JP2011076518A - Optical information reader and method for acquiring image data - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information reader for flexible gradation conversion of picked-up images to meet users' needs without using dedicated elements and also to provide a method for acquiring image data. <P>SOLUTION: A gradation converting mean of a CPU 2 performs gradation conversion of an image picked up by an image sensor 1, stores the image in an internal memory 20, and transfers the image from the internal memory 20 to a memory 3. A gradation conversion table 23 that defines the rule of the conversion can be selected arbitrarily by a user, and thereby an optical information reader that has the flexible rule of the conversion can be achieved. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical information reading technique for optically reading a two-dimensional code and the like, and more particularly to an optical information reading apparatus and an image data capturing method using a two-dimensional image sensor.

  For example, there is known an image sensing type optical information reading apparatus that images optical information such as a one-dimensional code and a two-dimensional code, and reads the optical information by decoding the captured optical information. . This image sensing type optical information reading apparatus analyzes and decodes image data for each frame. In optical information reading devices, optical information reading devices using a CMOS image sensor in an image pickup unit tend to become widespread, particularly from the viewpoint of reducing manufacturing costs and power consumption. In general, in a CMOS image sensor, a large amount of information is required due to a demand for high resolution in a captured image. For this reason, data output of 10 bits is becoming mainstream. On the other hand, in the optical information reading apparatus main body, there is a limit to the improvement of the processing capability and the expansion of the memory capacity from the viewpoint of reduction of manufacturing cost, size reduction, and speeding up of image processing. Also, in order to recognize a two-dimensional code such as a QR code, 8-bit image data is often sufficient. Therefore, an optical information reading apparatus has been proposed in which output data from a CMOS image sensor is converted into digital data having a smaller number of bits in accordance with a predetermined rule and image data is taken in. Patent Document 1 proposes a data capturing device that captures only 8 bits out of 10 bits as image data in accordance with upper bits.

Japanese Patent Laid-Open No. 2003-669

  In the conventional optical information reading device, a part of the data output of each pixel of the image data by the CMOS image sensor is dropped in a dedicated circuit in front of the CPU, and the data output of the remaining bits is used as effective image data. Can be taken in as However, a dedicated CPLD or gate array element is required, and it is not easy to change the conversion rule. For this reason, there is a drawback in that the method for reducing the number of bits cannot be changed in consideration of the application and accuracy of analysis for the captured image.

  The present invention has been made in view of the above-described problems, and can be flexibly adapted to the user's application without using a dedicated element, and can be captured by reducing the number of bits in consideration of analysis accuracy for a captured image. An optical information reading apparatus and an image data capturing method that can be used are provided.

  In order to solve this problem, an optical information reading apparatus according to the present invention includes an image pickup unit having a two-dimensional image pickup device that picks up an image of a read target, and a CPU, and the read target imaged by the image pickup unit is stored in a memory. An optical information reading apparatus comprising: a control unit that performs image processing and decoding when holding; and a memory that holds an image to be read captured by the imaging unit, wherein the control unit includes the imaging unit A tone converting unit that receives the image data from the image, executes tone conversion based on a predetermined condition, and stores the image data after the tone conversion in the memory; and the image data after the tone conversion stored in the memory And an arithmetic means for reading and decoding.

  Here, the CPU of the control unit has an internal memory, and the internal memory has a reception buffer that holds image data in units of rows obtained from the imaging unit, and a row after gradation conversion before being transferred to the memory. A transmission buffer that holds image data of a unit.

  Here, the internal memory is an SRAM, the reception buffer has at least two reception buffers, the transmission buffer has at least two transmission buffers, and the gradation converting means is imaged by the imaging unit. Data reception processing that alternately holds image signals in the two reception buffers in units of rows, gradation in which the image data in units of rows in the reception buffer is transferred to the transmission buffers alternately by reducing the number of data of each pixel The conversion process and the transfer process of alternately transferring to the memory from the two transmission buffers may be executed in parallel.

  Here, the imaging unit includes an image sensor that outputs image data of L columns and M rows, and the gradation converting unit includes i rows to i + N rows (1 ≦ i <N ≦ L) necessary for image processing. Are stored in the reception buffer, and image data in columns from j to j + K (1 ≦ j <K ≦ M) among the converted data in the transmission buffer are output from the transmission buffer to the memory. You may do it. In this case, there is no need to store unnecessary image data in the memory, so that the capacity of the memory can be reduced, and hardware resources can be used effectively.

  Here, the control unit may perform at least a part or all of the filtering process on the captured image and hold it in the transmission buffer.

  In order to solve this problem, the data capturing method of the optical information reading apparatus of the present invention receives a captured image signal, and alternately holds the image signal in the two reception buffers in units of rows. The image data in units of rows of the reception buffer is reduced in the number of data of each pixel, transferred to the transmission buffer alternately, and transferred from the transmission buffer to the memory in parallel.

  Here, the control unit performs different gradation conversion processing among the image data held in the reception buffer, holds the data in the transmission buffer, and transfers a plurality of image data to the memory. The means may perform the decoding process based on a plurality of pixel data held in the memory. Since a plurality of converted image data is held in the memory, the probability of decoding failure can be reduced. Here, the plurality of image data may be arranged in a continuous area of the memory. In this case, since it is possible to perform decoding using data of other image data even if data decoding processing is not completed for one image, an effect of shortening the standby time can be obtained.

  According to the present invention having such a feature, it is possible to perform gradation conversion of an image according to a conversion rule selected by the user and hold it in a memory. Therefore, gradation conversion corresponding to the user's application can be performed flexibly, and no dedicated hardware is required.

FIG. 1 is a block diagram showing the overall configuration of a two-dimensional code reader according to the first embodiment of the present invention. FIG. 2 is a diagram showing the movement of SRAM and data in the CPU according to this embodiment. FIG. 3 is a diagram showing details of the transfer of the SRAM and image sensor data and memory according to the present embodiment. FIG. 4 is a time chart showing a bit fetch process, a gradation conversion process, and a data transfer process to a memory. FIG. 5A is a graph showing the conversion output of 10-bit data to 8 bits according to the first method. FIG. 5B is a graph showing a conversion output of 10-bit data to 8 bits according to the second method. FIG. 5C is a graph showing a conversion output of 10-bit data to 8 bits according to the third method. FIG. 6A is a diagram illustrating an example of image data obtained by converting a 10-bit image into an upper 8-bit image according to the present embodiment. FIG. 6B is a diagram showing an example of image data obtained by converting a 10-bit image into an intermediate 8-bit image according to the present embodiment. FIG. 6C is a diagram showing an example of image data obtained by converting a 10-bit image into a lower 8-bit image according to the present embodiment. FIG. 7 is a diagram showing an example of a QR code recorded with a laser marker. FIG. 8 shows an example of an original QR code. FIG. 9 is a diagram showing processing after the start of operation according to the present embodiment. FIG. 10 is a flowchart showing the data fetching process after the operation is started according to this embodiment. FIG. 11 is a diagram showing an output from the image sensor, processing to the CPU, and a captured image to the memory. FIG. 12 is a diagram showing an image output from the image sensor, processing contents in the CPU, and an image to the memory. FIG. 13 is a schematic diagram showing a data fetch process according to the third embodiment of the present invention. FIG. 14 is a schematic diagram showing data fetching processing according to the third embodiment of the present invention. FIG. 15 is a time chart showing a decoding process after taking in data according to a conventional example. FIG. 16 is a time chart showing a decoding process after taking in data according to the present embodiment.

  FIG. 1 is a block diagram showing the configuration of a code reader having a two-dimensional image sensor according to the first embodiment of the present invention. The code reader according to this embodiment is installed adjacent to a product or product conveyance line on which a two-dimensional code or the like is printed, and reads information recorded on the two-dimensional code or the like. In FIG. 1, an image sensor 1 is a two-dimensional imaging device such as a CCD, and is an imaging unit that images a two-dimensional code or the like of a conveyed object. Here, the image sensor 1 outputs image data having, for example, a 10-bit gradation for each pixel. On the other hand, 8-bit image data is sufficient to recognize a two-dimensional code such as a QR code. Therefore, in this embodiment, the image output from the image sensor 1 is converted into data from 10 bits to 8 bits inside the CPU 2 and then taken into the memory 3. The communication control unit 4 receives a command from a host (not shown) and transfers a decoding result. The ROM 5 holds at least one conversion rule file for converting image data having 10-bit gradation into 8-bit image data, and a plurality of files can be selected by the user.

  The CPU 2 is a control unit that performs image processing when the reading target imaged by the imaging unit is held in the memory, and executes decoding using the image held in the memory, and an internal configuration thereof will be described. In the CPU 2, a DMA controller 10, an SRAM 20, and an arithmetic unit 30 for data transfer are provided. The SRAM 20 is an internal memory that temporarily holds data. The computing unit 30 is computing means for decoding the two-dimensional code based on the 8-bit one-dimensional image of the two-dimensional code held in the memory 3. In the SRAM 20, a reception buffer 21 that temporarily holds the transferred image data for one row, a transmission buffer 22 that holds the image data for one row after gradation conversion, and 10-bit data are stored. Each area of at least one gradation conversion table 23 to be converted into 8 bits is provided. The CPU 2 uses the SRAM 20 to receive image data from the imaging unit, execute gradation conversion based on a predetermined condition, and achieve a function of gradation conversion means for holding the image data after gradation conversion in a memory.

  FIG. 2 is a diagram showing the movement of data between the most basic image sensor 1 and the internal SRAM and memory 3 in the CPU 2. Before fetching data, the user selects a conversion rule file in the ROM 5 in advance and holds it as a gradation conversion table 23 in the SRAM 20 of the CPU 2. As shown in FIG. 2, the image sensor 1 captures an image including a two-dimensional code, and then transfers 10-bit image data per pixel sequentially in units of rows from the first row. This data is taken into the reception buffer 21 inside the CPU 2. Then, the 10-bit data held in the reception buffer 21 is converted into 8-bit data using the gradation conversion table 23 in the SRAM 20 of the CPU, and held in the transmission buffer 22. Then, the data is transferred from the transmission buffer 22 to the memory 3. By performing this processing in parallel, the image capture time is shortened.

  Next, FIG. 3 shows details of data from the SRAM 20 and the image sensor 1 in the CPU 2 and data to be transferred to the memory 3. As shown in this embodiment, the SRAM 20 in the CPU 2 has reception buffers 21a and 21b for holding 10-bit data for one row and transmission buffers 22a and 22b for holding 8-bit data for one row. ing.

FIG. 4 is a time chart showing a state in which data acquisition, data conversion, and data transfer are executed in parallel. The period T ₁ in the figure, hold the first row of data 10 bits obtained from the image sensor 1 in the reception buffer 21a. Then the period T ₂ receives a 10-bit data of the second line from the image sensor 1, is held in the reception buffer 21b. The period T _2, and converts the 8-bit image in accordance with the rules to be described later 10-bit image data of the first row held in the reception buffer 21a simultaneously, sequentially transferred to the transmission buffer 22a. In the next period T3, the _third row of image data obtained from the image sensor 1 is taken into the reception buffer 21a, and the second row of data held in the reception buffer 21b is converted into an 8-bit image and transmitted. Transfer to buffer 22b. At the same time, the converted data in the first row of the transmission buffer 22a is transferred to the memory 3. Uptake in the reception buffer 21b the image data of the fourth line obtained from the image sensor 1 in the period T _4, and further converted data in the third row held in the 8-bit image to the receiving buffer 21a transmit buffer 22a Forward to. At the same time, the converted data in the second row of the transmission buffer 22b is transferred to the memory 3. Similar processing is repeated by shifting the row numbers in subsequent periods T ₅ ... T _N , T _{N + 1} . By providing the two reception buffers 21a and 21b and the two transmission buffers 22a and 22b as described above, data fetching, data conversion, and data transfer processing can be executed in parallel.

  Next, three rules for converting the 10-bit image data into 8-bit image data will be described. 5A to 5C are diagrams showing the relationship between the 10-bit output from the image sensor and the 8-bit converted output. The first method is to delete the lower 2 bits of the 10 bits of the image sensor and use only the upper 8 bits as converted 8-bit image data. 5A (a), 0 to 1023 shown on the left side indicate the output of the image sensor 1, and 0 to 255 indicate the 8-bit output after conversion. In this case, as shown in the graph of FIG. 5A (b), the change of 1024 gradations changes linearly to 256 gradations.

  In the second method, the upper 2 bits are deleted from the 10-bit data, and the lower 8 bits are converted into 8-bit image data after conversion. In this case, as shown in the graph of FIG. 5B (b), the input linearly changes from 0 to 255 gradations, but is saturated at 255, and thereafter the maximum level is maintained.

  The third method is a substantially logarithmic conversion process in which 10-bit data to be input is changed to 8-bit data using a function including a logarithmic term. In this case, for example, as shown in the graph of FIG. 5C (b), the change of 1024 gradations changes to a curve of 256 gradations. In this conversion method, various curves can be obtained by selecting coefficients.

  In addition to the above three methods, a method of selecting intermediate 8 bits can be considered. In this embodiment, the input / output for any of these conversions is stored in advance in the gradation conversion table 23 as a table. In this way, it is possible to change the conversion method only by changing the conversion table without changing the hardware. As will be described later, the conversion method can be arbitrarily selected by the user.

  FIG. 6A is a diagram showing an example of four images converted into 8-bit image data using the upper 8 bits of 10-bit image data, and FIG. 6B is composed of intermediate 8 bits of 10-bit image data FIG. 6C is a diagram showing an example of four images converted into 8-bit image data using lower 8 bits of 10-bit image data. Further, the logarithmically converted image is an image in which a dark portion of upper 8 bits and a bright portion of lower 8 bits are configured.

  As described above, the bit selection can change the characteristics (brightness and gradation change) of the image held in the memory, which also affects the possibility of decoding performed by the CPU 2 using the image stored in the memory. For example, the leftmost QR code shown in FIGS. 6A to 6C is too dark in FIG. 6A and is difficult to decode, but in FIG. 6C, decoding is easy. On the other hand, the rightmost QR code is too bright in FIG. 6C and difficult to decode, but in FIG. 6A, it becomes easy to decode. That is, the gradation change affects the ease of black and white discrimination in the decoding process, and the brightness leads to erroneous recognition of code information due to expansion and contraction of each black and white dot or cell. An area for holding imaging conditions is provided as a bank parameter in the code reader, and a bit selection condition is set as a bank parameter together with imaging conditions such as a two-dimensional code. By capturing an image based on the parameters, the decoding success rate is improved.

  Next, the filtering process will be described. When converting 10-bit data into 8-bit data, filtering may be performed simultaneously. Examples of the filter processing include expansion filter processing and contraction filter processing. In the present embodiment, since gradation conversion is performed in units of one line, expansion filter processing and contraction filter processing can also be performed in units of rows. The expansion filter processing in this case refers to processing for replacing the luminance data of the target pixel with data of the maximum luminance among the three adjacent pixels and the target pixel. The contraction filter process is a process of replacing the luminance data of the target pixel with data of the minimum luminance among the three adjacent pixels and the target pixel. For example, if the QR code is a dotted line as shown in FIG. On the other hand, in the case of the original QR code, as shown in FIG. 8, the QR code is a straight line and can be decoded. In such a case, an image is appropriately converted by a filtering process so that it can be decoded.

  Next, the operation of the image capturing process according to this embodiment will be described. FIG. 9 is a flowchart showing a process immediately after the operation is started. When this process is started, the user is first prompted to select a conversion rule in step S1. Next, in step S2, the user is prompted to select a filter necessity and type. When the conversion rule and the filter are selected in this way, a table for converting input data into output data based on the conversion rule is created (step S3). This table is written in the SRAM 20 in the CPU 2 as the gradation conversion table 23 (step S4).

  Next, the processing after taking in data will be described with reference to FIG. When the process is started, data for one row is acquired from the image sensor 1 in the reception buffer 21 of the SRAM in step S11. In step S12, the data for one row is subjected to gradation conversion. Next, in step S13, it is determined whether or not image data filtering is necessary, and if necessary, data filtering for one row is performed (step S14). In step S15, the processed data is held in the transmission buffer 22. In step S16, the data for one row is transferred from the SRAM 20 to the memory 3, and it is determined whether or not the capturing process for the entire image has been completed (S17). If the process has not ended, the process returns to step S11 and the same process is repeated. When the process is completed, the capture process is terminated. The process of step S12 may be performed immediately before step S15.

  In this way, a dedicated chip for data gradation conversion processing or the like is not necessary, and the cost can be reduced. Since the data processing of gradation conversion is executed by software processing, free conversion such as selection of upper 8 bits, selection of lower 8 bits, intermediate 8 bits excluding upper and lower 1 bits, log conversion, etc. Rules can be chosen arbitrarily. Also, the filter process can be executed almost in parallel with the gradation conversion. Here, if filter processing is unnecessary, the filter selection in step S2 and steps S13 and S14 may be deleted.

  Next, a modification of the present embodiment will be described. In the filter processing of the first embodiment described above, the filter processing is performed in units of rows. Alternatively, expansion filter processing and contraction filter processing can be performed in units of three adjacent rows. The expansion filter processing in this case refers to processing for replacing the luminance of the center pixel of 3 × 3 pixels with the data of the maximum luminance among the adjacent nine pixels. Shrinkage filter processing refers to processing for replacing the luminance of the central pixel of 3 × 3 pixels with data of the minimum luminance among the surrounding nine pixels. In this case, two sets of three rows, that is, six reception buffers are required as buffers for receiving 10-bit image data. Similarly, two sets of buffers for three rows, that is, six transmission buffers are also used as transmission buffers. A buffer is required. In this way, if the filtering process in units of rows is performed simultaneously with the gradation conversion, the filtering process can be performed in a short time. Further, even when 3 × 3 pixel filter processing is performed, the filter processing may be performed once after being held in the memory 3 in units of rows and then read out from the memory 3.

  Next, a second embodiment of the present invention will be described. In the present embodiment, the area of the captured image in the SRAM of the CPU 2 is limited, and the basic configuration is the same as in FIG. Of the image data output from the image sensor 1, a necessary area may be a part of the entire area. In such a case, it is not necessary to fetch unnecessary areas into the memory 3, and it is sufficient to capture only necessary areas. Some image sensors such as CCD and CMOS sensors change the exposure time and hardware timing depending on the number of columns output from the sensor. Therefore, when the capture area is limited in units of columns, the exposure time timing of the image pickup device such as a CCD and the hardware timing design become complicated. Therefore, in the present embodiment, only the necessary rows in units of rows are subjected to gradation conversion as described above and taken into the memory.

  Assume that the image sensor 1 outputs 10-bit data of L rows and M columns. FIG. 11A shows an image output from the image sensor, and FIG. 12A shows image data corresponding to the image. As shown in FIG. 11A in the image data 40 of L rows and M columns, if a two-dimensional code is captured only in a part of the region, this region is designated as a region of interest (ROI) 41. And If the region of interest 41 is, for example, i to i + N rows and j to j + K columns (1 ≦ i <N ≦ L, 1 ≦ j <K ≦ M), if there is only image information in this region, the two-dimensional code is decoded. Is enough.

  Therefore, as shown in FIG. 11B, the CPU 2 alternately holds the data necessary for the processing of the two-dimensional code data, that is, the data of all the columns of i to i + N rows that are not hatched in the reception buffers 21a and 21b. . Then, 10 bits in these rows are converted into 8-bit data, which are sequentially held in the transmission buffers 22a and 22b. Among these, only the data of the jth to j + K columns are transferred to the memory 3. FIG. 11C shows an image constructed on the memory 3, and FIG. 12C shows the image data.

  For example, when the image data of the image sensor is 10-bit image data of 480 rows and 752 columns, the necessary areas are 101 to 200 rows and 101 to 200 columns. At this time, only the image data of the 101st to 200th lines are taken into the CPU 2 and converted from 10 bits to 8 bits and transferred to the memory 3. If the data from the 101st column to the 200th column among the 101th to 200th rows after the gradation conversion is transferred to the memory 3, 8-bit image data for 100 columns and 100 rows can be obtained in the memory. it can. As a result, as shown in FIG. 12C, the data that needs to be held in the memory 3 can be greatly reduced. Such processing is extremely useful when a two-dimensional code is targeted and only a region where the two-dimensional code is imaged is taken into the memory.

  Next, a third embodiment of the present invention will be described. In this embodiment, a plurality of image data subjected to gradation conversion using a plurality of conversion rules is held, and the basic configuration is the same as in FIG. When one piece of image data subjected to gradation conversion is held in the memory, it is read from the memory after being held, and is decoded using an arithmetic unit. However, if the exposure time and gain setting of the image sensor are not sufficient, it is necessary to capture the image again and capture it in the memory, or change the gradation conversion rule and transfer it to the memory. Therefore, there is a disadvantage that it takes time because a plurality of processes are required when decoding cannot be performed due to environmental changes. In this embodiment, it is assumed that a plurality of images are held simultaneously. FIG. 13 is a diagram showing the structure of the CPU 2 and the data transfer from the image sensor to the memory in this process. In FIG. 13, the CPU 2 includes the DMA controller 10, SRAM 20, and arithmetic unit 30 according to the first embodiment. In this embodiment, the SRAM 20 is provided with a reception buffer 21, transmission buffers 25 and 26, and a plurality of gradation conversion tables 23a and 23b. Then, as shown in the figure, the output from the image sensor 1 is temporarily held in the memory 3 as it is with 10-bit data via the CPU 2. Thereafter, the CPU 2 reads it and holds it in the reception buffer 21. Then, gradation conversion is performed using different gradation conversion tables 23a and 23b, and two 8-bit image data A and B are created and written into the memory 3 again. At this time, the two 8-bit image data A and B are image data converted by different conversion rules.

  Thus, by arranging two 8-bit image data in a continuous memory area as shown in FIG. 2, if they are handled together as one large image data, they will be processed together when filtering is performed later. Can do. Here, it is assumed that the two image data A and B use different conversion rules. For example, as described above, an arbitrary gradation conversion rule is selected from selection of upper 8 bits of 10 bits, selection of intermediate 8 bits of 10 bits, selection of lower 8 bits of 10 bits, log conversion, and the like. Two image data may be generated. In this way, two pieces of 8-bit image data having different brightness and the like can be held in a continuous area of the memory 3 by fetching the image data once.

  Alternatively, as shown in FIG. 14, if the CPU has sufficient processing capacity, 10-bit image data is temporarily held in the SRAM 20 of the CPU 2, and 8-bit image data A and B are respectively stored using this data. It may be created and transferred to the memory 3. As this buffer, reception buffers 21a and 21b for holding 10-bit image data and transmission buffers 25a, 25b, 26a and 26b for holding 8-bit image data are used. Thereby, data transfer, gradation conversion to two image data, and data transfer can be performed in parallel.

  Here, the decoding time of the conventional example and this embodiment will be compared and described. For example, an image captured under a certain condition is decoded, and if the decoding is not successful, a time-out is performed, and the process is repeated until the image is captured under the next imaging condition and decoded. In general, it is assumed that the time required for imaging is 30 ms, the time required for decoding when decoding is successful is 20 ms, and the time-out time for aborting the processing when decoding is not successful is 100 ms assuming that the time is 5 times the success time. The imaging conditions, for example, gains are changed to obtain conditions A, B, and C, and these conditions A, B, and C are sequentially decoded. In this case, as shown in FIG. 15A, the image was captured and decoded under the condition A, but the decoding was not successful, and then the image was captured and decoded under the condition B. However, the decoding did not succeed and both timed out and the condition C Suppose that imaging and decoding were successful. In this case, the required time is 310 ms. Next, for example, as shown in FIG. 15B, when the imaging and decoding are repeated and the decoding succeeds for the second time, the required time is, for example, 180 ms. Further, when the image capture and decoding are repeated and decoding succeeds for the first time, for example, as shown in FIG. Assuming that the probability of successful decoding under the above three conditions is equal, the expected value of the reading time in this case is 180 ms.

  On the other hand, in this embodiment, three images, for example, 10 bits of upper 8 bits of image data A, middle 8 bits of image data B excluding upper and lower 1 bits, and lower 8 bits of image data C are created, and A case will be described in which decoding processing is performed after generating one connected image having a size of three images arranged in a continuous region. In this case, the time required for acquiring a 10-bit image is 30 ms, the time required for developing a 10-bit image into three image data in the memory is 15 ms, and the time required for decoding when decoding is successful is proportional to the amount of image data Therefore, it is assumed that the time-out time for aborting the process when decoding is not successful is assumed to be 5 times the success time and 300 ms. Here, when a 10-bit image is captured and developed into three 8-bit images, and decoding is successful with an image C obtained by decoding a normal image, 105 ms is required as shown in FIG. Similarly, when decoding is successful for image B, 105 ms is required as shown in FIG. If the image A is successfully decoded, 105 ms is required as shown in FIG. Since the image data of 3 times is processed, the decoding time is 60 ms, which is 3 times that of the conventional example. However, the reading time is 105 ms regardless of any part of A, B, C, and the expected value shown in the conventional example It is shorter than that and there is an effect that there is no variation.

  In this embodiment, two types of different image data are held in the memory, but three or more types of image data may be held in a continuous area of the memory 3.

  In each of the embodiments described above, 10 bits are converted to 8 bits using the gradation conversion table, but the number of bits is not limited to this. In addition to the gradation conversion table, the gradation conversion rule may be held as a mathematical expression.

  In this embodiment, the two-dimensional code reader has been described as an example. However, the optical information reading apparatus according to the present invention is not limited to the two-dimensional code reader, and may be various optical information reading apparatuses that read two-dimensional image information. Can also be applied.

  The present invention is an optical information reading apparatus that optically reads a two-dimensional code or the like, and can convert the gradation of an image according to a conversion rule selected by the user in accordance with the user's application and hold it in a memory. It is useful for an optical information reader in a state.

1 Image sensor 2 CPU
3 Memory 4 Communication Control Unit 10 DMA Controller 20 SRAM
21, 21a, 21b Reception buffer 22, 22a, 22b, 25, 25a, 25b, 26, 26a, 26b Transmission buffer 23, 23a, 23b Gradation conversion table 30 Calculator 40 Image data 41 Area of interest

Claims (8)

An imaging unit having a two-dimensional imaging device for imaging a reading target;
A control unit having a CPU and performing image processing and decoding when the reading target imaged by the imaging unit is held in a memory;
A memory for holding an image to be read imaged by the imaging unit;
The control unit receives image data from the imaging unit, executes gradation conversion based on a predetermined condition, and stores gradation-converted image data in the memory;
An optical information reading apparatus comprising: arithmetic means for reading and decoding image data after gradation conversion stored in the memory. The CPU of the control unit has an internal memory,
The internal memory is
A reception buffer that holds line-by-line image data obtained from the imaging unit;
The optical information reading apparatus according to claim 1, further comprising: a transmission buffer that holds image data in units of rows after gradation conversion before being transferred to the memory. The internal memory is SRAM;
The receive buffer has at least two receive buffers;
The transmission buffer has at least two transmission buffers;
The gradation converting means is a data receiving process for alternately holding the image signals picked up by the image pickup unit in the two receiving buffers in units of rows, and sets the number of data of each pixel in the image data in units of rows of the receiving buffer. The optical information reading apparatus according to claim 2, wherein the gradation conversion process of reducing and transferring alternately to the transmission buffer and the transfer process of transferring alternately to the memory from the two transmission buffers are executed in parallel. The imaging unit includes an image sensor that outputs image data of L columns and M rows,
The gradation converting means takes in data from i rows to i + N rows (1 ≦ i <N ≦ L) necessary for image processing and holds them in the reception buffer,
4. The optical information reading device according to claim 2, wherein image data of a column from j to j + K (1 ≦ j <K ≦ M) among the converted data of the transmission buffer is output from the transmission buffer to the memory.   The optical information reading apparatus according to claim 2, wherein the control unit performs part or all of the filtering process on the captured image and holds the image in the transmission buffer. A data capturing method for an optical information reader according to claim 3,
The captured image signal is received, and the image signal is alternately held in the two reception buffers in units of rows, and the image data in units of rows of the reception buffer is reduced alternately in the number of pixels. Transfer to send buffer,
And a method of fetching data from the optical information reading apparatus, wherein the process of transferring data from the transmission buffer to the memory is executed in parallel. The control unit performs different gradation conversion processing among the image data held in the reception buffer, holds the transmission buffer, and transfers a plurality of image data to the memory,
The optical information reading apparatus according to claim 1, wherein the arithmetic unit performs a decoding process based on a plurality of image data held in the memory.   8. The optical information reading apparatus according to claim 7, wherein the plurality of image data are arranged in a continuous area of the memory.