JP2004106289A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which correction processing of bow or skew can be carried out with a small memory capacity while minimizing degradation in the quality of an output image. <P>SOLUTION: Noncompressed image data and image data compressed at a data compressing section 31 are sent to an image data selecting section 32. Correction amount of bow or skew is sent from a color gap amount calculating section 33 to the image data selecting section 32. At the image data selecting section 32, the correction amount is compared with a preset threshold value and the compressed image data is selected if the correction amount is larger otherwise the noncompressed image data is selected. At a color gap correcting section 36, address control for accessing a color gap correction memory 34 is performed based on the correction amount and the image data is read out. At a data developing section, compressed image data is developed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus that forms an image on which a correction process regarding an image position shift has been performed. More specifically, the present invention relates to an image forming apparatus that forms an image on which an appropriate correction process has been performed according to the attribute of the image.
[0002]
[Prior art]
Conventionally, in a tandem type color printer, toner images of each color of cyan (C), magenta (M), yellow (Y), and black (K) are formed on a photoconductor corresponding to each color. Then, the color images are formed by superimposing the toner images formed by the respective image forming units on the transfer belt. In such an image forming apparatus, image distortion (hereinafter, referred to as “（”) due to component accuracy and mounting accuracy, and image inclination (hereinafter, referred to as “skew”) due to the accuracy of the exposure device occur individually for each color. This may cause color misregistration. For this reason, it is necessary to perform a correction process in consideration of holes and skew.
[0003]
An image when a skew has occurred will be described specifically. First, it is assumed that if drawn in a normal state, there is a pattern that is a straight line parallel to the main scanning direction as shown in FIG. When this pattern is drawn by the image forming apparatus in which holes are generated, the pattern becomes irregularly distorted lines as shown in FIG. When the image is drawn by the image forming apparatus in which the skew occurs, a line having a predetermined inclination as shown in FIG. 12 is obtained. Further, when the image is drawn by the image forming apparatus in which both the skew and the skew are generated, a line in which the distortion of the skew and the skew is combined as shown in FIG.
[0004]
As the color shift correction processing, image data of each color is stored in a memory, and image data corresponding to the amount of tilt is created from the memory. For example, first, image data for a predetermined number of lines in the sub-scanning direction is stored in the memory as bitmap data. Further, a read address of the image data is generated based on the inclination amount. In addition, a method has been proposed in which corrected image data is read from the memory at the generated read address (for example, see Patent Document 1). In addition, there has been proposed a device that can store more image data in a memory by using compressed image data instead of bitmap data (for example, see Patent Document 2).
[0005]
[Patent Document 1]
JP 2001-80125 A [Patent Document 2]
JP 2000-280525 A
[Problems to be solved by the invention]
However, the conventional technique described above has the following problems. That is, uncompressed image data such as bitmap data requires a large-capacity memory. Further, when the correction range of the skew and the skew is expanded, the number of lines stored in the memory also increases, so that a larger capacity memory is required. On the other hand, when compressed image data is used, the number of lines of image data that can be stored in the memory is larger than that of uncompressed image data. However, data loss occurs when the image data is compressed, which degrades the quality of the output image.
[0007]
The present invention has been made in order to solve the problems of the above-described conventional technology. That is, it is an object of the present invention to provide an image forming apparatus which can perform correction processing for holes and skews with a small memory capacity, and on the other hand, minimize the deterioration of the output image quality.
[0008]
[Means for Solving the Problems]
An image forming apparatus designed to solve this problem is an image forming apparatus that forms an image, and is based on a compression unit that compresses image data and a correction amount calculated for each predetermined area in the main scanning direction. Image data selecting means for selecting one of the image data compressed by the compression means and the original image data for each area, and the image data selected by the image data selecting means. An image memory, image data reading means for reading image data stored in the image memory based on a correction amount calculated for each predetermined area in the main scanning direction, and image data read by the image data reading means. When there is an area of the compressed image data in the area, the image data of the area is expanded by the expansion means, and the image data read from the image data reading means and expanded by the expansion means. Image forming means for forming an image on the basis of the image data obtained from the compressed image data. The original image data is selected for the area of.
[0009]
In the image forming apparatus according to the present invention, the uncompressed image data and the image data compressed by the compression unit are sent to the image data selection unit. The image data selecting means compares a preset threshold value with the correction amount for the skew and skew. If the correction amount is larger, the compressed image data is selected. Is selected. The selected image data is stored in the image memory. The image data reading means reads the image data from the image memory based on the correction amount. If there is compressed image data in the read image data, the image data is expanded by expansion means. Then, the image forming means creates corrected image data based on the image data read from the image memory and the expanded image data. That is, in the image forming apparatus of the present invention, compressed image data is stored only in the area where the correction amount is large. Therefore, the frequency of reading out the compressed image data is low, and the area to be read out is also limited. Therefore, the output image can be maintained at a high quality. In addition, compressed image data is used for an area having a large correction amount. Therefore, a large-capacity memory is not required. As a result, it is possible to perform the correction process for the ball and the skew with a small memory capacity.
[0010]
Further, it is more preferable that the image forming apparatus of the present invention has a correction amount calculating unit that calculates a correction amount for each color. Thus, each time an image is formed, a correction amount according to the state can be obtained. Therefore, an image is formed based on a more appropriate correction value, and the output image is of high quality.
[0011]
In the image forming apparatus according to the present invention, the image data selecting means may be arranged such that, if at least one of the correction amounts of a certain area exceeds the threshold value, the image data compressed by the compression means for the other colors of the area. It is better to select. As a result, the image data that has been compressed for the same area and the uncompressed image data do not overlap. Therefore, color unevenness does not occur in the output image, and the output image is of high quality.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. In this embodiment, the present invention is embodied as a tandem type color printer.
[0013]
As shown in FIG. 1, the color printer 100 according to the present embodiment includes image forming units 9C, 9M, 9Y, and 9K that form toner images of respective colors of CMYK, and transfer to which the toner images formed by the image forming units are transferred. And a belt 1. Further, a registration sensor 2 for detecting passage of the toner image is provided downstream of the image forming section 9K. Further, it has an image control unit 3 for performing a correction process of image data. The image forming units are arranged in a line along the moving direction of the transfer belt 1. The toner images of the respective colors transferred and superimposed on the transfer belt are collectively transferred onto a sheet downstream of the registration sensor 2 to form a color image on the sheet.
[0014]
Next, details of the image control unit 3 will be described based on the block diagram of FIG. The image control unit 3 includes a data compression unit 31, an image data selection unit 32, a color misregistration amount calculation unit 33, a color misregistration correction memory 34, a color and skew correction amount memory 35, a color misregistration correction unit 36, And a data expansion unit 37. The data compression section 31 compresses image data. The image data selection unit 32 selects one of compressed image data and uncompressed image data. The color misregistration correction memory 34 stores the image data selected by the image data selection unit 32. The color misregistration amount calculation unit 33 calculates a correction amount for the bow and skew (hereinafter, referred to as a “both / skew correction amount”) based on the detection timing of the registration sensor 2. The body skew correction amount memory 35 stores the body skew correction amount calculated by the color misregistration amount calculation unit 33. The color misregistration correction unit 36 performs memory control for accessing the color misregistration correction memory 34 based on the amount of bow and skew correction. The data expanding section 37 expands the compressed image data.
[0015]
The data compression section 31 performs a compression process using the BTC method (hereinafter, referred to as “BTC compression”). In the BTC-compressed image data, data of 16 pixels of 4 lines in the sub-scanning direction × 4 dots in the main scanning direction are collected into one block (48 bits) (see FIG. 3). One block of data includes average value information LA (8 bits), gradation width information LD (8 bits), and code data for each pixel (2 bits). Therefore, for example, when uncompressed image data is composed of 8 bits (256 gradations) / dot, data of a total of 128 bits is compressed to 48 bits. In BTC compression, some data loss occurs during compression, so that it is not possible to completely restore the image before compression. Therefore, it is undeniable that some image deterioration occurs.
[0016]
Further, the color misregistration amount calculation unit 33 calculates a blue and skew correction amount for each color. As a procedure for calculating the skew correction amount, first, resist patterns 15 and 16 as shown in FIG. 4 are created. Each resist pattern is sensed by the resist sensor 2. Note that the resist pattern is created at predetermined intervals in the main scanning direction. Further, at least two resist patterns are required, but the number is not limited to two. BTC-compressed data is used for the resist pattern. This is so that the skew correction amount can be calculated even when the range of the skew correction amount is expanded. Also, because the quality of the resist pattern is not required to be good or bad, image deterioration during compression is not a problem. Next, assuming that the difference between the timings at which the respective resist patterns are sensed is Δty, the skew amount is obtained by Δty × V. V is the moving speed of the transfer belt 1. Then, the skew correction amount is determined by calculating the skew amount for the reference color (for example, K). The skew amount is calculated when the power of the color printer 100 is turned on or after a predetermined number of sheets are printed.
[0017]
On the other hand, the volume correction amount is non-linear, and it is necessary to provide at least three sensors for high-accuracy detection. That is, increasing the number of sensors causes an increase in cost. Therefore, in order to avoid this, the value individually measured for each image forming unit is previously set as the body correction amount. As a result, the resist pattern created by the color misregistration amount calculation unit 33 has already reflected the body correction amount. Therefore, the correction amount detected by the resist pattern is a hole and skew correction amount corresponding to the hole and the skew.
[0018]
Next, the operation of the image control unit 3 will be described based on the block diagram of FIG. First, the image data before correction (uncompressed data, data of 8 bits / dot) is sent to the data compression unit 31 and the image data selection unit 32. In the data compression section 31, the input image data is BTC-compressed. The BTC-compressed image data is sent to the image data selection unit 32 in which data for 16 pixels are combined into one block. On the other hand, from the color misregistration amount calculation unit 33, the amount of skew correction is sent to the image data selection unit 32 and the amount of skew correction memory 35 for each color.
[0019]
In the image data selection unit 32, a threshold value of the amount of correction of the skew is set in advance. Then, for the range in which the volume and skew correction amount sent from the color deviation amount calculation unit 33 does not exceed the threshold value, uncompressed image data is stored in the color deviation correction memory 34. On the other hand, for the range exceeding the threshold value, the BTC-compressed image data is stored in the color shift correction memory 34. Therefore, in the color misregistration correction memory 34, uncompressed image data and BTC-compressed image data are mixed and stored.
[0020]
The memory space of the color shift correction memory 34 is conceptually two-dimensional as shown in FIG. 5, where HA corresponds to the main scanning direction and VA corresponds to the sub-scanning direction. Also, 48 bits of data are allocated to one address of the memory. These 48 bits correspond to 6 dots in the main scanning direction in the case of uncompressed image data, and correspond to 1 block in the case of BTC-compressed image data. That is, the number of pixels in the HA direction per address differs between BTC-compressed image data and uncompressed image data. For this reason, the number of addresses per line in the HA direction is variable. For example, as shown in FIG. 6, when one area corresponds to 12 dots in the main scanning direction, if the area is uncompressed image data, BTC compression is performed for two addresses (2 × 6 = 12 dots). If it is an image data area, it is composed of data for three addresses (3 × 4 = 12 dots). The number of addresses required for one line in the HA direction is stored in a register or the like. The BTC-compressed image data has four lines of data per address. Therefore, in the area of the BTC-compressed image data, data corresponding to four times the number of lines is stored as compared with the area of the non-compressed image data. Therefore, even if the correction amount exceeds the threshold value, the correction process can be performed.
[0021]
In the color misregistration correction unit 36, address control for accessing the color misregistration correction memory 34 is performed based on the correction amount read from the blue / skew correction amount memory 35. Here, in the case of BTC-compressed image data, image data is read out every four dots, and in the case of uncompressed image data, image data is read out every six dots. The readout memory address A1 of the uncompressed image data and the readout memory address A2 of the BTC-compressed image data have a correction amount X, the number of addresses required for one line in the HA direction HAW, and a target pixel correction amount. Assuming that the memory address in the case of 0 is A0, it can be obtained by the following equations (1) and (2).
A1 = (X × HAW) + A0 (1)
A2 = (X / 4 × HAW) + A0 (2)
Then, the image data is read out by accessing the memory address obtained by the equations (1) and (2).
[0022]
Here, access to the color misregistration correction memory 34 when the threshold value of the correction amount is 60 will be described. First, when the read correction amount is 50, since the correction amount is smaller than the threshold value, the area of the uncompressed image data is accessed. Therefore, the memory address to be read is obtained by the following equation (3) by substituting the correction amount into the equation (1).
A1 = (50 × HAW) + A0 (3)
That is, as shown in the conceptual diagram of FIG. 7, a memory address (50 × HAW) ahead of the memory address A0 before correction is accessed.
[0023]
On the other hand, if the read correction amount is 64, the correction amount is equal to or larger than the threshold, so that the area of the BTC-compressed image data is accessed. Therefore, the read memory address can be obtained by the following equation (4) by substituting the correction amount into the equation (2).
A2 = (16 × HAW) + A0 (4)
16 in the equation (4) is a quotient generated in (X / 4) in the equation (2). That is, as shown in the conceptual diagram of FIG. 8, a memory address (16 × HAW) ahead of the memory address A0 before correction is accessed. Note that the remainder n generated in (X / 4) in equation (2) is sent to the data expansion unit 37 as a coefficient for reading out appropriate image data in the BTC-compressed image data.
[0024]
The data decompression unit 37 decompresses the BTC-compressed image data. Then, in the case of image data that has undergone BTC compression and decompression, a target pixel is extracted from the data corresponding to the memory address A2 and the coefficient n described above. That is, pixels (4 dots) for one line are extracted from image data (four lines in the HA direction) developed based on the coefficient n. On the other hand, in the case of image data that has not undergone BTC compression and expansion, a target pixel (6 dots) is extracted from the data corresponding to the memory address A1. Then, the corrected image data is formed based on the extracted pixels.
[0025]
Next, the operation of the ball skew correction processing will be described based on the flowchart of FIG. First, image data before correction is input (S1). The input image data includes uncompressed image data and BTC-compressed image data. Next, the skew correction amount is read for each color (S2). Next, it is determined whether or not the correction amount of the region of interest is larger than a preset threshold value (S3). If the correction amount is not larger than the threshold (S3: NO), uncompressed image data is selected (S4). Then, the skew correction process is performed on the area (S5). On the other hand, if the correction amount is larger than the threshold value (S3: YES), the image data compressed by BTC is selected (S6). Then, a bow and skew correction process is performed on the area (S7). Then, the compressed data after the correction is expanded (S8). After the skew correction process is performed for all the areas, the corrected image data is integrated (S9). As a result, the image data after the bow and skew correction processing is created, and the image data is output (S10).
[0026]
It should be noted that for each of the image forming units 9C, 9M, 9Y, and 9K, the amount of bow and skew correction is calculated. Then, in the image data selecting section 32, if even one color of the amount of skew correction of each image forming section exceeds the threshold value, the BTC-compressed image data is selected also for the same area of other colors. As a result, in the same area, image data that has undergone BTC compression and expansion of a certain color and image data that has not undergone BTC compression and expansion of another color do not overlap. Therefore, color unevenness does not occur in the output image.
[0027]
The image data selection unit 32 may select the BTC-compressed image data for the entire area if at least one of the volume and skew correction amounts in each area exceeds the threshold value. In this case, since the uncompressed image data and the BTC-compressed image data are not mixed in the color misregistration correction memory 34, the address control to the color misregistration correction memory 34 can be simplified.
[0028]
As described above in detail, in the color printer 100 of the present embodiment, the uncompressed image data and the image data that has been BTC-compressed by the data compression unit 31 are sent to the image data selection unit 32. In addition, the color / skew correction amount is calculated by the color misregistration amount calculation unit 33, and the color / skew correction amount is sent to the image data selection unit 32. The image data selection unit 32 compares the threshold value set in advance and the amount of correction of the skew. If the volume / skew correction amount is larger, BTC-compressed image data is selected. Otherwise, uncompressed image data is selected. Then, the selected image data is stored in the color misregistration correction memory 34. That is, the compressed image data is stored only for the region where the correction amount is large. Further, the color misregistration correction unit 36 reads out image data from the color misregistration correction memory 34 based on the amount of bow and skew correction. The image data is expanded by the data expansion unit 37 in the area of the BTC-compressed image data. As a result, image data after the correction for the ball and the skew is created. In the correction processing of this color printer, compressed image data is read only when the correction amount is large. Therefore, the frequency of reading the compressed image data is low, and the area to be read is limited. Therefore, the output image can be maintained at a high quality. Further, since compressed image data can be used for an area having a large correction amount, a large-capacity memory is not required. As a result, an image forming apparatus that can perform correction processing for holes and skews with a small memory capacity is realized.
[0029]
If at least one of the amount of skew correction of each image forming unit exceeds the threshold value, the image data selecting unit 32 determines that the same area of another color is also BTC-compressed image data. I have. Therefore, the image data that has been BTC-compressed for the same area and the uncompressed image data are not superimposed, and color unevenness does not occur in the output image. Therefore, the output image is of high quality.
[0030]
Note that the present embodiment is merely an example, and does not limit the present invention in any way. Therefore, naturally, the present invention can be variously modified and modified without departing from the gist thereof. For example, in the present embodiment, the present invention is applied to a color printer, but is not limited to this. That is, a copying machine, a facsimile, and the like can be applied as long as they are of the tandem type.
[0031]
Although the fixed value is set at the time of shipment for the correction value of the button, the correction amount may be obtained after shipment. However, for that purpose, it is necessary to provide at least three sensors. Although the skew correction value is variable even after shipment, a fixed value may be set from the time of shipment.
[0032]
【The invention's effect】
As is apparent from the above description, according to the present invention, an image forming apparatus capable of performing correction processing for holes and skews with a small memory capacity and at the same time minimizing the degradation of the output image is provided. ing.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a color printer according to an embodiment.
FIG. 2 is a diagram illustrating a block configuration related to a function of an image control unit.
FIG. 3 is a diagram illustrating a data structure of BTC-compressed image data.
FIG. 4 is a conceptual diagram illustrating a correction process using a resist pattern.
FIG. 5 is a conceptual diagram showing a memory space (an address unit) of a color misregistration correction memory.
FIG. 6 is a conceptual diagram showing a memory space (pixel unit) of a color misregistration correction memory.
FIG. 7 is a conceptual diagram illustrating memory access to uncompressed image data.
FIG. 8 is a conceptual diagram illustrating memory access to compressed image data.
FIG. 9 is a flowchart illustrating a processing procedure of a bow and skew correction process.
FIG. 10 is a diagram showing a resist pattern in a normal state.
FIG. 11 is a diagram showing a resist pattern when a hole occurs.
FIG. 12 is a diagram showing a resist pattern when a skew occurs.
FIG. 13 is a diagram showing a resist pattern when holes and skew occur.
[Explanation of symbols]
31 Data compression unit 32 Image data selection unit 33 Color shift amount calculation unit 34 Color shift correction memory 35 Baud / skew correction amount memory 36 Color shift correction unit 37 Data development unit 100 Color printer

Claims (3)

In an image forming apparatus for forming an image,
Compression means for compressing image data;
Image data selection for selecting either image data compressed by the compression means or original image data for each area based on the correction amount calculated for each predetermined area in the main scanning direction. Means,
An image memory for storing the image data selected by the image data selecting means; and image data for reading out the image data stored in the image memory based on the correction amount calculated for each predetermined area in the main scanning direction. Reading means,
Expanding means for expanding the image data of the area when the area of the compressed image data is present in the image data read by the image data reading means;
Image forming means for forming an image based on the image data read from the image data reading means and the image data expanded by the expanding means;
The image data selection means selects the image data compressed by the compression means for an area where the correction amount is larger than a threshold, and selects the original image data for an area below the threshold. Image forming device. The image forming apparatus according to claim 1,
An image forming apparatus comprising: a correction amount calculating unit that calculates a correction amount for each color. 3. The image forming apparatus according to claim 1, wherein the image data selecting means, when at least one of the correction amounts of a certain area exceeds a threshold value, sends the other color of the area to the compression means. An image forming apparatus for selecting image data compressed by compression.

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