Video output signal correcting method and apparatus

Claim 1

A method of generating correction factors with which a video signal, output of a sensor in an electro-optical document reading apparatus, is to be amplified in every pixel in order to compensate for apparatus performance anomalies, which method comprises the steps of developing an n-bit binary code correction work for an output value pertaining to each pixel in a scanning line or area taken as reference with which said output value has to be amplified to make it substantially equal to a predetermined reference signal level by performing a succesibe approximation procedure, said procedure comprising a sequence of checking cycles each including the steps of ampliying a sensor signal responsive to a uniformly irradiated line or area taken as reference with an initial n-bit binary code work having its most significant bit set to one and its other bits set to zero to give a modified video response signal and comparing said modified video response signal with said predetermined reference signal level to give a comparison signal; and changing the correction words bit by bit in dependance on said comparison signal and by changing a lower significant bit next to an amended bit to one in order to bring each of the correction works progressively into approximation with a required coded correction factor; wherein the successive approximation procedures for developing the plurality of correcting words are nested by performing in immediate succession to each other the sequence of checking cycles in respect of the most significant bits of different correction words, then performing in imediate succession to each other the sequence of checking cycles in respect of a next significant value bit of those correction words and so on until the successive approximation procedures for all the correction words are completed each sequency of checking cycles being performed after an exposure of said sensor to said uniformly illuminated reference line or area.

Claim 2

A method of generating correction factors with which a video signal, output of a sensor in an electro-optical document reading apparatus, is to be amplified in every pixel in order to compensate for apparatus performance anomalies, which method comprises the steps of developing an n-bit binary code correction work for an output value pertaining to each pixel in a scanning line or area taken as reference with which said output value has to be amplified to make it substantially equal to a predetermined reference signal level by performing a succesibe approximation procedure, said procedure comprising a sequence of checking cycles each including the steps of ampliying a sensor signal responsive to a uniformly irradiated line or area taken as reference with an initial n-bit binary code work having its most significant bit set to one and its other bits set to zero to give a modified video response signal and comparing said modified video response signal with said predetermined reference signal level to give a comparison signal; and changing the correction words bit by bit in dependance on said comparison signal and by changing a lower significant bit next to an amended bit to one in order to bring each of the correction works progressively into approximation with a required coded correction factor; wherein the successive approximation procedures for developing the plurality of correcting words are nested by performing in immediate succession to each other the sequence of checking cycles in respect of the most significant bits of different correction words, then performing in imediate succession to each other the sequence of checking cycles in respect of a next significant value bit of those correction words and so on until the successive approximation procedures for all the correction words are completed each sequency of checking cycles being performed after an exposure of said sensor to said uniformly illuminated reference line or area.