JP2003127454A - Imaging method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct at a low cost and effectively, shading caused by temperature irregularities of optical members, recording media or heat developing. SOLUTION: The imaging method is provided for forming images by exposing and recording while the recording medium is transferred in a vertical scanning direction orthogonal to a horizontal scanning direction during scanning by a scanning optical system in the horizontal scanning direction. In the imaging method, input image data inputted form an image data supply source is converted to exposure data with the use of characteristic data which shows a relation between exposures to the recoding medium and coloring densities of the recording medium. The correction is carried out by adding shading correction data for every pixel to the input image data converted to the exposure data, and then images are formed by exposing and recording the recording medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and apparatus, and more particularly to a shading correction technique when image processing is performed on input image data and the image data is output from a printer to a predetermined image recording medium.

[0002]

2. Description of the Related Art An original image is photoelectrically read by an image reading device such as a scanner and converted into digital image data.
On the other hand, an image recording apparatus has been widely used in which various kinds of digital image processing are performed to form image data for recording and output to a predetermined image recording medium.

Conventionally, as such an image recording apparatus, an image recording method such as an electrophotographic method, a melt transfer recording method, a sublimation recording method, or an ink jet method has been widely used. In terms of image quality such as reproducibility, image recording using a silver salt photosensitive material is advantageous. However, in image recording using a silver salt light-sensitive material, although a high-quality recorded image can be obtained, usually wet development processing such as development fixing, bleaching, and washing with water is essential. In terms of device management such as replenishment of processing liquid, it takes more labor than dry recording devices.

On the other hand, a heat-developable photosensitive material such as a pictographic photosensitive material manufactured by Fuji Photo Film Co., Ltd. is known as a silver salt photosensitive material which does not require wet development processing. Image recording using this photothermographic material is carried out by imagewise exposing the photothermographic material (donor film) and then applying an image forming solvent such as water to the photothermographic material to form an image receiving layer ( It is laminated with an image receiving material (receiver) having a dye fixing layer), and heat development is performed. By this heat development,
As the photosensitive material is developed to release the mobile dye,
This dye is transferred to the image receiving layer of the image receiving material to form a visible image on the image receiving surface of the image receiving material. After heat development is completed,
The photothermographic material and the image receiving photosensitive material are separated from each other, the image receiving material is output as a hard copy, and the photothermographic material is discarded. According to image recording using this heat-developable photosensitive material, a high-quality image made of a silver salt photosensitive material can be output without performing wet development processing.

By the way, in image recording using such a photothermographic material, color unevenness and density unevenness occur in the scanning direction due to temperature unevenness of a medium for heating for heat development. Because it has so-called shading,
Shading correction is performed to correct this.
For example, in Japanese Laid-Open Patent Publication No. 11-38517, a so-called solid image having a uniform density is formed, and the solid image is measured to calculate a correction coefficient for each image, which is used for shading correction. Shading correction is performed by multiplying the image data as correction data.
Further, by performing predetermined image processing such as correction by calibration on the image data and outputting the image data, shading caused by uneven density of heat development can be prevented and a high-quality image can be recorded stably. Is disclosed.

[0006]

However, in the shading correction method described in the above publication, the shading correction is performed by multiplying the image data by the correction data, but the shading correction is performed by the multiplication. Requires a multiplication in a light amount linear region, and in the light amount linear region, a resolution of 12 bits or more is required in consideration of the density resolution from the characteristics of the modulation device, which causes a problem of cost increase. is there.

Further, since the shading correction method disclosed in the above publication uses the same shading correction data in the sub-scanning direction, when the γ characteristic of the photosensitive material becomes high, the correction data will be changed. There is a problem that density unevenness (steps) is observed in the sub-scanning direction at changing positions. Further, in the shading correction method disclosed in the above publication, the shading amount is measured for each device to create the correction data, so that, for example, the shading of the exposure unit changes in a place such as a market where there is no measuring device. There is also a problem that it cannot be dealt with when the unit is replaced.

The present invention has been made in view of the above-mentioned problems of the prior art, and effectively corrects shading caused by temperature unevenness of an optical member, a recording medium, or heat development at a low cost, resulting in high image quality. An object of the present invention is to provide an image forming method and apparatus capable of realizing image recording.

[0009]

In order to solve the above-mentioned problems, a first aspect of the present invention is to perform recording in a sub-scanning direction orthogonal to the main scanning direction while scanning in the main scanning direction by a scanning optical system. An image forming method for forming an image by carrying out exposure recording while transporting a medium, wherein the input image data input from an image data supply source is related to the exposure amount to the recording medium and the color density of the recording medium. Is converted into exposure amount data using the characteristic data representing the image data, and the input image data converted into the exposure amount data is corrected by adding shading correction data for each pixel, and the recording medium is exposed and recorded. There is provided an image forming method characterized by forming an image by means of an image forming method.

When the input image is a color image, the shading correction data is created for each color,
When performing shading correction for each color, it is preferable to limit the colors for which shading correction is performed. Particularly, it is more preferable to limit the number of colors to be subjected to the shading correction to two colors.

Further, the shading correction data is
It is preferable to change the positions at different positions in the sub-scanning direction.

Further, it is particularly preferable that the changing point of the shading correction data is corrected every predetermined length in the sub-scanning direction.

Further, the shading correction data is
It is preferable that the density of a test chart image created by exposing and recording a predetermined test chart image on the recording medium is measured and created for each pixel.

Further, it is preferable that a plurality of types of the shading correction data are prepared in advance and the shading correction data to be used is selected from the plurality of types of shading correction data according to the image forming system.

Similarly, in order to solve the above problems,
A second aspect of the present invention is an image recording unit that forms an image by performing exposure recording while conveying a recording medium in a sub-scanning direction orthogonal to the main scanning direction while scanning in the main scanning direction by a scanning optical system. And an image input means for inputting image data from an image data supply source, and characteristic data representing the relationship between the exposure amount on the recording medium and the color density of the recording medium, and the image input means. Data conversion means for converting input image data into exposure amount data, and shading correction means for performing correction by adding shading correction data for each pixel to the input image data converted into the exposure amount data , Input image data is converted into exposure amount data, shading correction is performed by adding shading correction data to the logarithmic exposure area, and an image is formed by the image recording unit. To provide an image forming apparatus characterized by.

Further, in the image forming apparatus, further, density measuring means for measuring the density of a predetermined test chart image formed by image-exposure recording on the recording medium by the image recording section, and the measured test. It is preferable to include a correction data creating unit that creates shading correction data for each pixel from the density data of the chart image.

[0017]

DETAILED DESCRIPTION OF THE INVENTION The image forming method and apparatus of the present invention will be described below in detail with reference to the preferred embodiments shown in the accompanying drawings.

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of an image forming apparatus according to the present invention. As shown in FIG. 1, the image forming apparatus 10 of the present embodiment mainly includes an image input unit 12, an image processing unit 14, and an image recording unit 16.

The image input means 12 is not particularly limited, and a scanner that photoelectrically reads image data from a reflective original such as a photographic print or a printed matter or a transparent original such as a negative film or a reversal film by a CCD sensor or the like is preferable. It is illustrated in. Further, the image input means 12
Communication means such as computer communication (including those via a modem), imaging devices such as digital cameras and digital video cameras and built-in memory, image recording media for digital cameras such as PC cards and smart media, FD (flexible disk), Various image data sources such as a general-purpose image recording medium such as MO (magneto-optical recording medium) can be used, and these can be connected to the image processing unit 14 directly or via a driving device thereof. Image processing unit 14
Can receive digital image data from these image data sources.

The image processing section 14 is a section for performing various kinds of image processing on the image data input from the image input means 12 and controlling the entire image forming apparatus 10, and is particularly a feature of the present invention. A certain shading correction is performed. The image processing unit 14 includes a correction data creating unit 22 that creates shading correction data (shading correction LUT) for performing shading correction as shown in the figure, and data conversion that converts input image data that is density data into exposure amount data. It has a means 24 and a shading correction means 26 for performing shading correction on the input image data converted into the exposure amount data. Although not shown, the image processing unit 14 has a processing unit and a control unit for performing predetermined image processing in addition to the above,
In addition, the image processing unit 14 inputs and sets various conditions,
Displays an operation system such as a keyboard and mouse for inputting processing selections and instructions, instructions for color / density correction, etc., input images, various operation instructions, setting / registration screens for various conditions, etc. A display etc. is connected.

The image recording section 16 receives the image data subjected to the image processing from the image processing section 14 and forms an image on a predetermined recording medium. As the image recording unit 16, for example, a recording medium such as photographic paper is irradiated with laser light modulated according to image data input from the image processing unit 14, and an image (latent image) is formed on the recording medium by scanning exposure. There is a so-called laser printer as a light beam scanning type image recording apparatus that forms an image on a recording medium by performing various processes such as color development, bleach-fixing, washing with water, and drying after recording. Further, in addition to this, as the image recording unit 16, an image is exposed on a photosensitive material (donor film) by scanning with a light beam, the photosensitive material on which the image is exposed and the image receiving material are overlapped, and the image receiving material is transferred by heat development transfer. A heat-developable image recording device for forming an image can also be suitably used. In addition to this, the recording medium may be an electrophotographic photosensitive drum or the like.

The image recording unit 16 also outputs a test chart 18 for creating shading correction data (shading correction LUT). Further, a density measuring unit 20 is provided to measure the density of the test chart 18. The density measuring unit 20 includes the image processing unit 14.
The density value of the test chart 18 measured by the density measuring unit 20 is input to the correction data creating unit 22 of the image processing unit 14. The correction data creation unit 22 creates a shading correction LUT as data to be used for shading correction from the density value of the test chart 18 output by the image recording unit 16. The shading correction LUT is a look-up table indicating the shading correction amount corresponding to the main scanning position in the scanning exposure direction of the light beam in the image recording unit 16.

The data conversion means 24 is a characteristic data (first LU which will be described later) showing the relationship between the exposure amount of the recording material for outputting an image from the image recording section 16 and the color density of the recording material.
T) is used to convert the image data input from the image input means 12 from density data to exposure amount data. The shading correction means 26 performs shading correction on the input image data converted into the exposure amount data by the data conversion means 24 using the shading correction LUT.

FIG. 2 shows a basic configuration of shading correction which is a feature of the present invention. As shown in FIG. 2, the basic configuration for performing the shading correction of the present invention comprises three look-up tables. That is, the first LUT 30, which is a look-up table for converting the density data into the exposure amount data, the shading correction LUT 32, which is a look-up table for performing shading correction, and the second LUT 34, which is a look-up table for performing calibration. There are three. The lookup table, the first LUT 30, the shading correction LUT 32, and the second LUT 34 are set for each color.

The first LUT 30 represents characteristic data indicating the relationship between the exposure amount to the recording material and the color density of the recording material, and the data converting means 24 converts the input image signal into a logarithmic exposure amount region. It is a lookup table used at that time. The data conversion means 24 uses the first
Indicates the gradation value of the image to be recorded using the LUT 30 8
The bit image data is converted into 10-bit data corresponding to the exposure amount. In the present embodiment, the first LUT3
0 also serves to correct basic characteristics of the photosensitive material such as gray balance and gradation.

The shading correction LUT 32 is a look-up table showing a shading correction amount (shading correction data) corresponding to the main scanning position. The shading correction LUT 32, which will be described in detail later, measures the density of a gray solid image which is a test chart image for setting shading correction conditions output from the image recording unit 16, and from this measurement data, the density is distributed over all pixels. It is created by calculating a correction coefficient that makes each pixel uniform. At this time, a plurality of points are measured in the main scanning direction, but this set may be carried out at a plurality of positions at the sub scanning position and averaged.

The second LUT 34 converts the logarithmic exposure amount data into a modulation signal and, at the same time, absorbs the variation of the relationship between the logarithmic exposure amount of the recording material and the color density characteristic and the variation of the characteristic of the image recording section 16. It's an up table. The second LUT 34 converts the 10-bit exposure amount data into 12-bit data so as to be output from the image recording unit 16. The second LUT 34, which is this calibration lookup table, uses a characteristic curve representing the conversion characteristic from the logarithmic exposure amount data PD to the modulation signal MQ into a plurality of sections (in accordance with the logarithmic exposure amount corresponding to a plurality of predetermined target densities). i = 1 to N), set linear interpolation coefficients α [i] and β [i] for each section i,
The linear interpolation coefficient α for each section
It is created by using [i] and β [i], and determining by the following equation (1). MQ = 2 ^z (1) However, z = α [i] × PD + β [i]. Also,
Initial values are set in advance for the linear interpolation coefficients α [i] and β [i], and the conversion characteristic of the calibration (the second LUT 34) is initially set by this, but the linear interpolation coefficients α [i], β [i] is appropriately updated by calibration. Ie (calibration)
A test chart image is output, its density is measured, logarithmic exposure amount data required to develop the recording material to a target density is obtained, and the second LUT 34 is updated.

As shown in FIG. 2, in the shading correction according to the present invention, the density data is converted into logarithmic exposure amount data by the first LUT 30, and in the shading correction means 26, the shading correction LUT 32 is shaded in the logarithmic exposure amount region. The correction amount is added, and then the second LUT 34 calibrates and outputs it to the image recording unit 16.

Hereinafter, the reason why the shading correction by the addition (shift) in the logarithmic exposure amount region is possible and preferable is described. An image is recorded on the photosensitive material by two-dimensionally scanning and exposing the photosensitive material that moves in the sub-scanning direction by the light beam deflected in the main scanning direction.
In an image recording apparatus using so-called raster scan, an excessive or insufficient exposure amount (exposure amount deviation) on a scanning line due to a change in reflectance or transmittance of an optical member depending on an incident angle of the light beam, or a light beam on the scanning line Density unevenness, that is, shading occurs due to the exposure amount deviation due to the scanning speed difference.

The shading due to the light amount change (exposure amount deviation) due to the characteristics of the optical member of the exposure system can be corrected by addition / subtraction in the logarithmic exposure amount region or multiplication in the light amount linear region. But in the device,
Since the hypothetical area is assumed, it is important how the relationship with the actual area is. This relationship is defined by the characteristics of the modulation means.

FIG. 3 shows the characteristics when the modulation means is pulse width modulation. Further, FIG. 4 shows characteristics when the modulating means is an AOM (acousto-optic light modulator). In these figures,
Both axes are logarithmic, the horizontal axis is the output of the second LUT 34, and the second LUT 34 gives exponential characteristics. The condition that can be corrected by addition and subtraction in the virtual logarithmic exposure amount region is that the graphs showing the characteristics of the modulation means in these figures are straight lines.

As shown in FIG. 4, when the modulating means is an AOM, the graph showing the characteristic thereof is a straight line, so that it can be corrected by addition and subtraction in the virtual logarithmic exposure amount region. Also,
As shown in FIG. 3, when the modulation means is pulse width modulation,
Although the graph showing the characteristic is not a straight line, it does not pose a problem from the following viewpoints and can be corrected similarly to the case of AOM.

First, in the graph of FIG. 3, the high light amount side above the inflection point indicated by the symbol A is used, and the low light amount side below the inflection point indicated by the symbol B is not used. Designing the sensitive material characteristics to be high γ. Further, as described above, since the second LUT 34, which is the calibration lookup table, is divided into a plurality of sections, for example, 5 to 6 areas, and the exponential characteristic is given,
It should be a straight line within each section. Furthermore, on the low light level side, the characteristic of the sensitive material is low γ, and the density change is small even if there is an error because the graph lays down. From the above, even in the case of pulse width modulation, it is possible to perform correction by addition / subtraction in the logarithmic exposure amount region as well.

Further, as described above, in image recording using a photothermographic material, density unevenness and shading occur due to density distribution (temperature unevenness) of a medium heated for heat development. FIG. 5 shows the change in the density characteristic depending on the heat development temperature. The solid line is the standard temperature, the broken line is -5 ° C.
, And the one-dot chain line shows the case of + 5 ° C. As described above, the temperature and the concentration change have a relationship as shown in FIG. Therefore, according to the correction by the shift in the logarithmic exposure amount region, a correction density error occurs on the high density side, but since the allowable amount of the human eye is large on the high density side, there is no problem, and the low density is low. Since there is little change on the density side, it can be neglected, and even in this case, it can be sufficiently corrected.

Next, a method of creating the shading correction LUT 32, that is, a method of calculating the shading correction data will be described. First, the image recording unit 16 outputs a chart for setting shading correction conditions,
This concentration is measured. The image data of the chart may be the same as the setting of normal shading correction conditions.
Image data (gray solid image) having the same density over all pixels in the main scanning direction may be used. This density measurement is performed by measuring a plurality of points in the main scanning direction, but this set may be performed at a plurality of points in the sub scanning direction and averaged. The gray solid integration density obtained by the measurement is converted into the analysis density of each color material (CMY). Since the control in image recording is performed with the exposure amount corresponding to each color material,
This is because it is necessary to determine the density change of each color material alone.
Therefore, if the density of each solid image of each color is measured as a chart instead of the gray solid, this operation is unnecessary.

When converting the color material (CMY) into analytical density,
Since the spectral absorption of color materials is accompanied by sub-absorption on the short-wave side, the observed amount of each RGB sensor does not correspond one-to-one with each of CMY color materials. Also needs to be removed. Therefore, the analysis density is obtained by performing these conversions. A primary matrix represented by the following equation (2) is used to calculate the analytical concentration. C = 0.95Cg-0.02Mg-0.01Yg + 0.05 M = -0.08Cg + 1.01Mg-0.01Yg-0.02 Y = -0.07Cg-0.10Mg + 1.05Yg-0.01 ... (2) Since this is a conversion in a limited color space near the middle density gray, the accuracy is sufficient with the primary matrix. This matrix measures the density of single-layer color development with the same light amount as multiple gray patches, where the exposure amount was changed near gray,
It can be decided experimentally.

Next, the density difference (δC, δM, δ) from the reference correction position (C0, M0, Y0) is calculated by the following equation (3).
Y) is calculated. FIG. 6 shows the density difference data from the calculated reference correction position. The density difference data may be calculated before the conversion using the primary matrix.

Next, the analytical density is divided by γ of the photosensitive material to obtain the corrected logarithmic exposure amounts δLogEc, δLogEm, δLogEy by the following equation (4). δLogEc = −δC / γc + Sc δLogEm = −δM / γm + Sm δLogEy = −δY / γy + Sy (4) where Sc, Sm, and Sy are corrected logarithmic exposure amounts, respectively. This constant can be omitted if the reference is set to the lowest density position when obtaining the density difference from the reference correction position. Further, as will be described later, the offset amount due to Sc, Sm, and Sy is absorbed by adding the shading correction at the time of calibration.

Finally, by performing smoothing on the basis of the corrected logarithmic exposure amount in FIG. 6 and converting the horizontal axis into the pixel position in the main scanning direction, shading correction (for each color CMY) as shown in FIG. The LUT 32 is created. Since the shading due to the optical members and the thermal development is a smooth change, the shading correction LUT 32 is created by smoothing and converting the shading into the correction amount range digit. Note that the smoothing may be performed earlier than here.

As described above, the shading correction LUT 32 is used to add the shading correction amount data to the image input signal converted from the density data to the logarithmic exposure amount data by the first LUT 30, and then the second LUT 34 is used.
According to the above, the calibration is performed. The relationship between the shading correction and the calibration will be described.
The simplest way to prevent shading correction from affecting calibration is to place patches for density measurement at the same main scanning position when creating a calibration lookup table. By doing so, all patches have the same shading correction amount, so the calibration result is not affected.

However, if such an arrangement is difficult, consideration is required. In the calibration, as described above, for the virtual logarithmic exposure amount data,
A calibration look-up table (second LUT 34) is determined so that the target log density is determined, the density of the test chart is measured, and the virtual logarithmic exposure data becomes the target density. a) to (c)
Follow the procedure below. (A) Virtual logarithmic exposure amount data is defined by data before shading correction. (B) The calibration test chart is printed after performing shading correction. (C) The second LUT 34 is calculated assuming that there is no calibration correction. That is, when the calibration test chart is printed, the shading correction data is printed, and when the calibration calculation is performed thereafter, the calculation is performed based on the data before the shading correction. This is because if this is not done, there may be cases where the sickness will not be met.

As described above, the output image data obtained by performing the calibration after adding the shading correction data in the logarithmic exposure amount area is output as a print from the image recording unit 16, and a high quality image is obtained. It is formed. As described above, in the present embodiment, addition (shift) of shading correction amount data in the logarithmic exposure amount region
Since the shading correction is carried out by, it is well suited for shading caused by optical members and thermal development. Further, since the correction is performed by the shift calculation, the number of bits can be reduced, and the cost can be reduced.

In the above-described embodiment, each color (CM
Although the shading correction is performed for each Y), as another example, the colors to be corrected may be limited. That is, since the shading correction has a narrower tolerance of the tint change than the density change, a sufficient effect can be obtained by correcting only the tint change. Therefore, for example, by correcting only two colors, the cost can be reduced. Can be planned. At this time, it suffices to select a color having a large change. Further, when there is no difference in the degree of change between the colors, C and M that have a large contribution to the lightness may be selected.

For example, when the density difference data is as shown in FIG. 6, C and Y, which have a larger change than M, are selected.
For C and Y, the deviation from δM is calculated by the following equation (5) in addition to the matrix conversion by the equation (2) and the density difference calculation by the equation (3). δC '= δC-δM δY' = δY-δM (5)

After that, the same calculation as in the above equation (4) is performed for only C and Y to obtain the corrected logarithmic exposure amount, and then smoothing is performed, and the horizontal axis is converted into the pixel position to obtain the shading correction LUT 32. create. With this shading correction LUT 32, shading correction is performed only for C and Y. At this time, of course, only one color having a large change or a hue (M-G
The shading correction may be performed only in the direction (that is, only in M). By limiting the colors to be corrected in this way, it is possible to reduce the number of tables and reduce the cost.

Further, as shown in FIG. 8A, when the shading correction is performed in the main scanning direction S1 and the same correction is continuously performed in the sub-scanning direction S2, the shading correction as indicated by the symbol C is obtained. Steps may be observed. The degree of such stepped C depends on γ of the photosensitive material and the resolution of the logarithmic exposure amount region for shading correction.
Although this region has a higher resolution than the input signal (8 bits) to the printer, for example, γ of the linear portion of the photosensitive material characteristic is set to 3, the logarithmic exposure amount region is 10 bits, and the dynamic range is LogE = 2. If you do, 1 digit of this area
The concentration change per t is (2/1024) × 3 = 0.00
6, which is the amount visually recognized as uneven density by the silver salt printer with less grain. Although it can be solved by using 12 bits, naturally, the output of the second LUT 34 requires a larger number of bits, resulting in an increase in cost.

In order to avoid this, the data change point of the shading correction LUT 32 is corrected for each certain length in the sub-scanning direction S2. That is, as shown in FIG.
In order to prevent stepping due to shading correction from appearing in the sub-scanning direction S2, the data change point of shading correction is changed little by little for each length in the sub-scanning direction S2, and "fluctuation"
To give. At this time, if the “fluctuation” is made too large, as shown in FIG.
May cause unevenness in the same degree as in the sub-scanning direction S2.
Naturally, if the "fluctuation" is too large, the effect of shading correction becomes weak. Therefore, the width of the "fluctuation" cannot be made too large. The maximum value of the "fluctuation" in the main scanning direction S1 and the sub-scanning direction S2 shown in FIG. 8B is about the same, and is preferably 1 cm or less, for example.

As a method of giving "fluctuation", for example,
Random shift of the input position of the shading correction LUT 32 at random intervals of a certain sub-scan by setting the pixel position to y, a and b as predetermined constants and the input to the shading correction LUT 32 as a · y + b. Alternatively, an inclination may be added, or
A random number may be added to the output value of the shading correction LUT 32 at about ± 1 digit for each random sub-scanning interval. Or, although the degree of the effect is reduced, the image data itself is ± 1 dig in the logarithmic exposure amount region.
A random number of about it may be given. However, in this case, there is a slight graininess. Alternatively, a plurality of shading correction data may be prepared in advance, and appropriate shading correction data may be selected and used from among them at different sub-scanning positions to add fluctuation. In this way, by adding fluctuation to the correction, it is possible to avoid the occurrence of unevenness due to shading correction.

Further, the shading is determined by the characteristics of the optical member and the characteristics of the heat developing portion, but since a considerable part of these is determined by the design, the difference in strength varies, but the directionality of shading, etc. Often does not vary much. Therefore, as another example, a plurality of shading correction LUTs may be registered in advance and selected from among them to be used. In this way, if a plurality of shading correction LUTs are set in advance (for example, at the time of product shipment) in advance, when a unit such as an exposure unit where shading changes is replaced in a place such as a market where there is no measurement device, Is valid.

The shading correction LUT may be registered only in an assumed pattern, and an intensity coefficient may be separately provided. Further, for example, as shown in FIG. 9, the pattern is also corrected by the correction pattern generator 40 as a function of P1, P2, and P.
Shading correction LU
It may be set to T32. At this time, by switching the shading correction LUT 32 in the test mode,
It is also possible to print on one sheet, evaluate this, and indicate the shading correction LUT 32 to be selected. As described above, when the shading correction LUT is registered in advance and selected and used, there is an advantage that it is not necessary to individually measure the density of the test chart.

Although the image forming method and apparatus of the present invention have been described above in detail, the present invention is not limited to the above-described embodiments, and various improvements and modifications can be made without departing from the scope of the present invention. Of course, you can make changes. For example, in the above-described embodiment, the shading correction is performed only in the main scanning direction, but the shading correction may be performed also in the sub scanning direction to perform two-dimensional correction. Further, the shading measurement may be performed by the light amount of an optical unit such as ROS (raster optical system) instead of printing.

[0052]

As described above, according to the present invention, since shading correction is performed by addition (shift) in the logarithmic exposure amount region, even shading caused by an optical member or thermal development is well suited. Since it can be corrected with a small number of bits, the cost is low. Further, if the number of colors for correction is limited, the cost can be reduced, and if fluctuation is added to the correction, unevenness due to shading correction can be avoided. When the LUT is registered, selected and used, it is not necessary to measure the density of the test chart one by one, and the shading correction can be efficiently performed.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a basic configuration of shading correction which is a feature of the present invention.

FIG. 3 is a diagram showing characteristics when the modulation means is pulse width modulation.

FIG. 4 is a diagram showing characteristics when the modulation means is an AOM.

FIG. 5 is a diagram showing changes in density characteristics depending on heat development temperature.

FIG. 6 is a graph showing density difference data from a reference correction position.

FIG. 7 is a graph (shading correction LUT) showing a shading correction amount for each color.

8A is an explanatory diagram showing a step due to shading correction, and FIG. 8B is an explanatory diagram showing a state in which fluctuation is added to the shading correction.

FIG. 9 is an explanatory diagram showing a state of previously providing a plurality of shading correction LUTs.

[Explanation of symbols]

10 image forming apparatus 12 Image input means 14 Image processing unit 16 Image recording section 18 test chart 20 Concentration measuring means 22 Correction data creation means 24 Data conversion means 26 Shading correction means 30 First LUT 32 Shading correction LUT 34 Second LUT 40 Correction pattern generator

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) H04N 1/401 H04N 1/46 Z 5C079 1/46 B41J 3/00 B 1/60 H04N 1/40 D F term (reference) 2C061 KK18 KK25 KK26 2C262 BB03 BB15 BB18 BB21 BB29 BB30 BB31 BB33 BB34 BB38 BB42 BC01 BC17 EA06 EA11 EA12 EA13 EA14 FA13 2C362 AA41 AA46 CA10 CA11 CA14 CA18 CA24 CB47 CB73 CB80 5C074 AA08 BB17 DD01 EE02 EE08 EE11 FF16 5C077 LL04 MM27 MP01 MP08 PP06 PP33 PQ08 PQ23 SS02 TT03 5C079 HB02 KA08 LA19 LA31 MA04 MA10 NA25 PA03

Claims (9)

[Claims] 1. An image forming method for forming an image by performing exposure recording while conveying a recording medium in a sub-scanning direction orthogonal to the main scanning direction while scanning in the main scanning direction by a scanning optical system, Input image data input from an image data supply source is converted into exposure amount data using characteristic data representing the relationship between the exposure amount to the recording medium and the color density of the recording medium, and converted to the exposure amount data. An image forming method, comprising: adding shading correction data for each pixel to the input image data for correction, and exposing and recording the recording medium to form an image. 2. The shading correction data is created for each color when the input image is a color image, and when the shading correction is performed for each color, the colors to be subjected to the shading correction are limited. The image forming method described. 3. The image forming method according to claim 2, wherein the number of colors for which the shading correction is performed is limited to two. 4. The shading correction data is changed at different positions in the sub-scanning direction.
The image forming method according to any one of 3 above. 5. The image forming method according to claim 4, wherein the changing point of the shading correction data is corrected every predetermined length in the sub-scanning direction. 6. The shading correction data is created for each pixel by measuring the density of a test chart image created by exposing and recording a predetermined test chart image on the recording medium. 6. The image forming method according to any one of 5 above. 7. A plurality of types of shading correction data are prepared in advance, and the shading correction data to be used is selected from the plurality of types of shading correction data according to an image forming system.
6. The image forming method according to any one of 5 to 5. 8. An image recording section for forming an image by performing exposure recording while conveying a recording medium in a sub-scanning direction orthogonal to the main scanning direction while scanning in the main scanning direction by a scanning optical system, and image data. Image input means for inputting image data from a supply source, and characteristic data representing the relationship between the exposure amount on the recording medium and the color density of the recording medium are used to input image data input from the image input means. The input image data includes data conversion means for converting the exposure amount data, and shading correction means for performing correction by adding shading correction data for each pixel to the input image data converted into the exposure amount data. Is converted into exposure amount data, shading correction is performed by adding the shading correction data to the logarithmic exposure area, and image formation is performed by the image recording unit. A characteristic image forming apparatus. 9. In the image forming apparatus, further, density measuring means for measuring the density of a predetermined test chart image which is image-formed by exposure recording on the recording medium by the image recording section, and the measured test. The image forming apparatus according to claim 8, further comprising a correction data creating unit that creates shading correction data for each pixel from the density data of the chart image.