponding to measurements of charge associated with each element of the line of light sensitive CCD elements and removing from the measured illumination data in respect of each CCD element a component dependent upon illumination recorded by each of the other CCD elements through which the charge from the CCD element passed during the readout process.

1 . A method of processing data from a CCD having at least one line of light sensitive CCD elements, comprising the steps of:
 receiving measured illumination data readout from the CCD corresponding to a measurements of charge associated with each element of the line of light sensitive CCD elements; and   removing from the measured illumination data in respect of each CCD element a component dependent upon the illumination recorded by each of the other CCD elements through which the charge from the CCD element passed during the readout process   
     
     
         2 . The method according to  claim 1 , wherein the method further comprises the step of treating the illumination recorded for a lowest element, through which element charge is drawn from the line of CCD elements, as equal to a calculated illumination for the lowest CCD element. 
     
     
         3 . The method according to  claim 2 , wherein the method further comprises the steps of calculating, for each successive element starting with the second lowest CCD element, a calculated illumination by subtracting a component of the calculated illumination associated with each of the lower CCD elements. 
     
     
         4 . The method according to  claim 3 , wherein the method comprises the step of subtracting an offset from the measured data associated with the lowest CCD element before treating the resulting data for the lowest CCD element as equal to the calculated illumination for the lowest CCD element. 
     
     
         5 . The method according to  claim 1 , wherein the CCD comprises an array of CCD elements. 
     
     
         6 . The method according to  claim 5 , wherein the array of CCD elements forms a plurality of columns of which the line of CCD elements is one. 
     
     
         7 . The method according to  claim 1 , wherein the step of removing a component dependent upon the illumination recorded by other CCD elements comprises the step of treating the illumination data from the line of CCD elements as a vector and pre-multiplying the vector by a matrix. 
     
     
         8 . The method according to  claim 7 , wherein the matrix is an approximation of the inverse of a matrix operator that represents the measurement of illumination by the CCD. 
     
     
         9 . The method according to  claim 8 , wherein the approximation of the inverse of the matrix operator is obtained by inverting an approximation of the matrix operator. 
     
     
         10 . The method according to  claim 9  wherein the matrix operator is estimated based on knowledge of the exposure time of the CCD, the read-out time of the CCD and clearing patterns of the CCD. 
     
     
         11 . The method according to  claim 8 , wherein some CCD elements are selected as reference elements and expected illumination values are determined for these reference elements. 
     
     
         12 . The method according to  claim 11 , further comprising the steps of
 1) processing data using the estimated matrix to generate calculated illumination data, and   2) inspecting the calculated illumination data to see if the data corresponding to the reference elements has the expected illumination values.   
     
     
         13 . The method according to  claim 12 , further comprising the steps of:
 3) varying the estimated matrix   4) repeating steps 1 to 3 until the calculated data associated with the reference elements has the expected illumination values to within a predetermined tolerance.   
     
     
         14 . The method according to  claim 13 , wherein the CCD comprises an array of CCD elements arranged in rows and columns, and steps 1 to 3 are performed using a vector corresponding to a weighted average of data from CCD elements in an associated row of the CCD. 
     
     
         15 . The method according to  claim 14 , wherein the weighted average is calculated so as to lend greater weight to data corresponding to those columns of the CCD that have been subject to relatively high quantities of light. 
     
     
         16 . The method according to  claim 14 , wherein the matrix operator is adjusted to compensate for non-uniform sensitivity of the CCD elements by multiplying each row of the matrix by a sensitivity factor. 
     
     
         17 . The method according to  claim 1 , further comprising the step of removing from each CCD element a quantity approximately equal to the integral of the product of a measured illumination data function and a kernel function over the region below the CCD element. 
     
     
         18 . The method according to  claim 17 , wherein the kernel function is selected to compensate for non-uniform sensitivity of the line of CCD elements. 
     
     
         19 . The method according to  claim 17 , wherein the kernel function is a constant kernel parameter. 
     
     
         20 . A non-transitory computer readable medium having stored thereon a computer program comprising a set of instructions that, when run on processing means, performs a method according to  claim 1 .