Method and apparatus for processing image sensor output to improve image quality

A method of pixel processing comprises: subtracting a baseline value from a ixel value to produce a calibrated pixel value; selectively adjusting a baseline reference value to produce the baseline value; and, in respect of a plurality of pixel values, adjusting the baseline reference value for some of the pixel values and not adjusting the baseline reference value for the rest of the pixel values. A random or pseudo-random determination may be made regarding for which of the pixel values the baseline reference value is adjusted, e.g. using comparison of a random number with a comparator reference value, which may have shuffled bits. Adjustment of the baseline reference value may comprise adding one to its value, and the baseline reference value may comprise an integer or fractional part of a dark reference value. The plural pixel values may correspond to a row; baseline-adjusted pixels may be interspersed in the row that are not adjusted. Dark reference values may be fixed, user-adjustable, user-selected, or calculated from one or more dark reference pixel values.