1. A ditherless method of compensating non-uniformities among detector elements of a detector array that captures successive image frames of a scene, where each detector element of the array has at least one neighbor, the method comprising: (i) receiving a current image frame from the detector array and a previous image frame from an image frame memory, wherein the current and previous frames are image frames captured by the detector array at different times and which are represented as respective matrices each containing image pixel values representing output signals from the detector array; (ii) applying, at a correction unit, a plurality of predetermined correction terms to the current frame and the previous frame to generate a corrected current frame and a corrected previous frame; (iii) generating, at a delta-frame unit, a delta frame using the current frame and the previous frame; (iv) computing, at a gradient-calculation unit, a previous-frame gradient matrix of the corrected previous frame in a first direction, a current-frame gradient matrix of the corrected current frame in a second direction, and a first delta-frame gradient matrix in the first direction and a second delta-frame gradient matrix in the second direction of the delta frame, wherein the second direction is opposite to the first direction; (v) computing, at a gradient-processing unit, a first mask using the previous-frame gradient matrix and the first delta-frame gradient matrix, and a second mask using the current-frame gradient matrix and the second delta-frame gradient matrix, wherein the first mask preserves scene-gradient information of a scene associated with the corrected previous frame in the first direction, and the second mask preserves scene-gradient information associated with the corrected current frame in the second direction; (vi) computing, at a delta-correction unit, a plurality of delta-correction values as a function of the previous-frame gradient matrix, the current-frame gradient matrix, and the first and second masks, wherein each of the plurality of delta-correction values is associated with a different one of the detector elements of the array; and (vii) updating, at an update unit, each of the plurality of predetermined correction terms with a corresponding delta-correction value.