JP2003246093A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus in which the capacity of correction data, the installation cost of a memory, and the area (space) of a memory being mounted can be reduced. <P>SOLUTION: Capacity of correction data is reduced by lowering the correction accuracy preferentially from correction data corresponding to an LED element at the end part of an LED head inconspicuous to the user's eyes as compared with the central part of an LED head conspicuous to the user's eyes. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to copying, faxing,
Further, the present invention relates to an image forming apparatus such as a printer, and particularly to an image forming apparatus including an LED head as an exposure device.

[0002]

2. Description of the Related Art Conventionally, there is an image forming apparatus using electrophotography, which has an LED head as an exposure device for exposing a photosensitive member. The LED head is formed by arranging a plurality of LED elements. When printing is performed using this LED head, even if a constant current is applied by a constant current circuit when the LED element is turned on, The light amount varies among the LED elements. It has been confirmed that this phenomenon becomes particularly noticeable in a region coated with a uniform density and a line darker than the surroundings (or a line thinner than the surroundings) appears on the image.

In order to solve this phenomenon, LE has been conventionally used.
There is a method of correcting the current value that flows when each D element is turned on, in which a slightly larger current is supplied to an LED element having a smaller amount of light than the average, and conversely a slightly smaller current is supplied to an LED element having a larger amount of light than the average. There was a method of correcting the light amount by flowing it.

[0004]

However, if the conventional light amount correction method is adopted, it is necessary to hold, as information, the current value or the increase / decrease value of the current value that flows when each LED element is turned on. Hereinafter, this information will be referred to as correction data.

Here, the capacity of this correction data will be considered. For example, resolution of 600 dpi on A4 horizontal size paper
Considering that printing is performed with, if the correction data is 8 bits, approximately 5 kbytes are required. Considering the case of color, it is considered that four LED heads are used, and about 20 kbyte (5 kbyte × 4) is required. It depends on the accuracy and resolution to correct the light quantity,
It can be said that a memory is indispensable for holding the correction data, but there is a problem that the cost rises in proportion to the capacity to hold and the place where the memory is mounted also increases in proportion to the capacity.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a plurality of LED elements are formed as a means for exposing a photoconductor in a direction orthogonal to the moving direction of the photoconductor. In the image forming apparatus including the LED head, the LED head corrects the light emission variation of each LED element from the correction accuracy corresponding to the end LED element to the correction accuracy corresponding to the central LED element. Also, the image forming apparatus is preferentially lowered. Alternatively,
In an image forming apparatus including an LED head formed by forming a plurality of LED elements as a means for exposing a photoconductor in a direction orthogonal to the moving direction of the photoconductor, the LED head corrects light emission variation of each LED element. In this case, the image forming apparatus lowers the correction accuracy corresponding to the LED element that emits light in the center of the black pixel aggregate of the print data, in preference to the correction accuracy corresponding to the LED element that emits light other than the center. is there.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a part of an image forming apparatus using electrophotography such as copying, FAX, or printer. The image forming apparatus of the present invention includes at least CPU 1, ROM 2, RAM 3, ASIC 4,
The exposure apparatus 6 is configured.

The ROM 2 stores compressed correction data and C
The operation program and the like of PU1 are stored. RAM3
Is provided for the work area and temporarily stores print data. The CPU 1 controls the entire image forming apparatus and performs image processing of print data received from the external information processing apparatus 5 such as a personal computer. In addition, an ASIC 4 is provided to assist image processing and to communicate with the external information processing device 5.

In the image forming apparatus of the present invention, it is effective to compress the correction data and reduce the volume of the correction data to be held as described later. As a concrete compression method,
The correction data compressed by the external information processing device 5 may be transmitted to the image forming device. The correction data compressed by the external information processing device 5 is stored in the ROM 2, expanded at an appropriate time such as when the power switch of the image forming device is turned on, and stored in the RAM 3, and the exposure device 6 such as an LED head during image formation. Should be sent to.

The present invention is characterized in that the amount of correction data is reduced even before the correction data is compressed as described above. First, the first invention of the present invention will be described. The image forming apparatus prints on a medium such as paper, but there are LED elements located at both ends of the LED head that are located outside the printing area. Further, the LED elements located at both ends have less chance of emitting light as compared with the central portion. Therefore, the correction data for the LED elements located at N (N = 0, 1, 2, ...) Dots at both ends of the LED head are given priority over the correction data for the LED elements located at the central portion. As a result, the main correction data can be improved. In addition, it is possible to intentionally cost the main person (central portion) accordingly.

First, as a concrete method which can be simply considered, Lbit (L = 0,
(1, 2, ...) Holds the correction data, and the LED head end has a digit dropped kbit (k = 0, 1,
2, ... And k <L) is held.

As a further conceivable concrete method, as shown in the flow chart of FIG. 2, first, the frequency distribution table A and LE for the correction data of the end portion of the LED head are targeted.
Frequency distribution table B for the correction data at the center of the D head
Is created (steps 1 and 2). Next, the frequency distribution table C is created for the correction data that exists in the frequency distribution table A but does not exist in the frequency distribution table B (step 3), and whether it exists in the frequency distribution table B or in both the frequency distribution tables A and B. A frequency distribution table D is created for existing correction data (step 4). next,
The number of pieces of correction data having a frequency of 1 or more included in the frequency distribution tables C and D is obtained without duplication of the frequency distribution tables C and D (step 5).

Then, it is judged whether or not the number of correction data having a frequency of 1 or more is less than or equal to a preset target value I (step 6), and if less than I, the data to be compressed by the LZ compression method or the like. The correction data is compressed by a compression method that employs an algorithm in which the compression rate increases as the number of types decreases (step 10). If it is larger than I, it is judged whether or not the correction data having the frequency of 1 or more exists in the frequency distribution table C (step 7). If it exists, the correction data having the smallest frequency in the frequency distribution table C is determined. Of the frequency distribution tables C and D, the correction data having a frequency of 1 or more closest to the correction data is converted (step 8). If it does not exist, the correction data having the smallest frequency in the frequency distribution table D is converted into the correction data having a frequency of 1 or more, which is the closest to the correction data in the frequency distribution table D (step 9). The concrete conversion method in steps 8 and 9 is as shown in FIG.

When the conversion in step 8 or step 9 is completed, the process returns to step 5, and the number of correction data of frequency 1 or more contained in the frequency distribution tables C and D is the preset target value I.
The same process is repeated until the following.

With such a method, the correction data of the LED element located at the end of the LED head can be given priority over the correction data of the LED element located at the center to reduce the accuracy and reduce the volume of the correction data. It becomes possible to reduce the capacity by further compressing the correction data. The boundary between the end portion and the central portion may be appropriately changed according to the width of the fed paper, or may be determined from the capacity to be reduced.

Next, the second invention of the present invention will be described. Generally, in an image forming apparatus, a halftone expression method represented by an organized dither method is often used. When the systematic dither method is used, the pixel pattern is repeated at a specific cycle. For example, when a J × J size (J is a natural number) dither matrix of a dot set type generally called a screw type is used, a set of black pixels (0 or more) is generated in a J pixel cycle. In this case, since the central pixel of the black pixel aggregate existing in the J pixel cycle has a higher possibility that a plurality of dots will be gathered than the pixels at other positions, the exposure, development and fixing are more stable than the isolated black pixel. Is likely to be carried out.

In the second aspect of the invention, attention is focused on that point, and the compression ratio of the correction data is improved by preferentially reducing the accuracy of the correction data for the pixel at the center of the black pixel aggregate. . First, a concrete method that can be simply considered is to drop the digit for the LED element related to the pixel that is the center of the black pixel group, and set Mbit (M = 0, 1, 2,
...) correction data is held, and the LED elements related to the other pixels are kept in the same digit and Pbit (P =
This is a method of holding correction data of 0, 1, 2, ..., And M <P).

A concrete method that can be considered next is a frequency distribution table A for the correction data of the LED element for the pixel at the center of the black pixel group and LE for the other pixels.
This is a method of creating a frequency distribution table B for the correction data of the D element, and reducing and compressing the correction data as in the flow chart of FIG.

With such a method, the correction data of the pixel at the center of the black pixel aggregate is given priority to reduce the accuracy, and the volume of the correction data can be reduced. Further, the volume of the correction data can be further compressed to reduce the volume. It becomes possible to do.

[0020]

As described above, according to the image forming apparatus of the present invention, the correction accuracy corresponding to the LED element at the end portion is lowered prior to the correction accuracy corresponding to the LED element at the central portion. Alternatively, by lowering the correction accuracy corresponding to the LED element that emits light in the center of the black pixel aggregate of the print data, over the correction accuracy corresponding to the LED element that emits light other than the center, the capacity of the correction data is reduced. Therefore, it is possible to provide an image forming apparatus which can reduce the cost for installing the memory and also have a small area (space) of the mounted memory.

[Brief description of drawings]

FIG. 1 is a block diagram showing an image forming apparatus of the present invention.

FIG. 2 is a flowchart showing the operation of the image forming apparatus of the present invention.

FIG. 3 is a diagram showing a partial operation of the image forming apparatus of the present invention.

[Explanation of symbols]

1: CPU 2: ROM 3: RAM 4: ASIC 5: External information processing device 6: Exposure device

Claims (4)

[Claims] 1. An image forming apparatus comprising an LED head, which comprises a plurality of LED elements as means for exposing a photoconductor in a direction orthogonal to a moving direction of the photoconductor, wherein each LED element comprises an LED element. The image forming apparatus is characterized in that the correction accuracy corresponding to the LED element at the end portion is lower than the correction accuracy corresponding to the LED element at the central portion when correcting the variation in the light emission. 2. An image forming apparatus provided with an LED head, which comprises a plurality of LED elements formed as a means for exposing a photoconductor in a direction orthogonal to a moving direction of the photoconductor, wherein each LED element comprises an LED element. When correcting the variation in the light emission of, the correction accuracy corresponding to the LED element that emits light at the center of the black pixel aggregate of the print data should be lowered in preference to the correction accuracy corresponding to the LED element that emits light other than the center. A characteristic image forming apparatus. 3. The data for correcting the light emission variation of the LED head is compressed and stored.
Alternatively, the image forming apparatus described in 2. 4. The image forming apparatus according to claim 1, wherein data representing a value of a current flowing through the LED element or data indicating a degree of adjusting a light emission time is compressed and stored.