JPH11136500A - Image forming apparatus and control method thereof - Google Patents

Abstract

(57) [Problem] To provide an image forming apparatus capable of improving the image quality of an output image and a control method thereof. When an input image signal is a binary image signal, an image processing unit first converts the binary image signal into a multilevel image signal. An averaging process is performed on the multi-valued image signal. The resolution of the averaged image signal is converted to an output resolution.
An image based on the resolution-converted image signal is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus for forming an image based on an image signal input at a resolution different from an output resolution, and a control method therefor.

[0002]

2. Description of the Related Art In recent years, among image forming apparatuses such as copiers having a reader unit for reading an image and a printer unit for forming an image read from the reader unit, an image forming apparatus employing a digital system has become widespread. Here, the digital method refers to treating an image signal as a digital electric signal. Therefore, in a digital image forming apparatus, an image read by a reader unit is once converted into a digital electric signal and then sent to a printer unit. The printer unit modulates a light emitting process such as a laser based on the transmitted digital electric signal to emit light, and forms an image on an image carrier such as a photosensitive drum.

Particularly, in a digital copying machine connected to a network line, in addition to the function of the copying machine, a printer such as a facsimile or a computer for outputting a facsimile-received image signal is used by using a printer unit in the apparatus. It can be used as a printer that outputs an image signal input from an external device. In general, such a single device having functions of a copier, a facsimile, and a printer is called a digital multifunction peripheral, and has recently begun to spread.

In such a digital multifunction peripheral, since the functions of a copier, a facsimile, and a printer are performed, there are cases where a plurality of resolutions of image signals are input to the digital multifunction peripheral. In particular, in the case of a FAX and a printer, the FAX basically uses a resolution of a meter unit, while the printer uses a resolution of an inch unit. And the resolution of the image signal input from the external device is generally different. Therefore, in the case of outputting a FAX and a printer in a digital multifunction peripheral, unless the resolution of the printer unit is made variable, the resolution of either the FAX-received image signal or the image signal input from an external device may be changed. Needs to be converted to the output resolution set in the digital multifunction peripheral.

[0005]

However, in the above-described resolution conversion in the above-mentioned conventional digital multifunction peripheral, particularly, when the resolution conversion is performed on an image signal (binary image signal) received by facsimile, moiré is generated. In some cases, periodic density unevenness occurs, and the image quality of an output image is reduced.

The present invention has been made in view of the above problems, and has as its object to provide an image forming apparatus capable of improving the image quality of an output image and a control method thereof.

An image forming apparatus according to the present invention for achieving the above object has the following arrangement.
That is, an image forming apparatus for forming an image based on an image signal input at a resolution different from the output resolution, wherein when the input image signal is a binary image signal, the binary image signal is converted to a multi-valued image signal. Multi-level means for multi-level image signal, the image signal multi-level by the multi-level means,
Averaging processing means for performing averaging processing, resolution conversion means for converting the resolution of the image signal averaged by the averaging processing means to the output resolution, and an image signal whose resolution has been converted by the resolution conversion means And an image forming apparatus for forming an image based on the image.

[0007] Preferably, the averaging means averages the multi-valued image signal using a two-dimensional spatial filter.

[0008] Preferably, the image forming apparatus includes:
It is connected to an external device via a network line.

Preferably, the binary image signal is:
The image forming apparatus according to claim 1, wherein the image signal is an image signal received by facsimile from the external device.

A method for controlling an image forming apparatus according to the present invention for achieving the above object has the following arrangement. That is,
A control method of an image forming apparatus that forms an image based on an image signal input at a resolution different from an output resolution,
When the input image signal is a binary image signal, a multi-level conversion step of converting the binary image signal into a multi-level image signal, and an image multi-valued in the multi-level conversion step An averaging process for performing an averaging process on the signal, a resolution conversion process for converting the resolution of the image signal averaged in the averaging process to the output resolution, and a resolution conversion in the resolution conversion process. Forming an image based on the selected image signal.

A computer readable memory according to the present invention for achieving the above object has the following configuration.

That is, a computer-readable memory storing a program code for controlling an image forming apparatus for forming an image based on an image signal input at a resolution different from the output resolution, wherein the input image signal is 2 If the image signal is a value image signal, a program code of a multi-value process for multi-leveling the binary image signal into a multi-level image signal, and an image signal multi-valued in the multi-value process are averaged. A program code for an averaging process for performing the averaging process, a program code for a resolution conversion process for converting the resolution of the image signal averaged in the averaging process to the output resolution, and a resolution in the resolution conversion process. And a program code for a forming step of forming an image based on the converted image signal.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a cross-sectional view showing the internal structure of a digital multifunction peripheral using an electrophotographic system, which is an example of an image forming apparatus applicable to the embodiment of the present invention.

This digital multifunction peripheral is connected to an external device such as a computer via a network line 1001 in addition to a copier function, and functions as a printer for outputting an image signal transmitted from the external device. FAX
It also functions as a FAX that outputs a received image signal.

In FIG. 1, reference numeral 120 denotes a reader unit,
An original table glass 121 on which an original is placed, a fluorescent lamp 122 for illuminating the original, an optical sensor 123 as a photoelectric conversion element such as a CCD, and the like are provided. The original placed on the platen glass 121 is illuminated by a fluorescent lamp 122, and the reflected light is read by an optical sensor 123 so that the first light at the time of copying is read.
Is obtained. Note that the resolution of the first image signal is 600 dpi.

The first signal read by the optical sensor 123
Is subjected to predetermined image processing such as gradation conversion by the image signal processing unit 101 in the printer unit 130, and is output as a second image signal. Note that the resolution of the second image signal is 600 dpi. This second image signal is sent to the laser driver 102.

Next, the configuration of the printer unit 130 will be described.

The printer unit 130 includes the laser driver 10
2. Photoconductor drum 106, primary charger 112, developing unit 1
07, a transfer charger 113, a fixing device 114, and the like. The laser driver 102 is a circuit for driving the semiconductor laser 103, and according to the second image signal input from the image signal processing unit 101,
3 is caused to emit light. The laser light 104 is swung right and left by a rotating polygon mirror 105 to scan on a photosensitive drum 106.
The surface of the photosensitive drum 106 is uniformly charged to about -700 V by the primary charger 112. Accordingly, an electrostatic latent image is formed on the photosensitive drum 106 according to the input second image signal. In this embodiment, the writing resolution of the printer unit 130 is 600 dpi.

Then, the electrostatic latent image on the surface of the photosensitive drum 106 is developed into a toner image by a developing unit 107. In addition, the developing device 1
Reference numeral 07 denotes a developing bias (D) applied to a developer carrying member carrying a toner to which a negative charge is applied by utilizing a triboelectric charging phenomenon.
This is a reversal developing type developing device that develops toner with an electric field generated between the surface of the photosensitive drum 106 and the developer carrier by applying -600 V for the C component and 1000 Vpp for the AC component.

Next, after the toner image is developed on the photosensitive drum 106, the toner image is transferred to the transfer charger 113.
Is transferred onto a transfer material (not shown). In the present embodiment, a cut sheet is used as a transfer material. The transfer material is stored in a paper cassette mounted on the main body, is taken into the apparatus by a paper feed roller (not shown), and is supplied to a transfer portion of the photosensitive drum 106 in synchronization with the toner image. Then, after the toner image on the transfer material is fixed by the fixing device 114, the toner image is discharged out of the apparatus as an output image.

On the other hand, in the case of facsimile (fine mode), the image signal processing unit 101 sets the image signal processing unit to 8.0 pel × 7.7 pe.
The binary signal of 1 is input from the external device 1000 via the network line 1001 as a first image signal. At this time, since the resolution of the printer unit 130 is 600 dpi, it is necessary to perform resolution conversion in order to output an image having the same size as an image transmitted from the external device to the present device.

Although various conventional resolution conversion methods have been proposed, a method as shown in FIG. 2 is generally employed.

FIG. 2 is a diagram for explaining a conventional resolution conversion method.

In FIG. 2, for the sake of simplicity, only one-dimensional resolution conversion will be described.
A case of converting an image with a resolution of pi to an image with a resolution of 600 dpi (1.67 times) will be described. The width of the black portion in each unit pixel in the figure corresponds to the size of the multi-level signal.

The size of one pixel of a 360 dpi image is
It is 1.67 times the size of one pixel of an image of 600 dpi. Therefore, when one pixel of a 360 dpi image is input, the density is not preserved unless 1.67 pixels of a 600 dpi image are output. 1 of this 600 dpi image
The part (0.67 pixel) less than the pixel is converted to 600 dpi
Is represented as a multi-valued printer. At this time, the input signal of the image of 360 dpi and the image signal of 600 dpi
There are only two types of phase of the output signal of the image in relation to the resolution. First, when the center of the pixel of the input signal coincides with the center of the pixel of the output signal, half of the 0.67 pixel, that is, 0.33 pixel is output to both sides of the pixel of the output signal. Also, the leading or trailing edge of the pixel of the input signal is
If the output signal matches the leading or trailing edge of the pixel,
0.67 pixels are output to the adjacent pixel that does not match the pixel of the input signal of the output signal. The same applies when two pixels of a 360 dpi image are successively input, and the result is as shown on the right side of FIG.

Using such a resolution conversion method,
As long as the relationship between the resolution of the input signal and the resolution of the output signal is not an integral multiple, a periodic pattern different from the cycle of the input signal appears. At this time, if the reproducibility of the halftone density of the printer is unstable, density unevenness according to this pattern appears on the output image. This phenomenon is called moiré.

Therefore, the present invention eliminates moiré by performing resolution conversion as described below.

First, an outline will be described. For example, it is assumed that a binary signal of 8 pel × 7.7 pel is input to the image signal processing unit 101 as a first image signal. Next, the binary signal of "0" and "1" is converted into a multi-valued level. Here, “0” and “1” are converted into multi-level signals of “0” and “255”, respectively. Thereafter, a multi-level signal is averaged by applying a spatial filter of several pixels square to the multi-level signal. After that, resolution conversion is performed. By performing the resolution conversion after the averaging process, it is possible to perform the resolution conversion free from moiré.

Hereinafter, a specific description will be given with reference to FIG.

FIG. 3 is a diagram for explaining a specific example of the resolution conversion method according to the embodiment of the present invention.

First, a case in which resolution conversion is performed on an input signal as shown in FIG. Also, here, for simplicity of explanation, a case where an input signal of 360 dpi is converted into an output signal of 600 dpi will be described. In the figure, the width of the black portion in each unit pixel corresponds to the size of the multi-level signal. This multi-level signal is 360d
It is a halftone signal represented by a binary signal of pi × 360 dpi. This input signal is subjected to resolution conversion to obtain 6
When the output signal is set to 00 dpi × 600 dpi, an output signal as shown in FIG. 3B is obtained.

On the other hand, in the case of the resolution conversion according to the present invention,
First, by performing multi-valued and averaging processing, FIG.
An image signal as shown in (c) is obtained. In the present embodiment, the averaging process is performed using a 3 × 3 pixel spatial filter as shown in FIG. When the above-described conventional resolution conversion is performed on the image signal after the multi-leveling and averaging processing, an output signal as shown in FIG. 3D is obtained. FIGS. 4 to 7 show results when the input signal and the output signal described above are expressed by density. FIG. 4 shows FIG.
5A corresponds to FIG. 3B, FIG. 6 corresponds to FIG. 3C, and FIG. 7 corresponds to FIG.
(D).

As can be seen by comparing FIGS. 5 and 7, in FIG. 5, which is a result of the conventional resolution conversion, each pixel becomes a low-density portion around a small high-density portion. In FIG. 7, which is the resolution conversion result, each pixel has a halftone density as a whole. Thereby, moire can be made almost inconspicuous.

FIG. 3 shows a result of the conventional resolution conversion.
FIG. 3B is an output signal of FIG.
FIG. 8 shows a conversion result when one-dimensional fast Fourier transform is performed on the output signal of (d). As shown in FIG. 8, the resolution conversion according to the present invention can obtain an output signal having very low frequency components as compared with the conventional resolution conversion. That is, it is possible to reduce the occurrence of moire caused by high frequency components.

Regarding another example of the resolution conversion of the present invention,
This will be described with reference to FIG.

FIG. 9 is a diagram for explaining another specific example of the resolution conversion method according to the embodiment of the present invention.

Here, a case where resolution conversion is performed on a line signal (3 dots) as shown in FIG. 9A will be described.

First, when conventional resolution conversion is performed on this line signal, an output signal as shown in FIG. 6B is obtained.

On the other hand, when the resolution conversion according to the present invention is performed, first, multi-leveling and averaging are performed as shown in FIG.
An image signal as shown in (c) is obtained. When resolution conversion is performed on this image signal, an output signal as shown in FIG. 9D is obtained. FIGS. 11 to 13 show the results when the input signal and the output signal described above are represented by density.
Shown in FIG. 10 corresponds to FIG. 9A, FIG. 11 corresponds to FIG. 9B, FIG. 12 corresponds to FIG. 9C, and FIG. 13 corresponds to FIG. It corresponds to. As can be seen by comparing FIGS. 11 and 13 with the input signal of FIG. 10, there is almost no change between the input signal and the output signal after resolution conversion in FIG. While the resolution conversion is meaningless, in FIG. 13 which is the resolution conversion result of the present invention, the output signals are distributed to some extent evenly by the resolution conversion. This makes it possible to make moiré almost inconspicuous even in resolution conversion for a line image.

Next, as a summary of the processing executed in this embodiment, a flowchart of the processing executed in this embodiment is shown in FIG.

FIG. 14 is a flowchart showing processing executed in the embodiment of the present invention.

First, in step S101, the image processing unit 1
01 is input with a binary signal. In step S102, multi-level processing is performed on the binary signal input to the image processing unit 101. In step S103, an averaging process is performed on the multi-valued image signal. In step S104, resolution conversion is performed on the averaged image signal.

The present invention may be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.).

Another object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or apparatus, and to provide a computer (or CPU) of the system or apparatus.
And MPU) read and execute the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD
-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also an OS (Operating System) running on the computer based on the instruction of the program code. ) May perform some or all of the actual processing, and the processing may realize the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, based on the instruction of the program code, It goes without saying that the CPU included in the function expansion board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0050]

As described above, according to the present invention,
An image forming apparatus capable of improving image quality of an output image and a control method thereof can be provided.

[0051]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an internal structure of a digital multifunction peripheral using an electrophotographic method, which is an example of an image forming apparatus applicable to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a conventional resolution conversion method.

FIG. 3 is a diagram illustrating a specific example of a resolution conversion method according to the embodiment of the present invention.

FIG. 4 is a diagram showing a state in which an input signal and an output signal shown in the specific example of FIG. 3 of the embodiment of the present invention are represented by density.

FIG. 5 is a diagram showing a state in which an input signal and an output signal shown in the specific example of FIG. 3 of the embodiment of the present invention are represented by density.

FIG. 6 is a diagram showing a state in which an input signal and an output signal shown in the specific example of FIG. 3 of the embodiment of the present invention are represented by density.

FIG. 7 is a diagram showing a state in which an input signal and an output signal shown in the specific example of FIG. 3 of the embodiment of the present invention are represented by density.

FIG. 8 is a diagram showing a state in which an input signal and an output signal shown in the specific example of FIG. 3 of the embodiment of the present invention are represented by density.

FIG. 9 is a diagram for explaining another specific example of the resolution conversion method according to the embodiment of the present invention.

FIG. 10 is a diagram showing a state in which an input signal and an output signal shown in the specific example of FIG. 9 of the embodiment of the present invention are represented by density.

FIG. 11 is a diagram showing a state in which an input signal and an output signal shown in the specific example of FIG. 9 according to the embodiment of the present invention are represented by density.

FIG. 12 is a diagram showing a state in which an input signal and an output signal shown in the specific example of FIG. 9 of the embodiment of the present invention are represented by density.

FIG. 13 is a diagram showing a state in which an input signal and an output signal shown in the specific example of FIG. 9 of the embodiment of the present invention are represented by density.

FIG. 14 is a diagram showing a flowchart of processing executed in the present embodiment as a summary of processing executed in the present embodiment.

[Explanation of symbols]

 121 Platen glass 122 Fluorescent lamp 123 Optical sensor 101 Image signal processing unit 102 Laser driver 106 Photoconductor drum 112 Primary charging device 107 Developing device 113 Transfer charging device 103 Semiconductor laser 104 Laser beam 105 Rotating polygon mirror

Claims (9)

[Claims] 1. An image forming apparatus which forms an image based on an image signal input at a resolution different from an output resolution, wherein the input image signal is a binary image signal. Multi-leveling means for multi-leveling the image signal into multi-level image signals, averaging processing means for performing averaging processing on the image signal multi-valued by the multi-leveling means, and the averaging processing means Resolution converting means for converting the resolution of the image signal averaged in the above into the output resolution, and forming means for forming an image based on the image signal whose resolution has been converted by the resolution converting means. Image forming device. 2. The image forming apparatus according to claim 1, wherein the averaging unit averages the multi-valued image signal using a two-dimensional spatial filter. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus is connected to an external device via a network line. 4. The image forming apparatus according to claim 1, wherein the binary image signal is an image signal received by facsimile from the external device. 5. A method for controlling an image forming apparatus that forms an image based on an image signal input at a resolution different from an output resolution, wherein the input image signal is a binary image signal. A multi-level conversion step of multi-level conversion of the value image signal into a multi-level image signal; an averaging processing step of performing an averaging process on the image signal multi-valued in the multi-level conversion step; A resolution conversion step of converting the resolution of the image signal averaged in the conversion processing step to the output resolution, and a forming step of forming an image based on the resolution-converted image signal in the resolution conversion step. A method for controlling an image forming apparatus. 6. The method according to claim 5, wherein the averaging process averages the multi-valued image signal using a two-dimensional spatial filter. 7. The control method according to claim 5, wherein the image forming apparatus is connected to an external device via a network line. 8. The method according to claim 5, wherein the binary image signal is an image signal received by facsimile from the external device. 9. A computer-readable memory storing a program code for controlling an image forming apparatus for forming an image based on an image signal input at a resolution different from an output resolution, wherein the input image signal is 2 If the image signal is a value image signal, a program code of a multi-value process for multi-leveling the binary image signal into a multi-level image signal; A program code of an averaging process for performing an averaging process, a program code of a resolution conversion process for converting the resolution of the image signal averaged in the averaging process to the output resolution, and a resolution in the resolution conversion process. A program code for forming an image based on the converted image signal.