JPH04326856A - Binary picture forming device - Google Patents

Abstract

PURPOSE:To attain favorable gradation reproducibility in respect of the output picture of a half tone such as a photographic picture, etc., and in addition, to obtain the thick and clear picture in respect of the output picture such as a character, etc. CONSTITUTION:A first V-RAM 26 to store the binary video signal of a character code and a second V-RAM 28 to store the binary video signal of image data are provided. Then, only in the case that the binary video signal stored in the second V-RAM is outputted to a laser scanner unit 5, a control flag is added to the binary video signal. A laser control circuit 33 discriminates whether the control flag is added to the binary video signal or not, and if it is added, it modulates the binary video signal so that the pulse width of a laser beam on-signal becomes narrow.

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 that expresses characters or halftone images based on a binary video signal of print bits or non-print bits.

0002

[Prior Art] A laser printer charges the surface of a photoreceptor drum and controls the on/off state of a laser diode based on a binary signal consisting of print bits and non-print bits. A 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, which is developed with toner and then transferred to paper. For binary image data as shown in (a) of FIG. 1 (hatched areas are pixels of print bits, unhatched areas are pixels of non-print bits), an actual printed image as shown in (b) of the same figure is obtained. In other words, the actual print size of one dot is made larger than the size of one pixel in order to prevent white streaks from occurring between pixels of consecutive print bits due to tilting of the polygon mirror in the optical system or jitter in the paper transport system. The laser beam diameter was increased so that

However, binary image forming apparatuses having such output characteristics have the disadvantage that good gradation reproducibility cannot be obtained when forming halftone images such as photographs.

FIG. 7 shows the output characteristics of a binary image obtained by dithering using a well-known Bayer dithering matrix to obtain pseudo halftones. In other words, the image was binarized using a 16-level Bayer dithering matrix. At gradation levels higher than the 8th gradation, the density of the output image is saturated and becomes an almost solid black image, resulting in a dark image with poor gradation reproducibility.

Therefore, conventionally, the binarized pixel data of interest and the
By referring to a plurality of binarized surrounding pixel data located around the binarized pixel data of interest, one dot for the binarized pixel data of interest is determined based on the arrangement pattern of print bits and non-printing bits of the binarized surrounding pixel data. A technique is known that improves the gradation reproducibility of a binary image by varying the actual print size of the image. (Refer to Japanese Unexamined Patent Publication No. 124667/1983)

[0006]

However, in this prior art, not only halftone images such as photographs but also characters are processed in the same way, so that output images such as characters sometimes lack clarity.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a binary image forming apparatus that can obtain good gradation reproducibility for halftone images such as photographs and thick and clear images for output images such as characters. It is something to do.

[0008]

[Means for Solving the Problems] A binary image forming apparatus of the present invention includes a first image storage section that stores a binary video signal of character codes, and a second image storage section that stores a binary video signal of image data. an image storage section; a pulse generation section that generates an image forming pulse signal based on a binary video signal; and first and second pulse generation sections.
a signal transfer means for transferring the binary video signals respectively stored in the image storage sections of the image storage section to the pulse generating section; and an image forming a binary image by printing dots in accordance with the image forming pulse signal generated from the pulse generating section. the signal transfer means pulses the binary video signal by adding information for distinguishing from which storage unit of the first image storage unit and the second image storage unit the binary video signal is read. The pulse generator modulates the corresponding image forming pulse signal based on the additional information of the transferred binary video signal to variably control the actual print dot size. It is.

[0009]

[Operation] In the present invention having such a configuration, a binary video signal such as characters input from a keyboard etc. is stored in the first image storage section, and image data such as a photograph read by an image sensor etc. is stored in the first image storage section. The binary video signal is
The image is stored in the image storage unit of. Then, when outputting the image, the first
Alternatively, the binary video signal stored in the second image storage section is read out and transferred to the pulse generation section, and the generation section generates an image forming pulse signal corresponding to the binary video signal, and the binary video signal is generated by dot printing. An image is formed.

[0010] Here, when the binary video signal is transferred to the pulse generating section, the binary video signal read from either the first or second image storage section is added to the binary video signal. Information to distinguish between the two is added. In the pulse generating section, the pulse width of the corresponding image forming pulse signal is variably controlled based on the content of the additional information of the transferred binary video signal, and as a result, the dot size of the actual printing is variable. be done. Therefore, 2 images are stored in the first image storage section.
For characters and the like in which value video signals are stored, thicker and clearer images can be obtained by increasing the dot size.

On the other hand, for image data such as photographs in which binary video signals are stored in the second image storage section, by reducing the dot size, it is possible to achieve excellent gradation reproducibility without distortion even in areas where dots are densely packed. You will be able to get images.

0012

Embodiments Hereinafter, embodiments in which the present invention is applied to a laser printer will be described with reference to the drawings.

FIG. 1 is a block diagram of a laser printer, in which a drum unit 2 is provided approximately in the center of a housing 1. As shown in FIG. The drum unit 2 includes a photoreceptor drum 3 whose surface is formed of a photoreceptor. This photoreceptor drum 3 is driven to rotate in one direction clockwise in the figure, and around this photoreceptor drum 3 there is a charger 4 that charges the surface of the photoreceptor drum 3 according to an electrophotographic process. A laser scanner unit 5 that irradiates the surface of the photoreceptor drum 3 charged by the charger 4 with a laser beam to record information by exposure, and the exposed photoreceptor drum 3
A developing device 6 that attaches toner as a developer to the surface of the photoreceptor drum 2, a transfer charger 7 that transfers the toner image formed on the surface of the photoreceptor drum 2 to the conveyed paper, and a cleaning device 8 that removes toner from the photoreceptor drum 3. , photosensitive drum 3
A drum unit is constructed by sequentially arranging static elimination lamps 9 for eliminating static electricity.

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

Then, the toner image on the photosensitive drum 2 is transferred to the conveyed paper by the transfer charger 7, and the toner image is thermally fixed by the fixing device 12.
It is designed to be discharged 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 for the photosensitive drum 3. Further, inside the housing 1, a fan 15 for discharging internal heat to the outside,
An interlock switch 16, a power supply device 17, and the like are provided to detect the opening of the casing 1 and turn off the power.

FIG. 2 is a block diagram showing the main circuit configuration.
21 is a processor constituting the main body of the control unit; 22 is a communication interface that receives print data sent from a host device 23 via a transmission line 24; and 25 is a preset binary video signal corresponding to various character codes. CG
- ROM (read-only memory for character generator) 26 is a first image storage section that stores a binary video signal of character data inputted through the keyboard 27 among the print data received through the communication interface 22; A first V-RAM (random access memory for video signals) 28 stores a binary video signal of image data such as a photograph read by the image sensor 29 out of the received print data. The second V-RAM 30 as a storage unit is the first,
This is a video signal output circuit that outputs the binary video signals stored in the second V-RAMs 26 and 28 to the laser scanner unit 5.

The processor 21, the communication interface 22, the CG-ROM 25, the first V-RAM 26, the second V-RAM
- 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 that emits a laser beam, and a laser oscillator 3 that emits a laser beam.
2, a start sensor 34 consisting of a PIN diode, etc. that detects the start position of the laser beam, and a polygon motor drive circuit that rotationally drives the polygon mirror 35. 36 and a PLL control circuit 37 that controls the motor rotation speed by this drive circuit 36.

The processor 21 is programmed to execute the reception process shown in FIG. 3 when receiving data from the host device 23 via the communication interface 22.

That is, when the received data is print data, it is determined whether the print data is a character code generated by key input on the keyboard 27 or image data generated by reading the original by the image sensor 29. . And if it is a character code, CG-ROM2
5, converts the character code into a dot pattern, and develops it in the first V-RAM 26 as a binary video signal. In the case of image data, it has already been binarized by dither processing or the like in the host device 23, so it is expanded into the second V-RAM 28 as is. In addition, host device 2
If the data received from 3 is a print command,
Execute the printing process shown in .

That is, first, the first V-RAM 26 is searched to see if data (binary video signal) is stored therein. If it is stored, it is read out and sent to the laser scanner unit 5 via the video signal output circuit 30.
Output to.

On the other hand, if no data is stored in the first V-RAM 26, the data is stored in the second V-RAM 28.
to find out whether data (binary video signal) is stored. If it is stored, it is read out and output to the laser scanner unit 5 via the video signal output circuit 30. At this time, the second V-RAM 28
A control flag indicating that the data is a binary video signal read from the data is added to the data and output. In addition, the above 2nd V
-If no data is stored in RAM28,
Since there is no data to be printed, this process ends.

On the other hand, the laser control circuit 33 of the laser scanner unit 5 to which the binary video signal from the video signal output circuit 30 is input, as shown in FIG. Input circuit 33A,
A flag presence/absence determination circuit 33B determines whether or not the control flag is added to the binary video signal taken in by the input circuit 33A, and when the determination circuit 33B determines that the flag is present, the actual printed dots are A dot size determination circuit 33C determines the size to be a small dot, or a large dot if it is determined that there is no flag, and the laser beam is turned on based on the binary video signal taken in by the video signal input circuit 33A. / pulse generating circuit 33D that generates an off signal and outputs it to the laser oscillator 32.

Here, the pulse generation circuit 33D has a function of modulating the pulse width of the on/off signal based on the determination result by the dot size determination circuit 33C. Specifically, the pulse width of the on signal is shorter when the actual print dot size is a small dot than when it is a large dot (for example, the pulse width of the on signal when the dot is large is set to 1).
When the dot is small, it is modulated so that it becomes 3/5).

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. The data is expanded to the first V-RAM 26. 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 and sent to the laser scanner unit 5 via the video signal output circuit 30. It is output to the control circuit 33. This causes the laser control circuit 33 to output the laser oscillator 32.
A laser beam on/off signal is generated for the binary video signal, and the laser oscillator 27 generates a laser beam during the on-pulse period to form a binary image of characters according to the electrophotographic process.

In this case, since no control flag is added to the binary video signal input to the laser control circuit 33, the on-pulse width of the on/off signal generated from the laser control circuit 33 is relatively wide. . Therefore,
The beam diameter of the laser beam output from the laser oscillator 32 increases, and the size of an actual printed dot for one pixel becomes larger than that one pixel. As a result, the character data entered from the keyboard 27 is printed as a thick and clear image by this laser printer.

On the other hand, the image sensor 2 of the host device 23
9, when image data such as a photograph is input as print data, the image data, which has been binarized by dither processing etc., is sent to the second V-RAM 2 as a binary video signal.
It will be expanded to 8. When a print command is output from the host device 23, the second V-RAM 2
The binary video signal stored in the laser scanner unit 5 is read out and sent to the laser scanner unit 5 via the video signal output circuit 30.
It is output to the laser control circuit 33 of. As a result, the laser control circuit 33 generates a laser beam on/off signal for the binary video signal to the laser oscillator 32, and the laser oscillator 27 generates a laser beam for an on-pulse period to follow the electrophotographic process. A binary image of the image data is formed.

In this case, since a control flag is added to the binary video signal input to the laser control circuit 33, the on-pulse width of the on/off signal generated from the laser control circuit 33 is smaller than that for characters. It is modulated so that it becomes narrower. Therefore, the beam diameter of the laser beam output from the laser oscillator 32 becomes small, and becomes approximately equal to the actual print dot for one pixel. As a result, the image data read by the image sensor 29 is printed by this laser printer as a halftone image with excellent gradation reproducibility without collapse even in areas with dense dots.

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

Further, in the above embodiment, two of the image data
Although a control flag is added only when outputting a value video signal to the laser scanner unit 5, two types of control flags are prepared, and a binary video signal from the first V-RAM 26 and a binary video signal from the second V-RAM 28 are added. Different control flags may be added to distinguish between data storage locations. Furthermore, by variably adjusting the beam diameter in three or more types and preparing V-RAMs corresponding to the number, the actual printing dot size can be made into three or more types, improving the gradation reproducibility of halftone images. It is also possible to further improve the

Furthermore, the present invention is not limited to laser printers, but can of course be applied to thermal printers, inkjet printers, etc. that reproduce halftone images such as characters and photographs based on binary signals. .

[0033]

As described in detail above, according to the present invention, good gradation reproducibility can be obtained for half-tone output images such as photographic images, and thick and clear images can be obtained for output images such as characters. It is possible to provide a binary image forming apparatus that can obtain the following information and improve print quality.

[Brief explanation of the drawing]

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

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

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

FIG. 4 is a flowchart showing print processing of the processor in the same embodiment.

FIG. 5 is a functional block diagram of the laser control circuit.

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

FIG. 7 is a gradation characteristic diagram 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, 33B... Flag presence/absence determination circuit, 33C... Dot size determination circuit.

Claims (1)

[Claims] 1. A first image storage section that stores a binary video signal of character code, a second image storage section that stores a binary video signal of image data, and a second image storage section that stores a binary video signal of image data. a pulse generating section that generates a forming pulse signal; a signal transfer means that transfers binary video signals respectively stored in the first and second image storage sections to the pulse generating section; and an image forming means for forming a binary image by printing dots in response to an image forming pulse signal, and the signal transfer means includes:
The binary video signal is transferred to the pulse generating section with information for distinguishing from which storage section of the second image storage section the binary video signal is read out, and the pulse generating section transfers the binary video signal to the pulse generating section. A binary image forming apparatus is characterized in that the actual print dot size is variably controlled by modulating a corresponding image forming pulse signal based on the content of additional information of a binary video signal.