JP2000307862A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of consequently obtaining a more stable image with a line image, having resolution which is higher than standard resolution by detecting the environmental change of a temperature and humidity, etc., around a device main body, also providing an overlapping area by varying how to allocate the number of gradation representations of a threshold matrix in image processing and the number of scanning lines per inch, on the basis of density information obtained in the device and preparing a new line image by comparing an obtained density level with a threshold level. SOLUTION: This image forming device, having an image processing means 202 which performs prescribed image processing of inputted image data, is provided with environmental state detecting means 515 and 530, which detect an environmental state in the image forming device and a control means 520 which optimizes pixel density by changing the method of allocating the number of gradation representations of the thresholds per pixel of threshold matrices 512a and 512b, in which image data are compared according to the detected results of the means 515 and 530.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus for performing halftone processing, and forms a printing position line different from a standard printing position to obtain high resolution by forming an overlapping area exceeding a threshold value. An image forming apparatus for detecting an environmental state of an apparatus main body and optimizing an image density value by changing a method of allocating a number of gradations of a threshold value per pixel of a threshold matrix according to the detected value. About.

[0002]

2. Description of the Related Art FIG. 5 is a schematic configuration diagram of a laser beam printer which is a conventional image forming apparatus. This printer is a terminal device that is connected to a computer (personal computer) via a predetermined interface cable and prints and outputs a result of information processed by the computer on recording paper.

[0005] In FIG. 5, reference numeral 201 denotes a signal processing unit to which an image signal is input. The image signal is input via an image input unit (not shown). As the signal, a color image signal including R (red), G (green), and B (blue) components is input. The present invention is not limited to this color image signal. A pseudo halftone processing unit 202 adjusts the image density level of the color image signal. 2
03 is a laser driver, 204 is a laser driver 203
This is an amplifier that amplifies the output signal of. This amplifier 204
Is output to the semiconductor laser 205. 2
06 is a polygon mirror, 207 is an f-θ lens, 208
Denotes a reflection mirror and 209 denotes a photosensitive drum. The configuration and processing after the photosensitive drum 209 will be described later with reference to FIGS.

First, color image signals are R (red), G
(Green) and B (blue) components,
In the image signal processing unit 201, Y (yellow), M
(Magenta), C (cyan), and K (black), and the pseudo halftone processing unit 202 performs image processing.
FIG. 6 is an explanatory diagram showing a process of producing a pseudo halftone image in the pseudo halftone processing unit 202 shown in FIG. FIG.
When the original image 220 shown in (a) is input, A / D conversion is performed, and a digitized original image 221 as shown in FIG. 6B is obtained. Here, each pixel level (image density level) in the digitized original image 221 is:
Assume that you are at 7 levels. The original image 221 at the predetermined image density level is compared with each threshold (slice level) of a threshold matrix 222 having 4 × 4 pixels as one block as shown in FIG. 6C.

FIG. 7 is a block diagram of a comparator 230 for comparing the digitized original image shown in FIG. 6 with a threshold matrix. In FIG. 7, an original image 221 having a predetermined image density level is compared with a threshold matrix 222 having a predetermined threshold. Pixels having an image density level higher than the threshold value (slice level) are black, and conversely, if the image density level is low, white. Becomes With such a principle, a pseudo halftone image is formed. As a result, a pseudo halftone image 223 having an image density distribution as shown in FIG.

The pseudo halftone image 223 formed in the pseudo halftone processing unit 202 in this way is sent to the laser driver 203 shown in FIG.
The image information of each of (magenta), C (cyan), and K (black) is modulated and input to the amplifier 204. The amplifier 204 drives the semiconductor laser 205 according to the modulation signal from the laser driver 203. Semiconductor laser 20
5 is output from the polygon mirror 206, f-
The scanning is performed on the photosensitive drum 209 via the θ lens 207 and the reflection mirror 208.

Next, the printing process shown in FIG. 8 will be described. FIG. 8 is an explanatory diagram of a printing process in the image forming apparatus shown in FIG.

First, in the charging step 301, the surface of the photosensitive drum 209 is uniformly charged by laminating a photoconductor on a conductive substrate. In the developing step 303, each color is developed to visualize the electrostatic latent image formed in the exposing step 302. Details of the developing step 303 will be described based on the configuration of the developing roller 400 shown in FIG. FIG. 9 is a cross-sectional view illustrating the configuration of the developing unit in FIG. The developing roller 400 includes the fixed magnet 40
3 and a magnetic cylinder (sleeve) 40 rotating around its periphery
4, and the toner 402 is charged by friction with the sleeve 404. A distance of several hundred microns is maintained between the photosensitive drum 209 and the sleeve 404, and the toner 402 adheres to the photosensitive drum 209 according to the electrostatic latent image formed in the exposure process 302 while flying the toner 402 in the alternating magnetic field. Then, a visible image is obtained. Thus, in the developing step 303, the visualization by the toner 402 according to the electrostatic latent image is performed.

In a transfer step 304 shown in FIG. 8, the print paper supplied from the supply step 309 is brought into contact with the photosensitive drum 209 by synchronizing, and a charge having a polarity opposite to that of the toner is applied to the surface of the print paper by a transfer charger (not shown). , The toner on the photosensitive drum 209 is copied onto a print sheet. Photosensitive drum 209 with visible image taken
In the drum cleaning step 306, residual toner on the photosensitive drum 209 is removed by a cleaning blade (not shown). Note that the exposure process 3
02, development step 303, transfer step 304, and drum cleaning step 306 are performed according to the number of colors used, such as Y (yellow), M (magenta), C (cyan), and K.
(Black) is repeated four times, and when the transfer is completed for all the colors, in the next separation step 305, the print paper on which the toner image has been transferred in the above-described transfer step 305 is separated from the photosensitive drum 209, and in the fixing step 307 After the toner transferred onto the print paper is heat-fixed by a fixing roller (not shown) and the toner image is fixed on the print paper, the print paper on which the toner image has been fixed is discharged in a paper discharge process 308. .

[0010]

However, in the conventional image forming apparatus, since the threshold matrix used for the halftone processing is fixed, the toner matrix may be deteriorated due to the environmental condition of the image forming apparatus, for example, temperature and humidity. There is a problem that a difference occurs in the ratio at which the image flies over the photosensitive drum, and as a result, the image density and the resolution after being transferred to the printing paper are changed.

The present invention has been made in view of the above points, and detects a change in environment such as temperature and humidity around an apparatus body, and based on density information obtained in the apparatus, a threshold value in image processing. A method of allocating the number of gradations of the matrix and the number of scanning lines per inch are varied to provide a superposition area, and a new line image is created by comparing the obtained density level with a threshold level. It is another object of the present invention to provide an image forming apparatus capable of obtaining a more stable image of a line image having a higher resolution than the standard resolution.

[0012]

In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention comprises an image forming apparatus having image processing means for performing predetermined image processing on input image data. In the apparatus, an environmental state detecting means for detecting an environmental state in the image forming apparatus, and a gradation expression number of a threshold value per pixel of a threshold matrix for comparing the image data according to a detection result of the environmental state detecting means Control means for optimizing the pixel density by changing the allocation method.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image processing means forms a region where a threshold value of a line different from an original display position is overlapped, thereby achieving high resolution. And a pseudo-halftone processing means for converting to

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the environmental condition detecting means is a temperature and humidity sensor for detecting the ambient temperature and humidity of the main body of the image forming apparatus. And

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the environmental state detecting means detects a ratio of toner flying according to the electrostatic latent image to the photosensitive band. It is a detection sensor.

[0016]

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

(First Embodiment) Before describing the image forming apparatus of the present invention, DPI is used as a general unit for resolution. This is the number of halftone dots per inch, which is the number of halftone dots per inch, with the accuracy of a printer capable of forming halftone dots, more precisely, an independently visible or identifiable dot. Here, the laser lighting time and the light intensity are shown in FIG. FIG. 10 is a characteristic diagram showing a relationship between laser lighting time and light intensity.

As shown in the optical response characteristics, the recording beam is lit for a certain time, and by comparing with a predetermined threshold, draws a line image that is visible when lit more than a certain value. It is impossible to draw a line image that can be visually recognized. Here, the beam spot diameter generally has the highest intensity at the center position of the beam and is not a digital spot diameter. The beam tends to spread, and one point of the beam is far from the center of the point. It will affect the neighbors. By utilizing this characteristic,
The periphery of the pixel of interest should be drawn as a visible line image above the threshold, and conversely not drawn below the threshold, based on the sum of the exposures, that is, the sum of all the overlapping lights. Accordingly, it is possible to obtain an image which is hardly affected by the surrounding environment by means for detecting the surrounding environment and which has a higher resolution than a normal resolution.

Next, as shown in FIG. 11, the electrostatic curvature of the toner is generally not a straight line, and the toner density with respect to the exposure amount shows a characteristic in which it is difficult to extract an intermediate density. FIG. 11 is a characteristic diagram showing a relationship between the exposure amount and the toner density level.

Next, an image forming apparatus according to the present invention will be described with reference to FIGS. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention, FIG. 2 is an explanatory diagram showing a configuration example of a threshold matrix in FIG. 1, FIG. 3 is a diagram showing an example of an input characteristic of image density, and FIG. FIG. 13 is a characteristic diagram illustrating a state where a toner density value with respect to an image signal input level in the image forming apparatus of FIG. 3 changes depending on environmental conditions of temperature and humidity.
Since the overall flow of the image forming apparatus is the same as that of the conventional image forming apparatus shown in FIG. 5, the description is omitted, and the same parts are denoted by the same reference numerals.

As shown in FIG. 1, R in the signal processing unit 201
A / D input terminal of OM (read only memory) 501
The converted 8-bit color images are R (red),
It is input as G (green) and B (blue) signals.
The ROM 501 performs a process of converting the R, G, and B signals that are luminance signals into Y (yellow), M (magenta), C (cyan), and K (black) signals that are density signals. In order to perform this conversion processing, the input signals 00 (HEX) to FF (HE) are calculated using the coefficients expressed by the following equations (1) to (3).
The data corresponding to X) is output from an unshown LUT (look-up table).

Y = −log (aB) (1) M = −log (aB) (2) C = −log (aB) (3) where a is a coefficient.

The Y, M, C,
Each 8-bit data of the K signal is input to a UCR (under color removal) circuit 503 via a selector 502. This U
In the CR circuit 503, a Min (minimum value) detection circuit 504
The Y, M, C, and K signals are subjected to a masking process by a known under color removal using the
It is sequentially output as 8 bits of VDO7 to / VDO0. The Y, M, C, and K signals output in this manner are input to the pseudo halftone processing unit 202.

Next, the pseudo halftone processing section 20 according to the present invention
2 will be described. In FIG. 1, reference numeral 510 denotes an image memory for temporarily storing input image data.
This image memory 510 can also store pixels around the pixel of interest. Here, by reading the image data from the image memory 510 at twice the normal clock rate, it is possible to provide a region overlapping both ends of the target pixel. Here, since the pixels at both ends of the target pixel overlap according to the density level, image data is added in the same manner as adding energy leaked from the target pixel. This is shown in FIG. FIG. 12 is a characteristic diagram showing the relationship between the laser lighting time and the light intensity. The image density of the overlapping area adjacent to the target pixel is caused by the image density of the target pixel. That is, when the density level of the pixel of interest is high, the image density of the adjacent overlapping area is also high. Conversely, when the density level of the pixel of interest is low, the image density of the adjacent overlapping area is low.

Next, 512 is a threshold matrix 512
a threshold memory for storing the threshold defined by a and b. Reference numeral 513 denotes a Γ table for obtaining the actual pixel modulation intensity from the comparison result obtained for each pixel. The temperature / humidity sensor 515 is a sensor provided inside the image forming apparatus, detects the ambient temperature and the ambient humidity inside the image forming apparatus, and sends the detected signal X to the control unit 520. The control unit 520 is provided with a gradation expression number changing unit 521, and changes the allocation method of the gradation expression number of the threshold value per pixel in the threshold value memory 512 according to the detection value of the temperature / humidity sensor 515. To generate a selection signal A. By transmitting the generated selection signal A to the threshold value memory 512, the way of assigning the number of gradation representations per pixel in the threshold value matrix is changed.

In this embodiment, a plurality of (two) threshold matrices 512a and 512b (see FIG. 2 to be described later) having different ways of allocating the number of gradations of threshold values per pixel are prepared. 512a, 5
By selecting 12b based on the selection signal A,
It is possible to change the way of assigning the number of threshold gradations per pixel. The method of changing the allocation of the number of gradation representations will be described later. 514
Is a counter for counting the number H of processed pixels in the horizontal direction and the number V in the vertical direction. When the count values (H, V) of the counter 514 are input to the threshold memory 512, the threshold matrices 512a, 512 corresponding to the respective pixels are obtained.
The threshold value in b is selected.

In the initial state, the value of the counter 514 is (H,
V) = (0, 0), the size of the threshold matrices 512a, 512b is set to M × N (M, N in the horizontal direction and the vertical direction, respectively), and the gradation expression of the threshold value per pixel is performed. Assuming that the number is P, P types of thresholds corresponding to the address (0, 0) are loaded from the threshold memory 512 into the comparison processing unit 511. P comparators 230 (see FIG. 7) are arranged in parallel in the comparison processing unit 511, and the different P thresholds are input as their reference values.

FIG. 2 is an explanatory diagram showing an example of the configuration of the threshold value matrix shown in FIG. In FIG. 2, a typical fatning (concentration) in which the size of a threshold matrix is 4 × 4 (M × N) and the number of gradation representations of thresholds per pixel in each threshold matrix is 16 levels (P) 5 shows a threshold matrix 512a of a type and a threshold matrix 512b of a Bayer (dispersion) type. The numerical values in each of the threshold matrices 512a and 512b indicate the density level of the threshold corresponding to one pixel.

These threshold matrices 512a, 512
The input characteristic of the image density changes depending on the method of allocating the number of expressed gradations of one pixel in b. FIG. 3 shows an example of the input characteristic of the image density. In FIG. 3, it can be seen that the output level of the image density differs between the input characteristic A and the input characteristic B of the image density depending on the position of the input value. In general, since an image forming apparatus causes toner to fly onto a photosensitive drum by an electrostatic recording method, the toner is easily affected by temperature and humidity, and is particularly remarkable in a color image forming apparatus.

FIG. 4 is a characteristic diagram showing a state in which the value of the toner density with respect to the input level of the image signal in the image forming apparatus of FIG. 1 changes depending on the environmental conditions of temperature and humidity.
As is apparent from FIG. 4, in general, the toner density level tends to increase in a low-temperature and low-humidity environment compared to a normal-temperature and normal-humidity environment, and to decrease in a high-temperature and high-humidity environment. It is in. Therefore, in this embodiment, a temperature / humidity sensor 515 for detecting temperature and humidity is provided in the image forming apparatus to detect temperature / humidity, and the threshold value per pixel of the threshold matrixes 512a and 512b is determined in accordance with the detection result. Is controlled so as to change the allocation type of the expression gradation number. This control is executed by a gradation expression number changing unit 521 (control program stored in a storage unit such as a ROM) in the control unit 520. That is, the temperature and humidity sensor 5
When the signal X detected by the control unit 15 is input to the control unit 520, the gradation expression number changing unit 521 grasps the environmental condition in the image forming apparatus. When the environmental condition is low temperature and low humidity, the toner density is high from FIG. 4, so it is necessary to make adjustment so that the toner density is set low. Therefore, the control unit 5
Reference numeral 20 denotes a Bayer-type threshold matrix 51 shown in FIG.
A selection signal A for selecting 2b is generated.

On the other hand, when the environmental conditions in the image forming apparatus are high temperature,
In the case of high humidity, since the toner density is low from FIG. 4, it is necessary to make adjustment so that the toner density is set high. Therefore, the control unit 520 selects a selection signal A that selects the fatning type threshold matrix 512a in FIG.
Generate By inputting the selection signal A thus generated in the control unit 520 to the threshold memory 512, the threshold matrix 512a or 512b is selected. For example, when the threshold matrix 512a is selected, the threshold of the address corresponding to (H, V) of the counter 514 is sent to the comparison processing unit 511. At this time, assuming that the number of gradations of the threshold value per pixel in the threshold value matrix 512a is 16 levels, the 16 threshold values are input to the 16 comparators 230 in the comparison processing unit 511.
As a result, in the comparison processing unit 511, the comparison processing between the input image signal and the threshold is performed in parallel by the 16 comparators 230.

Here, when the image signal as the input value is larger than the threshold value, if the comparator 230 is set to output True, the output Tr
The numerical value of ue is input to the $ table 513. The pseudo halftone image 223 representing the n-bit pixel output from the Γ table 513 is output from the laser driver 203.
Is input to The pseudo halftone image 223 obtained in this manner is configured not to be affected by environmental changes, that is, the temperature and humidity of the image forming apparatus.

As described above, according to the present invention, the input image information is subjected to predetermined signal processing in the image processing unit 202 to form a halftone image having a converted image density level. By providing a superimposition area at both ends of the pixel of interest by reading out with a faster clock, that is, providing a superimposition area other than the standard line image position, and creating a line image according to the level, higher resolution is achieved. An image can be formed on the photosensitive zone. Then, one pixel of a threshold matrix having a threshold corresponding to each pixel of the image information in the image processing according to each detection result of the environmental state detecting means for detecting the environmental state of the apparatus body and the means for detecting the image density information A gradation expression number changing step of changing the method of assigning the number of gradation expressions per threshold, and overlapping the original standard line image position and the position (between lines), and the line image according to the signal level By forming an image using the line image expression process for producing the image, it is possible to prevent a change in environment such as temperature and humidity and to obtain a more stable image.

(Second Embodiment) Next, the first embodiment will be described.
A method different from that of the embodiment will be described with reference to FIG.
The description of the same parts as in the first embodiment is omitted.

As an environmental state detecting means, a toner sensor 5
By preparing 30, the photosensitive drum 209 is exposed to light, toner is adhered, and its density is detected by, for example, a photosensor to detect the reflectance. Then, the way of allocating the threshold value matrix is controlled by the detected value in the same manner as in the first embodiment.

Although the laser beam printer has been described as an example of the image forming apparatus of the present invention, the present invention is not limited to this, and the present invention can be applied to an electrostatic line image system such as a copying machine or a facsimile. Further, the temperature / humidity sensor and the toner concentration detection sensor are used as the environmental state detecting means, but the same applies when these are used together. In other words, the main purpose is to be able to form a more stable and optimized image by detecting the surrounding environment.

[0037]

As described above, according to the present invention, the gradation of the threshold value per pixel of the threshold value matrix for detecting the environmental state in the image forming apparatus and comparing the image data in accordance with the detection result. By optimizing the pixel density by changing the method of assigning the number of expressions, it is possible to form a stable halftone image that is not affected by the environmental conditions of the device, and it is possible to obtain an image forming device whose resolution has been converted.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a configuration example of a threshold matrix of FIG. 1;

FIG. 3 is a diagram illustrating an example of an input characteristic of an image density.

FIG. 4 is a characteristic diagram illustrating a state in which a toner density value with respect to an input level of an image signal in the image forming apparatus in FIG. 1 changes depending on environmental conditions of temperature and humidity.

FIG. 5 is a schematic configuration diagram of a laser beam printer as a conventional image forming apparatus.

6 is an explanatory diagram showing a process of producing a pseudo halftone image in a pseudo halftone processing unit 202 shown in FIG. 5;

FIG. 7 is a block diagram of a comparator that performs a comparison process between the digitized original image and the threshold matrix shown in FIG. 6;

8 is an explanatory diagram of a printing process in the image forming apparatus shown in FIG.

9 is a cross-sectional view illustrating a configuration of a developing unit in FIG.

FIG. 10 is a characteristic diagram showing a relationship between laser lighting time and light intensity.

FIG. 11 is a characteristic diagram illustrating a relationship between an exposure amount and a toner density level.

FIG. 12 is a characteristic diagram showing a relationship between laser lighting time and light intensity.

[Explanation of symbols]

 Reference Signs List 201 signal processing section 202 pseudo halftone processing section 203 laser driver 205 semiconductor laser 209 photosensitive drum 511 comparison processing section 512 threshold memory 512a, 512b threshold matrix 515 temperature and humidity sensor 520 control section 521 gradation expression number changing means 530 toner density detection sensor

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Claims (4)

[Claims] 1. An image forming apparatus having image processing means for performing predetermined image processing on input image data, wherein: an environmental state detecting means for detecting an environmental state in the image forming apparatus; Control means for optimizing pixel density by changing a method of allocating the number of gradation representations of threshold values per pixel of a threshold matrix for comparing the image data in accordance with the detection result of Forming equipment. 2. The image processing apparatus according to claim 1, wherein the image processing unit includes a pseudo halftone processing unit that converts the image into a high resolution by forming an area where a threshold value of a line different from an original display position is overlapped. An image forming apparatus according to claim 1. 3. An image forming apparatus according to claim 1, wherein said environmental condition detecting means is a temperature and humidity sensor for detecting an ambient temperature and humidity of the image forming apparatus main body. 4. An image forming apparatus according to claim 1, wherein said environmental condition detecting means is a toner density detecting sensor for detecting a rate at which toner according to an electrostatic latent image flies to a photosensitive zone. .