EP0202425A2 — System for reproducing mixed images

Claim 1

Independent Claim 139 words

A system for reproducing images having areas of text and of continuous tone the pixels of which have been converted into in binary format data according to their intensity values, comprising: means for dividing said binary format data into non-overlapping blocks of n by n pixels, classifying means for classifying said blocks as either of TEXT or IMAGE, based on the intensity values of the n'°`2 pixels within each block, means for eliminating short runs of adjacent blocks having the same classification, means for setting a threshold for the values of the pixels in the TEXT blocks, means for averaging the values of the pixels in the IMAGE blocks, means for then quantizing the values of the pixels in the IMAGE blocks, and means for mergin the thresholded TEXT blocks and the quantized IMAGE blocks into a binary image.

Claim 2

Independent Claim 139 words

A system for reproducing images having areas of text and of continuous tone the pixels of which have been converted into in binary format data according to their intensity values, comprising: means for dividing said binary format data into non-overlapping blocks of n by n pixels, classifying means for classifying said blocks as either of TEXT or IMAGE, based on the intensity values of the n'°`2 pixels within each block, means for eliminating short runs of adjacent blocks having the same classification, means for setting a threshold for the values of the pixels in the TEXT blocks, means for averaging the values of the pixels in the IMAGE blocks, means for then quantizing the values of the pixels in the IMAGE blocks, and means for mergin the thresholded TEXT blocks and the quantized IMAGE blocks into a binary image.

Claim 3

Dependent Claim 134 words

A system as in claim 1, wherein said classifying means comprises means for setting a threshold value W, above which a pixel intensity value is considered to be white, means for setting a threshold value B, below which a pixel intensity value is condiered to be black, means for determining the intensity values of the four corner pixels of each said block, first means for clasifying a block as TEST, if any of said four corner pixels has an intensity value equal to or greater than W, second means for classifying a block as TEXT, if the two lower corner pixels both have an intensity value less than or equal to B, and third means for classifying a block as IMAGE in the absence of a TEXT classification by said first and second means.

Claim 4

Dependent Claim 80 words

A system as in claim 1 or claim 2, wherein said means for eliminating short runs of blocks with the same classification comprises, means for eliminating short runs of adjacent TEXT blocks in a row by reclassifying them to IMAGE blocks if the number of such adjacent TEXT blocks is below a selected minimum number MIN, and there is at least one IMAGE block in the preceding row immediately above at least one of the TEXT blocks in the run.

Claim 5

Dependent Claim 54 words

A system as in claim 3, wherein said means for eliminating short runs of blocks with the same classification further comprises, means for eliminating short runs of adjacent IMAGE blocks in a row by reclassifying them to TEXT blocks if the number of such adjacent IMAGE blocks is below said selected minimum number MIN.

Claim 6

Independent Claim 91 words

A system as in any preceding claim, wherein said means for thresholding the values of the pixels in the TEXT blocks comprises, means for selecting a threshold value and comparing the values of the pixels of the blocks classified as TEXT thereto, means for setting the corresponding output pel for each pixel of a TEXT block having a value less than said threshold value to 1, and means for setting the corresponding output pel for each pixel of a TEXT block having a value greater than said threshold value to 0.

Claim 7

Independent Claim 52 words

A system as in claimed in any preceding claim, wherein said means for averaging the values of the pixels in the IMAGE blocks comprises, means for determining the avergae gray value of each block classified as IMAGE by summing the intensity values of n-2 pixels therein and dividing the sum by n-2.

Claim 8

Independent Claim 120 words

A system as claimed in any preceding claim, further comprising printer means for printing a set of pel patterns having n` 2+ discrete fray values. and wherein said quantizing means comprises means for comparing the average gray value of a first IMAGE block with the set of n"2 + discrete gray values of said printer means, means for selecting the discrete gray value closest to said average gray value for said first IMAGE block, means for determining the difference between said average gray value and said selected discrete gray value for said first IMAGE block, said difference being the error, and means for distributing said error to the adjacent IAMGE blocks to the right and below said first IMAGE block.

Claim 9

Dependent Claim 137 words

A system as claimed in claim 7, further comprising means for continuing the error distribution comprising, means for determining a modified average gray value for subsequent blocks classified as IMAGE by adding to their average gray value one half the sum of the errors distributed to them from IMAGE blocks adjacent to the left and above, means for comparing the modified average gray values of the subsequent IMAGE blocks with the set of n"2 + discrete gray values of said printer means and selecting the respective discrete gray values closes to their modified average gray values, the respective errors to be distributed being the differences between the respective modified average gray values and the selected discrete gray values, and means for choosing output pel patterns for said subsequent IMAGE blocks corresponding to their selected discrete gray values.

Claim 10

Dependent Claim 29 words

A system as in claim 8, further comprising means for merging the output pels of said thresholded TEXT blocks with the output pel patterns of said quantized IMAGE blocks.

Claim 11

Dependent Claim 120 words

A process for reproducing images having areas of text and of continuous tone the pixels of which have been converted to data in binary format according to their intensity values, comprising the steps of dividing said data into non-overlapping blocks of n by n pixels, classifying said blocks as either of TEXT or IMAGE, based on the intensity values of the n"2 pixels within each, eliminating short runs of blocks with the same classification, thresholding the values of the pixels in the TEXT blocks, averaging the values of the pixels in the IMAGE blocks, then quantizing the values of the pixels in the IMAGE blocks, and merging the threshold TEXT blocks and the quantized IMAGE blocks into a binary image.

Claim 12

Dependent Claim 120 words

A process for reproducing images having areas of text and of continuous tone the pixels of which have been converted to data in binary format according to their intensity values, comprising the steps of dividing said data into non-overlapping blocks of n by n pixels, classifying said blocks as either of TEXT or IMAGE, based on the intensity values of the n"2 pixels within each, eliminating short runs of blocks with the same classification, thresholding the values of the pixels in the TEXT blocks, averaging the values of the pixels in the IMAGE blocks, then quantizing the values of the pixels in the IMAGE blocks, and merging the threshold TEXT blocks and the quantized IMAGE blocks into a binary image.

Claim 13

Dependent Claim 118 words

A process as in claim 10 wherein said classifying step comprises setting a threshold value W, above which a pixel intensity value is considered to be white, setting a threshold value B, below which a pixel intensity value is considered to be black, determining the intensity values of the four comer pixels of each said block, classifying a blocks as TEXT, if any of said four comer pixels has an intensity value equal to or greater than W, classifying a block as TEXT, if the two lower comer pixels both have an intensity value less than or equal to B, and classifying a block as IMAGE in the absence of a TEXT classification in the two preceding steps.

Claim 14

Dependent Claim 75 words

A process as in claim 10, wherein said step of eliminating short runs of blocks with the same classification comprises, eliminating short runs of adjacent TEXT blocks in a row by reclassifying them to IMAGE blocks if the number of such adjacent TEXT blocks is below a selected minimum number MIN, and there is at least one IMAGE block in the preceding row immediately above at least one of the TEXT blocks in the run.

Claim 15

Dependent Claim 52 words

A process as in claim 12, wherein said step of eliminating short runs of blocks with the same classification further comprises: eliminating short runs of adjacent IMAGE blocks in a row by reclassifying them to TEXT blocks if the number of such adjacent IMAGE blocks is below said selected minimum number NIM.

Claim 16

Dependent Claim 84 words

A process as in claim 10, wherein said step of thresholding teh values of the pixels in the TEXT blocks comprises, selecting a threshold values and comparing the values of the pixels of the blocks classified as TEXT thereto, setting the corresponding output pel for each pixel of a TEXT block having a value less than said threshold value to 1, and setting the corresponding output pel for each pixel of a TEXT block having a value greater than said threshold value to 0.

Claim 17

Dependent Claim 48 words

A process as in claim 10, wherein said step of averaging the values of the pixels in the IMAGE blocks comprises, determining the average gray value of each block classified as IMAGE by summing the intensity values of the n**2 pixels therein and dividing the sum by n**2.

Claim 18

Dependent Claim 113 words

A process as in claim 10, further comprising the step of establishing a table for printing a set of pel patterns having n"2+1 discrete gray values, and wherein said quantizing step comprises comparing the average gray value of a firt IMAGE block with the set of n ** 2+1 discrete gray values of said pel patterns, selecting the discrete gray value closest to said average gray value for said first IMAGE block, determining the difference between said average gray value and said selected discrete gray value for said first IMAGE block, said difference being the error, distributing said error to the adjacent IMAGE blocks to the right and below said first IMAGE block.

Claim 19

Dependent Claim 132 words

A process as in claim 16, wherein the error distribution is continued by the steps comprising, determining a modified average gray value for subsequent blocks classified as IMAGE by adding to their average gray value one half the sum of the errors distributed to them from IMAGE blocks adjacent to the left and above, comparing the modified average gray values of the subsequent IMAGE blocks with teh set of n 2+1 discrete gray values of said pel patterns and selecting the respective discrete gray values closest to their modified average gray values, the respeciive errors to be distributed being the differences between the respective modified average gray values and the selected discrete gray values, and choosing output pel patterns for said subsequent IMAGE blocks cor- respoonding to their selected discrete gray values.

Claim 20

Dependent Claim 31 words

A process as in claim 17, comprising the further step of merging the output pets of said thresholded TEXT blocks with the output pel pat- tems of said quantized IMAGE blocks.

Claim 21

Dependent Claim 26 words

A process as in claim 17, comprising the further step of converting the output pel patterns of said image blocks from one pattern table to another.

System for reproducing mixed images

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