Once their own thermal signal has been compensated for by dark-frame subtraction (capture an image of a flat object kept at a constant 0K in an advanced laboratory, after allowing the thermal camera to warm up for several minutes to a constant operating temperature), so that a signal output of 0 means the object is at absolute 0 temperature how linear is its response? Obviously you need to apply a curve to convert linear radient energy readings to temperature, but that curve itself must have an input that is linear with regard to radient energy. So with an average microbolometer array (whether VOx, or amorphous silicon), once the dark frame has been subtracted, how linear is the actual signal? Is it quite linear with respect to radient energy? Or is it closer to linear with respect to temperature? Or is it completely non-linear (following some advanced transfer function regarding radiant energy input to signal output)?