JP3018628B2 - Image reading device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus for converting color digital image signals R, G, B signals into binary image signals.

[0002]

2. Description of the Related Art Next, the configuration of a conventional image reading apparatus will be described with reference to FIG. 2 is an object, 6 is an image input unit, 7 is a comparison reference signal generation circuit, and 8 is a binarization determination circuit. For example, the object 1 is a printed wiring board, and the image input unit 6 is a camera. If the pattern of the printed wiring board is photographed with a camera, the reflectance is different between the pattern and the pattern other than the pattern. Therefore, the pattern of the printed wiring board and the pattern other than the pattern can be read from the output of the image input unit 6.

The image of the object 1 is converted into a digital image signal 21 by the image input unit 6. Comparison reference signal creation circuit 7
Calculates the comparison reference signal 22 in advance from the density-frequency histogram of the image signal. The method of calculating the comparison reference signal 22 is described in, for example, Nobuyuki Otsu, “Automatic threshold value calculation method based on discrimination and least square criterion,” IEICE Transactions on Electronics
1. Described in J63-D〓4. In this method, a threshold value that maximizes the degree of separation of a class to be separated is obtained from a density-frequency histogram of an image signal.

Each time the image signal 21 is output from the image input unit 6, the binarization determination circuit 8 compares the image signal 21 with the comparison reference signal 22,
Value. The conditions for binarization are as follows. Image signal 21
> In the case of the comparison reference signal 22, the binary image signal 23 is set to a high level. 2 when image signal 21 ≦ comparison reference signal 22
The value image signal 23 is set to a low level.

Next, a graph of the pixel density versus the frequency of the number of pixels in the pattern portion and the portion other than the pattern when the object 1 is a printed wiring board will be described with reference to FIG. The horizontal axis in FIG. 4 is the pixel density, and the vertical axis is the frequency of the number of pixels. An overlap portion C exists between the density vs. frequency histogram A of the portion other than the pattern and the density vs. frequency histogram B of the pattern portion.

Next, the image of FIG.
The state when the value is converted will be described with reference to FIG. The horizontal axis in FIG. 5 is the density, and the vertical axis is the frequency. AB in FIG. 5 is a density vs. frequency histogram of the printed wiring board, which is obtained by combining the curves A and B in FIG. CA and CB in FIG. 5 correspond to the overlapping portion C in FIG. The overlapping part CB in FIG.
Is determined as a portion other than the pattern, and the overlapping portion CA is determined as a pattern and is binarized.

[0007]

It is difficult to correctly binarize an image signal having an overlapping portion C as shown in FIG. 4 using a density threshold. The present invention performs binarization on an image signal having an overlap with a density histogram.
Calculate brightness and saturation parameters from color image signals,
It is an object of the present invention to provide an image reading apparatus capable of comparing this parameter with a preset comparison reference signal and binarizing it.

[0008]

In order to achieve this object, according to the present invention, there is provided an image input unit for picking up an image of an object 1 and outputting an R signal 11, a G signal 12, and a B signal 13 of color digital image signals. 2, R signal 11, G signal 12, and B signal 1
3 as an input, a lightness-saturation signal generating circuit 3 for converting the signal into a lightness signal 14 and a saturation signal 15, and a lightness comparison reference signal 16
And a comparison reference signal 17 for outputting a comparison reference signal 17 for saturation and a high-level comparison signal 17 when the brightness signal 14> the comparison reference signal 16 for brightness and the saturation signal 15> the comparison reference signal 17 for saturation. A binarization determination circuit 5 that outputs a binary image signal 18 and outputs a low-level binary image signal 18 otherwise.
And

Next, the configuration of an image reading apparatus according to the present invention will be described with reference to FIG. 1 is an image input unit, 3 is a brightness-chroma signal generation circuit, 4 is a comparison reference signal generator, 5
Is a binarization determination circuit. The image input unit 2 is, for example, a video camera or an image scanner. The image input unit 2 captures an image of the object 1 and outputs an R signal 11, a G signal 12, and a B signal 13 of a color digital image signal. The signal creation circuit 3 converts the R signal 11, the G signal 12, and the B signal 13 from the image input unit 2 into a brightness signal 14 and a saturation signal 15.

[0010]

Next, the operation of the brightness-chroma signal generating circuit 3 will be described. From the R signal 11, G signal 12, and B signal 13 output from the image input unit 2, a lightness signal 14 and a saturation signal 15
Is obtained by the following equation. Brightness signal 14 = max (R, G, B) (1) Saturation signal 15 = {max (R, G, B) -min (R, G, B)} / max (R, G, B) ... (2) where max (R, G, B) = max (R signal 11,
G signal 12, B signal 13), min (R, G, B) = m
in (R signal 11, G signal 12, B signal 13).

For the brightness signal 14 and the saturation signal 15, a brightness comparison reference signal value and a saturation comparison reference signal value are set in advance in the comparison reference signal generator 4. The comparison reference signal 16 and the saturation comparison reference signal 17 are sent to the binarization determination circuit 5. In the binarization determination circuit 5,
The brightness signal 14 and the saturation signal 15 are input from the brightness-chroma signal generation circuit 3.

The binarization determination circuit 5 determines whether the lightness signal 14 is larger than the lightness comparison reference signal 16 or the saturation signal 15 is larger than the saturation comparison reference signal 17. Otherwise, it is low.

Next, the configuration of the brightness-chroma signal generation circuit 3 will be described. 1A to 3C are comparators, 3D is a subtractor,
3E is a divider. The comparator 3A receives the R signal 11 and the G signal 12, and the comparator 3A outputs the R signal 11 and the G signal 1.
The larger one of the two is a signal 31 and the smaller one is a signal 32. The signal 31 and the B signal 13 are input to the comparator 3B. The comparator 3B sets the larger one of the signal 31 and the B signal 13 as the brightness signal 14. The signal 32 is input to the comparator 3C.
And the B signal 13 are input, and the smaller one of the signal 32 and the B signal 13 is defined as a signal 33.

The brightness signal 14 is input to a of the subtracter 3D, and the signal 33 is input to b. The subtractor 3D is a-
The result of b is output as a signal 34. The signal 34 is input to a of the divider 3E, and the brightness signal 14 is input to b. The divider 3E outputs the result of a / b as the saturation signal 15.

Next, the configuration of the binarization determination circuit will be described with reference to FIG. 6A and 5B are comparators, and 5C is an AND gate. The brightness signal 14 is input to a of the comparator 5A, and the brightness comparison reference signal 16 is input to b. The comparator 5A outputs the signal 51 as a high level when a> b. The saturation signal 15 is input to a of the comparator 5B,
The comparison reference signal 17 for chroma is input to b. Comparator 5
B outputs the signal 52 as high level when a> b. The signal 51 and the signal 52 output the binary image signal 18 through the AND gate 5C.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The value of the R signal 11 in FIG.
Is "40" and the value of the B signal 13 is "30", the signal 31 is "40", the signal 32 is "20", and the brightness signal 14
Becomes "40". Further, the signal 33 becomes “20”, and the subtractor 3D subtracts “40” − “20” = “20”. The divider 3E divides “20” ÷ “40” = “0.5”, and the saturation signal 15 becomes “0.5”. As a result, when the value of the R signal 11 is “20”, the value of the G signal 12 is “40”, and the value of the B signal 13 is “30”, the lightness signal 14 is “40” and the saturation signal is 0.
It becomes 5.

At this time, the brightness comparison reference signal 16 becomes "3
Assuming that "0" and the saturation reference signal 17 are "0.4", the input terminal "a" of the comparator 5A of FIG.
Is input, the signal 51 is output at a high level. “0.5” is input to the input terminal a of the comparator 5B, and “0.4” is input to the input terminal b.
Is input, the signal 52 is output at a high level.
Both inputs of the AND gate 5C go high,
The binary image signal 18 has a high level.

Next, the distribution of lightness and chroma will be described with reference to FIG. 3 using a printed wiring board as an example. AA in FIG. 3 shows a distribution region of a portion other than the pattern of the printed wiring board, and BB shows a distribution region of the pattern portion. The image distributed as shown in FIG.
When converting into a value, it is larger than the brightness comparison reference signal 16,
By setting the binary image signal 18 to a high level when the saturation reference signal 17 is larger than the saturation reference signal 17 and to a low level otherwise, the BB portion is set to a high level and the AA portion is set to a low level. Become.

In FIG. 3, the minimum value of the brightness of the distribution AA of the substrate is "10", the maximum value is "100", the minimum value of the saturation is "0.1", the maximum value is "0.6", and the pattern distribution BB The minimum value of the brightness of
Assuming that "0", the maximum value is "150", the minimum saturation value is "0.4", and the maximum value is "0.9", the lightness comparison reference signal 16 is "50" and the saturation comparison reference signal 17 is "0.3". "Is set. In this case, since AA and BB do not overlap, binarization can be performed correctly.

[0020]

According to the present invention, a color image signal is extracted from an object, parameters of a brightness signal and a saturation signal are obtained from the image signal, and these parameters are compared with a preset comparison reference signal. Therefore, binarization can be performed with less binarization errors even for an image signal having an overlap in the density vs. frequency graph.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an image reading apparatus according to the present invention.

FIG. 2 is a configuration diagram of a conventional image reading apparatus.

FIG. 3 is a distribution diagram of brightness and chroma taking a printed wiring board as an example.

FIG. 4 is a graph of pixel density versus the number of pixels in a pattern portion and a portion other than the pattern.

5 is a state diagram when the image of FIG. 4 is binarized by a comparison reference signal 22. FIG.

FIG. 6 is a configuration diagram of a binarization determination circuit 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Object 2 Image input part 3 Brightness-chroma signal generation circuit 4 Comparison reference signal generator 5 Binarization judgment circuit 11 R signal 12 G signal 13 B signal 14 Lightness signal 15 Chroma signal 16 Lightness comparison reference signal 17 Saturation comparison reference signal 18 Binary image signal

Claims (1)

(57) [Claims] An image input unit (2) for imaging an object (1) and outputting an R signal (11), a G signal (12), and a B signal (13) of a color digital image signal; 11) is compared with the G signal (12), and the larger signal is used as the first signal (31), and the smaller signal is used as the second signal (32).
The second comparator (3B) compares the B signal (13) with the first signal (31) and determines the larger one as the brightness signal (14).
And a third comparator (3C) that compares the B signal (13) with the second signal (32) and determines the smaller one as the third signal (33);
A first subtractor (3D) for subtracting the third signal (33) from (14)
And a divider (3E) that divides the output of the first subtractor (3D) by the lightness signal (14) to obtain a saturation signal (15).
1), G signal (12), B signal (13) are lightness signal (14) and chroma signal
A brightness-saturation signal generating circuit (3) for converting to (15), a comparison reference signal generator (4) for outputting a brightness comparison reference signal (16) and a saturation comparison reference signal (17), and a brightness A fourth comparator (5A) that outputs a high level when the signal (14)> the brightness reference signal (16) and outputs a low level when the brightness signal (14) ≦ the brightness comparison reference signal (16) And the saturation signal (1
5) Outputs a high level when the saturation reference signal (17) is output,
A fifth comparator (5B) that outputs a low level when the saturation signal (15) ≦ the saturation reference signal (17), an output of the fourth comparator (5A) and a fifth comparator ( AND gate with the output of 5B) as input
(5C), comprising: a binary decision circuit (5) for outputting a binary image signal (18).