JPH10271339A - Image-processing method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfactorily suppress deterioration of image quality and to remove moires, without deteriorating edges of the image. SOLUTION: A main signal S is guided to a smoothing processing part 10 and a filter calculation part 50. An average density value is guided in a region larger than dot size regarding plural neighboring pixels of a pixel under consideration in the smoothing processing part 10. Contrasts in the vertical and horizontal directions are calculated in a vertical direction contrast extracting part 21 and a horizontal direction contrast extracting part 22, and reference values IDy, IDx are outputted based on the obtained contrasts in a vertical direction table reference part 31 and a horizontal table reference part 32. A set of weighting coefficients of an image filter is selected, based on the reference values IDy, IDx in a weighting coefficient set selecting part 40. Then an arithmetic operation is performed, based on each weighting coefficient of the image filter obtained in the weighting coefficient set selecting part 40 and a filtered signal S' is selected in a filter operation part 50.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for processing digital images obtained from a scanner, a digital camera, or another device.

[0002]

2. Description of the Related Art Conventionally, when a printed matter is generated, printing using halftone dots has been performed. Such a printed matter printed by halftone dots is, for example, 65 dpi to 200 dpi.
It has a resolution of about i.

FIG. 9 shows a case where a printed matter recorded with such halftone dots is read by an image input unit such as a scanner. FIG. 9 is a diagram showing a positional relationship between a halftone dot and a pixel to be read, and a halftone image as an original image has a density of 50%. That is, the hatched area shown in the figure is a part where the halftone dot is recorded. A case where such an original image is read by pixels P1 to P8 having a size indicated by a dotted frame will be described.

The size of one pixel shown in FIG. 9 is about 87.5% of the size of one halftone dot. In such a case, the density measured at the pixels P4 and P5 is 50%, which is equal to the density shown in the original image, so that the consistency is maintained, but the density measured at the pixels P1 and P8 is the pixel area. Contains a large number of blackened areas of halftone dots, so that it is larger than 50%. In practice, the density of pixels P1 and P8 is about 6
It is 2%. Pixels P2, P3, P6, P7
Are also greater than 50%. Thus, the density measured at the pixels P1,..., P8 periodically fluctuates between 50% and about 62%. This means that the image quality is degraded considering that the original image has a density of 50%.

This is because interference occurs because the halftone dot size of the original image and the pixel size to be read are different. Therefore, as the pixel size becomes smaller than the halftone dot size, the density of the halftone dot is read rather than the density of the original image, and the fluctuation of the density between pixels becomes larger. Further, when the pixel size is close to the halftone dot size, for example, the period of the change becomes long and becomes visually noticeable as moire.

The above phenomenon also occurs when the relationship between the pixel size and the pattern in the general original image or the pattern of the subject expressed by a method other than the halftone dot is the same as described above. That is, moire may occur in an image obtained by reading a transparent original or a reflective original with a scanner or an image obtained by a digital camera.

[0007] Conventionally, image processing using an image filter has been performed in order to remove such moiré and prevent deterioration in image quality.

FIG. 10 is a schematic configuration diagram of a conventional image processing apparatus. A main signal S for a pixel to be processed (hereinafter, referred to as a “pixel of interest”) is subjected to a filter operation by an image filter of a predetermined size set in advance by a filter operation unit 400, and a filtered signal S ′ is obtained. Generated. FIG. 11 shows an example of an image filter used at this time. In such a conventional image processing apparatus, the horizontal size and the vertical size of the image filter are set to be about twice or more of each halftone dot. Therefore, for example, in the case of the example of the image filter in FIG. 11, the size of one pixel is about "2/5" or more of the halftone dot size. In the conventional image processing apparatus, the filter operation unit 400 positions the center of the image filter at the target pixel, performs a weighted average of each density value based on the weighting coefficient assigned to the target pixel and its neighboring pixels, and performs filtering. The signal is output as a signal S '.

As described above, in the conventional image processing apparatus, by performing processing using an image filter as shown in FIG. 11, a weighted average of densities is obtained in an area (about twice) larger than a halftone dot size. The frequency component of the halftone dot pattern can be removed, and the influence of the halftone dot size can be eliminated. Therefore,
Moiré does not occur and the image quality does not deteriorate in the image subjected to the filter processing.

[0010]

Generally, an edge portion of a printed image recorded with halftone dots is reproduced at a resolution higher than the halftone dot size. FIG. 12 is an explanatory diagram showing a conventional method for generating one halftone dot. As shown in FIG. 12A, an area indicating one dot size is divided into four blocks B1,..., B4, and each block is further subdivided for each blackened area. Then, a corresponding threshold value is set in each blackened area as shown in FIG. On the other hand, as shown in FIG. 12B, the density value obtained by reading the original image
1, the position corresponding to B4 is "20", and the block B
When the position corresponding to B2 and B3 is "10", blackening is performed sequentially from the center of the halftone dot in comparison with the threshold value shown in FIG. Then, a halftone dot as shown in FIG. 12C is recorded.

FIG. 13 shows a case where an edge portion of an image is recorded by such a recording method. FIG. 13 is a diagram showing an edge portion of the halftone dot image, and a dotted line in the drawing is an edge of the image. The right side of the dotted line indicates 50% density, and the left side indicates 0% density. As shown in FIG. 13, since the halftone dot is recorded in the edge portion of the halftone dot image in accordance with the density value corresponding to each of the four divided blocks, the reproduction is performed at a high resolution.

However, in a conventional image processing apparatus, when smoothing is performed using an image filter as shown in FIG. 11 as a countermeasure against moiré and image quality deterioration, the edge of an image reproduced at a high resolution as described above is obtained. The part is also smoothed,
There is a problem of blurring.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an image processing method and apparatus capable of satisfactorily suppressing image quality deterioration and removing moire without deteriorating image edges. The purpose is to do.

[0014]

According to an aspect of the present invention, there is provided a method for performing a predetermined process for each pixel on an original image. Obtaining a mean density value for each of the plurality of neighboring pixels by performing a smoothing process on each of the plurality of neighboring pixels located in the vicinity of a certain pixel of interest in a predetermined area around the neighboring pixel; (B) determining a contrast for the pixel of interest based on a plurality of average density values obtained from a plurality of neighboring pixels; and (c) determining a weighting coefficient assigned to each component of the image filter according to the contrast. And (d) generating an output signal by performing a filter operation on the main signal of the target pixel using an image filter to which the weighting coefficient has been applied.

According to a second aspect of the present invention, there is provided a method for performing a predetermined process for each pixel on an original image obtained by reading a halftone dot document, wherein (a) By performing a smoothing process on each of a plurality of neighboring pixels located in the vicinity in a predetermined area larger than the individual halftone dot size constituting the halftone document around the neighboring pixel, A step of obtaining an average density value for each of the neighboring pixels, (b) a step of obtaining a contrast for the pixel of interest based on a plurality of average density values obtained from the plurality of neighboring pixels, and (c) according to the contrast Determining a weighting factor assigned to each component of the image filter, and (d) performing a filter operation on the main signal of the pixel of interest using the image filter to which the weighting factor has been applied to generate an output signal. It has a step of,
The size of the image filter applied in the step (d) is characterized in that it is larger than the size of each halftone dot constituting the halftone original.

According to a third aspect of the present invention, in the method according to the first or second aspect, the step (b) comprises a plurality of directions different from each other based on a plurality of average density values obtained from a plurality of neighboring pixels. The step (c) is characterized in that the step (c) includes a step of changing distributions of effective weighting coefficients in a plurality of directions according to the contrasts in the plurality of directions.

According to a fourth aspect of the present invention, there is provided an apparatus for performing a predetermined process on an original image for each pixel, wherein (a) each of a plurality of neighboring pixels located near a pixel of interest to be processed; A means for obtaining an average density value for each of the plurality of neighboring pixels by performing a smoothing process on a predetermined area around the neighboring pixels, and (b) a plurality of pixels obtained from the plurality of neighboring pixels. (C) means for determining a weighting coefficient assigned to each component of the image filter in accordance with the contrast, and (d) an image to which the weighting coefficient is applied. Means for performing a filter operation on the main signal of the pixel of interest using a filter to generate an output signal.

According to a fifth aspect of the present invention, there is provided an apparatus for performing a predetermined process for each pixel on an original image obtained by reading a halftone dot original, wherein (a) By performing a smoothing process on each of a plurality of neighboring pixels located in the vicinity in a predetermined area larger than the individual halftone dot size constituting the halftone document around the neighboring pixel, Means for calculating an average density value for each of the neighboring pixels, (b) means for determining the contrast of the pixel of interest based on a plurality of average density values obtained from the plurality of neighboring pixels, and (c) according to the contrast Means for determining a weighting coefficient assigned to each component of the image filter, and (d) performing a filter operation on the main signal of the pixel of interest using the image filter to which the weighting coefficient has been applied to generate an output signal. And a means for,
The size of the image filter applied by the means (d) is larger than the size of each halftone dot constituting the halftone original.

According to a sixth aspect of the present invention, in the device according to the fourth or fifth aspect, the means (b) includes a plurality of directions different from each other based on a plurality of average density values obtained from a plurality of neighboring pixels. And means (c) for changing distributions of effective weighting coefficients in a plurality of directions according to the contrasts in the plurality of directions.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

<1. Overall Configuration of Apparatus> First, an example of the overall configuration of an apparatus to which an embodiment of the present invention is applied will be described. FIG. 1 is a schematic diagram showing an overall configuration of an apparatus to which an embodiment of the present invention is applied. The image input unit 100 optically reads a document, such as an input scanner, and generates original image data indicating a multi-value density value for each pixel. Then, the generated original image data is transferred to the image processing unit 200. The image processing unit 200 is a processing unit to which the image processing device according to the embodiment of the present invention is applied. In the image processing unit 200, in addition to the image processing using the image filter according to the embodiment of the present invention, after performing predetermined processing on the original image data, the image output unit 300 such as an output scanner or the like is used. Is output to And the image output unit 30
At 0, recording is performed on a recording medium such as a film. In order to cause the image input unit 100, the image processing unit 200, and the image output unit 300 to perform desired operations of the operator, an operation input unit 201 such as a keyboard and a mouse and an information display unit 202 such as a display unit are provided. Are provided.

<2. Outline of Image Processing> Next, a processing mode in an image processing apparatus according to an embodiment of the present invention will be described. In the image processing device according to the embodiment of the present invention, image processing using an image filter is performed. That is, a process such as image smoothing is performed by scanning an M × N (M, N is an odd number of 3 or more) matrix image filter in the image plane.

FIG. 2 is an explanatory diagram showing an outline of image processing in the embodiment of the present invention. The image I shown in FIG. 2A is sequentially processed while scanning the target pixel OP pixel by pixel with the X direction (horizontal direction) as the main scanning direction and the Y direction (vertical direction) as the sub-scanning direction. I will go. At the time of processing by the image filter, the target pixel OP is positioned at the center of the image filter F as shown in FIG. FIG.
In the example of (b), a 5 × 5 (M = N = 5) matrix image filter is used. Then, based on the weighting coefficient assigned to each component of the image filter, a weighted average of the density value of the target pixel OP and the density values of the neighboring pixels is derived by calculation, and the obtained value is calculated as the filtered signal of the target pixel OP. I do.

[0023] That is, image filter F is the size of the matrix as shown in FIG. 3 (2m + 1) × ( 2n + 1), the weighting coefficient of each component k _-mn to k _mn is assigned . A filtered signal S ′ _xy obtained by performing a filter operation on the pixel of interest OP located at the coordinates (x, y) on the image plane using the image filter F is

[0024]

(Equation 1)

## EQU1 ## Here, S _xy is the density value of the pixel located at the coordinates (x, y) on the image plane of the original image.

In the image filter shown in FIG.
When all the weighting coefficients corresponding to the target pixel and its neighboring pixels are positive numbers, it is an image filter for performing image smoothing, and the frequency characteristic of the weighting coefficient is the characteristic of the image filter.

<3. Image Processing Apparatus> Next, an image processing apparatus according to an embodiment of the present invention will be described. FIG.
1 is a schematic configuration diagram illustrating an image processing apparatus according to an embodiment of the present invention. The main signal S, which is the density value of the pixel of interest, is guided to the smoothing processing unit 10 and the filter operation unit 50.

When the main signal S for the pixel of interest is input to the smoothing processing unit 10, the smoothing process is performed for pixels near the pixel of interest to obtain an average density value. The neighboring pixels of the target pixel for which the average density value is to be obtained can be, for example, four neighboring pixels such as an upper neighboring pixel, a lower neighboring pixel, a left neighboring pixel, and a right neighboring pixel. Then, as shown in FIG. 5A, pixels P1, P2, P3, and P4 located on the upper, right, lower, and left sides of the target pixel are upper neighboring pixels, respectively. The pixel P may be a right neighboring pixel, a lower neighboring pixel, or a left neighboring pixel. However, as shown in FIG.
5, P6, P7, and P8 may be upper neighboring pixels, right neighboring pixels, lower neighboring pixels, and left neighboring pixels, respectively.

Then, these upper neighboring pixels, right neighboring pixels,
For each of the lower neighboring pixel and the left neighboring pixel, a smoothing process is performed in a region (smoothing region) larger than the halftone dot size centered on each neighboring pixel. The reason why the smoothed area is set to be an area larger than the halftone dot size is to prevent the halftone dot shape from being detected, by using pixels near the center position of the halftone dot and pixels that are not so.
This is to prevent the density values from largely differing and to obtain the density value indicated by the original original image.

In the smoothing process performed here, the density values of pixels located in the smoothed area are simply averaged,
Alternatively, it is performed by weighted averaging. The average density value of the upper neighboring pixels thus obtained is YU, the average density value of the lower neighboring pixels is YL, the average density value of the left neighboring pixels is XL, and the average density value of the right neighboring pixels is XR. And Then, the smoothing processing unit 10 sends the average density values YU, YL for the upper neighboring pixels and the lower neighboring pixels to the vertical contrast extracting unit 21, and calculates the average density values XL, XR for the left neighboring pixels and the right neighboring pixels. This is sent to the horizontal contrast extraction unit 22.

The vertical contrast extracting section 21 extracts the vertical (Y-direction) contrast in the sub-scanning direction near the target pixel of the image. That is, by using the average density values YU and YL for the input upper and lower neighboring pixels,

[0032]

(Equation 2)

Thus, the vertical contrast Cy is obtained.
Then, the obtained vertical contrast Cy is sent to the vertical table reference unit 31.

Similarly, the horizontal contrast extraction unit 22 extracts the contrast in the horizontal direction (X direction), which is the main scanning direction, near the target pixel of the image. That is, the average density value X for the input left neighboring pixel and the right neighboring pixel.
Using L and XR,

[0035]

(Equation 3)

Thus, the lateral contrast Cx is obtained.
Then, the obtained horizontal contrast Cx is sent to the horizontal table reference unit 32.

In general, a high contrast indicates an edge portion of an image, and a low contrast indicates a flat portion with a small change in density of the image. Therefore, by determining the vertical and horizontal contrasts as described above, it is possible to determine what portion of the image the pixel of interest is. In addition, since the smoothing processing is performed in the smoothing processing unit 10,
The edge of the halftone dot itself is not detected.

The vertical table reference section 31 includes a storage medium such as a memory therein, and refers to a table stored in advance therein to obtain a reference corresponding to the input vertical contrast Cy. Output the value IDy.

Similarly, the horizontal direction table reference section 32 also has a storage medium such as a memory inside, and refers to a table stored in advance therein, thereby obtaining a table.
Reference value I corresponding to input horizontal contrast Cx
Dx is output.

FIG. 6A is a diagram showing the relationship between the vertical contrast Cy as an input and the reference value IDy as an output in the vertical table reference section 31, and FIG. 6B is a view showing the horizontal table reference section 32. 5 is a diagram showing a relationship between a horizontal contrast Cx as an input and a reference value IDx as an output in FIG. The relationship between such input and output is stored in a memory or the like as a table. As shown in FIGS. 6A and 6B, the contrast C in the vertical direction and the horizontal direction is also large.
The smaller the values of y and Cx, the smaller the output values of IDy and IDx, and the higher the contrast, the higher the values of IDy and IDx. In other words, if the target pixel is an edge portion of the image, the values of IDy and IDx increase, and if the target pixel is a flat portion of the image, the values of IDy and IDx decrease. The IDy and IDx obtained by the vertical table reference unit 31 and the horizontal table reference unit 32 are sent to the weighting coefficient set selection unit 40.

As shown in FIG. 6A, the relationship between the reference value IDy in the vertical direction and the contrast Cy in the vertical direction is such that the reference value IDy increases by 1 each time the contrast Cy shows a substantially constant increase. On the other hand, in the reference value IDx in the horizontal direction shown in FIG. 6B, the value of “1” extends to near the middle value of the contrast, and the value of “2” has a high contrast. Extending to the area. That is, even if the contrast in the horizontal direction and the vertical direction is the same, the reference value IDx in the horizontal direction may be smaller than the reference value IDy in the vertical direction. This takes into account that, when the input scanner of the image input unit 100 optically reads a document, the nature of noise differs between the main scanning direction (horizontal direction) and the sub-scanning direction (vertical direction). For example, reading of a document by an input scanner in the main scanning direction is performed by a CCD line sensor in which a plurality of pixels are arranged in a straight line, and reading in the sub-scanning direction is performed by a driving mechanism such as a motor. An apparatus performed by moving at a speed will be described. In such a device,
In the sub-scanning direction, noise appears for each pixel, but in the main scanning direction, it is possible to electrically scale. In such a case, the noise included in one pixel expands in the main scanning direction. Shrink. If the noise extends in the main scanning direction, it is desirable to perform a smoothing process using a large-sized smoothing filter in the main scanning direction.
It is sufficient to output a small reference value IDx in the main scanning direction as shown in FIG.

However, when there is no expansion or contraction of noise in the main scanning direction, the contrast Cx for the reference value IDx in the horizontal direction is similar to the reference value IDy in the vertical direction in FIG.
The value of the reference value IDx may be increased by 1 each time the value indicates a substantially constant increase.

Next, in the weighting coefficient set selection section 40, the reference value ID sent from each table reference section
Image filter weighting coefficient k _-mn corresponding to y, _IDx
Selecting and determining the ~k _mn. A storage unit such as a memory is provided inside the weighting coefficient set selection unit 40,
The storage unit stores weighting coefficients corresponding to input reference values IDy and IDx. Each weighting coefficient selected and determined by referring to the storage unit is sent to the filter operation unit 50.

FIG. 7 is a diagram showing an example of an image filter obtained in the weighting coefficient set selecting section 40. As the value of the reference value IDy in the vertical direction increases, the weighting coefficient that moves away from the center of the image filter in the vertical direction decreases. That is, since the contrast is high in the vertical direction,
Since the image is determined to be an edge portion of the image, the area or degree of smoothing is reduced. Similarly, as the value of the reference value IDx increases, the weighting coefficient that moves away from the center of the image filter in the horizontal direction decreases. An edge portion of an image having a high contrast in the horizontal direction has a smaller region or degree of smoothing in the horizontal direction. It is clear from Equation 1 that the component having the weighting coefficient “0” assigned to the image filter is not a valid coefficient for the processing by the image filter.

For example, when the reference value IDy obtained by the vertical table reference unit 31 is “3” and the reference value IDx obtained by the horizontal table reference unit 32 is “1”, FIG. Is selected. This image filter F13 has a large area to be smoothed in the horizontal direction, but has a small area to be smoothed in the vertical direction. This is because the contrast in the vertical direction is large and the contrast in the horizontal direction is small. When the contrast is large in both the vertical and horizontal directions (IDy = 3, I
In the case of Dx = 3), the image filter F33 shown in FIG. 7 is applied, and the area to be smoothed becomes the smallest. As a result, deterioration of the edge portion of the image can be minimized. When the contrast is small in both the vertical and horizontal directions (when IDy = 1 and IDx = 1), the image filter F11 shown in FIG. 7 is applied, and the entire 5 × 5 region is smoothed.

The image filter shown in FIG. 7 shows a case where the size of the image filter is 5 × 5 as an example, but the present invention is not limited to this. However, the size of the image filter needs to be larger than the individual halftone dot size of the original image in order to satisfactorily remove the deterioration of the image quality and the occurrence of moire due to the halftone dot size. The size is preferably about twice or more.

The filter operation unit 50 performs the operation shown in Equation 1 based on each weighting coefficient sent from the weighting coefficient set selection unit 40 to generate a filtered signal S ′. The filtered signal S ′ is an output signal of the image processing device according to the present embodiment. When the filtered signal S 'is obtained in this manner, the processing for the pixel of interest has been completed. Then, similar processing is performed with the next pixel to be processed in the next scanning order as a target pixel. By repeating this, the process ends for the entire image.

Here, the data output from the weighting coefficient set selecting section 40 to the filter calculating section 50 may be a weighting coefficient of each component, but is not limited to this.

When a plurality of weighting coefficients are stored in a storage member such as a RAM in advance in the filter calculation section 50,
The weighting coefficient set selection unit 40 can be omitted. That is, the vertical table reference unit 31 and the horizontal table reference unit 32 determine the contrast C in each direction.
If the offset value of the address for accessing the RAM of the filter operation unit 50 is output as reference values IDy and IDx according to y and Cx, the filter operation unit 50 outputs the reference value ID
By accessing the RAM based on the offset values indicated by y and IDx, it is possible to directly obtain the respective weighting coefficients corresponding to the vertical and horizontal contrasts.

As described above, according to the image processing apparatus of this embodiment, an image filter which does not deteriorate the edge is applied to the edge portion of the original image, and a larger size is applied to the flat portion of the image. Since the image filter is applied, without deteriorating the edge of the image,
It is possible to satisfactorily suppress deterioration of image quality and remove moiré.

Further, since each weighting coefficient of the image filter to be applied is selected and determined based on the contrast between the vertical direction and the horizontal direction, the directionality of the edge of the original image can be detected, and the edge is stored. A simple image filter can be obtained. Therefore, it is possible to apply an image filter that preserves edges and suppresses moire and deterioration of image quality.

<4. Modification> The size of the image filter applied by the filter operation unit 50 shown in FIG. 4 needs to be larger than the halftone dot size of the original image in order to favorably remove the occurrence of moire and the deterioration of the image quality. That has already been explained. Therefore, if the halftone dot size of the original image is changed, it may be necessary to change the size of the image filter applied by the filter operation unit 50. Even in such a case,
In order to perform the processing appropriately, the following processing may be performed.

That is, the image input unit 100 (see FIG. 1)
If the halftone dot size can be detected when the original image is read, the detected halftone dot size is input to this image processing apparatus. Then, the weighting coefficient set selection unit 40 in the image processing apparatus may change the size of the image filter to an appropriate size when selecting the weighting coefficient. Further, when the dot size is changed, the operator may set and input the dot size from the operation input unit 201, and may input the set and input dot size to the image processing apparatus. With this configuration,
An image filter of an appropriate size is always applied according to an arbitrary halftone dot size, and the image processing apparatus can suppress the deterioration of the image quality without deteriorating the edge of the image regardless of the original image. And moire can be removed.

Next, the extraction of the contrast described in the embodiment is performed in two directions, that is, the vertical direction and the horizontal direction. However, it is more preferable to extract the contrast in the oblique direction. For example, it is preferable to extract the contrast of the target pixel in the diagonally right-up diagonal direction and the diagonally right-up diagonal direction, and when the contrast is large in each direction, apply an image filter so as to preserve the edge in that direction.

Further, the contrast may be obtained in directions other than the vertical, horizontal and oblique directions. That is, in general, the directions may be different from each other in an image filter having a two-dimensional spread.

Next, in the above description, the reference values IDy and IDx obtained by the vertical table reference section 31 and the horizontal table reference section 32 are, as shown in FIG. 6A and FIG. 1 ”,“ 2 ”, and“ 3 ”.
8 (a) and 8 (b) to obtain multi-level values of three or more values, and perform necessary calculations based on nine image filters as shown in FIG. An image filter may be derived. When such processing is performed, the accuracy of image processing increases.

The contents described above are not limited to the case where the original image is a halftone original recorded by halftone dots, and the same processing may be performed if moire or the like occurs in other images. Therefore, it is possible to satisfactorily suppress deterioration of image quality and remove moiré without deteriorating image edges. For example, the present invention is applicable to image processing of an image or the like obtained by a digital camera.

[0058]

As described above, according to the first aspect of the present invention, for each of a plurality of neighboring pixels located in the vicinity of a pixel of interest to be processed, a predetermined number of pixels around the neighboring pixel are determined. By performing the smoothing process in the area of, an average density value is obtained for each of the plurality of neighboring pixels, and the contrast of the target pixel is obtained based on the obtained average density values. Then, a weighting coefficient assigned to each component of the image filter is determined according to the contrast, a filter operation is performed on the main signal of the pixel of interest using the image filter to which the weighting coefficient is applied, and the output signal is calculated. Since the image is generated, it is possible to satisfactorily suppress deterioration of the image quality and remove moire without deteriorating the edge of the image.

According to the second aspect of the present invention, since the size of the image filter applied in the filter operation is larger than the size of each halftone dot constituting the halftone original, the image quality due to the halftone dot effect is obtained. Degradation and moiré can be removed.

According to the third aspect of the present invention, when the contrast of the target pixel is obtained, the contrasts in a plurality of different directions are obtained based on a plurality of average density values obtained from a plurality of neighboring pixels. In determining the weighting coefficients assigned to each component of the image filter, the method includes a step of changing the distribution of effective weighting coefficients in a plurality of directions according to the contrast in the plurality of directions. An image filter according to the direction of the edge can be obtained. Therefore, it is possible to apply an image filter that preserves edges and favorably suppresses moiré and image quality deterioration.

According to the fourth aspect of the present invention, a smoothing process is performed on each of a plurality of neighboring pixels located near the target pixel to be processed in a predetermined area around the neighboring pixel. Thus, an average density value is obtained for each of the plurality of neighboring pixels, and a contrast for the pixel of interest is obtained based on the obtained plurality of average density values. Then, a weighting coefficient assigned to each component of the image filter is determined according to the contrast, a filter operation is performed on the main signal of the pixel of interest using the image filter to which the weighting coefficient is applied, and the output signal is calculated. Since the image is generated, it is possible to satisfactorily suppress deterioration of the image quality and remove moire without deteriorating the edge of the image.

According to the fifth aspect of the present invention, since the size of the image filter applied in the filter operation is larger than the size of each halftone dot constituting the halftone original, the image quality due to the halftone dot effect is obtained. Degradation and moiré can be removed.

According to the sixth aspect of the present invention, when obtaining the contrast for the pixel of interest, the contrast for a plurality of different directions is obtained based on a plurality of average density values obtained from a plurality of neighboring pixels. In determining the weighting factors assigned to each component of the image filter, the method includes a step of changing the distribution of effective weighting factors in a plurality of directions according to the contrast in the plurality of directions. An image filter according to the direction of the edge can be obtained. Therefore, it is possible to apply an image filter that preserves edges and favorably suppresses moiré and image quality deterioration.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an overall configuration of a device to which an embodiment of the present invention is applied.

FIG. 2 is an explanatory diagram illustrating an outline of image processing according to the embodiment of the present invention;

FIG. 3 is a diagram illustrating weighting coefficients of respective components of an image filter.

FIG. 4 is a schematic configuration diagram showing an image processing apparatus according to an embodiment of the present invention.

FIG. 5 is an explanatory diagram for explaining an upper neighboring pixel and the like.

FIG. 6 is a diagram showing a relationship between inputs and outputs in a vertical table reference section and a horizontal table reference section.

FIG. 7 is a diagram illustrating an example of an image filter obtained in a weighting coefficient set selection unit.

FIG. 8 is a diagram showing the relationship between inputs and outputs in a vertical table reference section and a horizontal table reference section.

FIG. 9 is a diagram showing a positional relationship between halftone dots and pixels to be read.

FIG. 10 is a schematic configuration diagram showing a conventional image processing apparatus.

FIG. 11 is a diagram illustrating an example of a conventional image filter.

FIG. 12 is an explanatory diagram showing a conventional method for generating one halftone dot.

FIG. 13 is a diagram showing an edge portion of a halftone dot image.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Smoothing processing part 21 Vertical contrast extraction part 22 Horizontal contrast extraction part 31 Vertical table reference part 32 Horizontal table reference part 40 Weighting coefficient set selection part 50 Filter operation part 100 Image input part 200 Image processing part 201 Operation input Unit 202 information display unit 300 image output unit S main signal S 'filtered signal

Claims (6)

[Claims] 1. A method of performing a predetermined process for each pixel on an original image, comprising the steps of: (a) for each of a plurality of neighboring pixels located in the vicinity of a pixel of interest to be processed; Performing a smoothing process on a predetermined area around the plurality of neighboring pixels to obtain an average density value for each of the plurality of neighboring pixels; and (b) obtaining a plurality of average density values obtained from the plurality of neighboring pixels. (C) determining a weighting coefficient assigned to each component of the image filter in accordance with the contrast, and (d) determining an image filter to which the weighting coefficient has been applied. Applying a filter operation to the main signal of the pixel of interest using
Generating an output signal. 2. A method for performing a predetermined process for each pixel on an original image obtained by reading a halftone dot original, comprising: (a) a plurality of neighborhoods located near a pixel of interest to be processed; For each of the plurality of neighboring pixels, by performing a smoothing process on each of the pixels in a predetermined area larger than the individual halftone dot size constituting the halftone document around the neighboring pixel. Obtaining a mean density value; (b) obtaining a contrast of the pixel of interest based on the plurality of average density values obtained from the plurality of neighboring pixels; (c) an image filter according to the contrast Determining a weighting coefficient assigned to each component of, (d) performing a filter operation on the main signal of the target pixel using an image filter to which the weighting coefficient is applied,
Generating an output signal, wherein the size of the image filter applied in the step (d) is larger than the size of each halftone dot constituting the halftone original document. Image processing method. 3. The method according to claim 1, wherein the step (b) comprises: comparing contrasts in a plurality of different directions based on the plurality of average density values obtained from the plurality of neighboring pixels. An image processing method, wherein the step (c) includes a step of changing a distribution of effective weighting coefficients for the plurality of directions, respectively, according to contrast in the plurality of directions. . 4. An apparatus for performing a predetermined process for each pixel on an original image, comprising: (a) for each of a plurality of neighboring pixels located in the vicinity of a target pixel to be processed; Means for obtaining an average density value for each of the plurality of neighboring pixels by performing a smoothing process on a predetermined area around the (a), (b) a plurality of average density values obtained from the plurality of neighboring pixels Means for determining the contrast of the pixel of interest based on: (c) means for determining a weighting coefficient assigned to each component of the image filter according to the contrast; and (d) an image filter to which the weighting coefficient has been applied. Applying a filter operation to the main signal of the pixel of interest using
Means for generating an output signal. 5. An apparatus for performing a predetermined process for each pixel on an original image obtained by reading a halftone original, comprising: (a) a plurality of neighborhoods located in the vicinity of a target pixel to be processed; For each of the plurality of neighboring pixels, by performing a smoothing process on each of the pixels in a predetermined area larger than the individual halftone dot size constituting the halftone document around the neighboring pixel. Means for obtaining an average density value; (b) means for obtaining a contrast for the pixel of interest based on the plurality of average density values obtained from the plurality of neighboring pixels; and (c) an image filter according to the contrast. Means for determining a weighting coefficient assigned to each component of, and (d) performing a filter operation on the main signal of the pixel of interest using an image filter to which the weighting coefficient has been applied,
Means for generating an output signal, wherein the size of the image filter applied in the means (d) is larger than the size of each halftone dot constituting the halftone dot document. Processing equipment. 6. The apparatus according to claim 4, wherein the means (b) adjusts contrast in a plurality of directions different from each other based on the plurality of average density values obtained from the plurality of neighboring pixels. An image processing apparatus, comprising: means for obtaining, wherein the means (c) includes means for respectively changing distributions of effective weighting coefficients for the plurality of directions according to contrast in the plurality of directions. .