JPH0584946B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a standard pattern creating device, and more particularly to a standard pattern creating device that creates a standard pattern for accurately and quickly recognizing stamped characters.

Prior Art Engraved characters have excellent environmental resistance and are resistant to changes over time, and are widely used as instruction characters that provide important information for production control and production management in various production processes. Particularly in the automobile production process, it is used to assign unique numbers to each part of the car body, engine, etc.

A character recognition device that recognizes such engraved characters obtains a grayscale image by capturing an image of the engraved character using an ITV camera, etc., and converts this grayscale image into two.
The value is converted into an image pattern, the image pattern is compared with a standard character pattern registered in advance (pattern matching), and the character type is recognized based on the degree of matching between the two.

Such standard character patterns are created by accumulating a plurality of binary image patterns of the same character type obtained under different conditions and extracting regions where each pixel has a high probability of becoming a character part.

Problems to be Solved by the Invention When performing character recognition by pattern matching, it is assumed that the line width of the character part in the image pattern is approximately equal to the line width of the character part in the standard character pattern registered in advance. .

However, with the currently widely used stamping machines, it is difficult to accurately control the stamping pressure and the inclination with respect to the stamping surface, and the groove depth etc. often vary for each stamped character. Furthermore, when characters have a large number of digits, such as a vehicle body number, the angles and orientations of the grooves of each character relative to the illumination become uneven. Therefore, in the case of engraved characters, the line width of the character portion of the image pattern varies even if the character type is the same.

Therefore, with normal pattern matching, there is a problem in that it is difficult to recognize the engraved characters.

Therefore, a technology has been proposed that changes the threshold value for obtaining a binary image pattern and selects the optimal threshold value, thereby bringing the line width of the character part of the image pattern closer to the line width of the character part of the standard character pattern. Proposed. Examples of such techniques include the technique disclosed in Japanese Patent Application Laid-Open No. 61-208178 and the technique disclosed in 1985 Electronics and Communication Engineers of Japan Comprehensive National Conference Lecture Abstracts, page 6-153.

However, even with these conventional techniques, a large amount of processing time is required to obtain the optimum threshold value, so there is a problem in that the stamped characters cannot be quickly recognized.

Purpose of the Invention The present invention was made in order to solve the above-mentioned problems in character recognition, and its purpose is to accurately recognize characters whose line widths vary, especially engraved characters. Another object of the present invention is to provide a standard pattern creation device that can quickly create standard patterns.

Means for Solving the Problem The standard pattern creation device of the present invention includes an image pattern detection means that obtains a plurality of binary image patterns of the same character type under different conditions; A cumulative pattern creating means for creating a cumulative pattern representing a frequency distribution of whether each pixel becomes a character part or a background part; and a character skeleton pattern by extracting a part that frequently becomes a character part from the cumulative pattern. a character skeleton pattern creation means for creating a standard character pattern; a standard character pattern creation means for creating a standard character pattern by thinning the character skeleton pattern;
Misaligned standard character pattern creation means for creating a misaligned standard character pattern by shifting the standard character pattern by a predetermined amount upward, downward, left, and right;
an average character pattern creation means for creating an average character pattern by extracting portions with a relatively high frequency of becoming characters from the cumulative pattern; and an average character pattern for each of character types other than the character types of the standard character pattern. A matching calculation means for comparing and calculating a matching degree, a similar character type selection means for selecting similar character types from each matching degree value, and a background skeleton pattern for extracting a portion that frequently becomes a background portion from the cumulative pattern. a background skeleton pattern creation means for creating a background skeleton pattern, and a product pattern in which a background part of a background skeleton pattern of a certain character type overlaps with a character part of each character skeleton pattern of similar character types of that character type is obtained for all similar character types of that character type; a background feature pattern creation means that uses a sum pattern of these as a background feature pattern; and a standard pattern creation device that outputs the standard character pattern, positional deviation standard character pattern, and background feature pattern as a set for each character type to a standard pattern memory. It is characterized in that it is equipped with the following.

EXAMPLES The present invention will be described in more detail below based on examples shown in the drawings. Here, FIG. 1 is a block diagram of a character recognition device equipped with a standard pattern creation device according to an embodiment of the present invention, and FIG. 2 is a detailed block diagram of main parts of the standard pattern creation device according to an embodiment of the present invention.
FIG. 3a is an explanatory diagram showing the state of creating a thinned character pattern for character type "2", FIG. 3b is an illustration of a background feature pattern for character type "2", and FIG. Figure 3a for ``
The corresponding diagram, FIG. 4b, is an illustration of a background feature pattern for the character type "7", and FIG. 5 is a flowchart of the operation of character recognition by the character recognition device shown in FIG. 1. Note that the present invention is not limited to the embodiments shown in the figures.

In FIG. 1, a stamped character B is engraved on a cowl panel A, which is a component of an automobile body. This stamped character B is, for example, an 11-digit character string consisting of alphabetic characters, alphanumeric symbols, and numbers.

The character recognition device 1 is for automatically reading the engraved character B, and illuminates the engraved character B with a fluorescent lamp 2 and images it with a CCD camera 3. The engraved character B is dark because the character part is grooved.
The CCD camera 3 captures a grayscale image in which the text is dark and the surface of the cowl panel A is bright.

The output signal of the CCD camera 3 is converted into a digital value by an A/D conversion circuit 4, and the output signal is transferred to a first image memory 5.
is memorized.

The grayscale image data stored in the first image memory 5 is binarized by a predetermined threshold value in a binarization circuit 6, and is stored in the second image memory 7 as binary image data. For example, a dark part, that is, a character part, of the grayscale image data is stored as "1", and a bright part, that is, a background part, is stored as "0".

The binary image data stored in the second image memory 7 is subjected to expansion processing and contraction processing once each in an expansion/deflation circuit 8. Such an expansion or contraction process may be a so-called 4-connection expansion or contraction process. Through expansion and contraction processing,
For example, deletions or discontinuities in the "1" portion, that is, the character portion, are corrected.

Next, in the character detection/cutout circuit 9, for example, 11
Each character is detected one by one from binary image data of a character string of digits, and cut out in a predetermined rectangular frame to generate binary image data for each character.

Next, the position normalization circuit 10 calculates the center coordinates of the character portion of the binary image data for each character, and sets the image data in which the character portion is aligned within a predetermined frame.

The aligned image data of each character is sent via the line switching circuit 11 to the coincidence calculation circuit 12 or the standard pattern automatic creation circuit 20.

Now, if the line switching circuit 11 is on the broken line side,
This character recognition device 1 is configured from the CCD camera 3 to the standard pattern automatic creation circuit 20.
now functions as a standard pattern creation device.

At this time, image data of the same character type is obtained under various conditions by changing the embossing position, embossing strength, illumination, etc., and inputting it to the standard pattern automatic creation circuit 20.

The configuration of the standard pattern automatic creation circuit 20 is as shown in FIG.
It is input to the cumulative pattern creation circuit 21.

The cumulative pattern creation circuit 21 calculates the frequency of whether each pixel of image data of the same character type becomes a character part or a background part, creates a cumulative pattern representing the frequency distribution, and stores it in the third image memory 22. Remember. For example, the cumulative pattern when the character type is "2" is schematically shown in FIGS. 3a and 3a. The area surrounded by the broken line is an area with a probability of 10% or more to be a text part, and the area filled in black is an area with a probability of 90% or more to be a text part.

The skeleton pattern creation circuit 23 extracts only regions with a probability of 90% or more to become character parts from the cumulative pattern stored in the third image memory 22, creates a character skeleton pattern, and stores it in the fourth image memory 24. do. For example, character skeleton patterns for character type "2" are illustrated in FIGS. 3a and 3b.

Further, the skeleton pattern creation circuit 23 extracts a portion having a probability of becoming a character portion of 10% or less from the cumulative pattern, and stores it in the fourth image memory 24 as a background skeleton pattern. For example, the background skeleton pattern for the character type "2" is illustrated in FIGS. 3a and 3i.

The character skeleton pattern stored in the fourth image memory 24 is thinned by the thinning circuit 25, and is stored in the fifth image memory 27 as a standard character pattern in which the line width of the character portion is 1 pixel. For example, standard character patterns for character type "2" are illustrated in FIGS. 3a and 3c.

The standard character pattern is further processed by the shift calculation circuit 26.
is input, and the shift calculation circuit 26 translates the standard character pattern by one pixel in each of four directions: up, left, down, and right, creates each positional shift standard character pattern, and converts them into a fifth image. It is stored in the memory 27. For example, the positional deviation standard character pattern for character type "2" is d, e, f, g in Figure 3 a.
For example:

On the other hand, the average character pattern creation circuit 28
An average character pattern is created by extracting a pixel region with a probability of 50% or more of becoming a character part from the cumulative pattern stored in the sixth image memory 22, and is stored in the sixth image memory 29. For example, average character patterns for character type "2" are illustrated in FIGS. 3a and 3h.

FIG. 3a shows various patterns for the character type "2", while FIG. 4a shows various patterns similarly created for the character type "7".

In this way, various patterns for all character types are created and stored in the fourth image memory 24 to the sixth image memory 29, respectively.

The coincidence degree calculation circuit 30 of the standard pattern automatic creation circuit 20 is composed of an exclusive OR operation circuit 31 and a coincidence degree memory 32, and includes a fifth image memory 27.
The standard character pattern stored in the standard character pattern is compared with the average character pattern stored in the sixth image memory 29 for character types other than the standard character pattern. That is, exclusive OR operation circuit 3
1, the ratio of the number of pixels that match "1" or "0" in both patterns to the total number of pixels is calculated as the matching degree, and is stored in the matching degree memory 32.

A similar character type selection circuit 33 selects a character type having an average character pattern with a high degree of coincidence with the standard character pattern of each character type, selects it as a similar character type, and stores the character type in a similar character type data memory 34. For example, if the standard character pattern for character type "2" (Fig. 3 a, c) and the average character pattern for character type "7" (Fig. 4 a, h) have a high degree of matching, then Character type "7" is selected as a similar character type. Conversely, the standard character pattern for character type "7" (Figure 4 a, c) and the average character pattern for character type "2" (Figure 3 a, h)
If the matching degree is high, character type "2" is selected as a character type similar to character type "7".

A plurality of similar character types may be selected, and if there is no similar character type, no similar character type may be selected.

The background feature pattern creation circuit 35 reads the background skeleton pattern of a certain character type, reads the character skeleton pattern of similar character types of the character type, and generates a product area where the background part of the background skeleton pattern and the character part of the character skeleton pattern overlap. Create a pattern for all similar character types of that character type. There are 2 similar character types
If there are more than one, a product area pattern is obtained for each case, and the sum area pattern is created by combining the product area patterns. The created sum area pattern is then stored in the seventh image memory 36 as a background feature pattern. For example, for character type "2", the overlap product of the background part of its background skeleton pattern (Fig. 3 a, i) and the character part of its similar character type "7" character skeleton pattern (Fig. 4 a, b) A background feature pattern as shown in FIG. 3b is obtained as a region pattern. Since "7" is the only similar character type, this becomes the background feature pattern, but if there are other similar character types, the pattern of the sum area that combines the patterns of their product areas becomes the background feature pattern. In addition, the background part of the background skeleton pattern for the character type "7" (Fig. 4 a, i) and the character skeleton pattern for the similar character type "2" (Fig. 3 a, b)
A background feature pattern shown in FIG. 4b is obtained as a pattern of an area where the character portions overlap.

The standard pattern creation circuit 37 generates standard character patterns and misaligned standard character patterns stored in the fifth image memory 27 and the seventh image memory 36.
The background feature patterns stored in the memory are grouped for each character type and output as standard patterns.

The output standard pattern is stored in the standard pattern memory 16 shown in FIG.

Thus, for the character type "2", Figure 3a
c, d, e, f, g and various patterns shown in FIG. 3b are stored as standard patterns. In addition, for the character type "7", c, d, e in Figure 4 a,
The various patterns f, g and FIG. 4b are stored as standard patterns.

Now, returning to FIG. 1, once standard patterns are created for all character types with the line switching circuit 11 set to the dotted line side, the line switching circuit 11 is switched to the solid line side. Thereby, the character recognition device 1 returns to its original function of recognizing unknown characters.

FIG. 5 is a flowchart for recognizing this unknown character, and the processes S1 to S5 are the processes up to the position normalization circuit 10 shown in FIG.

Steps S6 and S7 are performed by the exclusive OR operation circuit 13, and first, the image data of the unknown character and the thinned character pattern are matched. Here, the thinned character pattern refers to the standard character pattern and the misaligned standard character pattern. Through this matching in step S6, the ratio of the number of pixels that match "1" or "0" to the total number of pixels in both the image data of the unknown character and the thinned character pattern of each character type is determined as the degree of character partial matching. Calculated.

Next, in matching in step S7, the ratio of the number of pixels that match "1" or "0" in both the image pattern of the unknown character and the background feature pattern of each character type to the total number of pixels is calculated as the degree of background partial matching. .

These character part matching degree and background part matching degree are
It is stored in the coincidence degree memory 14.

The character type determination circuit 15 subtracts the background part matching degree from the character part matching degree for each character type, and sets it as the overall matching degree. The background partial matching degree has a low value for the character type itself, but has a high value for similar character types. Therefore, even if the difference between several types of similar characters is small in the degree of character matching and difficult to judge, by subtracting the degree of matching in the background part, the difference becomes large in the overall degree of matching, making it easier to judge.

Then, the one with the highest overall degree of agreement is the degree of agreement
If it is 90% or more and the next highest degree of matching is 80% or less, it is determined that the unknown character is the character type with the highest overall degree of matching. In other cases, it is assumed that there is an error in interpretation and the judgment cannot be made.

Thus, according to the character recognition device 1, since matching is performed with the standard pattern consisting of the standard character pattern, the misaligned standard character pattern, and the background feature pattern, it is possible to read the engraved characters quickly and accurately.

Note that once the standard pattern is stored, character recognition can be performed using the standard pattern memory, so the line switching circuit 11 and the standard pattern automatic creation circuit 20 can be made optional and shared by multiple character recognition devices. I can do it.

Effects of the Invention According to the present invention, there is provided an image pattern detecting means for obtaining a plurality of binary image patterns of the same character type under different conditions, and a means for accumulating a plurality of binary image patterns of the same character type so that each pixel is a character part. A cumulative pattern creating means for creating a cumulative pattern representing a frequency distribution of whether the character is a character part or a background part, and a character skeleton pattern creating means which creates a character skeleton pattern by extracting a part that frequently becomes a character part from the cumulative pattern means for creating a standard character pattern by thinning the character skeleton pattern; and a standard character pattern creating means for creating a standard character pattern by thinning the character skeleton pattern; an average character pattern creation means for creating an average character pattern by extracting portions with a relatively high frequency of character parts from the cumulative pattern; a matching calculation means for calculating a matching degree by comparing with each average character pattern of character types other than character types; a similar character type selection means for selecting similar character types from each matching degree value; and a similar character type selection means for selecting a similar character type from the cumulative pattern. A background skeleton pattern creation means that extracts frequently occurring parts and creates a background skeleton pattern, and a product pattern in which the background part of a background skeleton pattern of a certain character type and the character part of each character skeleton pattern of similar character types of that character type overlap. is obtained for all similar character types of the character type, and a background feature pattern creation means that uses the sum pattern as a background feature pattern; A standard pattern creating device is provided which is characterized by comprising standard pattern creating means for outputting to a standard pattern memory, and by using the standard pattern created thereby, the following effects can be obtained.

Among the standard patterns, the thin line character pattern is
It is extracted from a region that is a stable character part, and also uses patterns that are shifted, so even if the image pattern of an unknown character contains misalignment or noise, it will still be the same character type. Accurate recognition is possible because the degree of matching with the image does not decrease.

Among the standard patterns, the thin line character pattern is
Since the number of pixels forming the character part is small, the memory capacity of the standard pattern can be reduced.

Since the background feature pattern is added as one of the standard patterns, even if the difference in the degree of matching with similar character types is small with only the thinned character pattern, it can be increased by subtracting the degree of match of the background feature pattern. This allows you to distinguish between characters and accurately identify character types.

The processing time for character recognition can be made faster.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a character recognition device equipped with a standard pattern creation device according to an embodiment of the present invention;
FIG. 2 is a detailed block diagram of the main parts of a standard pattern creation device according to an embodiment of the present invention, FIG. FIG. 4A is a diagram corresponding to FIG. 3A for the character type "7"; FIG. 4B is an example diagram of the background feature pattern for the character type "7"; FIG. 5 is a flowchart of the operation of recognizing character types using the embodiment shown in FIG. (Explanation of symbols), 1...Character recognition device, 3...
CCD camera, 6...binarization circuit, 8...expansion/
Contraction circuit, 9...Character detection/cutting circuit, 10...
...Position normalization circuit, 12...Concordance calculation circuit, 1
5...Character determination circuit, 16...Standard pattern memory, 20...Standard pattern automatic creation circuit, 21...
...Cumulative pattern creation circuit, 23... Skeleton pattern creation circuit, 25... Thinning circuit, 26...
Shift calculation circuit, 28... Average character pattern creation circuit, 30... Matching degree calculation circuit, 33... Similar character type selection circuit, 34... Similar character type data memory, 35... Background feature pattern creation circuit, 37
...Standard pattern creation circuit, B...engraved characters.

Claims (1)

[Claims] 1. (a) An image pattern detection means for obtaining a plurality of binary image patterns for each character type under different conditions; (b) An image pattern detection means for obtaining a plurality of binary image patterns for the same character type. (c) a cumulative pattern creating means for creating a cumulative pattern representing a frequency analysis of whether each pixel becomes a character part or a background part; (d) standard character pattern creation means for creating a standard character pattern by thinning the character skeleton pattern; (e) character skeleton pattern creation means for creating a standard character pattern by thinning the character skeleton pattern; , misaligned standard character pattern creation means for creating a misaligned standard character pattern by shifting the position by a predetermined amount to the right; (g) a degree of coincidence calculating means that calculates the degree of coincidence by comparing the standard character pattern with each average character pattern of a character type other than the character type of the standard character pattern; (h) (i) a background skeleton pattern creation means for creating a background skeleton pattern by extracting a portion that frequently becomes a background portion from the cumulative pattern; j) Find the product pattern where the background part of the background skeleton pattern of a certain character type overlaps with the character part of each character skeleton pattern of similar character types of that character type for all similar character types, and use the pattern of their sum as the background feature. (k) standard pattern creation means for creating a standard pattern by combining the standard character pattern, the misaligned standard character pattern, and the background characteristic pattern for each character type; Features of standard pattern creation device. 2. Optical imaging means for reading characters; 2.
A value image means, an expansion/contraction calculation means, a character detection/cutting means, a position normalization means, a standard pattern memory, and a degree of coincidence calculation means for calculating the degree of coincidence between the standard pattern and the image pattern of the unknown character. ,
2. The standard pattern creation device according to claim 1, wherein the standard pattern creation device outputs the created standard pattern to the standard pattern memory of a character recognition device having a character type determination means for determining the character type based on the obtained degree of matching. 3. The standard pattern creation device according to claim 1 or 2, which creates a standard pattern used for recognizing engraved characters.