JP3011376B2 - Binary image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binary image forming apparatus such as a laser printer for expressing a character or a halftone image based on a binary video signal of a print bit or a non-print bit.

[0002]

2. Description of the Related Art A laser printer controls the on / off of a laser diode based on a binary signal consisting of a print bit and a non-print bit while charging the surface of a photosensitive drum, and is generated when the laser diode is turned on. The laser beam is reflected by a rotating optical polygon mirror to sequentially scan the charged surface of the photoreceptor drum to form an electrostatic image by exposure, developed with toner, and transferred to a sheet. With respect to the binary image data as shown in (a) (the hatched portion is a pixel of a print bit and the unhatched portion is a pixel of a non-print bit), an actual print image as shown in FIG. That is, in order to prevent white streaks from occurring between pixels of successive print bits due to surface tilt of the optical polygon mirror or jitter of the paper transport system, the actual print size of one dot is made larger than the size of one pixel. The diameter of the laser beam was increased so as to be as small as possible.

However, the binary image forming apparatus having such an output characteristic has a drawback that good tone reproducibility cannot be obtained when forming a halftone image such as a photograph.

FIG. 7 shows the output characteristics of a binary image obtained by obtaining a pseudo halftone by dither processing using a well-known Bayer dither matrix. The image becomes an almost black solid image because the density of the output image is saturated at a gradation level higher than the eighth gradation, and becomes a dark image with poor gradation reproducibility.

Therefore, conventionally, the binarized target pixel data and the
By referring to a plurality of binarized peripheral pixel data located around the binarized target pixel data, one dot corresponding to the binarized target pixel data is determined by an arrangement pattern of print bits and non-print bits of the binarized peripheral pixel data. A technique for improving the tone reproducibility of a binary image by changing the actual print size of the image is known. (See JP-A-63-124667)

[0006]

However, in this prior art, not only halftone images such as photographs but also characters are processed in the same manner, and thus output images such as characters may lack clarity.

Accordingly, the present invention is to provide a binary image forming apparatus capable of obtaining good gradation reproducibility for a halftone image such as a photograph and obtaining a thick and clear image for an output image such as a character. Is what you do.

[0008]

According to the present invention, a character code 2 is used.
A first image storage unit for storing a value video signal; a second image storage unit for storing a binary video signal of image data; and a binary video of a character code stored in the first image storage unit. A first modulating means for modulating a signal based on a first modulation degree to output a first image forming pulse signal; and binary data of image data stored in the second image storage section A second modulating unit that modulates the video signal based on the second modulation degree and outputs a second image forming pulse signal; a first image forming pulse signal output from the first modulating unit; The second output from the second modulating means
A synthesizing unit for synthesizing the image forming pulse signal to output an image forming pulse, and an image forming unit for forming a binary image by performing dot printing in accordance with the image forming pulse signal output from the synthesizing unit. A binary image forming apparatus characterized in that:

[0009]

In the present invention having such a configuration, a binary video signal such as a character input from a keyboard or the like is stored in the first image storage unit, and the image data of a photograph or the like read by an image sensor or the like is stored. The binary video signal is the second
Is stored in the image storage unit. Then, the binary video signal of the character code stored in the first image storage unit is modulated by the first modulation means based on the first modulation degree.
As a result, the first image forming pulse signal is output from the first modulating means. Further, the binary video signal of the image data stored in the second image storage section is modulated by the second modulation means based on the second modulation degree. As a result, the second image forming pulse signal is output from the second modulating means. That is, the pulse width and the image width of the first image forming pulse signal generated based on the binary video signal such as a character are changed by making the modulation degree modulated by the first modulation means and the second modulation means different. The pulse width of the second image forming pulse signal generated based on the binary video signal of data is made different. As a result, characters and images
The dot size of the actual print is changed.

Then, the first image forming pulse signal output from the first modulating means and the second image forming pulse signal output from the second modulating means are synthesized by the synthesizing means to form an image forming pulse. The signal is output to the image forming means as a signal, and a binary image is formed by dot printing. Therefore, for a character or the like in which a binary video signal is stored in the first image storage unit, a thick and clear image can be obtained by increasing the dot size.

On the other hand, with respect to image data such as a photograph in which a binary video signal is stored in the second image storage section, by reducing the dot size, excellent gradation reproducibility without tangling in the dot dense section is obtained. Images can be obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a laser printer will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a laser printer. A drum unit 2 is provided at a substantially central portion of a housing 1. The drum unit 2 includes a photoconductor drum 3 whose surface is formed of a photoconductor. The photosensitive drum 3 is driven to rotate in one direction in a clockwise direction in the figure, and a charging charger 4 for charging the surface of the photosensitive drum 3 around the photosensitive drum 3 according to an electrophotographic process. A laser scanner unit 5 that irradiates a laser beam to the surface of the photosensitive drum 3 charged by the charging charger 4 to record information by exposure, and attaches a toner as a developer to the exposed surface of the photosensitive drum 3. Developing device 6,
A transfer charger 7 for transferring a toner image formed on the surface of the photosensitive drum 2 to a conveyed sheet;
A cleaning unit 8 for removing toner from the apparatus and a discharge lamp 9 for discharging the photosensitive drum 3 are arranged in this order to constitute a drum unit.

The transfer charger 7 is located below the photosensitive drum 3, and is moved from a paper cassette 10 attached to one side of the housing 1 toward the transfer charger 7 by the operation of a pickup roller 11. Are transported one by one at a predetermined timing.

Then, the toner image on the photosensitive drum 2 is transferred to the conveyed sheet by the transfer charger 7, and is thermally fixed by the fixing unit 12.
It is designed to be discharged to the outside.

Here, a drive motor 14 is provided in the housing 1 as a common drive source for the paper transport mechanism and the rotation mechanism of the photosensitive drum 3. Further, a fan 15 for releasing internal heat to the outside is provided in the housing 1.
An interlock switch 16, a power supply device 17, and the like that detect the opening of the housing 1 and turn off the power supply are provided.

FIG. 2 is a block diagram showing a main circuit configuration.
Reference numeral 21 denotes a processor constituting a control unit main body, 22 denotes a communication interface for receiving print data transmitted from a host device 23 via a transmission line 24, and 25 denotes a binary video signal corresponding to various character codes set in advance. CG
A ROM (read only memory for character generator) 26, a first image storage unit for storing a binary video signal of character data input by a keyboard 27 among print data received by the communication interface 22; A first V-RAM (random access memory for video signal) as a second image 28 for storing a binary video signal of image data such as a photograph read by the image sensor 29 among the received print data. The second V-RAM 30 as a storage unit is the first V-RAM 30.
After the binary video signals stored in the second V-RAMs 26 and 28 are respectively modulated by different modulating means, the image forming pulse signals synthesized are combined with the laser scanner unit 5.
Is a video signal output circuit that outputs the video signal.

The processor 21, the communication interface 22, the CG-ROM 25, the first V-RAM 26, the second V
The RAM 28 and the video signal output circuit 30 are connected by a bus line 31;

The laser scanner unit 5 includes a laser oscillator 32 for emitting a laser beam,
A laser control circuit 33 for controlling the on / off of the laser beam from the laser beam 2 and its beam diameter, a start sensor 34 composed of a PIN diode or the like for detecting the start position of the laser beam, and a drive circuit for a polygon motor for driving the polygon mirror 35 to rotate. And a PLL control circuit 37 for controlling the number of rotations of the motor by the drive circuit.

When the processor 21 receives data from the host device 23 via the communication interface 22, the processor 21 is set to execute a receiving process shown in FIG.

That is, if the received data is print data, it is determined whether the print data is a character code generated by a key input on the keyboard 27 or image data generated by reading a document by the image sensor 29. . And if it is a character code, CG-ROM2
5, the character code is converted into a dot pattern, and developed as a binary video signal in the first V-RAM 26. In the case of image data, since it has already been binarized by the host device 23 by dither processing or the like, the image data is directly developed in the second V-RAM 28. If the data received from the host device 23 is a print command, the print processing shown in FIG. 4 is executed.

That is, the binary video signal of the character code stored in the first V-RAM 26 is modulated based on the first modulation degree to generate a first image forming pulse signal (first modulation means). The second V-RAM 28 modulates the binary video signal of the image data based on the second degree of modulation to generate a second image forming pulse signal (second modulation means). Then, the first image forming pulse signal and the second image forming pulse signal are synthesized to form an image forming pulse signal (synthesizing means). Then, the synthesized image forming pulse signal is output to the laser control circuit 33 via the video signal output circuit 30.

That is, as shown in FIG.
Upon receipt of the data from, the binary video signal of the character code is stored in the first V-RAM 26 and the binary video signal of the image data is stored in the second V-RAM 28. Then, the first V-RAM 26 or the second V-RAM 28
Are separately modulated by the first or second modulating means, respectively, and then output from the synthesizing means. Therefore, the character code is stored in the laser control circuit 33.
An image forming pulse signal, which is obtained by modulating a binary video signal of image code and a binary video signal of image data at different modulation degrees and then combining them, is input.

In this embodiment having such a configuration, when a character is input as print data from the keyboard 27 of the host device 23, the dot pattern of the character code is read out from the CG-ROM 25 and converted into a binary video signal. It is developed in the first V-RAM 26. On the other hand, the host device 2
When image data such as a photograph is input as print data by the third image sensor 29, the image data binarized by dither processing or the like is developed in the second V-RAM 28 as a binary video signal.

Then, when a print command is output from the host device 23, the binary video signal stored in the first V-RAM 26 is read out in response to the print command, and the first modulation means sets the first modulation degree. And a first image forming pulse signal is formed in accordance with the second V-RAM 2.
8 is read out and the second video signal
Is modulated according to the second modulation degree to form a second image forming pulse signal. Then, after the first and second image forming pulse signals are combined by the combining means, the video signal output circuit 3 outputs the image forming pulse signal.
The signal is output to the laser control circuit 33 of the laser scanner unit 5 through 0. Thereby, an on / off signal of a laser beam corresponding to the image forming pulse signal is generated from the laser control circuit 33 to the laser oscillator 32, and a laser beam is generated from the laser oscillator 27 during the on-pulse, and the laser beam is generated according to the electrophotographic process. A binary image of the character is formed.

In this case, the ON / OFF signal generated by the laser control circuit 33 in response to the first image forming pulse signal has a relatively wide ON pulse width. Therefore, the beam diameter of the laser beam output from the laser oscillator 32 increases, and the size of the actual print dot for one pixel becomes larger than that of the one pixel. As a result, character data input from the keyboard 27 is printed as a thick and clear image by the laser printer.

On the other hand, the ON / OFF signal generated from the laser control circuit 33 in response to the second image forming pulse signal is modulated so that the ON pulse width becomes narrower than in the case of a character. Accordingly, the beam diameter of the laser beam output from the laser oscillator 32 is reduced, and is substantially equal to one pixel of the actual print dot for one pixel. As a result, the image data read by the image sensor 29 is printed by the laser printer as a halftone image excellent in gradation reproducibility without blurring in a dot dense portion.

In this embodiment, the laser beam diameter is variably adjusted by modulating the pulse width of the ON signal to the laser oscillator 27. However, the laser beam diameter can be variably adjusted by changing the intensity of the ON signal.

Further, the present invention is not limited to a laser printer, but can be applied to a thermal printer, an ink jet printer, etc. for reproducing halftone images such as characters and photographs based on binary signals. .

[0030]

As described in detail above, according to the present invention, good gradation reproducibility is obtained for a halftone output image such as a photographic image, and a thick and clear image is obtained for a character or the like output image. And a binary image forming apparatus capable of improving print quality can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a laser printer according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a main circuit configuration of the embodiment.

FIG. 3 is a flowchart showing data reception processing of a processor in the embodiment.

FIG. 4 is a flowchart showing a printing process of a processor in the embodiment.

FIG. 5 is a timing chart for explaining the operation in the embodiment.

FIG. 6 is a diagram showing a conventional laser beam output characteristic.

FIG. 7 is a graph showing a gradation characteristic of a conventional output image.

[Explanation of symbols]

5 laser scanner unit, 21 processor, 26
... First V-RAM, 28... Second V-RAM, 30... Video signal output circuit, 33... Laser control circuit.

Claims (1)

(57) [Claims] 1. A first image storage unit for storing a binary video signal of a character code, a second image storage unit for storing a binary video signal of image data, and storage in the first image storage unit. A first modulating means for modulating the binary video signal of the character code based on the first degree of modulation to output a first image forming pulse signal; and a second modulating means which is stored in the second image storing section. The binary video signal of the image data
A second modulating means for modulating based on the degree of modulation to output a second image forming pulse signal; a first image forming pulse signal output from the first modulating means; and a second modulating means. Means for synthesizing the second image forming pulse signal output from the image forming apparatus and outputting an image forming pulse, and forming a binary image by dot printing in accordance with the image forming pulse signal output from the synthesizing means. A binary image forming apparatus, comprising: an image forming unit.