Method and apparatus for scanning an original and updating threshold values for use in the processing of data

Claim 3

A method according to claim 1, comprising determining the grey-level value frequency distribution of the respective zones by dividing a store section for each zone into a plurality of store cells whose contents are counted up or down in response to the value of the grey-level values received.

Claim 4

An optical scanner for entering information from an original and generating a digital data representation of the original in response to the entered information, said scanner comprising: a CCD unit for generating a data signal with grey-level values for points along a scanning line on the original, a threshold value calculating unit for calculating local threshold values for zones on the original in response to the statistical distribution of the grey-level values within respective zones, said threshold value calculating unit including means for currently updating the grey-level value frequency distribution of the zone, segments from the line last scanned replacing the oldest line segments in the zone, and determining updated threshold values before determining threshold values for a subsequent zone, a threshold value comparator receiving said data signal, by which the grey-level values are compared with the local threshold value of the zone to which the point belongs to generate a digital data representation of the point on the original in response to the comparison, a branched data bus for transferring data from the CCD unit to the threshold value calculating unit, said database having a first and a second branch between the CCD unit and the threshold value calculating unit, said second branch accommodating a delay element which introduces a delay of signals transmitted by this branch corresponding to the time it takes to transmit a plurality of lines, preferably corresponding to the number of line segments in a zone, from the CCD unit to the threshold value calculating unit through the first branch, said threshold value calculating unit having a processor which currently updates the statistical distribution of the respective zones by adding grey-level values transmitted via the first branch of the data bus and subtracting grey-level values transmitted via the second branch of the data bus, and said processor transmitting the updated threshold values to the threshold value comparator.

Claim 5

An optical scanner for entering information from an original and generating a digital data representation of the original in response to the entered information, said scanner comprising: a CCD unit for generating a data signal with grey-level values for points along a scanning line on the original, a threshold value calculating unit for calculating local threshold values for zones on the original in response to the statistical distribution of the grey-level values within respective zones, said threshold value calculating unit including means for currently updating the grey-level value frequency distribution of the zone, segments from the line last scanned replacing the oldest line segments in the zone, and determining updated threshold values before determining threshold values for a subsequent zone, a threshold value comparator receiving said data signal, by which the grey-level values are compared with the local threshold value of the zone to which the point belongs to generate a digital data representation of the point on the original in response to the comparison, a branched data bus for transferring data from the CCD unit to the threshold value calculating unit, said database having a first and a second branch between the CCD unit and the threshold value calculating unit, said second branch accommodating a delay element which introduces a delay of signals transmitted by this branch corresponding to the time it takes to transmit a plurality of lines, preferably corresponding to the number of line segments in a zone, from the CCD unit to the threshold value calculating unit through the first branch, said threshold value calculating unit having a processor which currently updates the statistical distribution of the respective zones by adding grey-level values transmitted via the first branch of the data bus and subtracting grey-level values transmitted via the second branch of the data bus, and said processor transmitting the updated threshold values to the threshold value comparator.

Claim 6

An optical scanner according to claim 3, wherein the threshold value calculating unit has an associated store, a store section of which being associated with each zone, and that said store section is divided into a plurality of store cells whose contents are counted up or down in response to the value of the grey-level values received.

Claim 7

An optical scanner according to claim 4, wherein the delay element in the second branch of the data bus is a buffer store.

Claim 8

An optical scanner according to claim 4, wherein the branched data bus includes decimation means which sort out a predetermined portion of the grey-level values in response to their position on the original.

Claim 9

An optical scanner according to claim 4, wherein a buffer store is provided between the CCD unit and the threshold value calculating unit, said buffer store delaying the grey-level data signals before transmission to the threshold value calculating unit.

Claim 10

An optical scanner according to claim 7, wherein the delay introduced with the buffer store between the CCD unit and the threshold value calculating unit corresponds to about half of the delay introduced with the delay element in the branched data bus.