JPH07123264A - Image forming device - Google Patents

Abstract

PURPOSE:To improve an output picture element by the dither method by using a pattern of the same matrix type as that of a dither pattern used for an output for a dot pattern for correcting gradation characteristic. CONSTITUTION:A control unit 61 of a printer engine section reads an output value from a photo sensor 60 and uses the same dither pattern as that for an output picture for the correction to make arithmetic operation to generate a gamma correction table. Then a gamma table stored in a memory 62 is replaced with the generated gamma correction table. An LD driver 63 is operated by the gamma correction table and an LD light emitting section 64 emits a light by the driver 63. Correction corresponding to the dither pattern is conducted by correcting image forming by the same multi-value dither method as that for an output picture and an output picture by the dither method is improved. Furthermore, the dither pattern used for the correction has preferably full dots without fail.

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 color copying machine, a color printer or a color facsimile.

[0002]

2. Description of the Related Art As a conventional technique relating to a color printer, a technique described in Japanese Patent Laid-Open No. 4-268874 is known. This conventional technique reads a predetermined gradation pattern on the photosensitive drum and updates the gradation correction means based on the read result.

[0003]

In this prior art, the pattern on the photosensitive drum does not correspond to the dot-concentrated multi-value dither method, and an image is obtained using the dot-concentrated multi-value dither method. Sometimes there was a problem that a good image could not be obtained.

It is an object of the present invention to provide an image forming apparatus capable of improving the output image by the dither method.

[0005]

The above-described object is to provide a pattern forming means for forming a toner pattern on a photoconductor by an electrophotographic process, a reading means for reading the toner pattern on the photoconductor, and an output of the reading means. In the image forming apparatus using the dot-concentrated multi-valued dither method, the same dither pattern as the matrix type, which has a computing means for creating a γ correction table by This is achieved by the first means in which the pattern is used as a gradation characteristic correction dot pattern.

[0006] Further, the above-mentioned object is, in the first means,
The pattern is achieved by the second means, which always has full dots.

Further, the above-mentioned object is, in the first means,
The pattern has at least two or more representative values
It is achieved by means of.

Further, the above-mentioned object is, in the first means,
This is achieved by the fourth means that calculates the highlight portion of the density measurement result and obtains the density measurement result.

[0009]

In the first means, the image formation is corrected by the same multi-valued dither method as that of the output image, so that the correction corresponding to each dither pattern can be performed.

Since the second means is compatible with the dot concentration type multi-valued dither method, an image can be output in a stable state.

In the third means, the number of patterns to be read can be reduced and the number of patterns to be processed can be reduced.

In the fourth means, the density change by the dither method is smoothed to eliminate the pseudo contour of the output image.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 is an explanatory view showing an embodiment of a color image forming apparatus (color printer) used in the present invention, FIG. 2 is a block diagram of a printer engine of a printer according to the embodiment of the present invention, and FIG. 3 is used for γ correction. FIG. 4 is an explanatory view showing an example of a correction calculation for a density measurement result by a photo sensor, FIG. 5 is an explanatory view showing a γ table generating method, and FIG. 6 is a control operation of the embodiment of the present invention. It is a flowchart shown.

In FIG. 1, reference numeral 1 denotes a flexible belt-shaped photosensitive member as a belt-shaped image bearing member. The belt-shaped photosensitive member 1 is installed between rotating rollers 2 and 3, and is a rotating roller. It is conveyed in the clockwise direction by driving a few. Reference numeral 4 is a charging member as a charging means, 5 is a laser writing system unit as an image exposing means, and 6 to 9 are a plurality of developing means, that is, developing devices each containing a developer of a specific color. The laser writing system unit 5 is housed in a holding case having a slit-shaped exposure opening formed on the upper surface and incorporated in the main body of the apparatus.

For the laser writing system unit 5, in addition to the optical system shown in the figure, an optical system in which a light emitting portion and a converging optical transmission body are integrated is also used.

The charging member 4 and the photoconductor cleaning device 15 are provided on one roller 2 of a plurality of rollers that bridge the belt-shaped photoconductor 1.

Each of the developing units 6, 7, 8, and 9 contains, for example, a yellow, magenta, cyan, and black developer, respectively, and comes into contact with or comes into contact with the belt-shaped photoreceptor 1 at a predetermined position. It has a developing sleeve and has a function of visualizing the latent image on the belt-shaped photoreceptor 1 by non-contact development or contact development.

Reference numeral 10 denotes an intermediate transfer belt as a transfer image carrier, and the intermediate transfer belt 10 has rotating rollers 11 and 1.
It is installed between the two and is conveyed counterclockwise by the driving of the rotating rollers 11 and 12. The belt-shaped photoreceptor 1
The intermediate transfer belt 10 and the intermediate transfer belt 10 are in contact with each other by the rotating roller 3, and the first visible image on the belt-shaped photoreceptor 1 is transferred onto the intermediate transfer belt 10 by the bias roller 13 provided in the intermediate transfer belt 10. Is transcribed to.

By repeating the same process, the second visible image and then the third visible image are obtained.
The fourth visible images are superimposed on the intermediate transfer belt 10 and transferred without causing positional deviation.

A transfer roller 14 is provided so as to come into contact with and separate from the intermediate transfer belt 10. 16 is an intermediate transfer belt 1
No. 0 cleaning device, the blade 16A of the cleaning device 16 is kept at a position separated from the surface of the intermediate transfer belt 10 during image formation, and is pressed against the surface of the intermediate transfer belt 10 as shown only during cleaning after image transfer. To be done.

As shown in FIG. 2, the printer engine unit reads the output value from the photosensor 60, performs a calculation, and generates a γ correction table;
A memory 62 for recording a table, an LD driver 63 operated by the γ table, and an LD light emitting section 64 for emitting light by the LD driver 63 are provided.

A color image forming process by the color image forming apparatus is performed as follows. First, the formation of a multicolor image according to this embodiment is performed according to the following image forming system. That is, the image data processing unit arithmetically processes the data obtained by the color image data input unit in which the image sensor scans the original image to create image data, which is temporarily stored in the image memory. Next, the image memory is taken out at the time of recording and is inputted to the recording unit, for example, the color image forming apparatus shown in the embodiment of FIG.

That is, when a color signal output from an image reading device separate from the printer is input to the laser writing system unit 5, the laser writing system unit 5 is started.
In FIG. 1, a laser beam generated by a semiconductor laser (not shown) is rotationally scanned by a polygon mirror 5B rotated by a drive motor 5A, an optical path is bent by the mirror through an fθ lens 5C, and is previously charged by a charging member 4. The peripheral surface of the belt-shaped photoreceptor 1 that is uniformly charged is exposed to light and an electrostatic latent image is formed.

Here, the image pattern to be exposed is a monochromatic image pattern obtained by color-separating a desired full-color image into yellow, magenta, cyan, and black. The formed electrostatic latent images are yellowed by the rotary developing devices 6 to 9,
It is developed into magenta, cyan, and black, and is developed and monochromatic to form a monochromatic image.

The monochromatic image formed on the belt-shaped photoreceptor 1 is transferred onto the intermediate transfer belt 10 which rotates counterclockwise while contacting the belt-shaped photoreceptor 1. The yellow, magenta, cyan, and black monochromatic images formed on the belt-shaped photoreceptor 1 are sequentially superposed on the surface of the intermediate transfer belt 10. Yellow superimposed on the intermediate transfer belt 10,
The magenta, cyan, and black images are transferred by the transfer roller 14 to the transfer paper conveyed from the paper supply table 17 through the paper supply roller 18 and the registration roller 19 to the transfer section. After the transfer is completed, the transfer paper is fixed by the fixing device 20 to complete a full-color image.

When the color printer uses multivalued dither for printing, the γ correction pattern formed on the belt-shaped photosensitive member 1 uses a representative value of the dither pattern used for printing. The pattern formed at this time always includes full dots. In this embodiment, 2 × 2 16-valued multi-value dither is used.

Typical values of the dither pattern used for the above-mentioned correction are shown in FIG. In this pattern, the part b shown in FIG. 3 is a full dot, the parts a and c are the parts where no dots are printed, and the part d is 17 It changes in stages. In FIG. 3, the numbers below the pattern indicate the respective steps, and the steps 0, 1, 2, and 16 are shown.

The pattern density thus formed is read by the photosensor 60. This work is repeated three times and averaged to obtain the measurement result. This reduces the measurement error. Calculation is performed on this measurement result.

FIG. 4 shows a corrected measured concentration curve obtained by calculating only the highlighted portion of the measurement result. In FIG. 4, the solid line in the highlight part is the measurement result, and the dotted line is the correction result. This work is to eliminate the false contour of the output image.

Next, a method of generating the γ correction table will be described. As shown in FIG. 5, the input and output levels are 0-2.
55 levels. Further, the measured density value is normalized to 0 to 255 by setting the minimum density value to 0 and the maximum density value to 255. The first quadrant of FIG. 5 is the γ characteristic of the measured color printer, the second quadrant is the target γ characteristic, and the third quadrant is the correction data for obtaining the target γ characteristic.

In the generation method, the density value at the input level j in the target γ characteristic of the first quadrant and the actual input level i for obtaining the same density value are obtained from the first quadrant. The obtained i is the output level of the correction γ table, and j is the input level of the correction γ table. The correction curve is replaced by the corresponding γ table among the plurality of basic γ tables held in the memory 62 in advance by the color printer according to the type and color of the dither matrix.

Next, the control operation of the above embodiment will be described with reference to FIG. In FIG. 6, in step 1, a pattern is created on the belt-shaped photoconductor 1. In step 2, the density of the pattern is measured by the photo sensor 60. Step 3
Then, it is judged whether the measurement is performed three times. In step 4, the results of three measurements are averaged. In step 5, the highlight part (see FIG. 4) is corrected and calculated. In step 6, a γ correction table is created. In step 7, the γ table recorded in the memory 62 is replaced with the γ correction table generated in step 6.

In the above embodiment, the pattern forming means for forming the toner pattern on the photoconductor 1 by the electrophotographic process, the reading means (60) for reading the toner pattern on the photoconductor 1, and the reading means ( Calculation means (6) for creating a γ correction table by the output of 60).
1) and a holding means (62) for holding the calculation result, and in an image forming apparatus using the dot concentration type multi-valued dither method, a dither pattern used for output and a pattern of the same matrix type have gradation characteristics. Since the same dither pattern as that of the output image is used for correction in order to use the correction dot pattern, it is possible to perform correction corresponding to each dither pattern. Therefore, the output image by the dither method becomes good.

In the above embodiment, since the pattern always has full dots, it is possible to stably output an image using the dot concentration type multi-valued dither method.

In the above embodiment, since the pattern has at least two representative values, it is possible to efficiently perform correction with a small number of processings by reducing the number of patterns to be processed.

In the above embodiment, since the highlight portion of the density measurement result is calculated and used as the density measurement result, it is possible to smooth the density change by the dither method and eliminate the pseudo contour of the output image.

[0037]

According to the first aspect of the invention, since the same dither pattern as that of the output image is used for the correction, the correction corresponding to each dither pattern can be performed. Therefore, the output image by the dither method becomes good.

According to the second aspect of the invention, it is possible to output an image using the dot-concentrated multi-value dither method in a stable state.

According to the third aspect of the invention, by reducing the pattern to be processed, the correction can be efficiently performed with a small number of processing times.

According to the fourth aspect of the invention, it is possible to smooth the density change by the dither method and eliminate the pseudo contour of the output image.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a printer according to an embodiment of the present invention.

FIG. 2 is a block diagram of a printer engine of the printer according to the embodiment of the invention.

FIG. 3 is an explanatory diagram showing an example of a pattern used for γ correction.

FIG. 4 is an explanatory diagram showing an example of correction calculation for a density measurement result by a photosensor.

FIG. 5 is an explanatory diagram showing a γ table generation method.

FIG. 6 is a flowchart showing the control operation of the embodiment of the present invention.

[Explanation of symbols]

 1 Belt-shaped Photoreceptor (Photoreceptor) 4 Charging Member (Pattern Forming Means) 5 Laser Writing System Unit (Pattern Forming Means) 6 Y Developing Unit (Pattern Forming Means) 7 M Developing Unit (Pattern Forming Means) 8 C Developing Unit ( Pattern forming means) 9 Black developing unit (pattern forming means) 60 Photo sensor (reading means) 61 Control unit (calculating means) 62 Memory (holding means)

Claims (4)

[Claims] 1. A pattern forming means for forming a toner pattern on a photoconductor by an electrophotographic process, a reading means for reading the toner pattern on the photoconductor, and a γ correction table by the output of the reading means. In the image forming apparatus using the dot concentration type multi-valued dither method, the same dither pattern as the matrix type pattern for gradation characteristic correction An image forming apparatus having a dot pattern. 2. The image forming apparatus according to claim 1, wherein the pattern always has full dots. 3. The image forming apparatus according to claim 1, wherein the pattern has at least two representative values. 4. The image forming apparatus according to claim 1, wherein the highlight portion of the density measurement result is calculated and used as the density measurement result.