JPH0735703A - Image processing method - Google Patents

Abstract

PURPOSE:To obtain a defection signal, from which fluctuation in the irradiation and sensitivity is removed while leaving useful signal components, by employing a detection signal subjected to flaw check as a reference signal for shading correction. CONSTITUTION:A light flux 3 is projected from a light source 1 to a hot rolled steel plate 2 and the image at a projected part 4 is picked up by means of a one-dimensional CCD camera 5. Output signal from the camera 5 is converted through an A/D converter 6 and fed to a signal processor 7 for extracting a defect signal. Thus extracted signal at detective part is delivered to an image processor 8 for deciding the type and rank of defect, which are subsequently presented on a display 9. The processor 7 uses a detection signal subjected to flaw check as a reference signal for shading correction. Alternatively, a reference signal determined during the pause of transfer of steel plate 2 is employed for shading correction. This method realizes shading correction reflecting the surface of the steel plate 2 faithfully.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method for performing shading correction on a signal obtained by receiving reflected light reflected by the surface of a material to be inspected which is successively conveyed,
In detail, for example, an image suitable for use in a surface defect inspection device or the like that obtains a signal of the surface of a strip-shaped inspected material that moves at high speed such as a hot-rolled steel plate by a light receiving device and detects surface defects based on the signal Regarding processing method.

[0002]

2. Description of the Related Art Conventionally, shading correction processing has been widely performed in the field of image processing. The shading correction process is a process for correcting light irradiation unevenness, sensitivity unevenness of the image pickup device, and the like included in the signal obtained by receiving the reflected light from the inspection material.

Conventionally, a shading correction method that has been performed in image processing has a correction table, and the shading effect is affected by performing an operation between the data in the table and the data obtained from the material to be inspected. As one of the methods, the data obtained by calculating the moving average of the input signal is used as the correction table data, for example.
The table data is subtracted from the input signal, or the input signal is divided by the table data.
There is a method of performing shading correction by adding an offset amount to the output signal or multiplying the output signal by a constant.

As another method, a reference signal is obtained in advance from a predetermined reference material offline, the reference signal is used as table data, and the same operation as the above is performed with the input signal while online. It is also known how to do it.

[0005]

However, according to the conventional moving average type shading correction method, the signal is made uniform without considering the original shape of the signal obtained from the object to be inspected. Therefore, when a signal component having a gentle change has an important meaning, there is a possibility that the useful signal will be erased.

Further, the method using the above-mentioned reference signal cannot cope with changes with time in the intensity of the light source and the sensitivity of the light receiving element which occur online, and for example, an on-line apparatus for inspecting surface defects of the materials to be inspected successively conveyed. Then, it is difficult to replace the original reference signal by obtaining the reference signal off-line with the device in order to cope with the change over time. The present invention solves the above problems, and obtains a detection signal of a material to be inspected in which uneven illumination of light from a light source and uneven sensitivity of an image sensor are removed while leaving a useful signal component having a gentle change. It is an object of the present invention to provide an image processing method that can perform shading correction that can be performed even when the intensity of a light source and the sensitivity of a light receiving element are changed.

[0007]

The present invention for achieving the above object provides a surface of a material to be inspected, which is obtained by receiving reflected light reflected by the surface of the material to be inspected successively conveyed by a predetermined light receiving device. The present invention relates to an image processing method in which shading correction is sequentially performed on a detection signal obtained by detecting in a predetermined one-dimensional direction or two-dimensionally while the material to be inspected is conveyed online.

In the first image processing method of the present invention, a predetermined reference material is arranged in the visual field of the light-receiving device at a level difference from the material to be inspected that is successively conveyed, and one material to be inspected is After leaving the field of view, the reference light is received by the light receiving device to receive the reflected light reflected by the surface of the reference material before the next material to be inspected appears in the field of view, and the reference signal is obtained based on the reference signal. It is characterized in that the detection signal obtained after the signal is subjected to shading correction.

In the second image processing method of the present invention, the presence or absence of a flaw on the surface of the material to be inspected is determined based on the detection signal, and based on the detection signal determined to be free of flaws, It is characterized in that the detection signal obtained later than the detection signal is subjected to shading correction.

[0010]

According to the image processing method of the present invention, a detection signal determined to have no flaw is used as a reference signal, or a reference signal is obtained by aiming at a gap between conveyances of a material to be inspected and the reference signal is used. Since the detection signal is subjected to the shading correction, the shading correction is performed while the surface of the material to be inspected is extremely faithfully reflected, and therefore, for example, a defect having a significant meaning in a portion where the signal change is gentle. Can be extracted.

In the present invention, it goes without saying that the first and second image processing methods described above may be combined, and further, it may be combined with a conventionally known method. Shading correction is performed using the reference signal obtained off-line, shading correction is performed using the detection signal that is determined to have no flaws on the way, and the reference material that was placed in advance in the gap between the conveyances of the inspected materials. It is also possible to adopt a method of calibrating by obtaining a reference signal from.

[0012]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a surface defect inspection apparatus to which an embodiment of the present invention is applied, showing a state in which the surface of a hot-rolled steel sheet moving at high speed is inspected. The light flux 1 is emitted from the light source 1 to the hot-rolled steel sheet 2, and the irradiated portion 4 of the hot-rolled steel sheet 2 is subjected to one-dimensional CC.
The D camera 5 takes an image. The one-dimensional signal output from the one-dimensional CCD camera 5 is A / D converted at high speed by the high-speed A / D converter 6.
The signal is D-converted, and the signal is input to the defect extraction signal processing device 7, and the defect signal is extracted. Further, the signal of the defective portion extracted by the signal processing device for defect extraction 7 is transferred to the image processing device 8 for defect determination, the defect type and defect rank are determined, and the output result is sent to the display device 9 for display. To be done. Power supply to the light source is performed by the light source power source 10. At this time, the shading correction processing corresponding to the embodiment of the present invention is performed in the defect extraction signal processing device 7, and therefore the one-dimensional signal transferred to the defect discrimination image processing device 8 and the display device 9 is subjected to the shading correction calculation. The processed signal.

FIG. 2 is a schematic diagram of the defect extraction signal processing device 7. The digital signal converted by the high-speed A / D converter 6 is digitized so as to correspond to the element pitch of the one-dimensional CCD camera. Therefore, the number n of signals for one line of the digital input signal 11 is one-dimensional. It corresponds to the number of images of the CCD camera. This digital input signal 11
Is transmitted to the shading correction calculation module 14, and in the shading correction calculation module 14,
A calculation process is performed using the input signal f (x) from the camera and the reference signal r (x) in the reference signal storage memory 13. As the initial value of the reference signal r (x), the one obtained offline is used. The initial value of the reference signal obtained offline can be externally input via the external interface 12. The output signal subjected to the shading correction is transmitted to the defect extraction module 15, where the defect signal is extracted. The reference signal storage memory 13 is provided with a function for updating the reference signal so as to cope with a change with time of the light source intensity, and this updating is performed by selecting a function via an external interface (external I / F). By controlling the module 17, two types of update functions can be switched.

The first function is to use the original signal of the signal in which no defect is detected by the defect extraction module 15 as a reference signal during the defect detection of the hot-rolled steel sheet 2, and the signal passes through the defect extraction module 15. The determined signal is transmitted to the determination module 16, and the signal in which no defect is detected is transmitted from the determination module 16 to the reference signal storage memory 13 through the function selection module 17 to update the reference signal.

The second function is to place the hot-rolled steel sheet, which is the material to be inspected, on the hot run table 19 as a sample coil 20 at a defect detection position on the table on which the hot-rolled steel sheet 2 travels. The function is to obtain a reference signal from the sample coil 20 until the inspection of one hot rolled steel sheet 2 is completed and the next hot rolled steel sheet 2 flows. As the sample coil 20, the same one as the hot-rolled steel sheet 2 which is most commonly used is used. Further, in order to compensate for the focus shift of the camera lens due to the position difference from the hot-rolled steel plate 2 which is the material to be inspected, a camera lens 21 having a deep depth of focus is used. Further, since the signal from the sample coil 20 in the second function is fed back to the reference signal storage memory 13 through the same path as in the first function,
If the sample coil 20 has a defective portion, sampling is not performed. The sample coil 20 is regularly replaced so as to maintain a good surface condition. When the hot-rolled steel sheet 2 which is the material to be inspected is a material whose surface property is obviously different from that of the sample coil 20, the function selecting module 17 is accessed through the external I / F to use the first function. Good.

FIG. 4 is an example of the reference signal r (x) obtained by using the one-dimensional image pickup device, and FIG. 5 is under the same conditions as when the reference signal was obtained from the sample of the hot-rolled steel sheet 2 having surface defects. FIG. 6 shows the obtained detection signal of the defective portion, and FIG. 6 shows the output signal after the shading correction. Here, shading correction was performed by the following calculation.

The reference signal as shown in FIG. 4 is r (x), and the detection signal on the surface of the hot rolled steel sheet as shown in FIG. 5 is f.
(X) and the output signal after shading correction is o
Assuming that (x), the output signal after shading correction as shown in FIG. 6 is obtained by performing the calculation of o (x) = f (x) / r (x) (1).

If o (x) = kf (x) / r (x) -θ (2), the dynamic range of the output signal can be increased and the output signal level can be kept within the desired range. It is possible. k may be a constant, and θ may be determined so that the output signal o (x) falls within a range that matches the level of the detection signal f (x) or the reference signal r (x).

As shown in FIG. 6, it is possible to obtain an output signal in which shading correction has been performed neatly and a defective portion is properly displayed.

[0020]

As described above, according to the image processing method of the present invention, the signal of a portion having no defect is acquired as the reference signal under the same condition as in the actual inspection.
The state of the surface of the material to be inspected can be reflected in the detection signal,
A large dynamic range can be secured in the part where the signal changes.

Further, by sequentially replacing the reference signal with a new one, it is possible to deal with a change with time in the light source intensity due to deterioration of the light source, a change in the sensitivity of the detection element, and the like.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a surface defect inspection apparatus to which an embodiment of the present invention is applied.

FIG. 2 is a schematic diagram of a defect extraction signal processing device.

FIG. 3 is a diagram showing a state in which sample coils are arranged on a hot run table.

FIG. 4 is an example of a reference signal acquired offline using a one-dimensional imaging device.

FIG. 5 is a detection signal of a defective portion obtained under the same conditions as when a reference signal was acquired from a sample of hot-rolled steel sheet having a surface defect.

FIG. 6 is an output signal after shading correction.

[Explanation of symbols]

 1 Light Source 2 Hot Rolled Steel Plate 3 Luminous Flux 4 Irradiated Area 5 One-dimensional CCD Camera 6 A / D Converter 7 Defect Extraction Signal Processing Device 8 Defect Discrimination Image Processing Device 9 Display Device 10 Light Source Power Supply 13 Reference Signal Storage Memory 14 Shading correction calculation module 15 Defect extraction module 16 Judgment module 17 Function selection module 19 Hot run table 20 Sample coil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryoichi Tanaki 1 Kawasaki-cho, Chuo-ku, Chiba City Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Satoshi Maruyama 1 Kawasaki-cho, Chuo-ku, Chiba Kawasaki Steel Co., Ltd. Technical Research Headquarters (72) Inventor Susumu Moriya 1 Kawasaki-cho, Chuo-ku, Chiba City Kawasaki Steel Co., Ltd. Technical Research Headquarters

Claims (2)

[Claims] 1. The surface of the material to be inspected is detected in a predetermined one-dimensional direction or two-dimensionally, which is obtained by receiving a reflected light reflected by the surface of the material to be inspected, which is successively conveyed, by a predetermined light receiving device. In the image processing method for sequentially performing shading correction on the detected signal while the material to be inspected is conveyed online, a predetermined reference material having a step with the material to be inspected is sequentially conveyed in the visual field of the light receiving device. It is arranged by referring to the light receiving device for receiving the reflected light reflected by the surface of the reference material after one of the inspection materials is out of the visual field and before the next inspection material appears in the visual field. An image processing method, comprising: obtaining a signal, and performing shading correction on the detection signal obtained after the reference signal based on the signal. 2. The surface of the material to be inspected is detected in a predetermined one-dimensional direction or two-dimensionally, which is obtained by receiving a reflected light reflected by the surface of the material to be inspected, which is successively conveyed, by a predetermined light receiving device. In the image processing method, in which shading correction is sequentially performed on the detected signal obtained while the inspection material is being conveyed online, the presence or absence of a flaw on the inspection material surface is determined based on the detection signal, and it is determined that there is no flaw. An image processing method characterized by performing shading correction on the detection signal obtained after the detection signal based on the detected signal.