JPH08331382A - Image processing unit - Google Patents

Abstract

PURPOSE: To improve the image quality by generating a noise signal and adding the noise signal to at least either of a received image signal and a reference signal so as to allow a longitudinal stripe pattern to be hardly visible in the case of halftone image recording and improving a gradation characteristic of a highlight part. CONSTITUTION: The processing unit is provided with a noise signal generating means 16 and a noise signal addition means 17. The noise signal generating means 16 generates a noise signal with a prescribed amplitude and an irregular period. The noise signal addition means 17 receives an image signal converted by a D/A converter section 12 and adds the noise signal generated by the noise signal generating means 16 to the received image signal and provides an output of the result to a comparator 15. That is, the noise signal is added to the image signal subject to D/A conversion. Thus, irregular dispersion takes place in a pulse width to be modulated in the case of pulse width modulation, that is, a pulse width of an output signal, and even when picture elements are consecutive in the subscanning direction, a longitudinal stripe pattern is hardly observed and transition of density getting gradually higher from absence of any picture element is made smooth.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for reproducing a halftone image such as a photograph with high quality, and more particularly to an image processing apparatus for expressing density gradation by pulse width modulation.

[0002]

2. Description of the Related Art In recent years, electrophotographic printers represented by laser printers, electrophotographic copying machines and the like are equipped with an image processing device for performing pulse width modulation on an input image signal, There is one in which an analog density gradation is expressed by this image processing apparatus to reproduce a halftone image such as a halftone dot or a photograph with high quality. As an image processing apparatus included in such a printer or a copying machine,
For example, there is one as shown in FIG. This image processing apparatus includes a CPU (not shown) included in a printer, a copying machine, or the like.
A pixel clock signal having a predetermined cycle is received from (Central Processing Unit) or the like, and operates in synchronization with the pixel clock signal.
Analog (hereinafter abbreviated as D / A) conversion unit 12 and 1/2
It is provided with a frequency divider 13, a triangular waveform generator 14, and a comparator 15.

The image signal input unit 11 receives an image signal input by a user (user) from a host device connected to a printer or an image reading unit such as a scanner in a copying machine. The D / A converter 12
The image signal received by the image signal input unit 11 is converted into an analog signal from a digital signal. The ½ frequency divider 13 divides the frequency of the pixel clock signal into ½ in order to improve the density gradation characteristics of the reproduced halftone image. The triangular waveform generator 14 generates a triangular wave as a reference signal when performing pulse modulation from the frequency division result of the 1/2 frequency divider 13. However, the triangular waveform generator 14 may generate a sawtooth wave instead of a triangular wave. Comparator 1
Reference numeral 5 compares the image signal analog-converted by the D / A converter 12 with the reference signal generated by the triangular waveform generator 14, and modulates the pulse width with the reference signal as a threshold. .

In the image processing apparatus thus constructed,
When the image signal input section 11 receives an image signal for reproducing a halftone image, the D / A conversion section 12 converts the image signal into an analog signal. At the same time, the 1/2 divider 13
Then, the frequency of the pixel clock signal as shown in FIG. 11A is divided in half, and further, in the triangular waveform generator 14,
From the frequency division result, a triangular wave as shown in FIG. 11B is generated as a reference signal. Then, the comparator 15 compares the image signal analog-converted by the D / A converter 12 with the reference signal generated by the triangular waveform generator 14 to perform pulse width modulation, and FIG. It outputs as an output signal such as.

According to this output signal, for example, when the printer engine provided in the printer records on the recording medium,
As shown in FIG. 11D, a pixel pattern corresponding to the pulse width of the output signal is recorded on the recording medium. Then, by repeating this pixel pattern, that is, recording for each line in the main scanning direction in the sub-scanning direction, FIG.
A halftone image having an image structure such as is recorded. That is, in this image processing apparatus, the gradation width is expressed by increasing the pulse width of the high density portion of the halftone image to be recorded and decreasing the pulse width of the low density portion of the image to be printed by a printer or a copying machine. It is possible to record not only letters and diagrams but also halftone images such as halftone dots and photographs.

By the way, in this image processing apparatus, since density gradation is expressed by pulse width modulation, when a halftone image is recorded by a printer engine or the like, the pixels of the pixel pattern are continuous in the sub-scanning direction, and the recording is performed. The resulting halftone image has a vertical stripe pattern. This vertical striped pattern is easily visually recognized by a viewer of the image, and as a result, it becomes a factor of lowering the evaluation of the image quality of the recorded halftone image. Therefore, for example, as in the device disclosed in Japanese Patent Laid-Open No. 4-150373, each time when recording of one line in the main scanning direction is repeated in the sub scanning direction, the phase is shifted by 180 ° to perform pulse width modulation, There is one in which the pixels of the pattern are not continuous in the sub-scanning direction to improve the visual gradation characteristics when reproducing a halftone image.

[0007]

However, in the apparatus disclosed in the above-mentioned Japanese Patent Laid-Open No. 4-150373, for example, a halftone image in which the density gradually increases from the white portion where no pixel is generated. When the pulse width modulation for recording is performed, no pulse is generated in the white part, and a pulse having a pulse width according to the density is generated in the other part and is output as an output signal. . Therefore, if you record an image according to the output signal,
The lack of continuity from the part that does not generate the pulse to the part having the pulse width according to the density makes it easy to visually understand the transition from the white part to the other part, and as a result, the density of the image The gradation in the low portion, so-called highlight portion, is not smooth.

Therefore, according to the present invention, when recording a halftone image, the vertical stripe pattern is made difficult to see, and the gradation characteristic in the highlight portion is further improved, thereby improving the image quality of the halftone image to be recorded. It is an object of the present invention to provide an image processing device that can do the above.

[0009]

SUMMARY OF THE INVENTION The present invention is an image processing device devised to achieve the above object, in which an input image signal is compared with a reference signal of a predetermined period to perform pulse width modulation and output. In an image processing device for outputting as a signal, a noise signal generating means for generating a noise signal which is an irregular signal, and the noise signal generated by the noise signal generating means is applied to at least one of the image signal and the reference signal. And a noise signal adding means for adding.

[0010]

In the image processing apparatus having the above construction, the noise signal generating means generates the noise signal, and the noise signal adding means adds the noise signal to at least one of the input image signal and the reference signal. As a result, in this image processing device, when the input image signal is compared with the reference signal and pulse width modulation is performed, since the noise signal is added to at least one of the image signal and the reference signal, the modulation is performed. The irregular pulse width depending on the noise signal is generated in the pulse width of the output signal, that is, the pulse width of the output signal. Therefore, if an image is recorded based on this output signal, the width of the pixel for recording the image will have irregular variations according to the pulse width of the output signal. It becomes difficult to see the vertical stripe pattern even after the continuous line, and it becomes more difficult to visually recognize the transition from the portion where no pixel is generated to the portion where the density is gradually increased.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An image processing apparatus according to the present invention will be described below with reference to the drawings. However, here, a case where the present invention is applied to an image processing apparatus included in a laser printer will be described.

[First Embodiment] An image processing apparatus according to the present invention will be described below. The image processing apparatus of this embodiment is configured as shown in FIG. 1 and is used in the system configuration as shown in FIG.

This system configuration comprises a host device 1 and a laser printer 2. The host device 1 is composed of, for example, a personal computer, a workstation, or the like, and when the image signal is input by the user, the image signal is sent to the laser printer 2. The laser printer 2 records an image signal from the host device 1 on a recording medium, and includes an image recording device 3 and an image processing device 10. The image recording device 3 includes, for example, a printer engine, and records an image on a recording medium by an electrophotographic method based on an output signal described later.

The image processing apparatus 10 used in such a system configuration receives an image signal from the host apparatus 1, subjects the image signal to pulse width modulation, and outputs it as an output signal to the image recording apparatus 3. . Also,
As shown in FIG. 1, this image processing device 10 includes an image signal input unit 11, a D / A conversion unit 12, and a 1/2 frequency divider, as in the conventional image processing device (see FIG. 10). 13, a triangular waveform generator 14, a comparator 15, and a noise signal generating means 16 and a noise signal adding means 17.

The noise signal generating means 16 is a noise signal having a certain amplitude and an irregular cycle, that is, a white signal which is an irregular signal including outputs of all frequencies within a certain frequency band. It causes noise. The noise signal adding means 17 includes the D / A conversion unit 1.
2 provided between the comparator 2 and the comparator 15, and D / A
The image signal converted by the conversion unit 12 is received, the noise signal generated by the noise signal generation means 16 is added to this image signal, and the image signal is sent to the comparator 15. That is,
The noise signal adding means 17 is adapted to add a noise signal to the analog-converted image signal.

Next, an operation example of the image processing apparatus 10 configured as above will be described with reference to the waveform chart of FIG. When an image signal is input by the user in the host device 1, the image signal input unit 11 receives the image signal (step 101, hereinafter step is abbreviated as S) and sends it to the D / A conversion unit 12. D / A converter 12
Then, the image signal from the image signal input unit 11 is converted from a digital signal to an analog signal in synchronization with the pixel clock signal (S102). By the conversion in the D / A converter 12, the image signal is converted into a high level signal in a high density portion and a low level signal in a low density portion.

At the same time that the D / A converter 12 performs analog conversion, the noise signal generating means 16 generates a noise signal (S103). Then, the noise signal adding means 1
In 7, the image signal from the D / A converter 12 is received,
The noise signal generated by the noise signal generating means 16 is added to the image signal (S104). Further, the 1/2 frequency divider 13 divides the frequency of the pixel clock signal into 1/2, and the triangular waveform generator 14 further divides the frequency of the pixel clock signal into 1/2.
On the basis of the frequency division result according to, a triangular wave having a period twice that of the pixel clock signal is generated as a reference signal (S10).
5).

When the noise signal is added to the image signal by the noise signal adding means 17 and the reference signal is generated by the triangular waveform generator 14, the comparator 15 uses the image signal to which the noise signal is added as the reference signal. And pulse width modulation is performed using this reference signal as a threshold (S106). The comparator 15 modulates a high-level image signal, that is, a high-density portion into a large pulse width, and a low-level image signal, that is, a low-density portion into a small pulse width. . However, since the noise signal is added to the image signal, the pulse width modulation result in the comparator 15 corresponds to the irregular frequency of the noise signal and within the range corresponding to the amplitude of the noise signal. , Irregular variations occur. That is, in the comparator 15, by adding the noise signal to the image signal, even the same image signal is modulated into a different pulse width each time the pulse width modulation is performed. Then, the comparator 15 outputs the pulse width modulation result to the image recording device 3 as an output signal.

As described above, the image processing apparatus 10 according to the present embodiment.
Then, the noise signal generated by the noise signal generating means 16 is added to the image signal by the noise signal adding means 17, pulse width modulation is performed on the image signal to which the noise signal is added, and the result is used as an output signal. It is designed to output. Therefore, the pulse width of the output signal irregularly varies depending on the noise signal, and thus the image recording device 3 that records a halftone image based on the output signal irregularly varies the pixel width of the pixel pattern. Due to this irregular variation, the halftone image recorded by the image recording device 3 is
Even if the pixel patterns are continuous in the sub-scanning direction, the vertical striped pattern becomes difficult to visually see. That is, when the image processing apparatus 10 of the present embodiment performs pulse width modulation, it is possible to improve the visual gradation characteristics when reproducing a halftone image,
As a result, the image quality of the halftone image can be improved.

Next, in the image processing apparatus 10 of the present embodiment, an operation example in the case of performing pulse width modulation of the highlight part will be described with reference to the waveform diagram of FIG. For example, when the image signal input unit 11 receives an image signal in which the density gradually increases from the white portion in which no pixel is generated, the D / A conversion unit 12 performs the same operation as in the above-described operation example. The image signal is converted to analog (S11
1). The D / A converter 12 converts the image signal into a signal of the lowest level in the white part, that is, a part in which no pixel is generated, and into a signal of a level corresponding to the density in the other parts.

When the image signal is converted to analog, the noise signal adding means 17 adds the noise signal generated by the noise signal generating means 16 to the converted image signal (S).
112). Then, the comparator 15 compares the image signal added with the noise signal with the reference signal (S113), and performs pulse width modulation with the reference signal as a threshold (S11).
4). At this time, since the noise signal is added to the image signal, when the pulse width modulation is performed by the comparator 15, irregular variations occur in the modulation result. In particular, in the portion where the image signal is at the lowest level, the noise signal is added, so that an irregular variation occurs such that the pulse of the output signal is generated or not generated every time the pulse width modulation is performed. Like

As described above, the image processing apparatus 10 according to the present embodiment.
In this case, since the noise signal is added to the image signal to perform pulse width modulation, the noise signal is not added to the image signal and compared with the reference signal as in the conventional image processing apparatus (S11).
5) Compared with the case of performing pulse width modulation (S11
6), especially at the lowest level of the image signal,
Irregular variations occur such that pulses of the output signal are generated or not generated. Therefore, the image recording device 3 for recording a halftone image based on this output signal
Then, irregular variations occur in the generation of pixels in the portion where the image signal has the lowest level, that is, the white portion. Due to this irregular variation, the transition from the white portion to another portion of the halftone image recorded by the image recording device 3 becomes difficult to visually recognize. That is, when pulse width modulation is performed by the image processing apparatus 10 according to the present exemplary embodiment, visual gradation characteristics when reproducing a halftone image are improved, and continuity of density change particularly in a highlight portion is improved. As a result, the gradation in the highlight portion can be smoothed.

In this embodiment, the case where the noise signal is added to the image signal has been described. However, as shown in FIG. 5, for example, the noise signal adding means 17 is provided in the triangular waveform generator 14.
Even when the noise signal is added to the reference signal and the comparator 15 to add the noise signal to the reference signal, the same effect as the above-described example can be obtained. Further, it can be implemented even when the noise signal is added to both the image signal and the reference signal, and in this case also, the same effect as in the case of adding the noise signal to the image signal can be obtained. To be

[Second Embodiment] An image processing apparatus according to the present invention will be described below. However, the same components as those in the first embodiment described above are designated by the same reference numerals, and the description thereof will be omitted. As shown in FIG. 6, the image processing apparatus of this embodiment is provided with an amplitude modulation means 18 in addition to the first embodiment.

The amplitude modulating means 18 is provided between the noise signal generating means 16 and the noise signal adding means 17, and generates a sine wave synchronizing with the cycle of the reference signal generated by the triangular waveform generator 14. It has a function of generating the noise signal and further modulates the amplitude of the noise signal generated by the noise signal generating means 16 according to a sine wave synchronized with the reference signal. That is, the amplitude modulation means 18 modulates the amplitude of the noise signal in synchronization with the cycle of the reference signal.

Next, an operation example of the image processing apparatus 10a configured as described above will be described with reference to the waveform chart of FIG. Similarly to the first embodiment described above, when the image signal input unit 11 receives an image signal, the D / A conversion unit 12
The image signal is converted to analog (S201). At the same time that the D / A converter 12 is performing analog conversion, the noise signal generating means 16 is generating a noise signal (S202). At this time, the amplitude modulation means 18
Then, generate a sine wave synchronized with the cycle of the reference signal (S2
03), and further, the amplitude of the noise signal generated by the noise signal generating means 16 according to the sine wave is modulated (S204).

When the D / A converter 12 performs analog conversion and the amplitude modulating means 18 modulates the amplitude of the noise signal, the noise signal adding means 17 performs the amplitude modulation on the image signal. Add a noise signal (S20)
5). Then, the comparator 15 compares the image signal to which the noise signal is added with the reference signal (S206), and performs pulse width modulation with the reference signal as a threshold (S207).
At this time, since the noise signal added to the image signal is modulated in synchronization with the cycle of the reference signal by the amplitude modulation means 18, its amplitude is modulated in a large pulse width by the pulse width modulation. It is small, and is large in the portion where the pulse width is modulated to a smaller pulse width.

Therefore, when the pulse width modulation is performed by the comparator 15, the pulse width of the output signal has a large variation when the image density is low, and the variation is small when the image density is high, as shown in FIG. Become. In the image recording device 3 that records a halftone image based on this output signal, a large variation occurs in the pixel width in the low density portion and a small variation in the pixel width in the high density portion. Therefore,
The halftone image recorded by the image recording device 3 has an improved image gradation characteristic in a low density portion, that is, a highlight portion, and further, an image due to a variation in pixel width in a high density portion. The occurrence of so-called jaggies is reduced.

Thus, the image processing apparatus 10 of this embodiment
In a, since the amplitude of the noise signal added to the image signal is modulated by the amplitude modulator 18, the pulse width of the output signal varies irregularly depending on the density of the image. Therefore, in the image recording apparatus 3 which records a halftone image based on this output signal, the visual gradation characteristic in the highlight portion is improved, and further, the image roughness in the high density portion of the image is reduced. . That is, the image processing apparatus 10 according to the present exemplary embodiment.
When the pulse width modulation is performed with a, when reproducing a halftone image, it is possible to improve the visual gradation characteristics in the highlight portion and prevent the occurrence of image roughness in the high image density portion. Can be done at the same time.

Although the amplitude modulating means 18 modulates the amplitude of the noise signal in accordance with the sine wave in the present embodiment, the present invention is not limited to this sine wave, and a reference signal is used. If the signal has a synchronized waveform,
It may be another. In this case, the relationship between the density of the image and the variation of the pulse width of the output signal can be arbitrarily set by selecting the waveform.

[Third Embodiment] Here, an image processing apparatus according to the present invention will be described. However, the same components as those in the first embodiment described above are designated by the same reference numerals, and the description thereof will be omitted. As shown in FIG. 9, the image processing apparatus of this embodiment is provided with an amplitude modulation means 18a and an edge strength recognition means 19 in addition to the first embodiment. The amplitude modulation means 18a is similar to the amplitude modulation means 18 of the second embodiment in that the noise signal generation means 16 is used.
Which modulates the amplitude of the noise signal generated in 1., unlike the amplitude modulating means 18 of the second embodiment, modulates the amplitude of the noise signal in accordance with the edge strength signal from the edge strength recognizing means 19 described later. Is.

The edge strength recognizing means 19 is provided between the image signal input section 11 and the D / A conversion section 12, receives the image signal from the image signal input section 11, and detects the edge of the image signal. It recognizes strength. The edge strength represents a difference in density between adjacent portions (for example, pixel units) when an image signal is recorded as an image, and the edge strength is strong in a portion where the difference in density suddenly increases. In addition, the edge strength is weakened in a portion where there is no difference in density. That is, the edge strength recognizing means 19 recognizes the magnitude of the difference in density between the adjacent portions in the image signal from the image signal input section 11. By recognizing the edge strength, for example, the image signal input section It is determined whether the image signal from 11 is for recording a character, a line drawing, or the like, or for recording a halftone image such as a photograph. Then, the edge strength recognizing means 19 sends the recognition result of the edge strength to the amplitude modulating means 18a as an edge strength signal.

Next, an operation example of the image processing apparatus 10b configured as above will be described. When the image input section 11 receives the image signal, the edge strength recognition means 19
The edge strength of the image signal is recognized, and the recognition result is sent to the amplitude modulation means 18a as an edge strength signal. The amplitude modulation means 18a receiving the edge strength signal modulates the amplitude of the noise signal generated by the noise signal generation means 16 based on the edge strength signal. At this time, the amplitude modulating means 18a modulates the noise signal into a small amplitude if the edge strength is strong, or modulates the noise signal into a large amplitude if the edge strength is weak, according to the edge strength of the edge strength signal.

When the edge strength recognizing means 19 recognizes the edge strength of the image signal, the D / A converter 12
The image signal is converted into an analog signal and sent to the noise signal adding means 17. Then, the noise signal adding means 17
Then, the amplitude modulation means 1 is applied to the analog-converted image signal.
The noise signal modulated by 8a is added. When the noise signal is added to the image signal, pulse width modulation is performed in the same manner as in the first and second embodiments described above, and the modulation result is output as an output signal. Therefore, the pulse width of the output signal has a small variation when the edge strength is strong, and has a large variation when the edge strength is weak.

In the image recording device 3 for recording a halftone image based on this output signal, a small variation in pixel width occurs in a portion having a strong edge strength, and a large variation in pixel width occurs in a portion having a weak edge strength. Occurs. Therefore, in the image recording apparatus 3, when recording a portion having a high edge strength such as a character or a line drawing, the occurrence of so-called jaggies, which is an image roughness due to the variation of the pixel width, is reduced.
Further, for example, the gradation characteristic is improved when recording a portion having a weak edge strength such as a halftone image.

Thus, the image processing apparatus 10 of this embodiment
In b, the edge strength recognizing means 19 recognizes the edge strength of the image signal, and the amplitude modulating means 18 is recognized based on the recognition result.
Since the amplitude of the noise signal added to the image signal is modulated by a, the pulse width of the output signal varies irregularly according to the edge strength of the image signal. Therefore, in the image recording apparatus 3 which records a halftone image based on this output signal, the roughness of the image is reduced in the portion having a strong edge strength, and the gradation characteristic is improved in the portion having a weak edge strength. That is, when pulse width modulation is performed by the image processing apparatus 10b of the present embodiment, a noise signal having a suitable amplitude can be added to any image, and when reproducing a halftone image, edge strength is reproduced. It is possible to prevent the image from being roughened in a portion having a strong edge and simultaneously improve visual gradation characteristics in a portion having a weak edge strength.

In the above-described first to third embodiments, the case where the present invention is applied to the image processing apparatus included in the laser printer has been described. However, the present invention is not limited to this and, for example, As in the case of application to a copying machine or the like, an image reading unit such as a scanner is provided instead of the host device in FIG. 2, and pulse width modulation is performed on the image signal input by the image reading unit. Good.

[0038]

As described above, in the image processing apparatus of the present invention, the noise signal generated by the noise signal generating means is added to the image signal by the noise signal adding means, and the image to which the noise signal is added is added. Pulse width modulation is applied to the signal,
The output signal is output. Therefore, since the pulse width of the output signal varies irregularly according to the noise signal, if the image is recorded based on this output signal, the width of the pixel for recording the image varies irregularly. Even if the pixels are continuous in the sub-scanning direction, the vertical stripe pattern becomes difficult to visually see, and the transition from the part where no pixel is generated to the part where the density is gradually increased becomes difficult to visually recognize. Therefore, according to the image processing apparatus of the present invention, by performing the pulse width modulation, it is possible to improve the visual gradation characteristics when a halftone image is recorded, and particularly, to improve the density of the highlight portion. The gradation can be smoothed, and as a result, the image quality of the reproduced halftone image can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a first embodiment of an image processing apparatus according to the present invention.

FIG. 2 is a block diagram showing a system configuration in which the image processing apparatus according to the present invention is used.

3 is a waveform diagram showing an operation example of pulse width modulation in the image processing apparatus of FIG.

4 is a waveform diagram showing an operation example of pulse width modulation of a highlight part in the image processing apparatus of FIG.

5 is a block diagram showing a schematic configuration of an application example of the image processing apparatus of FIG.

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

7 is a waveform diagram showing an operation example of pulse width modulation in the image processing apparatus of FIG.

8 is an explanatory diagram showing the relationship between image density and pulse width variation in the image processing apparatus of FIG.

FIG. 9 is a block diagram showing a schematic configuration of a third embodiment of the image processing apparatus according to the present invention.

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

11A and 11B are explanatory diagrams showing signals processed in an image processing apparatus of a conventional example, FIG. 11A shows a pixel clock signal, FIG. 11B shows a reference signal, and FIG. (D) shows a pixel pattern according to the output signal,
(E) shows an image structure recorded by the pixel pattern.

[Explanation of symbols]

 10, 10a, 10b Image processing device 11 Image signal input unit 12 D / A conversion unit 13 1/2 frequency divider 14 Triangular waveform generator 15 Comparator 16 Noise signal generating means 17 Noise signal adding means 18, 18a Amplitude modulating means 19 Edge strength recognition means

Claims (3)

[Claims] 1. An image processing device for comparing an input image signal with a reference signal having a predetermined period to perform pulse width modulation and outputting the output signal as a noise signal generating means for generating a noise signal which is an irregular signal. An image processing apparatus comprising: a noise signal adding means for adding the noise signal generated by the noise signal generating means to at least one of the image signal and the reference signal. 2. The image processing according to claim 1, further comprising amplitude modulation means for modulating the amplitude of the noise signal generated by the noise signal generation means in synchronization with the cycle of the reference signal. apparatus. 3. An edge strength recognizing means for recognizing the edge strength of the input image signal, and an amplitude modulating means for modulating the amplitude of the noise signal based on the edge strength recognized by the edge strength recognizing means. The image processing apparatus according to claim 1, wherein the image processing apparatus is provided.