Source: http://www.google.com/patents/US6977757?ie=ISO-8859-1&dq=5,960,411
Timestamp: 2014-07-11 10:18:06
Document Index: 238396175

Matched Legal Cases: ['Application No. 3', 'art 130', 'arts 131', 'art 134', 'arts 131', 'art 120', 'art 131', 'art 131', 'art 131', 'art 131', 'art 131', 'art 131', 'art 131', 'arts 131', 'art 134', 'art 131', 'art 134', 'arts 131', 'art 1140', 'arts 1145', 'art 1146', 'arts 1145', 'art 1130', 'art 1120', 'art 1145', 'art 1145', 'art 1145', 'art 1145', 'arts 1145', 'arts 145', 'art 1140', 'art 1141', 'art 1140', 'arts 1145', 'art 1146', 'arts 1145', 'art 1130', 'art 1120', 'art 1145']

Patent US6977757 - Image processing method, image processing apparatus and recording medium - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsAn image processing method of quantizing multi-tone image data by an error diffusion method, includes the steps of a) detecting change of the image data; and b) oscillating cyclically in image space a threshold for the quantization in an oscillation range controlled according to the detection result...http://www.google.com/patents/US6977757?utm_source=gb-gplus-sharePatent US6977757 - Image processing method, image processing apparatus and recording mediumAdvanced Patent SearchPublication numberUS6977757 B1Publication typeGrantApplication numberUS 09/695,992Publication dateDec 20, 2005Filing dateOct 26, 2000Priority dateOct 29, 1999Fee statusPaidAlso published asDE60001143D1, DE60001143T2, EP1126693A1, EP1126693B1, US7142330, US7636179, US20060055980, US20070092151Publication number09695992, 695992, US 6977757 B1, US 6977757B1, US-B1-6977757, US6977757 B1, US6977757B1InventorsHiroshi Takahashi, Etsuo Morimoto, Kazunari TonamiOriginal AssigneeRicoh Company, Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (13), Non-Patent Citations (4), Referenced by (17), Classifications (12), Legal Events (3) External Links: USPTO, USPTO Assignment, EspacenetImage processing method, image processing apparatus and recording mediumUS 6977757 B1Abstract An image processing method of quantizing multi-tone image data by an error diffusion method, includes the steps of a) detecting change of the image data; and b) oscillating cyclically in image space a threshold for the quantization in an oscillation range controlled according to the detection result of the step a).
Generally, the dithering method has advantages such that graininess is superior and it is possible to represent a halftone image smoothly. However, by such an area halftoning method, typically, the dithering method, resolution is degraded for achieving halftoning. Further, by the ditherintg method by which a cyclic image is generated, a moir� pattern is likely to be generated when a printed image such as that consisting of halftone spots is processed.
(1) An amount of error diffusion is increased as an edge amount increases for the purpose of eliminating generation of pseudo-contours and special stripe patterns (Japanese Laid-Open Patent Application No. 3-34772); (2) For the purpose of preventing generation of a white blank at a non-edge, light-shade portion and preventing generation of notches in characters, a fixed threshold is used for an edge portion of an image, while a variable threshold is used for a non-edge portion, and the level of the variable threshold is lower as the shade is lighter (Japanese Patent No. 2755307); and (3) For the purpose of preventing generation of moir� patterns and pseudo-contours when a multi-level printer of more than two levels is used, a dither signal having a magnitude according to an edge amount is added to image data for an edge portion of an image, while a fixed value is added to image data for a non-edge portion, and, the image data thus obtained is quantized into multilevel digital data using a fixed threshold (Japanese Patent No. 2801195). SUMMARY OF THE INVENTION An object of the present invention is to provide an improved image processing method and an improved image processing apparatus, for producing high quality images, in which, as a result of compensating defects of the error diffusion method, changing points of characters and other images are represented with high resolution, while portions of photographs and images where change is a little are represented smoothly and stably, and the portions of both types match one another without incompatibility.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a block diagram of one example an image processing apparatus according to the present invention;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the accompanying drawings, preferred embodiments of the present invention will now be described. For the sake of avoiding duplicated description, the same reference numerals are given to the same parts/components or corresponding parts/components in a plurality of drawings of the accompanying drawings.
In the second embodiment, the quantization threshold generating part 130 includes four threshold generating parts 131 � 0 through 130 � 3 which generate fluctuating values having oscillation ranges corresponding to the respective levels 0 through 3 of the edge degree, respectively, and a selecting part 134 which selects one of the fluctuating values generated by the threshold generating parts 131 � 0 through 130 � 3 according to the detection data input from the image data change detecting part 120. The threshold generating part 131 � 0 generates the fluctuating value fluctuating cyclically in image space with the largest oscillation range. The threshold generating part 131 � 1 generates the fluctuating value with the oscillating range smaller than that of the threshold generating part 131 � 0. The threshold generating part 131 � 2 generates the fluctuating value with the oscillating range smaller than that of the threshold generating part 131 � 1. The threshold generating part 131 � 3 generates the fluctuating value with the smallest oscillating range.
Each of these threshold generating parts may have the same configuration as that of the fluctuating value generating part 131 of the above-described first embodiment except the dither thresholds. In the second embodiment, the threshold generating parts 131 � 0 through 130 � 3 use the dither threshold tables shown in FIGS. 6, 7, 8 and 9, respectively, for example. These dither threshold tables are obtained as a result of each value of the dither threshold table shown in FIG. 12 being multiplied by 8, 5, 2 and 0, respectively, and then 128 being added thereto.
When the edge degree is the level 0, the selecting part 134 selected the fluctuating value having the largest oscillation range generated by the threshold generating part 131 � 0, and is provided to the comparator 111 as the quantization threshold.
Similarly, when the edge degree is one of the levels 1, 2 and 3, the selecting part 134 selects the fluctuating value generated by the respective one of the threshold generating parts 131 � 1, 131 � 2 and 131 � 4, and is provided to comparator 111 as the quantization threshold.
Further specifically, 4 types of 5�5 differential filters shown in FIG. 18 are used, respective edge amounts for four directions, i.e., the main scanning direction, sub-scanning direction, and directions +45� oblique from the main scanning direction, are detected, the one, the absolute value of which is the largest, is selected from the detected four edge amounts, and the absolute value of the selected edge amount is quantized into detection data representing the edge degree which may vary 9 levels from the level 0 to the level 8.
In the twelfth embodiment, the quantization threshold generating part 1140 includes four threshold generating parts 1145 � 0 through 1145 � 3 which generate fluctuating values having oscillation ranges corresponding to the respective levels 0 through 3 of the edge degree, respectively, and a selecting part 1146 which selects one of these fluctuating values generated by the threshold generating parts 1145 � 0 through 1145 � 3 according to the edge level indicated by the edge data input from the image characteristics extracting part 1130, and provides the selected fluctuating value to the quantizer 1121 of the error diffuison processing part 1120 (FIG. 16) as the dither threshold.
The threshold generating part 1145 � 3 corresponding to the edge level 3 (non edge) uses the dither threshold matrix obtained from multiplying each threshold of the dither threshold matrix used in any of the above-described seventh, eighth, ninth, tenth and eleventh (FIGS. 19 through 23) by 8, and then, adding 128 thereto, and generates the threshold oscillating in the maximum oscillating range.
The threshold generating part 1145 � 2 corresponding to the edge level 2 uses the dither threshold matrix obtained from multiplying each threshold of that dither threshold matrix in the above-described embodiment by 5, and then, adding 128 thereto, and generates the threshold oscillating in the smaller oscillating range.
The threshold generating part 1145 � 1 corresponding to the edge level 1 uses the dither threshold matrix obtained from multiplying each threshold of that dither threshold matrix in the above-described embodiment by 2, and then, adding 128 thereto, and generates the threshold oscillating in the further smaller oscillating range.
The threshold generating part 1145 � 0 corresponding to the edge level 0 (the highest edge degree) generates the fixed value (+128).
Furthermore, because the number of edge degree levels is small, i.e., 4, the memory amount needed for the threshold generating dither threshold tables in the threshold generating parts 1145 � 0 through 1145 � 3 is small.
For the purpose of achieving a similar object, it is also possible to switch the dither threshold matrix in each of the threshold generating parts 145 � 0 through 145 � 3 in the quantization threshold generating part 1140 shown in FIG. 24 according to the specified mode.
In this case, the quantization threshold table shown in FIG. 27A is used by the fluctuating value generating part 1141. Thereby, for an image flat portion, the quantization thresholds shown in FIG. 29 are generated in a dither threshold cycle of 4 pixels�4 pixels. Accordingly, output dots are generated in the order shown in FIG. 28. That is, the output dots (halftone spot) develop spirally clockwise from the inside to the outside. The states of development of dots in a light-shade (low-shade) portion, a medium-shade portion and a dark-shade (high-shade) portion of an image are shown in FIGS. 30, 31 and 32, respectively.
In the nineteenth embodiment, the quantization threshold generating part 1140 includes four threshold generating parts 1145 � 0 through 1145 � 3 which generate fluctuating values having oscillation ranges corresponding to the respective levels 0 through 3 of the edge degree, respectively, and a selecting part 1146 which selects one of these fluctuating values generated by the threshold generating parts 1145 � 0 through 1145 � 3 according to the edge level indicated by the edge data input from the image characteristics extracting part 1130, and provides the selected fluctuating value to the quantizer 1121 of the error diffuison processing part 1120 (FIG. 16) as the quantization threshold.
The threshold generating part 1145 � 3 corresponding to the edge level 3 (non edge) uses the dither threshold matrix obtained from multiplying each threshold of the dither threshold matrix used in any of the above-described fifteenth, sixteenth, seventeenth and eighteenth embodiments (FIGS. 27A, 27B, 37, 41 and 44) by 8, and then, adding 128 thereto, and generates the threshold oscillating in the maximum oscillating range.
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