JP2001352449A - Image-processing unit and image-forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly process image data realized in terms of signals of an image formed by pixels arranged two-dimensionally and to reduce the cost of an image-forming device. SOLUTION: A correction value storage means 34 stores correction value to correct image data as to positions on a two-dimensional coordinate, set at an interval larger than that of pixels arranged two-dimensionally. A correction value interpolating means 35 applies interpolation arithmetic operations to correction values, at positions other than the positions whose correction values are stored. A correction arithmetic means 36 uses the correction values to apply proper correction to all pixels of the image data received from an image input device 10. A correction value updating means 33 can properly update the correction values stored in the correction value storage means, and by measuring the density of an image actually outputted from an image output device 40 by a sensor 42 the new correction values can be decided based on it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for correcting, correcting, adjusting, etc., signalized data of an image formed by a predetermined number of pixels arranged two-dimensionally. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an image processing apparatus, and more particularly, to an image processing apparatus and an image forming apparatus that perform processing for improving density unevenness of a formed image.

[0002]

2. Description of the Related Art In recent years, with the development of computers and the maintenance of networks and the like, the appearance of large-capacity storage media, and the spread of scanners and digital cameras, the use of digital image data has been rapidly spreading. Under such circumstances, there is an increasing demand for printing out image data with high speed and high image quality, and electrophotographic or inkjet image forming apparatuses are often used. These image forming devices do not require photosensitive paper,
It has a wide range of applications, such as being able to form color images on plain paper. In particular, in the electrophotographic image forming apparatus, high-speed fixing has recently been performed, and instantaneous heating,
Improving fixability by applying pressure to the toner image,
It can output high-quality images at high speed.

In an electrophotographic image forming apparatus, an image portion is exposed by an optical scanning device after a photosensitive layer is uniformly charged, and toner charged by a developing unit is electrostatically attached to the photosensitive member. A toner image is formed. But,
The photoreceptor layer has uneven chargeability and photosensitivity depending on the two-dimensional position of the formed layer. For this reason, as disclosed in Japanese Patent Application Laid-Open No. H10-145596, there is a problem that even when uniform charging, exposure and development are performed, the density varies depending on the two-dimensional position.

In other image forming methods such as printing, silver halide photography, ink jet and thermal transfer, the density unevenness in the plane is very small, so that there is little visual problem. The average color difference in the plane may be about 3 to 6, which is likely to cause a visual problem. In particular, since the graininess has been greatly improved due to the reduction in the diameter of the toner and the development, development, transfer and fixing techniques, density unevenness has been more easily perceived than in the past.

[0005] The cause of the in-plane unevenness in the chargeability and photosensitivity of the photoreceptor is a large problem in the method and structure of the photoreceptor. Usually, the photoreceptor is manufactured by applying an organic photosensitive material or the like on a conductive pipe or belt made of aluminum or the like. The thickness of the applied photosensitive material is as thin as several tens of microns. The chargeability and photosensitivity of the photoreceptor are greatly affected by the thickness. For this reason, it is necessary to manufacture the film with a uniform thickness, but for that purpose, it is required to apply a photosensitive material precisely on the order of microns, and the cost of the photosensitive member increases, which is not practical.

Further, there is a problem that it is difficult to uniformly charge, expose and develop the photosensitive member. LED for exposure
When an optical scanning device having a plurality of light emitting elements in the main scanning direction such as an image bar is used, the light emission intensity of the light emitting elements varies, and the potential on the photoconductor varies. On the other hand, in development, if the distance between the developing roll having a thin layer of developer formed on the peripheral surface and the photoconductor is not constant, the amount of toner developed from the developing roll to the photoconductor will vary, and the development density will vary. . Since the distance between the developing roll and the photoreceptor is usually about several hundred microns, in order to solve the above problems, a high mechanical precision and rigidity are required for the frame for fixing the developing device and the photoreceptor, There is a problem that the cost and size of the image forming apparatus are increased.

On the other hand, in an image forming apparatus of an ink jet system or a thermal transfer system in which an image is formed by a recording head using a recording element corresponding to an arrangement of pixels, for example, JP-A-5-162338 and JP-A-5-42685. As disclosed in Japanese Unexamined Patent Application Publication No. H11-157, the variation in output for each printing element is obtained in advance, a correction value is held in a memory or the like, and the image data is corrected using the correction value for each printing element, thereby obtaining density unevenness. There is a technology for correcting

As described above, in the method of correcting the image data by the correction value for each recording element, it is possible to correct the one-dimensional density unevenness, and the cause of the density unevenness occurring in the electrophotographic image forming apparatus. Among them, it is effective for the case where an optical scanning device such as an LED image bar is used for exposure, and for density unevenness caused by the positional accuracy between the developing device and the photosensitive member.

[0009]

However, the density unevenness due to unevenness in the sensitivity of the photosensitive layer is a density unevenness in a two-dimensional plane.
In order to apply the technology disclosed in Japanese Patent Application Laid-Open No. H05-42685 and Japanese Patent Application Laid-Open No. 5-42685, correction values are set for each pixel at all recording positions in a plane on which an image is formed, and these are stored in a memory or the like. There must be. As described above, storing the correction values for all pixels forming an image requires an enormous memory capacity, resulting in an increase in cost of the image processing apparatus.

[0010] The invention according to the present application has been made in view of the above-mentioned circumstances, and the object thereof is to:
By processing signalized image data of an image formed by two-dimensionally arranged pixels, unevenness due to a two-dimensional position can be effectively corrected, and the memory capacity can be suppressed to be small to produce the image at low cost. It is an object of the present invention to provide an image processing apparatus or an image forming apparatus that can perform the processing.

[0011]

In order to achieve the above-mentioned object, the invention according to claim 1 is a method for storing a position on a two-dimensional coordinate in an image and an image recording signal representing a pixel at the position on the coordinate. An image processing apparatus for inputting image data including the image data and performing conversion and correction necessary for forming a visible image from the image data, wherein the image data is set at an interval larger than the interval between the two-dimensionally arranged pixels. For a position on the dimensional coordinates, a correction value storage unit in which a correction value for correcting image data is stored, and a correction value stored in the correction value storage unit, at a coordinate position other than the set position. Correction value interpolation means for calculating a correction value; and correcting the input image data using a correction value stored in the correction value storage means and a correction value calculated by the correction value interpolation means. And an image processing apparatus having a correction operation unit.

In this image processing apparatus, correction values for correcting image data are stored only at positions set at intervals larger than the pixel interval, and the correction values are set at a level lower than the resolution of the image. ing. Therefore, the number of data stored in the correction value storage means is significantly smaller than the number of pixels forming one image. Then, for a pixel at a position where a correction value is not stored, interpolation is performed by the correction value interpolation means from the correction value stored in the correction value storage means. Therefore, the input image data is corrected at the position where the correction value is stored in the correction value storage means using the correction value stored as it is, and the position where the correction value is stored. At positions between which no correction value is stored, the image data is corrected using the interpolated correction value. Thereby, appropriate correction is performed for all pixels of the entire image. Further, in this image processing apparatus, the correction values are stored only at positions set at intervals larger than the actual pixel interval, and a small memory capacity of the correction value storage means is sufficient. Therefore, the cost for installing the memory can be reduced.

According to a second aspect of the present invention, in the image processing apparatus of the first aspect, the image processing apparatus further includes a correction value updating unit that changes the correction value stored in the correction value storage unit to a new value.

In such an image processing apparatus, the correction values stored in the correction value storage means can be updated as needed, and there are parts replacement of the image output apparatus, changes in characteristics over time, and the like. Accordingly, appropriate correction can be made in response to this.

According to a third aspect of the present invention, in the image processing apparatus according to the first aspect, the correction value storage means is set in one direction of the two-dimensionally arranged pixels at the same interval as the pixel interval. It is assumed that the correction value is stored for the corrected position.

When a printing element arranged corresponding to a pixel is used when converting image data into a visible image, unevenness may occur due to a difference in characteristics between the printing elements. However, in the image processing apparatus, correction values are stored at the same intervals as the recording elements in the arrangement direction of the recording elements, and the difference in the characteristics is appropriately corrected to form a uniform image without unevenness. be able to.

According to a fourth aspect of the present invention, image data including a position on a two-dimensional coordinate in an image and an image recording signal representing a pixel at the position on the coordinate is input, and a visible image is obtained from the image data. An image processing device that performs conversion and correction necessary to form a, and an image output device that outputs a visible image based on image data input from the image processing device, the image processing device includes: Correction value storage means for storing a correction value for correcting image data at a position on two-dimensional coordinates set at an interval larger than the interval between the two-dimensionally arranged pixels; and storing in the correction value storage means Correction value interpolating means for calculating a correction value at a coordinate position other than the set position from the corrected correction value; and a correction value stored in the correction value storage means and the correction value interpolating means. Using the computed correction value I, there is provided an image forming apparatus and a correction calculation means for correcting the image data to be input.

In such an image forming apparatus, the correction values stored in the correction value storage means of the image processing apparatus are stored only at positions set at intervals larger than the pixel interval. It is small and can be manufactured at low cost. However, between the positions at which the correction values are stored, the correction values are interpolated, and the correction values can be set for the pixels at all positions. Therefore, it is possible to appropriately correct the unevenness of the image with the correction values corresponding to the individual characteristics of the image output device, and to form a good image.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the image output device includes an image carrier having a photosensitive layer on an endless peripheral surface, and an image formed on the image carrier. An optical scanning device that irradiates light, and a developing device that selectively transfers toner to an electrostatic latent image formed by irradiating the image light to form a visible image, wherein the correction value is , Is associated with a position on the peripheral surface of the image carrier, and is determined based on the density characteristics of the toner image formed at the position on the peripheral surface.

In general, the photoreceptor layer formed on the peripheral surface of the image carrier is likely to have a difference in charging characteristics and photosensitivity depending on the position on the peripheral surface. May also cause a difference in potential. The difference in potential affects the adhesion of the toner, resulting in a difference in image density. On the other hand, in the image forming apparatus described above, the correction value is associated with the position on the peripheral surface of the image carrier, and is determined based on the density characteristics of the toner image formed at each position. It is possible to offset the difference in density due to the difference in charging characteristics and light sensitivity of the image carrier used in the image data correction by correcting the image data.

The density unevenness caused by such a difference in the characteristics of the photoreceptor layer gradually changes as the position on the peripheral surface of the image carrier is moved. Absent. Therefore, if the correction values are appropriately determined at spaced positions, the image data can be appropriately corrected even if the correction values are obtained by interpolation in the meantime, and the density unevenness of the image can be eliminated. Can be.

According to a sixth aspect of the present invention, in the image forming apparatus of the fourth aspect, it is preferable that the image forming apparatus further includes a correction value updating unit that changes the correction value stored in the correction value storage unit to a new value.

An image carrier having a photoreceptor layer needs to be replaced when used repeatedly, but unevenness in the density characteristics of the photoreceptor layer differs for each individual. On the other hand, in the image forming apparatus, the correction value can be updated by the correction value updating unit, and the correction value stored in the correction value storage unit is changed to a value corresponding to the image carrier after replacement, and Appropriate image data correction can be performed even after the replacement of the carrier. Further, in addition to the replacement of the image carrier, it is possible to cope with a case where development conditions, latent image formation conditions, and the like change.

According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, the correction value updating unit is configured to transfer a state of the toner image formed on the image carrier to the image carrier or transfer the toner image to the image carrier. It is assumed that the measured value is measured on the measured medium, and a value determined based on the measured value is written in the correction value storage means.

In this image forming apparatus, since a correction value is determined based on a value obtained by actually forming a toner image and measuring a state such as a density, an image output device such as a photosensitive layer of an image carrier is used. Correction corresponding to individual differences is possible. Further, in this image forming apparatus, correction values are stored only for positions set at intervals larger than the pixel interval, and when the correction values are updated, the actual measurement of the state of the toner image such as density is also performed. It can be done easily.

According to an eighth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the optical scanning device scans a laser beam, and the correction value storage unit stores a laser beam in a main scanning direction. The correction value is stored at a position set at an interval larger than the pixel interval in the sub-scanning direction.

By writing a latent image by scanning with a laser beam, exposure can be performed evenly in both the main scanning direction and the sub-scanning direction. The correction values are mainly stored at positions spaced in the main scanning direction and the sub-scanning direction as in the above-described image forming apparatus. Can be corrected.

According to a ninth aspect of the present invention, in the image forming apparatus according to the fifth aspect, in the optical scanning device, light emitting elements are arranged for each pixel in a main scanning direction.
The correction value storage means stores a correction value for a position set at the same interval as the pixel in the main scanning direction, and a correction value for a position set at an interval larger than the pixel interval in the sub-scanning direction. Shall be stored.

In this image forming apparatus, a difference in characteristics may occur between the light emitting elements arranged in the main scanning direction, but correction values are stored at the same intervals as pixels in the main scanning direction. With these correction values, the difference in the characteristics can be corrected. On the other hand, image unevenness due to the optical scanning device is unlikely to occur in the sub-scanning direction, and even if interpolation values at other positions are interpolated from correction values at positions set at intervals, image unevenness in the sub-scanning direction will not occur. Can be eliminated. Therefore, it is possible to obtain a good image without unevenness in both the main scanning direction and the sub-scanning direction.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a color image output system using an image processing apparatus and an image forming apparatus according to an embodiment of the present invention. This color image output system includes an image input device 10 and an image forming device 20, and the image forming device 20 includes an image processing device 30 and an image output device 40.

The image input device 10 receives color images of various formats from the outside and outputs a color image signal and a position (x, y) in two-dimensional coordinates on a sheet on which the color image signal is printed. . In this example, R
(Red), G (green) and B (blue) or Y (yellow), M (magenta), C (cyan) and K (black) data, each of which has a total of 24 Bit RGB data or
An image signal composed of 32-bit YMCK data is output in association with a position (x, y) on a two-dimensional coordinate in an image to be formed. Here, the two-dimensional coordinates are, for example, x in the main scanning direction of the optical scanning device 55 described later and y in the sub-scanning direction.

Specific examples of the image input device 10 include a 35 mm color negative film, a positive film,
A silver halide photographic film represented by APS film
KODA to read as RGB data by D sensor
K ・ Image data is read from CD-ROM in PhotoCD format and converted to RGB data, shooting data is converted from digital camera such as Nikon D1 to RGB data, edited using computer, MO and Zi
one that reads color image data stored on a recording medium represented by p and converts it to RGB data, one that converts image information sent from a device connected on a network to RGB data,
These RGB data are recorded at the recording position (x, y)
And the image processing device 30
It has a function of transferring to

The image input device 10 is provided with a YMCK data color-separated for printing by a drum scanner or a CE for printing.
Alternatively, the YMCK data for printing output from the PS or the image setter may be received, and the data may be transferred to the image processing device 30 together with the coordinate data of the recording position (x, y) of the YMCK data. Further, the electronic document in the page description language created by the application and the printer driver on the personal computer is rasterized into raster data of YMCK data, and the image processing device is provided together with the coordinate data indicating the recording position (x, y) of the YMCK data. 30 may be used to transfer data.

The main part of the image processing device 30 is constituted by a color conversion means 31, a data correction means 32 and a correction value updating means 33. The color conversion unit 31 converts the RGB data or the YMCK data input from the image input device 10 into an image recording signal of a color space of the image output device 40.
This is converted to YMCK data.

As the color conversion means 31, for example, a matrix operation type color conversion circuit, a direct lookup table type color conversion circuit or a neural network type color conversion circuit widely used as a color conversion circuit can be used. This is possible, and in this embodiment, a direct look-up table type color conversion circuit is used. The color conversion coefficient of the color conversion means 31 is determined such that the input color and the output of the image output device 40 are colorimetrically matched.

It should be noted that the color conversion means 3
The color signals input to 1 are most commonly RGB data and YMCK data, but are used in the YMC color space and color management system used in PhotoCD.
Data in another color space such as the L * a * b * color space or the XYZ color space may be used. The color space of the image output device 40 is a YMCK color space in the following example, but may be another color space such as a YMC color space or an RGB color space.

The image processing apparatus 30 includes a correction value storage unit 34 for storing correction values for positions set at predetermined intervals in the main scanning direction and the sub-scanning direction, and a correction value stored in the correction value storage unit 34. For a position other than the stored position, a correction value interpolating means 35 for performing an interpolation calculation of a correction value, and a stored correction value or a correction value obtained by an interpolation calculation,
A correction operation unit 36 is provided for correcting the image data output from the color conversion unit 31 according to the characteristics of the image output device 40. Thereby, the YMCK from the color conversion means 31
The data is corrected for each color so that density unevenness does not occur in the image output device 40, and is transferred to the image output device 40. Then, in the image output device 40, an image is formed on a sheet using the corrected YMCK data.

The image processing apparatus 30 further includes a correction value updating unit 33 for updating the correction value stored in the correction value storage unit 34 to a new one. Is done. The detailed operation of the image processing device 30 will be described later.

The image output device 40 is for outputting a color image by an electrophotographic system, and its configuration is schematically shown in FIG. The image output device 40 includes an endless belt-shaped intermediate transfer body 51 whose peripheral surface is supported so as to be able to rotate.
Four image forming units 52a, 52b, 52c, and 52d for forming magenta, cyan, and black toner images are provided.

Each image forming unit 52a, 52b, 52
c and 52d have photoreceptor drums 53a, 53b, 53c and 53d on each of which an electrostatic latent image is formed, and the surface of each of the photoreceptor drums is substantially uniform around each of the photoreceptor drums. Charging devices 54a, 54b, 54
c, 54d, an optical scanning device 55 that scans the surface of each photoconductor drum with a laser beam to write an electrostatic latent image, and that each latent image formed on the photoconductor drum 53 has yellow, magenta, cyan, or Developing devices 56a, 56b, 56c, 56d for forming a toner image by transferring black toner
And transfer the toner image on each photosensitive drum 53 to the intermediate transfer member 51.
Transfer chargers 57a, 57b, 57c for primary transfer onto
57d. Further, a screen generator 58 is provided, which performs pulse width modulation on the image recording signal output from the image processing device 30 and inputs the modulated signal to the optical scanning device 55.

Inside the intermediate transfer member 51, support rolls 59a, 59b, 59c, a first heating roll 61 and a peeling portion roll 60 are provided, and the intermediate transfer member 51 is stretched over these rolls. It is driven to rotate in the direction of the arrow shown therein. Further, a second heating roll 62 for sandwiching and heating and pressing the recording paper P is disposed at a position facing the first heating roll 61 via the intermediate transfer body 51.
The transfer and fixing of the upper toner image are performed simultaneously.

The apparatus further includes a paper tray 63 for accommodating the recording paper P, a feed roll 64 for feeding the recording paper P one by one from the paper tray 63, and a first recording paper P.
And a pin roll 66 wound around the second heating roll 62 in order to preheat the recording paper in advance. I have.

Further, on the downstream side of the position where the two heating rolls 61 and 62 are pressed against each other in the circumferential direction of the intermediate transfer member 51, the recording adhered to the intermediate transfer member 51 via the intermediate transfer member 51 and the toner. A cooling device 67 that blows the paper P is provided, and cools the recording paper on which the toner image has been transferred and fixed in a state in which the recording paper is in close contact with the intermediate transfer body 51.

Hereinafter, each component constituting the present embodiment will be described in more detail. The photosensitive drums 53a, 53b, 53c, 53d are arranged on the surface of the drum.
Those having various inorganic photoreceptor layers such as Se, a-Si, a-SiC and CdS, or those having various organic photoreceptor layers can be used.

Transfer charging information 57a, 57b, 57c, 57
d indicates that the toner on the photosensitive drum 53 is efficiently rotated
The back surface of the intermediate transfer member 51 is
It is to provide a load. In this embodiment, the corotron
315 μC / m ^Two To give a charge density of
The voltage applied to the corotron wire is adjusted.

The belt-like intermediate transfer member 51 has a base layer and a surface layer. For the base layer, a heat-resistant polyimide film having a thickness of 70 μm to which carbon black has been added is used. In the present embodiment, in order to electrostatically transfer the toner image from the photosensitive drum 53 to the intermediate transfer body 51 without image disturbance, the volume resistivity of the base layer is changed to 10 ¹⁰ Ωcm by changing the addition amount of carbon black. I am adjusting. In addition, as the base layer, for example, a thickness of 10 to 30
It is possible to use a sheet with high heat resistance of 0 μm, and it is possible to use polymer sheets such as polyester, polyethylene terephthalate, polyethersulfone, polyetherketone, polysulfone, polyimide, polyimideamide, and polyamide. is there.

The surface layer of the intermediate transfer member 51 is used to electrostatically transfer the toner image from the photosensitive drums 53a, 53b, 53c and 53d onto the intermediate transfer member 51 without causing image disturbance. The volume resistivity is adjusted to 10 ¹⁴ Ωcm. Further, the toner image is transferred from the intermediate transfer body 51 to the recording paper P.
A silicone copolymer having a rubber hardness of 40 degrees and a thickness of 50 μm is used so that the intermediate transfer body 51 and the recording paper P are in close contact with each other with the toner image interposed therebetween when the toner image is transferred and fixed.

The silicone copolymer has elasticity, and its surface shows tackiness to the toner at normal temperature. Further, since the toner that has been melted and fluidized has a characteristic that it is difficult to be adsorbed, the toner can be efficiently transferred to the recording paper P, which is optimal for the material of the surface layer. As the surface layer, in addition to the above silicone copolymer, for example, a resin layer having a high releasability having a thickness of 1 to 100 μm can be used. For example, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer layer can be used. It is also possible to use coalescence, polytetrafluoroethylene or the like.

As the first heating roll 61 and the second heating roll 62, a metal roll or a metal roll on which a heat-resistant elastic layer such as silicone rubber is formed can be used. First heating roll 61 and second heating roll 6
Heat sources 61a and 62a are disposed in the interior of the printer 2. The heating temperature depends on the thermal melting characteristics of the toner and the thermal melting characteristics of the surface resin layer when a recording paper having a thermoplastic resin layer on the surface is used. Is determined by In this embodiment, the first heating roll 61 and the second heating roll 62
As the heat source 61a, 62a inside the first heating roll 61 and the second heating roll 62, a halogen material having an outer diameter of 50 mm obtained by laminating silicone rubber with a thickness of 2.0 mm on an aluminum hollow roll is used. You are using a lamp. In addition, the first heating roll 61 and the second heating roll 6
2 is 5.0 × 10 ⁵ Pa
And the contact area (nip width) is adjusted to be about 7.5 mm.

The structure for pressurizing and heating is not limited to the structure using the two heating rolls 61 and 62 as described above.
Any structure may be used as long as the pressure can be evenly applied without causing any lifting or displacement between them. For example, it may be a combination of one heating roll and one fixing pad, or a combination of one fixing pad. Further, although a halogen lamp is used as a heating source, the heating source is not limited to the halogen lamp,
Other heating means can be used.

The cooling device 67 is a fan that blows air to the back surface of the recording paper P adhered to the intermediate transfer body 51. When the recording paper separates from the intermediate transfer body at the position where the separation unit roll 60 is provided. The temperature of the surface of the recording paper in contact with the intermediate transfer member 51 is adjusted to 70 ° C.

The peeling portion roll 60 winds a belt-like intermediate transfer body 51 and uses the rigidity of the recording paper P itself to peel off the recording paper P from the intermediate transfer body 51 that moves by the curvature of the roll. Has become. That is, when the intermediate transfer body 51 is bent, the rigidity of the recording paper acts so as to resist bending following the intermediate transfer body 51, and the recording paper is peeled off from the intermediate transfer body 51. Go straight.

The toner used in the image output device 40 is composed of a thermoplastic binder containing yellow, magenta, cyan, and black dyes, and can be formed of a known material. In this embodiment,
A polyester toner having a weight average molecular weight (Mw) of 54000, a softening point of 113 ° C. and an average particle size of 7 μm is used. Further, the toner amount on recording paper for each color, the exposure conditions or development conditions are set so as to approximate a 0.4mg / cm ² ~0.7mg / cm ² by the content of the dye.

Next, the operation of the image forming apparatus will be described. In each of the image forming units arranged around the belt-shaped intermediate transfer body 51, the photosensitive drums 53a, 53b,
53c and 53d are charging devices 54a and 54b, respectively.
It is charged almost uniformly by 54c and 54d. afterwards,
Exposure is performed by the optical scanning device 55 which is turned on / off in response to an image signal, and an electrostatic latent image is formed.

Each of the photosensitive drums 53a, 53b, 53c,
The electrostatic latent images on 53d are developing devices 56 containing yellow, magenta, cyan, and black toners, respectively.
A so-called digital image, which is developed by a, 56b, 56c, and 56d and expresses density by area modulation, is formed as a toner image on each of the photosensitive drums 53a, 53b, 53c, and 53d. These color toner images are sequentially transferred onto the intermediate transfer body 51 by the transfer chargers 57 a, 57 b, 57 c, and 57 d in a superimposed manner, and a full-color toner image is formed on the intermediate transfer body 51.

On the other hand, the recording paper P is taken out one by one from the paper tray 63 by the field roll 64 and conveyed to the nip portion of the two heating rolls 61 and 62 by the paper feeding device 65. Then, the intermediate transfer body 51 holding the toner images of a plurality of colors and the recording paper P are superimposed on each other and sent to the nip portion between the two heating rolls 61 and 62. The toner image on the intermediate transfer body 51 is divided into two heating rolls 61 and 62.
Is heated when passing through the nip, and is pressed against the recording paper P in a molten state.

The toner image is conveyed between the intermediate transfer body 51 and the recording paper P in a state of being in close contact with each other, and is cooled and cooled to a melting temperature or lower to coagulate and solidify. Strong adhesion occurs. As a result, when the intermediate transfer body 51 is bent around with a large curvature at the position where the peeling portion roll 60 having a small radius of curvature is arranged, the recording paper P is separated from the intermediate transfer body 51 together with the toner by its own rigidity. Thus, a fixed image is formed on the recording paper P without causing an offset.

Next, the image processing device 30 will be described in detail. The correction value storage unit 34 included in the image processing device 30 stores a main scanning direction for each color of yellow (Y), magenta (M), cyan (C), and black (B) for forming an image in the image output device 40. The correction value is held at a resolution lower than the resolution in the sub-scanning direction. on the other hand,
An image recording signal input from the image input device 10 is associated with coordinate data indicating a recording position (x, y) on a sheet, and includes data for each pixel according to the resolution of the image. Therefore, in order to correct an image recording signal at a position where a correction value is not stored, a correction value at each position is required.

In the correction value interpolation means 35, the image input device 10
Recording position (x, y) on paper of image recording signal input from
The correction value .alpha. At the (x, y) coordinate is determined by interpolation from the coordinate data at .alpha. And the correction values .alpha.1, .alpha.2, .alpha.3 and .alpha.4 at the peripheral coordinate positions input from the correction value storage means 34. As a result, the correction value α is obtained for the position (x, y) where the correction value is not stored, and is transferred to the correction calculating means 36.

The correction calculation means 36 performs a correction calculation process on the image recording signal YMCK data input from the color conversion means 31 using the correction value α, and transfers the corrected image recording signal to the image output device 40. It has become.

The correction value storage means 34 stores correction values for positions set at intervals larger than the pixel interval. That is, the correction value is held at a resolution lower than the resolution of the image output device 40 in the main scanning direction and the sub-scanning direction. In contrast to the 600 SPI, the correction value storage means 34 has a 3 SPI resolution which is 1/2200 of that in both the main scanning direction and the sub-scanning direction.
The correction value is held at the resolution of. The resolution of 3SPI means that the correction value is recorded every 8.5 mm on the paper, but in the image output device 40 of the present embodiment, since the photoconductor is exposed by a single laser light source, It is not necessary to perform the correction by the recording element for each pixel, and the frequency of the sensitivity unevenness of the photoreceptor is not so high, so that the correction value has a sufficient resolution. In addition, density unevenness due to uneven spacing between the developing device and the photoconductor linearly changes in the main scanning direction, so that a low resolution of about 3 SPI can be sufficiently corrected. Note that the resolution of the correction value stored in the correction value storage unit 34 may be changed according to the level of the sensitivity unevenness of the photoconductor, and the resolution is not limited to the 3SPI resolution.

In the case where the correction values are held at the above resolution, the number of correction values is 1/200 of the number of pixels in both the main scanning direction and the sub-scanning direction. Compared with the case where the correction value is held for the recording position, the data amount becomes 1 / 40,000, and the memory capacity of the correction value storage means 34 can be made extremely small. Therefore, the cost is lower than that in which the correction values are stored for all the pixel positions.

On the other hand, unlike the image output device 40 of the present embodiment, when an exposure device having a variation in exposure energy for each recording element, such as an LED image bar, is used as the exposure device of the image output device, the recording is not performed. Since density unevenness occurs for each element, that is, for each pixel, the correction value storage unit 3
In 4, the correction value may be held at the same resolution as the image to be formed in the main scanning direction, and may be held at a lower resolution in the sub-scanning direction. Even in such a case, the storage capacity is as small as 200 times smaller than that in which the correction values are stored for all the pixel positions.

In the present embodiment, the correction value storage means 34 is configured to hold the correction value for each of the YMCK colors of the image recording signal input to the image output device 40. In an image output apparatus in which four color toner images are sequentially formed on this peripheral surface using a body drum and these are superimposed, it is also possible to perform correction using the same correction value for the image recording signal of each color of YMCK. .

The correction value interpolation means 35 calculates a correction value by a two-dimensional linear interpolation operation, and a schematic diagram of the correction operation is shown in FIG. In this figure, coordinate values x and y indicate the main scanning direction and the sub-scanning direction of the image output device 10, respectively. For the image recording position (x, y),
Surrounding four points (x1, y1), (x2, y1), (x1, y2) and (x2, y
The correction values in 2) are recorded in the correction value storage means 34, and the respective correction values are stored in α1, α2, α3 and α4.
Then, the correction value α at the image recording position (x, y) is calculated by a two-dimensional linear interpolation operation according to the following equation.

Α = [(x−x1) × (y−y1)] / [(x2−x1) × (y2−y1)] × α1 + [(x2−x) × (y−y1)] / [ (x2-x1) x (y2-y1)] x α2 + [(x-x1) x (y2-y)] / [(x2-x1) x (y2-y1)] x α3 + [(x2-x ) × (y2-y)] / [(x2-x1) × (y2-y1)] × α4 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (1)

In the present embodiment, the interpolation operation in the correction value interpolation means 35 uses a two-dimensional linear interpolation operation. However, the interpolation method is not limited to this, and the coordinate value (x, y) is used.
May be configured to output the correction value of the peripheral data closest to. In this embodiment, the interpolation is performed from four surrounding points. However, the correction value interpolating unit 35 may be configured to interpolate the correction values from more surrounding points.

The correction calculating means 36 calculates the correction value α calculated for each coordinate value (x, y) by the correction value interpolating means 35.
Is used to correct the image recording signal according to the following equation. Cin '= Cin × α (2)

Here, Cin is a dot area ratio of a pixel at each coordinate value (x, y) in the image recording signal input to the correction calculating means 36, that is, in the image data of each color of YMCK.
Cin 'indicates the dot area ratio after correction. Note that the correction processing in the correction calculation means 36 is not limited to the equation (2).
Using the image recording signal and the correction value, it is possible to use an arbitrary arithmetic expression capable of performing appropriate correction.

The correction value updating means 33 corrects the correction value held in the correction value storage means 34.
When the image output device 40 is manufactured or when the photosensitive drum is replaced,
Alternatively, it is desirable to update the correction value after outputting a certain number of sheets. It is also possible to periodically monitor the status of the image formed by the image output device 40 and correct the correction value according to the result.

As a method of generating a correction value in the correction value updating means 33, a method of setting a correction value by inputting a numerical value by an operator, a method of inputting a correction value generated by another device not shown, Various methods can be adopted, such as a method of generating a correction value with
In this embodiment, the image output device 40 is configured to measure the density unevenness of the image formed and to generate a correction value from the measured value.

The process of generating a new correction value by the correction value updating means 33 of this embodiment will now be described. In this method, a correction value α is calculated from the relationship between the halftone dot area ratio Cin and the lightness L *. A patch in which the halftone dot area ratio Cin is changed from 0% to 100% in advance is output to an image output device. The light is output at a plurality of positions in the image plane by using 40 and the lightness L * is measured using the sensor 42. The measured lightness L * is subjected to an averaging process to obtain the relationship between the dot area ratio Cin and the lightness L * as shown in FIG. Next, for each color of YMCK, the dot area ratio Cin is
A 50% image is output on the entire surface of the sheet, and the sensor 42 measures the lightness L * r at intervals between positions where the correction values are stored. As a means for measuring the lightness, a normal reflection original type scanner or a colorimeter such as DTP51 manufactured by X-Rite can be used.

When the lightness L * r is measured at each position where the correction value is set, the average lightness L * ave when the dot area ratio is 50%, that is, the dot area ratio Cin shown in FIG. The correction value α at each position where the lightness L * r is measured can be obtained by the following equation from the comparison between the lightness when the halftone dot area ratio is 50% in the relationship between the lightness L * r and the lightness L *. α = 50 / Cinr (3) That is, from FIG. 4, the halftone dot corresponding to the lightness L * r When the area ratio Cinr is determined and the lightness is larger than the average lightness L * ave, the correction value α is determined so as to increase the dot area ratio in proportion, and when the lightness L * r is smaller than the average lightness L * ave , The correction value α is determined so as to reduce the dot area ratio.

In this embodiment, the correction value is calculated by measuring the density unevenness at the halftone dot area ratio of 50%. However, the correction value may be calculated at another halftone dot area ratio. In this embodiment, the correction value α is calculated from the relationship between the halftone dot area ratio Cin and the lightness L *, but the method of calculating the correction value is not limited to this method.

Next, a description will be given of a result of comparing the density unevenness when the data correction means 32 performs the density unevenness correction and when the density unevenness correction is not performed in the color image output system. The comparison of density unevenness is based on the dot area ratio of each color of YMC 50.
% Process black is output on the entire surface of A3-size paper, and the colorimetric values L * a * b * of any 100 points on the surface are measured, and the average value of the color difference at each point from the averaged value is compared. It was done by doing. As a result, the average color difference when the correction processing of the density unevenness was not performed by the data correction unit 32 was about 6, whereas when the correction processing was performed, the average color difference was about 2 and the density unevenness was greatly improved. However, it has become possible to reduce it to a level that does not cause any problem.

Although the above-described embodiment uses an electrophotographic apparatus as an image output apparatus, the present invention relates to an electrostatic recording system, an ink jet system, and the like.
The present invention can also be applied to a device using a device such as a thermal transfer system.

[0077]

As described above, in the image processing apparatus or the image forming apparatus according to the present invention, the unevenness of the image formed based on the image data can be effectively improved, and the image processing apparatus or the image forming apparatus according to the present invention can improve the unevenness. In addition, it is possible to greatly reduce the capacity of the storage device required to hold the correction value, and to obtain an image at low cost and without density unevenness.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a color image output system including an image processing apparatus or an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram of an image output device used in the system of FIG. 1;

FIG. 3 is a diagram showing an interpolation method in a correction value interpolation unit of the image processing device shown in FIG.

FIG. 4 is a diagram illustrating a method of calculating a correction value in a correction value updating unit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 image input device 20 image forming device 30 image processing device 31 color conversion means 32 data correction means 33 correction value updating means 34 correction value storage means 35 correction value interpolation means 36 correction calculation means 40 image output device 41 visible image 42 sensor 51 Intermediate transfer member 52 Image forming unit 53 Photoreceptor drum 54 Charging device 55 Optical scanning device 56 Developing device 57 Transfer charger 58 Screen generator 59 Support roll 60 Peeling portion roll 61 First heating roll 62 Second heating roll 63 Paper tray 64 feed roll 65 paper feeder 66 pin roll 67 cooling device

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G06T 5/00 100 H04N 1/40 101E 5C077 H04N 1/29 B41J 3/00 A F-term (Reference) 2C262 AA04 AA24 AB05 AB20 AC02 AC05 AC08 BA02 BA09 BB03 BB37 BC10 BC11 BC15 EA04 GA02 GA14 2H027 DA09 DA10 EA18 EB04 EC03 2H030 AA02 AA03 AB02 AD13 AD16 BB02 BB42 5B057 BA02 CA01 CA08 CA12 CA16 CB01 DD16 CEB CB08 DD13 CEB CB08 DD13 CEB HH02 HH04 5C077 LL04 LL17 LL19 MP08 NP05 PP15 PP32 PP33 PP37 PQ12 PQ22 RR19 SS02 TT03

Claims (9)

[Claims] An image data including a position on a two-dimensional coordinate in an image and an image recording signal representing a pixel at the position on the coordinate is input, and necessary for forming a visible image from the image data. An image processing device for performing a conversion and a correction, wherein a correction value for correcting image data is stored for a position on two-dimensional coordinates set at an interval larger than the interval between the pixels arranged two-dimensionally. Correction value storage means; correction value interpolation means for calculating a correction value at a coordinate position other than the set position from the correction values stored in the correction value storage means; An image processing apparatus comprising: a correction operation unit that corrects the input image data using a correction value calculated by the correction value interpolation unit and a correction value calculated by the correction value interpolation unit. 2. The image processing apparatus according to claim 1, further comprising a correction value updating unit that changes a correction value stored in the correction value storage unit to a new value. 3. The correction value storage unit stores a correction value in one direction of two-dimensionally arranged pixels at a position set at the same interval as the pixel interval. 2. The image processing device according to 1. 4. Image data including a position on a two-dimensional coordinate in an image and an image recording signal representing a pixel at the position on the coordinate is input, and is necessary for forming a visible image from the image data. An image processing device that performs a conversion and a correction, and an image output device that outputs a visible image based on image data input from the image processing device. A correction value storage unit for storing a correction value for correcting image data for a position on two-dimensional coordinates set at an interval larger than the pixel interval; and a correction value stored in the correction value storage unit. Correction value interpolation means for calculating a correction value at a coordinate position other than the set position; correction values stored in the correction value storage means; and correction values calculated by the correction value interpolation means. Used, the image forming apparatus characterized by comprising a correction calculation means for correcting the image data to be input. 5. The image output device is formed by an image carrier having a photosensitive layer on an endless peripheral surface, an optical scanning device for irradiating the image carrier with image light, and irradiating the image light. And a developing device for selectively transferring toner to the electrostatic latent image to form a visible image, wherein the correction value is associated with a position on the peripheral surface of the image carrier, and The image forming apparatus according to claim 4, wherein the image forming apparatus is determined based on a density characteristic of a toner image formed at a position on a peripheral surface. 6. The image forming apparatus according to claim 4, further comprising a correction value updating unit that changes a correction value stored in the correction value storage unit to a new value. 7. The correction value updating means measures a state of a toner image formed on the image carrier on the image carrier or on a transferred medium, and determines the state based on the measured value. 7. The image forming apparatus according to claim 6, wherein the determined value is written into the correction value storage unit. 8. The optical scanning device scans a laser beam, and the correction value storage means stores a position set in the main scanning direction and the sub-scanning direction of the laser beam at an interval larger than a pixel interval. The image forming apparatus according to claim 5, wherein a correction value is stored for (c). 9. The optical scanning device according to claim 1, wherein the light-emitting elements are arranged for each pixel in the main scanning direction, and the correction value storage unit is set at the same interval as the pixel interval in the main scanning direction. 6. The image forming apparatus according to claim 5, wherein the correction value is stored for a position that has been set, and the correction value is stored for a position that is set at an interval larger than the pixel interval in the sub-scanning direction.