US 4,668,995 A · System for reproducing mixed images

A method for converting a scanned multi-bit image of pixels into a binary image of pels suitable for compression and printout on a printer having the capability to print a set of n.sup.2 +1 output pel patterns producing a respective set of discrete gray values, comprising the steps of:

dividing the pixels of said scanned image into rows of non-overlapping blocks of n x n pixels;
choosing a threshold value W, above which a pixel intensity value is considered to be white and a threshold value B, below which a pixel intensity value is considered to be black;
determining the intensity values of the four corner pixels of each block;
classifying a block as TEXT, if any of said four corner pixels has an intensity value equal to or greater than W or if the two lower corner pixels both have an intensity value less than or equal to B, otherwise classifying a block as IMAGE;
then, 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 MI, and there is at least one IMAGE block in the preceding row immediately above at least one of the TEXT blocks in the run;
then, 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 the selected minimum number MIN;
selecting a threshold value T 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 T to 1, otherwise setting said output pel to 0;
determining the average gray value of each block classified as IMAGE by summing the intensity values of the n.sup.2 pixels therein and dividing the sum by n.sup.2 ;
comparing the average gray value of a first IMAGE block with the set of n.sup.2 +1 discrete gray values of said printer and selecting the discrete gray value closest to its average gray value for said first IMAGE block, the error being the difference between its average gray value and the selected discrete gray value;
distributing said error to the adjacent IMAGE blocks to the right and below said first IMAGE block;
continuing the error distribution by:
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 the set of n.sup.2 +1 discrete gray values of said output pel patterns and selecting the respective discrete gray values closest to their modified average gray values, the errors being the difference between their modified average gray values and the selected discrete gray values;
choosing output pel patterns for said subsequent IMAGE blocks corresponding to their selected discrete gray values;
and
merging the output pels of said TEXT blocks with the output pel patterns of said IMAGE blocks.

14 more elements

A system 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:

means for dividing said data into non-overlapping blocks of n by n pixels;
means for classifying said blocks as either of TEXT or IMAGE, based on the intensity values of selected pixels of the n.sup.2 pixels within each and comprising:
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 considered to be black;
means for determining the intensity values of the four corner pixels of each said block;
first means for classifying a block as TEXT, 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;
means for eliminating short runs of blocks with the same classification;
means for thresholding 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;
means for choosing output pel patterns for said quantized IMAGE blocks corresponding to their quantized gray values;
and
means for merging the pels of the thresholded TEXT blocks and the pel patterns of the quantized IMAGE blocks into a binary image.

13 more elements

A system 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:

printer means for printing a set of pel patterns having n+1 discrete gray values;
and
means for dividing said data into non-overlapping blocks of n by n pixels;
means for classifying said blocks as either of TEXT or IMAGE, based on the intensity values of selected pixels of the n.sup.2 pixels within each;
means for eliminating short runs of blocks with the same classification;
means for thresholding 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, said quantizing means comprising:
means for comparing the average gray value of a first IMAGE block with the set of n.sup.2 +1 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 IMAGE blocks to the right and below said first IMAGE block;
means for choosing output pel patterns for said quantized IMAGE blocks corresponding to their quantized gray values;
and
means for merging the pels of the thresholded TEXT blocks and the pel patterns of the quantized IMAGE blocks into a binary image.

13 more elements

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 selected pixels of the n.sup.2 pixels within each, by the steps comprising:
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 corner pixels of each said block;
classifying a block as TEXT, if any of said four corner pixels has an intensity value equal to or greater than W;
classifying a block as TEXT, if the two lower corner pixels both have an intensity value less than or equal to B;
classifying a block as IMAGE in the absence of a TEXT classification in the two preceding steps;
and after classification:
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;
choosing output pel patterns for said quantized IMAGE blocks corresponding to their quantized gray values;
and
merging the pels of the thresholded TEXT blocks and the pel patterns of the quantized IMAGE blocks into a binary image.

13 more elements

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:

establishing a table for printing a set of pel patterns having n.sup.2 +1 discrete gray values;
and
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 selected pixels of the n2 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, said quantizing step comprising:
comparing the average gray value of a first IMAGE block with the set of n.sup.2 +1 discrete gray value 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;
choosing output pel patterns for said quantized IMAGE blocks corresponding to their quantized gray values;
and
merging the pels of the thresholded TEXT blocks and the pel patterns of the quantized IMAGE blocks into a binary image,

12 more elements

System for reproducing mixed images

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System for reproducing mixed images

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Abstract

Claims22