JPH03216362A - Image forming device - Google Patents

Abstract

PURPOSE:To always obtain a high-quality regenerated image by a method wherein with the judgement that both of a set of image data are not more than a reference value, the image data is converted, and when at least one of the data is more than the reference value, the data is outputted as an image without conversion. CONSTITUTION:A two-pixel data magnitude discriminating circuit 203 outputs a signal selecting the input side A of a selector 205 for the input of larger data of a set of two-pixel data and a signal selecting the input side B for the input of smaller data. The outputs from a delay circuit 201 and the selector 205 are respectively inputted to the sides A and B of a selector 206. When both of a set of two-pixel data are not more than a predetermined reference value, a reference value comparison circuit 204 outputs a signal selecting the input side B of the selector 206. When at least either of the data is more than the reference value, it outputs a signal selecting the input side A.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms an image by binarizing multivalued image data by pulse width modulation.

[Prior Art] Conventionally, when multivalued image data including a halftone image is binarized to form an image, good binarization methods include a dither method, a density pattern method, etc. using a threshold matrix. "Are known. In addition, in laser beam printers, etc., multilevel image data is compared with triangular waves, etc., and the density of the image data is modulated to correspond to the pulse width.
A binarization method called "pulse width modulation" has also been proposed.

[Problems that the invention attempts to solve] However, when these methods are used in an electrophotographic image forming apparatus such as a laser beam printer,
Due to the response characteristics of the laser driver and the characteristics of image formation using electrophotography, for example, if the resolution is set to such a resolution that line drawings such as characters can be reproduced, the gradation of halftone images such as photographs will decrease; If the gradation characteristics of 2 are obtained, the resolution of characters, etc. will decrease and the edges will become jagged, so it is necessary to distinguish between the character part and the halftone image part and form images with different resolutions for each area. had to be done.

The present invention has been made in view of the above-mentioned drawbacks of the conventional example, and provides an image forming apparatus that can provide a high-quality reproduced image on the palm of the hand without changing the resolution of the character part or halftone image part of a multivalued image. The purpose is to provide.

[Means and operations for solving the problems] In order to achieve the above object, the image forming apparatus of the present invention has the following configuration. That is, in an image forming apparatus that binarizes multivalued image data to form an image, two adjacent pixels of the multivalued image data are set as a set, and the image data in this set is compared with a predetermined reference value. an adding means for adding two pieces of image data in the set; and a converting means for converting an output value of the adding means;
When it is determined that both of the image data in the set are equal to or less than the reference value, converting the image data by the converting means,
When at least one of the image data in the set is larger than the reference value, an image is formed without performing the conversion.

Preferably, the conversion means includes a size comparison unit that compares the size relationship between the two image data in the set, and the conversion unit includes:
One aspect of the conversion is to convert two pieces of image data so that the larger one becomes the added value and the other becomes zero.

More preferably, the predetermined reference value is less than or equal to the maximum value of the image data.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Description of Configuration (FIGS. 1 and 5)> FIG. 1 is a block diagram showing a schematic configuration of an image signal processing section of a laser beam printer in this embodiment.

In the figure, 101 is a video data output section, and C
Image data from a CD sensor or video camera is A/D converted, and digital multi-value image data 114 of predetermined bits (8 bits in this embodiment) including density information is converted to a synchronous clock (
It is output in synchronization with RCLK) l l 5. Then, this digital image data 114 is temporarily stored in the buffer memory 102, and is synchronized with the horizontal synchronization signal (HSYNC) and video clock signal (VCLK) from the timing signal generation circuit 112.
It is read as 6. Furthermore, the synchronization and speed conversion of the image data from the video data output unit 101 is performed via the buffer memory 102 .

Video data 11 read from buffer memory 102
6 in the lookup table (LUT) 103,
After being corrected to a gradation that matches the latent image and development characteristics of this laser beam printer, it is input to the video data processing circuit 104. Data 119 that has been subjected to predetermined processing (described later) in this video data processing circuit 104 is sent to the next D/A.
It is converted into an analog video signal 120 by the converter 105 and input to one input terminal of the comparator 106 . Further, a pattern pulse 123 for binarizing (PWM modulating) the analog video signal 120 is input to the other input terminal of the comparator 106 . The modulation signal (PWM signal) 124 output from the comparator 106 is then passed through the gate circuit 107 to the laser driver 1.
08 is input.

Here, the laser driver 108 drives the semiconductor laser 1 for a time corresponding to the pulse width of the input modulation signal 125.
09 is driven with constant current. Laser light emitted from this semiconductor laser 109 scans the photoreceptor, and a copy image is formed by an electrophotographic process.

FIG. 5 is a block diagram showing a schematic configuration of the recording section of the laser beam printer. In the figure, 108 is the above-mentioned laser driver, and 109 is a semiconductor laser. 51 is a collimator lens, 52 is a polygon mirror, and 53 is an fθ lens. The thus modulated and fθ-corrected laser light scans the photoreceptor 50 by rask scanning to form an electrostatic latent image, and the image is transferred to recording paper by electrophotography. A beam detector (BD) 110 is provided near the start of one line of laser beam scanning and detects the start of laser beam scanning.

Here, returning to FIG. 1, the BD generation circuit 111 generates a BD signal 12 based on the signal from the beam detector (BD) 110.
1 is being created. This BD signal 121 and a clock 127 with a frequency four times higher than that of the input video data are input from a crystal oscillator 126 to a timing signal generation circuit 112, and a horizontal synchronization signal (HSYNC) and a video clock (VCLK) are generated. is output. Further, the timing signal generation circuit 112 includes a pattern pulse generation circuit 113.
A screen clock (SCLK) 122 is output to the

In the pattern pulse generation circuit 113, a screen clock 122 generates a pattern pulse 123 having a predetermined shape.

The pattern pulse 123 described above is synchronized with the screen clock 122 in this embodiment, and is synchronized with the screen clock 122.
It is a triangular wave with the same period as .

Further, as described above, the pattern clock 123 is connected to the PW
The analog image data 120 is input to the comparator 106 for binarization using M (pulse width modulation).

Description of Video Processing (Fig. 2)> Fig. 2 is a block diagram showing the detailed configuration of the video data processing circuit 104 in this embodiment.

The video data processing circuit 104 shown in FIG. 2 makes a set of two pixels each in the laser scanning direction (all scanning directions), and when both of the data of the two pixels are smaller than a reference value,
One of the two pixels is processed to be the sum of the two pixel data, and the other is set to zero, and if at least one of the two pixels is larger than the reference value, output data that does not undergo the above processing. This is a circuit for

Here, the delay circuit 201 is a circuit for delaying data by the processing delay when outputting video data without performing the above-described processing.

The two-pixel data addition circuit 202 is a circuit for adding data of two pixels in one set, and the added data is input to one input of the selector 205. Further, the other input of the selector 205 is fixed at zero. Then, from the 2-pixel data size discrimination circuit 203, 2 pixels in one set are
When the data of the pixel is larger, the selector 205 outputs a signal for selecting the A input side, and when the data is smaller, the selector 205 outputs a signal for selecting the B input side.

Outputs from the delay circuit 201 and the selector 205 are input to the A side and B side of the selector 206, respectively. When the reference value comparison circuit 204 determines that both data of two pixels in one set are smaller than a preset reference value, the selector 20
A signal for selecting the B input side of 6 is output, and when at least one of them is larger than the reference value, a signal for selecting the 8 input side is output.

Description of Examples of Modulation (FIGS. 1 and 3)> FIG. 3 is a diagram for explaining signal waveforms of each part of the image signal processing section shown in FIG. 1.

To explain with reference to FIG. 3, a clock 127 with a period more than four times that of the video clock 117 is input from the crystal oscillator 126 to the timing signal generation circuit 112, and the BD signal 1
21 and HSYNC signal 128 synchronized to clock 127
, a video clock signal 117, and a screen clock signal 122 are output. As described above, this screen clock 122 is a synchronizing signal for pattern pulse generation, and is input to the pattern pulse generation circuit 113.

Further, the analog video signal 120 is transmitted to the buffer memory 1
An example is shown in which the video data 116 read from 02 is converted into an analog signal by the D/A converter 105.As can be seen from FIG.
Each pixel data at analog level is output.

As shown in the figure, it is assumed that the lower the analog level is, the darker it becomes, and the higher the density becomes.

Further, a pattern pulse 123, which is an output of the pattern pulse generating circuit 113, is generated in synchronization with the screen clock 122 as shown in FIG. 3, and is input to the converter 106. Here, the modulation signal (PWM) 124 represents a signal obtained by comparing the video signal 120 with the pattern pulse 123 by the comparator 106 and converting it into a binary value, and becomes a drive signal for the laser driver 108 .

<Explanation of an example of image modulation (FIG. 4)> FIG. 4 is a diagram showing an example of image modulation in this embodiment.

In addition, for comparison with the conventional example, the video data processing circuit 1
An example without 04 is also shown.

As shown in the figure, when a video signal is input, the analog video signal 120 in this embodiment becomes like 311. It is assumed that the lower the analog level of the analog video signal 120, the blacker it becomes, and the higher the density. Further, it is assumed that the reference value compared in the video data processing circuit 104 is [7FH].

For each of the analog video signals 310 and 311 described above, the modulation signal 124 modulated by the pattern pulse signal 123 is 312 and 31
It will be like 3.

In other words, when comparing modulation signals 312 and 313,
In this embodiment, 301 and 302 are combined into 3
It can be seen that 303 and 304 are combined into 306 in 05.

In other words, in areas where halftone images are continuous, the on-signal is concentrated, resulting in good gradation, and in dark image areas such as text, the on-signal is output while maintaining the same resolution. The output is suitable for the image forming apparatus of this type.

According to this embodiment, it can be realized with a relatively simple circuit configuration,
Since the resolution of pulse width modulation does not change, only one pulse width modulation circuit is required, and there is no need for a means to distinguish between character areas and halftone image areas, which reduces costs and enables high-quality image formation. It can be carried out.

[Other Embodiments] Next, other embodiments according to the present invention will be described below with reference to FIG. 6.

FIG. 6 is a diagram showing an example of image modulation when the period of the pattern pulse signal 123 is doubled with respect to the video clock (VCLK) 1 1 7.

In the embodiment described above, line drawings such as characters are processed preferentially,
While the present embodiment is intended to improve the reproducibility of halftone images, this embodiment processes halftone images preferentially and furthermore aims to improve the reproducibility of line drawings.

In other words, as can be seen by comparing the modulation signals 501, 502 and the modulation signals 503, 504 shown in FIG. It is possible to prevent blurring in some areas.

[Effects of the Invention] As described above, according to the present invention, there is an effect that high-quality images can be formed without providing binarization means with different resolutions for the character portion and the halftone portion.

[Brief explanation of drawings]

Fig. 1 is a schematic block diagram showing the configuration of the laser beam printer in the embodiment, Fig. 2 is a block diagram showing details of the video data processing section in Fig. 1, and Fig. 3 is a timing diagram for explaining the operation of pulse width modulation. 4 is a timing chart illustrating image modulation in this embodiment. 5 is a diagram illustrating binary image formation in the recording section in the case of a laser beam printer as an example. 6 is a diagram illustrating another embodiment. It is a timing chart explaining image modulation in an example. In the figure, 101...video data output section, 102...
Buffer memory, 103...LUT, 104...Bidet data processing circuit, 105...D/A, 106...
・Combalay evening, 107...Gate, 108...Laser driver, 109...Semiconductor laser, 110...
・Beam detector, 111... BD generation circuit, 11
2...Timing signal generation circuit, 113...Pattern pulse generation circuit. +08

Claims (3)

[Claims] (1) In an image forming apparatus that binarizes multivalued image data to form an image, two adjacent pixels of the multivalued image data are set as a set, and the image data in this set is combined with a predetermined reference value. a comparison means for comparing, an addition means for adding two image data in the one set, and a conversion means for converting the output value of the addition means, and the comparison means allows the image data in the one set to be added. When both of the data are determined to be below the reference value, the image data is converted by the conversion means, and when at least one of the image data in the set is greater than the reference value, the conversion is performed. An image forming apparatus characterized in that an image is formed without any image formation. (2) It has a magnitude comparison means for comparing the magnitude relationship between the two image data in the set, and the conversion means sets the larger one of the two image data as an added value and sets the other as zero. The image forming apparatus according to claim 1, wherein the image forming apparatus performs the conversion as follows. (3) The predetermined reference value is 1/1 of the maximum value of the image data.
The image forming apparatus according to claim 1, wherein the number is 2 or less.