JPH0731717B2 - Optical reader - Google Patents

Description

The present invention relates to an optical reading device that optically reads characters and bar codes.

[Prior Art and its Problems] A hand-held OCR (optical character reading device) is described in JP-A-54-16133. Figure 5 shows an example of a handheld OCR. This is for reading characters by holding the hand scanner 21 with the hand 22 and moving it on the paper. Reference numeral 24 denotes a light source, which illuminates the paper surface and forms an image of the reflected light on the image sensor 26 via the lens system 25. Image sensor 26
The output signal of is amplified by the amplifier circuit 27, converted into the binary signal of "white" (paper) and "black" (character) by the binarization circuit 38, and then the identification circuit 29 identifies the character. .

An apparatus for reading both characters and bar codes is described in, for example, Japanese Patent Laid-Open Nos. 59-81766 and 60-201483. FIG. 6 shows the configuration of JP-A-59-81766. 21 to 29 in the figure are the same as those in FIG. There is a discrimination circuit 30 that discriminates characters in the discrimination circuit 29 and discriminates the bar code from the output signal of the binarization circuit 28. Based on the discrimination results sent from the discrimination circuits 29 and 30, the correct one is selected in the selection circuit 31. It is output as a reading result.

Since it is sufficient to detect the presence or absence of a line for identifying a character, it is sufficient if the minimum possible line width of a character can be correctly resolved. However, since the bar code is identified by detecting the difference in the line width between the bars, it cannot be correctly identified by a reader that can resolve the minimum line width of the bar.

Problems in bar code identification will be described with reference to FIG.
The width of the bar 32 is a and the width of the bar 33 is b, and b = 2a. Fourth
The pixel pitch of the image sensor 34 shown in the figure is the same as the width a of the thin bar 32, and the threshold value for binarization is 50%. Scanning at the position shown in FIG.
Since the two pixels of "black" are black, the number of "black" pixels is the same after scanning even though the bar widths of bar 32 and bar 33 actually have a double difference. Bar widths are considered to be the same. Therefore, the barcode cannot be identified.

The above-mentioned example is a case where only the quantization error is considered, and in the actual barcode, the unevenness of printing, the shading of ink,
The bar line width varies depending on conditions such as fluff on the paper surface. Now, the standard ratio of the width of the thin bar and the width of the thick bar is 1: 2.
However, if the thin bar is 20% thick and the thick bar is 20% thin, the actual ratio is 1.2: 1.6. Considering the above quantization error, the ability to resolve at least a width of 1/3 to 1/5 of the line width of the thin bar (about 1/4 mm) is necessary to accurately distinguish between the two. I need. That is, a resolution of at least 1/12 mm is required to perform barcode identification, and a resolution of 1/20 mm or more on the paper surface is required to obtain high identification performance.

On the other hand, character identification means that various basic patterns are prepared as a dictionary and the character is specified by repeatedly comparing the input pattern obtained from the image signal with the basic pattern of the dictionary. Can be detected. In other words, it is sufficient if the minimum line width of characters on the paper in both horizontal and vertical directions (the minimum line width of OCR characters including printing error is about 1/3 mm) can be resolved.

However, in order to simultaneously read the awards, which differ greatly in the required resolution of barcodes and characters, the device must satisfy the higher resolution requirements. That is, it is necessary to use an image sensor having a very small pixel pitch in accordance with the bar code identification request, but from the character identification, an excessive amount of information is obtained, and the following problems occur. .

(I) Since the amount of basic patterns must be adjusted according to the amount of input information, a huge storage capacity is required.

(Ii) Since the number of input information patterns increases in accordance with the amount of information, the identification algorithm becomes complicated and a huge amount of time is required for development.

(Iii) For the same reason, the processing time required for character recognition becomes enormous.

Originally, since the amount of information in character identification is larger and the processing time is longer in bar code identification and character identification, if an unnecessarily large amount of information is given to the character identification part as described above, imbalance between both identification operations will occur. Is further increased, and the efficiency of the entire bar code / character reading device is reduced.

[Object of the Invention] An object of the present invention is to improve the conventional drawbacks and to provide an optical reading device capable of highly accurately and efficiently identifying characters and bar codes.

[Means for Solving Problems] The configuration of the present invention is shown in FIG.

The output of the image sensor 4 is sent to the character identification circuit 6 as a pattern having a character resolution and to the bar code identification circuit 7 as a pattern having a bar code resolution via the resolution conversion circuit 5. The determination result of each identification circuit is sent to the selection circuit 8, and the correct one is the final output.

The structure of the image sensor is shown in FIG. The same figure (i) is n
It is a one-dimensional image sensor of a row. (Ii), (ii)
Each of i) is a two-dimensional image sensor having m rows and n columns. In any of the image sensors, the configuration of the present application is based on the premise that the pixel pitch in the horizontal direction (row direction) is sufficiently small for barcode identification. That is, in any image sensor, at least the horizontal pixel pitch is 1/3 times the minimum line width (1/4 mm) of the barcode, that is,
Finer than 1/12 mm.

However, the above discussion of resolution is on the paper surface, and the line width in the image formed on the image sensor is obtained by multiplying the line width on the paper surface by the image forming magnification M by the image forming optical system. Will be things. That is, in order to obtain a resolution equivalent to 1/12 mm on the paper surface, the pixel pitch of the image sensor must be M / 12 mm. Generally, the image forming optical system of the optical reading device is a reduction optical system in order to downsize the device and to obtain a wide field of view. For example, when M = 0.2, the horizontal pixel pitch of the image sensor is 1/60 mm. Further, in the same optical system, a pixel pitch of M / 3 = 1/15 mm is required to satisfy the resolution required for character recognition.

The high resolution required to identify barcodes is only required in the horizontal direction of the image sensor. FIG. 2I is an example of an image sensor in which the horizontal direction has a fine pixel pitch that can be used for bar code identification, and the vertical direction has a coarse pixel pitch that is required for character identification. On the other hand, most of the image sensors on the market have the same horizontal / vertical pixel pitch, so if you use a standard product, the same figure (ii
As in i), both horizontal and vertical have a pixel pitch that can support barcode identification.

Next, the operation of the resolution conversion circuit with respect to the image sensor output will be described. When the image sensor is a one-dimensional array as shown in FIG. 2 (i), if the resolution required for character recognition is 1/4 of the resolution of the image sensor, the resolution conversion circuit has 4 pixels. Minute data is added and the result is output. As a result, if the number of pixels of the one-dimensional image sensor is n, the data used for character recognition is equivalently k = n / 4 pixels. In (ii) and (iii), basically, the same as in the case of the one-dimensional array, and if the resolution required for characters is 1 / x as compared with the resolution of the image sensor in the horizontal or vertical direction, the data of x pixels. Is added and the result may be used for character identification.

When a one-dimensional sensor is used, the image sensor is moved in the vertical direction to identify a character and a two-dimensional image is obtained.

FIG. 7 is an example in which a pattern having an appropriate resolution is obtained by the present invention. The figure (i) is for characters. The figure (ii) shows the case of a barcode.

[Embodiment] FIG. 3 shows an embodiment of the resolution conversion circuit.

In the figure, the first holding circuit 53 holds the intermediate result A of the addition by the adder circuit 51, and the second holding circuit 54 holds the final result C of the addition. The first holding circuit 53 and the second holding circuit 54 are sample &
It is a hold circuit. In this embodiment, the resolution of the image sensor is equivalently reduced to 1/4.

The counting circuit 52 samples (1) to the first holding circuit 53 in synchronization with each clock during a period of 3 clocks out of 4 clocks.
Send a signal. During this time, the output of the first holding circuit 53 and the image signal output are added, and the total sum is recorded in the first holding circuit 53.

The sample (1) signal is not output in one clock section out of four clocks, and the sample (2) signal is sent to the second holding circuit 54, and the sum of the image signal outputs in the four-clock phase-division equal section is sent to the second holding circuit 54. Hold it. At the same time, a reset signal is sent to the first holding circuit 53 to reset the output of the first holding circuit 53.

By repeating the above cycle, the sum of the image signal outputs for 4 clocks is sent to the character identifying circuit once every 4 clocks.

On the other hand, the image signal output of the image sensor is sent to the barcode identification circuit as it is.

In this way, a signal having a resolution of 1/4 is equivalently sent to the character identifying circuit as compared with the image signal output sent to the bar code identifying circuit.

To determine whether it is a character or a bar code, choose one that is correctly identified, such as Japanese Patent Application No. 60-79083, filed on April 12, 1985, or select the height of the bar of the bar code as the height of the character. It may be possible to make a judgment by utilizing the fact that it is higher than that.

[Brief description of drawings]

FIG. 1 is a block diagram of the present invention. FIG. 2 is an explanatory diagram of resolution conversion, and FIG.
In the case of a dimensional sensor, Fig. 2 (ii) shows a two-dimensional sensor (horizontal pitch is for bar code, vertical pitch is for character).
2 (iii) is an explanatory view in the case of a two-dimensional sensor (horizontal and vertical bar code equivalent pitch). FIG. 3 shows an example. FIG. 4 is an explanatory diagram showing the relationship between bar width and pixels. FIG. 5 shows the configuration of a conventional handheld character reading device. FIG. 6 is a block diagram of a conventional handheld character and bar code reader. FIG. 7 is a pattern example after binarization in the present invention. 1: Printed matter, 2: Illumination light source, 3: Lens, 4: Image sensor,
5: Resolution conversion circuit, 6: Character identification circuit, 7: Bar code identification circuit, 51: Addition circuit, 52: Counting circuit, 53: First holding circuit, 5
4: Second holding circuit.

Claims (3)

[Claims] 1. An optical reading device for forming a character or a bar code on a sheet of paper on an image sensor by an image forming optical system to identify a bar code and a character, and a magnification determined by the image forming optical system. When M is set, the resolution in the horizontal direction of the image formed by the image forming optical system is set to be a fraction or less of a value M times the minimum line width in the barcode standard used. An image sensor installed in the first holding means, an addition means for adding the output of the image sensor and the output of the first holding means, and outputting the result to the first holding means and the second holding means, the first holding means, The second
The holding means is controlled so that the addition by the adding means is continued until the driving clock of the image sensor reaches a predetermined number of times, and when the driving clock reaches a predetermined number of times, the addition result from the second holding means to that time is displayed. A resolution conversion unit including a counting unit for outputting the output, a barcode identification unit for identifying the output of the image sensor as a barcode image, and a character identification unit for identifying the output of the resolution conversion unit for identifying a character image The bar code identification means and the selection means for selecting an appropriate one of the identification results output by the character identification means, and the predetermined number of times given to the resolution conversion means is the minimum line width of the character. An optical reading device, which is a number approximately equal to a value obtained by dividing a value of M times by the pitch of pixels in the horizontal direction. 2. The image sensor has a horizontal pixel pitch that is less than a fraction of M times the minimum line width in the bar code standard used, and the vertical pixel pitch is the minimum line width of a character. The optical reading device according to claim 1, wherein the optical reading device is a two-dimensional image sensor having a value equal to or less than M times the value of. 3. The one-dimensional image sensor is installed so that the pixel pitch is a fraction of M times the minimum line width in the bar code standard used, and the pixel array direction is horizontal. The optical reading device according to claim 1, wherein the optical reading device is an image sensor.