JP2013148981A - Two-dimensional code reading device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-dimensional code reading device which rarely fails in reading.SOLUTION: In order to execute disappearance correction with higher correction capability than that of detection correction when the detection correction fails, a gray flag is set to a cell with lower reliability of a binarization result (S12). For example, the gray flag is set to a cell whose luminance is ±α to a threshold th. Then, when detection correction processing (S14) fails (NO in S15), a code word including the gray flag is set to an error position (S16), and the disappearance correction is performed (S17). The disappearance correction has double correction capability than that of the detection correction. Thus, there is a possibility that correction can be performed even when the detection correction fails, the case that reading fails is reduced.

Description

  The present invention relates to a two-dimensional code reader, and more particularly, to binarization of cells.

  In order to decode a code word from a two-dimensional code, it is necessary to binarize the image in order to obtain the contrast (black and white) of the cells in the code. As a binarization method, a discriminant analysis method (Otsu's binarization) for obtaining a threshold value that maximizes a value called a degree of separation is well known.

  However, it is difficult to determine the threshold value uniformly because the image is unevenly illuminated and is subject to blurring. Therefore, Patent Documents 1 and 2 are known in which the threshold value is variable in accordance with a change in the image.

Japanese Patent Laid-Open No. 2-141886 JP 2000-259759 A

  However, when the influence of blur or the like becomes strong, the influence of the surrounding pattern of each cell increases, and it becomes difficult to determine the suitability threshold of each cell. As a result, the number of cases in which the light / dark classification of the cells fails even if the threshold value is variable increases. If the number of classification failures increases and the error correction limit of the code is exceeded, the code cannot be read.

  The present invention has been made based on this situation, and an object of the present invention is to provide a two-dimensional code reading apparatus that is less likely to fail in reading.

  In order to achieve the object, the invention according to claim 1 is directed to an image including a two-dimensional code for reading information from a two-dimensional code in which a plurality of data blocks and error correction code blocks are formed by a plurality of cells. Is a two-dimensional code reading device that binarizes and reads the color of each cell in the captured image, and determines each cell of the two-dimensional code in the captured image as either a bright cell or a dark cell Binarizing means, a gray setting means for setting a gray flag for a cell with low reliability of the binarization result by the binarizing means, and detection correction using the code of the error correction code block If the correction fails by the detection and correction means and the detection and correction means, the data block including the cell in which the gray flag is set is designated as the error position and the erasure correction is performed. Characterized in that it comprises a Cormorant erasure correction means.

  Although erasure correction requires that the error position is known, the correction capability is doubled compared to detection correction performed in a state where the error occurrence position is not specified. In the present invention, when error correction fails, a gray flag is set for a cell with low reliability of the binarization result so that erasure correction with higher correction capability than detection correction can be executed. . When detection and correction fails, erasure correction is performed by designating a data block including a cell with the gray flag set as an error position. Therefore, there are fewer cases where reading fails.

  In the invention described in claim 2, the binarization means tentatively determines whether each cell is a bright cell or a dark cell by two types of binarization processing different from each other, and the two binarization processing Based on the binarization result by the above, each cell is finally determined whether it is a bright cell or a dark cell, and the gray setting means is one of the two types of binarization processing. A temporary gray flag is set for a cell with low reliability of the binarization result, and a temporary gray flag is also set for the other cell with low reliability of the binarization result. The final gray flag is set based on the presence / absence of setting.

  In this way, binarization of each cell is performed by two types of binarization processing different from each other, a temporary gray flag is set based on the respective binarization processing results, and whether or not these two temporary gray flags are set If the final gray flag is set based on the value, it is possible to reduce the setting of the gray flag for the correct binarization result, and as a result, the number of cases where reading fails is further reduced. .

  In the invention of claim 3, the binarization means compares the brightness of each cell with a threshold value for determining the brightness of the cell, thereby determining whether each cell is a bright cell or a dark cell. When the difference between the brightness of each cell and the threshold value is within a preset range, the gray setting unit sets a gray flag for the cell.

  If the gray flag is set in this way, the gray flag can be set with high accuracy for a cell with low reliability of light / dark determination.

  The invention described in claim 4 is an invention embodying the two types of binarization processing in claim 2. In the invention according to claim 4, the binarization means sets a threshold based on a luminance change of surrounding cells existing around each cell, and based on a comparison between the set threshold and the luminance of the cell. , Local binarization means for determining whether each cell is a bright cell or a dark cell, and a partial area set to a range wider than a luminance range for threshold setting in the local binarization means A global binarization unit that sets a threshold value for each cell and determines whether each cell is a bright cell or a dark cell based on a comparison of the set threshold value and the luminance of a cell included in the partial region; including.

  In the invention according to claim 5, the binarization means sets a reference gradient to an intermediate gradient between the luminance gradient between the light cell and the dark cell and the luminance gradient between the same color cells, and for each cell. The brightness gradient of each cell is determined based on whether the luminance gradient between adjacent cells is steeper than the reference gradient and whether the luminance is higher than that of the adjacent cell. Whether the gray setting means sets a gray flag for these two cells based on whether or not the luminance gradient between adjacent cells is within a preset range with respect to the reference gradient. Decide whether or not.

  In this way, the gray flag can be set based on the luminance gradient. Further, since binarization is performed based on the luminance gradient, binarization can be performed correctly even if the cell center is dirty.

  In the invention according to claim 6, the gray setting means, even though the cells adjacent to each other are both set as dark cells or both light cells by the binarization means, the luminance gradient between the adjacent cells. Is equal to or greater than the reference gradient, and even if one of the cells adjacent to each other is set as a dark cell and the other as a bright cell by the binarization means, If the luminance gradient is any of the reference gradients or less, a gray flag is set for the cells adjacent to each other.

  When cells adjacent to each other are both set as dark cells or light cells, the luminance gradient between the adjacent cells should be gentle. Nevertheless, if the luminance gradient between the adjacent cells is greater than or equal to the reference gradient, there is a high possibility that the cell brightness determination is incorrect. In addition, when one of adjacent cells is set as a dark cell and the other is set as a bright cell, the luminance gradient between the adjacent cells should be a relatively steep gradient. Nevertheless, if the luminance gradient between the adjacent cells is less than or equal to the reference gradient, there is a high possibility that the cell brightness determination is incorrect. Therefore, by setting a gray flag in these cases, it is possible to set a gray flag for a cell that is highly likely to be erroneously determined to be bright or dark.

  In the invention according to claim 7, the binarization means uses a plurality of images obtained by imaging the two-dimensional code under different conditions, and each cell of the two-dimensional code is a bright cell or a dark cell for each image. Is temporarily determined, and based on the provisional determination results from these two images, it is finally determined whether each cell is a bright cell or a dark cell. A gray flag is set for a cell whose image binarization result is inconsistent.

  As described above, it is possible to accurately set the gray flag for the cells having low reliability of the brightness determination by setting the gray flag for the cells in which the binarization results of the two images do not match. . As a result, erasure correction is performed on a block including cells that are likely to be wrong in light / dark determination, so that the possibility of correcting light / dark errors is improved. Therefore, the possibility of successful reading is further improved.

  The invention according to claim 8 includes score setting means for setting a gray score based on a degree of confidence of the binarization result by the binarization means, and the gray setting means includes a cell in which a gray flag is set. The gray flag is set in order from the cell of the gray score on the side indicating that the degree of reliability of the binarization result is low within a range in which the number of blocks to be included does not exceed the preset erasure correction prescribed number.

  In this way, erasure correction beyond the erasure correction capability is suppressed. As a result, since the possibility of successful erasure correction increases, the possibility of successful reading is improved.

It is a block diagram which shows the mechanical structure of the two-dimensional code reader 10 used as embodiment of this invention. It is a flowchart which shows the outline | summary of a code reading process. It is a figure which shows the example of the threshold value th set by step S1 of FIG. 3 is a flowchart showing details of the mapping and decoding process of FIG. 2 performed in the first embodiment. It is a flowchart which shows the detail of the gray setting process of step S12. (A) is a schematic diagram showing a block arrangement of a QR code (registered trademark), and (B) is an example of data processing of an error block. It is a figure which shows the comparison result of 1st Embodiment and the conventional method with 10 sample images, (A) is a graph which compared the total number of errors, (B) is a graph which compared the correction cost. This is a gray setting process executed in the second embodiment. FIG. 9 is a part of a gray setting process executed subsequent to FIG. It is a figure which illustrates the surrounding cell in the binarization process performed by step S35 of FIG. It is the figure which expanded a part of picked-up image of a two-dimensional code. It is a graph which shows the luminance change of the part of (A) of FIG. 11, (B), (C). It is a figure explaining an example with no inconsistency of a brightness | luminance gradient and inconsistency. It is a flowchart which shows the gray setting process performed in 3rd Embodiment. FIG. 15 is a part of a gray setting process executed subsequent to FIG. 14. It is a flowchart which shows the code reading process performed in 4th Embodiment. It is a part of code reading process performed following FIG.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a mechanical configuration of a two-dimensional code reading apparatus 10 according to an embodiment of the present invention. The mechanical configuration is the same as that of a conventionally known two-dimensional code reader.

  The circuit unit 20 shown in FIG. 1 is accommodated in a housing (not shown). The circuit unit 20 mainly includes an optical system, a computer system, and a power supply system. The optical system includes a marker light projector 60, a light emitting diode 21, an area sensor 23, an imaging lens 27, and the like.

  The light emitting diode 21 is configured to be able to irradiate the illumination light Lf toward the reading surface R through a reading port (not shown) of the housing body. A two-dimensional code or the like is recorded on the reading surface R. The recording form includes printing, engraving, and the like.

  The area sensor 23 is configured to be able to receive the reflected light Lr irradiated and reflected on the reading surface R. For example, the area sensor 23 includes a light receiving element that is a solid-state image pickup element such as a C-MOS or a CCD. It is arranged in two dimensions of m rows and n columns in the order of 10,000. The light receiving element converts the received light into an electrical signal and outputs it.

  The light receiving surface 23a of the area sensor 23 is positioned so as to be visible from the outside of the housing main body through the above-described reading port, and the area sensor 23 receives incident light incident through the imaging lens 27 as the light receiving surface 23a. It is arranged so that it can receive light.

  The imaging lens 27 functions as an imaging optical system capable of condensing incident light incident from the outside via a reading port and forming an image on the light receiving surface 23a of the area sensor 23. And a plurality of condensing lenses housed in the lens barrel. The reflected light Lr that is reflected from the two-dimensional code by the illumination light Lf emitted from the light emitting diode 21 and is incident on the reading port is condensed by the imaging lens 27, and thereby the code image is formed on the light receiving surface 23 a of the area sensor 23. Forms an image. The marker light projector 60 projects the marker light M indicating the reading range of the two-dimensional code onto the reading surface R.

  Next, a configuration outline of the computer system will be described. The computer system includes an amplification circuit 31, an A / D conversion circuit 33, a memory 35, an address generation circuit 36, a synchronization signal generation circuit 38, a control circuit 40, an operation switch 42, an LED 43, a buzzer 44, a liquid crystal display 46, and a communication interface 48. Etc. This computer system can process the image signal of the code image captured by the optical system described above in hardware and software. The control circuit 40 also performs control related to the entire system of the two-dimensional code reader 10.

  The image signal (analog signal) output from the area sensor 23 of the optical system is amplified by a predetermined gain by being input to the amplifier circuit 31, and then input from the analog signal when input to the A / D conversion circuit 33. Converted into a digital signal. The digitized image signal, that is, image data (image information) is input to the memory 35 and stored. The synchronization signal generation circuit 38 is configured to generate a synchronization signal for the area sensor 23 and the address generation circuit 36. The address generation circuit 36 is based on the synchronization signal supplied from the synchronization signal generation circuit 38. Thus, the storage address of the image data stored in the memory 35 can be generated.

  The memory 35 is a semiconductor memory device, and corresponds to, for example, a RAM (DRAM, SRAM, etc.) or a ROM (EPROM, EEPROM, etc.). In addition to the image processing program, the ROM stores in advance a system program that can control each hardware such as the marker light projector 60, the light emitting diode 21, and the area sensor 23.

  The control circuit 40 is a computer that can control the entire two-dimensional code reader 10 and includes a CPU, a system bus, an input / output interface, and the like. The control circuit 40 is configured to be connectable to various input / output devices (peripheral devices) via a built-in input / output interface, and includes a power switch 41, an operation switch 42, an LED 43, a buzzer 44, and a liquid crystal display 46. The communication interface 48, the marker light projector 60, and the like are connected.

  Accordingly, for example, code reading processing, monitoring and management of the power switch 41 and the operation switch 42, turning on / off the LED 43 functioning as an indicator, turning on / off the buzzer 44 capable of generating a beep sound and an alarm sound, Is a screen control of the liquid crystal display 46 capable of displaying the code contents of the read two-dimensional code, communication control of the communication interface 48 enabling communication with an external device, and projection of the marker light M from the marker light projector 60. Control is possible.

  The power supply system includes a power switch 41, a battery 49, and the like. When the power switch 41 managed by the control circuit 40 is turned on and off, the conduction of the drive voltage supplied from the battery 49 to each device and each circuit described above is established. Or shut off is controlled.

  Next, the reading process of the control circuit 40 will be described. The reading process is a process of reading a character code from the captured code image. In the reading process, it is determined whether each cell constituting the two-dimensional code is a dark cell or a bright cell. In this cell color determination (cell light / dark determination), a binarization process of the cell center luminance is performed. The position of the cell center is determined based on the position of the feature pattern. Since the feature pattern has a predetermined position and range in the two-dimensional code, the center coordinates of each cell of the two-dimensional code can be determined based on the position of the feature pattern.

  FIG. 2 is a flowchart showing an outline of the code reading process. The code reading process will be described in more detail with reference to FIG. The process of FIG. 2 starts when an image including a code is captured by a user operation.

  First, in step S1, imaging data is acquired from the memory 35, and a threshold value th for distinguishing between bright cells and dark cells is set by a conventionally known method such as discriminant analysis. FIG. 3 shows an example of the threshold th. As shown in FIG. 3, for example, the threshold th is set to a luminance that indicates a minimum value between a luminance peak indicating a dark cell and a luminance peak indicating a bright cell. FIG. 3 also shows a margin α for this luminance. The size of the margin α is set in advance.

  In step S2, a feature pattern is detected from the code. For example, in a QR code (registered trademark), a cut-out symbol (finder pattern) is detected. In step S3, the center coordinates of each cell of the code are determined based on the feature pattern detected in step S2. Further, the brightness of each cell is determined from the brightness of the center coordinates. This process is also called mapping. In step S4, a decoding process is performed based on the brightness of each cell determined in step S3.

  FIG. 4 is a flowchart showing details of the mapping and decoding process of FIG. 2 performed in the first embodiment. First, in step S11, the center coordinates of each cell are determined. In step S12, a gray setting process is performed. Details of the gray setting process in step S12 are shown in FIG.

  In FIG. 5, the processes of steps S21 to S24 are performed for each cell. First, in step S21, the luminance with respect to the cell center coordinates determined in step S11 is compared with the threshold th set in step S1 of FIG.

  In step S22, as a result of the comparison in step S21, it is determined whether or not the luminance of the cell center coordinates is within ± α from the threshold th. If this determination is affirmative, the process proceeds to step S23, and a gray flag is stored (set) for the cell. Thereafter, the process proceeds to step S24. On the other hand, if the determination in step S22 is negative, that is, if the brightness of the cell center coordinates is more than ± α from the threshold th, the process proceeds directly to step S24 without going through step S23. In step S24, the brightness of the cell is stored based on the comparison result in step S21.

  Returning to FIG. 4, in step S13, a code word is obtained from each block of the code. In step S14, a known detection and correction process is performed. This detection and correction processing is error correction performed in a state where an error occurrence position is not specified, and an error correction code (for example, a Reed-Solomon code) included in the code as an error correction code is acquired and the acquired error correction is performed. The code is used to check whether the code word acquired in step S13 is correct.

  In step S15, it is determined whether or not the correction is successful as a result of the process in step S14. If step S15 is affirmative, the process proceeds to step S18. On the other hand, if the determination in step S15 is negative, that is, if the detection and correction process has failed, the process proceeds to step S16.

  In step S16, a gray flag reflection process is performed. This gray flag reflection process is a process of setting the position of a code word (that is, a block) including a cell for which the gray flag is set in FIG. 5 as an error position. FIG. 6A is a schematic diagram showing a block arrangement of a QR code (registered trademark). In FIG. 6A, a cross indicates a code word including a cell in which a gray flag is set. The code word including the cell marked with x is changed to a code indicating that it is incorrect, for example, “0” in FIG. 6B. This process is the process of step S16.

  In subsequent step S17, erasure correction is performed. More precisely, error correction is performed again, but erasure correction is performed for blocks whose error positions are known. Although the erasure correction is based on the premise that the error position is known, only one erasure numerical polynomial is obtained from the syndrome polynomial. Therefore, the correction capability is twice that of error correction. Therefore, even if the detection correction process is determined to have failed in step S15, the erasure correction in step S17 may be successful.

  In step S18, the result of the process in step S17 or step S14 is output. Specifically, if the result of step S15 is an affirmative determination, the result of correction success (that is, reading success) and the read data are output. When step S17 is executed, the success / failure of the correction is output, and when the correction is successful, the data obtained by the correction process is output.

  Here, the fact that the readability of the method of the present embodiment is improved as compared with the conventional method will be quantitatively described using the correction cost. The relational expression of the correction cost in the Reed-Solomon method is shown in (1). In Equation (1), ECC is the correction cost, P is the number of error detections, FP is the number of error detection errors, and E is the number of errors.

ECC = P + FP + (E−P) × 2 (1)
The error detection number P, error error detection number FP, and error number E will be described in detail as follows. The error detection number P is the number of blocks including cells that are actually erroneously binarized among the cells for which the gray flag is set. The error detection number FP is the number of blocks including cells for which a gray flag is set but binarization is not erroneous. The error number E is the number of blocks including cells in which the binarization result is incorrect. In addition, (E−P) in Expression (1) means the number of blocks including cells in which the binarization result was incorrect but the gray flag could not be set. About this, since erasure correction cannot be performed, that is, detection correction is performed, it is multiplied by a coefficient “2”.

  In the case of the conventional method in which no gray flag is set, P = 0 and FP = 0. Therefore, the correction cost ECC is 2E. On the other hand, in this embodiment, if all error positions can be detected, E = P and FP = 0. In this case, since the correction cost ECC is E, it can be seen that correction can be performed at half the cost of the conventional method.

  FIG. 7 is a diagram showing a comparison result between the present embodiment and the conventional method with 10 sample images, FIG. 7A is a graph comparing the total number of errors, and FIG. 7B shows the correction cost. It is the graph compared.

  As shown in FIG. 7A, in the present embodiment, there is a possibility that the gray flag is set even for those that are not actually in error, so the total number of errors increases from the actual number of errors E. However, as shown in FIG. 7B, the correction cost is lower than the conventional one. From the results of FIG. 7, it can be seen that the method of this embodiment has improved readability compared to the conventional method.

  As described above, according to the present embodiment described above, when detection correction fails, in order to perform erasure correction with higher correction capability than detection correction, for a cell with low reliability of the binarization result The gray flag is set. Specifically, when the luminance is ± α with respect to the threshold th, a gray flag is set for the cell (S23 in FIG. 5). If the detection correction process (FIG. 4: S14) fails (FIG. 4: S15 is NO), the code word including the gray flag is set to the error position (FIG. 4: S16), and the erasure correction is performed. Perform (FIG. 4: S17). The erasure correction is twice the correction capability than the detection correction. Therefore, according to the present embodiment, there is a possibility that the correction can be performed even if the detection / correction is unsuccessful.

(Second Embodiment)
Next, a second embodiment will be described. The second embodiment differs from the first embodiment in gray setting processing. FIG. 8 shows gray setting processing executed in the second embodiment. In the second embodiment, two kinds of different binarization processes are performed, and a temporary gray flag is set in each binarization process. Then, using the results of these two types of binarization processing, determination of the brightness of the cell and setting of the gray score are performed. The meaning of the gray score will be described later.

  First, in step S31, a first binarization process is performed. The first binarization process in the second embodiment performs binarization of each cell from a global viewpoint. The processing in step S31 corresponds to the global binarization means in the claims.

  The specific processing content of step S31 divides the two-dimensional code portion of the captured image into a plurality of partial areas, sets a first threshold th1 for each partial area, and includes the set first threshold th1 and the partial area. This is a process of comparing the brightness of cells to be compared. The size of the partial region is set to a range wider than a luminance range for setting a threshold value in a second binarization process (local binarization process) described later. For example, a two-dimensional code is divided into nine 3 × 3, and each divided area is set as a partial area. The first threshold th1 in the partial area is determined by the same method as in the first embodiment. The determined first threshold th1 is compared with the luminance of the center coordinates of each cell.

  In subsequent step S32, as a result of the comparison, it is determined whether or not the luminance of the cell center coordinates is within ± α from the first threshold th1. Note that α is set in advance, but need not be the same value as in the first embodiment.

  If the determination in step S32 is affirmative, the process proceeds to step S33, and the temporary gray flag 1 is stored (set) for the cell. Thereafter, the process proceeds to step S34. On the other hand, if the determination in step S32 is negative, that is, if the luminance of the cell center coordinates is more than ± α from the first threshold th1, the process proceeds directly to step S34 without going through step S33. In step S34, the brightness of the cell is stored based on the comparison result in step S31. The brightness of the cell stored here is defined as cell brightness 1.

  In step S35, a second binarization process is performed. The second binarization process binarizes each cell from a local viewpoint. The processing in step S35 corresponds to the local binarization means in the claims.

  The specific processing content of step S35 sets a threshold value (second threshold value th2) from the luminance change of surrounding cells existing around each cell, and compares the set second threshold value th2 with the luminance of the cell. FIG. 10 is a diagram illustrating neighboring cells. When setting the brightness of a circle-shaped cell, the brightness of eight cells surrounding the cell and the vertical and horizontal directions of the cell are two adjacent to the corresponding cell. This cell is also included. Therefore, a total of 12 cells are used as peripheral cells, and the threshold value (second threshold th2) of the cell at the center is determined based on the luminance of the 12 cells. The determined second threshold th2 is compared with the luminance of the center coordinates of each cell.

  In the subsequent step S36, it is determined whether or not the luminance of the cell center coordinates is within ± β from the second threshold th2 as a result of the comparison in step S35. This β is also set in advance. The value of β may be the same as or different from α.

  If the determination in step S36 is affirmative, the process proceeds to step S37, and the provisional gray flag 2 is stored (set) for the cell. Thereafter, the process proceeds to step S38. On the other hand, if the determination in step S36 is negative, that is, if the luminance of the cell center coordinates is more than ± β from the second threshold th2, the process proceeds directly to step S38 without going through step S37. In step S38, the brightness of the cell is stored based on the comparison result in step S35. The brightness of the cell stored here is defined as cell brightness 2.

  In step S39, the cell contrast 1 set in step S34 and the cell contrast 2 set in step S38 are compared. Also, the temporary gray flag 1 set in step S33 and the temporary gray flag 2 set in step S37 are compared. The subsequent processing is shown in FIG.

  In step S40, using the result of step S39, it is determined whether either one of the gray flags 1 and 2 is set. If this determination is affirmative, the process proceeds to step S42. On the other hand, if neither the gray flag 1 nor the gray flag 2 is set, the process proceeds to step S41.

  In step S41, it is determined as a result of the comparison in step S39 whether cell brightness 1 and cell brightness 2 are inconsistent. Even if they do not match, the process proceeds to step S42. On the other hand, if cell brightness 1 and cell brightness 2 match, the process proceeds directly to step S43.

  In step S42, a gray score is set. Here, step S42 is executed when step S40 is affirmative or when step S41 is affirmative. That is, either when the gray flag is set in one of the binarization processes, or when the binarization results (brightness and darkness) in the two types of binarization processes are different.

  The gray score is set to a larger value as the deviation from the threshold th is smaller. The smaller the deviation from the threshold th, the lower the reliability of the binarization result. Therefore, the greater the gray score, the lower the reliability of the binarization result.

  In the present embodiment, two threshold values, the first threshold value th1 and the second threshold value th2, are set. The gray score is determined based on the difference between the threshold th on one of these predetermined thresholds and the luminance of each cell in the binarization processing method corresponding to the threshold th. Moreover, you may determine a gray score using the one with the larger difference of the brightness | luminance of a threshold value and each cell among two types of binarization methods. Alternatively, the gray score may be determined based on a value obtained by averaging the difference between the threshold value and the luminance of each cell in both binarization methods.

  In step S43, the final cell brightness is stored. In the second embodiment, two types of binarization processing, ie, first binarization processing and second binarization processing, are performed. In step S43, the binarization results are integrated. If the two types of binarization results match, the cell contrast indicated by the binarization result is stored. If they do not match, the cell brightness on the preset side is stored as the final cell brightness.

  In step S44, the gray scores are sorted. Then, Steps S45 and S46 are executed for the cell for which the gray score is set. In step S45, it is determined whether or not the number of blocks including cells for which the gray flag is set has reached the erasure correction prescribed number. This specified number of erasure corrections is preset in a range not exceeding the number of error correction codewords. In erasure correction, the maximum number of error correction codewords can be corrected. Therefore, the specified number of erasure corrections is set in a range not exceeding the number of error correction codewords. Further, if the prescribed number of erasure corrections is set to the number of error correction codewords, that is, the maximum number, the gray score is not set, but the cell in which the binarization result is incorrect cannot be corrected. Therefore, the erasure correction prescribed number is set to an appropriate value within a range not exceeding the number of error correction codewords.

  If the determination in step S45 is negative, the process proceeds to step S46. In step S46, the gray flag is set to the cell with the highest gray score among the gray flag non-set cells. After executing step S46, the process returns to step S45, and the above-described determination is performed again. As a result, the gray flag is set in the descending order of the gray score until the number of blocks including the cells for which the gray flag is set reaches the erasure correction prescribed number. Then, when the erasure correction prescribed number is reached, the gray setting process of FIGS. Even if the erasure correction prescribed number is not reached, the gray setting process is also ended when the gray flag is set for all the cells for which the gray score is set.

  After the gray setting process is completed, step S13 and subsequent steps in FIG. 4 are executed as in the first embodiment.

  As described above, according to the second embodiment described above, two different types of binarization processing are performed (steps S31 and S35), and the temporary gray flags 1 and 2 are set based on the respective binarization processing results. (Steps S33 and S37). Then, the final gray flag is set based on whether or not these two provisional gray flags 1 and 2 are set (step S46). Thereby, it is possible to reduce the setting of the gray flag for the correct binarization result, and as a result, the number of cases in which reading fails is further reduced.

  In the second embodiment, when the final gray flag is set from the two provisional gray flags 1 and 2, a gray score indicating the reliability of the binarization result is set first. Gray flags are set in order from the cell with the highest score. Then, when the number of blocks including the cell for which the gray flag is set becomes the erasure correction prescribed number, the setting of the gray flag is finished. Therefore, it is possible to suppress erasure correction beyond the erasure correction capability. As a result, since the possibility of successful erasure correction increases, the possibility of successful reading is improved.

  In addition, by setting the gray flag in order from the cell with the highest gray score, it is possible to perform erasure correction for those with low reliability of the binarization processing result. This also increases the likelihood of successful reading.

(Third embodiment)
Next, a third embodiment will be described. The third embodiment is also different from the first embodiment in the gray setting process. In the third embodiment, the gray flag is set based on the degree of the luminance gradient between adjacent cells and the presence or absence of gradient inconsistency.

  First, the luminance gradient between adjacent cells and the gradient contradiction will be described. FIG. 11 is an enlarged view of a part of the captured image of the two-dimensional code. In this figure, a cross, a solid line, a broken line, (A), (B), and (C) are added for explanation. A cross indicates the cell center, and a solid line and a broken line connecting the crosses indicate locations where the luminance gradient is calculated. In particular, (A), (B), and (C) are appended to the solid line. FIG. 12 shows changes in luminance in the portions (A), (B), and (C).

  In FIG. 12, in each of (A), (B), and (C), the horizontal axis represents the image position, and the vertical axis represents the luminance. FIG. 12A shows a change in luminance between dark cells, and FIG. 12C shows a change in luminance between dark cells and bright cells. The luminance gradient in FIG. 12B is an intermediate gradient between these. When the luminance gradient is as shown in FIG. 12B, at least one of the two cells indicating the luminance gradient is brighter than the original light and darkness of the cell for some reason such as imaging conditions and dirt. Or, it can be said that the image is captured darkly. Therefore, in the third embodiment, a gray score is set for a cell having an intermediate luminance gradient as shown in FIG.

  In the third embodiment, not only the brightness gradient level but also the brightness gradient contradiction is determined, and the gray flag is set based on the determination result.

  FIG. 13 is a diagram for explaining an example where there is no contradiction in luminance gradient and there is a contradiction. In FIG. 13, squares with numbers 1, 2, 3, and 4 indicate one cell, and as shown in the legend on the right side of FIG. 13, the arrows have a certain luminance gradient. This indicates that the base end of the arrow is on the high brightness side and the tip is on the low brightness side.

  In FIG. 13, (a) and (b) are examples in which there is no contradiction in luminance gradient, and (c) and (d) are examples in which there is a contradiction in luminance gradient. In FIG. 13A, an arrow from cell 1 is entered for cell 2. From this, it can be estimated that cell 1 is a bright cell and cell 2 is a dark cell. Cell 2 also has an arrow from cell 4. From this, it can be estimated that the cell 4 is a bright cell and the cell 2 is a dark cell. The estimation results for cell 2 from the two arrows are consistent.

  In FIG. 13B, an arrow is entered from the cell 1 with respect to the cell 2. Further, an arrow from cell 3 is entered for cell 4. From these, it can be estimated that the cells 1 and 3 are bright cells and the cells 2 and 4 are dark cells. There are no arrows between the cells 1 and 3 that are both bright cells and between the cells 2 and 4 that are both dark cells. There is no contradiction in this respect.

  On the other hand, in FIG. From this, it can be estimated that cell 1 is a bright cell and cell 2 is a dark cell. Further, an arrow from cell 3 is entered for cell 4. From this, it can be estimated that the cell 3 is a bright cell and the cell 4 is a dark cell. Thus, although both cells 2 and 4 can be estimated as dark cells, an arrow is entered from cell 2 to cell 4. Therefore, the arrows between the cells 2 and 4 are contradictory.

  In FIG. 13D, an arrow is entered from the cell 1 with respect to the cell 2. From this, it can be estimated that cell 1 is a bright cell and cell 2 is a dark cell. An arrow is entered from the cell 4 to the cell 3. From this, it can be estimated that the cell 4 is a bright cell and the cell 3 is a dark cell. However, there is no arrow from cell 1 that can be estimated to be a bright cell to cell 3 that can be estimated to be a dark cell. Thus, cells 1 and 3 are contradictory. Similarly, there is no arrow from cell 4 that can be estimated to be a bright cell to cell 2 that can be estimated to be a dark cell. Therefore, the cells 2 and 4 are also contradictory.

  In the third embodiment, the gray flag is set based on the luminance gradient between adjacent cells and the presence or absence of the gradient inconsistency as described above. FIG. 14 is a flowchart showing gray setting processing executed in the third embodiment. First, step S51 is executed for each cell. In step S51, gradient information is collected. The gradient here is a gradient between four adjacent cells that are adjacent vertically and horizontally.

  In subsequent step S52, a reference gradient is set. The reference gradient is an intermediate gradient between the gradient when both adjacent two cells are dark cells, or when both adjacent two cells are bright cells, and when the adjacent two cells are both bright and dark cells. And In determining the reference gradient, a fixed pattern (for example, a finder pattern or an alignment pattern in the case of a QR code (registered trademark)) is detected in the two-dimensional code, and a bright cell and a dark cell in the fixed pattern are detected. Use the slope between. The reference gradient is determined by multiplying the luminance gradient of the bright cell and the dark cell in the fixed pattern by a predetermined coefficient (for example, 1/2). Also, if there is a place where two adjacent cells are both bright cells or both dark cells in the fixed pattern, the brightness gradient of those bright-light cells and dark-dark cells is also used, An average with the brightness gradient of the dark cell may be used as the reference gradient.

  Subsequently, steps S53 to S55 are executed for each cell. In step S53, it is determined whether or not the gradient information collected in step S51, that is, the gradient between the vertical and horizontal adjacent cells is within the reference gradient ± γ set in step S52. If any one of the vertical and horizontal gradients is within the reference gradient ± γ, an affirmative decision is made in step S53 and the operation proceeds to step S54.

  In step S54, a gray score is set. Similar to the second embodiment, the gray score is set based on a difference from a reference value (here, a reference gradient), and is set to a higher value as the difference is smaller, that is, closer to the reference gradient. .

  After executing step S54, the process proceeds to step S55. If step S53 is negative, the process proceeds directly to step S55. In step S55, the brightness of the cell is stored. The brightness of the cell is determined by comparing the gradient information collected in step S51 with the reference gradient set in step S52. If the gradient information collected in step S51 is higher than the reference gradient, the own cell is a bright cell if the luminance of the own cell is high, and the own cell is a dark cell if the luminance of the own cell is low. To do. If the gradient information collected in step S51 is lower than the reference gradient, it can be said that both the cell and the adjacent cell are dark cells or both bright cells. In this case, whether the cell is a bright cell or a dark cell is determined from the luminance of the own cell. At this time, the reference brightness of the bright cell and the dark cell is determined, and the determined reference brightness is compared with the brightness of the own cell. As the reference luminance, the luminance of a cell capable of estimating brightness and darkness in the fixed pattern used when the reference gradient is set is used. Further, the standard brightness of the bright cell and the dark cell may be determined from the brightness distribution of all the cells, and this standard brightness may be used as the reference brightness.

  In step S56, the brightness gradient inconsistency exemplified with reference to FIG. 13 is determined. More specifically, it is determined that there is a contradiction in the following cases (1) and (2). (1) is a case where the luminance gradient between the adjacent cells is equal to or higher than the reference gradient even though the cells adjacent to each other are both dark cells or bright cells in step S55. (2) is a case where the luminance gradient between the adjacent cells is equal to or less than the reference gradient even though one of the adjacent cells is a dark cell and the other is a bright cell in step S55. In addition, although the cell brightness is also set using the brightness gradient, the brightness gradient when determining the brightness of the cell may be only in one of the upper, lower, left, and right directions. The luminance gradient used in the contradiction determination in step S56 is a luminance gradient in a direction not used for the cell light / dark determination. In any of the cases (1) and (2), it is assumed that there is a contradiction between adjacent cells. After executing step S56, the process proceeds to step S57 in FIG.

  In step S57, the gray scores set in step 54 are sorted. Thereafter, Steps S58 and S59 are executed for the cell for which the gray score is set. In step S58, it is determined whether the number of blocks including cells for which the gray flag is set has reached the erasure correction prescribed number. The specified number of erasure corrections is set as appropriate as in the second embodiment.

  If the determination in step S58 is negative, the process proceeds to step S59. In step S59, a gray flag is set for a cell in which the gray flag is not set based on the contradiction determined in step S56 and the gray score set in step S54. Specifically, first, a gray flag is set for a cell determined to have a contradiction in a plurality of directions among cells determined to have a contradiction. In the contradiction determination in step S56, even if the cell contrast of the own cell is not incorrect, there is a possibility that the gradient is determined to be inconsistent if the contrast of the cell adjacent to the own cell is incorrect. However, when it is determined that there is a contradiction in a plurality of directions, it is highly possible that the brightness determination of the own cell, not the neighboring cell, is incorrect. Therefore, first, a gray flag is set for a cell that is determined to have inconsistencies in a plurality of directions.

  As a result, when the specified number of disappearances is not reached, a gray flag is set for a cell for which a gray score is set. Specifically, the gray flag is set in the cell having the highest gray score among the remaining cells in which the gray score is set but the gray flag is not yet set. Then, even if the gray flag is set for all the cells for which the gray score is set, if the erasure correction prescribed number is not yet reached, the cell is determined to have a contradiction, and is in one direction. A gray flag is set for cells that are determined to be inconsistent only in. If the gray flag cannot be set for all the cells determined to have inconsistency only in one direction, the gray flag is set in order from the cell having the smallest difference from the reference gradient.

  If it is determined in step S58 that the specified number of erasure corrections has been reached, the gray setting process of FIGS. Even if the erasure correction prescribed number is not reached, the gray setting process is also ended when the gray flag is set for all the cells for which the gray score is set. After the gray setting process is completed, step S13 and subsequent steps in FIG. 4 are executed as in the first and second embodiments.

  As described above, according to the third embodiment described above, binarization of each cell is performed using the luminance gradient of two adjacent cells (S51, S52, S55). It can also be valuated.

  In the third embodiment, the brightness gradient contradiction is determined (S56), and the gray flag is set using the brightness gradient conflict determination result. If there is a contradiction in the brightness gradient, it is highly possible that the binarization result of the cell is wrong. A gray flag can be set for a cell having a high possibility of being present. Therefore, the reading accuracy is further improved.

(Fourth embodiment)
Next, a fourth embodiment will be described. In the fourth embodiment, reading is performed using a plurality of captured images having different imaging conditions (herein described as two images). The imaging conditions to be varied are, for example, illumination conditions. Moreover, you may image simultaneously with several cameras. In this case, the imaging direction is different.

  FIG. 16 is a flowchart showing a code reading process performed in the fourth embodiment. This process starts when two images including a code are captured by a user operation.

  First, in step S61, the reading process 1 is executed. This reading process 1 is performed using one of the two captured images. As the content of the process, various conventionally known code reading processes can be used.

  In step S62, it is determined whether or not the reading process 1 in step S61 is successful. If this determination is affirmative, the process proceeds to step S75 in FIG. 17 and the read data is output. On the other hand, if step S61 is negative, the process proceeds to step S63.

  In step S63, reading process 2 is executed. In the reading process 2, an image on the side different from the image used in step S61 is used out of the two captured images. The content of the process can use various conventionally known code reading processes, and may be the same as or different from step S61.

  In step S64, it is determined whether or not the reading process 2 in step S63 is successful. If this determination is affirmative, the process proceeds to step S75 in FIG. 17 and the read data is output. On the other hand, if step S64 is negative, the process proceeds to step S65.

  In step S65, the presence / absence of map information is determined. The map information is the position of each cell in the two-dimensional code. If the position of each cell has not been determined in any one of the reading process 1 and the reading process 2, it is determined that there is no map information. In this case, the process proceeds to step S75, and the result of reading failure is output as the result of the reading process.

  On the other hand, if the position of each cell can be determined in both reading processes 1 and 2, it is determined that there is map information. In this case, the process proceeds to step S66.

  In step S66, the correspondence relationship of the map information of the reading processes 1 and 2 is determined. That is, each cell in the reading process 1 is determined to correspond to which cell in the reading process 2.

  Subsequently, steps S67 to S70 are executed for each cell. First, in step S67, the cell contrast results of the reading processes 1 and 2 are compared. In step S68, as a result of the comparison in step S67, it is determined whether or not the cell light / dark results of the reading processes 1 and 2 are inconsistent. If not, the process proceeds to step S69.

  In step S69, a gray score is set. The gray score determination method is set, for example, in the same manner as in the embodiments described so far. In step S70, the final cell brightness is stored. The cell contrast stored here is determined by the same method as in the second embodiment. That is, if the binarization results of the reading processes 1 and 2 match, the cell brightness indicated by the binarization result is stored. In the case of mismatch, the cell brightness in the reading process on the preset side is stored as the final cell brightness.

  Steps S71 and thereafter are shown in FIG. In step S71, the gray scores set in step 69 are sorted. Thereafter, Steps S72 and S73 are executed for the cell for which the gray score is set. In step S72, it is determined whether or not the number of blocks including cells for which the gray flag is set has reached the erasure correction prescribed number. This erasure correction prescribed number is appropriately set as in the second and third embodiments.

  In step S73, the gray flag is set to the cell with the highest gray score among the gray flag non-set cells. After executing step S73, the process returns to step S72, and the above-described determination is performed again. If it is determined that the erasure correction prescribed number has been reached, the process proceeds to step S74.

  In step S74, the position of the code word including the cell storing the gray flag is set as an error position, and erasure correction is performed. Thereafter, the process proceeds to step S75. If the erasure correction in step S74 is successful, the result of successful reading and the read data are output in step S75. On the other hand, if the reading cannot be performed even after the erasure correction, the fact that the reading has failed is output.

  As described above, according to the fourth embodiment described above, two reading processes of reading processes 1 and 2 are executed, and a gray flag is set for a cell in which the cell brightness results in these two reading processes do not match. It is set. As a result, the gray flag can be accurately set for a cell having low light / dark determination reliability. As a result, erasure correction is performed on a block including cells that are likely to be wrong in light / dark determination, so that the possibility of correcting light / dark errors is improved. Therefore, the possibility of successful reading is further improved.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned embodiment, The following embodiment is also contained in the technical scope of this invention, and also the summary other than the following is also included. Various modifications can be made without departing from the scope.

  For example, in the above-described third embodiment, the gray flag is set based on the luminance gradient between adjacent cells and the presence or absence of the luminance gradient contradiction, but the gray flag may be set only from either one.

  Further, the margin α may be determined according to the error correction capability instead of a fixed value. The error correction capability is input by the user, for example. Further, the error correction capability may be read from the code format information.

10: Two-dimensional code reading device, 20: Circuit section, 21: Light emitting diode, 23: Area sensor, 27: Imaging lens, 31: Amplification circuit, 33: A / D conversion circuit, 35: Memory, 36: Address generation Circuit 38: synchronization signal generation circuit 40: control circuit 41: power switch 42: operation switch 43: LED 44: buzzer 46: liquid crystal display 48: communication interface 49: battery 60: marker Optical projector, S12: Gray setting means, S14: Detection correction means, S17: Disappearance correction means, S31: Global binarization means, S35: Local binarization means, S42, S54, S69: Score setting means

Claims (8)

In order to read information from a two-dimensional code in which a plurality of data blocks and error correction code blocks are formed by a plurality of cells, an image including the two-dimensional code is captured, and the color of each cell in the captured image is binary. A two-dimensional code reading device that reads and converts
Binarization means for determining each cell of the two-dimensional code in the captured image as either a bright cell or a dark cell;
A gray setting unit that sets a gray flag for a cell having low reliability of a binarization result by the binarization unit;
Detection and correction means for performing detection and correction using a code of the error correction code block;
A two-dimensional code reader comprising: a erasure correction unit that performs erasure correction by designating a data block including a cell in which a gray flag is set as an error position when correction by the detection and correction unit fails . In claim 1,
The binarization means tentatively determines whether each cell is a bright cell or a dark cell by two different types of binarization processing, and based on the binarization result of the two binarization processing The final decision is whether each cell is a light cell or a dark cell,
The gray setting unit sets a provisional gray flag for a cell having low reliability of one of the two types of binarization processing and the reliability of the other binarization result. A two-dimensional code reading apparatus, wherein a temporary gray flag is set even for a low cell, and a final gray flag is set based on whether or not these two temporary gray flags are set. In claim 1,
The binarization means determines whether each cell is a bright cell or a dark cell by comparing the brightness of each cell with a threshold value for determining the brightness of the cell,
2. The two-dimensional code reading device according to claim 1, wherein the gray setting means sets a gray flag for a cell when the difference between the luminance of each cell and the threshold is within a preset range. In claim 2,
The binarization means includes
A threshold value is set based on a change in luminance of surrounding cells around each cell, and whether each cell is a bright cell or a dark cell is determined based on a comparison between the set threshold value and the luminance of the cell. Local binarization means to
A threshold is set for each partial region set in a range wider than the luminance range for threshold setting in the local binarization means, and based on a comparison between the set threshold and the luminance of cells included in the partial region And a global binarization means for determining whether each cell is a bright cell or a dark cell. In claim 1,
The binarization unit sets a reference gradient to an intermediate gradient between a luminance gradient between a light cell and a dark cell and a luminance gradient between cells of the same color, and for each cell, between the adjacent cells. Determining the brightness of each cell based on whether the brightness gradient is steeper than the reference gradient and whether it is brighter than its neighboring cells;
Whether the gray setting means sets a gray flag for these two cells based on whether or not the luminance gradient between adjacent cells is within a preset range with respect to the reference gradient. A two-dimensional code reader characterized by determining whether or not. In claim 5,
The gray setting means, when the binarization means sets both adjacent cells as dark cells or both as bright cells, but the luminance gradient between the adjacent cells is equal to or higher than the reference gradient. Even though one of the cells adjacent to each other is set as a dark cell and the other as a bright cell by the binarization means, the luminance gradient between the dark cell and the bright cell is less than the reference gradient. In any case, a two-dimensional code reading apparatus is characterized in that a gray flag is set for cells adjacent to each other. In claim 1,
The binarization means uses a plurality of images obtained by capturing the two-dimensional code under different conditions, provisionally determines whether each cell of the two-dimensional code is a bright cell or a dark cell for each image, and 2 Based on the tentative decision result from one image, each cell is finally decided whether it is a light cell or a dark cell,
The two-dimensional code reading device, wherein the gray setting means sets a gray flag for a cell in which the binarization results of the two images do not match. In any one of Claims 1-7,
Score setting means for setting a gray score based on the degree of confidence of the binarization result by the binarization means,
The gray setting means has a gray level on the side indicating that the degree of reliability of the binarization result is low in a range in which the number of blocks including cells with the gray flag set does not exceed a preset erasure correction prescribed number. A two-dimensional code reading device, wherein a gray flag is set in order from a score cell.