JP2008022062A - Image reading apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct deviation in the arrangement of image sensors by detecting a deviation in positions of zigzag arrangement. <P>SOLUTION: A prescribed mark is marked to part of an overlapped part of each of sensors (CIS) on a pressing plate arranged opposite to the sensors in an image reading apparatus 100 wherein the image sensors CIS 1 to CIS 3 are arranged zigzag and read parts of the image sensors adjacent to each other are arranged overlappingly in the main scanning direction by a prescribed number of pixels. Each CIS reads the mark, and the position of the mark read by each CIS or reading timing is compared to detect and correct positional deviations in the main scanning and the subscanning directions of the image sensors arranged zigzag. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for detecting and correcting a misalignment between main scanning and sub scanning of an image sensor arranged in a staggered pattern in an image reading apparatus.

  2. Description of the Related Art Conventionally, in an image reading apparatus that reads a document image, in order to guarantee reading characteristics, shading correction, which is a generally known technique, is performed to correct variations in main scanning direction data.

  In an image reading apparatus in which a plurality of image sensors are arranged in a staggered manner, output characteristics of each image sensor vary, and it is difficult to obtain a uniform density output over the entire surface.

  In addition, the side of the document reading ahead of the image sensors arranged in a staggered pattern temporarily adjusts the image data to be stored in the memory and later adjusted to the data of the image sensor on the side of reading the document.

  However, there is a case where the data is displaced in the main and sub-scanning directions due to uneven feeding during document conveyance and displacement of the image sensor.

Here, there is disclosed a technique capable of preventing the occurrence of a shading boundary or an image shift appearing at a joint portion of a plurality of image sensors arranged in a staggered manner (see, for example, Patent Document 1). .
JP 2003-46736 A

  However, the above-described conventional example is good for images such as characters and lines and images having a uniform halftone density. However, when the image sensors arranged in a staggered pattern are misaligned or when reading a document. When misalignment occurs due to paper conveyance unevenness, etc., the conventional seam correction processing will be weighted and added as it is even if there is a difference in the reading value caused by misalignment. In such a case, the density of the joint portion may decrease or the image may be blurred.

  In addition, the color image may be changed by performing the addition process in a state of being shifted, which is not an appropriate process.

  Therefore, in the present invention, the pressure plate portion that suppresses the overlapping paper of the image sensors arranged in a staggered manner is marked, and by reading the mark, the displacement of the staggered placement position is detected, and the displacement of the image sensor placement is detected. to correct. In addition, an image obtained by scanning a predetermined number of lines is temporarily stored in a storage device included in the image evaluation apparatus, the overlapping data is compared, the main scanning deviation and the sub-scanning deviation are detected, and the deviation amount of the read image is obtained. The purpose is to reduce the displacement of the image sensor in the main and sub-scanning directions by performing correction accordingly.

  The image reading apparatus according to claim 1, wherein a plurality of image sensors are arranged in a zigzag pattern, and the reading parts of adjacent image sensors are arranged to overlap each other in the main scanning direction by a predetermined number of pixels. A predetermined mark is put on a part of the position of the overlapping portion of each image sensor of the pressure plate arranged on the side opposite to the sensor of the apparatus, the mark is read, and the position of the mark read by each image sensor or the reading timing is compared. Thus, the image reading apparatus is characterized in that it detects and corrects misalignment between main scanning and sub-scanning of image sensors arranged in a staggered manner.

  An image reading apparatus according to a second aspect is the image reading apparatus according to the first aspect, comprising a storage device, temporarily storing an image read by a predetermined number of lines in the storage device, and storing the data of the overlapping portion. In comparison, a means for detecting a main scanning deviation and a sub-scanning deviation is provided, and correction is performed according to the deviation amount of the read image.

  The image reading apparatus according to claim 3 is the image reading apparatus according to claim 1, wherein the operation of reading a mark on the pressure plate, comparing the position of the mark, and performing correction is white shading correction before reading the document. It is characterized by being done before.

  An image reading apparatus according to a fourth aspect is the image reading apparatus according to the first aspect, wherein the misregistration detection can be performed for one line of marks to be read by a CIS arranged in a staggered pattern. It is characterized in that a shift between scanning and sub-scanning is detected at the same time.

  An image reading apparatus according to a fifth aspect is the image reading apparatus according to the second aspect, wherein the correction means performs a correction coefficient calculation according to the magnitude of the deviation even if the deviation is one pixel unit or less. It is characterized in that correction can be performed with high accuracy.

  An image reading apparatus according to a sixth aspect is the image reading apparatus according to the second aspect, wherein the number of temporarily stored lines can be arbitrarily changed.

  An image reading apparatus according to a seventh aspect is the image reading apparatus according to the second aspect, comprising a plurality of storage devices, so that the processing of the next line is completed immediately after the processing of the previously read line is completed. The processing can be speeded up by performing the processing.

  According to the present invention, the pressure plate portion that suppresses the overlapping paper of the image sensors arranged in a staggered manner is marked, and by reading the mark, the staggered position displacement is detected, and the image sensor placement displacement is detected. Correct. In addition, an image obtained by scanning a predetermined number of lines is temporarily stored in a storage device included in the image evaluation apparatus, the overlapping data is compared, the main scanning deviation and the sub-scanning deviation are detected, and the deviation amount of the read image is obtained. By performing correction accordingly, it is possible to reduce the deviation of the image sensor in the main and sub-scanning directions.

  FIG. 1 is a block diagram showing an outline of an image reading apparatus according to an embodiment of the present invention. The image reading apparatus 100 includes CIS 1 to 3 (image sensors) 101 to 103, A / D (analog / digital) converters 111 to 113, a connection processing block 120, storage devices (hard disk or memory) 131 to 133, and sub-scanning. It consists of delay memories 141 and 142.

  In this image reading apparatus 100, three image sensors CIS1 to CIS3 are arranged so as to overlap each other and read in the main scanning direction. Further, the sensors CIS2 are arranged in a staggered manner with an interval at the upstream side in the sub-scanning direction and the sensors CIS1 and CIS3 at the downstream side.

  Image data output from each of the image sensors CIS1 to CIS3 is converted into digital signals by A / D converters 101 to 103, and the data of CIS1 and CIS2 are stored in temporary memories 141 to 142 for delay adjustment in the sub-scanning direction. The Since CIS3 is on the most downstream side, data is transferred without being stored in the memory.

  On the other hand, although CIS1 is on the same line as CIS3, data is stored in the memory 141 because it is arranged several lines upstream for easy adjustment. The desired line delayed data in each of the CIS 1 to 3 is sent to the joint processing block 120. Here, the correction processing of the joint portion and the one-line processing are performed on the data of each of the CISs 1 to 3 that have flowed in parallel, and are passed to the subsequent processing.

  The detection of deviation in the CIS staggered arrangement will be described. In order to guarantee the reading characteristics, the image reading apparatus performs shading correction, which is a generally known technique, to correct variations in data in the main scanning direction. For this purpose, as shown in FIG. 2, a pressure plate that becomes a reference white color is installed on the opposite side of the CIS document.

  In the current seam correction, the seam correction is performed on the assumption that the CIS is accurately arranged in a staggered pattern. Therefore, if the CIS staggered layout is misaligned when the reading unit is assembled, the scanned image will also be misaligned. Therefore, a combination of diagonal lines and vertical lines is marked on the pressure plate as shown in FIG.

  This time, the mark is as shown in FIG. 2, but any combination of diagonal lines and vertical lines may be used.

  The position of the mark is the end of the overlapping portion of the CIS, and this portion is not used as a read image, but is used only for correcting the displacement of the CIS arrangement. When this mark is read, two straight lines appear in the read images of the overlapping portions of CIS 1 and 2 as shown in FIG. By looking at the pixel position for reading this vertical line, the position of each main scan can be found, and by looking at the length between the straight lines, the position in the sub-scanning direction can be found. From this, it is possible to calculate the amount of deviation when placing the CIS.

  The amount of deviation is calculated before the shading correction because the mark cannot be read after the shading correction. A method of detecting the deviation amount of the read image will be described later.

  The amount of misalignment is fed back to the controller of the joint correction block. If the main scanning is misaligned according to the amount of misalignment, the pixel at the joint position of CIS1, 2 and 3 is changed and read. Read the data by shifting the read timing for the number of lines.

  Next, detection of misalignment during document reading will be described. The image data read by the CIS is converted into digital data by an A / D converter, and the CIS1 and 2 data are connected to the I / Fs (121 to 123) of the CIS1 to 3 via a delay memory. Input to the correction block.

  The deviation due to the CIS arrangement is reduced by the above method. However, in the paper conveyance, the conveyance speed may be uneven between the leading edge and the trailing edge of the paper.

  In order to reduce the deviation due to the conveyance unevenness, first, the read data is accumulated in a plurality of lines or all in the storage devices 131 to 133. The number of lines to be stored can be arbitrarily set. The data of the overlapping portion of the data stored in the storage device is sent to the deviation amount detection 125 to detect the deviation amount. The detection of the deviation amount will be described later.

  The shift amount detected by the shift amount detection is sent to the controller 126, and if it is a main scanning shift according to the shift amount, it is read out by changing the pixel at the connecting position of CIS1, 2, 3 and the subscan shift. For example, the shift is reduced by shifting the reading timing for the line. The detection of the shift amount and the correction of one pixel or less will be described later.

  Further, when data is read from the storage device and the amount of deviation is detected, the storage device is in a busy state, so the processing speed decreases. In this regard, a storage device is prepared separately (or in a separate block inside), and data processing efficiency is improved by holding data from the CIS in that storage device.

  Hereinafter, a method for detecting a deviation at the time of document reading will be described. As a detection method, a method of calculating a deviation amount by searching for a feature point and comparing its position is adopted.

  In order to detect feature points, a moving average is first taken for each line of image data to cut high frequency components. The moving average score can be changed arbitrarily. It is detected whether or not there is a peak in the image data in the overlapping section of the main scan. As shown in FIG. 3, a point of interest is determined, and that value is compared with adjacent pixel data.

  The peak in FIG. 3 is detected. If “data [pos + 1] ≧ data [pos]” and “data [pos + 1] ≧ data [pos + 2]”, data [pos + 1] is the peak pku_data of the mountain and the data and the position pku_pos are stored.

  If “data [pos + 1] ≦ data [pos]” and “data [pos + 1] ≦ data [pos + 2]”, the data and the position pkd_pos are stored with data [pos + 1] as the valley peak pkd_data.

  When the first peak is found, a difference from data [pos] is obtained, and the value is stored as pku_sub if it is positive, and saved as pkd_sub if it is negative. If a peak is found after that, the peak of the mountain and the peak of the valley are set to pk_tmp, and the difference between pk_tmp and the immediately preceding peak (pku_data or pkd_data) is obtained.

  If the value is positive, it is compared with pku_sub. If the value is negative, it is compared with pkd_sub.

  The comparison is performed using absolute values. If the value of pk_temp is large, the values of pku_data, pku_pos, pkd_data, and pkd_pos are updated.

  If the value of pk_temp is small, the value is held as it is. By doing so, it is possible to detect the position and value of the pixel having the maximum amount of change within the range (see FIG. 4).

  This time, an example with 8 pixels is given as an example, but the number of pixels to be detected can be arbitrarily changed.

  The peak is set to | pku_sub (or pkd_sub) | ≧ 2 [digit] (8-bit conversion). If | pku_sub (or pkd_sub) | <2 [digit] (8-bit conversion), it is determined that there is no peak.

  This time, there are two peaks, a peak on the mountain side and a peak on the valley side. Ultimately, the absolute values of pku_sub and pkd_sub are compared, and the larger value is taken as the peak value of the line.

  Next, the peak value of the image read by CIS1 is compared with the peak value of the image read by CIS2. The difference between the position of the peak value on the CIS1 side and the position of the peak value on the CIS2 side is obtained, and that value is used as the main scanning deviation of the line. At the same time, the difference between the peak values of CIS1 and CIS2 is obtained.

  Here, in the comparison of the peak value of the line, when the comparison target is pis_sub of CIS1 and pkd_sub of CIS2 (or conversely, pkd_sub of CIS1 and pkd_sub of CIS2), and when the difference is 10 digits or more, Ignore the amount of line misalignment.

  Thereafter, an average value of the shift amounts of all the lines of the read image or arbitrary lines is obtained and set as the main scanning shift amount of the entire image. In this case, the difference to be ignored is set to 10 digits or more, but this value can be arbitrarily changed.

  The detection of the same peak value and the sub-scanning direction of the shift amount are performed in the same manner as the shift amount detection of the main scan. Although the amount of deviation may include a decimal value in calculation, the amount of deviation is corrected by a method described later.

  Hereinafter, the correction of displacement will be described. When the amount of deviation is obtained as described above and the amount of deviation is an integer value, correction is performed in the main scanning direction by changing the position of the joint portion of the CIS2 data as shown in FIG. For sub-scanning, correction is performed by changing the line delay time in the sub-scanning direction by the amount of deviation.

  When the amount of deviation includes a minority value, the deviation for an integer is corrected in the same manner as described above, and then the minority is corrected using a cubic function convolution method. In addition, this minority correction can be made through. The calculation of the predicted pixel value using the cubic function convolution method will be described later.

  This time, the correction coefficient is shown up to a shift amount of 1/8 pixel unit, but correction coefficients in other units can also be calculated from Equation 2 described later. This correction calculation is performed on the CIS1 and CIS3 pixels with reference to CIS2.

  Next, how to calculate the predicted pixel by cubic function convolution will be described with reference to FIGS. Using the four points of data of the point of interest (Si) in FIG. 6, the point after one line (Si + 1), the point after two lines (Si + 2), and the point before one line (Si-1), An expected point (σ) between the points Si + 1 is obtained and set as the value of the target point (Si). Formula 1 shown in FIG. 4 is used as an arithmetic expression for calculating the predicted point (σ).

  In FIG. 6, h (r) in Equation 1 is an equation representing the relationship between the inter-pixel distance and the correction coefficient, and is represented by the function shown in FIG.

  From the equation 2 shown in FIG. 7, as an example, FIG. 8 shows a correction coefficient table with an accuracy of 1/8 pixel. The coefficients of this table are substituted into Equation 1 to obtain the predicted point value.

The purpose and effect of each claim are described below.
According to a second aspect of the present invention, the image processing apparatus includes a storage device, temporarily stores an image read by a predetermined number of lines in the storage device, compares the data of the overlapping portion, and detects a main scanning shift and a sub-scanning shift. An object of the present invention is to make it possible to correct a positional shift caused by uneven conveyance during document conveyance by performing correction according to the amount of image deviation. A storage device is provided for temporarily storing an image read for a predetermined number of lines in the storage device, comparing data of overlapping portions, and detecting a main scanning shift and a sub-scanning shift. By performing correction according to the above, the shift of the joint portion can be made inconspicuous.

  According to the third aspect of the present invention, the operation of reading the mark on the pressure plate, comparing the position of the mark, and performing the correction is performed before the white shading correction before reading the document, so that shading correction due to the density of the mark is applied, and correction by the mark is performed. To prevent it from being impossible.

  According to the fourth aspect of the present invention, the position deviation can be detected by one line of the mark read by the CIS arranged in a staggered manner, and the deviation between the main scanning and the sub scanning is detected at the same time.

  According to the fifth aspect, the correcting means can correct the deviation with high accuracy by performing a correction coefficient calculation corresponding to the magnitude of the deviation even if the deviation is equal to or less than one pixel unit.

  According to the sixth aspect of the present invention, the number of lines temporarily stored in the image reading apparatus can be arbitrarily changed, so that the data can be passed to the subsequent processing quickly.

  With respect to claim 6, by providing a plurality of storage devices in the image reading apparatus, the processing of the next line is performed immediately after the processing of the previously read line is completed, thereby speeding up the processing.

  Each of the above-described embodiments is a preferred embodiment of the present invention, and various modifications can be made without departing from the scope of the present invention.

1 is a schematic diagram of an image reading apparatus in an embodiment of the present invention. It is a position figure of a pressure plate and CIS in an embodiment of the invention. FIG. 6 is a main scanning pixel position diagram according to the embodiment of the present invention. It is a peak value detection figure in embodiment of this invention. It is a main-scan joint position figure in an embodiment of the invention. It is a figure which shows the gradation calculation of the prediction pixel in embodiment of this invention. FIG. 5 is a relationship diagram between a pixel distance and a correction coefficient in the embodiment of the present invention. It is a figure which shows the structure of the correction coefficient table (accuracy 1/8 pixel) in embodiment of this invention.

Explanation of symbols

100 image reading apparatus 101-103 CIS 1-3 (image sensor)
111 to 113 A / D (analog / digital) converter 120 splicing processing block 131 to 133 storage device 141 and 142 sub-scanning delay memory

Claims (7)

In an image reading apparatus in which a plurality of image sensors are arranged in a staggered manner, and a reading portion of adjacent image sensors is arranged by overlapping a predetermined number of pixels in the main scanning direction,
A predetermined mark is put on a part of the position of the overlapping portion of each image sensor of the pressure plate arranged on the side opposite to the sensor of the image reading device, the mark is read, and the position of the mark read by each image sensor or the timing of reading is determined. An image reading apparatus characterized by detecting and correcting a positional deviation between main scanning and sub-scanning of image sensors arranged in a staggered manner by comparison.   The image reading apparatus according to claim 1, further comprising a storage device, temporarily storing an image read by a predetermined number of lines in the storage device, comparing data of overlapping portions, and comparing a main scanning shift and a sub-scanning shift. An image reading apparatus comprising a means for detecting the image and performing correction according to the amount of deviation of the read image.   The image reading apparatus according to claim 1, wherein an operation of reading a mark on the pressure plate, comparing the position of the mark, and performing correction is performed before white shading correction before reading a document. apparatus.   The image reading apparatus according to claim 1, wherein the positional deviation detection can be performed for one line of a mark to be read by a CIS arranged in a staggered manner, and a deviation between main scanning and sub scanning is simultaneously detected. An image reading apparatus characterized by the above.   3. The image reading apparatus according to claim 2, wherein the correction means can perform correction with high accuracy by performing a correction coefficient calculation in accordance with the size of the shift even if the shift is less than one pixel unit. An image reading apparatus.   3. The image reading apparatus according to claim 2, wherein the number of temporarily stored lines can be arbitrarily changed.   3. The image reading apparatus according to claim 2, wherein a plurality of storage devices are provided so that the processing of the next line is performed immediately after the processing of the previously read line is completed, thereby speeding up the processing. An image reading apparatus.

Images