JP5807602B2 - Information code reader - Google Patents

Description

  The present invention relates to an information code reader.

  An information code is generally formed by arranging bright cells and dark cells. In an apparatus that reads this type of information code, after the information code is imaged, each cell is identified and the cell is identified. Whether the cell belongs to a light cell or a dark cell is specified by binarization processing. As a method related to binarization of the information code, a follow-up method, a differentiation method, and the like are provided, and a related technology such as Patent Document 1 exists.

JP 2001-28045 A

  When binarizing each cell of the information code, in general, a threshold value for distinguishing light cells from dark cells is set, and each cell of the captured code image is compared with this threshold value. Yes. Then, as a result of the comparison, a technique is used in which a light cell is determined when the luminance is higher than the threshold, and a dark cell is determined when the luminance is lower than the threshold. Such a threshold setting is necessary for both the follow-up method and the differential method described above, and any method requires a threshold setting that can accurately distinguish light and dark.

  However, the above-described method of distinguishing between light and dark according to the threshold is effective in an imaging environment where the contrast is large and the brightness difference between the light cell and the dark cell is large. However, when blur occurs or the contrast decreases. There is a problem that erroneous determination is likely to occur. That is, in a code image obtained under such an imaging environment, even in a portion that should be determined as a light cell originally, the luminance is lowered due to luminance interference from the surrounding pattern, or vice versa. In addition, even in a portion that should be determined as a dark cell, luminance may increase due to luminance interference from surrounding patterns, and it is extremely difficult to appropriately set a threshold value that can distinguish between these light and dark. there were. For this reason, in an imaging environment in which blurring is likely to occur or the contrast is likely to decrease, there is a high risk of decoding failure due to a light / dark determination.

  The present invention has been made in order to solve the above-described problem. In an information code reading apparatus capable of reading an information code formed by arranging bright cells and dark cells, blur is present or the contrast is low. It is an object of the present invention to provide a configuration that can perform binarization processing with high accuracy and can effectively reduce processing time associated with binarization processing.

The present invention comprises an imaging means for imaging an information code including a light color cell and a dark color cell;
Image storage means for storing an image of the information code imaged by the imaging means;
Cell position detection means for detecting the position of each cell from the image of the information code stored in the image storage means;
Luminance detecting means capable of detecting the luminance at each cell position detected by the cell position detecting means;
Brightness / darkness cell detection means for detecting a lightness determination cell whose brightness detected by the brightness detection means is equal to or higher than a first threshold, and for detecting a darkness determination cell where the brightness is lower than a second threshold lower than the first threshold; ,
Intermediate luminance cell detecting means for detecting intermediate luminance cells whose luminance detected by the luminance detecting means is less than the first threshold and exceeds the second threshold;
Brightness / darkness that determines whether the intermediate luminance cell detected by the intermediate luminance cell detection means belongs to the light cell or the dark cell based on the light / dark pattern of a plurality of adjacent cells adjacent to the intermediate luminance cell. A determination means;
A frequency distribution generating unit that classifies the luminance of each cell position detected by the luminance detecting unit for each luminance level and generates a frequency distribution that can specify the frequency for each luminance level; and
In the frequency distribution generated by the frequency distribution generation unit, the light / dark cell detection unit sets the first peak value that peaks on the high luminance side as the first threshold value, and on the lower luminance side than the first peak value. A second peak value that is a peak is set as the second threshold value, a cell having a luminance equal to or higher than the first peak value is detected as the light color determination cell, and a cell having a luminance equal to or lower than the second peak value is set as the dark color determination cell. Detect
Selecting means for selecting the type of the frequency distribution generated by the frequency distribution generating means from a plurality of types determined in advance based on the content of the frequency distribution;
Determination template storage for storing a template group including a plurality of light color templates for determining the light cell and a plurality of dark color templates for determining the dark cell in association with each of the plurality of types. Means,
With
The brightness determination unit selects any one of the template groups stored in the determination template storage unit based on the type of the frequency distribution selected by the selection unit, and a plurality of adjacent brightness pixels A matching template is detected from among the plurality of light color templates and the plurality of dark color templates constituting the template group by pattern matching between the light and dark pattern of the adjacent cell and the template included in the selected template group. , And determining whether the intermediate luminance cell belongs to the light cell or the dark cell based on the detection result .

  According to the first aspect of the present invention, after determining a certain number of cells as bright cells or dark cells based on the first threshold value and the second threshold value, the brightness of the remaining cells (intermediate luminance cells) that cannot be determined is determined. For this reason, it is possible to minimize the processing that takes time for the light / dark determination (light / dark determination processing of the intermediate luminance cell by the light / dark determination means), and to shorten the processing time. Furthermore, since the brightness of the adjacent cells adjacent to the remaining cells (intermediate brightness cells) can be clarified and then the brightness of the intermediate brightness cells can be determined based on the brightness / darkness pattern of these adjacent cells. Even when the contrast is low, binarization can be performed more accurately.

Further , the brightness cell detection unit includes a frequency distribution generation unit that classifies the luminance of each cell position detected by the luminance detection unit for each luminance level and generates a frequency distribution that can specify the frequency for each luminance level, In the frequency distribution generated by the frequency distribution generating means, the first peak value that peaks on the high luminance side is set as the first threshold, and the second peak that peaks on the lower luminance side than the first peak value. The value is set as the second threshold value, a cell having a luminance equal to or higher than the first peak value is detected as the light color determination cell, and a cell having a luminance equal to or lower than the second peak value is detected as the dark color determination cell.
It is highly possible that both ends of the frequency distribution (histogram) (that is, the luminance of the area outside the first peak value and the second peak value) reflect the color of the cell. It is possible to narrow down the cell by accurately determining the brightness and to narrow down the cell.

In particular , for selecting the type of the frequency distribution generated by the frequency distribution generation unit from a plurality of types predetermined based on the content of the frequency distribution, and for determining the light cell A determination template storage means for storing a template group including a plurality of light color templates and a plurality of dark color templates for determining the dark color cells in association with each of the plurality of types; The means selects any one of the template groups stored in the determination template storage means based on the type of the frequency distribution selected by the selection means, and a plurality of adjacent cells adjacent to the intermediate luminance cell are selected. The template group is obtained by pattern matching between the light and dark pattern and the template included in the selected template group. A matching template is detected from the plurality of light color templates and the plurality of dark color templates, and whether the intermediate luminance cell belongs to the light color cell or the dark color cell is determined based on the detection result. To do.
As described above, if a template group is prepared for each type of frequency distribution (histogram) and a template group corresponding to the actually obtained frequency distribution is selected, a template that matches the actual imaging environment is selected. Therefore, it is possible to determine the lightness and darkness more accurately.

According to a second aspect of the present invention, the cell position detection means detects a predetermined representative position of each cell from the image of the information code stored in the image storage means, and the luminance detection means detects the cell position detection. The brightness at the representative position of each cell detected by the means is detected. Further, among the light color determination cell and the dark color determination cell detected by the light / dark cell detection means, neighboring cells are Reference cell detection means for detecting a cell that is not an intermediate luminance cell as a reference cell, a plurality of types of bright and dark cell patterns that can be configured in a predetermined size, and a plurality of templates of luminance value arrays in each bright and dark cell pattern A correction template storage unit storing a template, and the reference cell among a plurality of templates stored in the correction template storage unit Template selecting means for selecting a template corresponding to a cell arrangement of the reference cell detected by the output means and the cells adjacent to the periphery of the reference cell; the reference cell detected by the cell position detecting means; and the reference cell A shift state detection unit that shifts the position from each representative position of a cell adjacent to each other at a certain degree and detects the luminance state at each shifted change position by shifting in a plurality of directions with each representative position as a reference; and Each brightness state obtained by shifting in a plurality of directions from each representative position by the shift state detection means and the template selected by the template selection means are judged to be compatible, and each representative in the brightness state having the highest suitability Correction value detecting means for detecting the degree of displacement from the position as a correction value, and detected by the correction value detecting means. Based on the correction value, characterized by comprising a correction means for correcting the position of each cell other than the reference cell from the representative positions.
In this way, the exact coordinates of the reference cell (coordinates when the compatibility with the template is high) can be selected from the reference cell and the surrounding light and dark pattern and the template corresponding to the light and dark pattern. High accuracy can be measured.

According to a third aspect of the present invention, there is provided an area dividing unit that divides the image of the information code imaged by the imaging unit into a plurality of image areas, and the reference cell detecting unit is configured to generate the image divided by the area dividing unit. The reference cell is detected for each area, the correction value detection means obtains the correction value for each image area divided by the area division means, and the correction means detects the image area by the correction value detection means. A process of correcting the position of each cell from each representative position for each image area is performed so that each correction value obtained for each image area is reflected in each image area.
According to this configuration, correction with higher accuracy is possible. This is particularly advantageous in an environment where the code image is easily distorted or deformed.

FIG. 1 is a block diagram illustrating an information code reading apparatus according to the first embodiment of the invention. FIG. 2 is a flowchart illustrating a reading process in the information code reading apparatus of FIG. FIG. 3 is a graph schematically showing a histogram (frequency distribution) generated by the reading process of FIG. FIG. 4 is an explanatory diagram illustrating the parameters of the histogram measured in the reading process of FIG. FIG. 5 is an image diagram for explaining the point at which the sum of differences between measured histograms and template group parameters is obtained. FIG. 6 is an image diagram for explaining the contents of the template group used in the reading process of FIG. FIG. 7A is an explanatory diagram for explaining the bright and dark cells determined by the processing of S5 and the intermediate luminance cell not determined in the reading processing of FIG. 2, and FIG. It is explanatory drawing explaining about. FIG. 8A is an explanatory diagram for explaining a shift from the center position detected by temporary mapping, and FIG. 8B is represented by an evaluation value obtained by a difference between each shifted measurement result and the template. It is explanatory drawing explaining determining a position (corrected position). FIG. 9A is an explanatory diagram for explaining a target pattern for template matching, and FIG. 9B is an explanatory diagram for explaining the measured luminance of each cell of the target pattern. FIG. 10A to FIG. 10D are explanatory diagrams for explaining patterns that are candidates for the target pattern in FIG. 9A. FIG. 11A to FIG. 11D are explanatory diagrams for explaining a luminance value list for each pattern of FIG. 10A to FIG. 10D registered in the selected template group. FIG. 12 is an explanatory diagram for explaining the content of the finally obtained code. FIG. 13 is a graph illustrating another example of the correction method according to another embodiment.

[First embodiment]
Hereinafter, a first embodiment embodying the present invention will be described with reference to the drawings.
(overall structure)
First, the overall configuration of the information code reading apparatus according to the present embodiment will be described with reference to FIG. As shown in FIG. 1, the information code reader 1 according to the present embodiment is configured as a code reader that reads an information code Q such as a one-dimensional code or a two-dimensional code, and an outer case is configured by a case (not shown). In this case, various electronic components are accommodated in the case.

  The information code reader 1 mainly includes an optical system such as an illumination light source 21, a light receiving sensor 23, a filter 25, and an imaging lens 27, and a micro memory such as a memory 35, a control circuit 40, an operation switch 42, and a liquid crystal display 46. It is composed of a computer (hereinafter referred to as “microcomputer”) system and a power supply system such as a power switch 41 and a battery 49. These are mounted on a printed wiring board (not shown) or housed in a case (not shown).

  The optical system includes an illumination light source 21, a light receiving sensor 23, a filter 25, an imaging lens 27, and the like. The illumination light source 21 functions as an illumination light source capable of emitting illumination light Lf, and includes, for example, a red LED and a diffusion lens, a condensing lens, and the like provided on the emission side of the LED. In the present embodiment, illumination light sources 21 are provided on both sides of the light receiving sensor 23, and the illumination light Lf can be irradiated toward the reading object R through a reading port (not shown) formed in the case. It is configured.

  As this reading object R, for example, various objects such as paper, resin material, metal material, and the like are conceivable, and an information code Q is formed on such reading object R by printing, direct marking, or the like. In the following description, an example in which the information code Q is configured as a two-dimensional code D (data matrix code in FIG. 12) as shown in FIG. 12 will be described as a representative example, but includes a light color cell and a dark color cell. If it is an information code, it may be replaced with another two-dimensional code such as a QR code (registered trademark) or a maxi code.

  The light receiving sensor 23 is configured to be able to receive the reflected light Lr irradiated and reflected on the reading object R and the information code Q (two-dimensional code D as shown in FIG. 12). An area sensor in which light receiving elements, which are solid-state imaging elements such as CCDs, are two-dimensionally arranged corresponds to this. The light receiving sensor 23 is mounted on a printed wiring board (not shown) so that incident light incident through the imaging lens 27 can be received by the light receiving surface 23a. The light receiving sensor 23 corresponds to an example of “imaging means”.

  The filter 25 is an optical low-pass filter that allows passage of light that is less than or equal to the wavelength of the reflected light Lr and blocks passage of light that exceeds the wavelength, and a reading port (not shown) formed in the case. It is provided between the imaging lens 27. Thereby, unnecessary light exceeding the wavelength equivalent of the reflected light Lr is prevented from entering the light receiving sensor 23. Further, the imaging lens 27 is constituted by, for example, a lens barrel and a plurality of condensing lenses accommodated in the lens barrel. In the present embodiment, the imaging lens 27 is provided at a reading port (not shown) formed in the case. The incident reflected light Lr is collected, and a code image of the information code Q can be formed on the light receiving surface 23 a of the light receiving sensor 23.

  The microcomputer 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 microcomputer system is configured around a control circuit 40 and a memory 35 that can function as a microcomputer (information processing apparatus), and the image signal of the information code Q imaged by the optical system described above is signaled in hardware and software. It can be processed.

  An image signal (analog signal) output from the light receiving sensor 23 of the optical system is input to the amplification circuit 31 and amplified by a predetermined gain, and then input to the A / D conversion circuit 33, and the digital signal is converted from the analog signal. Is converted to The digitized image signal, that is, image data (image information) is input to the memory 35 and stored in the image data storage area of the memory 35. The synchronization signal generation circuit 38 is configured to be able to generate a synchronization signal for the light receiving 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. A storage address of 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 above-described image data storage area, the RAM of the memory 35 is configured to be able to secure a work area and a reading condition table that are used by the control circuit 40 in each processing such as arithmetic operation and logical operation. . The ROM stores in advance a predetermined program that can execute a reading process and the like that will be described later, and a system program that can control each piece of hardware such as the illumination light source 21 and the light receiving sensor 23.
Note that the memory 35 corresponds to an example of an image storage unit and functions to store an image of an information code captured by the imaging unit.

  The control circuit 40 is a microcomputer capable of controlling the entire information code reader 1, and includes a CPU, a system bus, an input / output interface, and the like, and has an information processing function. Various input / output devices (peripheral devices) are connected to the control circuit 40 via a built-in input / output interface. In this embodiment, a power switch 41, an operation switch 42, an LED 43, a buzzer 44, A liquid crystal display 46, a communication interface 48, and the like are connected. The communication interface 48 can be connected to a host computer HST corresponding to the host system of the information code reader 1.

  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. The battery 49 is a secondary battery that can generate a predetermined DC voltage, and corresponds to, for example, a lithium ion battery.

(Reading process)
Next, a reading process performed by the information code reading device 1 will be described.
In the reading process shown in FIG. 2, first, a code position detection process is performed as the process starts (S1). In this code position detection process, first, image data of the reading object R including the two-dimensional code D is acquired based on the light reception result of the light receiving sensor 23 and stored in the memory 35. This image data is configured as a set of pixel data corresponding to each light receiving element of the light receiving sensor 23. Then, a region of the two-dimensional code D (a code region in which cells are arranged) is specified from this image data by a known method.

  Then, provisional mapping processing for specifying the representative position of each cell in the specified code area is performed (S2). This temporary mapping process is the same as the process of specifying each cell position by a known information code decoding method. For example, as in the known decoding process of a data matrix or QR code (registered trademark), the code position (code area ) To determine the coordinates of a feature pattern (for example, an alignment pattern of a data matrix or a position detection pattern of a QR code (registered trademark)) included in the code area. Thereafter, the number of cells included in the code area is obtained by a known method, and after specifying the center coordinates of each cell included in the code area, the center coordinates are determined as the representative position of each cell. In this way, the representative position of each cell is mapped.

  Then, after the temporary mapping process of S2, each luminance at the center coordinate (representative position) of each cell specified in the process of S2 is sampled to create a histogram (frequency distribution) (S3). FIG. 3 is an example in which the histogram created in S3 is schematically graphed. In the histogram created here, as shown in FIG. 3, the first peak A1 on the low-luminance side mainly composed of dark (black in FIG. 3) cell pixels and the light (white in FIG. 3) cell pixels. A second peak A2 on the high-luminance side is formed, and due to the presence of blur or the like, a certain luminance distribution is also present between the first peak A1 and the second peak A2.

  Then, template selection is performed using the histogram shape and mapping information created in S3 (S4). The template selection at S4 is performed by selecting the template group close to the condition of the current image acquired at S1 from among a large number of template groups that are created in advance and stored in the memory 35, for example. Reduction and improvement of recognition performance.

  Specifically, first, a threshold value T for dividing the histogram is set as shown in FIG. In the case of a two-dimensional code composed of light cells and dark cells, the color of each cell is light (for example, white) and dark (for example, black), so the histogram is divided by using a general binarization method. The threshold T can be subtracted. The threshold value T may be a predetermined luminance, or an intermediate value between the peak of the first peak A1 on the low luminance side and the peak of the second peak A2 on the high luminance side may be used as the threshold T. Alternatively, the luminance of a predetermined cumulative frequency from the low luminance side may be used as the threshold value. By subtracting the threshold value T in this way, the luminance histogram shown in FIG. 3 is divided into a first mountain A1 (black mountain) on the low luminance side and a second mountain A2 (white mountain) on the high luminance side. .

  Then, the approximate contrast is estimated by obtaining the respective peaks of the low luminance side mountain (black mountain) and the high luminance side mountain (white mountain). In addition, blur estimation is performed simultaneously by evaluating the extent of each mountain. Specifically, for example, after dividing the histogram by the threshold T as shown in FIG. 3, Thr_L (peak position of the low brightness side peak (black peak)), Thr_H (high brightness side peak (white peak)) For the peak position). Since the mapping (center position detection) of each cell has been completed in S2 so far, the center coordinates of each cell are known, and a known method (for example, the distance between cells in the vertical direction and the horizontal direction). The cell size can be easily obtained by a method in which the average value of the cell size is used as the cell size or a method in which the distance between the cells in the vertical direction or the horizontal direction is used as the cell size).

  Next, paying attention to the first peak A1 (black peak) on the low luminance side or the second peak A2 (white peak) on the high luminance side, the degree of histogram rounding is measured by obtaining the half width. In the example of FIG. 3, attention is paid to the first peak A1 on the low brightness side, and the brightness Thr_L when the frequency is the peak Y1 and the brightness X1 when the frequency is ½ of the peak Y1 in the peak A1. The difference Wa is a half width. Further, a difference Thr_H−Thr_L between peaks is also obtained. Necessary parameters can be obtained by the above processing. FIG. 4 shows an example of parameters obtained by such processing.

  After the process of S3, a process for selecting a template is performed (S4). In the process of S4, a template group closest to the parameters shown in FIG. 4 may be selected from the template groups registered in advance. Specifically, the difference between each parameter of FIG. 4 obtained and each parameter set in each template group (for example, the total value of the difference of each parameter or the difference value of a specific parameter) is taken, A template group with the smallest difference is selected (see the image diagram in FIG. 5).

  Each template group includes a template in a specific image state (for example, a luminance value list for each cell array pattern for a 3 × 3 cell array pattern in the specific image state) as shown in the image diagram of FIG. 6. The parameters of the histogram indicating the specific image state are set. Specifically, for example, the parameter when the histogram is obtained for the brightness value list for each cell arrangement pattern is configured to be the parameter to be set. Accordingly, when selecting a template group, for example, for each template group, the sum of differences between the already obtained histogram parameters as shown in FIG. 4 and the parameters of each template group is obtained, and the sum is the smallest. A template group to be selected is selected. For example, if each template group is registered in increments of 2 pixels for the cell size, 10 increments for Thr_L and Thr_H, and 5 increments for the half width, the cell size is 4, Thr_L is 30, and Thr_H is 80. The difference from the template group with a half width of 10 is (| 32-30 | + | 84-80 | + | 52-50 | + | 11−10 | = 9), and the parameters in FIG. When the difference between each parameter set in the template group is calculated and the value of “9” is the smallest, the above template group (cell size 4, Thr_L30, Thr_H80, half width 10) is calculated. Template group) is selected. In this way, a template can be selected from the histogram and mapping information.

  The memory 35 corresponds to an example of a determination template storage unit, and functions to store a plurality of light color templates for determining light cells and a plurality of dark color templates for determining dark cells. Specifically, a template group including a plurality of light color templates for determining a light color cell and a plurality of dark color templates for determining a dark color cell is stored in association with each of a plurality of types. ing.

  After selecting a template in S4, rough binarization is performed (S5). The rough binarization of S5 is performed in order to reduce the processing time required for template matching. Specifically, for example, the peak position of the first peak A1 on the low brightness side and the peak position of the second peak A2 on the high brightness side obtained from the histogram of FIG. Rough binarization is performed so that a high luminance is a bright color and a low luminance that is lower than the peak of the first peak A1 is a dark color. By performing rough binarization in this way, a binarization result as shown in FIG. 7A is obtained. By doing so, it is only necessary to perform template matching only for the shaded portion of FIG. The rough binarization threshold is not limited to the setting method as described above. For example, in order to reduce the processing time as much as possible, the binarized range may be widened, and the processing time may be limited to some extent. If it is acceptable, the binarized range should be narrowed.

  In the present embodiment, the control circuit 40 corresponds to an example of a frequency distribution generation unit, and a frequency distribution that can classify the luminance at each cell position detected by the luminance detection unit for each luminance level and specify the frequency for each luminance level. Function to generate.

  The control circuit 40 corresponds to an example of a light / dark cell detection unit, detects a light color determination cell whose luminance detected by the luminance detection unit is equal to or higher than the first threshold value, and has a second threshold value lower than the first threshold value. It functions to detect a dark color determination cell which is as follows. More specifically, the light / dark cell detection means uses the first peak value Thr_H that peaks on the high luminance side in the frequency distribution generated by the frequency distribution generation means as the first threshold, and has a lower luminance than the first peak value. The second peak value Thr_L that becomes a peak on the side is set as the second threshold, a cell having a luminance equal to or higher than the first peak value is detected as a light color determination cell, and a cell having a luminance equal to or lower than the second peak value is detected as a dark color determination cell. .

  Further, the control circuit 40 corresponds to an example of an intermediate luminance cell detection unit, and functions to detect an intermediate luminance cell whose luminance detected by the luminance detection unit is less than the first threshold and exceeds the second threshold. .

  If cells that have not been determined are narrowed down due to rough binarization, the mapping process is performed again (S6). For example, in a blurred image, the color of a cell to be determined is affected not only by the color of the cell but also by the color of the peripheral cell, and the influence increases as the distance to the peripheral cell is approached. For this reason, it is necessary to calculate the cell center coordinates particularly accurately. In the present invention, the center coordinates of a cell whose color is known are strictly determined by rough binarization or template matching, thereby accurately calculating the center coordinates of other cells.

  Among the codes as shown in FIG. 7A obtained by rough binarization, the shaded cells are cells that need to be binarized by template matching (cells whose brightness is not discriminated). In the process of S6, in order to correct the center coordinates of the shaded cells, the coordinates of known peripheral cells are strictly determined. For example, as shown in FIG. 7B, three small areas R1, R2, and R3 are provided inside the code, and the four corner coordinates of each small area are determined strictly. The four corners of each small area are cells in which the surrounding pattern and its own color are known (the area outside the code may be determined as a light color, for example). That is, it can be said that the pattern is known but the exact coordinates are not known. Accordingly, in S6, template matching is performed in order to accurately obtain the coordinates of the reference cell using such a cell as a reference cell. Such an area may be specified for a partial area in the code as shown in FIG. 7B, or a plurality of areas may be specified for all areas.

  FIGS. 8A and 8B are diagrams for explaining template matching for obtaining the center coordinates of a cell. FIG. 8A relates to a corner portion of the region R1, and in the cell at the corner portion of R1, it is slightly shifted up, down, left, and right from the center coordinates obtained in S2 as indicated by a cross in the right figure. The surrounding cells are also shifted from the center coordinates obtained in S2 in the same direction and at the same degree as the shifting direction and the shifting degree in the corner cells, and the brightness list for each shifting direction (the corner and its surroundings). (Brightness list of the cell). Then, template matching is performed for each of the luminance lists, and an evaluation value is calculated. Specifically, in the template group selected in S4, the luminance value list of the pattern of interest (cell pattern corresponding to the cell pattern as shown in the right figure of FIG. 8A) is referred to, and this luminance value list and Then, the sum (evaluation value) of the difference from each of the above luminance lists (the luminance of the corner cell and the surrounding cells in each shifting direction) is obtained. The evaluation value is considered to be minimal when there is little deviation in coordinates, and the evaluation value is considered to increase when there is deviation in coordinates. In the case of FIG. 8A, among the nine luminance lists sampled, each position corresponding to the luminance list whose evaluation value is minimized (in the corner and surrounding cells when each luminance of the luminance list is acquired). Let each position) be the center coordinates of the corner cell and surrounding cells. In the example of FIG. 8, the sampling in each cell is 9 points, but the interval and number of sampling points can take any value depending on the required calculation time and coordinate accuracy.

  With the above processing, the center coordinates of the cell whose color and surrounding pattern are known can be obtained. By repeating this, the center coordinates of the corner cell of each of the small regions R1, R2, and R3 are obtained. You can fix it. For each small area, high accuracy of the cell center coordinates can be realized by newly re-determining the center coordinates of each cell by performing equal division or projective transformation based on the center coordinates of the corner cells. . It should be noted that such recalculation of the center coordinates may be performed only for some cells or all cells.

  In the present embodiment, the control circuit 40 corresponds to an example of a cell position detection unit, and a predetermined representative position (specifically, detected in S2) of each cell from the information code image stored in the image storage unit. It functions to detect the center position and the correction position detected in S6.

  Further, the control circuit 40 at least detects the luminance at each cell position detected by the cell position detecting means, specifically, the luminance at the representative position of each cell (that is, the representative position detected at S2 and S6). It functions to detect the brightness of the corrected representative position.

  Further, the control circuit 40 capable of performing the process of S6 corresponds to an example of an area dividing unit, and functions to divide an information code image captured by the imaging unit into a plurality of image areas.

  Further, the control circuit 40 capable of performing the process of S6 corresponds to an example of the reference cell detection means, and among the light color determination cells and dark color determination cells detected by the light / dark cell detection means, neighboring cells are intermediate luminance cells. It functions to detect a cell that is not a reference cell, and specifically functions to detect a reference cell for each image region divided by the region dividing means.

  Further, the control circuit 40 capable of executing the process of S6 corresponds to an example of a shift state detecting unit, and is a certain degree from each representative position of the reference cell detected by the cell position detecting unit and the cell adjacent to the reference cell. The function of shifting the position and detecting the luminance state at each shifted change position is performed so as to be shifted in a plurality of directions with each representative position as a reference.

  The memory 35 corresponds to an example of a correction template storage unit, and defines a plurality of types of bright and dark cell patterns that can be configured in a predetermined size, and stores a plurality of templates that are templates of luminance value arrays in the respective light and dark cell patterns. To do.

The control circuit 40 capable of executing the process of S6 corresponds to an example of a template selection unit, and the reference cell detected by the reference cell detection unit from the plurality of templates stored in the correction template storage unit. It functions to select a template corresponding to the cell array of cells adjacent to the periphery of the reference cell.
Furthermore, the control circuit 40 corresponds to an example of a correction value detection unit, and the compatibility between each luminance state obtained by shifting in a plurality of directions from each representative position by the shift state detection unit and the template selected by the template selection unit. And the function of detecting the degree of shift from each representative position in the most suitable luminance state as a correction value, specifically, for each image region divided by the region dividing means The correction value is obtained.
The control circuit 40 corresponds to an example of a correction unit, and functions to correct the position of each cell other than the reference cell from each representative position based on the correction value detected by the correction value detection unit. Specifically, a process of correcting the position of each cell from each representative position for each image area is performed so that each correction value obtained for each image area by the correction value detection unit is reflected in each image area. .

  After the process of S6, the brightness of the undetermined cell (intermediate luminance cell) is determined by template matching with the template group selected in S4. A general method can be used for matching with the template. For example, cosine similarity or square error is used as the evaluation value. The number of template windows and the number of sample points can take any value depending on the required accuracy and processing time.

  Specific examples of template matching may be as shown in FIGS. In FIG. 9A, in the cell pattern of 3 rows and 3 columns, the shaded cells are undetermined (intermediate luminance cells whose brightness is not determined in S5), and specific luminance values (representative of each cell). FIG. 9B shows the position (measured luminance value at the representative position remapped in S6). In this case, there are four types of cell patterns assumed in FIGS. 10A to 10D, and the luminance value list of these patterns in the template group selected in S4 is shown in FIG. Suppose that it is (D). In this case, the sum of the differences between the measured brightness values in FIG. 9B and the brightness value lists in FIGS. 11A to 11D is obtained, and the pattern having the smallest sum is selected. In this case, since the sum of the differences from the list of FIG. 11B is the smallest, the pattern of FIG. 10B is selected, the undetermined center position is light color, and the position below it is It is determined that the color is dark.

  In this way, for example, by performing pattern matching in the same manner from the upper left 3 × 3 portion to the lower right 3 × 3 portion, it is possible to determine the light and darkness of each undetermined cell. Such a result can be obtained.

  In the present embodiment, the control circuit 40 that can perform the process of S4 corresponds to an example of a selection unit, and a plurality of types of frequency distributions generated by the frequency distribution generation unit are determined in advance based on the contents of the frequency distribution. Select from the types.

  Further, the control circuit 40 capable of performing the process of S7 corresponds to an example of light / dark determination means, and whether the intermediate brightness cell detected by the intermediate brightness cell detection means belongs to the bright brightness cell or the dark color cell. It determines based on the light-dark pattern of several adjacent cells adjacent to a cell. More specifically, one of the template groups stored in the determination template storage unit is selected based on the type of frequency distribution selected by the selection unit, and the light-dark pattern of a plurality of adjacent cells adjacent to the intermediate luminance cell A matching template is detected from among a plurality of light color templates and a plurality of dark color templates constituting the template group by pattern matching between the template and the template included in the selected template group, and based on the detection result It is determined whether the intermediate luminance cell belongs to a light cell or a dark cell.

  Then, decoding is performed by a known method based on the light / dark pattern of each cell finally determined in S7 (S8). The control circuit 40 corresponds to an example of a decoding unit, and decoding is performed based on the detection result of the light color determination cell and the dark color determination cell by the light / dark cell detection unit and the light / dark determination result of the intermediate luminance cell by the light / dark determination unit. Function.

(Main effects of the first embodiment)
In this embodiment, since a certain amount of cells are determined as light cells or dark cells based on the first threshold value and the second threshold value, the brightness of the remaining cells (intermediate luminance cells) that cannot be determined is determined. Processing that takes time for light / dark determination (light / dark determination processing of the intermediate luminance cell by the light / dark determination means) can be reduced as much as possible, and the processing time can be shortened. Furthermore, since the brightness of the adjacent cells adjacent to the remaining cells (intermediate brightness cells) can be clarified and then the brightness of the intermediate brightness cells can be determined based on the brightness / darkness pattern of these adjacent cells. Even when the contrast is low, binarization can be performed more accurately.

In addition, the brightness detection unit includes a frequency distribution generation unit that classifies the luminance of each cell position detected by the luminance detection unit for each luminance level and generates a frequency distribution that can specify the frequency for each luminance level. In the frequency distribution generated by the distribution generation means, the first peak value that peaks on the high luminance side is the first threshold value, and the second peak value that peaks on the lower luminance side than the first peak value is the second threshold value. A cell having a luminance equal to or higher than the first peak value is detected as a light color determination cell, and a cell having a luminance equal to or lower than the second peak value is detected as a dark color determination cell.
It is highly possible that both ends of the frequency distribution (histogram) (that is, the luminance of the area outside the first peak value and the second peak value) reflect the color of the cell. It is possible to narrow down the cell by accurately determining the brightness and to narrow down the cell.

Also, a determination template storage unit that stores a plurality of light color templates for determining a light cell and a plurality of dark color templates for determining a dark cell is provided, and the light / dark determination unit is adjacent to the intermediate luminance cell. A matching template is detected from a plurality of light color templates and a plurality of dark color templates by pattern matching between the light and dark patterns of a plurality of adjacent cells and a template stored in the determination template storage means, and based on the detection result Thus, it is determined whether the intermediate luminance cell belongs to a light cell or a dark cell.
According to this configuration, even if there is an intermediate luminance cell for which it is difficult to determine the brightness, it is possible to determine the brightness with higher accuracy based on the template in the same environment.

The frequency distribution generated by the frequency distribution generation means is selected from a plurality of types determined in advance based on the content of the frequency distribution, and a plurality of bright colors for determining a light cell. A template storage unit for determination that stores a template group including a plurality of dark color templates for determining a color template and a dark color cell in association with each of a plurality of types, and the light / dark determination unit includes: Based on the selected frequency distribution type, one of the template groups stored in the determination template storage means is selected, and the light and dark patterns of a plurality of adjacent cells adjacent to the intermediate luminance cell and the selected template group are selected. A plurality of bright templates and a plurality of dark templates constituting the template group are obtained by pattern matching with the included templates. Detecting a matching template from the template, the intermediate brightness cell to determine whether belongs to the bright cells or dark cells on the basis of the detection result.
As described above, if a template group is prepared for each type of frequency distribution (histogram) and a template group corresponding to the actually obtained frequency distribution is selected, a template that matches the actual imaging environment is selected. Therefore, it is possible to determine the lightness and darkness more accurately.

The cell position detecting means detects a predetermined representative position of each cell from the information code image stored in the image storage means, and the luminance detecting means detects the representative position of each cell detected by the cell position detecting means. In addition, a reference for detecting, as a reference cell, a cell in which a neighboring cell is not an intermediate luminance cell from among the light color determination cell and the dark color determination cell detected by the light / dark cell detection means. A cell detection unit; a correction template storage unit that stores a plurality of templates in which a plurality of types of light and dark cell patterns that can be configured in a predetermined size are defined, and a luminance value array in each light and dark cell pattern is templated; and a correction template storage The reference cell detected by the reference cell detection means from among a plurality of templates stored in the means and adjacent to the reference cell The template selection means for selecting a template corresponding to the cell arrangement of the cell to be detected, and the reference cell detected by the cell position detection means and the representative positions of the cells adjacent to the reference cell are shifted and shifted by a certain degree. A process for detecting the brightness state at each changed position is performed by shifting the process in a plurality of directions with respect to each representative position, and each brightness state obtained by shifting the process from the representative position in a plurality of directions by the shift state detection unit. A correction value detecting means for determining suitability with the template selected by the template selecting means and detecting a shift degree from each representative position in the luminance state with the highest suitability as a correction value; and a correction value detecting means Correction means for correcting the position of each cell other than the reference cell from each representative position based on the correction value detected by And said that there were pictures.
In this way, the exact coordinates of the reference cell (coordinates when the compatibility with the template is high) can be selected from the reference cell and the surrounding light and dark pattern and the template corresponding to the light and dark pattern. High accuracy can be measured.

Further, the image processing apparatus includes an area dividing unit that divides the information code image captured by the imaging unit into a plurality of image areas, and the reference cell detection unit detects and corrects the reference cell for each image area divided by the area dividing unit. The value detecting means obtains a correction value for each image area divided by the area dividing means, and the correcting means reflects each correction value obtained for each image area by the correction value detecting means to each image area. In addition, a process of correcting the position of each cell from each representative position for each image region is performed.
According to this configuration, correction with higher accuracy is possible. This is particularly advantageous in an environment where the code image is easily distorted or deformed.

[Other Embodiments]
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.

  Further, when it is desired to obtain the center coordinates with an accuracy equal to or higher than the sampling interval for performing template matching, it is performed by interpolating the evaluation value of each point. FIG. 13 is an example of the idea of interpolation of evaluation values in the case of one dimension for the sake of simplicity. This is because template matching is performed at intervals of 0.5 pixels and an evaluation value is calculated. Then, a point where the evaluation value is minimized is first obtained, and then a point on the left side from the point where the evaluation value is minimized and the evaluation value This is an interpolation method in which an approximate straight line is obtained for a point on the right side from a point where is minimal, and the intersection is regarded as a true center coordinate. In the example of FIG. 13, since the vicinity of −0.3 is an intersection, a point shifted to the left by about 0.3 pixels may be set as the center coordinate.

  In the above embodiment, the position corrected from the representative position (for example, the center position of each cell) is set as each cell position. However, the center position of each cell acquired in S2 may be used as it is without being corrected. That is, the process of S6 may be omitted and the process of S7 may be performed based on the mapping result in S2.

DESCRIPTION OF SYMBOLS 1 ... Information code reader 23 ... Imaging means 35 ... Memory (Image storage means, determination template storage means, correction template storage means)
40... Control circuit (cell position detection means, luminance detection means, light / dark cell detection means, intermediate luminance cell detection means, light / darkness determination means, frequency distribution generation means, selection means, reference cell detection means, template selection means, shift state detection means Correction value detection means, correction means, area dividing means)

Claims (3)

An imaging means for imaging an information code including a light cell and a dark cell;
Image storage means for storing an image of the information code imaged by the imaging means;
Cell position detection means for detecting the position of each cell from the image of the information code stored in the image storage means;
Luminance detecting means capable of detecting the luminance at each cell position detected by the cell position detecting means;
Brightness / darkness cell detection means for detecting a lightness determination cell whose brightness detected by the brightness detection means is equal to or higher than a first threshold, and for detecting a darkness determination cell where the brightness is lower than a second threshold lower than the first threshold; ,
Intermediate luminance cell detecting means for detecting intermediate luminance cells whose luminance detected by the luminance detecting means is less than the first threshold and exceeds the second threshold;
Brightness / darkness that determines whether the intermediate luminance cell detected by the intermediate luminance cell detection means belongs to the light cell or the dark cell based on the light / dark pattern of a plurality of adjacent cells adjacent to the intermediate luminance cell. A determination means;
A frequency distribution generating unit that classifies the luminance of each cell position detected by the luminance detecting unit for each luminance level and generates a frequency distribution that can specify the frequency for each luminance level; and
In the frequency distribution generated by the frequency distribution generation unit, the light / dark cell detection unit sets the first peak value that peaks on the high luminance side as the first threshold value, and on the lower luminance side than the first peak value. A second peak value that is a peak is set as the second threshold value, a cell having a luminance equal to or higher than the first peak value is detected as the light color determination cell, and a cell having a luminance equal to or lower than the second peak value is set as the dark color determination cell. Detect
Selecting means for selecting the type of the frequency distribution generated by the frequency distribution generating means from a plurality of types determined in advance based on the content of the frequency distribution;
Determination template storage for storing a template group including a plurality of light color templates for determining the light cell and a plurality of dark color templates for determining the dark cell in association with each of the plurality of types. Means,
With
The brightness determination unit selects any one of the template groups stored in the determination template storage unit based on the type of the frequency distribution selected by the selection unit, and a plurality of adjacent brightness pixels A matching template is detected from among the plurality of light color templates and the plurality of dark color templates constituting the template group by pattern matching between the light and dark pattern of the adjacent cell and the template included in the selected template group. An information code reading device for determining whether the intermediate luminance cell belongs to the light cell or the dark cell based on the detection result . The cell position detection means detects a predetermined representative position of each cell from the image of the information code stored in the image storage means,
The luminance detection means detects the luminance at the representative position of each cell detected by the cell position detection means,
Further, reference cell detection means for detecting, as a reference cell, a cell in which a neighboring cell is not the intermediate luminance cell among the light color determination cell and the dark color determination cell detected by the light / dark cell detection means When,
A correction template storage means for storing a plurality of templates in which a plurality of types of light and dark cell patterns that can be configured in a predetermined size are defined and an array of luminance values in each light and dark cell pattern is templated;
A template for selecting a template corresponding to a cell arrangement of the reference cell detected by the reference cell detection means and a cell adjacent to the periphery of the reference cell from a plurality of templates stored in the correction template storage means A selection means;
The process of detecting the luminance state at each changed position shifted from the representative position of each of the reference cell detected by the cell position detecting means and the cell adjacent to the reference cell at a certain degree. Shifting state detecting means for shifting in a plurality of directions with reference to
The brightness state obtained by shifting in a plurality of directions from each representative position by the shift state detection means and the suitability between the template selected by the template selection means are determined, and each brightness state in the highest suitability brightness state is determined. Correction value detection means for detecting the degree of shift from the representative position as a correction value;
Correction means for correcting the position of each cell other than the reference cell from each representative position based on the correction value detected by the correction value detection means;
Information code reader according to claim 1, characterized in that with a. An area dividing means for dividing the image of the information code imaged by the imaging means into a plurality of image areas;
The reference cell detection means detects the reference cell for each of the image areas divided by the area dividing means,
The correction value detecting means obtains the correction value for each of the image areas divided by the area dividing means,
The correction means corrects the position of each cell from each representative position for each image area so that each correction value obtained for each image area by the correction value detection means is reflected in each image area. information code reader according to claim 2, wherein the performing.

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