JP4408771B2 - Image reading device - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus that reads a document image by dividing a plurality of image sensors in a staggered manner in a copier / scanner that performs digital image processing, and more particularly to a joint portion of each sensor in an output image The present invention relates to an image reading apparatus capable of preventing the occurrence of a light / dark boundary or image shift appearing in FIG.

In general, there is known an image reading apparatus in which a plurality of image sensors are arranged in a zigzag manner and a document image is divided and read. In such an image reading apparatus, in order to guarantee reading characteristics, shading correction, which is a generally known technique, is performed to correct variations in main scanning direction data.
However, in such an image reading apparatus in which a plurality of image sensors are arranged in a staggered manner, output characteristics of the image sensors vary, and a uniform density output cannot be obtained on the entire surface. The image sensor on the upstream side (the side that reads the original document first) arranged in the form of a temporary memory stores image data and adjusts it to match the data line of the image sensor on the downstream side (the side that reads the original document later). However, line deviation in the sub-scanning direction may occur in the data of the downstream image sensor and the upstream image sensor due to uneven feeding during document conveyance.
In order to solve such a problem, among a plurality of image sensors arranged in a zigzag pattern, an image sensor arranged on one side in the sub-scanning direction is obtained from a read pixel that is not used for creating image data of the entire document image. Image data obtained from a read pixel that overlaps in the main scanning direction with the read pixel that stores the stored image data in the image sensor arranged on the other side in the sub-scanning direction based on the stored data A method for correcting the above has been proposed (see, for example, Patent Document 1).
As a prior art, Japanese Patent Laid-Open No. 2003-46736 discloses the creation of image data of an entire original image in an image sensor arranged on one side in the sub-scanning direction among a plurality of image sensors arranged in a staggered pattern. Image data obtained from unused read pixels is stored, and based on this stored data, the read pixel that overlaps in the main scanning direction with the read pixel obtained in the image sensor arranged on the other side in the sub scanning direction A technique configured to correct image data obtained from pixels is disclosed.
JP 2003-46736 A

However, the above prior art method is good for images such as characters and lines and images with uniform halftone density, but in the case of a halftone image composed of halftone dots, etc., it is adapted to the image information. Since this is not correction, when the lines are shifted by several lines in the sub-scanning direction, the peak density of the halftone dots at the joints is not preserved, and the density may be lowered or blurred. When the main scanning enlargement processing is performed in the subsequent image processing as it is, the joint correction portion may be enlarged and become conspicuous.
The present invention has been made in order to solve the above-described conventional problems, and an object of the present invention is to provide an image that can prevent occurrence of a gray-scale boundary or an image shift appearing at a joint portion of each sensor in an output image. It is to provide a reader.

In order to achieve the above object, an invention according to claim 1 is an image reading apparatus for reading an image from an original by an image sensor, and a plurality of image sensors arranged in a staggered manner, and the image In the image data read by the sensor, joint density correction means for correcting the density of image data corresponding to a joint portion between the adjacent image sensors, and the original image is at least a halftone dot image or a non-halftone dot image Halftone dot detection means for determining whether there is a halftone dot at the joint portion based on the determination result of the halftone dot detection means. The joint portion is directly connected without performing the step, and when there is no halftone dot in the joint portion, a normal joint density correction process is performed. To.
Further, in the invention described in claim 2, the halftone dot detecting means counts the number of change points of the image at the joint portion, and when the number of change points is equal to or larger than a predetermined value, the halftone dot portion. If the value is less than the predetermined value, it is determined that it is a non-halftone dot portion.
According to a third aspect of the present invention, the halftone dot detecting means counts the number of change points of the image at the joint portion, and when the number of change points is less than the first predetermined value, If the number of point portions and the number of change points is greater than or equal to the first predetermined value and less than a second predetermined value that is greater than the first predetermined value, an intermediate point between the halftone dot portion and the non-halftone dot portion If the area is equal to or greater than the second predetermined value, it is determined as a halftone dot portion.
According to a fourth aspect of the present invention, the joint density correction unit has a plurality of density correction weighting coefficients corresponding to the determination result of the halftone dot detection unit.
Further, in the invention according to claim 5, the joint density correction unit is configured to calculate the weighting coefficient based on whether the determination result of the halftone dot detection unit is a halftone dot portion or an intermediate region between a halftone dot portion and a non-halftone dot portion. And the joint density correction process is performed.
The invention according to claim 6 is characterized in that the joint density correcting means changes a main scanning correction width in accordance with a scaling factor of main scanning.

According to the present invention, when the correction processing is performed on the joint portion, image recognition (halftone dot detection) of the original is performed, and when the halftone dot exists in the joint portion, the correction processing of the joint portion is not performed. In this way, the density of the joints is prevented from being lowered, and when the dots are not halftones (characters, lines, halftones), the joint density correction processing is performed, and density variations between adjacent image sensors and deviations in the sub-scanning direction are performed. Has eased.
Further, according to the present invention, a plurality of weighting coefficients for the joint density correction coefficient are prepared, and the joint density correction coefficient is changed in the halftone part, the non-halftone part, and the intermediate area based on the halftone detection result. Therefore, correction suitable for the document image can be performed.
In addition, according to the present invention, the range for performing the joint density correction process can be varied according to the main scanning magnification, so that the processing part of the joint part can be made inconspicuous at the time of enlargement.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic view of an embodiment relating to a main part of an image reading apparatus according to the present invention.
As shown in FIG. 1, in this image reading apparatus, five image sensors CIS1 to CIS5 are arranged so as to be read with emphasis overlapping with adjacent sensors in the main scanning direction, and sensors CIS1 and CIS3 are arranged. , CIS5 are arranged in a staggered manner at intervals in the sub-scanning direction on the upstream side and sensors CIS2 and CIS4 on the downstream side. That is, the image sensors CIS1 to CIS5 are arranged in a zigzag overlapping manner.
Image data output from each of the image sensors CIS1 to CIS5 is converted into digital signals by the A / D converter 6, and data of the image sensors CIS1 and CIS3 to CIS5 are temporarily stored in the memories 7 for delaying in the sub-scanning direction. Accumulated in. Here, since the image sensor CIS2 is on the most downstream side, data is transferred without being stored in the memory 7. The image sensor CIS4 is on the same line as the image sensor CIS2, but is stored in the memory 7 because it is arranged several lines upstream for easy adjustment.
The desired line-delayed data for each image sensor CIS is sent to the one-line processing unit 8 and the main scanning one-line memory 9 is used for the data of each image sensor CIS flowing in parallel. One line processing is performed. Further, the one-line processing unit 8 uses the halftone dot detection processing unit 10 to perform density correction processing for the joint portion and pass it to the subsequent processing. In other words, the halftone dot detection processing unit 10 receives overlapping seam data of each image sensor CIS from the one-line processing unit 8, performs a process as to whether or not it is a halftone dot, and determines the determination result as a one-line processing unit 8. Returning to step 1, the one-line processing unit 8 performs density correction processing for the joint portion according to the determination result.

Next, the joint density correction processing in the one-line processing unit 8 will be described in detail.
FIG. 2 is an explanatory diagram of density correction processing at a joint between image sensors.
Here, as shown in FIG. 2, description will be made by taking as an example a joint between the image sensor CIS1 and the image sensor CIS2. The same applies to the joint of the image sensor CIS2 and the image sensor CIS3, the image sensor CIS3 and the image sensor CIS4, and the image sensor CIS4 and the image sensor CIS5.
Here, the overlapped left and right overlapping parts are set to 128 pixels, and the image sensor CIS1 applies weights of 7/8, 6/8,. In the sensor CIS2, on the contrary, the weights of 7/8, 6/8,... 1/8 are applied from the right side of the overlapping portion. Then, the density after the weighting calculation of each of the image sensors CIS1 and CIS2 is added to obtain the image density of the joint overlap portion. As a result, the image density at the time of reading can be stored after the joint density correction processing. It should be noted that the density correction process at the joint between the image sensors is performed in the one-line processing unit 8.
FIG. 3 is an explanatory diagram showing the image density after the joint density correction process when there is a density difference between the image sensor CIS1 and the image sensor CIS2.
As shown in FIG. 3, it can be seen that even when there is a density difference, the density level difference is absorbed by gradually connecting the density of the overlap portion in stages.

Next, a modification of the joint density correction process in the one-line processing unit 8 will be described in detail.
FIG. 4 is an explanatory diagram showing a modification in which the weighting coefficient of the joint density correction process is changed.
In this modification, in the image sensor CIS1, weights of 15/16, 14/16,... 12/16 are sequentially applied from the left side of the overlap part to the overlap center, and 4 / 16, 3/16 ... 1/16 weighting is applied.
In the image sensor CIS2, on the contrary, weighting of 15/16, 14/16,..., 12/16 is applied from the right side of the overlapping portion to the overlap center, and 4/16, 3 on the left side from the overlap center. /16...Weighing 1/16.
Then, the image sensor CIS1 and the image sensor CIS2 are added with the density after the weighting calculation to obtain the image density of the joint overlap portion. In the weighting coefficient of this modification, the left side of the overlap center (image sensor CIS1 side) gives weight to the image density data of the image sensor CIS1, and the right side of the overlap center (image sensor CIS2 side) A weight is assigned to the image density data of the image sensor CIS2. Even if the weighting coefficient is changed, the image density at the time of reading can be stored after the joint density correction processing.

Next, another embodiment of the joint density correction process in the one-line processing unit 8 will be described in detail.
FIG. 5 is an explanatory diagram showing an operation when the weighting coefficient of the joint density correction process is not changed stepwise.
As shown in FIG. 5, in the image sensor CIS1, a weight of 1 is applied from the left side of the overlap portion to the overlap center, and a weight of 0 is applied from the overlap center to the right side.
In the image sensor CIS2, on the contrary, a weighting of 1 is applied from the right side of the overlapping part to the overlapping center, and a weighting of 0 is applied to the left side from the overlapping center.
Then, the image sensor CIS1 and the image sensor CIS2 are added with the density after the weighting calculation to obtain the image density of the joint overlap portion. In this case, the data of the image sensors CIS1 and CIS2 are directly connected with the overlap center as a boundary, and there is no correction.

Next, halftone dot detection processing in the halftone dot detection processing unit 10 will be described.
FIG. 6 is an explanatory diagram of halftone dot detection processing in the halftone dot detection processing unit 10.
As shown in FIG. 6, in the halftone dot detection process, the image data of the joint portion is input, and the filter process 100 is first performed. Here, an example of the filter coefficient is shown in FIG. Next, simple binarization processing 101 is performed on the image after the filter processing. Further, if the number of change points (white → black (0 → 1) or black → white (1 → 0)) of the image in the region of interest in the simple binarized image data is equal to or greater than a certain value, the halftone dot If it is less than a certain value, two types of halftone dot determination 102 are performed in which a non-halftone dot is determined.
Further, as a halftone dot determination result, the following modifications are also conceivable. That is, as shown in FIG. 8, at least two change points (THl and TH2) are provided, (1) less than T1 (non-halftone dot), (2) T1 or more and less than T2 (intermediate region), (3) T2 or more. Three types of output of the halftone dot determination result can be prepared as (halftone dot). A plurality of change points may be provided and a plurality of halftone dot determination results may be output. In short, the number of lines of halftone dots may be determined.
When the halftone dot determination is performed in two ways, as described later, these two halftone dot determinations correspond to ON / OFF of the joint density correction processing (see FIG. 9). In this case, as will be described later, the weighting coefficient of the joint density correction processing is changed in accordance with the halftone dot detection result by these three halftone dot determinations (see FIG. 10).
Note that the halftone dot detection range uses the overlap area as the halftone dot detection range, and uses data on either the image sensor CIS upstream side or the image sensor CIS downstream side. Alternatively, halftone dot detection may be performed on data on both the image sensor CIS upstream side and the image sensor CIS downstream side, and the respective detection results may be combined to obtain a final detection result. For example, when there are two halftone dot detection results (halftone dot or non-halftone dot), if either one is determined to be a halftone dot, the final output is a halftone dot, and the other is a non-halftone dot.

Here, in the first embodiment of the present invention, when it is determined that the halftone detection processing result from the halftone detection processing unit 10 is not a halftone dot, the joint density correction processing in the one-line processing unit 8 is: When the joint density correction processing is performed using the weighting coefficient shown in FIG. 2 (correction ON), and it is determined that the halftone detection processing result from the halftone detection processing unit 10 is a halftone, 1 The joint density correction process in the line processing unit 8 is not performed using the weighting coefficient shown in FIG. 5 (correction OFF).
Therefore, according to the first embodiment, image recognition is performed when the joint density correction process is performed, and when there is a halftone dot at the joint part, the joint part is directly connected without performing joint density correction. Thus, the density of the joint portion is prevented from being lowered, and when it is not a halftone dot, a normal joint density correction process is performed to reduce the density variation between sensors and the deviation in the sub-scanning direction.
Further, in the second embodiment of the present invention, as described above, the result of the halftone dot detection processing from the halftone dot detection processing unit 10 is ambiguous whether or not it is (1) not halftone (2) halftone (intermediate) (Region) (3) halftone dot ”, correction processing is performed using the weighting coefficient shown in FIG. 2 in the case of (1), and shown in FIG. 4 in the case of (2). In the case of (3), the correction process is not performed using the weighting coefficient shown in FIG.
Therefore, according to these two embodiments, a case where the result of the dot detection is a halftone dot determination is dealt with, and a plurality of weighting coefficients for the joint density correction coefficient are prepared, The joint density correction coefficient is varied corresponding to the non-halftone portion and the intermediate region between the halftone dot and the non-halftone dot.
Further, in the third embodiment of the present invention, the joint density correction region is set to 128 pixels as described above when the variable magnification setting from the operation unit or the like is the same magnification, and the joint is performed at the time of enlargement (for example, at 200%) as described above. Considering that the density correction area is also enlarged, the joint density correction area is performed for 64 pixels that are halved with the overlap center unchanged. That is, the joint density correction region = (100 / X) × 128, X = magnification (100 to 400), and 128 pixels may be left at the time of reduction.
Therefore, according to the third embodiment, in order to alleviate the conspicuousness caused by the enlargement process of the joint density corrected portion when the main scan is enlarged, the main scan correction width for the joint density correction process is reduced during enlargement. Yes. That is, the main scanning correction width is changed in accordance with the main scanning magnification.
Further, the halftone dot detection area does not have to be changed by the scaling factor. The present embodiment shows an example of halftone dot detection processing, and various methods other than the present method are conceivable, and the present embodiment is not limited by these methods.
In this embodiment, three types of weighting coefficients are shown, and the weighting coefficients are used in units of 1/8 and 1/16, but may be further subdivided. Further, the number of divisions of the overlap portion is 8 blocks in the present embodiment, but this can be further subdivided.

1 is a schematic diagram of an embodiment relating to a main part of an image reading apparatus according to the present invention. Explanatory drawing of the density correction process of the joint between image sensors. Explanatory drawing which shows the image density after a joint density correction process in case there exists a density difference with image sensor CIS1 and image sensor CIS2. Explanatory drawing which shows the modification which changed the coefficient of the weight of a joint density correction process. Explanatory drawing which shows the process in the case of not changing the weighting coefficient of a joint density correction process in steps. Explanatory drawing of the halftone detection process in a halftone detection process part. Explanatory drawing which shows an example of a filter coefficient. Explanatory drawing of the modification which made the output of a halftone dot determination result into 3 types. The figure which shows the response | compatibility of a joint density correction process at the time of performing halftone dot determination. The figure which shows the response | compatibility of a joint density correction process at the time of performing halftone dot determination.

Explanation of symbols

1-5 Image sensor CIS, 6 converter, 7 memory, 8 line processing unit, 9 line memory, 10 halftone detection processing unit

Claims (6)

  An image reading apparatus for reading an image from a document by an image sensor, wherein a plurality of image sensors arranged in a staggered manner and a joint portion between adjacent image sensors in image data read by the image sensor A seam density correction unit that performs density correction of image data corresponding to the image data, and a halftone dot detection unit that determines whether the image of the document is at least a halftone image or a non-halftone image. Based on the determination result of the halftone dot detection means, the density correction means connects the joint portion directly without performing the joint density correction when the halftone dot exists in the joint portion, and the halftone dot is connected to the joint portion. An image reading apparatus that performs normal joint density correction processing when it does not exist. The dot detecting unit counts the number of changing points of the image at the joint portion, halftone portion if the number of said change point is not less than a predetermined value determined in advance, in the case of less than the predetermined value Hiami The image reading apparatus according to claim 1, wherein the image reading apparatus is determined to be a point portion.   The halftone dot detection means counts the number of change points of the image at the joint portion, and when the number of change points is less than a first predetermined value, the non-halftone dot portion, the number of change points is In the case where it is greater than the first predetermined value and less than a second predetermined value greater than the first predetermined value, an intermediate region between a halftone dot portion and a non-halftone dot portion, greater than the second predetermined value The image reading apparatus according to claim 1, wherein the image reading device is determined as a halftone dot portion.   The image reading apparatus according to claim 3, wherein the joint density correction unit has a plurality of weighting coefficients for density correction of the density correction unit corresponding to the determination result of the halftone dot detection unit.   The joint density correction unit performs joint density correction processing by changing the weighting coefficient based on whether the determination result of the halftone dot detection unit is a halftone part or an intermediate region between a halftone part and a non-halftone part. The image reading apparatus according to claim 4.   6. The image reading apparatus according to claim 1, wherein the joint density correction unit changes a main scanning correction width in accordance with a scaling factor of main scanning.

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