EP0208355A1
Expired / Lapsed
EP
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Method of enlarging/reducing dithered images
Assignee: Canon Production Printing Netherlands BV
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Filing: 1986-06-11
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Granted: —
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Expires: 2006-06-11
Abstract
Abstract A method of enlarging/reducing a dithered image obtained from a rastered gray level image by means of a dither matrix consisting of a unique combination of thresholds, consisting of the following steps: a) defining contiguous input areas of b × b pixels in the dithered image, which input areas have to be imaged with a conversion factor of a/b on output areas of a × a pixels, b) determining that standard pattern which most closely approximates the average gray level of the dither pattern in the input area, from a series of standard patterns each obtained by dithering, with a first dither matrix, an area filled uniformly with a unique gray level, c) determining the pixels in the input area which deviate from the determined standard pattern, d) generating, for each output area, by means of a second dither matrix, a standard pattern corresponding to the gray level determined for the corresponding input area, e) determining, for each of the deviating pixels in an input area, by linear transformation, the co-ordinates of a corresponding pixel in the output area and allocating that pixel in the output area the same level as the deviating pixel in question in the input area. In this method the information content of the original image remains substantially unaffected, the occurence of Moiré distortion is avoided and the signal/noise ratio of the image is only affected insignificantly.
Inventors
- 👤 Etienne Ludovicus Mathilde Emelia Van Dorsselaer
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-10 02:36
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/40; H04N1/40068; H04N1/40075
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
200 words
A method of enlarging/reducing a dithered image obtained from a rastered gray level image by means of a dither matrix consisting of a unique combination of thresholds, characterised by the following steps: a) defining contiguous input areas of b × b pixels in the dithered image, which input areas have to be imaged with a conversion factor of a/b on output areas of a × a pixels, b) determining that standard pattern which most closely approximates the average gray level of the dither pattern in the input area, from a series of standard patterns each obtained by dithering, with a fist dither matrix, an area filled uniformly with a unique gray level, c) determing the pixels in the input area which deviate from the determined standard pattern, d) generating, for each output area, by means of a second dither matrix, a standard pattern corresponding to the gray level determined for the corresponding input area, e) determining, for each of the deviating pixels in an input area, by linear transformation, the co-ordinates of a corresponding pixel in the output area and allocating that pixel in the output area the same level as the deviating pixel in question in the input area.
Claim 2
Independent Claim
200 words
A method of enlarging/reducing a dithered image obtained from a rastered gray level image by means of a dither matrix consisting of a unique combination of thresholds, characterised by the following steps: a) defining contiguous input areas of b × b pixels in the dithered image, which input areas have to be imaged with a conversion factor of a/b on output areas of a × a pixels, b) determining that standard pattern which most closely approximates the average gray level of the dither pattern in the input area, from a series of standard patterns each obtained by dithering, with a fist dither matrix, an area filled uniformly with a unique gray level, c) determing the pixels in the input area which deviate from the determined standard pattern, d) generating, for each output area, by means of a second dither matrix, a standard pattern corresponding to the gray level determined for the corresponding input area, e) determining, for each of the deviating pixels in an input area, by linear transformation, the co-ordinates of a corresponding pixel in the output area and allocating that pixel in the output area the same level as the deviating pixel in question in the input area.
Claim 3
Dependent Claim
36 words
A method according to claim 1, characterised in that the number of gray levels of the second dither matrix used in step d) is equal to the number of gray levels of the first dither matrix.
Claim 4
Dependent Claim
67 words
A method according to claim 1 or 2, characterised in that in step c) each of the deviating pixels is allocated an amplitude level equal to the difference between the threshold associated with the pixel from the first dither matrix and the average gray level, and in that only those deviating pixels whose amplitude is greater than a predertimined threshold are imaged on the corresponding output area.
Claim 5
Independent Claim
34 words
A method according to any one of the preceding claims, characterised in that the dimensions of each input area are equal to the dimensions of the first dither matrix or a whole multiple thereof.
Claim 6
Independent Claim
94 words
A method according to any one of the claims 1 to 3, characterised in that if the dimensions of the first dither matrix are not equal to the dimensions of the input areas in step b), use is made each time of an auxiliary matrix, which is to be determined separately for each input area, and which is found by placing a contiguous array of first dither matrices on the contiguous array of input areas, the thresholds of the dither matrices which fall within each area together forming the auxiliary matrix for that area.
Claim 7
Independent Claim
88 words
A method according to any one of the preceding claims, characterised in that to generate the standard patterns associated with the various gray levels of the output area in step d), use is made each time of an auxiliary matrix, which is to be determined separately for each area, and which is found by placing a contiguous array of second dither matrices on the contiguous array of output areas, the thresholds of the dither matrices which fall within each area together forming the auxilliary matrix for that area.
Claim 8
Independent Claim
44 words
A method according to any one of the preceding claims, characterised in that in the case of enlargement in step e), depending upon the enlargement factor, a deviating pixel from the input area is imaged on a number of pixels in the output area.
Claim 9
Independent Claim
47 words
A method according to any one of the preceding claims, characterised in that both the input areas and the output areas are so dimensioned that the dither matrix fits at least approximately a whole number of times both on the input areas and on the output areas.
Claim 10
Independent Claim
61 words
A method according to any one of the preceding claims, characterised in that to perform step b) the sum is formed of the number of positions in which each of the standard patterns differs from the pixel pattern in the input area and then that standard pattern for which this sum is minimal is selected as the average gray level pattern.
Claim 11
Independent Claim
105 words
A method according to any one of the claims 1 to 8, characterised in that to perform step b) an estimated gray level is first determined by counting the number of pixels having the value 1 in the input area, and the standard pattern having the same number of 1-levels is selected as estimated gray level pattern, whereafter iterative comparison of this estimated gray level pattern with the neighbouring standard pattern (which have a 1-level more or less each time) is applied to determine that pattern at which the number of deviating pixels is minimal, which pattern is selected as the average gray level pattern.
Claim 12
Independent Claim
131 words
A method according to any one of the claims 1 to 8, characterised in that to perform step b) the pixels of an input area are ordered in a series in ascending sequence of the associated thresholds, in that to each of the elements of this first time series a value is added equal to the value added to the preceding element of the series increased by 1 if the element then reached from the series is a 1 or reduced by 1 if the element then reached is a 0, subject to the proviso that a fixed predetermined value is added to the first element of the series, which added values form a a new series which has a minimum at the value corresponding to the average gray level threshold.
Claim 13
Dependent Claim
26 words
A method according to claim 11, characterised in that the predetermined fixed value is at least equal to the number of elements of the first series.
Claim 14
Independent Claim
133 words
A method according to any one of the claims 1 to 8, characterised in that to perform step b) the pixels of an input area are ordered in a series in ascending sequence of the associated thresholds, in that to each of the elements of this first series a first value is added equal to the number of zeroes signalled on reaching the associated element on the passage of the series in ascending threshold sequence and a second value is added equal to the number of ones signalled on reaching the associated element on the passage of the series in the opposite direction, whereafter a new series is formed consisting of the sums of both added values, which second series has a minimum at the sum corresponding to the average gray level threshold.
References Cited (Backward Citations)
US4266249A
Cited
EP0024902A2
Cited
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