JPH10276332A - Image processing method and its unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration in image quality and to eliminate moire without deteriorating an edge of an image. SOLUTION: A main signal S as to a noted pixel is led to a mean density extract section 10, an integration device 51, and a filter arithmetic section 30. The filter arithmetic section 30 makes calculation based on an image filter with a size larger than a dot size to generate a filtered signal S'. Then the mean density extract section 10 extracts the mean density in an area larger than the dot size and gives it to a table reference section 20. The table reference section 20 introduces a mixing reatio M of the main signal S and a mixing rate (1-M) of the filtered signal S' in accordance with the mean density D. The integration device 51 generates a signal Sa (=M.S) and an integration device 52 generates a signal Sb (=(1-m).S'). Then an adder 53 mixers the signals Sa,Sb to produce an output signal S".

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. 7 shows a case where a printed matter recorded with such halftone dots is read by an image input unit such as a scanner. FIG. 7 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 the part where the recording is performed by the halftone dots. 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. 7 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.

[0006] Such moiré is conspicuous in a portion where the density level is flat, and is not so conspicuous in an intermediate density region where the density is 50%, but is high in a high density region or a low density region. Appears remarkably in the low-density region, causing deterioration in image quality.

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.

[0008] Conventionally, image processing using an image filter has been performed in order to remove such moiré and prevent deterioration in image quality.

FIG. 8 is a schematic configuration diagram of a conventional image processing apparatus. The pixel to be processed (hereinafter referred to as “target pixel”)
When the main signal S is input, the filter operation unit 40
1 and sent to the main signal adjustment unit 402. Filter operation unit 4
At 01, the main signal S is subjected to a calculation by a two-dimensional image filter to generate a filtered signal S '. Then, the main signal adjustment unit 402 generates a signal Sa (= M · S) obtained by multiplying the main signal S by M based on a preset mixing ratio M of the main signal S. Here, M is a numerical value satisfying “0 ≦ M <1”. On the other hand, the filtered signal S ′ generated by the filter operation unit 401 has the filtered signal S ′ according to the mixing ratio (1−M) of the filtered signal S ′ preset in the filtered signal adjustment unit 403 ( 1-M) times the signal Sb (= (1-
M) · S ′). Then, the signal Sa from the main signal adjustment unit 402 and the signal S from the filtered signal adjustment unit 403
The output signal S ″ is generated by mixing (adding) b with the adder 404.

In such a conventional image processing apparatus,
In order to remove moiré and prevent image quality from deteriorating, the filter operation unit 401 performs a filter operation using an image filter of a predetermined size. FIG. 9 shows an example of an image filter used at this time. In such a conventional image processing apparatus, the size of the image filter is set to be about twice or more the size of one halftone dot.
Therefore, for example, in the case of the example of the image filter of FIG. 9, 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 401 positions the center of the image filter at the pixel of interest, performs weighted averaging of each density value based on the weighting coefficient assigned to the pixel of interest and its neighboring pixels, and performs filtering. The signal is output as a signal S '. That is,
In order to calculate the weighted average in an area larger than the halftone dot size, the filtered signal S 'has a density value from which the frequency component of the halftone dot pattern has been removed and the influence of the halftone dot has been removed. Therefore, in the filtered signal S ′, moiré and the cause of image quality deterioration are removed.

Since the main signal S and the filtered signal S 'are mixed at a mixing ratio "M: (1-M)", the smaller the value of the mixing ratio M, the higher the mixing ratio of the filtered signal S'. (1-
M) increases, and the output signal S ″ becomes the filtered signal S ′.
Is reflected at a higher rate. In other words, the effect of the image processing using the image filter depends on the preset mixing ratio M.

The value of the mixing ratio M can be set by the operator before the image processing is started.
It is a fixed value from the start of processing on the original image to the end of processing.

[0013]

Generally, an edge portion of a printed image recorded with halftone dots is reproduced at a resolution higher than the halftone dot size. FIG. 10 is an explanatory diagram showing a conventional method for generating one halftone dot. As shown in FIG. 10A, 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 for each blackened area as shown in FIG. On the other hand, as shown in FIG. 10B, 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 as compared with the threshold value shown in FIG. Then, a halftone dot as shown in FIG. 10C is recorded.

FIG. 11 shows a case where an edge portion of an image is recorded by such a recording method. FIG. 11 is a diagram showing an edge portion of a 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. Each square area divided by the grid indicates an individual halftone dot area. As shown in FIG. 11, 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. Further, the edge portion of the halftone dot image reproduced at such a high resolution is distributed in a relatively intermediate density region of the original image.

However, in the conventional image processing apparatus, even if the image signal is smoothed using an image filter as shown in FIG. Since the mixture ratio “M: (1−M)” of S and the filtered signal S ′ is always constant regardless of the density range of the image, the edge portion of the image reproduced at the high resolution as described above. Is also smoothed and blurred.

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

[0017]

According to an aspect of the present invention, there is provided a method for performing a predetermined process on an original image for each pixel, comprising the steps of: Generating a filtered signal by applying an image filter of a predetermined size to the main signal, and (b) obtaining an average density value from a pixel group including a target pixel and its neighboring pixels,
(c) deriving a mixing ratio between the main signal and the filtered signal according to the average density value; and (d) generating an output signal by mixing the main signal and the filtered signal based on the mixing ratio. And

According to a second aspect of the present invention, in the method according to the first aspect, when the average density value is in a high density range or a low density range, a ratio corresponding to the filtered signal is large. That is, when the average density value is in the intermediate density range, the ratio corresponding to the main signal is determined to be large.

According to a third aspect of the present invention, there is provided a method for performing a predetermined process for each pixel on an original image, wherein (a) applying an image filter of a predetermined size to a main signal of a target pixel. (B) deriving a mixing ratio between the main signal and the filtered signal according to the filtered signal; and (c) converting the main signal and the filtered signal based on the mixing ratio. Generating an output signal by mixing.

According to a fourth aspect of the present invention, in the method according to the third aspect, when the filtered signal is in a high density range or a low density range, a ratio corresponding to the filtered signal is large. That is, when the filtered signal is in the intermediate density range, the ratio corresponding to the main signal is determined to be large.

According to a fifth aspect of the present invention, there is provided an apparatus for performing a predetermined process on an original image for each pixel, wherein (a) applying an image filter of a predetermined size to a main signal of a target pixel. Means for generating a filtered signal, (b) means for calculating an average density value from a pixel group including a pixel of interest and its neighboring pixels, and (c) a main signal and a filtered signal according to the average density value. Means for deriving a mixing ratio; and (d) means for generating an output signal by mixing the main signal and the filtered signal based on the mixing ratio.

According to a sixth aspect of the present invention, in the device according to the fifth aspect, when the average density value is in a high density range or a low density range, a ratio corresponding to the filtered signal is large. That is, when the average density value is in the intermediate density range, the ratio corresponding to the main signal is determined to be large.

According to a seventh aspect of the present invention, there is provided an apparatus for performing a predetermined process on an original image for each pixel, wherein (a) an image filter of a predetermined size is applied to a main signal of a target pixel. Means for generating a filtered signal, (b) means for deriving a mixing ratio of the main signal and the filtered signal according to the filtered signal, and (c) a main signal and the filtered signal based on the mixing ratio. Means for generating an output signal by mixing.

According to an eighth aspect of the present invention, in the device according to the seventh aspect, when the filtered signal is in a high-density region or a low-density region, a ratio corresponding to the filtered signal is large. That is, when the filtered signal is in the intermediate density range, the ratio corresponding to the main signal is determined to be large.

[0025]

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 example of an overall configuration of a device 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 In the image output unit 300, the image is recorded on a recording medium such as a film. The image input unit 100 and the image processing unit 20
0, and an operation input unit 201 such as a keyboard and a mouse, and an information display unit 20 such as a display unit in order to cause the image output unit 300 to perform an operator's desired operation.
2 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 apparatus according to the embodiment of the present invention, image processing using an image filter is performed in order to prevent moire and deterioration of image quality. That is, M
A process such as smoothing an image is performed by scanning a matrix of image filters of N (M and N are odd numbers of 3 or more) 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 F is used. Then, a weighted average of the density value of the target pixel OP and the density values of neighboring pixels is derived by calculation based on the weighting coefficient assigned to each component of the image filter F, and the obtained value is a filtered signal of the target pixel OP. And

That is, it is _assumed that the image filter F is in the form of a matrix having a size of (2m + 1) × (2n + 1) as shown in FIG. 3, and each component is assigned a weighting coefficient of k- _mn to kmn. . 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

[0029]

(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. First Embodiment> Next, an image processing apparatus according to a first embodiment of the present invention will be described. FIG. 4 is a schematic configuration diagram illustrating the image processing apparatus according to the first embodiment. The main signal S, which is the density value of the pixel of interest, is guided to the average density value extraction unit 10, the integrator 51, and the filter calculation unit 30.

The average density value extraction unit 10 calculates an average density value D from a pixel group including the pixel of interest and its neighboring pixels. Here, the area formed by the pixel of interest for calculating the average density value D and its neighboring pixels is the size of each halftone dot (strictly speaking, 10 dots) of the original image so as not to detect the halftone dot shape.
(A size corresponding to 0% halftone dot). If the area to be averaged is not wide enough, it is close to the center of the halftone dot,
This is because the density value may be different from the original density value indicated by the original image. By this averaging, the average density value D becomes a density value originally indicated by the original image which is not affected by the halftone dots. The method of obtaining the average density value D may be a simple average of a pixel group including the target pixel and its neighboring pixels, or a weighted average. The average density value D obtained by the average density extraction unit 10 is stored in the table reference unit 2.
Sent to 0.

In the table reference section 20, the mixing ratio M is derived according to the average density value D to be inputted. Here, the relationship between the average density value D and the mixing ratio M is shown in FIG. As shown in FIG.
A possible value of the mixing ratio M is “0 ≦ M <1”. Then, as the average density value D becomes higher or lower, the value of the mixing ratio M becomes smaller. When the average density value D becomes an intermediate density range, the mixing ratio M becomes larger. Then, the table reference unit 20 stores the table in which the relationship of FIG. I do. Since the mixing ratio M indicates the mixing ratio of the main signal S to the output signal, the table reference unit 20 derives the mixing ratio (1-M) of the filtered signal based on the mixing ratio M. . Therefore, the possible value of the mixing ratio (1-M) is “0 <(1-M) ≦ 1”.
Becomes The mixing ratio M is sent to the integrator 51, and the mixing ratio (1-M) is sent to the integrator 52.

Then, in the integrator 51, the main signal S
Is integrated with the mixing ratio M to generate a signal Sa (= M · S). This signal Sa is sent to the adder 53.

On the other hand, the filter operation section 30 performs a filter operation process using an image filter having a predetermined size. The image filter used at this time is, for example, an image filter as shown in FIG. 9 similar to the conventional image processing apparatus. Also in the image processing apparatus of this embodiment,
It is preferable that the size of the image filter applied by the filter calculation unit 30 is set to be about twice or more the size of one halftone dot. For example, in the case of the example of the image filter of FIG. 9, the size of one pixel is equal to or larger than about "2/5" of the halftone dot size. Then, in the filter calculation unit 30, the center of the image filter is positioned at the target pixel, the calculation shown in Formula 1 is performed based on the weighting coefficients assigned to the target pixel and its neighboring pixels, and a weighted average is applied to perform filtering. The signal is output as a signal S '. Then, in order to calculate the weighted average in an area larger than the dot size, the filtered signal S ′ has a density value in which the frequency component of the dot pattern has been removed and the influence of the dot has been removed. ing. Therefore, in the filtered signal S ′, moiré and the cause of image quality deterioration are removed. The filtered signal S ′ obtained in this way is
Sent to 2.

Then, in the integrator 52, the filtered signal S 'and the mixing ratio (1-M) are integrated, and a signal Sb (= (1-M) .S') is generated. Then, the obtained signal Sb is sent to the adder 53.

In the adder 53, the signal Sa and the signal Sb are mixed (added) to generate an output signal S ″. This output signal S ″ is an output signal of the image processing device of the present embodiment.

In the image processing apparatus according to the present embodiment, the main signal S and the filtered signal S ′ are mixed at a mixing ratio “M: (1-
M) ”. Then, the mixture ratio is determined according to the average density value D obtained from a pixel group including the target pixel and its neighboring pixels. This makes it possible to change the mixture ratio according to the density range of the original image, so that the effect of image processing using the image filter can be changed according to the density range of the original image.

In the image processing apparatus of this embodiment, since the mixing ratio of the main signal S is set large in the intermediate density range where moire is not conspicuous, the output signal S ″ to be output is The components of the signal S are included in a comparatively large amount, and the edge portion of the image is not deteriorated. Further, in a high density region or a low density region where moiré and image quality degradation are conspicuous, the mixing ratio of the filtered signal S ′ is set large, so that the output signal S ″ to be output is filtered. The components of the signal S ′ are included in a comparatively large amount, and it is possible to prevent the occurrence of moire in the high-density region or the low-density region and the deterioration of the image quality.

In FIG. 5, when the average density value D is in the intermediate density range, the reason why the mixing ratio M is not "1" is that halftone dots are not degraded to the extent that the edge is degraded. This is because the filtered signal S ′ is included in the output signal S ″ in order to remove the influence. This makes it possible to remove moiré which is not visually noticeable but exists in the intermediate density range.

<4. Second Embodiment> Next, an image processing apparatus according to a second embodiment of the present invention will be described. FIG. 6 is a schematic configuration diagram illustrating an image processing apparatus according to the second embodiment. The main signal S, which is the density value of the pixel of interest, is guided to the filter operation unit 30 and the integrator 51.

In the filter operation section 30, as in the first embodiment, the filter operation is performed by an image filter having a predetermined size. The image filter used at this time is, for example, an image filter as shown in FIG. 9 similar to the conventional image processing apparatus. Also in the image processing apparatus according to this embodiment, it is preferable that the size of the image filter applied by the filter operation unit 30 is set to be about twice or more the size of one halftone dot. And
The filter operation unit 30 performs the operation shown in Expression 1 based on the weighting coefficients assigned to the target pixel and its neighboring pixels, performs weighted averaging, and outputs the result as a filtered signal S ′. Then, in order to calculate the weighted average in an area larger than the dot size, the filtered signal S ′ has a density value in which the frequency component of the dot pattern has been removed and the influence of the dot has been removed. ing. Therefore, in the filtered signal S ′, moiré and the cause of image quality deterioration are removed. The filtered signal S ′ thus obtained
Is sent to the table reference unit 20 and the integrator 52.

In the table reference section 20, the mixing ratio M is derived according to the input filtered signal S '. Here, the relationship between the filtered signal S ′ and the mixture ratio M is the same as the relationship between the average density value D and the mixture ratio M shown in FIG. 5, and the “average density value D” in FIG. What is necessary is just to read as "signal S '." That is, the value of the mixing ratio M becomes smaller as the filtered signal S ′ becomes higher or lower density region, and the mixing ratio M becomes larger when the filtered signal S ′ becomes intermediate density region. It is set as follows. Then, the table reference unit 20 stores a table in which the above relationships are associated with each other in a storage member such as a memory, and when the filtered signal S ′ is input, refers to the table to obtain the corresponding mixing ratio M. To win. This mixing ratio M
Indicates the mixing ratio of the main signal S to the output signal, and the table reference unit 20 derives the mixing ratio (1−M) of the filtered signal S ′ based on the mixing ratio M. The mixing ratio M is sent to the integrator 51, and the mixing ratio (1
−M) is sent to the integrator 52.

In the integrator 51, the main signal S
Is integrated with the mixing ratio M to generate a signal Sa (= M · S), which is sent to the adder 53. The integrator 52
, The filtered signal S ′ is multiplied by the mixing ratio (1−M) to generate a signal Sb (= (1−M) · S ′), and the obtained signal Sb is added to the adder 53. Sent to

In the adder 53, the signal Sa and the signal Sb are mixed to generate an output signal S ″. This output signal S ″ is an output signal of the image processing device of the present embodiment.

In the image processing apparatus of this embodiment, the filtered signal S 'is guided to the table reference section 20 to generate the mixing ratio M, (1-M). The filtered signal S ′ is a signal on which weighted averaging is performed as shown in Expression 1 based on an image filter as shown in FIG. Therefore, even if this weighted average filtered signal S ′ is used instead of the average density value D shown in the first embodiment,
The effect obtained for the output signal S ″ is the same. Also, as in this embodiment, when the filtered signal S 'is input to the table reference unit 20, the average density value extraction unit 10 (see FIG. 4) shown in the first embodiment needs to be provided. Not
This is advantageous in that the configuration is efficient.

As described above, also in the image processing apparatus of this embodiment, the main signal S and the filtered signal S ′ are mixed at the mixing ratio “M: (1−M)”, and the output signal S ″ is output. Generated. Then, the mixture ratio is determined according to the filtered signal S ′. This makes it possible to change the mixture ratio in accordance with the density range of the original image that is not affected by the halftone dots, so that the effect of the image processing using the image filter can be changed in accordance with the density range of the original image. It can be changed.

In the image processing apparatus according to this embodiment, the mixing ratio of the main signal S is set large in the intermediate density region where moire is not conspicuous. The components of the signal S are included in a comparatively large amount, and the edge portion of the image is not deteriorated. Further, in a high density region or a low density region where moiré and image quality degradation are conspicuous, the mixing ratio of the filtered signal S ′ is set large, so that the output signal S ″ to be output is filtered. The components of the signal S ′ are included in a comparatively large amount, and it is possible to prevent the occurrence of moire in the high-density region or the low-density region and the deterioration of image quality.

<5. Modifications> Although it has been described that the size of the image filter applied by the filter operation unit 30 of the image processing apparatus shown in the first and second embodiments is larger than the halftone dot size, It may be different depending on the original image. Therefore, when the halftone dot size of the original image is changed, it is necessary to change the size of the image filter to an appropriate size.

When the original image is read by the image input unit 100, the halftone dot size is measured and detected. When the operator sets the original image on the image input unit 100, the operator himself / herself inputs the halftone dot from the operation input unit 201. By setting and inputting the dot size, dot information on the dot size is obtained.
Then, the halftone information obtained in this way is configured to be sent to the image processing apparatus. Then, in the image processing apparatus, if the filter calculation unit changes the size of the image filter to be applied based on the input dot information, even if the dot size of the original image is changed, the filter operation unit immediately changes the size. It is possible to correspond to the specified dot size.

In the embodiment, as an example, when the average density value D or the filtered signal S 'is in the high density range or the low density range, the value of the mixing ratio M becomes small, and when the average density value D or the filtered signal S' is in the intermediate density range. Has described the case where the value of the mixing ratio M is large, but the present invention is not limited to such a relationship, and as a result, the average density value D or the filtered signal S ′ may have a high density range or a low density range. The filtered signal S '
May be set so as to increase the mixing ratio of the main signal S when indicating the intermediate density range.

Further, in the table reference section 20, FIG.
By changing the relationship shown in (1) to another relationship, the effect of the processing by the image filter can be changed for an arbitrary density range. Therefore, if the image processing apparatus of this embodiment is applied, it is possible to remove the deterioration of the image quality and the occurrence of moire in an arbitrary density range.

The image filter applied in the above-described image processing apparatus can be generally expressed by M × N
(M and N are odd numbers of 3 or more), and the target pixel is located at the center of the image filter.

[0055]

As described above, according to the first aspect of the present invention, a filtered signal is generated by applying an image filter of a predetermined size to the main signal of the target pixel, and the filtered signal is generated. An average density value is obtained from a pixel group including the neighboring pixels, a mixing ratio between the main signal and the filtered signal is derived according to the average density value, and the main signal and the filtered signal are calculated based on the obtained mixing ratio. To generate an output signal by mixing, the effect of image processing using an image filter,
It is possible to change the density according to the density range of the original image, and it is possible to satisfactorily suppress the deterioration of the image quality and remove the moire without deteriorating the edges of the image.

According to the second aspect of the present invention, when the average density value is in the high density range or the low density range, the ratio corresponding to the filtered signal is large, and the mixing ratio is intermediate. In the case of the density region, the ratio corresponding to the main signal is determined so as to be large.Therefore, in the intermediate density region where the moire is not conspicuous, the output signal contains a relatively large amount of the main signal component, and the edge portion of the image is In a high-density region or a low-density region where deterioration and image quality are conspicuous, the output signal contains a relatively large amount of filtered signal components. And deterioration of image quality can be prevented.

According to the third aspect of the present invention, a filtered signal is generated by applying an image filter of a predetermined size to the main signal of the target pixel, and the main signal and the filter are generated in accordance with the filtered signal. The output signal is generated by deriving a mixing ratio with the filtered signal and mixing the main signal and the filtered signal based on the obtained mixing ratio, so that the configuration can be simplified and an image filter is used. It is possible to change the effect of the image processing performed according to the density range of the original image, and it is possible to satisfactorily suppress the deterioration of the image quality and remove the moire without deteriorating the edges of the image.

According to the fourth aspect of the present invention, when the filtered signal is in a high density range or a low density range, the mixing ratio has a large ratio corresponding to the filtered signal, and the mixed signal has an intermediate value. In the case of the density region, the ratio corresponding to the main signal is determined so as to be large.Therefore, in the intermediate density region where the moire is not conspicuous, the output signal contains a relatively large amount of the main signal component, and the edge portion of the image is removed. In a high-density region or a low-density region where deterioration and image quality are conspicuous, the output signal contains a relatively large amount of filtered signal components. And deterioration of image quality can be prevented.

According to the fifth aspect of the present invention, a filtered signal is generated by applying an image filter of a predetermined size to the main signal of the target pixel, and a pixel group including the target pixel and its neighboring pixels From the average density value, and according to the obtained average density value, derive the mixing ratio of the main signal and the filtered signal,
Since the output signal is generated by mixing the main signal and the filtered signal based on the mixing ratio, the effect of image processing using the image filter can be changed according to the density range of the original image. Accordingly, it is possible to satisfactorily suppress the deterioration of the image quality and remove the moire without deteriorating the edge of the image.

According to the sixth aspect of the present invention, when the average density value is in the high density range or the low density range, the ratio corresponding to the filtered signal is large, and the mixing ratio is intermediate. In the case of the density region, the ratio corresponding to the main signal is determined so as to be large.Therefore, in the intermediate density region where the moire is not conspicuous, the output signal contains a relatively large amount of the main signal component, and the edge portion of the image is removed. In a high-density region or a low-density region where deterioration and image quality are remarkably noticeable, the output signal contains a relatively large amount of filtered signal components. And deterioration of image quality can be prevented.

According to the seventh aspect of the invention, a filtered signal is generated by applying an image filter of a predetermined size to the main signal of the target pixel, and the main signal and the filter are generated in accordance with the filtered signal. The output signal is generated by deriving a mixing ratio with the filtered signal and mixing the main signal and the filtered signal based on the obtained mixing ratio, so that the configuration can be simplified and an image filter is used. It is possible to change the effect of the image processing performed according to the density range of the original image, and it is possible to satisfactorily suppress the deterioration of the image quality and remove the moire without deteriorating the edges of the image.

According to the eighth aspect of the present invention, when the filtered signal is in a high density range or a low density range, the mixing ratio has a large ratio corresponding to the filtered signal, and the mixed signal has an intermediate value. In the case of the density region, the ratio corresponding to the main signal is determined so as to be large.Therefore, in the intermediate density region where the moire is not conspicuous, the output signal contains a relatively large amount of the main signal component, and the edge portion of the image is removed. In a high-density region or a low-density region where deterioration and image quality are remarkably noticeable, the output signal contains a relatively large amount of filtered signal components. And deterioration of image quality can be prevented.

[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 illustrating an image processing apparatus according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between an average density value D and a mixing ratio M according to the embodiment of the present invention.

FIG. 6 is a schematic configuration diagram illustrating an image processing apparatus according to a second embodiment of the present invention.

FIG. 7 is a diagram showing a positional relationship between halftone dots and pixels to be read.

FIG. 8 is a schematic configuration diagram showing a conventional image processing apparatus.

FIG. 9 is a diagram illustrating an example of a conventional image filter.

FIG. 10 is an explanatory diagram showing a conventional method for generating one halftone dot.

FIG. 11 is a diagram showing an edge portion of a halftone dot image.

[Explanation of symbols]

 Reference Signs List 10 average density value extraction unit 20 table reference unit 30 filter calculation unit 51, 52 integrator 53 adder 100 image input unit 200 image processing unit 201 operation input unit 202 information display unit 300 image output unit S main signal S 'filtered signal S '' output signal M, (1-M) mixing ratio D average density value

Claims (8)

[Claims] 1. A method for performing a predetermined process for each pixel on an original image, comprising: (a) generating a filtered signal by applying an image filter of a predetermined size to a main signal of a pixel of interest; (B) obtaining an average density value from a pixel group including a pixel of interest and its neighboring pixels; and (c) deriving a mixing ratio between the main signal and the filtered signal according to the average density value. And d) generating an output signal by mixing the main signal and the filtered signal based on the mixing ratio. 2. The method according to claim 1, wherein, when the average density value is in a high density range or a low density range, a ratio corresponding to the filtered signal increases, and the mixing ratio increases. An image processing method characterized in that, when the density value is in an intermediate density range, the ratio corresponding to the main signal is determined to be large. 3. A method of performing a predetermined process for each pixel on an original image, comprising: (a) generating a filtered signal by applying an image filter of a predetermined size to a main signal of a pixel of interest; (B) deriving a mixing ratio between the main signal and the filtered signal according to the filtered signal; and (c) mixing the main signal and the filtered signal based on the mixing ratio. And generating an output signal. 4. The method according to claim 3, wherein the mixing ratio has a larger ratio corresponding to the filtered signal when the filtered signal has a high density range or a low density range. An image processing method characterized in that, when the processed signal is in the intermediate density range, the ratio corresponding to the main signal is determined to be large. 5. An apparatus for performing a predetermined process for each pixel on an original image, comprising: (a) generating a filtered signal by applying an image filter of a predetermined size to a main signal of a pixel of interest; Means, (b) means for obtaining an average density value from a pixel group including the pixel of interest and its neighboring pixels, and (c) deriving a mixing ratio between the main signal and the filtered signal according to the average density value. Means for generating an output signal by mixing the main signal and the filtered signal based on the mixing ratio. 6. The apparatus according to claim 5, wherein, when the average density value is in a high density range or a low density range, a ratio corresponding to the filtered signal increases, and An image processing apparatus characterized in that when a density value is in an intermediate density range, a ratio corresponding to the main signal is determined to be large. 7. An apparatus for performing a predetermined process on an original image for each pixel, wherein (a) generating a filtered signal by applying an image filter of a predetermined size to a main signal of a target pixel Means, (b) means for deriving a mixing ratio between the main signal and the filtered signal according to the filtered signal, and (c) mixing the main signal and the filtered signal based on the mixing ratio. Means for generating an output signal by performing the operation. 8. The apparatus according to claim 7, wherein a ratio of the mixture ratio corresponding to the filtered signal increases when the filtered signal is in a high-density region or a low-density region. An image processing apparatus characterized in that when the processed signal is in the intermediate density range, the ratio corresponding to the main signal is determined to be large.