JP3171059B2 - License plate automatic recognition device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to automatically recognize automatic license plate recognition equipment the large / medium-sized vehicles from the license plate of the vehicle.

[0002]

2. Description of the Related Art Generally, a license plate of a vehicle is shown in FIG.
As shown in the figure, the land transportation office code C1 and the vehicle type code C2 are displayed in the upper row, and the use code C3 and the serial number C are displayed in the lower row.
4 is displayed. Most of such license plates are of two types, large and medium, and the license plate size, character size, character spacing, and the like are standardized for large and medium, respectively, as shown in FIG.

On the other hand, in the conventional license plate automatic recognition device, when determining whether the license plate is large or medium, a license plate portion of the vehicle is imaged, and a serial number C4 of the license plate is extracted from the obtained image. The size (height) of the extracted serial number C4 or the character spacing of the serial number C4 is compared with a preset threshold to determine the large / medium size of the license plate (that is, the large / medium size of the vehicle type). I have.

[0004]

However, the automatic license plate recognition apparatus is, as shown in FIG.
When the imaging timing is different, the distance between the camera 1 and the vehicles 2a and 2b is different, and even if the license plates have the same size, the apparent size changes. That is, FIG. 10A shows the vehicle 2b.
10B, the size of the license plate is different when the image is taken at the position of the vehicle 2a in FIG. 10B. For this reason, there is a problem that it is not possible to accurately determine whether the license plate is large or medium.

For example, even if a large license plate is imaged at the position of the vehicle 2b, it may be determined that the license plate is a medium license plate. In some cases, the image may be judged to be a large number plate when the image is taken. Accordingly, the present invention has been made in view of such problems, and an object thereof is to provide an automatic license plate recognition equipment which can accurately determine the size / medium-size license plate.

[0006]

According to a first aspect of the present invention, there is provided a license plate automatic recognizing apparatus, comprising: an image capturing means for capturing an image of a license plate portion of a vehicle; and symbols portion extracting means for extracting a symbol portion of the license plate from the image and, from the symbol portion extracted by the symbol part extraction means, serial
The height of the serial number in the number part and the symbol part other than the serial number
And a vehicle type determining means for calculating a ratio to the height of the vehicle and determining the vehicle type from the ratio. Claim 2
The automatic license plate recognition device described in claim 1 is a device according to claim 1.
In the same configuration as the
Using the ratio between the interval and the interval between the serial number and the application code
Determine the vehicle type.

Furthermore, automatic license plate recognition system according to claim 3, wherein, in the structure similar to the device of claim 1,
The height of the serial number in the symbol part, and the upper and lower symbols
The vehicle type is determined using the ratio to the serial number and the interval.

[0008]

Equipment of the effects of the present invention, from the symbol portion extracted from the image of the captured license plate, series number in the symbol part
The ratio of the height of the issue to the height of the sign other than the serial number,
The character spacing of the serial number in the symbol part,
Or the height of the serial number in the symbol part
And the ratio of the interval between the upper symbol and the lower serial number is calculated, and the large / medium size of the license plate is determined from the ratio, and the height of the serial number or the It is different from judging by character spacing . Therefore, even if the timing of imaging with a camera is different as shown in FIG. 8 and the apparent size of the license plate changes,
Since the ratio does not change, it is possible to accurately determine whether the license plate is large or medium, and based on this, it is also possible to accurately determine the vehicle type.

[0009]

BRIEF DESCRIPTION based on the equipment embodiment of the present invention. The recognition device according to the present invention includes an imaging unit that images a license plate portion of a vehicle, a symbol portion extraction unit that extracts a symbol portion of a license plate from an image obtained by the imaging unit, and an extraction unit that extracts the symbol portion. The height of the serial number in the symbol part
The ratio to the height of the symbol part other than the serial number, one in the symbol part
The character spacing of serial numbers, the spacing between serial numbers and usage codes,
Or the height of the serial number in the symbol part and the upper
Calculating a ratio of the distance between the No. and the lower sequence number, but and a vehicle type discriminating means for discriminating the vehicle type from the ratio, there is a feature particularly recognition theory (vehicle type identification means), center the theory of its Will be described. <Example 1>" The height of the serial number in the symbol part and symbols other than the serial number
Method of Determining Vehicle Type from Ratio to Part Height "An example of the algorithm in this case is shown in the flowchart of FIG. 1 (only the main part) . As a method for calculating the heights of the symbol portions other than the sequence number of a series number, there are three ways in (1) to (3). (1) The height of one representative character The height of one character of the serial number (the most significant digit, the least significant digit, etc. of the serial number) One character of the symbol part other than the serial number (one character of the use code, land transportation office code) As the specific example, an example of calculating the height of the least significant digit of the serial number and the height of one character of the application code will be described. Prior to the calculation of the height ratio, in FIG. 2, the serial number of the symbol portion of the license plate is projected in the vertical and horizontal directions, and each character is cut out according to the projection length. Similarly, projection is performed on the application code to extract characters. Therefore, in step (hereinafter abbreviated as ST) 1, the height a of the serial number is calculated, the height b of the character “A” of the use code is calculated in ST2, and the ratio of the heights a and b is calculated in ST3. Value (a / b)
Is determined, and the value of the ratio is compared with a preset threshold value (2.5 in this case) to determine whether the license plate is large or medium. That is, if the value of the ratio is smaller than 2.5, it is determined to be a medium-sized license plate, and if the value of the ratio is 2.5 or more, it is determined to be a large-sized license plate.

The reason why the threshold value is set to 2.5 in FIG.
The serial number height a is 120 mm for large license plates and 80 mm for medium license plates.
And the height b of the application code is 40
mm, the value of the height ratio (a / b) is 3 for the large size and 2 for the medium size, and the threshold value is, for example, an intermediate value between 2 and 3. Since the value of the ratio is constant irrespective of the apparent size of the license plate, by setting the threshold value to 2.5, if the value of the ratio (a / b) is 2.5 or more, the ratio is large.
If it is smaller than 2.5, it can be determined that it is medium.

In this calculation example, the ratio between the height of the least significant digit of the serial number and the height of the application code is obtained. However, the height of the most significant digit of the serial number and the height of the land transportation office code or vehicle type code are determined. Height may be used. (2) Average height of all characters The height (excluding dots and bars) of all individual characters in the serial number is determined, and the average value is calculated. Alternatively, histograms are taken in the horizontal direction for all the characters of the serial number, and a range of a histogram that exists more than a predetermined amount among those histograms is set as a height (a histogram having a low height such as a dot or a bar is removed as noise). ), And calculate the average value. Average height of all characters of land transportation office code, vehicle type code, and usage code In this case, average height a of the serial number and average height of characters other than the serial number (land transportation office code, vehicle type code, usage code) After calculating b, a height comparison (a / b) is performed and a /
medium number plate if b is less than 2.5,
If it is 2.5 or more, it is determined to be a large license plate. (3) Average height of characters excluding effects of dirt, etc. Average height of characters excluding characters whose absolute value is larger than the average height of sequence numbers (excluding dots and bars). Average height of characters other than the serial number excluding characters having a large absolute value of the difference from the average height A specific flow chart in this case is shown in FIG. First, ST
At 11, the height of each character of the serial number (excluding dots and bars) is determined. The serial number "1234" corresponds to the license plate shown in FIG. Next, the average height of the serial numbers (excluding dots and bars) is determined (ST1).
2) An absolute value (ratio) of the difference between the average height and the height of each character is determined (ST13). Then, an average height a of only characters whose absolute value (ratio) of the difference is within a predetermined threshold value is obtained (ST14). ST11 to ST14 correspond to the above.

On the other hand, in ST15, the height of each character other than the serial number (land transportation office code, vehicle type code, application code) is determined. Similarly, the license plate in FIG. 7 corresponds to “Tokyo”, “55”, and “A”. Next, the average height of characters other than the serial number is determined (ST16), and the absolute value (ratio) of the difference between the average height and the height of each character is determined (ST17). Then, an average height b of only characters whose absolute value (ratio) of the difference is within a predetermined threshold value is obtained (ST18). Steps ST15 to ST18 correspond to the above. Thereafter, similarly, the value of the height ratio (a / b) is calculated (ST1).
9) If a / b <2.5, it is determined that the license plate is a medium-sized one.

According to the above methods (2) and (3),
The accuracy of the height is increased compared to the method (1), and the large size /
A medium size can be determined. <Example 2> “ Character spacing between serial numbers in symbol part, serial number, and usage”
Method of Determining Vehicle Type from Ratio to Code Interval "FIG. 4 shows an example in this case . Like the actual Example 1 performs projection in a direction perpendicular to the lower application code and serial number of the license plate, cutting out characters by the projective length.
That is, a histogram of black pixels in the vertical direction is obtained, and a histogram having a predetermined threshold or more is recognized as a character as a measure against noise. Then, in the obtained histogram of each character, the use code “A” and the highest digit “●” of the serial number
(Dot) and the serial number 1
An interval L2 between the fourth digit (the least significant digit) “4” and the second digit “3” is obtained. Here, each of the intervals L1 and L2 is the length between the centers of the width of the histogram of each character.

The ratio of the distances L1 and L2 (L1 / L2) can be expressed by specific numerical values with reference to FIG. 8: Medium: L1 / L2 = 55/55 = 1.0 Large: L1 /L2=67.5/80≒0.84. Therefore, if the intermediate value 0.92 between 1.0 and 0.84 is set as the threshold value, it is possible to discriminate between a large size and a medium size (see ST3 in FIG. 1). <Example 3>" The height of the serial number in the symbol part,
Method of Determining Vehicle Type from Ratio to Interval of Serial Number] FIGS. 5 and 6 show an example of this case. <br/> in FIGS. 5 and 6, and calculates the height of the sequence number in the Symbol moiety, the ratio of the distance between the upper symbol (land transportation office code and vehicle type code) and the lower sequence number I have.

In FIG. 5, histograms of black pixels in the horizontal direction are obtained for the characters in the upper and lower parts of the license plate.
A histogram in a range equal to or more than a predetermined threshold is used. Widths (character heights) a and b of the two obtained histograms;
The interval c between the two histograms is obtained, and the ratio (a / c) between the width a and the interval c is calculated. A specific example of the ratio (a / c) is
Similarly, referring to FIG. 8, in the case of medium size: a / c = 80/15 ≒ 5.33 In the case of large size: a / c = 120/15 = 8.0. Therefore, an intermediate value 6.67 between 5.33 and 8.0 may be set as the threshold.

In FIG. 6, the widths a and b of the two histograms are obtained as in FIG. 5, and the distance d between the centers of the widths a and b is obtained.
Ask for. Then, the ratio (a / d) between the width a and the interval d or the ratio (b / d) between the width b and the interval d is calculated. Specifically, when a / d is used, in the case of the medium size: a / d = 80/75 ≒ 1.07 In the case of the large size: a / d = 120/95 ≒ 1.26, and the intermediate value 1.17 is obtained. The threshold is used. When b / d is used, in the case of the medium size: b / d = 40/75 ≒ 0.53 In the case of the large size: b / d = 40/95 ≒ 0.42, and the intermediate value 0.48 is set as the threshold value .

In the first to third embodiments, by comparing the calculated ratio value with the set threshold value, it is possible to determine whether the license plate is large or medium, and thus to accurately determine the type of the imaged vehicle.

[0018]

As described above, according to the present invention, equipment of the present invention,
From the symbol part extracted from the image of the license plate taken, the height of the serial number in the symbol part and other than the serial number
The ratio of the height of the symbol part to the height, the sentence of the serial number
The ratio of the character spacing to the spacing between the serial number and the usage code, or
The height of the serial number in the symbol part, the upper
Calculating a ratio of the distance between the sequence number, Ru der which determine large / medium-size license plate from the ratio. Therefore,
The ratio does not change even if the appearance of the license plate changes due to different timings at which images are taken by the camera, so that it is possible to accurately determine whether the license plate is large or medium. Can be performed accurately.

[Brief description of the drawings]

FIG. 1 is the height of the serial number in the symbol part of the license plate
FIG. 11 is a partial flow diagram showing an example of determining whether a license plate is large or medium based on the ratio of the height of a symbol portion other than the serial number .

FIG. 2 is a diagram for explaining a specific example of the flowchart of FIG. 1;

FIG. 3 is the height of the serial number in the symbol part of the license plate
FIG. 13 is a partial flowchart showing another example of determining the large / medium size of the license plate from the ratio of the height of the symbol portion other than the serial number .

FIG. 4 is a sentence of a serial number in a symbol portion of a license plate.
It is explanatory drawing which shows an example which discriminate | determines the large / medium size of a license plate from the ratio of the character space and the space | interval of a serial number and an application code .

FIG. 5 is the height of the serial number in the symbol part of the license plate.
FIG. 11 is an explanatory diagram showing an example in which a large / medium license plate is determined based on the ratio of the interval between the upper symbol and the lower serial number .

FIG. 6 shows the height of the serial number in the symbol part of the license plate.
It is explanatory drawing which shows another example which discriminate | determines the large / medium type of a license plate from the ratio of the space | interval of the symbol of an upper part, and the serial number of a lower part .

FIG. 7 is a view showing a license plate of the vehicle.

FIG. 8 is a diagram showing dimensional specifications of large and medium-sized license plates.

FIG. 9 is a diagram showing timing when a license plate of a vehicle is imaged by a camera.

FIG. 10 is a diagram illustrating a change in the apparent size of the license plate of each vehicle when the image is captured at the timing of FIG. 9;

[Explanation of symbols]

 C1 Land Transport Office Code C2 Vehicle Type Code C3 Application Code C4 Serial Number

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G08G 1/015 G06K 9/36 G06T 1/00 G08G 1/04

Claims (3)

(57) [Claims] 1. An image pickup means for picking up an image of a license plate portion of a vehicle, a sign part extracting means for extracting a sign part of a license plate from an image obtained by the image pickup means, and a sign part extracted by the sign part extracting means. From the symbol part, the height of the serial number in the symbol part and the description other than the serial number
An automatic license plate recognizing device comprising: a vehicle type discriminating means for calculating a ratio with respect to a height of a signal portion and discriminating a vehicle type from the ratio. 2. Photographing a license plate portion of a vehicle.
Image means, and a number from the image obtained by the image pickup means.
Symbol part extracting means for extracting the symbol part of the bar plate
And the symbol part extracted by this symbol part extraction means.
The character spacing of the serial number in the
Calculate the ratio to the gap with the usage code, and determine the vehicle type from the ratio.
Features and to Luna Nba <br/> over plate automatic recognition device that includes a separate to the vehicle type identification means. 3. An image pickup device for picking up an image of a license plate portion of a vehicle.
Image means, and a number from the image obtained by the image pickup means.
Symbol part extracting means for extracting the symbol part of the bar plate
And the symbol part extracted by this symbol part extraction means.
And the height of the serial number in the symbol part, and the upper and lower symbols
Calculate the ratio to the serial number of the
It features and to Luna emissions <br/> bar plate automatic recognition device further comprising a vehicle type discriminating means for discriminating.