JPH01158465A - Image forming device - Google Patents

Abstract

PURPOSE:To improve the quality of a recorded image by displacing the position in a subscanning direction of a recorded image element according to the density of the recorded image element. CONSTITUTION:When the reading of an original is started in a state where a fineness mode is set, image signals DV' are inputted in an image signal generation part 18 from a 4/2 bit converter 17 to decide the image element values of the respective recorded image elements in an image element value decision part 23 and image element value signals DP, which are the decided results, are sequentially outputted to a control part 24. The control part 24 sequentially accumulates the inputted image element value signals DP in an image memory 25. When the accumulation of the image element value signals DP equal to one page is completed, the control part 24 starts a motor driving control part 28 so as to move a photosensitive body 1 at 1/2 subscanning speed of a reference and reads out the image element values in the unit of line with 1/2 pitch of a reference from the image memory 25 so as to sequentially output the image signals RD corresponding to the image element value of the respective image elements to a recording control part 26. Thus, the recorded image of high definition can be recorded and outputted.

Description

[Detailed description of the invention] [Technical field] The present invention relates to an image forming apparatus.

[Prior Art] In recent years, with the spread of so-called office automation, various information processing devices have been introduced into office environments. Devices used in such environments are required to suppress elements such as noise and vibration that adversely affect the environment as much as possible.

By the way, dot impact printers have been widely used for printing documents created with Japanese word processors etc. as hard copies, but these dot impact printers produce a lot of printing noise and vibration. This tendency was especially strong with high-speed machines, and they often interfered with the work of those around them.

To solve this problem, non-impact printers that form images using an electrophotographic process, such as laser beam printers, liquid crystal shutter printers, or LED printers, have been put into practical use.

Unlike the above-mentioned dot-impact printers, this printer produces very low printing noise because there is no part where the paper is struck when forming an image, and it is also a page printer that basically records images on a page-by-page basis. Therefore, high-speed recording is possible.

In such an image forming apparatus (page printer), the size of recording pixels is generally constant, and each recording pixel is recorded as a binary image of white and black.

For this reason, for example, with a digital scanner, it is possible to
), when an image is read that has an edge that intersects with the direction in which the recorded pixels are arranged, the edge of the recorded image becomes jagged as shown in (b) of the same figure, and the original image is distorted. This caused an inconvenience in that the smoothness was lost.

[Objective] The present invention has been made in order to eliminate the disadvantages of the prior art, and an object of the present invention is to provide an image forming apparatus that can improve the quality of recorded images.

[Structure] In order to achieve this object, the present invention displaces the position of a recording pixel in the sub-scanning direction depending on the density of the recording pixel.

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

FIG. 1 shows a liquid crystal shutter printer according to an embodiment of the present invention.

In the figure, the surface of a photoreceptor 1 is uniformly charged by a charger 2, and an optical writing device 3 exposes a light image corresponding to a recorded image to form an electrostatic latent image corresponding to the recorded image on its surface. be done.

The optical writing device 3 includes a fluorescent lamp 3a used as a light source.
, a liquid crystal micro shutter array (hereinafter simply referred to as a liquid crystal shutter) 3b that turns on and off the light from the fluorescent lamp 3a in pixel units corresponding to one line of recorded image; and an image light formed by the liquid crystal shutter 3b is transmitted to the photoreceptor It is composed of a 1-magnification linear imaging element 3c made of a convergent fiber array or the like that forms an image on the image plane 1 and exposes it to light. Further, the cover 3d is provided to prevent light from the fluorescent lamp 3a from leaking to the outside.

The electrostatic latent image formed on the surface of the photoreceptor 1 is developed with toner by the developer 4, and the toner image thus formed on the surface of the photoreceptor 1 is transferred to a recording sheet conveyed by a paper feeding system (not shown). is transferred by the transfer charger 5.

The toner image transferred to the recording paper is then thermally fixed by the fixing device 6, thereby forming a recorded image on the recording paper.

Further, residual toner and residual charges on the photoreceptor 1 are removed by a cleaner 7.

In this way, in this liquid crystal shutter printer, an electrostatic latent image is formed on the surface of the photoreceptor 1 by generating image light line by line with the optical writing device 3 in synchronization with the rotation of the photoreceptor 1. Since the image is recorded based on the electrostatic latent image, the moving speed of the photoreceptor 1 is set to the standard speed of 172 without changing the writing speed of one line of the optical writing device 3, or If the writing speed of one line of the optical writing device 3 is set to double without changing the moving speed of the photoconductor 1, the optical writing device 3 will move to the photoconductor as shown in FIGS. 2(a) and (b). A light dot Dt irradiated on the surface of 1
The interval in the sub-scanning direction becomes the interval d2, which is 1/2 of the reference interval d1, so that the dimension in the sub-scanning direction becomes d2.

A standard number of recording pixels of 172 can be formed.

As a result, in this liquid crystal shutter printer,
Figure 3 (
As shown in a)-(d), the pixel value P1 is completely white, the pixel value P2 is completely black, the pixel value P3 is black in the upper half, and the pixel value P3 is black in the lower half.
/2 can take four states with black pixel value P4.

In addition, in the same figure, the areas separated by the dashed grid indicate the planar areas set for each recording pixel (the same applies hereinafter). In addition, in this example, as an electrostatic photographic process, the exposure position is set to a black pixel. A case will be explained in which a positive-positive method is used.

In this way, by shifting the position of the optical dot Dt that the optical writing device 3 irradiates onto the surface of the photoreceptor 1 from the reference position in the sub-scanning direction, the area of the black portion occupying the recording pixel area is changed in multiple stages. Therefore, in the above example, the number of pixel states that can be expressed by one recorded pixel increases to four.

In the above example, the ratio of black pixels to the recording pixel area (hereinafter referred to as black pixel ratio) can be set to three states: 1, 0, and 1/2, so the density of the recording pixels can be set using a 2-bit signal. As shown in Table 1 below, four states of black pixel ratio are assigned to each value of this 2-bit signal.

The relationship between the density of a pixel (which is inversely proportional to the amount of reflected light) and the value taken by a 2-bit signal is shown in FIG. 4 for the case where an image is read by a scanner.

Furthermore, as shown in FIG. 5, the pixel value taken by a recording pixel whose 2-bit signal value is "10" is the pixel of interest (hereinafter referred to as the pixel of interest) B and the recording pixel ( This is determined by an algorithm as shown in FIG. 6 according to the density change tendency of A and C (hereinafter referred to as adjacent pixels).

First, it is checked whether the density of the adjacent pixel A and the density of the adjacent pixel C are the same (decision 101), and if the result of determination 101 is YES, the pixel value P of the white pixel in the pixel of interest B is determined.
1 is set (process 102).

When the result of judgment 101 is YES, the adjacent pixel A
It is checked whether the density of the adjacent pixel C is greater than the density of the adjacent pixel C (determination 103). When the result of judgment 103 is YES, it means that the density of the previous line is greater than the density of the next line, so the pixel value P3 of the upper half of the pixel B is black.
(processing 104).

When the result of judgment 103 is NO, the density of the next line is greater than the density of the previous line, so the pixel value P4 of which the lower 1/2 is black is assigned to the pixel of interest B (process 105).
.

Therefore, for example, as shown in FIG. 7(a), if the boundary line between the black image and white image of the read image passes diagonally through the pixel of interest B, and the black image is located above the boundary line, Since the pixel value P3 is assigned to the pixel of interest B, the optical dot Dt of the optical writing device 3 is assigned as shown in FIG.
is irradiated, and an image as shown in FIG. 3(c) is formed.

Furthermore, when reading images as shown in FIG. 8(a), FIG. 9(a), and FIG. 10(a), FIG. 8(b), FIG. 9(b), Then, as shown in FIG. 10(b), the optical dots Dt of the optical writing device 3 are irradiated, thereby causing the dots Dt in FIG.
Images as shown in Figure (C) and Figure 10 (C) are formed.

Note that among the pixels represented by the nine grids indicated by broken lines in FIGS. 8, 9, and 10, the pixel located in the center corresponds to the pixel B of interest.

As a result, for example, when reading an image in which the black-and-white boundary line is diagonal in the horizontal direction, as shown in FIG. Although it is noticeable, in the present invention, the jaggedness of the dots is alleviated and the quality of the recorded image is improved, as shown in FIG.

FIG. 12 shows a digital copying machine according to an embodiment of the present invention. Here, in the following description, the operating mode for performing the same image recording as the conventional one will be referred to as the standard mode, and the operating mode for performing high-precision image recording as described above will be referred to as the fineness mode.

In the figure, a line image sensor 1O reads an image for one line in synchronization with a reading optical system (not shown), and an analog image signal AV output from a line image sensor 10 is amplified via an amplifier 11. After that, it is added to the variable gain amplifier 13 of the shading correction section 12.

The variable gain amplifier 13 adjusts the gain of the analog image signal AV pixel by pixel based on the stored contents of a correction data memory 14 that stores a digital image signal for one line (described later) when a reference white image is read. change, thereby
This is to correct variations in sensitivity of each element of the line image sensor 10.

The image signal AV' corrected by the shading correction section 11 is applied to a peak hold circuit 15 and a 4-bit digital/analog converter 16.

The peak hold circuit 15 receives the image signal AV' line by line.
The peak of PH is detected and held, and the held output PH is used as a reference level for the digital/analog converter 16.

Thereby, the digital/analog converter 16 converts the image signal AV' into a corresponding 4-bit digital image signal Dv with the background correction performed line by line.

This digital image signal DV is stored in the correction data memory 14 when a reference white image is read immediately before reading the image of the input original, and thereafter is output to the 472-bit converter 17.

The 472-bit converter 17 converts the 4-bit digital image signal Dv output from the analog/digital converter 16 into
The image signal DV' is converted into a 2-bit image signal DV' having the above-mentioned values "00", "10", and "11", and the image signal DV' after the conversion is transmitted through the cascade connection of the image signal generation section 18. The data is sequentially stored in the three line memories 19, 20, and 21.

The line memories 19, 20, and 21 each store one line of image signal DV'', and the outputs of the respective line memories 19, 20, and 21 correspond to the adjacent pixels A, C, and the pixel of interest B described above. Three pixels are extracted and added to a register 22 that stores both signals Dv' of those pixels.

The pixel value determination unit 23 executes the above-mentioned algorithm based on the stored contents of the register 22 to determine the pixel value of the pixel of interest B, and uses the determination result of the pixel value determination unit 23 to determine the pixel value of the target pixel B. The value signal DP is output to the control section 24.

The control unit 24 is for controlling the image forming unit of this digital copying machine, and includes an image memory 25 for storing image signals for one page of recorded images, and a pixel value determination unit. The pixel value signals DP input from 23 are sequentially stored in this image memory 25. When the accumulation of pixel value signals DP for one page is completed, the pixel value of each pixel is read out from the image memory 25, and a pixel signal RD corresponding to the read pixel value is formed for each pixel, The image signal R
D is a recording control unit 2 that controls recording of the optical writing device 3.
Output to 6.

Note that, as described above, the pixel value P3. The distance P4 moves in the sub-scanning direction is 1/2 of the standard distance. Therefore, when the fineness mode is set, the number of scanning lines is doubled, and the image memory 25 is stored in this fineness mode. It has a storage capacity that can store all image information.

The control unit 24 also controls a motor drive control unit 28 that controls the drive of the motor 27 for rotationally driving the photoreceptor 1 .

The motor drive control unit 28 drives the motor 27 at a reference speed when the standard mode is set by the control unit 24, and drives the motor 27 at the reference speed when the definition mode is set.
The motor 27 is driven at a speed of 2.

As a result, in the former case, the photoreceptor l moves at the standard sub-scanning speed in synchronization with the main scanning, and in the latter case, 1! It moves at 1/2 the sub-scanning speed.

The definition mode is set by operating an operation section (not shown) by an operator of the digital copying machine or the like. Also, if standard mode is set,
The pixel value determining unit 23 simply performs a binarization process on the pixel B of interest and determines the pixel value of the pixel B of interest.

With the above configuration, when the digital copying machine starts reading a document with the definition mode set, the image signal DV' is input from the 4/2 bit converter 17 to the image signal generator 18, and thereby , the pixel value of each recorded pixel is determined by the pixel value determination section 23, and pixel value signals DP as the determination results are sequentially output to the control section 24.

The control unit 24 sequentially stores the input pixel value signals DP in the image memory 25, and when the storage of the pixel value signals DP for one page is completed, controls the motor drive control unit 28 with the definition mode specified. When activated, the photoreceptor l is moved at the standard sub-scanning speed of 172, and pixel values are read line by line from the image memory 25 at the standard pitch of 172, and both signals corresponding to the pixel value of each pixel are generated. The RDs are sequentially output to the recording control section 26.

As a result, an image is recorded in units of standard 172-pitch lines, and as described above, a high quality recorded image is recorded and output.

In this case, on the same line as in standard mode,
Pixels with pixel values PI, P2 are recorded, and a line located between these lines has pixel values P3. P4 pixels are recorded.

Incidentally, in the above-described embodiment, the pixels are read into a 2-bit multi-value signal, but the present invention can be applied even when the pixel is read into a multi-value signal with a larger number of bits.

In addition, in the above-mentioned embodiment, as an electrostatic photographic process,
Although a case has been described in which a positive-positive type electrophotographic process is used in which the exposure position is a black pixel, the present invention can be applied in the same way even when a positive-negative type electrostatic photographic process is used in which the exposure position is a white pixel.

Furthermore, in the above-mentioned embodiments, the present invention is applied to a digital copying machine that uses a liquid crystal shutter device as an optical writing device, but the present invention can also be applied to a digital copying machine that uses other optical writing devices. Further, the present invention can be similarly applied to an image forming apparatus that records a recorded image generated by an image generating apparatus in which recording pixels are flooded with multivalued signals.

[Effect] As explained above, according to the present invention, the recorded pixel is displaced from the reference position in the sub-scanning direction according to the density of the recorded pixel and the density change tendency of the surrounding area. The effect is that the image quality can be improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a configuration example of a liquid crystal shutter printer according to an embodiment of the present invention, FIGS. 2(a) and (b) are schematic diagrams for explaining the present invention in detail, and FIG. a) ~ (d
) is a schematic diagram illustrating possible pixel values, FIG. 4 is a schematic diagram illustrating the relationship between pixel density and 2-bit signal value, and FIG.
The figure is a schematic diagram illustrating a pixel of interest and adjacent pixels, Figure 6 is a flowchart illustrating a pixel value determination algorithm, Figures 7 (a) to (C), Figures 8 (a) to (c), and 9
Figures (a) to (c) and Figures 10 (a) to (C) are schematic diagrams showing an example of pixel value determination, Figure 11 (a) is a schematic diagram showing an example of a read image, and Figure 11 (a) is a schematic diagram showing an example of a read image. (b) is a schematic diagram showing a conventional example of a recorded image, (C) is a schematic diagram showing an example of a recorded image according to the present invention, and Fig. 12 is a control system of a digital copying machine according to an embodiment of the present invention. Block diagram illustrating 13th
Figure (a) is a schematic diagram showing an example of a read image, and Figure (b) is a schematic diagram showing an example of a recorded image by a conventional apparatus. DESCRIPTION OF SYMBOLS 1... Photoreceptor, 16... Analog/digital converter, 17... 4/2 bit converter, 18... Image signal generation section, 19-21... Line memory, 22... Register, 23... Pixel value determination unit, 24... Control unit, 2
5... Image memory, 26... Recording control unit, 28...
・Motor beating control section. Figure 1 Figure 2 Figure 3 Figure 4, Figure 5 Figure 6 Figure 7 (a) (b) (c) Figure 9 (a) (b) (c) Figure 11 (a) ( b) (c)

Claims (1)

[Claims] An electrostatic latent image is generated line by line on a photoreceptor using an optical writing device that generates recorded image light modulated by a recorded image signal, and a recorded image corresponding to the electrostatic latent image is created using an electrostatographic process. In an image forming apparatus using the image forming apparatus, a pixel displacement control means for displacing the position of a recording image light for recording a recording pixel in the sub-scanning direction from a reference position according to the density of the recording pixel, and the scanning start position An image forming apparatus comprising: a displacement direction determination means for setting the displacement direction of the displacement means according to a density change tendency of the recording pixel and recording pixels adjacent to the recording pixel in the sub-scanning direction.