Method for correcting shading effects in video images

Claim 1

A method for compensating for two-dimensional non-uniformities in an optical system at each pixel location along a scan line, comprising the steps of: establishing two-dimensional non-uniformity characteristics; characterize the two-dimensional non-uniformity in terms of two orthogonal functions along first and second orthogonal axes; storing in a first memory the correctional factors associated with said first orthogonal axis; storing in a second memory the correctional factors associated with said second orthogonal axis; accessing said stored correctional factors in said first and second memories according to the coordinates of the pixel being processed; and combining the correctional factors obtained from said first and second memories to compensate for nonuniformities at that pixel location.

Claim 2

A method for compensating for two-dimensional non-uniformities in an optical system at each pixel location along a scan line, comprising the steps of: establishing two-dimensional non-uniformity characteristics; characterize the two-dimensional non-uniformity in terms of two orthogonal functions along first and second orthogonal axes; storing in a first memory the correctional factors associated with said first orthogonal axis; storing in a second memory the correctional factors associated with said second orthogonal axis; accessing said stored correctional factors in said first and second memories according to the coordinates of the pixel being processed; and combining the correctional factors obtained from said first and second memories to compensate for nonuniformities at that pixel location.

Claim 3

A method of providing shading correction values for an optical system at different pixel locations along a scan line comprising the steps of: establish correctional functions associated with each pixel location along a scan line in terms of first and second orthogonal correction functions; storing correctional data for said first orthogonal correction function in a first memory; storing correctional data for said second orthogonal correction function in a second memory; address memory locations in said first memory using the pixel location along said scan line; address memory locations in said second memory, using the line count associated with the pixel location; combining the correctional factors obtained from each memory to obtain a corrected value for the current pixel being corrected.

Claim 4

A method of providing shading correction values for an optical system at different pixel locations along a scan line comprising the steps of: establish correctional functions associated with each pixel location along a scan line in terms of first and second orthogonal correction functions; storing correctional data for said first orthogonal correction function in a first memory; storing correctional data for said second orthogonal correction function in a second memory; address memory locations in said first memory using the pixel location along said scan line; address memory locations in said second memory, using the line count associated with the pixel location; combining the correctional factors obtained from each memory to obtain a corrected value for the current pixel being corrected.

Claim 7

A method for providing shading correction for an image scanner in which the picture signal level for a reference all white image is different at different locations along a scan line comprising the steps of: storing multibit correction data in a pair of orthogonal memories such that the content of each orthogonal value specifies the degree of attenuation of said picture signal level at each pixel element resulting from a one-dimensional correction function contained in each orthogonal memory respectively; addressing each memory based on the specific coordinates of the pixel element being corrected to obtain a one-dimensional correction value from each orthogonal memory; and combining the multibit correction values to provide a correction factor for each pixel value at its specific coordinate.

Claim 8

A method for providing shading correction for an image scanner in which the picture signal level for a reference all white image is different at different locations along a scan line comprising the steps of: storing multibit correction data in a pair of orthogonal memories such that the content of each orthogonal value specifies the degree of attenuation of said picture signal level at each pixel element resulting from a one-dimensional correction function contained in each orthogonal memory respectively; addressing each memory based on the specific coordinates of the pixel element being corrected to obtain a one-dimensional correction value from each orthogonal memory; and combining the multibit correction values to provide a correction factor for each pixel value at its specific coordinate.