Universal thresholder/discriminator

Claim 2

A thresholding mode-switching device for automatically selecting an optimum operational mode for printing copies of documents having a mixed format, said mode-switching device comprising: scanning means for generating a stream of pixel values representative of reflectance characteristics of a scanned document; input buffer means for storing a predetermined number of pixel values; look-ahead logic means coupled to said buffer means for supplying look-ahead signals based on values of pixels subsequent to said pixel of interest; hysteresis means coupled to said buffer means for supplying hysteresis signals based on values of pixels preceding said pixel of interest; and controller means responsive to said look-ahead signals, said hysteresis signals, and the stored value of said pixel of interest for selecting an optimum operational mode.

Claim 3

The thresholding mode-switching device of claim 1 further including a thresholding means coupled to the controller for thresholding continuous tone images.

Claim 4

The thresholding mode-switching device of claim 1 wherein the hysteresis means includes: a first plurality of counter means for storing a first plurality of counts representative of hysteresis in the X-direction; a second plurality of counter means for storing a second plurality of counts representative of hysteresis in the Y-direction; and a plurality of serial memory means coupled to the second plurality of counter means for cycling said second plurality of counts.

Claim 5

A thresholding mode-switching device as claimed in claim 1 further including: gradient means coupled to the buffer means for generating gradient signals representative of a gradient associated with the values of pixels surrounding a pixel of interest and wherein said controller is also responsive to said gradient signals.

Claim 6

The thresholding mode-switching device of claim 4 further including a thresholding means coupled to the controller and for thresholding continuous tone images.

Claim 7

The thresholding mode-switching device of claim 4 wherein the hysteresis means includes: a first plurality of counter means for storing a first plurality of counts representative of hysteresis in the X direction; a second plurality of counter means for storing a second plurality of counts representative of hysteresis in the Y direction; and a plurality of serial memory means coupled to the second plurality of counter means for cycling said second plurality of counts.

Claim 8

Method for processing and printing a mixed format document, said method comprising the following steps: (a) generating a stream of digital signals indicative of PELs representing the informational contents of said document; (b) selecting one of a plurality of thresholders for processing the digital signals; (c) setting a predetermined count within a counting means; (d) using the thresholder of step (b) for generating "print/no-print" decision for the data of step (a); (e) decrementing the predetermined count on a PEL of indecision; (f) repeating steps (d)-(e) until the count is zero; and (g) switching from the present thresholder to another one of the plurality of thresholders.

Claim 9

Method for processing and printing a mixed format document, said method comprising the following steps: (a) generating a stream of digital signals indicative of PELs representing the informational contents of said document; (b) selecting one of a plurality of thresholders for processing the digital signals; (c) setting a predetermined count within a counting means; (d) using the thresholder of step (b) for generating "print/no-print" decision for the data of step (a); (e) decrementing the predetermined count on a PEL of indecision; (f) repeating steps (d)-(e) until the count is zero; and (g) switching from the present thresholder to another one of the plurality of thresholders.

Claim 10

The method recited in claim 7 wherein the selecting step comprises: (a) generating a "white" level; (b) generating a "black" level; (c) fetching a PEL of interest; (d) comparing the PEL against said "white" level; (e) comparing the PEL against said "black" level; and (f) selecting a line copy or continuous tone thresholder depending on the contents of hysteresis counters, gradient comparison and look-ahead comparison.

Claim 11

Apparatus for reproducing an original represented by a serial stream of digital data, each item of data having a PEL value corresponding to the value of a surface characteristic (e.g. reflectance) of the elemental area (PEL) of the original represented by the item of data, said apparatus being capable of operating in more than one mode to produce copies of different or mixed nature (e.g. continuous tone, line or printed) originals and comprising: buffer means for receiving and buffering the serial stream of data; means for comparing the value of each item of data with first and second threshold values and operable to generate contrast signals indicative of whether the PEL value is greater than the first threshold value, between the threshold values, or below the second threshold value; first means effective in operation to cause the apparatus to operate in a first mode according to a first algorithm; second means effective in operation to cause the apparatus to operate in a second mode according to a second algorithm; and selection means connected to receive the contrast signals and operative selectively to render the first or second means operative, said apparatus being characterized by further comprising look-ahead means connected to receive the PEL values successively stored in a first group of buffer positions and operative to generate a succession of selection signals indicative of whether any PEL value in each group lies in the band of values between the first and second threshold values or outside that band, each selection signal being associated with the PEL value occupying a particular location in the first group, being supplied to the selection means and being used by the selection means in selecting the operational mode of the apparatus.

Claim 12

Apparatus for reproducing an original represented by a serial stream of digital data, each item of data having a PEL value corresponding to the value of a surface characteristic (e.g. reflectance) of the elemental area (PEL) of the original represented by the item of data, said apparatus being capable of operating in more than one mode to produce copies of different or mixed nature (e.g. continuous tone, line or printed) originals and comprising: buffer means for receiving and buffering the serial stream of data; means for comparing the value of each item of data with first and second threshold values and operable to generate contrast signals indicative of whether the PEL value is greater than the first threshold value, between the threshold values, or below the second threshold value; first means effective in operation to cause the apparatus to operate in a first mode according to a first algorithm; second means effective in operation to cause the apparatus to operate in a second mode according to a second algorithm; and selection means connected to receive the contrast signals and operative selectively to render the first or second means operative, said apparatus being characterized by further comprising look-ahead means connected to receive the PEL values successively stored in a first group of buffer positions and operative to generate a succession of selection signals indicative of whether any PEL value in each group lies in the band of values between the first and second threshold values or outside that band, each selection signal being associated with the PEL value occupying a particular location in the first group, being supplied to the selection means and being used by the selection means in selecting the operational mode of the apparatus.

Claim 13

Apparatus as claimed in claim 9 further characterized by comprising hysteresis means operable to generate and store hysteresis signals representative of preceding operational mode and/or preceding PEL values.

Claim 14

Apparatus as claimed in claim 10 further characterized in that the hysteresis means comprises a first x-counter and a first y-counter associated with a first mode of operation of the apparatus, a first predetermined value being set in the counters in response to detection by the apparatus of a first predetermined data sequence in the incoming stream of data and the values in the first counters being decremented in response to detection of a subsequent second predetermined data sequence in the incoming stream of data.

Claim 15

Apparatus as claimed in claim 11 further characterized in that the hysteresis means further comprises a second x-counter and a second y-counter associated with a second mode of operation of the apparatus, a second predetermined value being set in the second counters in response to detection by the apparatus of a third predetermined data sequence in the incoming stream of data and the values in the second counters being decremented in response to detections of a subsequent fourth predetermined data sequence in the incoming data sequence.

Claim 16

Apparatus as claimed in claims 11 or 12, in which the stream of incoming data is generated by scanning the original in the y-direction, further characterized in that each y-counter has an associated serial storage shift register having a number of stages equal to the number of PELs in the y-scan direction of the original.

Claim 17

Apparatus as claimed in claim 9 further characterized by comprising gradient means connected to receive the PEL values stored in a second group of buffer positions and operative to generate for each second group a gradient signal, the gradient signal being associated with the particular PEL value occupying a predetermined buffer location in the second group and having a value dependent on the rate of change of the surface characteristic in a region of the original contiguous to the PEL corresponding to the particular PEL value; and means for comparing the value of each generated gradient signal with a predetermined datum gradient value and operable to generate transition signals indicative of whether the value of each generated gradient signal is greater or smaller than the datum gradient value, said transition signals being supplied to the selection means and being used by the selection means in selecting the operational mode of the apparatus.

Claim 18

Apparatus for reproducing an original represented by a serial stream of digital data, each item of data having a PEL value corresponding to the value of a surface characteristic (e.g. reflectance) of the elemental area (PEL) of the original represented by the item of data, said apparatus being capable of operating in more than one mode to produce copies of different or mixed nature (e.g. halftone, line or printed) originals and comprising: buffer means for receiving and buffering the serial stream of data; means for comparing the value of each item of data with first and second threshold values and operable to generate contrast signals indicative of whether the item value is greater than the first threshold value, between the threshold levels or below the second threshold value; gradient means connected to receive the PEL values stored in a first group of buffer positions and operable to generate for each first group a gradient value signal which is associated with the PEL value occupying a particular location in the first group; means for comparing the generated gradient values with a predetermined datum gradient value and operable to generate transition signals indicative of whether the generated gradient value is greater or less than the predetermined datum gradient value; and controller means, connected to receive the stream of digital data together with the transition signals, for selecting the operational mode of the apparatus, said apparatus being characterized by further comprising look-ahead means connected to receive the PEL values stored in a second group of buffer positions and operable to generate a selection signal for each group indicative of whether any PEL value in the group lies in the band of values between the first and second threshold values or outside that band, each selection signal being associated with the PEL value occupying a particular location in the second group, being supplied to the controller means, and being used by the controller means in selecting the operational mode of the apparatus.

Claim 19

Apparatus for reproducing an original represented by a serial stream of digital data, each item of data having a PEL value corresponding to the value of a surface characteristic (e.g. reflectance) of the elemental area (PEL) of the original represented by the item of data, said apparatus being capable of operating in more than one mode to produce copies of different or mixed nature (e.g. halftone, line or printed) originals and comprising: buffer means for receiving and buffering the serial stream of data; means for comparing the value of each item of data with first and second threshold values and operable to generate contrast signals indicative of whether the item value is greater than the first threshold value, between the threshold levels or below the second threshold value; gradient means connected to receive the PEL values stored in a first group of buffer positions and operable to generate for each first group a gradient value signal which is associated with the PEL value occupying a particular location in the first group; means for comparing the generated gradient values with a predetermined datum gradient value and operable to generate transition signals indicative of whether the generated gradient value is greater or less than the predetermined datum gradient value; and controller means, connected to receive the stream of digital data together with the transition signals, for selecting the operational mode of the apparatus, said apparatus being characterized by further comprising look-ahead means connected to receive the PEL values stored in a second group of buffer positions and operable to generate a selection signal for each group indicative of whether any PEL value in the group lies in the band of values between the first and second threshold values or outside that band, each selection signal being associated with the PEL value occupying a particular location in the second group, being supplied to the controller means, and being used by the controller means in selecting the operational mode of the apparatus.

Claim 20

Method for reproducing mixed format documents comprising the following steps: generating a stream of PEL video data representative of the informational contents of the mixed format document; utilizing a first discriminator to determine if the PEL represents line copy or nonline copy and to generate a stream of simulated PELs; utilizing a second discriminator to process either the PEL video data or the stream of simulated PELs and to generate a stream of decision classifying the process PELs as line copy or nonline copy; utilizing a third discriminator to examine the stream of decisions to reclassify the decision of any PEL which is different from surrounding PELs and to generate an adjusted stream of decision classifying the process PELs as line copy or nonline copy; thresholding the stream of PEL video data against a first thresholder for PELs identified as line copy by the adjusted stream of decision; and thresholding the stream of PEL video data against a second thresholder for PELs identified as nonline copy by the adjusted stream of decision.

Claim 21

Method for reproducing mixed format documents comprising the following steps: generating a stream of PEL video data representative of the informational contents of the mixed format document; utilizing a first discriminator to determine if the PEL represents line copy or nonline copy and to generate a stream of simulated PELs; utilizing a second discriminator to process either the PEL video data or the stream of simulated PELs and to generate a stream of decision classifying the process PELs as line copy or nonline copy; utilizing a third discriminator to examine the stream of decisions to reclassify the decision of any PEL which is different from surrounding PELs and to generate an adjusted stream of decision classifying the process PELs as line copy or nonline copy; thresholding the stream of PEL video data against a first thresholder for PELs identified as line copy by the adjusted stream of decision; and thresholding the stream of PEL video data against a second thresholder for PELs identified as nonline copy by the adjusted stream of decision.

Claim 22

The method of claim 16 further including the following step, using the values outputted from the thresholder to drive a bilevel printer so that a copy of the mixed format document is reproduced.

Claim 23

The method of claim 16 wherein the first discriminator is a defocus symmetry technique.

Claim 24

The method of claim 18 wherein the defocus/symmetry technique includes the following steps: generating a first stream of simulated pixels with each simulated pixel being formed from a horizontal weighted average of an original pixel of interest and its surrounding neighbors; generating a second data stream of simulated pixels with each simulated pixel being formed from a vertical weighted average of the original pixel of interest and its surrounding neighbors; computing a gradient (G H ) for the simulated pixel of the first data stream; computing a gradient (G V ) for the simulated pixels of the second data stream; computing an overall gradient (G)=(G V -G H ); comparing the overall gradient G with a predetermined threshold level; characterizing the original PEL as line copy for G having a value more than the predetermined threshold level; and characterizing the original PEL as nonline copy for G having a value less than the predetermined threshold level.

Claim 25

The method of claim 16 wherein the third discriminator is an information homogeneity technique.

Claim 26

The method of claim 20 wherein the information homogeneity technique includes the following steps: (a) generating line copy (LC)/nonline copy (NLC) decisions for the original PELs of interest; (b) generating a map for the decisions; (c) calculating a misclassification probability P for the PEL, with the misclassification probability being based on PEL surroundings and hysteresis; (d) generating a predetermined threshold level; (e) comparing the probability P with the threshold level; and (f) reclassifying the decision for PELs whose probability P are less than the threshold.

Claim 27

The method of claim 21 further including the steps of switching the decision for PELs having a probability (P) greater than the threshold; raising the threshold level; and repeating steps (c) through (f).

Claim 28

The method of claim 16 wherein the second discriminator is a line copy/nonline copy continuous tone technique.

Claim 29

The method of claim 16 wherein an error diffusion technique is the second thresholder.

Claim 30

Apparatus for reproducing mixed format documents comprising: means for including an optical scanner for generating a stream of PEL video data representative of the informational contents of the mixed format document; a first discriminator means coupled to the scanner, said first discriminator means being operable for determining the characteristic of the PEL and for generating a stream of simulated PELs; a second discriminator means coupled to the first discriminator means, said second discriminator means being operable for processing either the PEL video data or the stream of simulated PELs and to generate a stream of decisions classifying the processed PELs as line copy or nonline copy; a third discriminator means coupled to the second discriminator means, said third discriminator means being operable to examine the stream of decisions to reclassify the decision of any PEL which is different from surrounding PELs and to generate an adjusted stream of decision classifying the process PELs as line copy or nonline copy; means coupled to the third discriminator, said means being operable for thresholding line copy PELs; and means coupled to the third discriminator, said means being operable for thresholding nonline copy PELs.

Claim 31

Apparatus for reproducing mixed format documents comprising: means for including an optical scanner for generating a stream of PEL video data representative of the informational contents of the mixed format document; a first discriminator means coupled to the scanner, said first discriminator means being operable for determining the characteristic of the PEL and for generating a stream of simulated PELs; a second discriminator means coupled to the first discriminator means, said second discriminator means being operable for processing either the PEL video data or the stream of simulated PELs and to generate a stream of decisions classifying the processed PELs as line copy or nonline copy; a third discriminator means coupled to the second discriminator means, said third discriminator means being operable to examine the stream of decisions to reclassify the decision of any PEL which is different from surrounding PELs and to generate an adjusted stream of decision classifying the process PELs as line copy or nonline copy; means coupled to the third discriminator, said means being operable for thresholding line copy PELs; and means coupled to the third discriminator, said means being operable for thresholding nonline copy PELs.

Claim 34

In a document reproduction device wherein a document is being scanned, thresholded and reproduced, an improved thresholder for processing and printing documents having a continuous tone format or a text format comprising: means for buffering a stream of video pixels representative of the information contents for the document; means responsive to said buffering means for generating gradient signals using pixels surrounding a pixel of interest; means responsive to said buffering means for generating a look-ahead signal representative of reflectance characteristic of pixels following the pixel of interest; means responsive to said buffering means for storing level information signals representative of reflectance characteristics of a document to be reproduced; and control means for correlating the gradient signals, the look-ahead signals, and said level information signals to select an optimum thresholder for processing text or continuous tone.

Claim 35

In a document reproduction device wherein a document is being scanned, thresholded and reproduced, an improved thresholder for processing and printing documents having a continuous tone format or a text format comprising: means for buffering a stream of video pixels representative of the information contents for the document; means responsive to said buffering means for generating gradient signals using pixels surrounding a pixel of interest; means responsive to said buffering means for generating a look-ahead signal representative of reflectance characteristic of pixels following the pixel of interest; means responsive to said buffering means for storing level information signals representative of reflectance characteristics of a document to be reproduced; and control means for correlating the gradient signals, the look-ahead signals, and said level information signals to select an optimum thresholder for processing text or continuous tone.