JP3673526B2 - Image forming apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an image forming apparatus, and more particularly to an apparatus that visualizes a digital image signal represented by a digital printer or a digital copying machine.
[0002]
[Prior art]
A conventional image forming apparatus of this type that forms a visualized image corresponding to a digital image signal corresponding to the density of an arbitrary pixel has a method as described below.
[0003]
The surface of the image carrier uniformly charged by the charging means is scanned with a laser beam that emits light corresponding to the image signal to form an electrostatic latent image on the surface of the image carrier, and the electrostatic latent image is developed by the developing means. For example, a laser beam printer that develops a toner image on the transfer material, transfers the toner image onto a transfer material by a transfer means, and fixes and outputs the toner image on the transfer material to the transfer material by a fixing means is widely used. As the developing means, there is an apparatus that develops an electrostatic latent image on the surface of an image carrier into a toner image by causing a developer carrier to which a bias voltage including at least a direct current component is applied to face the image carrier.
[0004]
In an image forming apparatus that visualizes a digital image signal, a plurality of types of input paths are provided, one type of path is selected from the plurality of types of input paths, and an image signal input from the selected input path Some of them perform image formation according to the above. These image signals can be divided into two types described below. First, a binary digital image signal that conveys only the shape of a solid image having dots, lines, and a two-dimensional continuous area, such as an image signal of a document created by an image signal creation means such as a computer, Secondly, there are two types of multi-value digital image signals that convey not only the shape of the image but also the gradation expression of the density, such as an image signal read from an original by an image reading means using a CCD or the like.
[0005]
When the binary image signal is visualized by the above-mentioned laser beam printer or the like, it is only necessary to reproduce the shape of the image, so if the electrostatic latent image is formed by performing only on / off modulation on the laser beam. Good. In a laser beam printer that visualizes binary image signals, the size of each output pixel is about 1 or 2 pixels, so that the dots and lines of the width can be easily seen with the naked eye. The output is preferably about 10 to 30% larger than the pixel size. In the prior art, there has been proposed a method for reproducing the size of each pixel larger by increasing the development contrast of the developing means. FIG. 4 shows an example of the relationship between the development contrast and the line width for one pixel. A printer that visualizes a binary image signal requires a means for changing the output characteristics so that the line width is increased. Therefore, as a means for changing the line width to be narrower (10% thicker than the theoretical value), normal (20% thicker than the previous value), or thicker (30% thicker than the previous value), a method of adjusting the previous development bias is used. .
[0006]
On the other hand, a laser beam printer that visualizes a multi-valued image signal is a signal inputted for each pixel as shown by a straight line 2 in FIG. 7 in order to reproduce not only the shape of the image but also the gradation expression of density. It is necessary to output an image having a density that is linearly related to the value. The relationship between the input signal value and the density of the output image when the laser beam is emitted with an amount of light proportional to the multi-value signal value for each pixel (hereinafter this relationship is referred to as “gamma conversion through characteristics” of the printer). ) Is determined by the photosensitive characteristics of the image carrier and the developing characteristics of the developing means. Among the characteristics of image carriers and developing means that have been practically used, the gamma conversion through characteristics of printers are non-linear. FIG. 6 shows an example of gamma conversion through characteristics. In the prior art, in order to correct the non-linear gamma conversion through characteristic of a printer to a linear output density characteristic as shown in FIG. 7, gamma conversion processing is performed on the multi-value image signal input to the printer, and the gamma conversion process is performed. Means for emitting light so that the light quantity per pixel of the laser beam is proportional to the converted multi-value signal value is widely used.
[0007]
In a printer or the like that visualizes a multi-value image signal, means for changing output characteristics in accordance with the state of the document is necessary. Specifically, when the original has a white background, only the white background is thinned, and when the image density of the original is generally low, the output characteristics of lines 1 and 3 in FIG. The gamma conversion process is changed so that is obtained.
[0008]
As described above, since the means for changing the output characteristic is different between the multi-value image signal and the binary image signal, two operation units for the operator to select the output characteristic are required.
[0009]
[Problems to be solved by the invention]
A combination of the above-described prior arts includes two types of digital image signal input paths of binary and multi-value, and one type of path is selected from the plurality of types of input paths and input from the selected input path In the case of configuring an apparatus for forming an image corresponding to the image signal, there is a drawback as described below.
[0010]
An independent operation unit is provided for changing the reproducibility of the size of each pixel in the binary image signal and for changing the gradation expression of the density in the multi-value image signal. There is a need to. Such a structure is expensive and complicated to operate. Therefore, if one of the means is used to change the image output characteristics, the following disadvantages occur.
[0011]
When the means for changing the document contrast is used as the means for changing the image output characteristics, the characteristics of the output image of the multivalued image signal do not change as shown in FIG. At the same time, the size of one pixel output from the multi-valued image signal changes, and this causes a problem that the gradation in a halftone image or the like is lowered. When means for changing the gamma conversion process is used as means for changing the image output characteristics, since the gamma conversion is conversion for a multi-value signal, a problem occurs in the signal value of the binary image signal.
[0012]
An object of the present invention is to be able to always form an optimal image regardless of whether an input digital image signal is a binary image signal or a multi-value image signal with an inexpensive and simple operation. An image forming apparatus is provided.
[0013]
[Means for Solving the Problems]
The present invention includes an input means for inputting a digital image signal, and a developing means for developing an electrostatic latent image formed on an image carrier by performing scanning exposure based on the image signal input to the input means. And a setting unit that can variably set the output image density, and a changing unit that changes an image forming condition in accordance with the output image density set by the setting unit, and a gamma for forming an image signal In the image forming apparatus that sets the output density by changing the development process or the developing bias of the developing unit, the setting unit is common regardless of the digital image signal, and the digital image signal is a binary image signal. The changing means changes the developing bias without changing the gamma conversion characteristics, and when the digital image signal is a multi-valued image signal, the changing means sets the developing bias to It is characterized in changing the gamma conversion characteristics so that the inclination of the input over output increases without further.
[0014]
【Example】
Example 1
FIG. 2 is a block diagram showing the flow of image signals and control signals in the image forming apparatus embodying the present invention.
[0015]
In this embodiment, there are two types: a reader 20 that converts image information of a document or the like into a multi-value digital image signal from 0 to 255, and a computer 21 that can create and edit binary digital image signals of 0 and 1. The input path from the image signal output device is provided. Although the specific configuration of the reader 20 is not illustrated, the original is irradiated with light by a halogen lamp, a fluorescent lamp, or the like, and the reflected light from the original is projected onto a photoelectric conversion means such as a CCD by an optical system such as a lens or a mirror. The generated analog electrical signal is converted into a multi-value digital image signal from 0 to 255 by the A / D conversion means.
[0016]
The two types of image signal output devices are connected to an interface 22 in the image forming apparatus. The interface 22 is instructed by the operator to select one of the reader 20 and the computer 21 via the CPU 24, or either one of the reader 20 or the computer 21 is used as an image forming apparatus. By transmitting the image signal, the one device is automatically selected, and the image signal of the one device is transmitted to the printer unit 23. The interface 22 does not perform any conversion into a signal value when the input signal is a multi-value image signal from 0 to 255 of the reader 20, but in the case of a binary image signal of 0 and 1 of the computer 21, 0 is converted to 0, and 1 is converted to 255.
[0017]
FIG. 5 is a schematic cross-sectional view of the main part of the printer unit 23 in the image forming apparatus embodying the present invention. The surface of the image carrier 10 uniformly charged by the charging unit 11 is scanned with a laser beam 12 that emits light in response to a signal obtained by performing a gamma conversion process on the input multivalued image signal from 0 to 255. Then, an electrostatic latent image is formed on the surface of the image bearing member, the electrostatic latent image is developed into a toner image by the developing unit 13, and the toner image is transferred to the transfer material 15 by the transfer unit 14, and then illustrated. The toner image on the transfer material is fixed on the transfer material by the fixing means that does not, and is output. In this embodiment, the uniform charging potential on the surface of the image carrier 10 is −700 V, the latent image potential corresponding to the image signal value = 0 is −700 V, and the latent image potential corresponding to the image signal value = 255 is −250 V. is there. The developing unit 13 is a device that develops the electrostatic latent image on the surface of the image carrier into a toner image by causing the developer carrier 16 to which a bias voltage including a DC component is applied to face the image carrier 10. The developing method of the developing means 13 is a reversal developing method using a negative polarity toner. Bias voltage is supplied to the developer carrier 16 by a bias power source 17. The bias power supply 17 changes the value of the DC component of the bias voltage supplied to the developer carrier 16 in accordance with a control signal sent from the CPU 24.
[0018]
FIG. 1 shows a flowchart of specific operations performed in this embodiment. FIG. 3 shows the configuration of the operation unit 26 for selecting output characteristics in the present embodiment. The CPU 24 determines whether the signal transmitted from the interface 22 to the printer 23 is a binary image signal or a multi-value image signal.
[0019]
When the image signal transmitted to the printer 23 is a multi-value signal, the CPU 24 performs gamma conversion according to the density value set by the operation unit 26 in FIG. 3, and the development bias voltage is fixed to −550V. Thus, a control signal is sent to the gamma converter 25 and the bias power source 17. The gamma conversion at this time is set so that the output density characteristic becomes the straight line 3 in FIG. 7 when the operation unit input is 3, that is, when the output density is set high, and when the operation unit input is 1, that is, it is set light. When the operation unit input is 2, that is, when it is set normally, the line 2 shown in FIG. The printer 23 executes image formation corresponding to the image signal after performing gamma conversion according to the selected output characteristic.
[0020]
When the input image signal is a binary signal, the gamma conversion is not changed, and the line width set by the operation unit 26 is set to the value of the DC component of the bias voltage supplied to the developer carrier 16. Change according to the adjustment signal. The development bias voltage value at this time is −580 V (development contrast = 330 V) when the operation unit input 1 is output, that is, when the line width is narrowed, and when the operation unit input 3 is output, that is, when the line width is wide It is set to −640 V (development contrast = 390 V), and −610 (development contrast = 360 V) when the operation unit input is 2. The printer 23 executes image formation in a state where a bias voltage corresponding to the set line width signal is supplied to the developer carrier 16.
[0021]
Example 2
The image signal input path and image processing block diagram of the image forming apparatus are the same as those in the first embodiment shown in FIG. The configuration and operation of the reader 20, the computer 21, the interface 22, and the printer 23 are as described in the first embodiment.
[0022]
In the first embodiment, binary input image signals of 0 and 1 are converted into 0 and 255 and transmitted to the printer unit as binary output image signals. In the present invention, in addition to the above case, in order to enlarge the image signal, the image signal enlargement is performed by converting the binary image signal into the multi-value image signal and interpolating the signal value between the interface and the gamma converter. The same effect can be obtained when the means is provided.
[0023]
FIG. 9 is a block diagram showing the flow of image signals and control signals in this embodiment. When a binary image signal of 0 and 1 is transmitted from the computer 21 to the interface 22 in the image forming apparatus, the interface 22 is set to 0 when the signal value is 0, and to 255 when the signal value is 1. The image signal after the above conversion is transmitted to the image signal enlargement device 27.
[0024]
FIG. 10 shows an example of an interpolation model of image signal values performed by the image signal enlargement device 27. The enlargement ratio is 1.333 times. FIG. 10A shows an image signal transmitted to the image signal enlarging device 26. FIG. 10B is an image signal obtained by enlarging the pixel size and the signal value of the image of FIG. FIG. 10C is an image signal obtained by performing a linear interpolation operation on the image signal of FIG. When this processing is performed, the binary image signal becomes a multi-value image signal.
[0025]
In the present embodiment, the image signal after the enlargement process is performed on the binary image signal transmitted from the computer 21 has the same output characteristics as the binary image signal not subjected to the enlargement process. Perform image formation. As described above, the line width can be reproduced with a value corresponding to the set value from the operation unit 26 even in the image signal after the enlargement process.
[0026]
Example 3
In the present invention, the same effect can be obtained by changing the AC component of the bias voltage applied to the developer carrier 16 according to the type of the selected image signal. The image signal input path of the image forming apparatus and the block diagram in the image forming apparatus are the same as FIG. The configuration and operation of the reader 20, the computer 21, and the interface 22 are as described in the first embodiment. The printer unit 23 has a configuration described below. In this embodiment, the uniform charging potential on the surface of the image carrier 10 is −700 V, the latent image potential corresponding to the image signal value = 0 is −700 V, and the latent image potential corresponding to the image signal value = 255 is −250 V. It is. The developing unit 13 is a device that develops the electrostatic latent image on the surface of the image carrier into a toner image by causing the developer carrier 16 to which a bias voltage including an AC component is applied to face the image carrier 10. The developing method of the developing means 13 is a reversal developing method using a negative polarity toner. Bias voltage is supplied to the developer carrier 16 by a bias power source 17. The bias power source 17 changes the potential difference between the large and small peaks of the AC component of the bias voltage supplied to the developer carrier 16 in accordance with a control signal sent from the CPU 24. The DC component of the bias voltage is always -550V.
[0027]
FIG. 8 shows a flowchart of specific operations performed in this embodiment. When the image signal is a multi-value signal from the reader 20, the CPU 24 performs the same operation as that of the first embodiment on the signal relating to the density from the operation unit 26. At this time, the potential difference between the large and small peaks of the AC component of the bias voltage supplied to the developer carrier 16 is set to 1000V. In this case, the gamma conversion apparatus performs gamma conversion processing corresponding to the gamma conversion through characteristic when the potential difference between the large and small peaks of the AC component of the bias voltage supplied to the developer carrier 16 is 1000V. The gamma conversion at this time is set so that the output density characteristic becomes the straight line 3 in FIG. 7 when the operation unit input is 3, that is, when the output density is set high, and when the operation unit input is 1, that is, it is set light. When the operation unit input is 2, that is, when it is set normally, the line 2 in FIG.
[0028]
When the input image signal is binary, the peak potential difference of the AC component of the bias voltage supplied to the developer carrier 16 is changed according to the line width signal set by the operation unit 26. Specifically, when the operation unit input is 1, that is, when the line width is output narrowly, 1100 V, when the operation unit input is 3, that is, when the line width is output thickly, 1300 V, and when the operation unit input is 2, Set to 1200V. The printer 23 performs image formation in a state where a bias voltage corresponding to the line width adjustment signal set by the operation unit is supplied to the developer carrier 16. FIG. 11 shows the relationship between the magnitude of the AC component of the developing bias and the line width.
[0029]
【The invention's effect】
As described above, according to the present invention, an optimal image is always formed with a low-cost and simple operation regardless of whether the input digital image signal is a binary image signal or a multi-value image signal. can do.
[Brief description of the drawings]
FIG. 1 is a flowchart of specific operations performed in the first embodiment.
FIG. 2 is a block diagram showing the flow of image signals and control signals in the image forming apparatus embodying the present invention.
FIG. 3 illustrates an operation unit for changing output characteristics in the image forming apparatus according to the exemplary embodiment.
FIG. 4 shows the relationship between the development contrast and the line width for one pixel reproduced at the development contrast.
FIG. 5 is a schematic diagram of a main cross section of a printer unit according to an embodiment.
FIG. 6 shows the gamma conversion through characteristics of a printer.
FIG. 7 illustrates output characteristics of the printer after gamma conversion.
FIG. 8 is a flowchart showing specific operations performed in the third embodiment.
FIG. 9 is a block diagram illustrating the flow of an image signal and a control signal in the second embodiment.
FIG. 10 shows an example of an interpolation calculation model in image signal enlargement processing.
FIG. 11 shows the relationship between the magnitude of the AC component of the developing bias and the reproducibility of the line width.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Image carrier 11 Charging means 12 Laser beam 13 Developing means 14 Transfer means 15 Transfer material 16 Developer carrier 17 Bias power supply 20 Reader 21 Computer 22 Interface 23 Printer section 24 CPU
25 Gamma Conversion Device 26 Operation Unit 27 Image Signal Enlargement Device

Claims (1)

An input means for inputting a digital image signal; a developing means for developing an electrostatic latent image formed on the image carrier by scanning exposure based on the image signal input to the input means; and an output image density And a changing unit for changing the image forming condition according to the output image density set by the setting unit, and a gamma conversion process or development when forming an image signal In the image forming apparatus for setting the output density by changing the developing bias of the means,
The setting unit is common regardless of the digital image signal,
When the digital image signal is a binary image signal, the changing means changes the developing bias without changing the gamma conversion characteristics,
When the digital image signal is a multi-value image signal, the changing unit changes the gamma conversion characteristic so as to increase the slope of input-output without changing the developing bias.

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