JPH05161048A - Automatic dimmer device - Google Patents

Abstract

PURPOSE:To optimize an exposure with respect to a picture input device at a high speed by calculating a proper shutter speed from plural reflection level signals obtained through a changed shutter speed. CONSTITUTION:A reflected luminous quantity detection section 7 detects a signal whose level is highest among image pickup signals P1 fed from a picture input device 3 as a reflecting level signal P6. A shutter speed calculation section 8 changes the shutter speed of the device 3 through a shutter speed control section 9 to obtain a proportional coefficient between plural obtained signals P6 and the shutter speed thereby calculating an optimum shutter speed based on the proportional coefficient and the desired signal P6. In this case, since a radiation quantity of the lighting means 2 having a slow response speed is constant, the exposure is optimized at a high speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic light control device suitable for application to an image processing apparatus such as an industrial microscope which requires adjustment of an exposure amount.

[0002]

2. Description of the Related Art In an image processing apparatus such as an industrial microscope for inspecting a semiconductor substrate, reflected light from an illuminated object to be measured forms an image on a light receiving surface of an image pickup device through an objective lens. To be done. Then, an enlarged image of the object to be measured is displayed on a monitor image receiver or the like using the image pickup signal output from the image pickup device, and defect detection or the like is performed by applying predetermined image processing to the image pickup signal. In this case, the reflectance of the illumination light varies depending on the measurement target, and the illuminance on the light-receiving surface of the image sensor changes depending on the magnification of the objective lens, etc. In order to carry out stable measurement with a small amount of light, a dimming mechanism for adjusting the exposure amount for the image pickup device is required.

FIG. 3 shows an image processing apparatus having a conventional dimming mechanism. In FIG. 3, reference numeral 1 denotes a microscope, and an object to be measured in the microscope 1 has an appropriate light quantity by an illumination system 2 having a lamp. It is illuminated by. Reference numeral 3 denotes an image input device including a camera using a two-dimensional charge-coupled image pickup device (CCD). Reflected light from the measurement object is received by the image pickup device of the image input device 3 via the objective lens of the microscope 1. An image is formed on the surface, and an image pickup signal P1 is output from the image input device 3. The image pickup signal P1 is supplied to the image processing unit 4 and the reflected light amount detection unit 5.

The image processing section 4 subjects the image pickup signal P1 to predetermined image processing and supplies defect information and the like obtained by this processing to a computer (not shown). In addition, the image pickup signal P
1 is also supplied to the reflected light amount detection unit 5, and the reflected light amount detection unit 5
In, the signal P4 corresponding to the level of the amount of reflected light from the measurement object is generated by, for example, averaging the image pickup signal P1, and this signal P4 is supplied to the illumination system light control unit 6.
The illumination system light control section 6 adjusts the illuminance of the illumination system 2 so that the signal P4 becomes a predetermined level. That is, conventionally, the amount of light (exposure amount) input to the image pickup device in the image input device 3 is controlled by changing the amount of light emitted from the illumination system 2.

[0005]

However, in the conventional image processing apparatus, since the responsiveness of the lamps constituting the illumination system 2 is poor, the image input apparatus 3 is immediately conditioned immediately after the irradiation light amount of the illumination system 2 is changed. It takes a very long time, for example, seconds, until the amount of reflected light from the measuring object entering the image pickup element becomes stable, resulting in a problem that the measuring time becomes long. The present invention has been made in view of the above circumstances, and an object thereof is to provide an automatic light control device capable of optimizing an exposure amount for an image input device at high speed.

[0006]

The automatic light control device according to the present invention, for example, as shown in FIG. 1, includes an illumination means (2) for illuminating an object to be measured, and a reflected light from the illuminated object to be measured. Image input means (3) having a shutter function for adjusting the shutter speed that is the integration time and obtaining image data of the object to be measured according to the shutter speed.
And a reflected light amount detection means (7) for generating a reflected level signal P6 corresponding to the amount of reflected light from the illuminated measurement object, and shutter speed control for controlling the shutter speed of the image input means (3). It has a means (9) and a shutter speed calculation means (8) for calculating an appropriate shutter speed from a plurality of reflection level signals P6 obtained by changing the shutter speed.

The image input means (3) obtains image data of the object to be measured by a charge storage type image pickup device (for example, a two-dimensional CCD) and changes the charge storage time of the charge storage type image pickup device. By doing so, the shutter function may be realized.

[0008]

According to the present invention, if the shutter speed of the image input means (3) is increased, the total amount of light incident on the image input means (3), that is, the exposure amount is decreased, and conversely, the shutter speed can be decreased. For example, the principle that the amount of exposure to the image input means (3) increases is used. That is, the present invention utilizes the fact that there is a proportional relationship between the shutter speed and the reflection level signal P6 corresponding to the exposure amount.

Therefore, even if the amount of light emitted from the illumination means (2) to the object to be measured is constant, the shutter speed of the image input means (3) is changed to detect the exposure amount to the image input means (3). Thus, the proportional coefficient between the shutter speed and the reflection level signal P6 can be obtained. Then, the optimum shutter speed is obtained from the proportional coefficient and the desired reflection level signal P6.
In this case, the irradiation light amount of the illumination means (2) having a slow response speed is constant, and the exposure amount is optimized at high speed.

When the image input means (3) realizes the shutter function by changing the charge storage time of the charge storage type image pickup device, it means that a so-called electronic shutter is used. In this case, the shutter mechanism is integrated with the image sensor and is very small, and the shutter speed can be changed for each scanning time of the image sensor, so that the exposure amount is optimized at a higher speed. ..

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an automatic light control device according to the present invention will be described below with reference to FIGS. In FIG. 1, parts corresponding to those of the image processing apparatus of FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted. FIG. 1 shows an image processing apparatus of this example. In FIG. 1, an object to be measured in a microscope 1 is illuminated with an appropriate amount of illumination light from an illumination system 2.
The illuminance by the illumination system 2 is constant. The reflected light from the measuring object is imaged on the light receiving surface of the image pickup device of the image input device 3 through the objective lens in the microscope 1. In this example, a two-dimensional CCD is used as an image sensor of the image input device 3. Further, the charge accumulation time for each scan of the two-dimensional CCD can be controlled externally as a shutter speed. That is, the image input device 3 has an electronic shutter function.

An image pickup signal P1 is output from the image input device 3, and the image pickup signal P1 is supplied to the image processing unit 4 and the reflected light amount detection unit 7.
Is supplied to. The reflected light amount detection unit 7 detects a signal having a highest level than the image pickup signal P1 as a reflection level signal P6, and supplies this reflection level signal P6 to the shutter speed calculation unit 8. The image pickup signal P1 has a saturation voltage Ec of 750.
It is a voltage signal of about mV, and the reflection level signal P6 is a similar voltage signal. The shutter speed calculator 8 supplies a signal P7 instructing the shutter speed to the shutter speed control circuit 9. The shutter speed control circuit 9 controls the two-dimensional C of the image input device 3 by the control signal P8.
The shutter speed of the CD is set to a value corresponding to the signal P7.

In this example, an example of the operation for optimizing the shutter speed will be described. In this case, the shutter speed calculation unit 8 first sets the shutter speed S of the image input device 3 to an arbitrary certain value Sa via the shutter speed control unit 9. Then, at this time, the level Ea of the reflection level signal P6 detected by the reflected light amount detector 7 is stored. Next, the shutter speed calculation unit 8 changes the shutter speed S of the image input device 3 to another certain value Sb, and then stores the level Eb of the reflection level signal P6 detected by the reflected light amount detection unit 7 again. .. If necessary, the shutter speed calculator 8 further changes the shutter speed S of the image input device 2 and stores the reflection level signal P6.

Thereafter, the shutter speed calculator 8 obtains the slope of the reflection level signal P6 with respect to the shutter speed S by linear approximation. Then, after the preset voltage level of the optimum reflection level signal P6 is applied to the approximate straight line to obtain the optimum shutter speed S, the shutter speed calculation unit 8 causes the shutter speed control unit 9 to operate the image input device. Optimize the shutter speed of the image sensor of No. 3. After that, the image processing unit 4 performs normal image processing using the image pickup signal P1 output from the image input device 3.

Next, a specific example of a method of calculating the optimum shutter speed S will be described with reference to FIG. The horizontal axis of FIG. 2 represents the shutter speed S of the image sensor of the image input device 3, and the vertical axis represents the reflection level signal P6. Since the reflection level signal P6 is the maximum value of the image pickup signal P1 whose saturation voltage is Ec, the saturation voltage of the reflection level signal P6 is also Ec. Therefore, in the saturation area SA where the shutter speed S exceeds the predetermined value Sc, the reflection level signal P6 has its saturation voltage Ec.
If the shutter speed S is equal to or less than the predetermined value Sc, the shutter speed S and the reflection level signal P6 are in a proportional relationship.

An analog output voltage obtained when the shutter speed S of the image pickup device of the image input device 3 is set to the first value Sa in a state where the object to be measured is illuminated by the illumination system 2 with an appropriate amount of light. The level of the reflection level signal P6 is set to the first level Ea. Next, the shutter speed S of the image sensor is set to the second value Sb, and the level of the reflection level signal P6 obtained at this shutter speed is set to the second level Eb. If both the first level Ea and the second level Eb are lower than the saturation voltage Ec, the coordinates (Sa, E
A straight line 10 passing through a) and the coordinates (Sb, Eb) is a straight line representing the proportional relationship between the shutter speed S and the reflection level signal P6. Further, the value Sc of the shutter speed S at the intersection of this straight line 10 and a straight line 11 parallel to the horizontal axis and having a value equal to the saturation voltage Ec is the maximum value of the shutter speed S in a proportional relationship.

On the other hand, the first level Ea and the second level Ea
When at least one of the levels Eb of the above reaches the saturation voltage Ec, the value of the shutter speed S is changed to the smaller side and the reflection level signal P6 is repeated until two signals whose values are smaller than the saturation voltage Ec are obtained. Is taken in. Therefore, the line 10 in FIG. 2 can be obtained by repeating the operation of setting the shutter speed S and fetching the reflection level signal P6 at least twice.

In this example, the optimum value of the shutter speed S is set to the shutter speed when the reflection level signal P6 becomes a value slightly smaller than the saturation voltage Ec. The shutter speed S set by this becomes a value slightly smaller than the proportional maximum value Sc. Since the reflection level signal P6 is the maximum value of the image pickup signal P1, the maximum value of the image pickup signal output from all the pixels of the image pickup device of the image input device 3 is smaller than the saturation voltage Ec. By setting in this way, it is possible to prevent the saturation of the output of all the pixels of the image sensor and to always obtain a good image signal P1 having a high SN ratio.

In this case, a two-dimensional CCD as an image pickup device
The time for one scan of is, for example, about 33 ms. Further, in this example, since the optimum shutter speed S can be determined by scanning two to three times, the time required for optimum light control is about 100 ms. On the other hand, since the conventional method for adjusting the illuminance of the illumination system requires time in seconds, it can be understood that the present example can perform automatic dimming at a very high speed. Further, generally, in a lamp used in the illumination system 2, the color temperature changes when the flowing current changes. On the other hand, in this example, since the light amount of the illumination system is constant, there is also an advantage that the color temperature of the illumination system does not change. Furthermore, CCD
In the electronic shutter operation, the accumulation time of the light quantity is shortened, the influence of dark current is less likely to occur, and the SN ratio is further advantageous.

In the above embodiment, the reflection level signal P6
Although the maximum value of the image pickup signal P1 is used as, the signal indicating the average value of the image pickup signal P1 may be used instead. Alternatively, for example, a signal obtained by averaging the image pickup signals P1 obtained from pixels in a predetermined area in the center of the image pickup device may be used. Further, although a two-dimensional CCD electronic shutter is used as a shutter mechanism in the image input device 3, a mechanical shutter may be used in addition to the electronic shutter to control the shutter speed. As described above, the present invention is not limited to the above-described embodiments, and various configurations can be taken without departing from the gist of the present invention.

[0021]

According to the present invention, an appropriate shutter speed is calculated by changing the shutter speed in the image input means to obtain a plurality of reflection level signals. Therefore, there is an advantage that the exposure amount for the image input means can be optimized at a very high speed. Also, since the light quantity of the illumination means does not change,
There is also an advantage that the color temperature of the illumination light does not change.

When the image input means changes the shutter speed by changing the charge storage time of the charge storage type image pickup device, the shape of the apparatus can be downsized and the exposure amount can be optimized. There is an advantage that the required time can be greatly reduced to about several times of scanning time of the image pickup device. Further, there is an advantage that the image pickup device is less likely to be affected by the dark current due to the shutter operation.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic light control device according to the present invention.

FIG. 2 is a diagram showing a relationship between a shutter speed S and a reflection level signal P6 in the embodiment.

FIG. 3 is a block diagram showing an image processing apparatus including a conventional light control mechanism.

[Explanation of symbols]

 1 microscope 2 illumination system 3 image input device 4 image processing unit 7 reflected light amount detection unit 8 shutter speed calculation unit 9 shutter speed control unit P1 imaging signal P6 reflection level signal

Claims (2)

[Claims] 1. An illumination means for illuminating an object to be measured, and a shutter function for adjusting a shutter speed which is a time for integrating reflected light from the illuminated object to be measured, and the measurement according to the shutter speed. Image input means for obtaining image data of the object, reflected light amount detection means for generating a reflection level signal corresponding to the amount of reflected light from the illuminated measurement object, and controlling the shutter speed of the image input means. An automatic light control device comprising: shutter speed control means; and shutter speed calculation means for calculating an appropriate shutter speed from a plurality of the reflection level signals obtained by changing the shutter speed. 2. The image input means realizes the shutter function by changing the charge storage time of the charge storage type image pickup device while obtaining the image data of the object to be measured by the charge storage type image pickup device. The automatic light control device according to claim 1, wherein: