JP2011159317A - Device and method for reading two-dimensional code - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably and accurately binarize a barcode without being affected by an environmental condition in imaging, particularly, illuminance unevenness of illumination. <P>SOLUTION: It is determined whether a fluctuation level difference between a gradation level of a target pixel in a direction of reading a two-dimensional code in multi-gradation image data with a gradation level of a pixel at least one before this target pixel in the direction of reading the two-dimensional code is a boundary determination level difference for determining a boundary between a black bar portion and a background portion thereof in a preset two-dimensional code or less. When the level difference is the preset boundary determination level difference or less as a result of the determination, a threshold is increased or decreased. When the level difference is not the preset boundary determination level difference or less, the increase or decrease of the threshold is not performed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention binarizes multi-gradation image data obtained by imaging a two-dimensional code such as a barcode attached to a product with an imaging device using a threshold value, and the binarized data. The present invention relates to a two-dimensional code reader and method for reading information contained in a two-dimensional code.

  For example, there is a two-dimensional code reader that recognizes a barcode, a symbol, or the like by imaging a barcode, a symbol, or the like with an imaging device such as a CCD camera and performing image processing on a video signal output from the imaging device. In such an apparatus, preprocessing for acquiring image data composed of multiple gradations from a video signal output from the imaging apparatus, binarizing the multi-value image data, and acquiring binarized data is performed. The two-dimensional code reader performs various processes such as barcode decoding and pattern recognition based on the binarized data acquired by the preprocessing.

Examples of techniques for binarizing multi-valued image data include an average method, a P tile method, a mode method, and a discriminant analysis method. In any of these methods, a fixed threshold value is set within a predetermined area, and multi-value image data is binarized based on the threshold value.
On the other hand, as a method of not fixing the threshold level, there is, for example, Patent Document 1. In this patent document 1, the threshold level for determining “black” or “white” is not fixed, but the threshold level is set according to the density (whiteness) of the background of the barcode label. Disclose.

Japanese Patent No. 2678009 (Japanese Patent Laid-Open No. 1-252067)

  For example, when a barcode attached to a product is imaged by an imaging device, the barcode is illuminated. For example, there is almost no illumination unevenness in the central portion of the illumination area, but in the vicinity of the central portion. Lighting unevenness occurs. For this reason, for example, the imaging direction of the imaging device and the illumination direction are matched at the focus position of the imaging device. As a result, the imaging device sets the direction of the imaging region toward the center of the illumination region where there is almost no illumination unevenness so that illumination unevenness does not occur when the barcode is captured. Although the imaging direction and illumination direction of the imaging device are set in this way, illumination unevenness occurs between, for example, the central portion and the periphery of the illumination area. Illumination unevenness occurs between the peripheral portions. However, if the barcode is placed at the center on the imaging surface of the imaging device by an operator, for example, the illumination is not uneven on the barcode, but the barcode is placed at the peripheral portion on the imaging surface of the imaging device. As a result, uneven illumination occurs on the barcode.

  FIG. 6 shows a binarization process when the barcode 2 is arranged in the peripheral portion on the imaging surface 1 in the imaging apparatus. When the barcode 2 is arranged in the peripheral portion on the imaging surface 1 in the imaging device in this way, illumination unevenness occurs on the barcode 2, so that the gradation level of the multi-value image data on the line m is, for example, It fluctuates and is lower at its peripheral part than at the central part on the imaging surface 1.

  When the binarization processing is performed using the threshold value th1 that is fixedly set for the multivalued image data with the gradation level fluctuating as described above, the multivalued image data in the central portion on the imaging surface 1 is processed. Can reproduce the barcode 2 by binarization processing, but the illuminance decreases as it goes to the periphery on the imaging surface 1, that is, the right side in FIG. The tone level becomes lower than the threshold value th1, and it becomes impossible to reproduce the barcode 2 despite the presence of the barcode 2.

Patent Document 1 presupposes that a threshold level is set according to the density (whiteness) of the background of the barcode label, and that the background of the barcode to be read has a predetermined density level. To do. In particular, when reading a barcode attached to a product by holding the product over a barcode reader, the illumination is uniformly applied when the barcode is captured at the center of the imaging surface of the imaging device (the front of the device). Therefore, there is no problem in binarization.
However, even in Patent Document 1, when the barcode is captured at the peripheral portion on the imaging surface, since the illuminance at the peripheral portion is reduced, a difference occurs in multi-gradation levels at both ends of the barcode region as described above. . That is, in Patent Document 1, a threshold level is set in accordance with the density (whiteness) of the background of the barcode label, and this set threshold level is acquired by imaging with an imaging device. It is variably set for each of a plurality of different image data. That is, each threshold level set for each of a plurality of image data is a constant value that does not change within one image data, similarly to the threshold th1 shown in FIG. For this reason, even in Patent Document 1, the threshold level set for one image data is the same as that fixedly set as in the description shown in FIG. Therefore, even if binarization processing is performed using the threshold level disclosed in Patent Document 1, as described above, the illuminance decreases toward the peripheral portion on the imaging surface. The gradation level of the multi-value image data becomes lower than a threshold value indicating a constant value, and it becomes impossible to reproduce the barcode despite the presence of the barcode.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a two-dimensional code reading apparatus and method that can binarize a bar code stably and accurately without being affected by environmental conditions at the time of imaging, particularly illumination unevenness of illumination.

  The two-dimensional code reader according to the main aspect of the present invention has at least one gradation level of a pixel of interest in the direction of reading a two-dimensional code in multi-tone image data and a direction of reading the two-dimensional code from the pixel of interest. It is determined whether or not the level difference of fluctuation from the gradation level of the pixel before the pixel is equal to or smaller than the boundary determination level difference for determining the boundary between the black bar portion and the background portion in the preset two-dimensional code. As a result of this determination, if the level difference is less than or equal to a preset boundary determination level difference, the threshold value is increased or decreased, and if the level difference is not less than or equal to the preset boundary determination level difference, the threshold value is increased. A threshold variable setting unit that does not increase or decrease the value is provided.

  The two-dimensional code reading method according to the main aspect of the present invention includes at least one gradation level of a target pixel in a direction of reading a two-dimensional code in multi-tone image data and a direction of reading the two-dimensional code from the target pixel. It is determined whether or not the level difference of fluctuation from the gradation level of the pixel before the pixel is equal to or smaller than the boundary determination level difference for determining the boundary between the black bar portion and the background portion in the preset two-dimensional code. As a result of this determination, if the level difference is less than or equal to a preset boundary determination level difference, the threshold value is increased or decreased, and if the level difference is not less than or equal to the preset boundary determination level difference, the threshold value is increased. Do not increase or decrease the value.

  According to the present invention, it is possible to provide a two-dimensional code reading apparatus and method capable of binarizing a bar code stably and accurately without being affected by environmental conditions at the time of imaging, in particular, illuminance unevenness of illumination.

The block diagram which shows one Embodiment of the two-dimensional code reader which concerns on this invention. FIG. 5 is a schematic diagram illustrating pixels when a level difference is calculated by a threshold variable setting unit in the same device. The figure for demonstrating the fluctuation | variation of the gradation level of multi-gradation image data when it transfers to the background part from the black bar part in the barcode in the apparatus, for example. The figure which shows the order of the binarization process in the same apparatus. The figure which shows the fluctuation | variation of the gradation level of multi-tone image data when illumination nonuniformity arises on the barcode acquired by imaging of the imaging part in the same apparatus. The figure which shows the binarization process when a barcode is arrange | positioned in the peripheral part on the imaging surface of the conventional imaging device.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration diagram of a two-dimensional code reader. This two-dimensional code reader is used for an electronic cash register, for example. This two-dimensional code reader is equipped with a CPU (Central Processing Unit) 10 as a control unit main body. The CPU 100 is connected to a ROM (Read Only Memory) 11, a RAM (Random Access Memory) 12, a communication interface (communication I / F) 13, and an imaging unit 14, and receives a command from the CPU 100. The binarization processing unit 15, the decoding unit 16, and the threshold variable setting unit 17 operate.

  In the ROM 11, for example, a business program for executing a business of an electronic cash register and a two-dimensional code reading program are stored in advance. The two-dimensional code reading program captures, for example, the barcode 2 attached to the product 18 by the imaging unit 14 to acquire multi-gradation image data, and uses the threshold th2 for the multi-gradation image data. When binarization is performed and the information of the product 18 included in the barcode 2 is read from the binarized data, the threshold th2 is variably set according to the variation of the gradation level in the multi-gradation image data. The multi-tone image data is binarized using the set threshold value th2.

The RAM 12 has a work area for temporarily storing various data. For example, the multi-gradation image data Da acquired by the imaging of the imaging unit 14 is temporarily stored in the work area or decoded by the decoding unit 16. Information included in the barcode 2 is temporarily stored in the work area.
The communication I / F 13 is connected to an external device such as a POS system server through a transmission path (not shown). The communication I / F 13 performs data communication between external devices through a transmission path.
The image pickup unit 14 picks up an image of an area including the barcode 2 attached to the product 18 and outputs a video signal of multiple gradations, for example, 0 to 255 gradations. For example, an image sensor composed of a CCD or the like is used. It is done.

The binarization processing unit 15 binarizes the multi-gradation image data acquired by imaging by the imaging unit 14 using the threshold value th2, and acquires binarized data Db. The threshold value th2 used for the binarization processing in the binarization processing unit 15 is variably set by a threshold value variable setting unit 17 described later.
The decoding unit 16 reads information included in the barcode 2 from the binarized data Db acquired by the binarization processing unit 15.

The threshold variable setting unit 17 variably sets the threshold th2 according to the variation of the gradation level in the multi-gradation image data Da acquired by the imaging of the imaging unit 14, for example, the variation of the gradation level For example, the threshold value th <b> 2 of the binarization processing unit 15 is increased or decreased according to the change in the gradation level of the background portion with respect to the black bar portion in the barcode 2.
The threshold value variable setting unit 17 reads the gradation level of the target pixel in the multi-gradation image data Da in the direction in which the barcode 2 is read, that is, in the same direction as the scanning direction when the imaging unit 14 captures the barcode 2. And the threshold th2 is increased or decreased based on the level difference between the gradation level of the pixel at least one pixel before the target pixel. For example, as shown in FIG. 2, the gradation level of the pixel of interest i is p (i), and the gradation level of the pixel i−1 immediately before the pixel of interest i is p (i−1). ), The threshold variable setting unit 17 calculates the level difference Δd between the gradation level p (i−1) of the pixel i−1 one pixel before and the gradation level p (i) of the pixel of interest i. To do.
Δd = p (i−1) −p (i) (1)
As a result of calculating the level difference Δd between the gradation level p (i−1) of the pixel i−1 one pixel before and the gradation level p (i) of the pixel of interest i, the threshold variable setting unit 17 It is determined whether there is no level difference Δd, zero “0”, a positive value (Δd> 0), or a negative value (Δd <0). That is, the level difference Δd is “0” because the level difference Δd between the gradation level p (i−1) of the pixel i−1 one pixel before and the gradation level p (i) of the pixel of interest i. Indicates no change. A positive level difference (Δd> 0) indicates that the level difference Δd is increasing. The level difference Δd being a negative value (Δd <0) indicates that the level difference Δd is decreasing.

As a result of determining whether the level difference Δd is “0”, a positive value (Δd> 0), or a negative value (Δd <0), the threshold variable setting unit 17 determines that the level difference is “0”. If there is, the threshold value th2 of the binarization processing unit 15 is maintained without being changed.
The threshold variable setting unit 17 increases the threshold th2 if the level difference Δd is a positive value (Δd> 0). For example, the threshold variable setting unit 17
th2 = th2 + 1 (2)
And the threshold value th2 of the binarization processing unit 15 is increased by “1”.
If the level difference Δd is a negative value (Δd <0), the variable threshold setting unit 17 decreases the threshold th2. For example, the threshold variable setting unit 17
th2 = th2-1 (3)
And the threshold value th2 of the binarization processing unit 15 is decreased by “1”.

  The threshold variable setting unit 17 sets the gradation level p (i) of the pixel of interest i in the multi-tone image data Da and the gradation level p (1) of the pixel i−1 immediately before the pixel of interest i. It is determined whether or not the level difference Δd from i−1) is equal to or smaller than a preset boundary determination level difference th3. That is, the threshold variable setting unit 17 determines whether or not the target pixel i is, for example, in the black bar portion of the barcode 2 or in the background portion of the black bar portion. In other words, it is determined whether the target pixel i is in the same color, that is, black in the black bar portion, or white in the background portion from the immediately preceding pixel. In this determination, if the barcode 2 is in the black bar portion or the background portion, the gradation level fluctuation in the multi-tone image data Da is slow, and the threshold value in the black bar portion or the background portion is slow. This is for changing the setting of th2. Note that, at the boundary portion between the black bar portion and the background portion, the gradation level in the multi-gradation image data Da changes steeply, and the threshold value th2 is not changed.

  For example, as shown in FIG. 3, when the barcode 2 moves from the black bar portion to the background portion or from the background portion to the black bar portion, the gradation level of the multi-tone image data Da is set to a preset boundary. It fluctuates more than the judgment level difference th3. Thereby, if it is in the black bar portion or the background portion, the gradation level of the multi-tone image data Da is within the preset boundary determination level difference th3.

  Accordingly, if the level difference Δd is equal to or less than the preset boundary determination level difference th3 as a result of the determination, the threshold value variable setting unit 17 determines that it is within the black bar portion or the background portion, and as described above. Depending on whether the level difference Δd is “0”, a positive value, or a negative value, the threshold th2 is not changed, increased by “1”, or decreased by “1”.

Next, the barcode reading operation by the apparatus configured as described above will be described with reference to the binarization processing sequence shown in FIG.
For example, the product 18 is placed in the imaging area of the imaging unit 14 by the operator. At this time, the operator places the barcode 2 attached to the product 18 toward the imaging unit 14 and places the product 18 on the imaging unit 14 so that the barcode 2 is arranged at the focus position of the imaging unit 14. Move closer to or away from it. For example, the imaging unit 14 images a region including the barcode 2 attached to the product 18 held by an operator and outputs the video signal. The video signal output from the imaging unit 14 is sequentially sent to the RAM 12 in accordance with a command from the CPU 10 and finally stored as multi-gradation image data Da including the entire barcode 2.

  Here, when the barcode 2 attached to the product 18 is imaged by the imaging unit 14, the barcode 2 is illuminated. For example, uneven illumination is provided between the central portion and the peripheral portion of the illumination area. Occurs. Since the imaging unit 14 sets the direction of the imaging region so that illumination unevenness does not occur when the barcode 2 is captured at the central part on the imaging surface 1, the central part on the imaging surface 1 in the imaging unit 14 is set. Illumination unevenness occurs between the peripheral portion and the periphery thereof. However, when the bar code 2 is arranged in the peripheral part on the imaging surface 1 in the imaging unit 14 by the operator, illumination unevenness occurs on the bar code 2. For example, FIG. 5 shows a change in the gradation level of the multi-tone image data Da when illumination unevenness occurs on the barcode 2. The gradation level on the imaging surface 1 in the imaging unit 14 decreases from the central part toward the peripheral part.

In step # 1, the threshold variable setting unit 17 performs binarization in the same direction as the binarization target line m in the multi-tone image data Da, that is, the scan direction when the imaging unit 14 captures the barcode 2. A threshold value th2 for binarization is initialized for the conversion target line m. As an initial setting method, for example, a value n obtained by using an average method, a P-tile method, a mode method, a discriminant analysis method, or the like is applied to the entire multi-gradation image data Da or a line m unit of interest. Initially set as the threshold value th2. That is, the threshold value th2 = n.
Next, the threshold variable setting unit 17 sets the initial coordinate x of the pixel of interest i in step # 2. For example, the initial coordinate x of the pixel of interest i is set to the leftmost x on the binarization target line m in the imaging surface 1 of the imaging unit 14 shown in FIG. For example, i = x.

Next, in step # 3, the threshold value variable setting unit 17 sets the gradation level p (i) of the pixel of interest i and the gradation level p (i of the pixel i-1 one pixel before as shown in FIG. -1) is obtained by calculating the above equation (1).
Next, in step # 4, the threshold variable setting unit 17 determines that the target pixel i is in the same color, that is, black in the black bar from the previous pixel, or in the white background. In order to determine whether or not there is, the gradation level p (i) of the pixel of interest i in the multi-gradation image data Da and the gradation level p (i of the pixel i−1 immediately before the pixel of interest i, for example, immediately before the pixel of interest i. -1) is determined whether or not the level difference Δd is equal to or less than a preset boundary determination level difference th3. For example, as shown in FIG. 3, when the barcode 2 moves from the black bar portion to the background portion or from the background portion to the black bar portion, the gradation level of the multi-tone image data Da is set to a preset boundary. It fluctuates more than the judgment level difference th3.

  As a result of the determination, the level difference Δd between the gradation level p (i) of the pixel of interest i and the gradation level p (i−1) of the pixel i−1 immediately before the pixel i of interest, for example, is previously determined. If it is equal to or smaller than the set boundary determination level difference th3, the threshold value variable setting unit 17 determines that the bar code 2 is in the black bar portion or the background portion, and proceeds to step # 5. If it is not in the black bar portion or the background portion in the barcode 2, it is the boundary between the black bar portion and the background portion, and the boundary determination level difference th3 in which the gradation level of the multi-tone image data Da is set in advance. As described above, the threshold variable setting unit 17 proceeds to step # 9.

  Next, when the threshold variable setting unit 17 determines that the black bar portion or the background portion is in the barcode 2, it determines whether or not the level difference Δd is “0” in step # 5. . If the level difference Δd is “0” as a result of this determination, the threshold value variable setting unit 17 maintains the threshold value th2 without changing it, proceeds to step # 9, and the binarization processing unit 15 Make binarization. That is, the level difference Δd being “0” means that the gradation level p (i) of the pixel of interest i is the same as the gradation level p (i−1) of the pixel i−1 one pixel before, This indicates that the illumination intensity of the pixel i of interest with respect to the barcode 2 is the same as the illumination intensity of the previous pixel.

  On the other hand, if the level difference Δd is not “0” as a result of the determination, the threshold value variable setting unit 17 proceeds to Step # 6 and determines whether the level difference Δd is a negative value (Δd <0). To do. As a result of this determination, if the level difference Δd is a negative value (Δd <0), the threshold variable setting unit 17 proceeds to step # 7, calculates the above equation (2), and performs the binarization processing unit 15 Is increased by "1". That is, the level difference Δd between the gradation level p (i) of the pixel of interest i and the gradation level p (i−1) of the pixel i−1 one pixel before is a negative value (Δd <0). The gradation level p (i) of the pixel of interest i is higher than the gradation level p (i-1) of the pixel i-1 one pixel before, and the illumination intensity of the pixel of interest i with respect to the barcode 2 is 1. It shows that it is higher than the illuminance of the illumination of the pixel before the pixel.

  On the other hand, if the level difference Δd is a positive value (Δd> 0), the threshold value variable setting unit 17 proceeds to step # 8, calculates the above equation (3), and sets the threshold value th2 to “1”. Decrease. That is, the level difference Δd between the gradation level p (i) of the pixel of interest i and the gradation level p (i−1) of the pixel i−1 one pixel before is a positive value (Δd> 0) The gradation level p (i) of the pixel of interest i is lower than the gradation level p (i-1) of the pixel i-1 one pixel before, and the illumination intensity of the pixel of interest i with respect to the barcode 2 is 1. It shows that it is lower than the illuminance of the illumination of the pixel before the pixel.

As a result, as shown in FIG. 5, the threshold variable setting unit 17 calculates the gradation level p (i) of the pixel of interest i and the gradation level p (i-1) of the pixel i-1 one pixel before. As the level difference Δd is a negative value (Δd> 0) and the illumination intensity of the pixel i of interest with respect to the barcode 2 becomes higher than the illumination intensity of the illumination of the previous pixel, the threshold value of the binarization processing unit 15 Th2 is increased by “1”.
On the other hand, the threshold variable setting unit 17 has a positive level difference Δd between the gradation level p (i) of the pixel of interest i and the gradation level p (i-1) of the pixel i-1 one pixel before. The threshold th2 is decreased by “1” as the value (Δd <0) and the illuminance of the illumination of the pixel i of interest with respect to the barcode 2 becomes lower than the illuminance of the illumination of the pixel one pixel before. If the illuminance of the illumination of the pixel i of interest with respect to the barcode 2 is the same as the illuminance of the illumination of the pixel one pixel before, the threshold variable setting unit 17 sets the threshold th2 of the binarization processing unit 15. Do not change.

Next, in step # 9, the binarization processing unit 15 uses the threshold th2 that has not been changed by the threshold variable setting unit 17 and the threshold th2 that has been increased or decreased. The binarization processing is performed on the multi-gradation image data Da acquired by the above, and the binarized data Db is acquired.
Next, the decoding unit 16 reads information included in the barcode 2 from the binarized data Db acquired by the binarization processing unit 6. That is, the decoding unit 16 scans the area of the barcode 2 by scanning the binarized data Db in multiple directions, for example, and verifies the continuous side width of the binarized data Db obtained by this scanning. Barcode 2 is decoded. The decoding result of the barcode 2 is sent to an external device such as a POS system through the communication I / F 13 according to a command from the CPU 10.

As described above, according to the above-described embodiment, for example, the barcode 2 attached to the product 18 is captured by the imaging unit 14 to obtain the multi-gradation image data Da, and the multi-gradation image data Da is obtained. When binarization is performed using the threshold value th2, and the information of the product 18 included in the barcode 2 is read from the binarized data Db, the threshold value is determined according to the variation of the gradation level in the multi-gradation image data Da. Th2 is variably set, and the multi-tone image data Da is binarized using the variably set threshold value th2.
Thereby, for example, when the barcode 2 is arranged in the peripheral portion on the imaging surface 1 in the imaging unit 14 by an operator, illumination unevenness occurs on the barcode 2, but even if this illumination unevenness occurs, The threshold value can be changed to an appropriate threshold value th2 according to the illuminance, and the barcode 2 can be binarized stably and accurately without being affected by the environmental conditions at the time of imaging, particularly the illuminance unevenness of illumination. As a result, the information included in the barcode 2 can be accurately read from the binarized data Db acquired by binarization.

  The operator places the barcode 2 attached to the product 18 toward the imaging unit 14 and brings the product 18 close to the imaging unit 14 so that the barcode 2 is arranged at the focus position of the imaging unit 14. The barcode 2 is not always arranged at the center of the image pickup surface 1 of the image pickup unit 14. It also occurs that the barcode 2 is arranged in the peripheral portion on the imaging surface 1 of the imaging unit 14. Even in such a case, the binarization of the barcode 2 is not impossible.

Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.
The threshold variable setting unit 17 calculates a level difference Δd between the gradation level p (i) of the pixel of interest i and the gradation level p (i−1) of the pixel i−1 one pixel before. However, the present invention is not limited to this, and the level difference Δd of each gradation level between the pixel of interest i and a plurality of pixels before the pixel of interest i, for example, two pixels before, may be calculated.
In the above-described embodiment, the case where the present invention is applied to the barcode 2 has been described. However, the present invention is not limited to this, and the present invention can also be applied to changing and setting a threshold value when, for example, reading a QR code as a two-dimensional code.

  It is determined whether the boundary between the black bar portion and the background portion is in the black bar portion or in the background portion from two pixels before the pixel of interest i, but is not limited to two pixels immediately before the pixel of interest i. For example, it may be determined whether the pixel is in the black bar portion or the background portion from the pixel three pixels or more immediately before.

  1: imaging surface of imaging device, 2: barcode, 10: CPU 101: ROM, 12: RAM, 13: communication interface (communication I / F), 14: imaging unit, 15: binarization processing unit, 16: decoding Part, 17: Threshold variable setting part, 18: Product.

Claims (6)

At least a two-dimensional code is imaged by an imaging device to obtain multi-gradation image data, the multi-gradation image data is binarized using a threshold value, and the two-dimensional code is obtained from the binarized data. In a two-dimensional code reader for reading information contained in
The gradation level of the pixel of interest in the direction of reading the two-dimensional code in the multi-gradation image data and the gradation level of a pixel at least one pixel before the pixel of interest in the direction of reading the two-dimensional code. It is determined whether or not the level difference of the fluctuation is equal to or less than a boundary determination level difference for determining the boundary between the black bar portion and the background portion in the preset two-dimensional code. If the difference is less than or equal to the preset boundary determination level difference, the threshold value is increased or decreased. If the difference is not less than or equal to the preset boundary determination level difference, the threshold value is increased. Or a threshold variable setting unit that does not decrease,
A two-dimensional code reading device comprising:   The threshold variable setting unit, when the level difference is equal to or less than the preset boundary determination level difference, the gradation level of the target pixel and the gradation of the pixel at least one pixel before the target pixel. 2. The two-dimensional code reading device according to claim 1, wherein the threshold value is increased or decreased based on the level difference from the level.   The threshold variable setting unit, when the level difference is equal to or less than the preset boundary determination level difference, the gradation level of the target pixel and the gradation of the pixel at least one pixel before the target pixel. It is determined whether the level change between levels is zero, increasing, or decreasing. If the level difference is zero as a result of this determination, the threshold is not changed. 3. The threshold value is increased if the level difference is in the increasing direction, and the threshold value is decreased if the level difference is in the decreasing direction. Two-dimensional code reader. At least a two-dimensional code is imaged by an imaging device to obtain multi-gradation image data, the multi-gradation image data is binarized using a threshold value, and the two-dimensional code is obtained from the binarized data. In a two-dimensional code reading method for reading information contained in
The gradation level of the pixel of interest in the direction of reading the two-dimensional code in the multi-gradation image data and the gradation level of a pixel at least one pixel before the pixel of interest in the direction of reading the two-dimensional code. It is determined whether or not the level difference of fluctuation is equal to or less than a boundary determination level difference for determining a boundary between the black bar portion and the background portion in the preset two-dimensional code,
As a result of this determination, if the level difference is less than or equal to the preset boundary determination level difference, the threshold value is increased or decreased,
If the level difference is not less than or equal to the preset boundary determination level difference, the threshold value is not increased or decreased.
A two-dimensional code reading method.   When the level difference is equal to or less than the preset boundary determination level difference, based on the level difference between the gradation level of the target pixel and the gradation level of a pixel at least one pixel before the target pixel 5. The two-dimensional code reading method according to claim 4, wherein the threshold value is increased or decreased. When the level difference is equal to or less than the preset boundary determination level difference, the level difference between the gradation level of the target pixel and the gradation level of a pixel at least one pixel before the target pixel is zero. Determine whether the direction is increasing or decreasing.
If the level difference is zero as a result of the determination, the threshold value is not changed, and if the level difference is in the increasing direction, the threshold value is increased and the level difference is decreased. If the direction, decrease the threshold,
The two-dimensional code reading method according to claim 5.

Images