JP2012004868A - Image processing method for image reader, and image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing method capable of reproducing a high-quality image in which occurrence of a light/dark stripe is suppressed.SOLUTION: An image processing method for an image reader which reads the image of a conveyed document 20 by disposing adjacent image sensors 13 partially overlapping each other comprises: a step of black/white correction on each piece of image data output by the image sensors; a step of deviation correction in the sub-scanning direction of each piece of corrected image data; a brightness correction processing step (processing D) which corrects the brightness of an image so that the average values of the pixel values of the overlapping areas of the adjacent image sensors are coincident; and an image connection processing step for reproducing an image by connecting each piece of brightness-corrected image data. The brightness correction processing step (processing D) subjects an area in which the average luminance of the overlapping area is calculated to weighting in a manner such that small weight is put to the periphery and large weight is put to the center.

Description

  The present invention relates to an image reading apparatus in which a plurality of line-shaped image sensors are arranged in a staggered manner and adjacent image sensors are partially overlapped in the longitudinal direction, and an image processing method thereof, in particular. The present invention relates to luminance correction between image data output from the respective light receiving elements of adjacent image sensors.

As an image reading apparatus that reads a paper document and creates or copies image data, a plurality of line-shaped image sensors composed of a large number of light receiving elements are arranged in a zigzag pattern, and adjacent image sensors are arranged in the longitudinal direction. There is an apparatus that is arranged so as to overlap each other and includes a reading optical system such as a lens on these image sensors (see Patent Document 1).
FIG. 4 shows the configuration of such an image reading apparatus.
In this image reading apparatus, the document (paper) 20 is conveyed to the fixed image reading apparatus 10, or the document 20 is fixed and the image reading apparatus 10 scans the document 20.
At this time, the original 20 is illuminated by illumination light 11 emitted from a light source such as a lamp or LED (not shown) inside the image reading apparatus 10, and the light reflected and scattered by the original 20 passes through the reading optical system 12 such as a lens. The image is formed on the image sensor 13.
The formed light is output as image data to a memory (not shown) by the light receiving element of the image sensor 13.
As shown in FIG. 4, a plurality of line-shaped image sensors arranged in a line in the longitudinal direction is also referred to as “line sensor”.

In FIG. 4, the document 20 is conveyed to the fixed image reading device 10.
The image data output from the image sensor 13 is sequentially taken into the memory in time series with the conveyance of the document 20, and the image data of the entire document 20 is acquired.
Adjacent image sensors 13 are arranged in a staggered pattern on the substrate 14 so as to partially overlap in the main scanning direction (direction perpendicular to the document transport direction).
4 shows a state in which a plurality of first, second,..., Nth,..., Zth image sensors 13 are arranged in a staggered manner.
A portion of the image data of the image sensor 13 that overlaps with the image data of the adjacent image sensor 13 is referred to as an overlap region.

FIG. 5 is a diagram showing a flow of a conventional image combining process in which image data output from each image sensor 13 is connected to create a reproduced image (copy image) that is faithful to the original.
The line-shaped image sensor 13 is arranged so as to be orthogonal to the conveyance direction of the document 20.
Therefore, image data output from the image sensor 13 (hereinafter, image data output from the image sensor is also referred to as “initial image”) is obtained by cutting the document 20 in the main scanning direction as shown in FIG. It becomes strip-shaped image data.
In FIG. 5A, “n”, “n + 1”, “n + 2”,... Output from the “n” th image sensor 13, “n + 1” th image sensor 13, “n + 2” image sensor 13. Image data (initial image) to be processed.
Actually, since the processing (flow) of FIG. 5 is performed in real time while reading the document 20, the data size in the sub-scanning direction (see FIG. 4: the direction opposite to the document transport direction) is only a few pixels. As the document 20 is conveyed, the image data whose processing has been confirmed is deleted by one pixel (output from the memory to the outside of the printer, for example), and the newly read image data is added by one pixel, and the images are sequentially combined. Processing is performed.

FIG. 5 shows a case where image combination processing is performed on an image after the document 20 has been read once in the sub-scanning direction for easy understanding.
As processing A, black correction and white correction (shading correction) are performed on the initial image output from the image sensor 13.
Black correction means that “the reading optical system 12 is in a dark room state with no illumination light 11 based on the pixel values (red (R), green (G), and blue (B) signal intensities) of the obtained initial image. Correction to subtract the output (background) of the image sensor 13 at the time. This background is obtained (measured) in advance before reading the document.

White correction means that “when a document serving as a white reference is read, the pixel value after black correction is set to a set value (for example, 250 for an 8-bit image and 1000 for a 10-bit image). Correction to multiply ".
The set value of the pixel value is theoretically, for example, 255 for an 8-bit image and 1023 for a 10-bit image. However, when this value is set, the input value is a white reference value due to variations in input data. If the value exceeds, the data will be saturated, so set it to a slightly smaller value.
This gain is calculated in advance for each of R, G, and B by reading (measuring) the white reference plate 15 in advance before reading the document.
In white correction, the illuminance distribution in the main scanning direction of the illumination light 11 (see FIG. 4), the peripheral light amount ratio of the reading optical system 12, the sensitivity of each light receiving element of the image sensor 13, and the like are set as “white when reading a white document 20”. All error factors that do not output image data are corrected simultaneously.
By processing A (black correction / white correction), a reproduced image (copy image) having a uniform brightness can be obtained when a document 20 having a uniform brightness (luminance / density) is read (Patent Document 2, 3).
FIG. 5B shows an image after the process A.
The background and gain have unique values for each light receiving element of all image sensors 13, that is, for each pixel in the main scanning direction of all image data.

Next, as processing B, image data after processing A (that is, image data after black correction and white correction) is corrected for deviation in the sub-scanning direction.
As will be described later, since the reading position 16 of each image sensor 13 on the document 20 varies in the sub-scanning direction, the initial image from each image sensor 13 is shown in FIG. 5A and FIG. Thus, when viewed from data at the same time (same timing), the image (picture) is shifted in the sub-scanning direction.
In the next process C, in order to smoothly join the image data of the image sensors 13, it is necessary to correct the amount of deviation in the sub-scanning direction and perform alignment in the sub-scanning direction between adjacent image data.
For alignment in the sub-scanning direction, an overlap area in the image data is used.
The overlap area of adjacent image data includes the same information on the surface of the document 20, and each image data is moved in the sub-scanning direction to match the shading pattern of the overlap areas. A shift in the sub-scanning direction is corrected (see Patent Document 4).

Finally, the image combining operation is performed as the process C on the image data after the process B.
Various calculations are performed on pixel values in the overlap region between adjacent image data that have been aligned in the sub-scanning direction (see Patent Document 5).
As a result, the image data from the image sensors 13 are joined in the main scanning direction to form one image.
In an image reading apparatus using a plurality of image sensors, a reproduced image (copy image) is obtained by such an image combining process.

JP 2008-236054 A JP 2003-219164 A JP 2007-267359 A JP 2007-150870 A JP 2006-67031 A

In some cases, although the white correction is performed in the image combining process A shown in FIG. 5, the overall brightness (luminance) is different between the image data of the image sensors 13.
For example, when reading a document 20 having a uniform brightness, there is a case where each image data does not have a uniform brightness after the process A.
In such a case, “light and dark stripes” that do not exist in the actual document 20 appear in the main scanning direction even after the process C, and the obtained reproduced image is a “low-quality image” that is not faithful to the image of the document 20. End up.

Such a phenomenon occurs when the following factors (a) to (d) are combined.
(A) The height / distance of the conveyed document 20 from the reading optical system 12 is not the same as that of the white reference plate 15 used for white correction. [Due to design constraints]
(B) Depending on the height and distance from the reading optical system 12, the illuminance distribution of the illumination light 11 in the main scanning and sub-scanning directions changes. [Due to design constraints]
(C) The reading position 16 on the surface of the original 20 of the two rows of image sensors 13 (odd-numbered image sensor 13 and even-numbered image sensor 13 shown in FIG. 4) arranged in a staggered pattern is in the sub-scanning direction. The center of the illuminance distribution in the sub-scanning direction of the illumination light 11 is deviated from the center of the two columns. [Due to manufacturing error]
(D) The reading position 16 of each image sensor 13 on the surface of the document 20 varies in the sub-scanning direction. [Due to manufacturing error]
(In particular, the reading positions 16 of the odd-numbered image sensors 13 and the even-numbered image sensors 13 are separated in the sub-scanning direction as described in (c) above.)

With regard to (a) above, the distance from the reading optical system 12 changes even during the conveyance of one original.
In particular, the periphery of both ends in the sub-scanning direction of the document 20 is transported only on one side of the upstream or downstream side of a transport roller (not shown) positioned on the upstream side and the downstream side in the transport direction of the document 20. Therefore, the height and distance from the reading optical system 12 are likely to change.
With respect to (d) above, the optical axis of the reading optical system 12 is tilted in FIG. 4, and the reading position 16 on the surface of the document 20 is made coincident with the sub-scanning direction by the odd-numbered image sensor 13 and the even-numbered image sensor 13. There is also an image reading apparatus (not shown).

However, in any image reading apparatus, the reading position 16 of each image sensor 13 varies in the sub-scanning direction due to manufacturing errors of the reading optical system 12 and the like.
When these factors (a) to (d) are combined, the illuminance at the reading position 16 of each image sensor 13 during document reading is different from that during white correction, and the illuminance change is uniform in all image sensors 13. It will not be.
For this reason, even when the above-described white correction is performed to make the brightness of the entire image data uniform, bright and dark stripes appear in the main scanning direction in the obtained reproduced image, resulting in a low quality image.

As described above, the problems (problems) of the conventional image reading apparatus are composed of a plurality of design factors and manufacturing factors, so that it has been difficult to solve by hardware.
Further, even if correction is performed using any reference chart (test chart) as described in Patent Document 2 or Patent Document 3, “the distance from the reading optical system 12 changes during document conveyance” or “reference The problem (problem) cannot be easily solved due to factors such as the distance from the reading optical system 12 is different in the document 20 having a thickness different from that of the chart.
In addition, when the image output from the adjacent image sensor is shifted in the sub-scanning direction and a part of the image with a large difference in brightness falls around the area where the average luminance is calculated, Thus, a bright and dark stripe in the main scanning direction occurs in the reproduced image.

  The present invention has been made to solve such a problem, and without adding special hardware or performing advance correction before reading a document by using a special reference chart, An object of the present invention is to provide an “image processing method for an image reading apparatus” capable of obtaining “a high-quality reproduced image faithful to an image of a document” in which occurrence of “stripes” is suppressed.

In the image processing method of the image reading apparatus according to the present invention, a plurality of elongated image sensors in which a large number of light receiving elements are arranged in a straight line are arranged in a staggered manner, and the adjacent image sensors are arranged in the longitudinal direction. An image processing method of an image reading apparatus that reads an image of a document that is conveyed while being partially overlapped, and performs black correction and white correction on each image data output from the image sensor A correction for correcting a deviation in the sub-scanning direction so that the corrected image data corrected in the correction / white correction processing step and the corrected image data in the black correction / white correction processing step are joined together smoothly. For each image data in which the deviation in the sub-scanning direction is corrected in the correction processing step and the deviation correction processing step, the image data is output from the adjacent image sensor. Correct the brightness of the image by multiplying all pixel values of the image data by each image sensor by a gain corresponding to each image sensor so that the average values of the pixel values of the overlapping areas in the image data match. A brightness correction processing step, and an image combination processing step for combining the image data whose brightness has been corrected in the brightness correction processing step to reproduce an image, wherein the brightness correction processing step overlaps The area where the average luminance of the area is calculated is weighted with a small peripheral part and a large central part.
In the image reading apparatus according to the present invention, a plurality of elongated image sensors in which a large number of light receiving elements are arranged in a straight line are arranged in a staggered manner, and the adjacent image sensors are partially in the longitudinal direction. An image reading apparatus that reads an image of a conveyed document that is arranged in an overlapping manner, and performs black correction and white correction processing on each image data output from the image sensor. Shift correction processing means for correcting shift in the sub-scanning direction so that the image data after correction corrected by the black correction / white correction processing means are smoothly joined together, and A region in which image data output from the adjacent image sensor overlaps each image data in which the shift in the sub-scanning direction is corrected by the shift correction processing unit Brightness correction processing means for correcting the brightness of the image by multiplying all pixel values of the image data by each image sensor by a gain corresponding to each image sensor so that the average pixel values of the image sensors coincide with each other. And image combination processing means for combining and reproducing the image data whose brightness has been corrected by the brightness correction processing means, wherein the brightness correction processing means calculates the average luminance of the overlapped area For the area to be performed, the peripheral part is small and the central part is weighted heavily.

According to the present invention, it is possible to perform correction that suppresses “occurrence of bright and dark stripes in the main scanning direction” in a reproduced image without adding special hardware or performing advance correction before reading a document using a special reference chart. It is possible to obtain a “high quality image that is more faithful to the original” directly from the image data read from the original.
Further, even when there is a shift in the combined position in the sub-scanning direction of the image output from the adjacent image sensor, and a part of the image having a large contrast difference is applied around the area for calculating the average luminance, By performing a weighting process with a small peripheral portion and a large central portion, it is possible to reduce calculation errors during brightness correction, and there is an effect of reducing bright and dark stripes in the main scanning direction that occur in a reproduced image. .

It is a figure showing the flow of the image processing method of the image reading apparatus which concerns on this invention. It is a figure for demonstrating an overlap area | region. It is a figure for demonstrating the weight of an overlap area | region. 1 is a diagram illustrating a configuration of an image reading apparatus to which the present invention is applied. It is a figure showing the flow of the conventional image processing method.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
FIG. 4 described above also shows the configuration of an image reading apparatus to which the image processing method according to the present invention is applied.
Although overlapping with the description in the background art section, the configuration of the image reading apparatus to which the present invention is applied will be described again.
As described above, in the image reading device 10, the document (paper) 20 is conveyed to the fixed device 10, or the document 20 side is fixed, and the image reading device 10 scans the document 20.
Then, the document 20 is illuminated by illumination light 11 emitted from a light source such as a lamp or LED (not shown) inside the image reading apparatus 10, and the light reflected and scattered by the document 20 passes through a reading optical system 12 such as a lens. The image is formed on the image sensor 13. The formed light is output as image data to a memory (not shown) by the light receiving element of the image sensor 13.

In FIG. 4, the document 20 is conveyed to the fixed image reading device 10.
The image data output from the image sensor 13 is sequentially taken into the memory in time series with the conveyance of the document 20, and the image data of the entire document 20 is acquired.
Adjacent image sensors 13 are arranged in a staggered pattern on the substrate 14 so as to partially overlap in the main scanning direction.
A portion of the image data of the image sensor 13 that overlaps with the image data of the adjacent image sensor 13 is referred to as an overlap region.

FIG. 1 is a diagram illustrating a flow of an image processing method of the image reading apparatus according to the first embodiment. The image data output from each image sensor is connected, and a reproduced image (copy image) that is more faithful to the document than before. This represents a flow of “image combining processing of the image reading apparatus”.
As described in the background art section, since the line-shaped image sensor 13 is arranged so as to be orthogonal to the conveyance direction of the document 20, image data (initial image) output from the image sensor 13 is shown in FIG. As shown in FIG. 1 (a), it becomes strip-shaped image data obtained by cutting the document 20 in the main scanning direction.
In FIG. 1A, n, n + 1, n + 2,... Are output from the nth image sensor 13, the n + 1th image sensor 13, the n + 2th image sensor 13,. Image data (initial image) to be processed.
In practice, since the processing (flow) of FIG. 1 is performed in real time while reading the document 20, the data size in the sub-scanning direction is only a few pixels. One pixel is deleted (output from the memory to the outside such as a printer), and image combining processing is sequentially performed while adding newly read image data for one pixel.

Similar to FIG. 5, FIG. 1 shows a diagram in which image combination processing is performed on an image after the document 20 has been read once in the sub-scanning direction for easy understanding.
As processing A, black correction and white correction (shading correction) are performed on the initial image output from the image sensor 13.
As described above, the black correction is “a signal of pixel values (red (R), green (G), and blue (B)) of an obtained initial image (that is, image data output from the image sensor 13). "Intensity)" is a correction to subtract the output (background) of the image sensor 13 when there is no illumination light 11 and the reading optical system 12 is in a dark room state. This background is obtained (measured) in advance before reading the document.

Further, white correction means that “when a white document is read, the pixel value is adjusted to the pixel value after black correction so that the pixel value is near the maximum value (for example, 250 for an 8-bit image and 1000 for a 10-bit image). It is a correction to multiply by.
Note that the pixel value setting value is made smaller than the theoretical value 255 in the case of an 8-bit image, for example, and the theoretical value 1023 in the case of a 10-bit image, as described above, due to variations in input data. This is to prevent the data from being saturated when the white reference value is exceeded.
This gain is calculated in advance for each of R, G, and B by reading (measuring) the white reference plate 15 in advance before reading the document.
In the white correction, the illuminance distribution in the main scanning direction of the illumination light 11, the peripheral light amount ratio of the reading optical system 12, the sensitivity of each light receiving element of the image sensor 13, and the like are read. All error factors "are corrected simultaneously.
By processing A (black correction / white correction), a reproduced image (copy image) having a uniform brightness can be obtained when a document 20 having a uniform brightness (luminance / density) is read.
However, in practice, due to the above-described factors (a) to (d), even if white correction is performed to make the brightness of the entire image data uniform, a reproduced image in which bright and dark stripes appear in the main scanning direction is obtained. .
FIG. 1B shows an image after the process A.
The background and gain have unique values for each light receiving element of all image sensors 13, that is, for each pixel in the main scanning direction of all image data.

Next, correction in the sub-scanning direction is performed as processing B on the image data after processing A (that is, image data after black correction and after white correction).
Since the reading position 16 (see FIG. 4) on the document 20 of each image sensor 13 varies in the sub-scanning direction, the initial image from each image sensor 13 is shown in FIG. 1 (a) and FIG. 1 (b). As shown, when viewed from data at the same time (same timing), the image (picture) is shifted in the sub-scanning direction.
Note that the processing A (black correction / white correction) and the processing B (shift correction in the sub-scanning direction) are the same as the processing A and processing B in the background art described above.
The present embodiment is characterized in that a process D (brightness correction) is provided between the process B and the process C shown in FIG. 5 to reduce an error when calculating the luminance correction value.

As in the background art, processing A (black correction and white correction) and processing B (correction of deviation in the sub-scanning direction) are performed on the initial image output from the image sensor 13.
A process D for matching the overall brightness (luminance) between the image data is performed on the image data after the process B using the overlap region.
Thereafter, processing C (combination work) is performed on the image data after processing D.
In the processing A, processing B, processing D and processing C, as described above, the processing (flow) is actually performed in real time while reading the document 20, so the data size in the sub-scanning direction is only for several pixels.
The data size may be the whole. The data size depends on the memory size described later.

Details of the process D (brightness correction) will be described below.
As shown in FIG. 1C, an overlap region on the “image data In + 1 by the (n + 1) th image sensor 13” side in “image data In by the nth image sensor 13” is defined as Rn. On the other hand, the overlap area on the image In side in the image In + 1 is defined as Ln + 1.
As described above, since the image combining process is sequentially performed while reading the document 20, the overlap regions Rn and Ln + 1 are both about ((several tens of pixels in the main scanning direction) × (ten pixels in the sub scanning direction). Is.
Since the image In and the image In + 1 are corrected in the sub-scanning direction by the process B, the overlap areas Rn and Ln + 1 should be the same area data on the surface of the document 20, and the brightness thereof The same (pixel value) must be the same.

Therefore, the average values of the pixel values of red (R), green (G), and blue (B) in the region Rn are obtained and are referred to as ARn (R), ARn (G), and ARn (B), respectively.
Similarly, the average values of the R, G, and B pixel values in the region Ln + 1 are obtained and are designated as ALn + 1 (R), ALn + 1 (G), and ALn + 1 (B), respectively.
If the ratio in each of R, G and B is αn + 1 (R), αn + 1 (G), αn + 1 (B),
These are represented by the following formula (1).

These ratios represent the magnification (gain) for adjusting the brightness of the image In + 1 to the brightness of the image In.
That is, R, G, and B are multiplied by αn + 1 (R), αn + 1 (G), and αn + 1 (B), respectively, with respect to all pixel values constituting the image In + 1. The brightness of the image In + 1 matches the brightness of the image In.

Similarly, αn + 2 (R), αn + 2 (G), and αn + 2 (B) are obtained.
As a result, the magnification for adjusting the brightness of the image In + 2 by the n + 2nd image sensor 13 to the brightness of the image In is set to αn + 1 (R) × αn + 2 (R) for R, G, and B, respectively. αn + 1 (
G) × αn + 2 (G), αn + 1 (B) × αn + 2 (B).
That is, the brightness of the images in all the image sensors 13 can be matched based on the brightness of the image I1 by the first image sensor 13.
For example, the magnification of the mth image Im is represented by the following equation (2) for each of R, G, and B.

Here, details of the overlap region will be described with reference to FIG.
In the actual input image, the overlap regions Rn and Ln + 1 do not neatly overlap in units of pixels, but due to manufacturing errors of the reading optical system 12 and the image sensor 13, as shown in FIG. There is a shift of less than one pixel in any of the sub-scanning directions.
For this reason, in the process B (correction of deviation in the sub-scanning direction) shown in FIG. 1, alignment in the sub-scanning direction between adjacent image data is performed in units of less than one pixel, for example, 0.1 pixel.
Also, in the main scanning direction, the overlap area is calculated in units of 0.1 pixels, for example, by reading the reference chart in advance.
In the overlap region, the sizes of the regions Rn and Ln + 1 for calculating the correction gain shown in the equation (1) are set to u pixels in the main scanning direction and v pixels in the sub scanning direction, as shown in FIG. Assume that the difference between the image data In and In + 1 is k pixels in the main scanning direction and 1 pixel in the sub-scanning direction. However, 0 ≦ k, l <1.
In this case, assuming that the brightness of the pixel (t, r) on the image data In + 1 is Etr and the brightness of the pixel (s, q) on the image data In is Es, q, Etr is expressed by the following equation (3). Become.

Hereinafter, the luminance of the pixel on the image data In corresponding to the pixel (t, r) on the image data In + 1 is described as E′t, r.
As described above, the image data In and In + 1 are aligned with less than one pixel, but there may be an error due to the influence of deviation correction accuracy, optical system variations, and the like.
If there is no error,
Et, r = E't, r
However, a difference occurs due to the above error, and a fringe in the main scanning direction occurs due to an error in calculating the correction gain.
In order to suppress the occurrence of the fringes, the following processing is performed.
In order to calculate the correction gain, the average value of the regions Rn and Ln + 1 is calculated. The average value is calculated by multiplying the size (u, v) of the regions Rn and Ln + 1 by the above formula. (1) is expanded to the following equation (4).

Where Ki, j is the weight, E (R) i, j is the luminance value of the red component at coordinates (i, j), E (G) i, j is the luminance value of the green component at coordinates (i, j), E (B) i, j is the luminance value of the blue component of coordinates (i, j)
0 ≤ ki, j <1
It is.
As the weights ki, j, trapezoidal shapes and Hanning windows (not shown) as shown in FIG. 3 are set.
The Hanning window is a window function represented by “y = 0.5−0.5 * Cos (2πx) (0 ≦ x ≦ 1)”.
When the image included in the regions Rn and Ln + 1 for which the correction gain is calculated has a uniform luminance with little luminance change, or when a pattern (an image having a large contrast difference) is included in the regions Rn and Ln + 1, the weight ki, j The calculation accuracy does not change without multiplying by. However, when a part of the pattern is placed on the outer periphery of the regions Rn and Ln + 1, it is affected by the alignment error.
Therefore, in the present embodiment, the influence of the peripheral portions of the regions Rn and Ln + 1 is reduced by performing a weighting process that changes to a trapezoidal shape having a small peripheral portion and a large central portion as shown in FIG. In addition, the influence of the central portion of the regions Rn and Ln + 1 is increased, and light and dark stripes in the main scanning direction are reduced.

As described above, in the image processing method of the image reading apparatus according to the present embodiment, a plurality of elongated image sensors in which a large number of light receiving elements are arranged in a straight line are arranged in a staggered manner, and adjacent to each other. An image processing method of an image reading apparatus that reads an image of a conveyed document by arranging image sensors so as to partially overlap each other in the longitudinal direction, and black correction is performed on each image data output from the image sensor And the black correction / white correction processing step (Process A) for performing white correction and the corrected image data corrected in the black correction / white correction processing step so that they are smoothly connected. A deviation correction processing step (Process B) for correcting a deviation in the scanning direction and each image data in which the deviation in the sub-scanning direction is corrected in the deviation correction processing step are adjacent to each other. In the image data output from the image sensor, all the pixel values of the image data by each image sensor are multiplied by a gain corresponding to each image sensor so that the average values of the pixel values of the overlapped regions match each other. A brightness correction processing step (Process D) for correcting the brightness of the image, and an image combining processing step (Process C) for combining the image data whose brightness has been corrected in the brightness correction processing step and reproducing the image. In the brightness correction processing step (Process D), the peripheral portion is smaller and the central portion is weighted higher than the area for calculating the average luminance of the overlapped region.
Therefore, according to the present embodiment, even when a shift occurs in the coupling position of images output from adjacent image sensors and a part of an image with a large difference in brightness is applied to the periphery of the area for calculating the average luminance, the peripheral portion Since the weighting process is large in the central portion, it is possible to reduce the calculation error at the time of brightness correction, and it is possible to reduce bright and dark stripes in the main scanning direction generated in the reproduced image.

Further, in the image processing method of the image reading apparatus according to the present embodiment, the size of the overlapped area in the sub-scanning direction of the image data is about 10 pixels, and among the image data output from each image sensor 13, The image data in the scanning direction is multiplied by the pixel value by one pixel at a time, and the image data for one pixel in the sub-scanning direction for which processing has been determined is sequentially deleted in time series, and the newly read one in the sub-scanning direction. While adding image data for pixels, the reproduction of the entire document 20 is obtained by repeating the calculation of the gain by the average value of the pixel values of the overlapped area and the multiplication of the gain for the pixel value of the image data. .
Therefore, according to the present embodiment, it is possible to perform image reproduction (combination) processing of the entire document in real time while reading the document.

Embodiment 2. FIG.
In the first embodiment described above, the calculated gains βm (R), βm (G), and βm (B) are multiplied by the input image. However, it is unlikely that the calculated gains change abruptly, and the deviation correction processing is not performed. This is considered to be a calculation error due to the influence of errors and optical system variations.
For this reason, the calculated gain is not directly multiplied by the input image, but is averaged for several pixels in the sub-scanning direction and multiplied by the gain of the input image.
That is, the image processing method of the image reading apparatus according to the present embodiment smoothes the gain between adjacent image sensors in the sub-scanning direction.
Further, the gain smoothing is performed with an average value of gains in a set range (that is, an area for calculating the average luminance of the overlapped area).
That is, the gain is smoothed by calculating the average value of the gain of the area for calculating the average luminance.
Thereby, bright and dark stripes in the main scanning direction that are not present in the original image due to calculation errors can be reduced.

Embodiment 3 FIG.
In the second embodiment, the averaging process for several pixels is performed in the sub-scanning direction to reduce the light and dark stripes in the main scanning direction due to the calculation error. However, when the averaging process is performed, the gain distribution in the average range is a normal distribution. If not, a gain that does not originally exist is output.
For this reason, the median value (median value) of gain values for several pixels in the sub-scanning direction is calculated and multiplied as the gain of the input value.
That is, the gain smoothing is performed by calculating the median value of the gain in the set range (the area for calculating the average luminance of the overlapped area).
In this way, it is possible to cope with a case where the gain value changes stepwise due to the influence of the document.
That is, even when the gain value changes stepwise, the generation of bright and dark stripes in the main scanning direction can be reduced.

  INDUSTRIAL APPLICABILITY The present invention is useful for providing an “image processing method for an image reading apparatus” capable of obtaining a “high quality reproduced image” in which occurrence of “light and dark stripes in the main scanning direction” is suppressed.

DESCRIPTION OF SYMBOLS 10 Image reader, 11 Illumination light 12 Reading optical system 13 Image sensor 14 Board | substrate 15 White reference board 16 Reading position 20 Original

Claims (6)

A plurality of elongate image sensors in which a large number of light receiving elements are arranged in a straight line are arranged in a staggered manner, and the adjacent image sensors are partially overlapped in the longitudinal direction and conveyed. An image processing method of an image reading apparatus for reading an image of a document,
Black correction and white correction processing steps for performing black correction and white correction for each image data output from the image sensor;
A deviation correction processing step for correcting deviation in the sub-scanning direction so that each of the image data after correction corrected in the black correction / white correction processing step is smoothly connected;
The average value of the pixel values of the overlapped areas in the image data output from the adjacent image sensors matches each image data in which the deviation in the sub-scanning direction is corrected in the deviation correction processing step. In addition, a brightness correction processing step of correcting the brightness of the image by multiplying all pixel values of the image data by each image sensor by a gain corresponding to each image sensor, and
An image combining processing step for combining the image data whose brightness has been corrected in the brightness correction processing step and reproducing the image,
An image processing method of an image reading apparatus, wherein the brightness correction processing step performs weighting with a small peripheral part and a large central part with respect to an area for calculating an average luminance of the overlapped area.   The image processing method of the image reading apparatus according to claim 1, wherein the weighting changes to a trapezoidal shape.   The image processing method of the image reading apparatus according to claim 1, wherein a gain between the adjacent image sensors is smoothed in a sub-scanning direction.   The image processing method of the image reading apparatus according to claim 3, wherein the smoothing of the gain is an average value of gains in a set range.   The image processing method of the image reading apparatus according to claim 3, wherein the smoothing of the gain is a median value of gains in a set range. A plurality of elongate image sensors in which a large number of light receiving elements are arranged in a straight line are arranged in a staggered manner, and the adjacent image sensors are partially overlapped in the longitudinal direction and conveyed. An image reading apparatus for reading an image of a document, and black correction / white correction processing means for performing black correction and white correction on each image data output from the image sensor;
Deviation correction processing means for correcting deviation in the sub-scanning direction so that the image data after correction corrected by the black correction / white correction processing means is smoothly connected;
The average value of the pixel values of the overlapped areas in the image data output from the adjacent image sensors matches each image data in which the shift in the sub-scanning direction is corrected by the shift correction processing unit. As described above, brightness correction processing means for correcting the brightness of an image by multiplying all pixel values of image data by each image sensor by a gain corresponding to each image sensor,
Image combining processing means for combining the image data whose brightness has been corrected by the brightness correction processing means and reproducing the image,
The image reading apparatus according to claim 1, wherein the brightness correction processing unit weights a small peripheral part and a large central part with respect to an area for calculating an average luminance of the overlapped area.

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