JPH10271340A - Image-processing method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfactorily suppress deterioration in image quality and to remove moires, without deteriorating edges of an image. SOLUTION: A main signal S regarding a pixel under consideration is guided to a smoothing processing part 10, an integrator 51 and a filter operation part 40. An arithmetic operation is performed based on an image filter, size of which is larger than a dot size and a filtered signal S' is generated in the filter operation part 40. An average density value of neighboring pixels of a pixel under consideration is extracted in a region larger than the dot size in the smoothing processing part 10. A contrast C of the pixel under consideration is guided, based on the average density value of the neighboring pixels of the pixel under consideration in a contrast extracting part 20. A mixing rate M, (1-M) is guided according to the contrast C in a table reference part 30. A signal Sa is generated in the integrator 51, and a signal Sb is generated in an integrator 52. Then an output signal S" is generated by mixing the signal Sa and the signal Sb in an integrator 53.

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. 8 shows a case where a printed matter recorded with such halftone dots is read by an image input unit such as a scanner. FIG. 8 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. 8 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. 9 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. 10 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. 10, one pixel size is approximately “2 /
5 "or more. 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 dot size, the filtered signal S ′ is a density value in which the frequency component of the dot pattern has been removed and the influence of the dot has been removed. . Therefore, the filtered signal S ′
In the, the causes of moiré and 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 an 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.

[0012]

Generally, an edge portion of a printed image recorded with halftone dots is reproduced at a resolution higher than the halftone dot size. FIG. 11 is an explanatory diagram showing a conventional method for generating one halftone dot. As shown in FIG. 11A, 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.
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. 11C is recorded.

FIG. 12 shows a case where an edge portion of an image is recorded by such a recording method. FIG. 12 is a diagram illustrating an edge portion of the halftone dot image, and a dotted line in the diagram indicates 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. 12, since the halftone dot is recorded in the edge portion of the halftone dot image according to the density value corresponding to each of the four divided blocks, the reproduction is performed at a high resolution.

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 for one image, the edge portion of the image reproduced at a high resolution as described above is also smoothed. There is a problem that it is blurred.

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 image quality deterioration and removing moire without deteriorating image edges. The purpose is to do.

[0016]

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. Generating a filtered signal by applying an image filter of a predetermined size to a main signal of a certain pixel of interest; and (b) for each of a plurality of neighboring pixels located in the vicinity of the pixel of interest, By performing a smoothing process in a predetermined area around the pixel, a step of obtaining an average density value for each of the plurality of neighboring pixels, and (c) based on a plurality of average density values obtained from the plurality of neighboring pixels Calculating the contrast of the pixel of interest; (d) deriving a mixing ratio between the main signal and the filtered signal according to the contrast; and (e) mixing the main signal and the filtered signal based on the mixing ratio. Generate an output signal And a degree.

According to a second aspect of the present invention, in the method according to the first aspect, a ratio corresponding to the filtered signal increases as the contrast decreases.
The ratio corresponding to the main signal is determined to increase as the contrast increases.

According to a third aspect of the present invention, there is provided a method of performing predetermined processing on an original image for each pixel, comprising the steps of: (a) applying a process to a target pixel and a plurality of neighboring pixels located in the vicinity of the target pixel Generating a filtered signal by applying an image filter of a predetermined size; and (b) obtaining a contrast for the pixel of interest based on the filtered signals for a plurality of neighboring pixels located near the pixel of interest. (C) deriving a mixing ratio between the main signal and the filtered signal for the pixel of interest according to the contrast, and (d) mixing the main signal and the filtered signal for the pixel of interest based on the mixing ratio. And generating an output signal for the pixel of interest.

According to a fourth aspect of the present invention, in the method according to the third aspect, the ratio corresponding to the filtered signal increases as the contrast decreases, and
The ratio corresponding to the main signal is determined to increase as the contrast increases.

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, comprising: (a) an image having a predetermined size for a main signal of a pixel of interest to be processed; Means for applying a filter to generate a filtered signal;
(b) For each of the plurality of neighboring pixels located in the vicinity of the pixel of interest, a smoothing process is performed in a predetermined area around the neighboring pixel to obtain an average density value for each of the plurality of neighboring pixels Means, (c) means for obtaining a contrast for the pixel of interest based on a plurality of average density values obtained from a plurality of neighboring pixels, and (d) a mixing ratio of the main signal and the filtered signal according to the contrast. And (e) 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, the ratio corresponding to the filtered signal increases as the contrast decreases, and
The ratio corresponding to the main signal is set to increase as the contrast increases.

According to a seventh aspect of the present invention, there is provided an apparatus for performing a predetermined process for each pixel on an original image, comprising the steps of: (a) applying a process to a target pixel and a plurality of neighboring pixels located near the target pixel; Means for generating a filtered signal by applying an image filter of a predetermined size; and (b) means for obtaining a contrast for the pixel of interest based on the filtered signals for a plurality of neighboring pixels located in the vicinity of the pixel of interest. (C) means for deriving a mixing ratio between the main signal and the filtered signal for the pixel of interest according to the contrast, and (d) mixing the main signal and the filtered signal for the pixel of interest based on the mixing ratio. Means for generating an output signal for the pixel of interest.

According to an eighth aspect of the present invention, in the apparatus according to the seventh aspect, the ratio corresponding to the filtered signal increases as the contrast decreases, and
The ratio corresponding to the main signal is set to increase as the contrast increases.

[0024]

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

[0028]

(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 smoothing processing unit 10, the integrator 51, and the filter operation unit 40.

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 an area (smoothing area) larger than the individual dot size of the original image centered on each neighboring pixel. The smoothing area is set to be an area larger than the halftone dot size, so that the halftone dot shape is not detected, and the pixels close to the center position of the halftone dot and the pixels that are not so prevent the density value from being largely different, This is for obtaining the density value indicated by the original original image.

In the smoothing process performed here, the density values of the 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 converts the average density values YU, YL, XL, and XR of the upper neighboring pixel, the lower neighboring pixel, the left neighboring pixel, and the right neighboring pixel into the contrast extracting unit 2.
Send to 0.

The contrast extracting section 20 extracts a contrast C near the target pixel of the image based on the average density values YU, YL, XL and XR. That is,

[0036]

(Equation 2)

Thus, the contrast C is obtained. Equation 2 is
This averages the vertical contrast and the horizontal contrast of the pixel of interest. Then, the obtained contrast C is sent to the table reference unit 30.

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 contrast in the vicinity of the target pixel as described above, it is possible to determine what part of the image the target pixel is. Further, since the smoothing processing is performed in the smoothing processing unit 10, the edge of the halftone dot itself is not detected.

In the table reference section 30, the mixing ratio M is derived in accordance with the input contrast C. Here, the relationship between the contrast C and the mixing ratio M is shown in FIG. As shown in FIG. 6, a possible value of the mixing ratio M is “0 ≦ M <1”.
Then, as the contrast C increases, the mixing ratio M
Increases, and conversely, as the contrast C decreases, the value of the mixing ratio M decreases. In other words, if the pixel of interest is an edge portion of the image, the value of the mixture ratio M is large, and if the pixel of interest is a flat portion where the density of the image is small, the value of the mixture ratio M is small.

The table reference unit 30 stores a table in which the relations shown in FIG. 6 are associated with each other in a storage member such as a memory, and when the contrast C is input, refers to the table to determine the corresponding mixing ratio M. To win. Since the mixing ratio M indicates the mixing ratio of the main signal S to the output signal, the table reference unit 30 uses the mixing ratio M to calculate the mixing ratio (1-M) of the filtered signal.
Lead. Therefore, the possible value of the mixing ratio (1-M) is
“0 <(1−M) ≦ 1”. 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 calculation section 40 performs a filter calculation process on the pixel of interest using an image filter of a predetermined size. The image filter used at this time is, for example, an image filter as shown in FIG. 10 similar to a 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 operation unit 40 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. 10, the size of one pixel is equal to or larger than about "2/5" of the halftone dot size. Then, in the filter operation unit 40, the center of the image filter is located at the target pixel, and the weighted coefficient assigned to the target pixel and its neighboring pixels is used to perform the arithmetic operation shown in Equation 1 to perform a weighted average to perform the 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 ′ thus obtained is sent to the integrator 52.

Then, in the integrator 52, the filtered signal S 'is multiplied by the mixing ratio (1-M) to generate a signal Sb (= (1-M) .S'). 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 this 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 contrast C near the target pixel. This makes it possible to change the mixing ratio according to the contrast C of the original image, so that the effect of the image processing using the image filter can be changed according to the contrast C of the original image.

In the image processing apparatus according to this embodiment, when the pixel of interest is an edge portion of the image, the ratio of the main signal S to be mixed is set to be large. '' Includes many components of the main signal S in comparison, and does not degrade the edge portion of the image. Also,
In the case of a flat portion where the density change of the image is small, the mixing ratio of the filtered signal S ′ is set to be large, so that the output signal S ″ to be output includes the component of the filtered signal S ′. Are included in comparison, and the occurrence of moire and the deterioration of image quality can be prevented.

In FIG. 6, when the contrast C is sufficiently large, the reason why the mixing ratio M is not "1" is that the influence of the halftone dots is removed to such an extent that the edge is not deteriorated. For this reason, the filtered signal S ′ is included in the output signal S ″. This makes it possible to remove moiré that is not visually noticeable but actually exists.

<4. Second Embodiment> Next, an image processing apparatus according to a second embodiment of the present invention will be described. FIG. 7 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 40 and the integrator 51.

In the filter operation section 40, as in the first embodiment, the filter operation is performed by an image filter having a predetermined size. At this time, the image filter used is, for example, as shown in FIG.
Is an image filter as shown in FIG. Also in the image processing apparatus of this embodiment, it is preferable that the size of the image filter applied by the filter operation unit 40 is set to be about twice or more the size of one halftone dot. Then, the filter operation unit 40 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 signal as a filtered signal. 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, the filtered signal is free from moiré and image quality degradation factors.

By the way, the filter operation unit 40 of the image processing apparatus according to this embodiment also generates a filtered signal for a pixel adjacent to the target pixel in addition to the target pixel.
The neighboring pixels of the target pixel 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 as described in the first embodiment. Then, a filtered signal is generated for each of the upper neighboring pixel, the lower neighboring pixel, the left neighboring pixel, and the right neighboring pixel. Then, the obtained filtered signals of the upper neighboring pixel, the lower neighboring pixel, the left neighboring pixel, and the right neighboring pixel are sent to the contrast extracting unit 20. The filtered signal S ′ for the pixel of interest is calculated by the integrator 5
Sent to 2.

The contrast extracting section 20 extracts the contrast C near the target pixel of the image based on the filtered signals of the upper neighboring pixel, the lower neighboring pixel, the left neighboring pixel, and the right neighboring pixel. Here, the method of obtaining the contrast C may be the same as that described in the first embodiment. Then, the obtained contrast C
Is sent to the table reference unit 30.

In the table reference section 30, the mixing ratio M is derived in accordance with the input contrast C. The details of the table reference unit 30 are the same as those described in the first embodiment. Since the mixing ratio M indicates the mixing ratio of the main signal S to the output signal, the table reference unit 30 calculates the mixing ratio (1-M) of the filtered signal S ′ based on the mixing ratio M. Lead. 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), 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, a filtered signal for a pixel in the vicinity of the pixel of interest is guided to the contrast extracting unit 20 to obtain a contrast, and the mixing ratio M, (1) is determined according to the obtained contrast. −
M). The filtered signal for the pixel in the vicinity of the target pixel 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 averaged filtered signal is used instead of the average density value 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 is input to the contrast extraction unit 20, there is no need to provide the smoothing processing unit 10 (see FIG. 4) shown in the first embodiment.
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 ′ for the target pixel are mixed at the mixing ratio “M: (1−M)”.
An output signal S '' is generated. Then, the mixture ratio is determined according to the contrast. This makes it possible to change the mixture ratio in accordance with the contrast of the original image which is not affected by the halftone dots, and thus changes the effect of the image processing using the image filter in accordance with the contrast of the original image. It becomes possible.

In the image processing apparatus according to this embodiment, when the pixel of interest is an edge portion of the image, the ratio of the main signal S to be mixed is set to be large. '' Includes many components of the main signal S in comparison, and does not degrade the edge portion of the image. Also,
In the case of a flat portion where the density change of the image is small, since the mixing ratio of the filtered signal S ′ for the pixel of interest is set to be large, the output signal S ″ to be output is the filtered signal The component of S ′ is included in a comparatively large amount, so that occurrence of moiré and deterioration of image quality can be prevented.

<5. Modifications> Although it has been described that the size of the image filter applied by the filter operation unit 40 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 image input unit 100 reads the original image and measures and detects the halftone dot size, or when the operator sets the original image in the image input unit 100, the operator himself / herself uses the operation input unit 201 to change the halftone dot size. 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, FIG.
As described above, the case where the value of the mixing ratio M increases as the contrast C increases, and the value of the mixing ratio M decreases as the contrast C decreases, is not limited to such a relationship. As a result, when the contrast C is large, the mixing ratio of the filtered signal S ′ for the target pixel is increased, and the contrast C is increased.
May be set to increase the mixing ratio of the main signal S for the target pixel when is small.

Next, the contrast extraction 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, when the contrast is extracted, the accuracy of the contrast extraction is increased by referring to the neighboring pixels in the diagonally right-upward and leftward diagonal directions for the target pixel. Therefore, it is possible to satisfactorily preserve edges.

Further, the contrast may be obtained in directions other than the vertical, horizontal and oblique directions. That is, in general, it is sufficient if the directions are different from each other and have a two-dimensional spread centered on the target pixel.

The image filter applied in the image processing apparatus described above is, in general terms, an M × N (M, N is an odd number of 3 or more) image filter, and the pixel of interest is the image filter of the image filter. It is configured to be located at the center.

The contents described above are not limited to the case where the original image is a halftone original recorded with 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 can be applied to image processing of an image or the like obtained by a digital camera.

[0065]

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 a main signal of a target pixel to be processed. By performing a smoothing process on each of a plurality of neighboring pixels located in the vicinity of the pixel of interest in a predetermined area around the neighboring pixel, an average density value is obtained for each of the plurality of neighboring pixels. The contrast of the pixel of interest is obtained based on the obtained plurality of average density values, a mixing ratio between the main signal and the filtered signal is derived according to the contrast, and the main signal and the filtered signal are calculated based on the mixing ratio. Since the output signal is generated by mixing, the output signal has the processing effect of the image filter corresponding to the contrast of the original image, and does not deteriorate the edge portion of the image. , It is possible to prevent well the deterioration of moire generation and image quality.

According to the second aspect of the present invention, the mixing ratio is such that the proportion corresponding to the filtered signal increases as the contrast decreases, and the proportion corresponding to the main signal increases as the contrast increases. Therefore, the ratio corresponding to the filtered signal becomes large for a flat portion where the density change of the image is small,
The occurrence of moiré and the deterioration of image quality can be prevented well.
In addition, as for the edge portion of the image, the ratio corresponding to the main signal increases, and the edge portion of the image does not deteriorate.

According to the third aspect of the present invention, a filtered signal is generated by applying an image filter of a predetermined size to a target pixel and a plurality of neighboring pixels located in the vicinity of the target pixel. The contrast of the pixel of interest is obtained based on the filtered signal of the neighboring pixel, the mixture ratio of the main signal and the filtered signal of the pixel of interest is derived according to the obtained contrast, and the pixel of interest is obtained based on the mixture ratio. The output signal for the pixel of interest is generated by mixing the main signal and the filtered signal for the pixel of interest, so that the output signal has the processing effect of the image filter corresponding to the contrast of the original image, and the edge portion of the image Without deteriorating the image quality, the occurrence of moire and the deterioration of the image quality can be satisfactorily prevented, and efficient processing becomes possible.

According to the fourth aspect of the present invention, the mixing ratio is such that the proportion corresponding to the filtered signal increases as the contrast decreases, and the proportion corresponding to the main signal increases as the contrast increases. Therefore, the ratio corresponding to the filtered signal becomes large for a flat portion where the density change of the image is small,
The occurrence of moiré and the deterioration of image quality can be prevented well.
In addition, as for the edge portion of the image, the ratio corresponding to the main signal increases, and the edge portion of the image does not deteriorate.

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 to be processed, and is located near the target pixel. By performing a smoothing process on each of the plurality of neighboring pixels in a predetermined area around the neighboring pixel, an average density value is obtained for each of the plurality of neighboring pixels. The contrast of the pixel of interest is determined based on the contrast, a mixing ratio of the main signal and the filtered signal is derived according to the contrast, and an output signal is generated by mixing the main signal and the filtered signal based on the mixing ratio. As a result, the output signal has a processing effect by an image filter corresponding to the contrast of the original image, and the generation of moiré and image quality can be achieved without deteriorating the edge portion of the image. It is possible to prevent the deterioration good.

According to the sixth aspect of the invention, the mixing ratio is such that the proportion corresponding to the filtered signal increases as the contrast decreases, and the proportion corresponding to the main signal increases as the contrast increases. Since the setting is made, the ratio corresponding to the filtered signal becomes large in a flat portion where the density change of the image is small, and the occurrence of moire and the deterioration of the image quality can be prevented well. In addition, as for the edge portion of the image, the ratio corresponding to the main signal increases, and the edge portion of the image does not deteriorate.

According to the seventh aspect of the present invention, a filtered signal is generated by applying an image filter of a predetermined size to a target pixel and a plurality of neighboring pixels located in the vicinity of the target pixel. The contrast of the pixel of interest is obtained based on the filtered signal of the neighboring pixel, the mixture ratio of the main signal and the filtered signal of the pixel of interest is derived according to the obtained contrast, and the pixel of interest is obtained based on the mixture ratio. The output signal for the pixel of interest is generated by mixing the main signal and the filtered signal for the pixel of interest, so that the output signal has the processing effect of the image filter corresponding to the contrast of the original image, and the edge portion of the image is obtained. , The occurrence of moiré and the deterioration of the image quality can be satisfactorily prevented, and an efficient device configuration can be achieved.

According to the eighth aspect of the present invention, the mixing ratio is such that the proportion corresponding to the filtered signal increases as the contrast decreases, and the proportion corresponding to the main signal increases as the contrast increases. Since the setting is made, the ratio corresponding to the filtered signal becomes large in a flat portion where the density change of the image is small, and the occurrence of moire and the deterioration of the image quality can be prevented well. In addition, as for the edge portion of the image, the ratio corresponding to the main signal increases, and the edge portion of the image does not deteriorate.

[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 an explanatory diagram for explaining an upper neighboring pixel and the like.

FIG. 6 shows a contrast C according to the embodiment of the present invention.
FIG. 6 is a diagram showing a relationship between the mixing ratio M and the mixing ratio M.

FIG. 7 is a schematic configuration diagram illustrating an image processing apparatus according to a second embodiment of the present invention.

FIG. 8 is a diagram showing a positional relationship between halftone dots and pixels to be read.

FIG. 9 is a schematic configuration diagram showing a conventional image processing apparatus.

FIG. 10 is a diagram illustrating an example of a conventional image filter.

FIG. 11 is an explanatory diagram showing a conventional method for generating one halftone dot.

FIG. 12 is a diagram showing an edge portion of a halftone dot image.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Smoothing processing part 20 Contrast extraction part 30 Table reference part 40 Filter calculation part 51,52 Integrator 53 Adder 100 Image input part 200 Image processing part 201 Operation input part 202 Information display part 300 Image output part S Main signal S ' Filtered signal S '' Output signal M, (1-M) Mixing ratio C Contrast

Claims (8)

[Claims] 1. A method for performing a predetermined process for each pixel on an original image, comprising: (a) applying a predetermined size image filter to a main signal of a pixel of interest to be processed; Generating a signal; (b) for each of the plurality of neighboring pixels located in the vicinity of the pixel of interest, performing a smoothing process in a predetermined area around the neighboring pixel, thereby obtaining the plurality of neighboring pixels. Obtaining an average density value for each of the pixels; (c) obtaining a contrast for the pixel of interest based on the plurality of average density values obtained from the plurality of neighboring pixels; and (d) obtaining the contrast. Deriving a mixing ratio between the main signal and the filtered signal accordingly; and (e) generating an output signal by mixing the main signal and the filtered signal based on the mixing ratio, Have Image processing method, characterized in that. 2. The method according to claim 1, wherein the mixing ratio is such that a ratio corresponding to the filtered signal increases as the contrast decreases, and a ratio corresponding to the main signal increases as the contrast increases. Is determined to be larger. 3. A method for performing a predetermined process for each pixel on an original image, comprising: (a) applying an image filter of a predetermined size to a target pixel and a plurality of neighboring pixels located in the vicinity of the target pixel; Generating a filtered signal by applying; (b) obtaining a contrast for the pixel of interest based on a filtered signal for a plurality of neighboring pixels located near the pixel of interest; (c) Deriving a mixing ratio between the main signal and the filtered signal for the pixel of interest according to the contrast; (d) mixing the main signal and the filtered signal for the pixel of interest based on the mixing ratio. Generating an output signal for the pixel of interest. 4. The method according to claim 3, wherein the mixing ratio is such that a ratio corresponding to the filtered signal increases as the contrast decreases, and a ratio corresponding to the main signal increases as the contrast increases. Is determined to be larger. 5. An apparatus for performing a predetermined process for each pixel on an original image, comprising: (a) applying an image filter of a predetermined size to a main signal of a pixel of interest to be processed; Means for generating a signal, (b) for each of a plurality of neighboring pixels located in the vicinity of the pixel of interest, by performing a smoothing process in a predetermined area around the neighboring pixel, the plurality of neighboring pixels Means for obtaining an average density value for each of the pixels; (c) 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; Means for guiding a mixing ratio between the main signal and the filtered signal in response thereto; (e) means for generating an output signal by mixing the main signal and the filtered signal based on the mixing ratio, Equipped The image processing apparatus characterized by. 6. The apparatus according to claim 5, wherein the mixing ratio is such that a ratio corresponding to the filtered signal increases as the contrast decreases, and a ratio corresponding to the main signal increases as the contrast increases. Is set to be large. 7. An apparatus for performing a predetermined process for each pixel on an original image, comprising: (a) applying an image filter of a predetermined size to a target pixel and a plurality of neighboring pixels located near the target pixel; Means for applying to generate a filtered signal; (b) means for obtaining a contrast for the pixel of interest based on a filtered signal for a plurality of neighboring pixels located in the vicinity of the pixel of interest; (c) Means for deriving a mixing ratio between the main signal and the filtered signal for the pixel of interest according to the contrast; (d) mixing the main signal and the filtered signal for the pixel of interest based on the mixing ratio Means for generating an output signal for the pixel of interest. 8. The apparatus according to claim 7, wherein the mixing ratio is such that a ratio corresponding to the filtered signal increases as the contrast decreases, and a ratio corresponding to the main signal increases as the contrast increases. Is set to be large.