JPH05153393A - Image processor - Google Patents

Abstract

PURPOSE:To obtain the smooth image of high picture quality by preventing the sudden change of an output image when the character images, etc., mixed in a halftone dot image for instance. CONSTITUTION:A halftone dot candidate detector means 400 detects a halftone dot candidate number B of a block of (3X3) picture elements including a center noted one. Meanwhile an edge candidate detector means 500 detects the edge intensity through a primary differential filter to binarize the edge intensity and detects an edge candidate number A. A calculator means 700 calculates the mixture rate between the data E emphasized by a sharpening processor means 200 and the data S smoothed by a smoothing processor means 300 with the higher preference given to the number B than the number A. Then a mixture means 600 shifts the mixing area of both data E and S based on the mixture ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for high-quality halftone image processing.

[0002]

2. Description of the Related Art In recent years, due to the development of various digital image processing, image quality can be improved, and image quality adjustment such as processing and correction to an image different from the original image can be performed. In addition, it has become possible to output a satisfactory image by improving the gradation and resolution. This is not possible in a conventional analog copying machine, etc. Further, although this kind of image processing technology influences the image quality of a printer etc., on the other hand, various problems which did not exist in the analog copying machine etc. occur. There is.

As a conventional example of this kind, for example, O Plus
E, 1990.9, pp132-144, image processing techniques in high-definition recording are known. This technology deals with the problems of moire and halftone dots, and when switching the filter processing according to the image type, the mixing ratio of the smoothing filter and the emphasizing filter in the transition region is used as the edge detection signal. It is proposed to adjust according to the level. Then, when the filter is switched only based on the edge intensity information and the halftone dot in the halftone image is recognized as the edge and the emphasis process is performed, moire occurs, but in order to solve this problem, the level of the transition region is The parameters are set by simulation and mixed by a preset ratio to suppress the abrupt change of the transition.

As a method for determining whether it is a halftone dot area or the like, for example, Japanese Patent Laid-Open Nos. 2-53185 and 2 are known.
-103684, Japanese Patent Application Laid-Open No. 2-105271, and Japanese Patent Application Laid-Open No. 2-140887.
Specifically, in Japanese Patent Application Laid-Open No. 2-53185, the determination is made based on the number of pixels in a predetermined density range existing around the target pixel, and in Japanese Patent Application Laid-Open No. 2-103684, attributes of pixels around the target pixel are determined. The determination is made by changing the correction reference according to the above, and in JP-A-2-105271, it is determined whether or not the edge density of the local area surrounding the pixel of interest exceeds a threshold value. Further, in Japanese Patent Laid-Open No. 2-140887, the density of the pixel of interest is quantized by a threshold value according to the average density of the block including the pixel of interest.

[0005]

However, the above-mentioned O
In the image processing technique shown in Plus E, 1990.9, pp132-144, since the smoothing filter and the enhancement filter are switched only by the edge strength of the pixel of interest, for example, when a character image and the like are mixed in the halftone dot image, There is a problem in that the smoothing process and the emphasis process are rapidly switched in the vicinity of the threshold for edge detection, so that the output image vibrates rapidly and a smooth image cannot be obtained.

In view of the above conventional problems, the present invention can prevent a sudden change in an output image when a character image and the like are mixed in a halftone image, and obtain a smooth high quality image. It is an object of the present invention to provide an image processing device that can be used.

[0007]

In order to achieve the above object, a first means is a sharpening means for sharpening image data, a smoothing means for smoothing image data, and an M × including a target pixel. The number of halftone dot candidates detecting means for detecting the number of halftone dot candidates in the block of N pixels, the number of edge candidate detecting means for detecting the number of edge candidates in the block, and the number of halftone dot candidates and the number of edge candidates in the target pixel Calculating means for calculating a mixing ratio of the sharpening data and the smoothing data, and image data sharpened by the sharpening means and smoothed by the smoothing means according to the mixing ratio calculated by the calculating means. And mixing means for shifting and mixing the mixed area of the image data.

A second means is a sharpening means for sharpening the image data, a smoothing means for smoothing the image data, and an average pixel density of each pixel in the block of M × N pixels including the target pixel. Number of halftone dot candidates detecting means for detecting the halftone dot quantized data, edge strength detecting means for detecting the edge strength of the target pixel in the block, and sharpening in the target pixel by the halftone dot quantized data and the edge strength. Calculation means for calculating a mixing ratio of the data and the smoothed data, and image data sharpened by the sharpening means and an image smoothed by the smoothing means in accordance with the mixing ratio calculated by the calculating means And a mixing means for shifting and mixing an area for mixing data.

A third means is a sharpening means for sharpening the image data, a smoothing means for smoothing the image data, and an average density of each pixel in a block of M × N pixels including the target pixel, and the pixel of interest. The number of halftone dot candidates for detecting the halftone dot quantized data, the calculating means for calculating the mixing ratio of the sharpening data and the smoothed data in the target pixel by the halftone dot quantized data, and the calculating means The image data sharpened by the sharpening unit and the image data smoothed by the smoothing unit are shifted and mixed in accordance with the mixed ratio. And

A fourth means is a sharpening means for sharpening the image data, a smoothing means for smoothing the image data, and a mesh for detecting the number of halftone dot candidates in a block of M × N pixels including the target pixel. Point candidate number detection means, calculation means for calculating a mixture ratio of the sharpening data and smoothed data in the pixel of interest based on the number of halftone dot candidates, and the sharpening according to the mixture ratio calculated by the calculating means. The image data sharpened by the means and the image data smoothed by the smoothing means are mixed and shifted by a mixing means.

[0011]

According to the first means, the area for mixing the sharpened image data and the smoothed image data is shifted by the mixing ratio according to the number of halftone dot candidates and the number of edge candidates by the above-mentioned configuration. When a character image and the like are mixed in the halftone image, it is possible to prevent the output image from rapidly changing and obtain a smooth high-quality image.

In the second means, the area in which the sharpened image data and the smoothed image data are mixed is shifted in accordance with the halftone dot quantized data and the mixing ratio of the target pixel according to the edge strength. For example, when a character image and the like are mixed in a halftone dot image, it is possible to prevent a sudden change in the output image and obtain a smooth high-quality image.

In the third means, the area where the sharpened image data and the smoothed image data are mixed is shifted by the mixing ratio according to the halftone dot quantized data, so that, for example, in the halftone dot image, When images and the like are mixed, it is possible to prevent the output image from abruptly changing and obtain a smooth high-quality image.

In the fourth means, the area in which the sharpened image data and the smoothed image data are mixed is shifted depending on the mixing ratio according to the number of halftone dot candidates. It is possible to prevent the output image from abruptly changing and to obtain a smooth high-quality image in the case where these and the like are mixed.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing an embodiment of an image processing apparatus according to the present invention, FIG. 2 is an explanatory view showing pixel data for each block, and FIG. 3 is an explanation showing a primary differential filter of the edge strength candidate detecting means of FIG. FIG. 4 is an explanatory view showing the calculation method of the calculation means of FIG. 1, and FIG. 5 is an explanatory view showing the transition of the area where the edge emphasis data and the halftone dot smoothing data are mixed.

In FIG. 1, a document image is read by a reading unit 100 such as a scanner, amplified, and A / D converted, and then shading is performed according to uneven light amount of a light source of the reading unit 100 and sensitivity error of a CCD image sensor. After the correction, the image data has a sharpening processing means 200 for enhancing a character image and the like, a smoothing processing means 300 for smoothing a halftone dot image and the like, and a halftone dot candidate detecting means as described later. 400 and the edge candidate detecting means 500. The data E emphasized by the sharpening processing means 200 and the data S smoothed by the smoothing processing means 300 are mixed by the mixing means 600 at the mixing ratio calculated by the calculating means 700 as described later, and this mixed data is obtained. D is output to the output means 800 such as a printer.

As shown in FIG. 2, the halftone dot candidate detecting means 400 detects the number of halftone dot candidates B in the block of 3 × 3 pixels including the pixel of interest in the center, and the edge candidate detecting means 5
00 is a main scanning direction filter as shown in FIG.
The edge strength is detected and binarized by the primary differential filter of the sub-scanning direction filter as shown in FIG. 3B, and the number A of edge candidates in the block of 3 × 3 pixels as shown in FIG. 2 is detected. Note that, in FIG. 2, star marks indicate halftone dot candidates and triangle marks indicate edge candidates. Then, in FIG. 2B, the pixel of the mark in which the star mark and the triangle mark are superimposed indicates that it is near the threshold value of the halftone dot candidate and the edge candidate.

The calculation means 700 uses the table as shown in FIG. 4, the number of halftone dot candidates B and the number of edge candidates A, and the data E emphasized by the sharpening processing means 200 with priority given to the number of halftone dot candidates B. And the mixing ratio of the data S smoothed by the smoothing processing means 300 is calculated. The mixing means 600 shifts the area in which the data E emphasized by the sharpening processing means 200 and the data S smoothed by the smoothing processing means 300 are mixed based on the equation 1, and this mixed data D is printed by a printer or the like. Output to the output means 800.

[0019]

## EQU1 ## Therefore, in the block shown in FIG. 2A, the number of halftone dot candidates is B = 3 and the number of edge candidates is A = 6. A mixing ratio of Th3 is selected, and mixing is performed at a mixing ratio as shown in FIG. On the other hand, in the block shown in FIG. 2B, since the number of halftone dot candidates B = 5 and the number of edge candidates A = 6, the halftone dot candidate number B = 5 is prioritized and the mixture ratio of the threshold Th5 in FIG. The transition regions are selected and mixed with the shifted mixing ratio as shown in FIG. Similarly, in the case of the threshold Th8, the transition regions are mixed at the shifted mixing ratio as shown in FIG.

Therefore, according to the above-described embodiment, the area where the data E emphasized by the sharpening processing means 200 and the data S smoothed by the smoothing processing means 300 are mixed is the number of halftone dot candidates B and the number of edge candidates. Since the shift is performed according to A, it is possible to prevent the output image from abruptly changing and obtain a smooth high-quality image when a character image and the like are mixed in the halftone image.

Next, a second embodiment will be described with reference to FIG. FIG. 6 is a block diagram showing the image processing apparatus of the second embodiment, which is a reading section 100 and a sharpening processing means 200.
Since the smoothing processing means 300 and the output unit 800 are the same as those shown in FIG. 1, the same reference numerals are given and detailed description thereof will be omitted.

The halftone dot quantization number detecting means 401 quantizes the density of the pixel of interest in accordance with the average density of a block of 3 × 3 pixels including the pixel of interest as shown in FIG. It outputs to the calculation means 701. Further, the edge strength detecting means 501 detects the edge strength by a primary differential filter as shown in FIG. 3 and outputs the strength data A ′ to the calculating means 701. The calculation means 701 calculates the halftone dot quantized data B ′ and the edge strength data A ′ so as to satisfy the condition shown in the equation 2, and the mixing means 601 calculates the sharpening processing means 200 by the equation 3 based on the calculation result. The area where the data E emphasized by and the data S smoothed by the smoothing processing means 300 are mixed is shifted, and this mixed data D is output to the output means 800 such as a printer.

[0023]

## EQU2 ## B '+ A' = 1

[0024]

Therefore, in the second embodiment as well, the data E emphasized by the sharpening processing means 200 and the data S smoothed by the smoothing processing means 300 are similarly obtained. Since the area in which is mixed is shifted according to the halftone dot quantized data B ′ and the edge strength data A ′, it is possible to prevent the output image from abruptly changing when a character image or the like is mixed in the halftone dot image. As a result, a smooth high quality image can be obtained. Note that the arithmetic expression shown in Expression 3 is a simple product-sum operation, but instead, another statistical method such as the least square method may be used.

FIG. 7 shows a modification of the second embodiment described above.
The edge strength detecting means 501 in the second embodiment is omitted, as shown in FIG. 8, the halftone dot quantization number detecting means 401 detects only the halftone dot quantized data, and the judging means 702 detects this quantized data. By comparing a predetermined threshold value, the mixing ratio of the data E emphasized by the sharpening processing means 200 and the data S smoothed by the smoothing processing means 300 is determined. In this case, the mixing result D of the mixing means 602
Can be represented by Equation 4.

[0026]

## EQU00004 ## D = .alpha..multidot.S + .beta..multidot.E (where .alpha. +. Beta. = 1) FIGS. 9 and 10 show a modification of the first embodiment, and the edge candidate detecting means 500 in the first embodiment is omitted. 1, only the number of halftone dot candidates is detected by the halftone dot candidate detecting means 400, and the determining means 703 detects the number of halftone dot candidates.
As shown in 0, the data E emphasized by the sharpening processing means 200 and the smoothing processing means 3 from the detection rate of the number of halftone dot candidates.
The mixing ratio of the data S smoothed by 00 is determined.
In this case as well, the mixing result D of the mixing means 603 is
It can be represented by Equation 4.

[0027]

As described above, according to the invention of claim 1, the sharpening means for sharpening the image data, the smoothing means for smoothing the image data, and the M × N pixels including the target pixel The number of halftone dot candidates detecting means for detecting the number of halftone dot candidates in the block, the number of edge candidate detecting means for detecting the number of edge candidates in the block, and the sharpening data in the target pixel by the number of halftone dot candidates and the number of edge candidates And calculation means for calculating a mixture ratio of the smoothed data, and image data sharpened by the sharpening means and image data smoothed by the smoothing means in accordance with the mixture ratio calculated by the calculating means. Since a mixing means for shifting and mixing the area for mixing is provided, for example, when a character image or the like is mixed in the halftone dot image, it is possible to prevent the output image from abruptly changing. It is possible to obtain an image of's high-quality.

According to a second aspect of the present invention, there is provided a sharpening means for sharpening the image data, a smoothing means for smoothing the image data, and an average density of each pixel in the block of M × N pixels including the target pixel. Halftone dot candidate number detecting means for detecting halftone dot quantized data of the target pixel; edge strength detecting means for detecting the edge strength of the target pixel in the block;
Calculating means for calculating the mixture ratio of the sharpening data and the smoothing data in the pixel of interest based on the halftone dot quantized data and the edge strength, and the sharpening means for sharpening according to the mixture ratio calculated by the calculating means. Since there is provided a mixing unit that shifts and mixes a region for mixing the image data that has been converted and the image data that has been smoothed by the smoothing unit,
For example, when a character image and the like are mixed in a halftone dot image, it is possible to prevent a sudden change in the output image and obtain a smooth high-quality image. According to a third aspect of the present invention, the sharpening means for sharpening the image data, the smoothing means for smoothing the image data, and the average density of each pixel in the block of M × N pixels including the target pixel The number of halftone dot candidates detecting means for detecting the halftone dot quantized data, the calculating means for calculating the mixture ratio of the sharpening data and the smoothed data in the target pixel by the halftone dot quantized data, and the calculating means According to the mixing ratio, the image data sharpened by the sharpening means and the image data smoothed by the smoothing means are provided with a mixing means for shifting and mixing a region for mixing. When a character image and the like are mixed in the image, it is possible to prevent the output image from rapidly changing and obtain a smooth high-quality image.

According to a fourth aspect of the present invention, the sharpening means for sharpening the image data, the smoothing means for smoothing the image data, and the number of halftone dot candidates in the block of M × N pixels including the target pixel are detected. Means for detecting the number of halftone dot candidates, calculating means for calculating the mixture ratio of the sharpening data and the smoothed data in the pixel of interest based on the number of halftone dot candidates, and the sharpening device according to the mixture ratio calculated by the calculating means. Since the mixing means for shifting and mixing the area where the image data sharpened by the smoothing means and the image data smoothed by the smoothing means are mixed, for example, a character image or the like is mixed in the halftone dot image. In this case, the output image can be prevented from changing rapidly and a smooth high-quality image can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an image processing apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing pixel data for each block.

FIG. 3 is an explanatory diagram showing a first-order differential filter of the edge strength candidate detecting means of FIG.

FIG. 4 is an explanatory diagram showing a calculation method of a calculation means in FIG.

FIG. 5 is an explanatory diagram showing a transition of a mixed area of edge emphasis data and halftone dot smoothing data.

FIG. 6 is a block diagram showing an image processing apparatus of a second embodiment.

FIG. 7 is a block diagram showing a modification of the second embodiment.

8 is an explanatory diagram showing halftone dot data in FIG. 7. FIG.

FIG. 9 is a block diagram showing a modification of the first embodiment.

FIG. 10 is an explanatory diagram showing a determination method in the determination means of FIG.

[Explanation of symbols]

 200 sharpening processing means 300 smoothing processing means 400 halftone dot candidate detecting means 401 halftone dot quantization number detecting means 500 edge candidate detecting means 501 edge strength detecting means 600, 601, 602, 603 mixing means 700, 701, 702, 703 Calculation method

Claims (4)

[Claims] 1. A sharpening means for sharpening image data, a smoothing means for smoothing image data, and a halftone dot candidate number detection for detecting the number of halftone dot candidates in a block of M × N pixels including a target pixel. Means, an edge candidate number detecting means for detecting the number of edge candidates in the block, and a calculating means for calculating a mixture ratio of the sharpening data and the smoothed data in the pixel of interest by the number of halftone dot candidates and the number of edge candidates, Mixing means for shifting and mixing a region in which the image data sharpened by the sharpening means and the image data smoothed by the smoothing means are mixed according to the mixing ratio calculated by the calculating means, An image processing apparatus equipped with. 2. A sharpening means for sharpening image data, a smoothing means for smoothing image data, and a halftone dot quantum of a pixel of interest based on an average density of each pixel in a block of M × N pixels including the pixel of interest. Halftone dot candidate number detecting means for detecting the pixelized data, edge strength detecting means for detecting the edge strength of the target pixel in the block, and sharpening data and smoothing for the target pixel by the halftone dot quantized data and the edge strength. Calculating means for calculating a mixing ratio of the data, and the image data sharpened by the sharpening means and the image data smoothed by the smoothing means are mixed according to the mixing ratio calculated by the calculating means. An image processing apparatus comprising: a mixing unit that shifts and mixes regions. 3. A sharpening means for sharpening image data, a smoothing means for smoothing image data, and a halftone dot quantum of a pixel of interest based on an average density of each pixel in a block of M × N pixels including the pixel of interest. Halftone-dot-candidate-number-detecting means for detecting the quantized data, calculating means for calculating the mixture ratio of the sharpening data and the smoothed data in the pixel of interest by the halftone-dot quantized data, and the mixture ratio calculated by the calculating means. Accordingly, the image processing apparatus comprises: a mixing unit that shifts and mixes a region in which the image data sharpened by the sharpening unit and the image data smoothed by the smoothing unit are shifted and mixed. 4. A sharpening means for sharpening image data, a smoothing means for smoothing image data, and a halftone dot candidate number detection for detecting the number of halftone dot candidates in a block of M × N pixels including a target pixel. Means, a calculation means for calculating a mixture ratio of the sharpening data and the smoothed data in the target pixel by the number of halftone dot candidates, and sharpening by the sharpening means according to the mixture ratio calculated by the calculating means. An image processing apparatus comprising: a mixing unit that shifts and mixes a region in which the image data and the image data smoothed by the smoothing unit are mixed.