JPH09191407A - Image forming apparatus and method - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To reduce the size of each pixel in order to obtain a higher resolution, and to increase the number of divisions for each pixel in order to realize a higher gradation, in a predetermined section. Only the gradation can be reproduced. SOLUTION: Multi-valued image data from an input terminal 1 is converted into parallel multi-valued image data by a serial / parallel converter 2, and a pulse width modulated image signal is output to an LED array 8 by a pulse width modulator 9. It At this time, the amplitude and bias of the triangular wave output from the triangular wave generator 7 are adjusted so that appropriate pulse width modulation can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and method, and more particularly to an image forming apparatus and method for performing multi-valued image formation by modulating each pixel based on an input multi-valued image signal. .

[0002]

2. Description of the Related Art Conventionally, in an LED printer which uses an LED array as a light source, the printing resolution is determined by the array density of each LED element of the LED array, and due to the recent development of semiconductor technology, it has a sufficiently high-quality binary value. High resolution LED arrays capable of outputting images have been developed. As a method of forming a multi-valued image, a dither method,
The density pattern method and the like are known, but in these methods, since a halftone is expressed by treating a plurality of pixels as one block, an image having multi-value gradation is formed while maintaining high resolution. I couldn't.

In addition to this, pulse width modulation (hereinafter referred to as PWM modulation) is adopted as a method for forming a multi-valued image, but in the PWM modulation adopted in the conventional LED printer, the photosensitive member is used. Each pixel on the drum is equally divided, and it is determined whether or not light is applied to the divided area in each pixel in proportion to the value of the input image data.

[0004]

However, in the PWM modulation of the above-mentioned conventional example, each pixel is made smaller in order to obtain higher resolution, and the pixel-by-pixel division is made in order to realize higher gradation. When the number is increased, generally, the area ratio where the light is applied to the photoconductor drum and the density of the resulting image have a relationship as shown in FIG. 4, so that only in the section from point a to point b in FIG. There was a problem that the gradation could not be reproduced.

For example, if one pixel is divided into 20 and the level of the input image data is divided into 20 levels, as shown in FIG. Does not occur at all, and at the level of 18, the density becomes 100% instead of 18/20, and the original density of the input image data cannot be reproduced, leading to deterioration of image quality. Was there.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an image forming apparatus and method capable of forming an image having high resolution and higher gradation.

[0007]

In order to achieve the above object, the image forming method of the present invention has the following steps.

That is, an input step of inputting a plurality of multi-valued image signals representing respective image densities of a plurality of pixels, and a conversion for converting the plurality of multi-valued image signals input in the input step into parallel multi-valued image signals A step, a pulse width modulation step of performing pulse width modulation on each of the plurality of multi-valued image signals that have been parallel-converted by the conversion step, and a plurality of pulse width modulated image signals that are pulse-width modulated by the pulse width modulation step. In order to achieve the above object, the image forming apparatus according to the present invention has the following configuration.

That is, input means for inputting a plurality of multi-valued image signals representing respective image densities of a plurality of pixels, and conversion for converting a plurality of multi-valued image signals input by the input means into parallel multi-valued image signals Means, pulse width modulation means for performing pulse width modulation on each of the plurality of multi-valued image signals converted in parallel by the conversion means, and a plurality of pulse width modulation means based on the plurality of image signals pulse width modulated by the pulse width modulation means. In such a configuration including a forming unit for forming pixels,
A plurality of multi-valued image signals representing image densities of a plurality of pixels are input, the plurality of multi-valued image signals are converted into parallel multi-valued image signals, and a pulse width is applied to each of the plurality of parallel-converted multi-valued image signals Modulation is performed to form a plurality of pixels based on a plurality of pulse width-modulated image signals, and the amplitude and bias of a reference signal to be compared with a multi-valued image signal can be adjusted.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing the structure of an LED printer as an image forming apparatus according to this embodiment.
The LED printer body 100 is based on image data supplied from an externally connected host computer or the like.
The LEDs arranged in a line on the LED array are caused to emit light to form an electrostatic latent image on the photosensitive drum. The electrostatic latent image on the photoconductor drum is developed by a developing device to form a toner image on a recording sheet, which is a recording medium.

The operation panel 300 is composed of various switches for operation and an LCD display. The printer control unit 101 controls the entire LED printer and processes image data and the like supplied from a host computer, and mainly converts the image data into a video signal to convert the LED driver 1
Output to 02.

The LED driver 102 is a signal processing section for receiving image data from the printer control unit 101 and converting it into a signal for driving the LED array 103. The LED driver 102 is arranged on the LED array according to a finally input video signal. Each LED element is switched on and off. LED
By the light emitted from the array 103, the photosensitive drum 1
An electrostatic latent image of the image is formed on 06. This latent image is
After being developed by the developing unit 107 around the photosensitive drum 106, it is transferred to a recording sheet. A cut sheet is used as the recording paper, is stored in a paper cassette attached to the LED printer, is taken into the apparatus by the paper feed roller 109 and the conveyance rollers 110 and 111, and is fed to the photosensitive drum 106. After that, the recording paper is separated from the photosensitive drum 106, fixed by the fixing unit 112, and discharged from the paper discharge unit 113 to the paper discharge tray unit 114.

Next, details of signal processing of the LED driver 102 for generating a video signal for driving the LED array 103 by the PWM modulation method will be described.

FIG. 2 is a block diagram showing a detailed configuration of the signal processing section. In the figure, 1 is an input terminal for image data, 2 is a circuit for converting image data into serial-parallel,
Reference numeral 3 is a circuit for latching respective parallel data, 4 is a D / A converter, 5 is a comparator, 6 is an input terminal of a clock (hereinafter referred to as / LSYNC) which is output every time one line is printed, and 7 is / LSYNC generates a triangular wave from the triangular wave generator, 8 is a signal from the comparator 5 LE
It is an LED array that forms an image by turning D on or off. The PWM modulator 9 is composed of the latch 3, the D / A converter 4, the triangular wave generator 7, and the comparator 5.

FIG. 3 is a time chart showing the timing of each signal of the signal conversion section shown in FIG. The image data input from the image data input terminal 1 is accumulated for one line of the LED array by the serial / parallel conversion unit 2 including a shift register, and the LE on the LED array is stored.
Image data corresponding to the positions of the D elements are output in parallel. Next, the image data generated by the serial-parallel conversion unit 2 is input to the latch 3 and the / LSYN
It is latched by the clock from the C input terminal 6.

The output from the latch 3 is, as shown in FIG.
It is held until the next / LSYNC is input, and this image data is input to the D / A converter 4 and converted into an analog signal. That is, if the input image data is 8 bits, it becomes an analog signal corresponding to 256 levels and is input to one terminal of the comparator 5.

On the other hand, the clock from the input terminal 6 of / LSYNC generates a triangular wave as shown in FIG. 2 which is synchronized with the synchronous clock for each line by the triangular wave generator 7 and inputs it to the other terminal of the comparator 5. To be done. Then, in the comparator 5, the analog image signal and the triangular wave are compared, and the PW
It is output as an M signal. The PWM signal is the LED array 8
And an image is formed by the LED array 8,
Is output.

Here, when the output of the latch 3 is at the lowest level (for example, 0), the time corresponding to the area of the point a shown in FIG. 4, and the output of the latch 3 is at the highest level (for example, the image data is 8 bits). In the case of 255), the LED is turned on for a time corresponding to the area of the point b shown in FIG.
The triangular wave generator 7 is configured to generate a triangular wave having an amplitude and a bias such that a PWM output signal is output.

By the series of operations described above, it is possible to form an image of high resolution and high gradation by using PWM modulation in the LED printer.

It should be noted that the present invention is not limited to the above-described embodiment, but can be variously modified based on the gist of the present invention. For example, in the present embodiment, a PWM modulator using a triangular wave will be described. However, as long as it is a PWM modulator, the same effect can be obtained with a PWM modulator using a digital counter, and it goes without saying that these are not excluded from the scope of the present invention.

The present invention also provides a "host computer,
The invention may be applied to a system including a plurality of devices such as an interface and a printer, or to an apparatus including one device such as a copying machine. Further, it goes without saying that the present invention can be applied to the case where it is implemented by supplying a program to a system or an apparatus. In this case, the storage medium storing the program according to the present invention constitutes the present invention. Then, by reading the program from the storage medium to the system or device, the system or device operates in a predetermined manner.

[0023]

As described above, according to the present invention,
It is possible to form high resolution and high gradation images,
It is possible to form an image with higher image quality.

[0024]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the structure of an LED printer according to the present embodiment.

FIG. 2 is a block diagram showing a detailed configuration of a signal processing unit in the present embodiment.

FIG. 3 is a time chart showing the timing of each signal of the signal processing unit.

FIG. 4 is a diagram showing a relationship between an area ratio of a pixel to which light is applied and print density.

FIG. 5 is a diagram illustrating a place where light in a pixel is exposed and an example of a print result when one pixel is divided into 20.

[Explanation of symbols]

 1 Image Data Input Terminal 2 Serial / Parallel Converter 3 Latch Circuit 4 D / A Converter 5 Comparator 6 / LSYNC Input Terminal 7 Triangular Wave Generator 8 LED Array 9 PWM Unit 10 Image Clock Input Terminal 100 LED Printer Main Body 101 Printer Control Unit 102 LED driver 103 LED head 106 Photosensitive drum 107 Developing unit 109 Paper feeding roller 110 Conveying roller 111 Conveying roller 112 Fixing unit 113 Discharging section 114 Discharging tray 300 Operation panel

Claims (6)

[Claims] 1. An input unit for inputting a plurality of multi-valued image signals representing respective image densities of a plurality of pixels, and a conversion for converting the plurality of multi-valued image signals input by the input unit into parallel multi-valued image signals. Means, pulse width modulation means for performing pulse width modulation on each of the plurality of multi-valued image signals parallel-converted by the conversion means, and a plurality based on the plurality of image signals pulse-width modulated by the pulse width modulation means An image forming apparatus comprising: a forming unit configured to form pixels. 2. The image forming apparatus according to claim 1, wherein the pulse width modulation means includes adjustment means for adjusting the amplitude and bias of a reference signal to be compared with the multi-valued image signal. 3. The image forming apparatus according to claim 1, wherein the forming unit forms an image using an LED array. 4. An input step of inputting a plurality of multi-valued image signals representing respective image densities of a plurality of pixels, and a conversion of converting the plurality of multi-valued image signals input by the input step into parallel multi-valued image signals. A step, a pulse width modulation step of performing pulse width modulation on each of the plurality of multi-valued image signals parallel-converted by the conversion step, and a plurality of pulse width modulation step based on the plurality of image signals pulse width modulated by the pulse width modulation step. An image forming method, comprising: a forming step of forming pixels. 5. The image forming method according to claim 4, wherein the pulse width modulation step includes an adjustment step of adjusting an amplitude and a bias of a reference signal to be compared with the multi-valued image signal. 6. The image forming method according to claim 4, wherein in the forming step, an image is formed using an LED array.