JPH05324826A - Image processor - Google Patents

Abstract

PURPOSE:To reduce deterioration in picture quality by reducing moire without deteriorating the sharpness of an image and also suppressing emphasis on the moire due to edge emphasis. CONSTITUTION:This image processor consists of a separation part (1st smoothed value calculating means and difference value calculating means) 301 which calculates the means value (smoothed value) the inverse of D of local image data of input image data D, calculates the difference value DELTAD between the means value the inverse of D and image data D, and separately outputs the means value D' and difference value DELTAD, a difference value correction part 302 which corrects the difference value DELTAD outputted from the separation part 301, a means value correction part (2nd smoothed value calculating means) 303 which corrects the mean value the inverse of D outputted from the separation part 301 by further averaging it, and a composition part 304 which puts the corrected amplitude value the inverse of DELTAD outputted from the difference value correction part 301 and the corrected means value the inverse of D outputted from the means value correction part 303 together.

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 applied to a digital copying machine, a facsimile machine, an image scanner, an image printer, etc., and more specifically, to correct or convert image data in image processing. The present invention relates to an image processing apparatus for improving image quality, and particularly for improving image quality by reducing moire with respect to a halftone image original or the like.

[0002]

2. Description of the Related Art Conventionally, in an image processing apparatus which decomposes a document image into pixels and processes the density of each pixel as multi-tone image data, when a halftone image or the like is processed, the document image is decomposed into pixels. It is known that due to the interference between the sampling frequency and the halftone dot frequency (both spatial frequencies) of the original image, a repetitive pattern (so-called moire) peculiar to the reproduced image is generated and the image quality is deteriorated. Has been.

FIG. 6 is an explanatory diagram showing a state of image data when a halftone image having a uniform darkness is read. Each section indicates a pixel, and a numerical value in the section indicates a gradation value. As shown in the figure, it is difficult to recognize the presence of moire when viewed locally, but it is possible to clearly recognize the presence when viewed in a wide range. Further, as shown in FIG. 6, the main scanning direction x, in which the MTF deterioration during reading is relatively small, tends to stand out more than the sub scanning direction y.

It is known that the moire can be reduced by a known technique for locally smoothing image data.

[0005]

However, according to the conventional image processing apparatus, if the moiré is reduced by simply executing the smoothing process, the sharpness of the edge portion of the image is also lost due to the smoothing. Therefore, there is a problem in that the contrast of a line drawing portion such as characters is deteriorated due to blurring and the image quality is deteriorated.

Further, the image processing apparatus generally performs image processing for enhancing edges (that is, high-frequency components) such as MTF correction. At this time, however, moiré is also enhanced, so that image quality due to moiré is enhanced. There is also a problem that it further accelerates the deterioration of.

The present invention has been made in view of the above, and reduces the moiré without degrading the sharpness of the image and suppresses the moiré enhancement by the edge enhancement, thereby reducing the degradation of the image quality. The purpose is to

[0008]

In order to achieve the above object, the present invention is an image processing apparatus that decomposes an original image into pixels and processes the density of each pixel as multi-tone image data. , And a first smooth value calculating means for calculating a smooth value in the peripheral portion of the pixel, and a difference value calculating means for calculating a difference value between the smooth value calculated by the first smooth value calculating means and the image data, Second smooth value calculating means for calculating the smooth value of the smooth value calculated by the first smooth value calculating means, smooth value calculated by the second smooth value calculating means, and difference value calculating means An image processing apparatus including a combining unit that combines the difference values is provided.

In order to achieve the above-mentioned object, the present invention is an image processing apparatus for decomposing a document image into pixels and processing the density of each pixel as multi-tone image data. Smoothing value calculating means for calculating a smoothing value in the peripheral portion of the, a difference value calculating means for calculating a difference value between the smoothing value calculated by the smoothing value calculating means and the image data, and a difference value calculated by the difference value calculating means The present invention provides an image processing apparatus comprising: a difference value correcting unit that corrects the difference value; and a combining unit that combines the difference value corrected by the difference value correcting unit and the smoothed value calculated by the smoothed value calculating unit.

In order to achieve the above object, the present invention is an image processing apparatus which decomposes an original image into pixels and processes the density of each pixel as multi-tone image data. A smoothing value calculating means for calculating a smoothing value in the peripheral portion, a difference value calculating means for calculating a difference value between the smoothing value calculated by the first smoothing value calculating means and the image data, and a difference value calculating means Difference value correction means for correcting the difference value calculated by the above, second smooth value calculation means for calculating the smooth value of the smooth value calculated by the first smooth value calculation means, and second smooth value calculation means The image processing apparatus is provided with a smoothing value calculated by the above and a synthesizing means for synthesizing the difference value corrected by the difference value correcting means.

[0011]

The image processing apparatus according to the present invention calculates the smoothed value (average value) of the image data in the pixel of interest and the peripheral portion of the pixel, calculates the difference value between the average value and the image data, and calculates the average value. Further averaging is performed, and the averaged average value and the difference value are combined.

Further, the image processing apparatus according to the present invention calculates a smoothed value (average value) of image data in a pixel of interest and a peripheral portion of the pixel, calculates a difference value between the average value and image data, and calculates The corrected difference value is corrected, and the corrected difference value and the average value are combined.

Further, the image processing apparatus according to the present invention calculates a smoothed value (average value) of image data in a pixel of interest and a peripheral portion of the pixel, calculates a difference value between the average value and image data, and further The calculated difference value is corrected, the average value is further averaged, and the averaged average value and the corrected difference value are combined.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a perspective view of a digital copying machine 100 to which this embodiment is applied. As shown in the figure, an operation panel 101 and a document table 102 are arranged on the upper part of the device,
On the side surface of the apparatus, paper feed cassettes 103 and 104 in which recording paper of each size is set, and a paper ejection tray 105 from which recording paper on which an image is formed are ejected are arranged. A document (not shown) set on the document table 102 is read by being decomposed into pixels of 400 dpi by a CCD line sensor (not shown). Reading in the main scanning direction is performed by the light of one line of the original entering the CCD line sensor, and reading in the sub scanning direction is performed by moving a scanner (not shown) with respect to the original.

FIG. 2 is a block diagram showing a schematic configuration of a control system of the digital copying machine 100. An image reading unit 201 for reading an original image and a moire correction for image data output from the image reading unit 201. An image processing unit 202 that executes various image processes including an image writing unit 203 using an electrophotographic method that drives a laser using image data output from the image processing unit 202 and outputs an image on a recording sheet.
And a control unit 204 that controls the entire apparatus.

The operation of the above configuration will be described. The image reading unit 201 uses a scanner, a CCD line sensor, or the like to read an original image placed on the original table 102.
The image data output from the CCD line sensor is amplified by A / A
Processing such as D conversion is performed. As a result, the image data is output to the image processing unit 202 as image data quantized into 6 bits (that is, 64 gradations).

The image processing unit 202 converts the input image data from white to gradation value 0 and black into gradation value 63, shading correction, halftone processing,
In addition to image processing such as requantization processing and MTF correction, moire correction according to this embodiment is executed. The image data that has been subjected to these image processes is output to the image writing unit 203.

The image writing unit 203 writes an image at 400 dpi on a photoconductor (not shown) by driving a laser using the image data input from the image processing unit 202. The electrostatic latent image formed on the photoconductor is subjected to development processing, transfer processing, fixing processing, etc., and a reproduced image is output on the recording paper.

FIG. 3 is a block diagram showing a schematic configuration of the moiré correction unit 300 which performs moiré correction in the image processing unit 202 shown in FIG. As illustrated, the moire correction unit 300 calculates an average value (smooth value) bar D of local image data of the input image data D, and calculates a difference value ΔD between the average value bar D and the image data D. , A mean value bar D, a separation unit 301 for separating and outputting the difference value ΔD, and a separation unit 3
01, the difference value correction unit 302 that corrects the difference value ΔD, the average value correction unit 303 that corrects the average value bar D output from the separation unit 301, and the correction difference output from the difference value correction unit 302 A combining unit 30 that combines the value ΔD ′ and the corrected average value bar D ′ output from the average value correction unit 303.
4 and.

The operation of the above configuration will be described. The separating unit 301, as shown in FIG. 4, includes latches 401 to 407 that hold 6-bit image data, image data D, and image data D ₁ that each latch 401 to 407 holds.
~ Average value calculator 408 for calculating average value bar D of D ₇
And a subtractor 409 for calculating the difference value ΔD between the image data D ₃ and the average value bar D. CK in the figure is a pixel clock synchronized with the transfer of the image (pixel) data D in the main scanning direction x. Therefore, each latch 401-
The average value calculator 407 holds the image data D _{1 to} D ₇ of ₇ pixels in which the arrangement in the main scanning direction x is continuous.
The output value of 08 is the average value of the continuous image data of 8 pixels. Equation 1 shows the formula for calculating the average value bar D.

[0021]

[Equation 1]

The subtractor 409 subtracts the average value bar D from the image data D ₃ , that is, the difference value ΔD of the image data D is calculated. Here, in FIG. 4, the difference value ΔD is the difference value (ΔD = D ₃ −bar D) of the image data D ₃ , but this expression will be used hereinafter to avoid confusion.

The difference value correction unit 302 corrects the difference value ΔD by using the formula shown in Equation 2 in order to suppress the periodic fluctuation of the image data D due to moire. The difference value correction unit 302
The value of the correction difference value ΔD ′ corresponding to the difference value ΔD calculated by the equation 2 is stored in advance in the ROM (not shown), and when the difference value ΔD is input to the ROM, the difference from the ROM is calculated. A correction difference value ΔD ′ corresponding to the value ΔD is output.

[0024]

[Equation 2]

The average value correction unit 303 outputs a corrected average value bar D ′ obtained by correcting the average value bar D input from the separation unit 301. The correction of the average value bar D is, as shown in Equation 3,
The average value of the eight consecutive image data D output from the separating unit 301 (bars D ₀ to D ₇ ) is calculated,
This is performed by setting the average value as a corrected average value bar D '. Therefore, the configuration is substantially the same as that of the separating unit 301. Further, in Expression 3, the smaller the numerical value of the subscript, the more the average value bar D is newly output.

[0026]

[Equation 3]

The synthesizing unit 304 synthesizes the corrected difference value ΔD ′ output from the difference value correction unit 302 and the corrected average value bar D ′ output from the average value correction unit 303. Specifically, the correction difference value ΔD ′ is added to the correction average value bar D ′ to combine them, and the combined data is output as image data after moiré correction (corrected image data D ′).
Therefore, the combining unit 304 is composed of an adder.

FIGS. 5A and 5B are explanatory views showing the execution results of the moire correction processing according to this embodiment. Figure 5
As shown in (a), the image data D fluctuates greatly in the main scanning direction x, and the periodic fluctuation of the average value bar D of the image data is not small. However, as shown in FIG. 5B, when the average value bar D is corrected, that is, averaged over a wider pixel range, the periodic fluctuation of the average value (that is, the corrected average value bar D ′) is small. When the difference value ΔD is corrected, the periodic fluctuation of the difference (amplitude) is also reduced. Therefore, by synthesizing (adding) the correction average value bar D ′ and the correction difference value ΔD ′, it is possible to reduce the periodic fluctuation of the image data due to the moire and suppress the deterioration of the image quality. Further, even when edge enhancement such as MTF correction is performed, the periodic fluctuation of the image data is reduced, so that the enhancement of moire can be suppressed and the deterioration of image quality can be reduced. Here, in the present embodiment, the reason why the calculation of the average value bar D is the image data of the pixels in which the arrangement in the main scanning direction x is continuous is that moire tends to be noticeable in the main scanning direction. This is to reduce the moire in.

As described above, moire can be reduced without performing the image smoothing process, that is, without deteriorating the sharpness of the image, and the degradation of the image quality can be reduced. Further, since the processing is performed using the image data that is continuously transferred, real-time processing can be easily performed, and there is an advantage in terms of processing time. Further, since the device can be realized with a simple structure, there is an advantage that an increase in the cost of the device can be suppressed.

As another embodiment, the difference value correction unit 302 may be omitted from the moire correction unit 300 of this embodiment, and the correction average value bar D'and the difference value ΔD may be combined. .. Even at this time, since the periodic fluctuation of the corrected average value bar D ′ is minute, the periodic fluctuation of the combined image data D ′ can be reduced,
It is possible to reduce moire generated in a reproduced image.

The average value correction unit 303 is omitted from the moiré correction unit 300 of this embodiment, and the average value bar D '
And the correction difference value ΔD ′ may be combined. Even at this time, since the periodic variation of the correction difference value ΔD ′ is reduced, the periodic variation of the combined image data D ′ can be reduced, and the moire generated in the reproduced image can be reduced. Wear.

Further, in the present embodiment, the moire correction is carried out by using the image data of the continuous pixels in the main scanning direction, but it may be carried out by using the image data of the continuous pixels in the sub scanning direction. Moire correction may be performed simultaneously in both the scanning direction and the sub-scanning direction. Further, in the present embodiment, the average value is corrected to be the average value (smooth value) of image data of continuous pixels in a wider range.
For example, the correction method of the difference value may be applied to correct the average value. Further, the method of correcting the difference value is not limited to the method of the present embodiment, and for example, a value set in advance corresponding to the difference value may be added (or subtracted), and output in the previous time. The difference value output this time may be corrected in consideration of the calculated difference value.

In this embodiment, moire correction is performed using digital image data, but analog image data (real time processing at this time) can be easily performed. Even at this time, the device can be realized with a simple configuration and low cost. Further, the moiré correction according to the present invention may be performed by using a program. At this time, for example, the range of the average value (bar D) is set to perform the moiré correction in consideration of noise on the image. You can also

Further, for example, the image data is divided using a certain threshold value, and the divided image data is corrected according to a preset method so that the difference value in this embodiment is corrected. Correction can also be performed. In this case, the device can be realized with a simpler configuration and at lower cost, and real-time processing can be further facilitated.

[0035]

As described above, according to the present invention, in an image processing apparatus that decomposes an original image into pixels and processes the density of each pixel as multi-tone image data, the pixel of interest and the peripheral portion of the pixel. In the first smooth value calculating means, a difference value calculating means for calculating a difference value between the smooth value calculated by the first smooth value calculating means and the image data, and a first smooth value calculating means. Second smoothing value calculating means for calculating a smoothing value of the smoothing value calculated by: and a combining means for combining the smoothing value calculated by the second smoothing value calculating means and the difference value calculated by the difference value calculating means With the above, it is possible to reduce the deterioration of the image quality by reducing the moire without deteriorating the sharpness of the image and suppressing the emphasis of the moire by the edge emphasis processing.

Further, as described above, according to the present invention, in the image processing apparatus which decomposes the original image into pixels and processes the density of each pixel as multi-tone image data, the pixel of interest and the peripheral portion of the pixel. Smoothing value calculating means for calculating a smoothing value, a difference value calculating means for calculating a difference value between the smoothing value calculated by the smoothing value calculating means and the image data, and a difference value calculated by the difference value calculating means. Since the difference value correcting means and the combining means for combining the difference value corrected by the difference value correcting means and the smooth value calculated by the smooth value calculating means are provided, moire can be reduced without degrading the sharpness of the image. Moreover, by suppressing the moire enhancement due to the edge enhancement processing, it is possible to reduce the deterioration of the image quality.

Further, as described above, according to the present invention, in the image processing apparatus which decomposes the original image into pixels and processes the density of each pixel as multi-tone image data, the pixel of interest and the peripheral portion of the pixel are processed. In the first smooth value calculating means, a difference value calculating means for calculating a difference value between the smooth value calculated by the first smooth value calculating means and the image data, and a difference value calculating means. Difference value correction means for correcting the difference value, second smooth value calculation means for calculating the smooth value of the smooth value calculated by the first smooth value calculation means, and second smooth value calculation means. Since the smoothing value and the difference value corrected by the difference value correcting means are combined with each other, the moire is reduced without deteriorating the sharpness of the image and the enhancement of the moire by the edge emphasis processing is suppressed. It makes it possible to reduce the deterioration of image quality.

[Brief description of drawings]

FIG. 1 is a perspective view showing a digital copying machine to which this embodiment is applied.

FIG. 2 is a block diagram showing a schematic configuration of a control system of a digital copying machine to which this embodiment is applied.

FIG. 3 is a block diagram showing a schematic configuration of a moire correction unit according to the present embodiment.

FIG. 4 is a circuit diagram showing a configuration of a separation unit according to this embodiment.

FIG. 5 is an explanatory diagram showing a state of image data when moiré correction according to the present embodiment is executed.

FIG. 6 is an explanatory diagram showing a state of image data when a halftone image having a certain darkness is read.

[Explanation of symbols]

202 Image processing unit 300 Moiré correction unit 301 Separation unit 302 Difference value correction unit 303 Average value correction unit 304 Compositing unit 401 to 407 Latch 408 Average value calculator 409 Subtractor

Claims (3)

[Claims] 1. An image processing apparatus for decomposing an original image into pixels and processing the density of each pixel as multi-gradation image data, the first value for calculating a smoothed value in a target pixel and a peripheral portion of the pixel. Smoothing value calculating means, difference value calculating means for calculating a difference value between the smoothing value calculated by the first smoothing value calculating means and the image data, and the smoothing value calculated by the first smoothing value calculating means. A second smoothing value calculating means for calculating a smoothing value; and a combining means for combining the smoothing value calculated by the second smoothing value calculating means and the difference value calculated by the difference value calculating means. An image processing device characterized by. 2. An image processing apparatus for decomposing a document image into pixels and processing the density of each pixel as multi-tone image data, a smooth value calculation for calculating a smooth value in a pixel of interest and a peripheral portion of the pixel. Means, difference value calculation means for calculating a difference value between the smooth value calculated by the smooth value calculation means and the image data, difference value correction means for correcting the difference value calculated by the difference value calculation means, and An image processing apparatus comprising: a difference value corrected by the difference value correcting means and a combining means for combining the smoothed value calculated by the smoothed value calculating means. 3. An image processing apparatus for decomposing an original image into pixels and processing the density of each pixel as multi-gradation image data, wherein a first smoothing value is calculated for a target pixel and a peripheral portion of the pixel. Smoothing value calculating means, difference value calculating means for calculating a difference value between the smoothing value calculated by the first smoothing value calculating means and the image data, and difference for correcting the difference value calculated by the difference value calculating means Value correcting means, second smoothing value calculating means for calculating a smoothing value of the smoothing value calculated by the first smoothing value calculating means, smoothing value calculated by the second smoothing value calculating means, An image processing apparatus, comprising: a combining unit that combines the difference values corrected by the difference value correcting unit.