JPH1028225A - Mtf-correcting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an image quality by reducing rough surfaces due to an edge enhancement processing. SOLUTION: An arithmetic part 101 is provided with an edge enhancement filter, smoothing filter, and filter which does nothing. An edge-detecting part 104 calculates an edge degree E, and a standard deviation detecting part 105 calculates a standard deviation (rough surface level) S. A discriminating part 106 and a filter-selecting part 107 selects the edge enhancement filter, when a reference value < E < S, selects the smoothing filter when the reference value <S<E or S < the reference value < E, and selects the filter which does nothing, when S < E < the reference value or E < S < the reference value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an MTF correction device for optimizing edge enhancement and noise removal for digital image data.

[0002]

2. Description of the Related Art Conventional MTF correction processing is based on uniform processing over the entire surface using an edge enhancement filter or a smoothing filter. As another conventional example, a method for preventing moiré has been proposed as disclosed in, for example, JP-A-5-324826. Also, Japanese Unexamined Patent Publication No. 6-32685
In Japanese Patent Application Laid-Open No. 9-208, at least three or more feature values of an image are detected, and at least three
A method for selecting one of the above dither tables has been proposed, and Japanese Patent Application Laid-Open No. 6-326868 proposes a method for switching between a boundary component enhancement mode of an image, a smoothing mode for a uniform region of the image, and a normal mode. Have been.

[0003]

In an image forming apparatus using multi-level laser power, halftone processing is performed by regularly arranging multi-level power in a two-dimensional manner by dither processing. At this time, even if the input signal level is a uniform image signal, a certain texture pattern is formed by dither processing. However, the on-off state of the toner particles due to this pattern, that is, the variation is not a problem when viewed at a sufficiently long distance from the image, but when viewed closely or when edge enhancement processing is performed. Has the problem of becoming visible grainy.

[0004] That is, although the edge enhancement processing has the effect of improving the sharpness of an image, it may increase roughness. In particular, as described above, when the texture structure by the halftone processing is increased to some extent, the sharpness is improved by the edge enhancement processing, but there is a problem that the roughness of the image of the uniform portion increases.

The present invention has been made in consideration of the above-described conventional problems, and has as its object to provide an MTF correction device capable of improving image quality by reducing roughness due to edge enhancement processing.

[0006]

In order to achieve the above object, a first means is an edge enhancement processing means for performing edge enhancement processing on image data, a smoothing processing means for performing smoothing processing on image data, and an image processing apparatus. Processing means for outputting the value as is, first detecting means for detecting the size E of the edge based on the image data, and second means for detecting the roughness S of the image based on the standard deviation of the image data. And the output of the edge enhancement processing means is selected when the preset reference value <E <S, and the reference value <S <E or S
Selecting means for selecting an output of the smoothing processing means when <reference value <E, and selecting an output of the image processing means when S <E <reference value or E <S <reference value. It is characterized by the following.

A second means for transferring and fixing, on the transfer paper, a density patch in which the reference value in the first means is equal to or less than 50% and a full developing amount is developed at a constant developing potential;
The transfer paper is read by a scanner, and is a value obtained by processing a standard deviation of the read value.

The third means is characterized in that the reference value in the first means is a value obtained by calculating a standard deviation based on a part of an image obtained by reading a user's document.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an MTF correction apparatus according to the present invention. FIG. 2 is an explanatory diagram showing respective filters for performing edge enhancement processing, smoothing processing, and non-processing of an arithmetic unit in FIG. FIG. 4 is an explanatory diagram showing an example of an image, and FIG. 4 is a configuration diagram showing a copying machine to which the MTF correction device of FIG. 1 is applied.

In FIG. 1, for example, an image signal read by the scanner shown in FIG. 3 is subjected to edge enhancement processing or smoothing by an arithmetic unit 101, or is not subjected to any processing, and is used as it is. Is output. The arithmetic unit 101 is, for example, a 3D as shown in FIGS.
Each type of filter has a 3 × 3 matrix. FIG. 2A shows an edge enhancement filter, FIG. 2B shows a smoothing filter,
FIG. 2C shows filters that output input data as they are without performing any processing. These filters are selected by a selection signal of the filter selection unit 107.

In such a configuration, first, a copying machine as shown in FIG. 4 transfers a density patch developed with a constant development potential with a full exposure amount of 50% or less onto transfer paper and fixes it. Then, the transfer sheet is read by a scanner, a reference value obtained by processing the standard deviation of the read value is calculated by a reference value setting circuit 102, and is set in a reference value register 103. Instead of the reference value, the standard value may be set by calculating a standard deviation based on a part of an image obtained by reading a user's document.

When an actual user's original is read after the reference value is set as described above, the read signal is sent to the arithmetic unit 101, the edge detecting unit 104, and the standard deviation detecting unit 1.
05. Here, the original is, for example, as shown in FIG.
As shown in (a), in the case of a document having a slightly bright “cloud (CD)” and a slightly dark “mountain (MN)” on the background of a bright “sky (SY)”, the direction of scanning in the main scanning direction indicated by the arrow in FIG. The density data along the direction is data in which an edge exists at the boundary between “sky (SY)”, “cloud (CD)”, and “mountain (MN)” as shown in FIG.

The edge detection unit 104 convolves and integrates the read signal P _ij of 5 × 3 pixels by an edge detection filter of 5 pixels in the main scanning direction × 3 lines in the sub-scanning direction as follows, and further multiplies by a coefficient P. The calculated edge degree E is calculated.

[0014]

(Equation 1)

A standard deviation detecting unit 105 convolves and integrates a read signal of 3 × 5 pixels by a standard deviation filter of 3 × 5 in the main scanning direction and further multiplies by a coefficient Q to obtain a standard deviation (roughness). Calculate S.

Then, the discriminating section 106 judges as follows, and the filter selecting section 107 selects a filter of the arithmetic section 101 based on the result.

When reference value <E <S: an edge enhancement filter When reference value <S <E or S <reference value <E: a smoothing filter S <E <reference value or E <S <reference value: no processing is performed According to such a configuration, a flatter and smoother image can be obtained in a flat portion of the image, and an image with higher sharpness can be obtained in the edge portion. Further, when it is desired to determine a reference set value based on an image signal of a specific portion of a document, especially when the document is a reprint of a printed matter having a small number of halftone dots or a copy document, the roughness of the solid uniform portion ( (Granularity) can be reduced.

Next, the configuration of a full-color copying machine to which the present invention is applied will be described with reference to FIG. The original on the original platen 1 is illuminated by a fluorescent lamp 10, converted into a color image signal by a color-magnification CCD 8, applied to an IPU (image processing unit) unit 12, and processed by the IPU unit 12 for Y, M, and C. , And Bk, a color image is printed out on paper by the color printer shown in FIG. The paper is fed from the manual feed tray 13 and the cassette 14 and is conveyed from right to left in the drawing, and the photosensitive drums 15 for Bk, Y, M and C are moved along the conveyance direction.
Bk, 15Y, 15M, 15C and a fixing device 16 are arranged.

The four types of image data of Y, M, C, and Bk are scanned in the main scanning direction by two systems of writing devices, and are respectively exposed to the photosensitive drums 15Bk, 15Y, 15M, and 1M.
A latent image of that color is formed on 5C. That is, the laser beam corresponding to the image data of Bk or C is emitted from a common first laser diode (not shown) and scanned by the common first polygon mirror 17a, and the mirror group is used to scan the photosensitive drum 15Bk or 15C. Is reflected by Also, M
Alternatively, a laser beam corresponding to the image data of C is emitted from a common second laser diode (not shown), scanned by a common second polygon mirror 17b, and reflected by the mirror group onto the photosensitive drum 15Y or 15M. You.

The photosensitive drums 15Bk, 15Y, 15M, 1
5C rotates in the sub-scanning direction (clockwise direction), around which a developing device 18 for developing a latent image in each color is used.
Is provided. Photosensitive drums 15Bk, 15Y, 15
The toner images developed on M and 15C are transferred so as to be superimposed on the conveyed paper, and as a result, a color image is printed out on the paper, and this toner image is fixed by the fixing device 16. .

[0021]

As described above, according to the first aspect of the present invention, a preset reference value <edge size E <
Edge enhancement is performed when the image roughness is S, and smoothing is performed when the reference value <S <E or S <reference value <E,
Since the processing is not performed in the case of S <E <reference value or E <S <reference value, it is possible to improve the image quality by reducing the roughness due to the edge enhancement processing.

According to the second aspect of the present invention, a density patch developed by developing a fixed developing potential having a full exposure amount of 50% or less is transferred and fixed onto a transfer sheet, and the transfer sheet is read by a scanner. Since the reference value obtained by processing the standard deviation is used, roughness due to edge enhancement processing can be reduced and image quality can be improved.

According to the third aspect of the present invention, since the reference value obtained by calculating the standard deviation based on a part of the image read from the user's original is used, the image quality can be improved regardless of the image quality of the user's original. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an MTF correction device according to the present invention.

FIG. 2 is an explanatory diagram showing filters that respectively perform an edge emphasizing process, a smoothing process, and a non-process of an arithmetic unit in FIG. 1;

FIG. 3 is an explanatory diagram illustrating an example of an image.

FIG. 4 is a configuration diagram showing a copying machine to which the MTF correction device of FIG. 1 is applied.

[Explanation of symbols]

 Reference Signs List 101 calculation unit 102 reference value setting circuit 103 reference value register 104 edge detection unit 105 standard deviation detection unit 106 determination unit 107 filter selection unit

Claims (3)

[Claims] 1. An image processing apparatus comprising: edge enhancement processing means for performing edge enhancement processing on image data; smoothing processing means for performing smoothing processing on image data; image processing means for outputting image data as it is; First to detect edge size E
A second detection means for detecting the degree of roughness S of the image based on the standard deviation of the image data; and selecting an output of the edge enhancement processing means when a predetermined reference value <E <S And selecting the output of the smoothing processing means when reference value <S <E or S <reference value <E,
Selecting means for selecting the output of the image processing means when S <E <reference value or E <S <reference value
Correction device. 2. The reference value is obtained by transferring and fixing a density patch developed with a constant development potential having a full exposure amount of 50% or less on transfer paper, reading the transfer paper with a scanner, and standard deviation of the read value. 2. The MTF correction device according to claim 1, wherein the value is obtained by processing. 3. The MTF correction device according to claim 2, wherein the reference value is a value obtained by calculating a standard deviation based on a part of an image of a document read by a user.