Dither correction for infrared detector arrays

A weighted method of calculating gain correction values to compensate gain errors of detector elements of an infrared-detector array, using a dither pattern of said array, comprising the steps of:

• calculating a gain correction value for a current detector element by calculating gain ratios of a first set of neighboring detector elements of said current detector element;
• multiplying said gain correction value by a weighting factor, ∝;
• adding to the results of said multiplying step, a correction term of (1−∝), thereby obtaining a gain correction value for said current detector element;
• and
• repeating all of the above steps for additional detector elements, thereby determining a weighted gain correction value for each of a number of current detector elements.

A weighted method of calculating offset correction values to compensate offset errors of detector elements of an infrared detector array, using a dither pattern of said array, comprising the steps of:

• averaging dithered output values from a first set of neighboring detector elements of a current detector element;
• multiplying the results of said averaging step times a correction factor, said correction factor being a value less than one, thereby obtaining a weighted average;
• multiplying the output of said current detector element times said correction factor, thereby obtaining a weighted output;
• subtracting said weighted average from said weighted output, thereby obtaining an offset correction value for said current detector element;
• and
• repeating all of the above steps for additional sets of neighboring detector elements, thereby determining an offset correction value for a each of a number of current detector elements.

An interpolation method of calculating offset correction values to compensate offset errors of detector elements of an infrared detector array, using a dither pattern of said array where the dither step is a distance different from the dimensions of said detector elements, comprising the steps of:

• interpolating non-dithered output values of a first set of neighboring detector elements of a current detector element;
• averaging dithered output values of said neighboring detector elements;
• subtracting the result of said averaging step from the result of said interpolating step, thereby obtaining an offset correction value for said current detector element;
• and
• repeating all of the above steps for additional sets of neighboring detector elements, thereby determining offset correction values for a each of a number of current detector elements.

A method of determining gain correction values to compensate gain errors of detector elements of a detector array, comprising the steps of:

• effecting a dither movement of the array while obtaining information from a scene;
• evaluating for each detector element whether a criterion is satisfied, the criterion being a function of scene information obtained during the dither movement;
• and
• selectively determining the gain correction values only for those detector elements for which the criterion is satisfied;
• wherein said evaluating step is carried out by using for a given detector element a criterion which is a function of whether scene information in the region of the given detector element has a gradient which exceeds a threshold.