JPH0985984A - Image forming device and image formation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the quality of an image by eliminating the adverse effect of an unevenness in the luminous intensity of a light emitting element, in a device for forming an image using plural light emitting elements. SOLUTION: An image processing device 30 loads in the memory the multivalued data di of an image signal 40 from an external source, then reads a weight factor based on the data relative to the previously measured luminescent intensity of each of LEDs of an LED array, and multiplies the multivalued data di by the weight factor of each of the corresponding LEDs to perform the binary processing of data relative to the calculation result by an error dispersion method. Further, the two-valued signal obtained by this binary processing is connected to an LED driver 20, and the light emitted by each of the LEDs of the LED array is switched ON/OFF to form a latent image on a latent image carrier moving in an orthogonal direction with the LED array 10. In addition, the latent image is developed by a publicly known electrophotographic recording method, and then is transferred to a recording paper. Finally, the paper is thermally fixed and discharged.

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 an image forming method, and more particularly, to a copying apparatus, a printer, and a copying apparatus for forming / recording an image by an electrophotographic recording method using an exposure device including a light emitting element such as an LED array. The present invention relates to an image forming apparatus such as a facsimile machine and an image forming method.

[0002]

2. Description of the Related Art Conventionally, a digital recording type copying apparatus,
An exposure apparatus using a semiconductor laser optical system has been widely used in printers and the like.

However, in an exposure apparatus using a semiconductor laser, many members, such as a laser beam deflecting device and a coupling optical system, which are practically impossible to be further miniaturized, are used. There is a limit to miniaturization. In addition, there is a mechanical limit to the accuracy of polygon mirrors (rotating polygon mirrors) that are often used as deflectors and folding mirrors that are incorporated in optical systems.
In a strict sense, the laser beam is used as a latent image carrier (for example,
It is also known that it cannot be guided to an accurate position of the photosensitive drum. This is extremely disadvantageous as an exposure device for a high-speed printer or a color printer using a plurality of laser beams, for example.

For this reason, so-called solid-state light-emitting devices having no moving parts, such as LED heads in which a plurality of LEDs (light-emitting diodes) are arranged in a line, have been used as exposure apparatuses, especially in small printers. .

The LED head is generally composed of a plurality of Ls arranged in a straight line along the horizontal scanning direction as shown in FIG.
ED chip 101 and a plurality of Ls arranged in the vicinity thereof
Base 1 on which the ED driver chip 102 is mounted
03 and a selfoc lens array (trademark name of a kind of gradient index lens) 104 arranged at a predetermined position in front of the LED chip 101.

The individual LEDs in the LED chip 101 are
As shown in FIG. 6, they are arranged at a pixel density pitch.
Since the light emitted from these LEDs has the property of diffusing, the light emitted from the LEDs is used as a selfoc lens array 10
It is arranged so as to form an image on the latent image carrier through 4. The SELFOC lens array 104 is small in size, has uniformity in the axial direction, and forms an erecting equal-magnification real image.

[0007]

However, due to the nature of the semiconductor manufacturing process, it is practically possible to form the LED array on the LED head having exactly the same properties over the entire longitudinal direction. Can not. For this reason, particularly when an image is formed by the electrophotographic recording method, the variation in the exposure amount directly changes the image density. Therefore, the variation in the emission intensity of the LED array is an obstacle for improving the image quality of the recorded image. It was.

The present invention has been made in view of the above points, and an object thereof is an image forming apparatus and an image forming method for improving the image quality of a recorded image by eliminating the influence of unevenness of the emission intensity of the light emitting element. To provide.

[0009]

To achieve the above object, the apparatus of the present invention is an image forming apparatus for forming an image according to an input image signal using a plurality of light emitting elements arranged in the scanning direction. And an image processing unit that corrects the input image signal so as to eliminate the image unevenness of the output image caused by the unevenness of the light emission intensity, based on the measurement data of the light emission intensity of each of the light emitting elements.

As a form of the apparatus of the present invention, the image processing means includes a storage means for storing a weighting coefficient set according to measurement data of emission intensity of each of the light emitting elements, and the input image. An arithmetic means for multiplying the signal by the corresponding weighting factor can be provided.

In another form, the apparatus of the present invention is
The image processing means sets storage means for storing measurement data of emission intensity of each of the light emitting elements, and sets a weighting coefficient for eliminating image unevenness of an output image caused by uneven emission intensity according to the measurement data. It is possible to have a weighting factor setting means and a computing means for multiplying the input image signal by the corresponding weighting factor.

In another form, the device of the present invention is
The image processing means may include a binarization processing means for performing binarization processing by an error diffusion method on the data of the calculation result of the calculation means.

In another form, the device of the present invention is
When the input image signal is binary data, the image processing means divides the binary data into line data and gradation data before the arithmetic processing of the arithmetic means, and processes the line data. It can be characterized in that it further comprises a pre-processing means for performing the output directly as it is and for the gradation data to be pseudo-multi-valued once based on the binary data.

As another form of the apparatus of the present invention,
When the input image signal is binary data, the preprocessing means determines a low density portion of the gradation image from the input image signal, and a low density portion of the gradation image determined by the determination means. It can be characterized in that it has at least the pre-processing unit and the control unit that does not process the input image signal.

In order to achieve the above object, the method of the present invention is an image forming apparatus for forming an image according to an input image signal using a plurality of light emitting elements arranged in the scanning direction. A weighting factor setting step of setting a weighting factor for eliminating the image unevenness of the output image due to the emission intensity unevenness according to the measurement data of the emission intensity, and an operation of multiplying the input image signal by the corresponding weighting factor. It is characterized by including a step and a binarization processing step of performing a binarization processing by an error diffusion method on the data of the calculation result of the calculation step.

Further, as one form of the method of the present invention, when the input image signal is binary data, the binary data is converted into line data and gradation data prior to the arithmetic processing of the arithmetic step. It can be characterized by further including a preprocessing step of performing division, performing direct output of the line data without performing any processing, and performing grayscale data once on the basis of binary data.

In addition, the method of the present invention, in another form,
When the input image signal is binary data, the step of determining the low density portion of the gradation image from the input image signal and the input image signal of the low density portion of the gradation image determined in the determination step It can be characterized by having at least the pre-processing step and a control step in which the processing of the calculation step is not performed.

In the present invention, since the input image signal is corrected on the basis of the light emission intensity data of the light emitting element for exposure, it is possible to make the light emission unevenness of the light emitting element inconspicuous on the image. That is, in the present invention, since, for example, the error diffusion method is applied after multiplying the multivalued image signal from the outside by the weight of the light amount data of the light emitting element array, the pixel with a small exposure amount, that is, the same image data. In comparison with the actual data, more dots are arranged around the pixels where the density is lower than that of the actual data, so it is possible to increase the apparent density. On the other hand, since the dots are arranged around the pixel having the higher density than the actual data, the apparent density can be lowered. As a result, the image density unevenness caused by the unevenness of the emission intensity of the light emitting element can be much reduced as compared with the normal binarization process, and can be made almost inconspicuous on the recorded image.

Further, according to the present invention, the binary image signal from the outside is once subjected to the pseudo multi-value processing, and then the multi-value signal is multiplied by the weight of the light quantity data of the light emitting element array. Since the error diffusion method is applied, it is possible to reduce the image density unevenness in the high density portion of the gradation image as compared with the result output without performing the processing.

[0020]

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

(First Embodiment) FIG. 1 shows the configuration of a first embodiment of an image forming apparatus to which the present invention is applied. In FIG. 1, 10 is an LED array in which a plurality of LEDs as light emitting elements for exposure are arranged in a straight line, 20 is an LED driver for driving this LED array, and 30 is a signal obtained by binarizing and processing an input image signal 40. Is an image processing device that supplies the LED driver to the LED driver. In this example, the LED array 10 has a resolution of 600 dpi (dots / inch) for binary recording, for example. In addition, LED
The structure of the head itself is substantially the same as that of the conventional example shown in FIGS.

Reference numeral 50 denotes a memory in which each LED of the LED array 10 stores in advance a weighting coefficient corresponding to the emission intensity data of the LED. This weighting coefficient is a correction coefficient for eliminating image unevenness caused by the uneven emission intensity,
It is set based on the emission intensity data of the LED measured in advance, and is stored in an appropriate memory 50 such as an IC-ROM or a ROM card when the LED array (LED head) is shipped as a product, for example. The memory 50 is used by the image processing device 3
Of course, it may be built in 0.

The image processing device 30 receives an image signal 4 from the outside.
Enter 0. The data of the image signal 40 is a multi-valued signal. On the other hand, since the LED array 10 for binary recording is used as the output element, the image processing device 30 needs to perform the binarization process on the input image signal 40. Normally, the error diffusion method is used for binarization, but in this example, the error diffusion method is applied after the input image signal 40 is multiplied by the weight of the light amount data of the LED array.

That is, as shown in FIG. 2, the image processing device 3
At 0, the image signal 40 from the outside is input, and its multivalued data di (i is a natural number) is written to a buffer memory (not shown) (S1), and the weighting factor fj (j) based on the light emission intensity data of the LED array 10 is inputted. Is 1 to n: n is the same as the number of LEDs) from the memory 50 (S2), and then the multi-valued data di is multiplied by the weighting factor fj of the corresponding LED (LED to be emitted) ( S3),
Binarization processing by the error diffusion method is performed on the calculation result (S4).

The signal thus corrected and binarized is supplied to the LED driver 20. LE
The D driver 20 is an LED according to the input binary data.
By supplying a drive current to each LED of the array 10, the light emission of each LED is ON / OFF controlled, and the LED array 10
A latent image is formed on a latent image carrier (not shown) that rotates or moves in a certain direction at a right angle (or perpendicular) to. The latent image on the latent image carrier is developed with toner by a known electrophotographic recording system process, transferred to recording paper, and then the paper is thermally fixed and discharged to the outside. Since the process itself of the electrophotographic recording system is a well-known technique, its detailed description is omitted.

As described above, in this example, since the error diffusion method is applied after multiplying the multi-valued image signal 40 from the outside by the weight of the light amount data of the LED array, the pixel with a small exposure amount is used. That is, since more dots are arranged around the pixels whose density is lower than that of the same image data as compared with the actual data, the apparent density can be increased. In addition, since dots are arranged in the periphery of a pixel having a large amount of exposure, that is, a pixel having a high density with respect to the same image data, a smaller number of dots than the actual data, so that the apparent density can be lowered. As a result, the image density unevenness caused by the uneven light emission intensity of the light emitting element can be significantly reduced as compared with the normal binarization process, and can be made almost inconspicuous on the recorded image.

(Second Embodiment) FIG. 3 shows a configuration of a second embodiment of an image forming apparatus to which the present invention is applied. In this example, when a binary image signal 41 is given from the outside, the image processing device 31 processes the signal and outputs the binary signal to the LED driver 20. LED
The contents of the driver 20, the LED array 10 and the memory 51 are the same as those in the first embodiment shown in FIG.

FIG. 4 is a flowchart showing the algorithm of the processing method of the image processing apparatus 31 of this example.
In the image processing device 31, first, an image signal 41 from the outside is input, and its binary data Di (i is a natural number) is written into a buffer memory (not shown) (S11), and the binary data Di is converted into line data and floor data. It is divided into the key data (S12), and the line data is directly output without any processing (S13, S18). The gradation data is once pseudo-multi-valued based on the binary data (S14).

Subsequently, as in the case of the above-described first embodiment, the memory 50 stores the weighting factor fj (j is 1 to n: n is equal to the number of LEDs) based on the emission intensity data of the LED array 10. (S15), and then the LEDs corresponding to the pseudo multi-valued multi-valued data di
Multiply the weighting factor fj of (LED to be emitted) (S
16) Then, the operation result is binarized by the error diffusion method (S17). The signal processed in this way is supplied from the image processing device 31 to the LED driver 20.

The result of data conversion using the above algorithm of the present example and output can reduce the image density unevenness in the high density portion of the gradation image more than the result output without performing the processing. .

However, in the low density portion of the gradation image, the effect of pseudo-multi-valued image resulted in an increase in "feeling of roughness". Originally, in the low-density portion of the gradation image, the dot of the image is independent, so that the uneven light emission of the exposure element is not noticeable. Therefore, the input image signal 4
The low density portion of the gradation image is determined from 1 and the above-described image processing of FIG. 4 is not performed on the input image signal of the low density portion of the gradation image, and the binary data of the input image signal is unchanged. L
By controlling so as to supply to the ED driver 20, it was possible to solve the problem that the above-mentioned "feeling of roughness" increases.

(Other Embodiments) In the above embodiments, the case where the weighting factor fj based on the light emission intensity data of the LED array 10 is stored in the memory 50 has been described as an example.
The measured emission intensity data of the LED array 10 is stored in the memory 5
The weighting coefficient may be stored in 0 and the weighting coefficient may be set by calculation in the image processing device based on the emission intensity data, or the weighting coefficient may be obtained using a look-up table. Further, it goes without saying that the arithmetic processing of the above steps S3 and S16 can be replaced with a lookup table.

In the above-mentioned embodiments, the LED array is exemplified as the light emitting element, but the present invention is not limited to this, and a light emitting element having another structure such as one using an OFT (optical fiber tube) may be used. Good. Further, the present invention can be applied to a liquid crystal array using a liquid crystal shutter.

Although the error diffusion method is exemplified as the binarization processing in the above embodiment, the present invention can be applied to other binarization processing methods.

In the above-described embodiment, the weighting coefficient corresponding to the light emission intensity data of each LED of the LED array 10 is stored in advance, but if the light emission intensity characteristics are substantially uniform in LED chip units, for example. The weighting factor may be set based on the average light emission intensity of each LED chip.

In addition to the electrophotographic recording method, the present invention can be applied to, for example, a silver lead photographic recording method using an LED array.

[0037]

As described above, according to the present invention, since the input image signal is corrected on the basis of the light emission intensity data of the light emitting element for exposure, the unevenness of the light emission intensity of the light emitting element is displayed on the image. The effect that can be made inconspicuous with is obtained.

That is, according to the present invention, the multi-valued image signal from the outside is multiplied by the weight of the light amount data of the light emitting element array, and then the error diffusion method is applied. Dots are arranged around the pixels with low density for the same image data as compared with the actual data, so that the apparent density can be increased and the pixels with large exposure amount, that is, the same Since the dots are arranged around the pixels whose density is higher than the image data, the apparent density can be lowered, and as a result, normal binarization processing is performed. Moreover, it is possible to significantly reduce the image density unevenness caused by the uneven light emission intensity of the light emitting element, and to make the image almost inconspicuous on the recorded image.

Further, according to the present invention, the binary image signal from the outside is once subjected to the pseudo multi-value processing, and then the multi-value signal is multiplied by the weight of the light quantity data of the light emitting element array. Since the error diffusion method is applied, it is possible to reduce the image density unevenness in the high density portion of the gradation image as compared with the result output without performing the processing.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of an image forming apparatus to which the present invention has been applied.

FIG. 2 is a flowchart showing an image processing algorithm of the image processing apparatus of FIG.

FIG. 3 is a block diagram showing a configuration of a second embodiment of an image forming apparatus to which the present invention has been applied.

FIG. 4 is a flowchart showing an image processing algorithm of the image processing apparatus of FIG.

FIG. 5 is a perspective view showing a configuration example of a general LED head.

6 is an enlarged front view showing details of the LED chip of FIG. 5. FIG.

[Explanation of symbols]

 10 LED array 20 LED driver 30, 31 Image processing device 40 Multi-valued input image signal 41 Binary input image signal 50 Memory 101 LED chip 102 LED triver chip 103 Base 104 Selfoc lens array

Claims (9)

[Claims] 1. An image forming apparatus for forming an image according to an input image signal by using a plurality of light emitting elements arranged along a scanning direction, wherein the light emission is based on measurement data of light emission intensity of each light emitting element. An image forming apparatus comprising: an image processing unit that corrects the input image signal so as to eliminate image unevenness of an output image due to unevenness of intensity. 2. The image processing means multiplies the storage means for storing a weighting coefficient set according to the measurement data of the emission intensity of each light emitting element, and the input image signal by the corresponding weighting coefficient. The image forming apparatus according to claim 1, further comprising a computing unit that matches the image forming unit. 3. The image processing means stores the measurement data of the light emission intensity of each of the light emitting elements, and eliminates the image unevenness of the output image due to the light emission intensity unevenness according to the measurement data. The image forming apparatus according to claim 1, further comprising: a weighting factor setting unit that sets a weighting factor; and an arithmetic unit that multiplies the input image signal by the corresponding weighting factor. 4. The image processing means has a binarization processing means for performing a binarization processing by an error diffusion method on the data of the calculation result of the calculation means.
Alternatively, the image forming apparatus according to item 3. 5. The image processing means, when the input image signal is binary data, divides the binary data into line data and gradation data before the arithmetic processing of the arithmetic means, 5. The method according to claim 2, further comprising a pre-processing unit which outputs the data as it is without any processing, and the gradation data is once subjected to pseudo multi-value conversion based on the binary data. The image forming apparatus described. 6. The pre-processing means, when the input image signal is binary data, a determining means for determining a low density portion of a gradation image from the input image signal, and a gradation image determined by the determining means. 7. The image forming apparatus according to claim 5, further comprising at least the pre-processing unit and a control unit that does not process the input image signal of the low-density portion. 7. An image forming apparatus for forming an image according to an input image signal by using a plurality of light emitting elements arranged along a scanning direction, wherein unevenness of light emission intensity is obtained according to measurement data of light emission intensity of each light emitting element. A weighting factor setting step of setting a weighting factor for eliminating image unevenness of the output image, an operation step of multiplying the input image signal by the corresponding weighting factor, and data of an operation result of the operation step. And a binarization processing step of performing binarization processing by an error diffusion method for the image forming method. 8. When the input image signal is binary data, the binary data is divided into line data and gradation data before the arithmetic processing of the arithmetic step, and the line data is not processed. 8. The image forming method according to claim 7, further comprising a pre-processing step in which the output is performed as it is, and the gradation data is once subjected to pseudo multi-value conversion based on the binary data. 9. When the input image signal is binary data, a step of determining a low density portion of a gradation image from the input image signal, and an input image of a low density portion of the gradation image determined in the determination step 9. The image forming method according to claim 8, further comprising at least a control step in which the processing of the preprocessing step and the calculation step is not performed on the signal.