JP6136406B2 - Image reading apparatus, image forming apparatus, and image processing method - Google Patents

Description

  The present invention relates to an image reading apparatus, an image forming apparatus, an image processing program, and an image processing method, and more particularly to processing of a boundary portion of a read signal of a line image sensor arranged in a staggered pattern.

  In recent years, there has been a tendency to digitize information, and image processing apparatuses such as printers and facsimiles used for outputting digitized information and scanners used for digitizing documents have become indispensable devices. Such an image processing apparatus is often configured as a multifunction machine that can be used as a printer, a facsimile, a scanner, or a copier by providing an imaging function, an image forming function, a communication function, and the like.

  Among such image processing apparatuses, one aspect of a scanner used for digitizing information is a wide image reading apparatus such as A0 size. In a wide-width image reading apparatus, a plurality of relatively short line image sensors such as A4 size are arranged in a staggered manner in the main scanning direction for cost reduction, and image data from each line image sensor is synthesized. Some have made it possible to perform wide reading processing.

  However, in the case of a configuration in which a plurality of line image sensors of A4 size or the like are arranged in a staggered manner in the main scanning direction, the position of the line image sensor in the sub scanning direction is different. There is a problem that the image data for each line image sensor is shifted at the joint portion due to the sheet conveyance speed.

  In order to solve such a problem, a technique has been proposed in which, when image data for each line image sensor is synthesized, correction processing such as blurring processing is performed in the vicinity of the joint, thereby making the shift inconspicuous (for example, , See Patent Document 1).

  However, in the technique disclosed in Patent Document 1, if the image is a so-called halftone dot image in which the shading of pixels changes periodically in the vicinity of the joint, the image is faded or the image becomes blurred by performing correction processing. There is a problem that it disappears and the shift near the joint becomes conspicuous.

  The present invention has been made in consideration of the above situation, and an object of the present invention is to obtain a good read image with a simple configuration in a wide reading apparatus.

In order to solve the above problem, one aspect of the present invention, there is provided an image reading apparatus, the end portions of the main scanning direction in the adjacent image sensor is in a zigzag shape so as to overlap when viewed from the sub-scanning direction and arranged reading means, and cycle detecting means for detecting the period of the magnitude of the reading in the main scanning direction from the image data read respectively by the image sensor, a correction value based on the detected period by said period detecting means Correction value calculating means for calculating, and correction means for correcting the image data based on the correction value calculated by the correction value calculating means, wherein the correction value calculating means includes the period and a function of the period. Is calculated in advance as a correction value by using a function corresponding to the period detected by the period detecting means with reference to a table associated in advance. Positive means multiplies each said weighting factors to the image data, by adding align the pixel position in the main scanning direction, and corrects the image data included in the overlapping portions.
Another embodiment of the present invention is an image reading apparatus, wherein reading units are arranged in a staggered manner so that ends in the main scanning direction of adjacent image sensors overlap when viewed from the sub-scanning direction. A period detecting means for detecting a period of a read value in the main scanning direction from image data read by the image sensor, and a correction value calculating means for calculating a correction value based on the period detected by the period detecting means. And a correction unit that corrects the image data based on the correction value calculated by the correction value calculation unit, wherein the cycle detection unit detects the cycle for each pixel position of the overlapping portion. The correction value calculation means calculates a weighting coefficient for each pixel position as the correction value based on the period for each of the image data, and The image data included in the overlapped portion is corrected for each pixel position by multiplying the image data by the weighting coefficient and adding the pixel positions in the main scanning direction. To do.
Furthermore, an aspect of the present invention is an image reading apparatus, wherein reading units are arranged in a staggered manner so that ends in the main scanning direction of adjacent image sensors overlap when viewed from the sub-scanning direction. A period detecting means for detecting a period of a read value in the main scanning direction from image data read by the image sensor, and a correction value calculating means for calculating a correction value based on the period detected by the period detecting means. And a correction unit that corrects the image data based on the correction value calculated by the correction value calculation unit, wherein the cycle detection unit detects the cycle for each of the image data in the overlapping portion. The period detected for each image data with respect to the same pixel is compared and calculated to obtain a detected value of the period.

  According to another aspect of the present invention, there is provided an image forming apparatus including the above-described image reading apparatus.

  According to another aspect of the present invention, there is provided an image processing program to be executed by an image reading apparatus, wherein reading is performed in a staggered manner so that ends of adjacent image sensors in the main scanning direction overlap in the sub scanning direction. A first step of detecting a period of a read value in a main scanning direction from image data read by the image sensor, for an image reading device that synthesizes pixel data generated by the image sensor of the unit; A second step of calculating a correction value based on the period detected by the period detection unit and a third step of correcting the image data based on the correction value calculated by the correction value calculation unit are executed. It is characterized by making it.

Another aspect of the present invention, there is provided an image reading method, reading end portions of the main scanning direction in the adjacent image sensor that is arranged in a zigzag pattern to overlap when viewed from the sub-scanning direction section An image processing method for synthesizing image data generated by the adjacent image sensors, wherein a first period for detecting a magnitude cycle of a read value in a main scanning direction from the image data read by the image sensor; A second step of calculating a correction value based on the period detected in the first step, and a third step of correcting the image data based on the correction value calculated in the second step. run the door, in the second step, using a function and a function of the period and the period reference to associated beforehand table, corresponding to the period detected by said first step A weighting coefficient is calculated as the correction value, and in the third step, the weighting coefficient is multiplied with the image data, and the pixel positions in the main scanning direction are aligned and added to be included in the overlapping portion. The image data is corrected .
Further, the aspect of the present invention is generated by the adjacent image sensors of the reading units arranged in a staggered manner so that the ends of the adjacent image sensors in the main scanning direction overlap when viewed from the sub-scanning direction. An image processing method for combining image data, wherein a first step of detecting a magnitude cycle of a read value in the main scanning direction from image data read by the image sensor, and detected in the first step Performing a second step of calculating a correction value based on the calculated period, and a third step of correcting the image data based on the correction value calculated in the second step, and In the step, the period is detected for each pixel position of the overlapping portion, and in the second step, the weighting coefficient for each pixel position is based on the period for each image data. The correction values are respectively calculated, and in the third step, the weighting coefficients are respectively multiplied with the image data, and the pixel positions in the main scanning direction are aligned and added to thereby add the images included in the overlapping portion. The data is corrected for each pixel position.
Further, the aspect of the present invention is generated by the adjacent image sensors of the reading units arranged in a staggered manner so that the ends of the adjacent image sensors in the main scanning direction overlap when viewed from the sub-scanning direction. An image processing method for combining image data, wherein a first step of detecting a magnitude cycle of a read value in the main scanning direction from image data read by the image sensor, and detected in the first step Performing a second step of calculating a correction value based on the calculated period, and a third step of correcting the image data based on the correction value calculated in the second step, and In the step, the period is detected for each of the image data in the overlapping portion, and the period detected for each of the image data for the same pixel is compared and calculated to detect the period. Characterized in that it.

  According to the present invention, it is possible to obtain a good read image with a simple configuration in a wide reading apparatus.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the structure of the process block which concerns on embodiment of this invention. It is a figure which shows the structure of the process block which concerns on embodiment of this invention. It is a figure which shows the halftone dot period detection process which concerns on embodiment of this invention. It is a figure which shows the structure of the joint correction process part which concerns on embodiment of this invention. It is a figure which shows the weighting coefficient of the joint correction process which concerns on embodiment of this invention. It is a figure which shows the correction effect (1) with respect to the halftone dot image of the high line number which concerns on embodiment of this invention. It is a figure which shows the correction effect (2) with respect to the halftone dot image of the high line number which concerns on embodiment of this invention. It is a figure which shows the correction effect (3) with respect to the halftone dot image of the high line number which concerns on embodiment of this invention. It is a figure which shows the correction effect (1) with respect to the dot image of the low line number which concerns on embodiment of this invention. It is a figure which shows the correction effect (2) with respect to the halftone dot image of the low line number which concerns on embodiment of this invention. It is a figure which shows the correction effect (3) with respect to the halftone dot image of the low line number which concerns on embodiment of this invention. It is a figure which shows the weighting coefficient of the joint correction process which concerns on embodiment of this invention. It is a figure which shows the weighting coefficient of the joint correction process which concerns on embodiment of this invention. It is a figure which shows the structure of the process block which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment, a copying machine including a wide image reading apparatus corresponding to the A0 size, that is, an image forming apparatus will be described as an example. Note that the present invention can be realized not only as an image forming apparatus but also as a wide image reading apparatus.

  FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus 1 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment is roughly composed of an upper image reading device section 2 and a lower image output section 3. Further, inside the image forming apparatus 1, a control unit 4 that performs overall control and an image processing unit 5 that performs various arithmetic processes relating to images are provided.

  The image reading unit 2 is further configured by a lower document table 7 and an upper document cover 8. The document table 7 includes a reading unit 11, rollers 12 and 13, a document insertion sensor 14, a size detection sensor 15, and a document discharge sensor 16.

  The reading unit 11 reads an image of the document MN with an image sensor described later. The rollers 12 and 13 are respectively arranged before and after the reading unit 11 and are rotated about a predetermined rotation axis by transmitting a driving force of a motor (not shown). The document insertion sensor 14 detects whether or not the document MN is inserted between the document table 7 and the document cover 8. The size detection sensor 15 detects the size of the document MN in the main scanning direction, that is, in the left-right direction.

  The document cover 8 includes a white reference plate 17 and rollers 18 and 19. The white reference plate 17 is a shading correction plate and is installed at a position facing the reading unit 11 of the document table 7. The rollers 18 and 19 are installed at positions facing the rollers 12 and 13 of the document table 7, respectively, and are rotated about a predetermined rotation shaft by transmitting a driving force of a motor (not shown).

  The image reading unit 2 sandwiches the document MN between the document table 7 and the document cover 8 and sandwiches the document MN between the rollers 12 and 13 and the rollers 18 and 19 in the direction of the arrow J1, that is, the front. The image is read from the lower surface of the document MN by the reading unit 11 while being conveyed in the sub-scanning direction from the back to the back.

  The image output unit 3 includes a paper feeding unit 21 and an image forming unit 22. The paper supply unit 21 stores a medium such as a printing paper, and supplies the medium to the image forming unit 22 one by one. The image forming unit 22 prints an image read by the image reading device unit 2 on a medium, and discharges it along the discharge path RJ1 or RJ2.

  The control unit 4 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a HDD (Hard Disk Drive), and the like (not shown).

  In the control unit 4, in such a hardware configuration, a program stored in a recording medium such as a ROM or an HDD is read out to the RAM, and the CPU performs an operation according to the program, whereby the software control unit is configured. Is done. A functional block that realizes the functions of the image forming apparatus 1 according to the present embodiment is configured by a combination of the software control unit configured as described above and hardware.

  Next, the reading unit 11 and the image processing unit 5 according to the present embodiment will be described with reference to FIG. FIG. 2 is a diagram illustrating processing blocks of the reading unit 11 and the image processing unit 5 according to the present embodiment.

  In addition to the first image sensor 31, the second image sensor 32, and the third image sensor 33 configured as a contact image sensor (CIS), the reading unit 11 includes analog / digital (A / D) converters 34, 35, and 36 and memories 37 and 38.

  The first image sensor 31 is attached in the document table 7 (FIG. 1) so that the main scanning direction is directed to the left and right, and includes a light source, a lens, and a sensor. The sensor is a so-called line image sensor in which a plurality of elements are arranged in a straight line along the longitudinal direction (that is, the main scanning direction).

  That is, the first image sensor 31 irradiates a document MN on a contact glass (not shown) with light, detects the amount of reflected light reflected from the document MN by each element of the sensor, and digitally determines the magnitude of the amount of light. The first pixel data D1 is generated by sequentially arranging the converted pixel values. The first image data D1 represents a part of the document MN as an image (line image) elongated in the main scanning direction.

  The second image sensor 32 is configured as a line image sensor similar to the first image sensor 31, and generates the second image data D2. Although the second image sensor 32 has the main scanning direction turned to the left and right like the first image sensor 31, a predetermined distance between the first image sensor 31 and the first image sensor 31. It is attached so as to precede the sub-scanning direction. The second image sensor 32 partially overlaps the portion near the left end of the reading range with the portion near the right end in the reading range of the first image sensor 31 when viewed from the front-rear direction.

  The third image sensor 33 is configured as a line image sensor similar to the first image sensor 31 and the second image sensor 32, and generates third image data D3. Although the third image sensor 33 has the main scanning direction turned to the left and right like the first image sensor 31 and the second image sensor 32, the third image sensor 33 is rearward from the second image sensor 32 by a predetermined distance between the sensors. The second image sensor 32 is attached so as to follow in the sub-scanning direction. Further, the third image sensor 33 partially overlaps the portion near the left end of the reading range with the portion near the right end in the reading range of the second image sensor 32 when viewed from the front-rear direction.

  That is, the reading unit 11 includes the first image sensor 31, the second image sensor 32, and the third image sensor 33 arranged in a so-called staggered pattern.

  The first image sensor 31 generates an analog pixel signal by reading the document MN, converts it into digital first image data D1 by an analog / digital converter 34, and supplies this to the image processing unit 5. To do.

  The second image sensor 32 generates an analog pixel signal by reading the document MN, converts it into digital second image data D2 by the analog / digital converter 35, and stores it in the memory 37 once. . The memory 37 reads out the second image data D2 in synchronization with the first image data D1 after the elapse of a predetermined delay time, and supplies the second image data D2 to the image processing unit 5.

  The third image sensor 33 reads an original MN, generates an analog pixel signal, converts it into digital third image data D3 by an analog / digital converter 36, and stores it in the memory 38 once. . The memory 38 reads out the third image data D3 in synchronization with the first image data D1 and the second image data D2 after a predetermined delay time has passed, and supplies the third image data D3 to the image processing unit 5.

  The image processing unit 5 includes a line synthesis processing unit 41 and a memory 42, and performs various processes related to images such as an image synthesis process for synthesizing a plurality of images and a correction process for correcting images.

  The line composition processing unit 41 performs a predetermined line composition process (details will be described later) based on the first image data D1, the second image data D2, and the third image data D3, thereby synthesizing image data for one line. DA is generated and output to the subsequent stage. The memory 42 stores the first image data D1, the second image data D2, and the third image data D3 over a predetermined number of lines and reads them in accordance with a request from the line composition processing unit 41.

  Next, the line composition processing unit 41 of the image processing unit 5 according to the present embodiment will be described with reference to FIG. FIG. 3 is a diagram illustrating processing blocks of the line composition processing unit 41 according to the present embodiment.

  The line composition processing unit 41 includes a halftone dot detection unit 51, a halftone dot period detection unit 52, a weighting coefficient calculation unit 53, a joint correction processing unit 54, and a one-line processing unit 55.

  A halftone dot detection unit 51 detects a halftone dot in the main scanning direction from each overlapping portion of the first image data D1, the second image data D2, and the third image data D3, and the detection result is a halftone dot period detection unit. 52 and the joint correction processing unit 54. The halftone dot period detection unit 52 detects the halftone dot period T detected by the halftone dot detection unit 51 and supplies it to the weighting coefficient calculation unit 53. The weighting coefficient calculation unit 53 calculates weighting coefficients G1, G2, and G3 based on the detected halftone dot period, and supplies them to the joint correction processing unit.

  The joint correction processing unit 54 uses the weighting coefficients G1, G2, and G3 supplied from the weighting coefficient calculation unit 53 to overlap the first image data D1 and the second image data D2, as well as the second image data D2 and the second image data D2. A joint correction process is performed on the overlapping portions of the three image data D3, and the generated image data is supplied to the one-line processing unit 55. The one-line processing unit 55 generates one-line combined image data DA by combining the overlapping portion image data generated by the joint correction processing unit 54 with the image data of other portions.

  Next, with reference to FIG. 4, the halftone dot period detection process by the halftone period detector 52 will be described. FIG. 4A is a diagram showing the relationship between the pixel value and the halftone dot period, FIG. 4B is a flowchart showing the detection process procedure of the halftone dot period, and FIG. It is a figure showing a coefficient.

  For example, when the halftone dot period detection unit 52 is a joint portion between the first image sensor 31 and the second image sensor 32, the first image data D <b> 1 is used and the joint between the second image sensor 32 and the third image sensor 33 is used. If it is a portion, the second image data D2 is used.

  The halftone dot period detection unit 52 detects the halftone dot period from a wide range including outside the overlapped area. For example, if the halftone dot period is a joint portion between the first image sensor 31 and the second image sensor 32, The first image data D1 may be used for the left portion from the first and the second image data D2 may be used for the right portion from the center of the joint.

  Further, the halftone dot period detection unit 52 may individually detect the halftone dot period for each of the first image data D1 and the second image data D2. In this case, the halftone dot period detection unit 52 may use the average value of the detected halftone dot periods as the detection result, or may select either the long or short as the detection result.

  As shown in FIG. 4A, the halftone dot period detection unit 52 corresponds to, for example, a total of 31 pixels including a predetermined pixel of interest and 15 pixels on the left and right of the pixel of interest in the first image data D1. A halftone dot detection process is performed as a region of interest to be performed.

  Next, the halftone dot period calculation process by the halftone dot period detection unit 52 will be described by taking as an example the case where the halftone dot period is detected from the overlapping portion of the first image data D1. When the halftone dot is detected by the halftone dot detection unit 51, the halftone dot period detection unit 52 starts the halftone dot period detection processing procedure shown in FIG. 4B, and proceeds to step S1.

  In step S1, the halftone dot period detection unit 52 acquires the first image data D1 of the attention area from the halftone dot detection unit 51, and proceeds to the next step S2. In step S2, the halftone dot period detection unit 52 performs filter calculation processing on the first image data D1 using the filter coefficient shown in FIG. 4C, and proceeds to the next step S3.

  In step S3, the halftone dot period detection unit 52 performs a simple binarization process on the first image data D1 on which the filter calculation process has been performed, and proceeds to the next step S4. As a quantization threshold at this time, a value “128” is set when the data of each pixel of the first image data D1 is 8 bits, and a value “512” is set when the data is 10 bits.

  In step S4, the halftone dot period detection unit 52 counts the number of rising change points that change from the value “0” to the value “1” in the region of interest from the binarized first image data D1, and A change point interval which is a pixel interval between adjacent rising change points is extracted. Subsequently, the halftone dot period detection unit 52 performs a statistical calculation such as a simple average process or a multiple addition average process on the extracted change point interval, determines the calculation result as a halftone period, and then calculates a halftone period calculation process. Exit.

When performing the simple average process in step S4, the halftone dot period detection unit 52 sets the number of detected rising change points as I and sets each change point interval as Ti (where 1 ≦ i ≦ I−1). The halftone dot period T (n) at the target pixel position is calculated by the equation (1).

  When the first image data D1 and the like are so-called color images, the halftone dot period detection unit 52 may generate a single plane image from the R / G / B values and perform a series of processes, or R This processing may be performed on each plane image of / G / B.

  The halftone dot period detection unit 52 performs the same processing not only on the rising change point but also on the falling change point that changes from the value “1” to the value “0”. The accuracy may be improved by determining the point period.

  Next, the seam correction processing by the seam correction processing unit 54 will be described with reference to FIG. FIG. 5 is a diagram illustrating a circuit configuration of the joint correction processing unit 54. The joint correction processing unit 54 includes first to third correction processing circuits 61, 62, and 63 for performing correction processing on the first image data D1, the second image data D2, and the third image data D3, respectively, and addition. A circuit 70 is provided.

  The first to third correction processing circuits 61, 62, and 63 are configured in the same way, and the first to third cubic function convolutions 64, 65, and 66 and the first to third multiplication circuits 67 are provided. , 68 and 69.

  The first correction processing circuit 61 supplies the first image data D1 to the first cubic function convolution 64 and the first multiplication circuit 67, respectively. The first cubic function convolution 64 performs processing using a cubic function on the first image data D 1 and supplies the processed data to the first multiplication circuit 67.

  The first multiplication circuit 67 receives the weighting coefficient G1 calculated by the weighting coefficient calculation unit 53 in addition to the first image data D1 and the data from the first cubic function convolution 64, and multiplies them. Thus, the first corrected image data D1S is generated and supplied to the adding circuit 70.

  The second correction processing circuit 62 and the third correction processing circuit 63 generate and add the second correction image data D2S and the third correction image data D3S, respectively, by the same processing as the first correction processing circuit 61. Supply to circuit 70.

  The adding circuit 70 adds the first corrected image data D1S, the second corrected image data D2S, and the third corrected image data D3S to generate the joint corrected image data DS, and outputs this to the subsequent stage.

  Incidentally, the seam correction processing unit 54 actually has two types of image data in which the image sensors are adjacent to each other and have overlapping portions, for example, only the first image data D1 and the second image data D2, or the second image. Only data D2 and third image data D3 are input. Therefore, the adding circuit 70 adds only two types of corrected image data based on the two types of image data.

  As described above, the joint correction processing unit 54 multiplies the first image data D1, the second image data D2, and the third image data D3 by the weighting coefficients G1, G2, and G3, respectively, and adds them to each other. Data DS is generated.

  Next, the calculation processing of the weighting coefficients G1, G2, and G3 by the weighting coefficient calculation unit 53 will be described with reference to FIG. Here, the weighting coefficients G1 and G2 will be described as an example.

  FIG. 6 is a diagram showing a relationship among a part of the first image sensor 31 and the second image sensor 32 centering on the overlapping portion, the halftone dot period T, and the weighting coefficients G1 and G2 in the present embodiment. Yes, examples in which the period T and the weighting coefficients G1 and G2 are different from each other are shown by (a), (b), and (c).

  The weighting coefficient calculation unit 53 acquires the period T in the main scanning direction of the halftone dot detected by the halftone dot period detection unit 52. Here, it is assumed that the period T is constant in the overlapping portion. Or it is good also considering the average value of the period in an overlap part as the period T. FIG.

  Subsequently, the weighting coefficient calculation unit 53 calculates the weighting coefficients G1 and G2 used in the joint correction process described above as functions of the period T based on the acquired period T.

Specifically, the weighting coefficient calculation unit 53 calculates weighting coefficients G1 and G2 according to the following equation (2).

However, in the formula (2), n represents the position in the main scanning direction when the left end of the overlapping portion is set to the value “1”, and N represents the number of pixels in the overlapping portion. Α represents a constant that determines the curve of the curve representing the weighting coefficient. Furthermore, the variable TS is a value calculated by the following equation (3), and Tmax represents the maximum value of the period range to be detected.

  Here, as specific examples of the weighting coefficients G1 and G2 calculated by the equations (2) and (3), FIG. 6A shows the period T1 and FIG. 6B shows the period T2. FIG. 6C shows the period T3. However, the number of pixels in the overlapping portion of the image is N = 128 pixels, the maximum value of the period range to be detected is Tmax = T1, and the constant α = 1 for determining the curve of the weighting coefficient is set. Further, a relationship of T1> T2> T3 is established between the periods T1, T2, and T3.

  FIG. 6A shows a case where the halftone dot period T is the longest period T1, and at this time, the image of the document MN is assumed to be a line drawing, a gradation, or a solid image. In the case of such an image, it is considered preferable to link the first image data D1 to the second image data D2 step by step as the correction process moves from left to right along the main scanning direction. .

  For this reason, in the case of FIG. 6A, the calculated weighting coefficient G1 has a linear shape that monotonously decreases as it moves to the right in the overlapping portion, and the calculated weighting coefficient G2 moves to the right in the overlapping portion. It becomes a straight line that monotonously increases with the time.

  FIG. 6C shows a case where the halftone dot period T is the shortest period T3. At this time, the image of the document MN is assumed to be a high-line-number dot image. In the case of such an image, it is preferable that the correction process is performed so that the first image data D1 is switched to the second image data D2 sharply as it moves from the left to the right along the main scanning direction. Conceivable.

  For this reason, in the case of FIG. 6C, the calculated weighting coefficient G1 has a polygonal line shape that decreases at a stretch so as to draw a rectangle in the approximate center of the overlapping portion, and the calculated weighting coefficient G2 is approximately the center of the overlapping portion. A polygonal line that increases at a stretch like a rectangle is drawn.

  On the other hand, FIG. 6B shows the case where the halftone dot period T is intermediate between the period T1 and the period T3. At this time, the image of the document MN is a halftone dot image of characters or a low number of lines. It is assumed that there is. In the case of such an image, it is not the alternative method of FIG. 6 (a) or FIG. 6 (c), but is connected so as to obtain a good feature of both, that is, left along the main scanning direction. It is considered that it is preferable to connect the first image data D1 to the second image data D2 in a stepwise manner as it moves from right to right.

  For this reason, in the case of FIG. 6B, the calculated weighting coefficient G1 gradually increases so as to draw a part of the arc that swells upward from the left end of the overlapping portion to almost the center. From almost the center to the right end, this time, it becomes a complicated curve shape with a decreasing width gradually decreasing so as to draw a part of a circular arc swelled downward. The calculated weighting coefficient G2 is vertically symmetrical with the weighting coefficient G1 in the overlapping portion, and the increasing width gradually increases so as to draw a part of the arc swelled downward from the left end of the overlapping portion to almost the center. Then, from the substantially center of the overlapping portion to the right end, this time, it becomes a complicated curved line shape in which the increase width gradually decreases so as to draw a part of the arc swelled upward.

  As described above, the weighting coefficient calculation unit 53 calculates the weighting coefficients G1 and G2 used in the joint correction processing as a function of the period T detected by the halftone period detection unit 52. It is possible to finely adjust the weighting factors G1 and G2 according to the halftone dot period T of the image, not the halftone dot or non-halftone image.

  Next, effects and the like according to the present embodiment will be described using the simulation results of FIGS.

  First, FIGS. 7 to 9 are simulation results assuming that the document MN is a halftone dot image with a high number of lines. In this case, as the input image data, that is, the first image data D1 and the second image data D2, the halftone image having a high line number that changes to black and white is represented in a pseudo manner by a sine wave having a period of 6 pixels. did. The amount of pixel shift in the main scanning direction between D1 and D2 is 4 pixels. As for the pixel position in the main scanning direction, the leftmost pixel of the overlapping portion is “0”, and the right end is “128”.

  FIG. 7 assumes a case where joint correction processing is performed in a stepwise manner as in the case of FIG. FIGS. 7A and 7B show weighting coefficients G1 and G2, respectively, which are substantially the same as those in FIG.

  FIG. 7C shows the read value of the pixel data after the joint correction process, and shows how the amplitude decreases from both ends toward the center of the joint (64 pixels). FIG. 7D shows MTF (Modulation Transfer Function), which is an index of the resolution of the image, and shows a state in which it is greatly deteriorated at the center of the joint.

  FIG. 8 assumes a case where a moderately graded joint correction process is performed as in the case of FIG. FIGS. 8A and 8B show weighting coefficients G1 and G2, respectively, which are substantially the same as those in FIG. 6B.

  FIG. 8C shows the read value of the pixel data after the seam correction process. Although the degree is smaller than that in the case of FIG. 7C, it goes from the both ends toward the joint center (64 pixels). As a result, the appearance of the amplitude becoming smaller appears. FIG. 8 (d) shows the MTF as in FIG. 7 (d). Although the degree is still smaller than in the case of FIG. 7 (d), it shows a slight deterioration at the center of the joint. Yes.

  FIG. 9 assumes a case where joint correction processing is performed so as to switch sharply, that is, a simple connection is made at the center position (64 pixels), as in the case of FIG. FIGS. 9A and 9B show weighting coefficients G1 and G2, respectively, which are substantially the same shape as FIG. 6C.

  FIG. 9C shows the read value of the pixel data after the seam correction processing as in FIG. 7C, and the change in the reading place is locally observed near the center (64 pixels) of the seam. However, the change in amplitude as shown in FIG. 7C does not appear. FIG. 9D shows the MTF similarly to FIG. 7D, and no deterioration appears unlike the case of FIG. 7D.

  From FIG. 7 to FIG. 9, when the document MN is a halftone dot image with a high line number, as shown in FIG. 9, a joint correction process that switches sharply is performed, that is, the center position (64 pixels). It can be said that it is preferable to simply connect them in ().

  Next, FIGS. 10 to 12 show simulation results assuming that the document MN is a halftone dot image with a low number of lines. In this case, as the input image data, that is, the first image data D1 and the second image data D2, a halftone dot image with a low line number that changes to black and white is represented in a pseudo manner by a sine wave with a period of 20 pixels. did. The amount of pixel shift in the main scanning direction between D1 and D2 is 4 pixels. As for the pixel position in the main scanning direction, the pixel at the left end of the overlapping portion is set to “0” and the right end is set to “128” as in FIGS.

  FIG. 10 assumes a case where joint correction processing is performed in a stepwise manner as in the case of FIGS. FIGS. 10A and 10B show the weighting factors G1 and G2, respectively, as in FIGS. 7A and 7B.

  FIG. 10C shows the read value of the pixel data after the seam correction process, as in FIG. 7C, and the amplitude is slightly smaller from both ends toward the center of the seam (64 pixels). The appearance is becoming apparent. FIG. 10 (d) represents the MTF as in FIG. 7 (d), and shows that the degradation has occurred over a relatively wide range from the center of the joint.

  FIG. 11 assumes a case where a moderately graded joint correction process is performed as in the case of FIGS. 6B and 8. FIGS. 11A and 11B show the weighting coefficients G1 and G2, respectively, similarly to FIGS. 8A and 8B.

  FIG. 11C shows the read value of the pixel data after the seam correction processing as in FIG. 8C, and the amplitude is slightly smaller from both ends toward the center of the seam (64 pixels). However, the degree of change is smaller than in the case of FIG. FIG. 11 (d) shows the MTF as in FIG. 8 (d), which deteriorates to some extent as it goes from the both ends to the center of the joint, but the degree is higher than in the case of FIG. 10 (d). Is getting smaller.

  FIG. 12 assumes a case where a joint correction process that switches sharply is performed, that is, a simple connection at the center position (64 pixels), as in the case of FIGS. 6C and 9. . FIGS. 12A and 12B show weighting coefficients G1 and G2, respectively, as in FIGS. 9A and 9B.

  FIG. 12C, like FIG. 9C, shows the read value of the pixel data after the seam correction process, and the first image sensors 31 and 32 are misaligned. Particularly, the change in the reading value is conspicuous due to the dot image having a low line number. FIG. 12 (d) represents the MTF as in FIG. 9 (d), and shows a state of local degradation near the center of the joint.

  10 to 12, when the document MN is a halftone dot image with a low number of lines, the change in the read value at the joint portion is reduced while the range in which the MTF deteriorates is narrowed. It can be said that it is preferable to perform a moderately stepwise seam correction process like 11.

  As described above, in the present embodiment, the joint correction processing is performed using the weighting coefficients G1 and G2 calculated as a function of the halftone dot period T according to the equations (2) and (3).

  That is, in the present embodiment, when the period T is large and is a line drawing, gradation, or so-called solid image, stepwise joint correction processing is performed, and when the period T is small and the image is a halftone dot, it is switched sharply. A seamless seam correction process is performed, and if it is in the middle, a moderately graded seam correction process is performed according to the period T.

  Accordingly, in the present embodiment, it is possible to make the joint of the image inconspicuous while always suppressing the deterioration of the MTF satisfactorily regardless of the period T.

  In the present embodiment, since the weighting coefficients G1 and G2 are functions of the halftone dot period T, the degree of correction by the joint correction process can be continuously changed. Compared with the case of making it, a seam correction process can be performed more favorably.

  As described above, according to the present embodiment, the weighting coefficient is calculated as a function of the period T, and the seam correction processing is performed using the weighting coefficient, whereby the image data generated by the plurality of image sensors is combined. Therefore, it is possible to connect without making the shift conspicuous, and it is possible to obtain a good read image.

  The second embodiment differs from the first embodiment in the weighting coefficient calculation process, but is the same in other parts.

  FIG. 13 is a diagram illustrating the weighting coefficient calculation process according to this embodiment. Here, as shown in FIG. 13 (b), weighting coefficients G1 and G2 to be multiplied by overlapping portions in the first image sensor 31 and the second image sensor 32, that is, the first image data D1 and the second image data D2, respectively. Explained as an example. In this embodiment, similarly to the first embodiment, it is assumed that the period T is constant or averaged in the overlapping portion.

  In this embodiment, the weighting coefficient calculation unit 53 uses the period T in the main scanning direction of the halftone dots detected by the halftone period detection unit 52 and the table TBL1 shown in FIG. And G2.

  The table TBL1 is associated with the period T and the weighting coefficients G1 and G2. In the table TBL1, the cycle T is classified into four stages with thresholds of three types of cycles Ta, Tb and Tc (Ta> Tb> Tc) as shown in FIG.

  In the table TBL1, the weighting coefficient G1 is expressed as functions fa (n), fb (n), fc (n), and fd (n) that are different for each stage. Here, similarly to the first embodiment, the variable n represents the position of the pixel in the overlapping portion, and the left end is the value “1”.

  As shown in FIG. 13D, when the functions fa (n), fb (n), fc (n), and fd (n) are graphed, all of them pass through a value of 0.5 at the center of the overlapping portion. This is expressed as a combination of an inclined portion and a horizontal portion having a value “1” or a value “0”. For this reason, all of the functions fa (n), fb (n), fc (n), and fd (n) can be expressed as a combination of a linear function and a constant of the variable n.

  The function fa (n) is the same as that in FIG. 6A, and the function fd (n) is the same as that in FIG. Further, the inclination angle of each function in the inclined portion is fa (n) <fb (n) <fc (n) <fd (n).

  In the table TBL1, the weighting coefficient G2 is a value obtained by subtracting the weighting coefficient G1 from the value “1” at each stage. Further, when the weighting coefficient G2 is graphed, as shown in FIG. 13E, the weighting coefficient G2 is substantially symmetrical with the weighting coefficient G1.

  As described above, in this embodiment, the period T is roughly classified into four stages, and the weighting coefficients G1 and G2 are set as linear functions or constants of the variable n for each stage, so that the period T is compared with the first embodiment. Thus, the calculation processing of the weighting coefficients G1 and G2 can be simplified.

  As a result, also in this embodiment, as in the first embodiment, when the document MN is a halftone dot image, the pixel data generated by a plurality of image sensors are connected without making the shift conspicuous. Therefore, a good read image can be obtained.

  As described above, according to the present embodiment, the period T is classified step by step, the weighting coefficient is calculated based on the function associated with each step in the table TBL1, and seam correction is performed using this. By performing the processing, it is possible to connect the image data generated by the plurality of image sensors without making the shift conspicuous, and it is possible to obtain a good read image.

  The third embodiment differs from the first embodiment in the weighting coefficient calculation process, but is the same in other parts.

  FIGS. 14A and 14B correspond to FIG. 6 described for the first embodiment, and are diagrams for explaining the weighting coefficient calculation processing according to the present embodiment. In the present embodiment, it is assumed that the period T in the main scanning direction of the halftone dot detected by the halftone dot period detection unit 52 changes in the middle of the overlapping portion.

  Specifically, in FIG. 14A, the period T is a period T1 that is relatively larger on the left side than the position slightly on the right side from the center of the overlapping portion (hereinafter referred to as the period change position). The right side is a relatively small period T3.

  In this case, in the document MN, the portion of the cycle T1 that is on the left side of the cycle change position is a line image or gradation, or a so-called solid image, and the portion of the cycle T3 that is on the right side of the cycle change position is a halftone dot with a high line number. It is considered to be an image.

  In FIG. 14A, the weighting coefficients G1 and G2 have the same values as those in FIG. 6A in the range where the period is T1, and in the range where the period is T3, the weighting coefficients G1 and G2 are as shown in FIG. The values are the same, and both are connected in a polygonal line at the coupling portion, that is, at the period change position.

  Further, in FIG. 14B, the period T is a period T1 in which the range on the left side of the overlapped portion is about 1/4 and the range on the right side is slightly larger than the position on the right side from the center. That is, the range in the vicinity of the center of the overlapping portion is a relatively small cycle T3.

  In this case as well, the document MN is considered to have a line image, gradation, or a so-called solid image in the period T1, and a dot image with a high line number in the period T3.

  The weighting coefficients G1 and G2 have the same values as in FIG. 6A in the range of the period T1, and the same values as in FIG. 6C in the range of the period T3.

  Also in FIG. 14B, the weighting coefficients G1 and G2 are the same values as in FIG. 6A in the range where the period is T1, and in the range where the period is T3, the weighting coefficients G1 and G2 are as shown in FIG. In the joint portion, adjacent portions are connected in a polygonal line shape.

  That is, in the present embodiment, even if the period T is different for each position in the main scanning direction in the overlapping portion, the period T is set to the period T by the expressions (2) and (3) for each range where the period T is the same. Weighting coefficients G1 and G2 can be obtained by calculating the respective coefficients based on them and arranging them along the main scanning direction and connecting them in a polygonal line shape.

  Thereby, in this embodiment, even when a line drawing or gradation with a low number of lines or a so-called solid image and a halftone image with a high number of lines coexist in the overlapping portion, the respective periods T are appropriately detected. Since appropriate coefficients can be calculated according to the period T, appropriate weighting coefficients G1 and G2 can be calculated by connecting them.

  As a result, also in this embodiment, as in the first embodiment, when the document MN is a halftone dot image, the pixel data generated by a plurality of image sensors are connected without making the shift conspicuous. Therefore, a good read image can be obtained.

  As described above, according to the present embodiment, the coefficient is calculated according to the period T for each position of the overlapping portion, and the weighting coefficient is calculated by connecting them along the main scanning direction. By performing the joint correction process, the image data generated by the plurality of image sensors can be connected without making the shift conspicuous, and a good read image can be obtained.

  In the first embodiment, the weighting coefficients G1 and G2 are calculated by the function of the period T expressed by the expressions (2) and (3). However, the present invention is not limited to this, and the periods expressed by various expressions. A function of T may be used. In this case, the function may be a function that approaches FIG. 6A when the period T increases, and approaches FIG. 6C when the period T decreases.

  In the second embodiment, the period T is classified into four stages based on the periods Ta, Tb, and Tc as three thresholds, and the weighting coefficient is calculated using a different function for each stage. However, the present invention is not limited to this. Alternatively, the weighting coefficient may be calculated using a function that is classified into three stages or less or five stages or more and that is different for each stage. In this case, the function used to calculate the weighting coefficient is not limited to a linear function, and may be a higher-order function of a second or higher order or various functions.

  Further, in the third embodiment, when the period T is different for each range in the overlapping portion, the coefficient based on the period T is calculated in each range, and these are connected in a polygonal line. For example, the coefficient may be changed stepwise by performing weighted addition processing at the joint between the coefficients.

  Further, in the third embodiment, the coefficient based on the period T is calculated using the equations (2) and (3) as in the first embodiment. However, the present invention is not limited to this. Similarly to the embodiment, the coefficient may be calculated using a function corresponding to the stage to which the period T belongs with reference to the table TBL1.

  Further, in the above embodiment, in the line composition processing unit 41 (FIG. 3), the halftone dot is detected by the halftone dot detection unit 51, and the halftone dot period is set by the halftone dot period detection unit 52 only when it is determined as a halftone dot. Although the case where the detection is performed has been described, the present invention is not limited to this, and as shown in FIG. 15, the halftone dot detection unit 51 is omitted, and the halftone dot period detection unit 52 detects the halftone dot period T unconditionally. You may do it.

  In this case, if the period T is relatively large, it will be a non-halftone dot, but a stepwise seam correction process is performed as shown in FIG. A joint correction process suitable for the point is performed. As a result, simplification of the configuration and reduction in the amount of calculation associated with omission of the halftone dot detection unit 51 can be achieved.

  Furthermore, in the above-described embodiment, the halftone dot detection unit 51, the halftone dot period detection unit 52, the weighting coefficient calculation unit 53, the joint correction processing unit 54, and the one-line processing unit 55 of the image processing unit 5 are configured by hardware. Although the case has been described, the present invention is not limited to this, and some or all of these may be configured by software.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 4 Control part 5 Image processing part 11 Reading part 31 1st image sensor 32 2nd image sensor 33 3rd image sensor 41 Line composition process part 51 Halftone dot detection part 52 Halftone dot period detection part 53 Weighting coefficient calculation part 54 Joint Correction Processing Unit 55 1-Line Processing Processing Unit D1 First Image Data D2 Second Image Data D3 Third Image Data DA Composite Image Data G1 Weighting Factor G2 Weighting Factor T Period T1 Period T2 Period T3 Period

JP 2009-135919 A

Claims (8)

A reading means arranged in a zigzag pattern to overlap when the ends of the main scanning direction in the adjacent image sensor is viewed from the sub-scanning direction,
A period detecting means for detecting a period of a read value in the main scanning direction from image data read by each of the image sensors;
Correction value calculating means for calculating a correction value based on the period detected by the period detecting means;
Correction means for correcting the image data based on the correction value calculated by the correction value calculation means;
With
The correction value calculating means refers to a table in which the period and a function of the period are associated in advance, and calculates a weighting coefficient as the correction value using a function corresponding to the period detected by the period detecting means. And
The image reading apparatus corrects the image data included in the overlapping portion by multiplying the image data by the weighting coefficient, and aligning and adding pixel positions in the main scanning direction . Reading means arranged in a staggered manner so that ends in the main scanning direction of adjacent image sensors overlap when viewed from the sub-scanning direction;
A period detecting means for detecting a period of a read value in the main scanning direction from image data read by each of the image sensors;
Correction value calculating means for calculating a correction value based on the period detected by the period detecting means;
Correction means for correcting the image data based on the correction value calculated by the correction value calculation means;
With
The period detection unit detects the period for each pixel position of the overlapping portion,
The correction value calculation means calculates a weighting coefficient for each pixel position as the correction value based on the period for each of the image data ,
The correction means corrects the image data included in the overlapping portion for each pixel position by multiplying the image data by the weighting coefficient, and aligning and adding pixel positions in the main scanning direction . Image reading device. The period detection means divides the pixel position of the overlapping portion into blocks for each predetermined number of pixels and detects the period in units of the blocks,
The correction value calculation means calculates a correction value based on the period in the block unit,
Wherein the correction means includes an image reading apparatus according to claim 1, characterized in that to correct the image data based on the correction value in units of blocks. Reading means arranged in a staggered manner so that ends in the main scanning direction of adjacent image sensors overlap when viewed from the sub-scanning direction;
A period detecting means for detecting a period of a read value in the main scanning direction from image data read by each of the image sensors;
Correction value calculating means for calculating a correction value based on the period detected by the period detecting means;
Correction means for correcting the image data based on the correction value calculated by the correction value calculation means;
With
Said period detecting means, the cycle was detected in the overlapping portion for each of the image data, the detection value of the cycle period between detected for each of the image data for the same pixel comparison operation, the image reading apparatus . An image forming apparatus comprising an image reading apparatus according to any one of claims 1 to 4. Image processing ends in the main scanning direction in the adjacent image sensor that synthesizes the image data generated by the adjacent image sensor of the reading unit arranged in a zigzag pattern to overlap when viewed from the sub-scanning direction A method,
A first step of detecting a period of a read value in a main scanning direction from image data read by each of the image sensors;
A second step of calculating a correction value based on the period detected in the first step;
A third step of correcting the image data based on the correction value calculated in the second step ;
Run
In the second step, referring to a table in which the period and the function of the period are associated in advance, a weighting coefficient is used as the correction value using a function corresponding to the period detected in the first step. Calculate
In the third step, the image processing method corrects the image data included in the overlapping portion by multiplying the image data by the weighting coefficient and aligning and adding the pixel positions in the main scanning direction. . Image processing for synthesizing image data generated by the adjacent image sensors of the reading units arranged in a staggered manner so that the ends of the adjacent image sensors in the main scanning direction overlap when viewed from the sub-scanning direction A method,
A first step of detecting a period of a read value in a main scanning direction from image data read by each of the image sensors;
A second step of calculating a correction value based on the period detected in the first step;
A third step of correcting the image data based on the correction value calculated in the second step;
Run
In the first step, the period is detected for each pixel position of the overlapping portion,
In the second step, for each of the image data, a weighting coefficient for each pixel position is calculated as the correction value based on the cycle,
In the third step, the image data included in the overlapping portion is corrected for each pixel position by multiplying the image data by the weighting coefficient and aligning and adding the pixel positions in the main scanning direction. An image processing method . Image processing for synthesizing image data generated by the adjacent image sensors of the reading units arranged in a staggered manner so that the ends of the adjacent image sensors in the main scanning direction overlap when viewed from the sub-scanning direction A method,
A first step of detecting a period of a read value in a main scanning direction from image data read by each of the image sensors;
A second step of calculating a correction value based on the period detected in the first step;
A third step of correcting the image data based on the correction value calculated in the second step;
Run
In the first step, the period is detected for each of the image data in the overlapping portion, and the period detected for each of the image data for the same pixel is compared and calculated as a period detection value. Way .