JPH0930038A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain resolving power and gradation properties while keeping desired image density by binarizing read image data from different threshold values to divide the image data of one line into a plurality of line data and differentiating the lighting times of respective LEDs. SOLUTION: Image data LD is binarized on the basis of TH1 being a first threshold value to obtain first line data LD1 expressing the image data LD as the largest main dot (S3) and subsequently binarized on the basis of TH2 being a second threshold value to obtain second line data LD2 expressing the image data LD as a next large first sub-dot (S4). In the same way, the image data LD is binarized to obtain third line data LD3 (S5). The formed first line data LD1 is transmitted to an LED array (S8) and the surface of a photosensitive member is exposed for an exposure time for forming the main dot (S9). Subsequently, second and third line data LD2a, LD3a are transmitted to the LED array (S10, S12) to be exposed for an exposure time forming the sub-dot at the position between them (S11, S13).

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 such as a copying machine or a printer which outputs line data subjected to digital image processing by means of an LED array, and particularly, the image data read by an image sensor is set to a plurality of threshold values. The present invention relates to an image forming apparatus that converts a plurality of line data based on the line data, and turns on an LED for an exposure time corresponding to each line data to form an image.

[0002]

2. Description of the Related Art There is known an image forming apparatus which digitizes image data read by an image sensor or the like and exposes it as an optical information to an image forming portion by an LED array as an exposing means to form an image. In such an image forming apparatus, a document is conveyed at a constant speed in the sub-scanning direction, and the reading pixels arranged in a row in the width direction of the document in the image sensor as the main scanning direction are arranged from the front end to the rear end in the width direction of the document. Are sequentially scanned to read line data for each scanning line. When digitizing this image data,
Normally, there is one threshold value which is separated into a white area and a black area, and an image to be output is temporarily stored in the memory, and line data for one line is stored in this memory. Then, when all the line data for one line is stored in the memory of the exposure means, this light information is exposed from the LED array toward the image forming section at once. During this time, the image sensor reads the next line data, stores this line data in the memory, and stores the line data in the memory of the exposure means after the previous line data is exposed from the LED array.

[Problems to be Solved by the Invention]

When the read image data is digitized, the above-mentioned image forming apparatus binarizes it by separating it into a black area and a white area by a single threshold value TH set as shown in FIG. In order to obtain a desired image density, the operator appropriately adjusts the threshold value and the set value of the developing bias of the developing device using the operation panel or the like. However, these methods cannot form a halftone image. For example, in the case of a document that gradually changes from a dark image to a light image as shown in FIG.
It is not possible to represent a medium density region, so-called halftone, with only one threshold value. By setting the threshold value so that it is good for light images, it is possible to maintain good image density for light images, but for dark images, the thin lines are rendered thick and the background It has a bad influence on the resolution, such as picking up the object and expressing an unnecessary image. Further, if the threshold value is set so that the dark image becomes good, the fine line can be faithfully reproduced for the dark image, but the image becomes thin for the light image. Alternatively, if the developing bias is set high to increase the image density and the potential difference during image formation is increased more than necessary, in the two-component developer, not only the toner adheres to the image carrier but also the carrier adheres. Will end up.

On the other hand, in the image forming apparatus using the LED array, since the line data for one line is output at the same time, it is not possible to output by changing the dot diameter for each dot. Therefore, the exposure times of all the LED lines are adjusted in a unified manner so that the desired image density is set on the entire surface of the image.

As described above, in the LED array, all the exposure times are the same for each dot. Therefore, if the exposure time of the LED is increased by setting the image density to be high, the diameter of each dot becomes large on the image carrier. Expressed, for example, in a solid area, the toner can be adsorbed on the image carrier at a high density to obtain a good final image. But,
In the area of the thin line or rectangular ladder pattern, the original image cannot be faithfully reproduced, and the thin line is expressed thickly or is not expressed as a ladder pattern, resulting in poor resolution and gradation. A so-called image crushing phenomenon occurs. In addition, the longer exposure time shortens the life of the LED array.

Further, when the image density is set to be low and the exposure time of the LED is shortened, the diameter of each dot is expressed small, and an image with good gradation can be obtained in the area of fine lines or ladder patterns. However, in the solid region, the toner is not adsorbed on the image carrier at a high density, the image density becomes low, and uneven density occurs.

Although the image density is controlled by changing the exposure time of the LED as described above, it becomes difficult to set suitable conditions in the image quality such as image resolution, gradation and uneven density. There is.

The present invention solves the above problems by
Image data for a line is binarized with different thresholds to create a plurality of line data, and by exposing with LED exposure time according to each line data, the original image or image is maintained while maintaining a desired image density. (EN) Provided is an image forming apparatus having resolution and gradation which are not inferior to those of data and capable of expressing a large difference in grayscale of print.

[0009]

The present invention has been made in view of the above problems, and binarizes image data read by an image reading unit to convert the image data into line data for each line, and the line data is converted into LED data. In an image forming apparatus that sequentially outputs to a photoconductor by an array to form an image, the image data of one line is divided into a plurality of line data by binarizing the image data with different thresholds. The lighting time of each LED for a plurality of divided line data is made different.

Further, the main dot which is the maximum dot is converted into the first line data based on the first threshold value in the image data, and the main dot is converted into the main line based on the second threshold value in an area other than the area where the main dot is formed. The first sub-dot, which is the next size after the dot, is converted as the second line data, and the first sub-dot is formed based on the third threshold value in the area other than the area where the main dot and the first sub-dot are formed. Two smaller sub-lines are converted between the smaller second sub-dots as the third line data to output the first line data, and two sub-lines between the N + 1 line which outputs the first line data in the next line. Is provided, and exposure is sequentially performed according to the lighting time of the LED corresponding to the first line data, the second line data, and the third line data. The features.

Further, the exposure time of the LED is shortened in the order of the first line data, the second line data, and the third line data.

[0012]

With this structure, each line data in the main scanning direction of the original image is sequentially read by the image sensor. The read image data for one line is the first
The first line data is converted to the first line data on the basis of the threshold value, and the first line data is output to the surface of the photoconductor at the lighting time of the LED set to be the main dot. Then, in an area other than the area where the main dots are formed, the LED is set to be converted into the second line data based on the second threshold value and set as the first sub-dot of the size next to the main dot. Second line data is output on the first sub-line obtained by dividing the N line and the N + 1 line into three on the surface of the photoconductor in time. Furthermore, it is converted into the third line data based on the third threshold value, and the second line having the second largest size after the first sub-dot is converted.
The third line data is output on the second sub-line on the surface of the photoconductor at the lighting time of the LED set to be the sub-dot. In this way, by changing the dot diameter of the line data for each line to form an image, the difference between the print density of black and white, that is, the gradation expression is improved, and the thin line is expressed as a thin line and a smooth image quality is obtained. Let it be expressed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing an example of the basic configuration of an image forming apparatus in which the present invention is preferably used. The image forming apparatus 1 mainly includes a scanner unit 2 and a printer unit 5, and the printer unit 5 includes a printer control unit 6 and
It has an LED exposure control section 7 and an image forming section 13 including an LED array 9. The scanner unit 2 is provided with a conveyance unit 14 including a motor 8 for inserting the document 12 into the document insertion port 11 and conveying the document 12 at a constant speed, and a document image is digitally displayed at an appropriate position on the conveyance path of the document 12. CCD to read
An image sensor 4 such as a (charge coupled device) or CIS (sequential storage type) sensor is provided. Further, the scanner unit 2 is provided with a reading control unit, performs image processing on the image data read from the image sensor 4 by an error diffusion method, a dither method, or the like, and outputs the image-processed image signal to the LED exposure control unit. I am sending to 7.

When an operator inputs an operation panel (not shown) provided in the printer unit 5 for outputting a desired image, the printer control unit 6 operates the scanner unit 2, the LED exposure control unit 7, based on the input data. The image forming unit 13 is controlled to operate.

The image forming section 13 includes a photosensitive drum 10 rotating at a predetermined rotation speed, a charging corona discharger 15 arranged so as to sequentially act around the photosensitive drum 10, and an LED.
Array 9, developing device 16, transfer corona discharger 17, separation corona discharger 18, cleaner 19, eraser lamp 2
0, and also has a roll paper feeding device 21 for guiding the transfer material to the photosensitive drum, and a fixing device 22 for fixing the transfer material in the form of a visible image. Charged corona discharger 15
The exposure light is imaged on the surface of the photosensitive drum 10 which is uniformly charged in advance, and the image data sent from the LED exposure controller 7 is formed into an electrostatic latent image by the LED array 9. The developing device 16 causes the developing device 16 to adsorb toner to the surface of the photosensitive drum 10 to form a toner image. on the other hand,
The transfer material is guided from the roll paper feeding device 21 so as to contact the surface of the photosensitive drum 10 in synchronization with the peripheral speed of the photosensitive drum 10, and the toner image formed on the photosensitive drum 10 is transferred onto the transfer material by a corona discharge. It is transferred by the action of the electric device 17. Next, the transfer material is separated from the surface of the photosensitive drum 10 by the separation corona discharger 18. The separated transfer material is a guide means 23.
Is conveyed to the fixing device 22, fixed as a permanent image, and discharged to the outside. The toner remaining on the surface of the photosensitive drum 10 after transfer is removed by the cleaner 19, and the surface of the photosensitive drum 10 is gradually charged by the eraser lamp 20 to prepare for the next image formation.

The LED exposure controller 7 will be described in detail with reference to FIG. FIG. 2 shows a flowchart of image data in the above-mentioned image forming apparatus. In step 1, image data LD for one line read by the image reading unit is stored. In the next step 2, this image data is digitally image-processed so as to be an image having gradation, based on threshold values TH1, TH2, TH3 described later.

The thresholds TH1, TH2 and TH3 are used to set which part of the image data is to be black and white as shown in FIG. Although these threshold values are set in advance, they may be adjusted by the operator before the image formation.
Further, the threshold value may be automatically adjusted according to the density of the document. FIG. 3 shows the image density on the vertical axis and the image data LD for one line on the horizontal axis.
H1 represents the threshold value of the main dot that forms the largest dot, TH2 represents the threshold value of the first sub-dot that forms the next largest dot after the main dot, and TH3 represents the second threshold that forms the smallest dot. The threshold value of subdots is shown.

Image processing in the above-mentioned image data LD will be described with reference to the flowchart of FIG. First, in step 3, the first image data LD is represented by the largest main dot based on the first threshold TH1.
Are binarized to the line data LD1. In step 4, the image data LD is calculated based on the second threshold value TH2.
2 is binarized into the second line data LD2 that expresses the second largest sub-dot. In step 5, the image data LD is binarized into the third line data LD3 which is represented by the smallest second sub-dot based on the third threshold value TH3.

The first line data LD1 is the direct LED
The second line data L is sent to the array for exposure.
D2 is the first line data LD in step 6.
The area determined to be black in 1 is removed, and the second line data LD2a is created. Also, the third line data L
D3 is the second line data LD in step 7.
The area determined to be black in 2 is removed, and the third line data LD3a is created.

The created first line data LD1 is
In step 8, it is transferred to the LED array, and in step 9, the surface of the photoconductor is exposed for the exposure time for forming the main dots. Next, the second line data LD2a is transferred to the LED array in step 10, and the second line data LD2a is located between the line in which the main dot is formed in step 11 and the line formed by the next main dot. Then, the surface of the photoconductor is exposed for the exposure time for forming the first subdot. Then, in step 12, the third line data LD3a is transferred to the LED array, and in step 13, the third line data LD3a.
The surface of the photoconductor is exposed for the exposure time for forming the second subdot based on a. The image shown in FIG. 5 is obtained by the steps described above. In FIG. 5, the second line data and the third line data are output in the vicinity of the first line data, but this position is not limited and, for example, 3
The positions may be equally divided.

The above-mentioned steps are repeated for the next image data to perform image processing for exposure, and the process is repeated until the image ends. After the latent image is formed on the surface of the photoconductor in this way, the image is formed on the transfer material by the well-known developing method, transfer method, and fixing method, and then discharged to the outside of the apparatus.

Although the above-described image forming apparatus forms three types of dots using three types of threshold values, the number is not limited. Further, although the original 12 is read by the image sensor 4, for example, an output signal from the outside, such as image (raster) data from a computer, may be directly input to the LED exposure controller.

[0023]

As described above, according to the present invention, a plurality of line data are created by using a plurality of threshold values for the read image data, and the exposure time of the LED array is selected so that each has a desired dot diameter. By outputting the image and forming an image, an image having good gradation and resolution can be formed, a large difference in grayscale between prints can be expressed, and a smooth image quality can be expressed. Also, fine lines can be expressed well.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a flowchart of an image forming apparatus according to the present invention.

FIG. 3 is a diagram in which image data is binarized with one threshold value.

FIG. 4 is a diagram in which image data is binarized with three threshold values.

FIG. 5 is a diagram showing a state of an image output using the image forming apparatus according to the present invention.

[Explanation of symbols]

 1 Image Forming Apparatus 2 Scanner Section 3 Reading Control Section 4 Image Sensor 5 Printer Section 6 Printer Control Section 7 LED Exposure Control Section 8 Motor 9 LED Array 10 Photosensitive Drum 11 Original Insertion Port 12 Original 13 Image Forming Section 14 Conveying Means 15 Charging Corona Discharger 16 Developing device 17 Transfer corona discharger 18 Separation corona discharger 19 Cleaner 20 Eraser lamp 21 Roll paper feeding device 22 Fixing device 23 Guide means 24 Memory control section 25 First memory 26 Second memory 27 Comparison circuit 28 Third memory

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Fujiwara 4-21-3 Shimomaruko, Ota-ku, Tokyo Katsurakawa Electric Co., Ltd.

Claims (3)

[Claims] 1. An image in which image data read by an image reading unit is binarized and converted into line data for each line, and the line data is sequentially output to a photoconductor by an LED array to form an image. In the forming apparatus, the image data of one line is divided into a plurality of line data by binarizing the image data with different threshold values, and the lighting time of each LED for the divided plurality of line data is made different. An image forming apparatus characterized by the above. 2. A main dot, which is the largest dot, is converted into first line data based on a first threshold value in the image data, and a main dot is converted into a main line based on a second threshold value in an area other than the area where the main dot is formed. The first sub-dot, which is the next size after the dot, is converted as the second line data, and the first sub-dot is formed based on the third threshold value in the area other than the area where the main dot and the first sub-dot are formed. N which converts the smaller second sub-dots into the third line data and outputs the first line data N
Two sub-lines are provided between the line and the N + 1 line that outputs the first line data in the next line,
2. The image forming apparatus according to claim 1, wherein the exposure is sequentially performed according to the lighting time of the LED corresponding to the first line data, the second line data, and the third line data. 3. The image forming apparatus according to claim 1, wherein the exposure time of the LED is shortened in the order of the first line data, the second line data, and the third line data.