JP3019522B2 - 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 and B signals into binary 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 from the density vs. frequency histogram of the image signal in advance. 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 versus 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 number of pixels of 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 of FIG. 4 is the pixel density, and the vertical axis is the number of pixels. An overlap portion C exists in the density vs. frequency histogram A of the pattern portion and the density vs. frequency histogram B of the portion other than the pattern.

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 an image density vs. frequency curve, 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 portion CB in FIG. 5 is determined to be a portion other than the pattern, and the overlapping portion CA is determined to be 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. According to the present invention, lightness and hue parameters are obtained from a color image signal of the object 1, and these parameters are compared with a preset comparison reference signal to be binarized.
2 for image signals that overlap in the density vs. frequency graph
It is an object of the present invention to provide an image reading device that can be converted into a value.

[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-hue signal generation circuit 3 for converting the lightness signal 14 and the hue signal 15 into a lightness-hue signal 15,
And a comparison reference signal generator 4 that outputs a hue comparison reference signal 17. If the brightness signal 14 is greater than the brightness comparison reference signal 16, it outputs a high level, and if the hue signal 15 is greater than the hue comparison reference signal 17. A binarization determination circuit that outputs a high level and outputs a binary image signal;

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-hue 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 R signals 11 and G of color digital image signals.
A signal 12 and a B signal 13 are output, and the lightness-hue signal creation circuit 3 outputs the R signal 11, the G signal 12,
The signal 13 is converted into a lightness signal 14 and a hue signal 15.

[0010]

Next, the operation of the lightness-hue signal generation 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 brightness signal 14 and a hue signal 15
Is obtained by the following equation. Brightness signal 14 = max (R, G, B) (1) When hue signal 15 max (R, G, B) = R signal 11, [｛max (R, G, B) -signal B｝ / ｛max (R,
G, B) -min (R, G, B)｝]-[｛max
(R, G, B) -signal G / max (R, G, B)-
min (R, G, B)} + “1” When max (R, G, B) = G signal 12, [{max (R, G, B) −signal R} / {max (R,
G, B) -min (R, G, B)｝]-[｛max
(R, G, B) -Signal B｝ / ｛max (R, G, B)-
min (R, G, B)} + “3” When max (R, G, B) = B signal 13, [{max (R, G, B) −signal G} / {max (R,
G, B) -min (R, G, B)｝]-[｛max
(R, G, B) -signal R｝ / ｛max (R, G, B)-
min (R, G, B)｝] + “5” …………………
(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 lightness signal 14 and the hue signal 15, a lightness comparison reference signal value and a hue comparison reference signal value are set in advance in the comparison reference signal generator 4. The signal 16 and the hue comparison reference signal 17 are sent to the binarization determination circuit 5. In the binarization determination circuit 5,
A lightness signal 14 and a hue signal 15 are input from the lightness-hue signal creation circuit 3.

The binarization determination circuit 5 determines whether the brightness signal 14 is greater than the brightness comparison reference signal 16 or the hue signal 15 is greater than the hue comparison reference signal 17. Otherwise, it is low.

Next, the configuration of the brightness-hue signal generation circuit 3 will be described. 3A to 3C of the brightness-hue signal generation circuit 3 are comparators, 3D is a subtractor, 3E and 3F are selectors, 3G and 3H.
Is a subtractor, 3J and 3K are dividers, 3L is a subtractor, 3M is a selector, and 3N is an adder. The comparator 3A has an R signal 1
1 and the G signal 12 are input, and the comparator 3A sets the larger one of the R signal 11 and the G signal 12 to the signal 31 and sets the smaller one to the 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 and the B signal 13 are input to the comparator 3C.
The smaller one of the three signals is signal 33. Subtractor 3
The brightness signal 14 is input to a of D, and the signal 33 is input to b. The subtractor 3D outputs the result of ab as a signal 34.

The selector 3E has R signal 11, G signal 12,
The B signal 13 and the brightness signal 14 are input, and the signal 35 is extracted. In this case, when the brightness signal 14 = R signal 11, the B signal 13 becomes the signal 35, when the brightness signal 14 = G signal 12, the R signal 11 becomes the signal 35, and when the brightness signal 14 = B signal 13, the G signal becomes The signal 12 becomes the signal 35.

The selector 3F includes an R signal 11, a G signal 1
2, the B signal 13 and the brightness signal 14 are input, and the signal 36
Is taken out. In this case, the brightness signal 14 = the R signal 11
, The G signal 12 becomes the signal 36, and the brightness signal 14 =
When the G signal 12, the B signal 13 becomes the signal 36, and when the brightness signal 14 = B signal 13, the R signal 11 becomes the signal 36.

The brightness signal 14 is input to a of the subtracter 3G, and the signal 35 is input to b. The subtractor 3G is ab
And outputs the result as a signal 37. The lightness signal 14 is input to a of the subtracter 3H, and the signal 36 is input to b. The subtractor 3H calculates ab and outputs the result as a signal 38.

A signal 37 is input to a of the divider 3J.
The signal 34 is input to b. The divider 3J calculates a / b and outputs a signal 39. The signal 38 is input to a of the divider 3K, and the signal 34 is input to b. The divider 3K calculates a / b and outputs the result as a signal 40. The signal 39 is input to a of the subtractor 3L, and the signal 40 is input to b.
Is entered. The subtractor 3L calculates a-b, and outputs the signal 41
Output as

The selector 3M includes an R signal 11, a G signal 1
2, the B signal 13 and the brightness signal 14 are input, and the signal 42
Is taken out. In this case, the brightness signal 14 = the R signal 11
In this case, "1" is output, when the brightness signal 14 = G signal 12, "3" is output, and when brightness signal 14 = B signal 13, "5" is output. The signal 41 is input to a of the adder 3N, and the signal 42 is input to b. The adder 3N is a +
b is calculated and output as the hue 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 the comparator 5A at a, and the brightness reference signal 16 is input to b. a>
The signal 51 goes high when b, and goes low when a ≦ b. The comparator 5B outputs the hue signal 15 to a
And the hue comparison reference signal 17 is input to b. When a> b, the signal 52 goes high, and a ≦ b
When it is low level. The signal 51 and the signal 52 are A
The binary image signal 18 is output through the ND gate 5C.

[0020]

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 selector 3E has "20" for a and "4" for b.
“0”, “30” is input to c, and “40” is input to s. At this time, since the brightness signal 14 = the G signal 12, the signal 35 = R
The signal 11 becomes "20". "20", b for "a" of the selector 3F
"40", "30" for c, and "40" for s. At this time, since the brightness signal 14 = the G signal 12, the signal 36 = the B signal 13 "30".

The subtractor 3G subtracts the brightness signal 14 “40” −the signal 35 “20” = the signal 37 “20”, and the subtractor 3H performs the brightness signal 14 “40” −the signal 36 “30” = the signal 38 ”. 1
Subtract "0". In the divider 3J, the signal 37 “20” ÷ the signal 34 “20” = the signal 39 “1” is divided, and the divider 3K
Then, the signal 38 “10” ÷ the signal 34 “20” = the signal 40 “0.
Divide 5 ”. The subtracter 3L subtracts the signal 39 “1” −the signal 40 “0.5” = the signal 41 “0.5”.

The selector 3M has "20" for "a" and "4" for "b".
“0”, “30” is input to c, and “40” is input to s. At this time, since the brightness signal 14 = the G signal 12, the signal 42 becomes "1". The adder 3N adds the signal 41 "0.5" + the signal 42 "1" = the hue signal 15 "1.5". As a result, the value of the R signal 11 is “20” and the value of the G signal 12 is “4”.
0 ”and the value of the B signal 13 is“ 30 ”.
Is "40" and the hue signal 15 is "1.5".

In the binarization determination circuit 5 shown in FIG.
4 is "40", the value of the hue signal 15 is "0.5", the value of the lightness comparison reference signal 16 is "30", and the value of the hue comparison reference signal is "0.4". a is "40",
Since "30" is input to b, the signal 51 goes high. “0.5” is input to a of the comparator 5B, and “0.4” is input to b, and the signal 52 becomes high level. AND gate 5
All the inputs of C become high level, and the binary image signal 18 becomes high level.

Next, the distribution of lightness and hue will be described with reference to FIG. 3 using a printed wiring board as an example. AA in FIG. 3 shows the distribution of the portion other than the pattern of the printed wiring board, and BB shows the distribution of the pattern portion. When the image distributed as shown in FIG. 3 is binarized, the binary image signal 18 is set to a high level when it is larger than the lightness comparison reference signal 16 and larger than the hue comparison reference signal 17, and otherwise. In some cases, by setting the level to a low level, the BB portion becomes a high level and the AA portion becomes a low level.

In FIG. 3, the minimum value of the lightness of the distribution AA other than the pattern is "10", the maximum value is "100", the minimum value of the hue is "0.5", and the maximum value is "3.5". The minimum value of the brightness of the distribution BB is “70”, and the maximum value is “150”.
Assuming that the hue minimum value is "2.5" and the hue maximum value is "4.5", the brightness comparison reference signal 16 is set to "60" and the hue comparison reference signal 17 is set to "2.0". In this case, AA
And BB do not overlap, so that binarization can be correctly performed.

[0029]

According to the present invention, a color image signal is extracted from an object, parameters of a lightness signal and a hue signal are obtained from the image signal, and these parameters are compared with a preset comparison reference signal. Since the binarization is performed, binarization can be performed with less binarization errors even for an image signal having an overlap in the density versus 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 lightness, saturation, and hue taking a printed wiring board as an example.

FIG. 4 is a graph of pixel density versus frequency of 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 determination circuit 5.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Object 2 Image input part 3 Lightness-hue 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 Hue signal 16 Lightness comparison reference signal 17 Hue 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)
, R signal (11), G signal (12), B signal (13) and brightness signal
(14) as input, outputs B signal (13) when brightness signal (14) = R signal (11), and outputs R signal (11) when brightness signal (14) = G signal (12). , A first selector (3E) that outputs a G signal (12) when the brightness signal (14) = B signal (13), an R signal (11),
The signal (12), the B signal (13) and the brightness signal (14) are input, and when the brightness signal (14) = R signal (11), the G signal (12) is output, and the brightness signal (14) = G signal. A second selector (3F) that outputs a B signal (13) when (12) and an R signal (11) when the brightness signal (14) = B signal (13); and a brightness signal (14) To first selector (3E)
And a third subtractor (3H) for subtracting the output of the second selector (3F) from the brightness signal (14).
A first divider (3J) for dividing the output of the second subtractor (3G) by the output of the first subtractor (3D), and the output of the third subtractor (3H) to the first A second divider (3) that divides by the output of the subtractor (3D)
K), a fourth subtractor (3L) for subtracting the output of the second divider (3K) from the output of the first divider (3J), an R signal (11), a G signal (12), B signal (13) and brightness signal (14) are input, and when brightness signal (14) = R signal (11), "1" is output and brightness signal is output.
When (14) = G signal (12), "3" is output, and brightness signal (14)
A third selector (3M) that outputs "5" when = B signal (13)
And an adder (3N) that adds the output of the fourth subtractor (3L) and the output of the third selector (3M) to generate a hue signal (15).
A brightness-hue signal generation circuit (3) for converting the R signal (11), the G signal (12), and the B signal (13) into a brightness signal (14) and a hue signal (15)
A comparison reference signal generator (4) that outputs a brightness comparison reference signal (16) and a hue comparison reference signal (17); and high when the brightness signal (14)> the brightness comparison reference signal (16). A fourth comparator (5A) that outputs a level and outputs a low level when the brightness signal (14) ≦ the brightness reference signal (16); and a hue signal (15)> a hue comparison reference signal (17). )), A fifth comparator (5B) that outputs a high level, and a low level when the hue signal (15) ≦ the comparison reference signal (17) of the hue, and a fourth comparator
AN having the output of (5A) and the output of the fifth comparator (5B) as inputs
An image reading device comprising a D gate (5C) and a binary decision circuit (5) for outputting a binary image signal (18).