JP2006211052A - Image processor, image processing method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct density unevenness without requiring a large-sized memory. <P>SOLUTION: The image processor 10 includes an image acquisition 11 for acquiring a test image, in which uneven correction positions of an image are shown, from an image input device 20, an image storage 12 for storing the acquired test image, an arrangement position deciding part 13 for deciding arrangement positions of LUTs on the basis of the correction positions shown in the test image, an arrangement position storage 14 for storing the decided arrangement positions, an LUT generator 15 for generating the LUTs as a conversion table respectively arranged to the decided arrangement positions, an LUT storage 16 for storing the generated LUTs, and a converter 17 which converts an image signal input from the image input device 20 by referring to the LUTs and outputs it to an image forming device 30. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus that performs processing for improving in-plane density and color non-uniformity of an output image.

  2. Description of the Related Art In recent years, image forming apparatuses such as printers that perform image formation by an electrophotographic method have become widespread. In this electrophotographic system, an electrostatic latent image is written by performing exposure after uniformly charging the photoconductor, and developing the electrostatic latent image with a developing device of a corresponding color, whereby toner is formed on the photoconductor. Form an image. Then, the toner image is primarily transferred to the intermediate transfer belt, and then the image is formed by secondary transfer from the intermediate transfer belt to the recording material.

As described above, since the electrophotographic method employs a complicated image forming process, there is a problem that the in-plane density and color uniformity of the output image are inferior to those of offset printing or the like.
Hereinafter, the cause of such a problem will be described.
For example, when paying attention to the photosensitive member, it is difficult to apply a photosensitive material having a uniform film thickness. Therefore, the charging property and photosensitivity of the photosensitive member generally vary depending on the position in the plane. Therefore, even if charging and exposure are performed uniformly, it is difficult to form a uniform electrostatic latent image.
It is also difficult to configure the mechanism to uniformly charge, expose and develop the photoreceptor. As for charging, if the distance between the charger and the photosensitive member is not constant, charging cannot be performed uniformly. As for exposure, when laser light is used, the potential on the photoconductor becomes uneven due to the positional accuracy of the exposure device and the photoconductor. As for development, if the distance between the developing roll and the photoconductor is not constant, the amount of toner adhering to the photoconductor will vary.
On the other hand, when paying attention to the intermediate transfer belt, the volume resistivity is usually not uniform over the entire circumference of the belt, and it is inevitable that the density varies depending on the position in the surface.

  Therefore, in view of such a problem that the in-plane density and color of the output image become non-uniform, in the image processing apparatus that processes the image input from the image input apparatus and outputs the processed image to the image forming apparatus, the laser scanning direction There has been proposed a method for converting such an image signal using position information such as the position X in the (main scanning direction) and the position Y in the rotation direction (paper feeding direction) of the photoconductor and the like to improve such nonuniformity. (For example, refer to Patent Document 1).

JP 2002-135610 A (Pages 8-10, FIGS. 3, 4)

However, the method of Patent Document 1 stores a lookup table (hereinafter referred to as “LUT”) that is referred to when converting an image signal, even if the in-plane non-uniformity problem is solved. There is a problem that a very large memory is required.
When correcting streak-like density unevenness, a resolution that can correct the streak portion using four LUTs is ideal. For example, in the case of stripe-shaped density unevenness having a width of 24 mm, it is desirable to provide one LUT for 6 mm. Therefore, if streaky density irregularities having a width of 24 mm extend in the longitudinal direction on A3 size paper, it is necessary to provide about 50 LUTs in the short direction (about 300 mm) of the paper. Become. That is, when the density unevenness is not corrected, about 50 LUTs, which are one, are required, and thus a memory size of about 50 times is required. Further, when correcting the longitudinal direction of the paper (about 420 mm), a total of about 3500 (= 50 × 70) times as much memory is required.

  The present invention has been made to solve the technical problems as described above, and its purpose is to correct streaky density unevenness requiring high resolution without requiring a large-sized memory. There is to be able to do it.

  For this purpose, in the present invention, the conversion table is arranged at the recording position coordinates in accordance with the input of the specific recording position coordinates to be corrected. That is, the image processing apparatus according to the present invention includes: a receiving unit that receives information about a specific recording position coordinate to be corrected among the recording position coordinates indicating a position where an image is recorded on the medium; and a specific recording position coordinate. Arrangement means for arranging a conversion table used for converting an image signal at recording position coordinates determined based on the conversion table, and a conversion table in which the first image signal at each recording position coordinate is arranged at each recording position coordinate And converting means for converting to a second image signal.

  Here, conversion tables can be arranged with high resolution for specific recording position coordinates to be corrected, and conversion tables can be arranged sparsely for other recording position coordinates. That is, the accepting means accepts information for identifying the first area where the image non-uniformity on the medium is to be corrected and the second area other than that as the information related to the specific recording position coordinates. The conversion table arranged at each recording position coordinate corresponding to each point in one area is made denser than the conversion table arranged at each recording position coordinate corresponding to each point in the second area. It is also possible to adopt a configuration of arranging.

  In the present invention, the conversion table can also be regarded as a method for arranging the conversion table at the recording position coordinates in accordance with the input of the specific recording position coordinates to be corrected. In that case, the image processing method according to the present invention includes a step of receiving information regarding a specific recording position coordinate to which the image is to be corrected among the recording position coordinates indicating the position where the image is recorded on the medium, and the specific recording position coordinate. A step of arranging a conversion table used for converting the image signal at the recording position coordinates determined based on the image, a first image signal at each recording position coordinate, the recording position coordinates, the conversion table, and the conversion And converting to a second image signal based on the recording position coordinates on which the table is arranged.

  On the other hand, the present invention can also be understood as a program for realizing a predetermined function in a computer. In this case, the program of the present invention has a function of receiving information on a specific recording position coordinate for correcting the image among the recording position coordinates indicating the position at which the image is recorded on the medium, and the specific recording position coordinate. A function of arranging a conversion table used for converting an image signal at a recording position coordinate determined based on the first image signal at each recording position coordinate, each recording position coordinate, a conversion table, This is for realizing the function of converting to the second image signal based on the recording position coordinates where the conversion table is arranged.

  According to the present invention, streaky density unevenness requiring high resolution can be corrected without requiring a large-sized memory.

The best mode for carrying out the present invention (hereinafter referred to as “embodiment”) will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing the overall configuration of a system to which the present embodiment is applied.
As shown in FIG. 1, the system includes an image processing device 10, an image input device 20, and an image forming device 30.
Here, the image input device 20 is, for example, a scanner or a personal computer (hereinafter referred to as “PC”) connected via a network, and is a device for inputting an image as a source of image formation.
The image forming apparatus 30 is an apparatus for receiving an image subjected to image processing by the image processing apparatus 10 and forming an image on a predetermined recording medium by an electrophotographic method. Specifically, although not shown, a photoconductor, a charger, an exposure device, a developing device, an intermediate transfer member, and the like are provided. In such a configuration, the charger uniformly charges the photosensitive member, and the exposure unit performs exposure according to the image received from the image processing apparatus 10 to form an electrostatic latent image, and the developing unit sets the static image. The electrostatic latent image is developed with a corresponding color developer to form a toner image on the photoreceptor. Then, the toner image is primarily transferred to the intermediate transfer member, and then secondarily transferred from the intermediate transfer member to the recording medium, thereby forming an image.
However, the configuration illustrated in FIG. 1 is merely an example, and the image processing apparatus 10 may be realized as a part of the image forming apparatus 30, or a PC is assumed as the image input apparatus 20. It may be realized as a part of the PC.

The image processing apparatus 10 includes an image acquisition unit 11, an image storage unit 12, an arrangement position determination unit 13, an arrangement position storage unit 14, an LUT generation unit 15, an LUT storage unit 16, and a conversion unit 17. It has.
The image acquisition unit 11 has a function of acquiring from the image input device 20 a test image indicating a non-uniform correction position of the image, and the image storage unit 12 is a memory for storing the acquired test image. It is a part of. The arrangement position determination unit 13 has a function of determining the arrangement position of the LUT based on the correction position indicated in the test image, and the arrangement position storage unit 14 is a memory for storing the determined arrangement position. It is a part of. Here, the arrangement position means associating the LUT with the position or partial area in the image. The LUT generation unit 15 is a part that generates an LUT that is a conversion table arranged at each determined arrangement position, and the LUT storage unit 16 is a part as a memory that stores the generated LUT. Note that the arrangement position determination unit 13 and the LUT generation unit 15 may be combined and understood as “arrangement means”.
On the other hand, the conversion unit 17 has a function of converting the image signal input from the image input device 20 with reference to the LUT and outputting the converted signal to the image forming device 30.
Each of these functions can be realized only by hardware, but can also be realized by a combination of hardware and software. In the latter case, each functional unit is realized by a CPU (not shown) of the image processing apparatus 10 reading and executing a program stored in a memory (not shown), for example.

Next, the operation of the image processing apparatus 10 having such a functional configuration will be described.
In the present embodiment, first, a test image is output by the image forming apparatus 30. Here, it is assumed that a test image is output on A3 size paper. Then, it is assumed that the user writes a mark indicating a section where density unevenness exists in this test image. An example of a test image in which marks are written in this way is shown in FIG. If the origin (O), the X axis, and the Y axis are set as shown in the figure, there are uneven density in 40 ≦ X <80 and 240 ≦ X <290, so that X = 40, 80, Marks are written at positions 240 and 290.
In this embodiment, the density unevenness is uniform in the Y direction. That is, only the LUT arrangement in the X direction is considered here.
Then, by inputting such a test image to the image input device 20, the operation of the present embodiment starts.

When a test image is input to the image input device 20, in the image processing device 10, the image acquisition unit 11 acquires the test image and stores it in the image storage unit 12. It should be noted that the operation of whether the conversion unit 17 receives the information passed from the image input device 20 or the image acquisition unit 11 can be switched, for example, by switching the operation mode.
Under such circumstances, the arrangement position determining unit 13 determines the X coordinate of the position where the LUT is to be arranged.

The operation in that case will be described with reference to FIG.
In the present embodiment, prior to the operation, a parameter K indicating how many times the LUT is arranged other than the correction section with respect to the section indicated by the mark on the test image (hereinafter referred to as “correction section”). Is set in advance. In addition, as the LUT, the value of N when the LUT (0), LUT (1), LUT (2),..., LUT (N) are arranged is also set.

First, the arrangement position determination unit 13 defines the following function W (X) indicating a weight value indicating the density at which the LUT is arranged for each X position (step 101).
W (X) = 1 (When X does not exist in the correction section)
W (X) = K (when X is in the correction section)

For example, as shown in FIG. 2, assuming that 40 ≦ X <80 and 240 ≦ X <290 are correction intervals, and K = 5, the following function is defined.
W (X) = 1 (0 ≦ X <40, 80 ≦ X <240, 290 ≦ X ≦ 300)
W (X) = 5 (40 ≦ X <80, 240 ≦ X <290)
This is shown by a graph in FIG.

Next, the arrangement position determination unit 13 obtains a function SUM (X) indicating a cumulative value for a section from 0 to X of the function W (X) (step 102). Specifically, the function W (X) is integrated with respect to X. At that time, adjustment is performed so that the maximum value of SUM (X) becomes equal to N. That is, SUM (X) is a function as follows.
SUM (X) = (X + C ₁ ) × (N / MAX) (when X does not exist in the correction section)
SUM (X) = (KX + C ₂ ) × (N / MAX) (when X is in the correction section)
However, MAX represents the maximum value of SUM (X) before adjustment. C ₁ and C ₂ are integral constants, and are defined so that SUM (X) is a continuous function over the entire interval.

For example, assume that the function shown in FIG. 4A is integrated and the integration constant is determined so that the function obtained by the integration becomes a continuous function over the entire interval. Then, the function SUM ′ (X) obtained here is as follows.
SUM '(X) = X (0 ≦ X <40)
SUM ′ (X) = 5X−160 (40 ≦ X <80)
SUM ′ (X) = X + 160 (80 ≦ X <240)
SUM ′ (X) = 5X−800 (240 ≦ X <290)
SUM '(X) = X + 360 (290 ≦ X ≦ 300)

Since MAX = 660, when N = 20, SUM (X) is as follows.
SUM (X) = X / 33 (0 ≦ X <40)
SUM (X) = (5X−160) / 33 (40 ≦ X <80)
SUM (X) = (X + 160) / 33 (80 ≦ X <240)
SUM (X) = (5X−800) / 33 (240 ≦ X <290)
SUM (X) = (X + 360) / 33 (290 ≦ X ≦ 300)
This is shown by a graph in FIG.

Next, the arrangement position determination unit 13 sets 0 to the index i representing the LUT number (step 103). Then, X satisfying SUM (X) = i is set as the arrangement position of the i-th LUT, and this is set as x (i) (step 104). Further, 1 is added to i (step 105), and it is determined whether i exceeds N (step 106). As a result, if i does not exceed N, the processes of steps 104 and 105 are repeated.
In the above-described example, this processing causes x (0) = 0, x (1) = 33.0, x (2) = 45.2, X (3) = 51.8, x (4) = 58. 4, x (5) = 65.0. Similarly, x (6), x (7),..., X (20) can be obtained.

  On the other hand, if i exceeds N, the arrangement position determination unit 13 stores the correspondence between all i and x (i) in the arrangement position storage unit 14 (step 107). In the case of the above-described example, the correspondence relationship as illustrated in FIG. 5 is stored in the arrangement position storage unit 14.

  Next, an LUT that is arranged at the arrangement position thus obtained is generated. The LUT stores values that are converted to the same density for the same signal based on the tone reproduction characteristics. More specifically, the input signal is corrected to a signal that can output the density that should be output by the input signal (hereinafter referred to as “target density”), and the input signal is used as an input value to obtain a corrected signal. Is stored as an output value.

The operation in that case will be described with reference to FIG.
In the present embodiment, for the input signals from the first stage to the M-th stage, the correspondence between the input signal and the corrected signal is stored in the LUT. In the following description, the j-th stage input signal is denoted as S (j).
First, the LUT generation unit 15 sets 0 to the index i indicating the LUT number (step 201), and sets 1 to the index j indicating the stage of the input signal (step 202). Then, an input signal Si (j) for obtaining a target density for the input signal S (j) at x (i) is obtained (step 203). Next, 1 is added to j (step 204), and it is determined whether j exceeds the number of signal stages M (step 205). As a result, if j does not exceed the number of signal stages M, the processes of steps 203 and 204 are repeated.
On the other hand, if j exceeds the number of signal stages M, the correspondence between S (j) and Si (j) for all j is stored in the LUT storage unit 16 as LUT (i).
For example, if N is 20 as in the example described above, 21 LUTs having the contents shown in FIG. 7 are generated.

Here, a specific example of how to determine an input value and an output value in the LUT will be described in detail.
First, in this specific example, as shown in FIG. 2, a test image is prepared in which a band of an image parallel to the X axis by the same signal is output for several stages of signals. FIG. 8 shows a portion of such a test image with a percentage of the amount of input signal. In this specific example, as shown in FIG. 8A, the input signals for j = 1, 2, 3, 4, 5, 6 are respectively 100%, 80%, 60%, 40%, 20%, 10%. Further, when the density unevenness does not occur, the density of the image output by these signals is as shown in FIG. That is, the image output by the 100% input signal has the highest density, the image output by the 80% input signal has the next density, and the image output by the 60% input signal is the next. The image output by the 40% input signal becomes the density of the next stage, the image output by the 20% input signal becomes the density of the next stage, and by the 10% input signal. The output image has the lowest density.

Here, consider a certain i. FIG. 9 shows the change in density on the test image due to the input signal at x (i) corresponding to i and the change in target density with respect to the input signal. Here, the target density may be any technique as long as it is a technique for obtaining the density that should be output by each input signal. For example, an average value of the density output by each signal in the test image is obtained. Can be adopted.
Then, based on such a change in density with respect to the input signal, it is possible to determine what value the input signal should have in order to obtain a target density for a certain input signal.
For example, FIG. 9A shows that the input signal needs to be 35% in order to obtain the target density at the input signal 20%. FIG. 9B shows that the input signal needs to be 53% in order to obtain the target density at the input signal 40%. Further, FIG. 9C shows that the input signal needs to be 72% in order to obtain the target density at the input signal 60%.

Similarly, it can be seen that the input signals need to be 22% and 95% for the input signals of 10% and 80%, respectively. According to the graph of FIG. 9, the input signal for obtaining the target density at 100% of the input signal exceeds 100%, but 100% is the maximum, so this is set to 100%.
As described above, the LUT (i) is generated with the input signal as an input value and the corrected signal for obtaining a target density in the input signal as an output value. FIG. 10 shows this LUT (i).

Next, the operation of the conversion unit 17 that converts the image signal DataIN into the image signal DataOUT using the LUT generated in this way will be described with reference to FIG.
First, an image signal DataIN and a coordinate signal x indicating which recording position coordinate the image signal is input to the image processing apparatus 10 of FIG. 1 from the image input apparatus 20 of FIG.
At this time, unlike the case of LUT generation using a test image, the normal operation mode is set, so the conversion unit 17 acquires the image signal DataIN and the coordinate signal x.
Then, in the conversion unit 17, the comparator 17 a determines whether the value of x is located between the X coordinate corresponding to what number and what number LUT. If the value of x is between x (i) corresponding to LUT (i) and x (i + 1) corresponding to LUT (i + 1), the output for DataIN in LUT (i) and LUT (i + 1) Are data1 and data2, respectively, the linear interpolation circuit 17b performs linear interpolation of “(Data2−Data1) / (x (i + 1) −x (i)) × (x−x (i)) + Data1”. And outputs the result as DataOUT.

Here, this operation will be described using the specific example described above.
For example, if x = 100, since x exists between x (7) and x (8), the image signal is converted using LUT (7) and LUT (8). Assuming that the output value for the input value 60 is 58 in the LUT (7) and the output value for the input value 60 is 62 in the LUT (8), the input signal 60 is “(62−58) / (104.0”. −78.2) × (100−78.2) +58 ”, and as a result, a signal 61.38 is output.

Finally, the effects brought about by this embodiment will be described in comparison with the prior art.
FIG. 12 shows an arrangement of LUTs for correcting in-plane density unevenness. In the present embodiment, as shown in FIG. 12A, the LUT is applied with high resolution (about 6 mm) to the portion that the user wants to correct, and the LUT is sparsely applied to other portions. On the other hand, in the prior art, when correction is performed with the same resolution, as shown in FIG. 12B, LUTs are applied at intervals of 6 mm over the entire width of the paper to convert the image signal.
That is, in the present embodiment, the number of LUTs to be arranged is reduced, and the necessary memory amount can be reduced. In the example shown in FIG. 12, it was able to reduce to about 40% (60% reduction) compared with the prior art.

In the present embodiment, in order to simplify the description, the case where the black density unevenness is corrected and the case where the LUT is arranged in the X direction have been described. However, the method of the present embodiment can be applied to the color image and also to the arrangement of the LUT in the XY coordinates.
In the present embodiment, the position where the density unevenness is to be corrected is specified by writing a mark in the test image. However, any other method may be used. For example, an output image may be displayed on the screen, and a correction position may be designated on the screen. Here, the mark designating the correction position indicates both ends of the correction section, but it may be a mark directly indicating the correction section.

Further, in the present embodiment, the arrangement position of each LUT is made to correspond to the coordinate point in the image, but each LUT may be made to correspond to the area in the image, and the image signal in the area may be converted.
In addition, each LUT may use the same LUT, and in determining the arrangement position, the type of LUT may be associated with a coordinate point or region in the image.
In the present embodiment, the values converted by using a plurality of LUTs arranged in the vicinity of each recording position coordinate are interpolated based on the positional relationship between the recording position coordinates and the arrangement coordinate points of each LUT. In this case, a new LUT is generated from a plurality of LUTs arranged in the vicinity of each recording position coordinate based on the positional relationship between the recording position coordinates and the arrangement coordinate points of each LUT, and the image signal is converted. May be.
Furthermore, in this embodiment, the LUT is arranged outside the designated area. However, by setting the weight outside the designated area to 0 in FIG. 4A, the LUT is not arranged outside the designated area. Also good. In addition, the weight of FIG. 4A can be designated for each designated area in accordance with an instruction from the operator, and the density of the LUTs arranged according to the degree of density unevenness may be adjusted.

  Thus, in this embodiment, the density of the LUT arrangement is determined according to the user's will. As a result, LUTs can be placed with high resolution at locations where correction of streaky density unevenness, etc. is desired, and with low resolution at other locations, and images with uniform density can be reproduced without increasing the memory size. can do.

1 is a diagram showing an overall configuration of a system to which an embodiment of the present invention is applied. It is the figure which showed an example of the test image used by embodiment of this invention. It is the flowchart which showed the operation | movement of the arrangement position determination part in the image processing apparatus of embodiment of this invention. It is a figure for demonstrating the determination method of the arrangement position in the image processing apparatus of embodiment of this invention. It is the figure which showed an example of the arrangement position memorize | stored in the arrangement position memory | storage part in the image processing apparatus of embodiment of this invention. It is the flowchart which showed operation | movement of the LUT production | generation part in the image processing apparatus of embodiment of this invention. It is the figure which showed an example of the LUT memorize | stored in the LUT memory | storage part in the image processing apparatus of embodiment of this invention. It is a figure explaining the test image used in embodiment of this invention in detail. It is a figure for demonstrating the production | generation method of LUT in the image processing apparatus of embodiment of this invention. It is the figure which showed an example of the LUT produced | generated by the LUT production | generation part in the image processing apparatus of embodiment of this invention. It is the figure which showed the more detailed structure of the conversion part in the image processing apparatus of embodiment of this invention. It is a figure for demonstrating the effect brought about by this invention in contrast with a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image processing apparatus, 11 ... Image acquisition part, 12 ... Image memory | storage part, 13 ... Arrangement position determination part, 14 ... Arrangement position memory | storage part, 15 ... LUT production | generation part, 16 ... LUT memory | storage part, 17 ... Conversion part, 17a ... Comparator, 17b ... Linear interpolation circuit, 20 ... Image input device, 30 ... Image forming device

Claims (6)

Receiving means for receiving information on a specific recording position coordinate for correcting the image among recording position coordinates indicating a position for recording the image on the medium;
Arranging means for arranging a conversion table used for converting an image signal at recording position coordinates determined based on the specific recording position coordinates;
An image processing apparatus comprising: conversion means for converting the first image signal at each recording position coordinate into a second image signal based on the conversion table arranged at each recording position coordinate. . The accepting unit accepts information for identifying a first region to be corrected for image non-uniformity on the medium and a second region other than the first region as information on the specific recording position coordinates,
The arrangement means converts the conversion table arranged at each recording position coordinate corresponding to each point in the first area into a recording position coordinate corresponding to each point in the second area. The image processing apparatus according to claim 1, wherein the image processing apparatus is arranged so as to be denser than the table.   The arrangement means arranges an interval of the conversion table arranged at each recording position coordinate corresponding to each point in the first area at each recording position coordinate corresponding to each point in the second area. The image processing apparatus according to claim 2, wherein a length obtained by multiplying an interval between conversion tables by a predetermined numerical value is used.   The conversion means converts to a second image signal based on the conversion table arranged in the vicinity of each recording position coordinate and the recording position coordinates where the conversion table is arranged. The image processing apparatus according to claim 1 or 2. A step of receiving information relating to a specific recording position coordinate for correcting the image among recording position coordinates indicating a position for recording the image on the medium;
Arranging a conversion table used for converting an image signal at recording position coordinates determined based on the specific recording position coordinates;
Converting the first image signal at each recording position coordinate into a second image signal based on each recording position coordinate, the conversion table, and the recording position coordinate where the conversion table is arranged. An image processing method comprising: On the computer,
A function of receiving information regarding a specific recording position coordinate for which the image is to be corrected among the recording position coordinates indicating the position where the image is recorded on the medium;
A function of arranging a conversion table used for converting an image signal at recording position coordinates determined based on the specific recording position coordinates;
A function of converting the first image signal at each recording position coordinate into a second image signal based on each recording position coordinate, the conversion table, and the recording position coordinate where the conversion table is arranged. A program to make it happen.

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