JPH08191413A - Back light correction device - Google Patents

Abstract

PURPOSE: To automate the back light correction in which a sufficient correction effect is obtained by discriminating a follow light or a back light so as to control an image pickup signal level of a CCD. CONSTITUTION: An integration circuit 10 integrates image pickup signals from a solid-state image pickup element 3 to average the signals, a dark level generating arithmetic circuit 12 generates a reference value changing with the average value, circuits from a comparator circuit 14 up to an arithmetic circuit 17 compare the reference value with the image pickup signal to detect a dark area of a picked-up image. The comparator circuit 19 discriminates the condition of follow light or back light based on the average value and a ratio of the dark area to the entire area. The stop value of an iris 2 is controlled based on the result of discrimination or a charge sweepout pulse of the solid-state image pickup element 3 is controlled by a CCD iris circuit 21 to control a level of the image pickup signal obtained by the solid-state image pickup element 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight compensation device, and is particularly suitable for a video camera.

[0002]

2. Description of the Related Art When taking a picture with a camera or a video camera, for example, when a back light of a bright light source such as the sun is present in the background of a person, a phenomenon occurs in which the person's face appears black. For example, in a video camera, in order to prevent such a phenomenon at the time of backlighting, the iris and the gain of an AGC (automatic gain control) amplifier are controlled so that the image pickup signal maintains a predetermined level. Has been done. FIG. 3 shows an example of a backlight correction device that is mounted on the video camera and corrects the backlight.

In the structure of FIG. 3, light from a desired subject is condensed on the light receiving surface of a solid-state image sensor (CCD) 54 through a lens 53 and an iris 52. As a result, an image of the subject is formed on the light receiving surface of the solid-state image sensor 54. The solid-state image sensor 54
Is a color filter having a complementary color system provided on the light receiving surface. An output signal obtained from each pixel of the solid-state image sensor 54 is output at a raster scanning timing via the sample hold circuit 55. The output signal Ss of the sample hold circuit 55 is sent to an AGC (auto gain control) amplifier 57 and applied to a detection circuit 56.

The level of the detection output from the detection circuit 56 is proportional to the amount of incident light on the solid-state image pickup device 54, and the detection output is applied to the comparison circuit 58. The comparison circuit 58 is supplied with either the reference voltage Vref1 or Vref2 selected by the switch SW1 as a comparison voltage. The reference voltage Vre
f1 is a standard (for forward light) reference voltage, and the reference voltage Vref2 is a backlight reference voltage.

That is, in a normal state (during forward light), the standard reference voltage Vref1 is selected by the switch SW1 and supplied to the comparison circuit 58. At this normal time, the comparison circuit 58 compares the detection output from the detection circuit 56 with the reference voltage Vref1, and the diaphragm amount of the iris 52 is controlled according to the comparison result. As a result, in the normal state, the amount of incident light on the solid-state image sensor 54 is suppressed to a predetermined value or less, and the image pickup signal Ss output from the sample hold circuit 55 is controlled to be a predetermined signal level or less.

On the other hand, at the time of backlight compensation, it is necessary to open the diaphragm amount of the iris 52 larger than in standard time (in normal light). Therefore, the switch SW1 is switched to change the reference voltage Vref2.
Is supplied to the comparison circuit 58. That is, at the time of the backlight, the comparison circuit 58 compares the detection output from the detection circuit 56 with the reference voltage Vref2, and the diaphragm amount of the iris 52 is controlled according to the comparison result. As a result, at the time of the backlight, the iris 52
I try to open it up.

The output signal Ss of the sample-hold circuit 55 is amplified by the AGC amplifier 57 and output from the terminal 62 to the subsequent stage configuration, and the detection circuit 6 is also provided.
It is detected by 0. The detection output of the detection circuit 60 is sent to one input terminal of the comparison circuit 61. The reference voltage V is applied to the other input terminal of the comparison circuit 61.
ref3 is supplied, and therefore the comparison circuit 61 compares the detection output with the reference voltage Vref3. The AGC amplifier 57 includes the comparison circuit 6
The gain is controlled according to the comparison result of 1.

According to this control loop, the gain of the AGC amplifier 57 is controlled to be large when the brightness of the subject is dark and the light amount is insufficient even when the iris 52 is fully opened. Will keep a predetermined level.

As described above, according to the backlight correction device, the iris 52 is controlled and the AGC is performed during the standard time (in the normal light).
By controlling the gain of the amplifier 57, the signal level of the image pickup signal output from the AGC amplifier 57 is maintained at a predetermined level. Further, during backlight compensation, the signal level is closer to the saturation level than the standard time by the control of the iris 52 and the gain control of the AGC amplifier 57, and the image pickup signal at a high level is output from the AGC amplifier 57. In the example of FIG. 3, the switch SW1 is operated to change the reference voltage to perform backlight compensation. However, the output signal level of the detection circuit (the iris control detection circuit 56) should be lowered during backlight compensation. However, the same backlight compensation is possible.

[0010]

In the conventional backlight correction device shown in FIG. 3, the user manually operates the switch SW1 to perform backlight correction.

However, it is complicated for the user to manually operate the switch SW1, and the user sometimes forgets to operate the switch SW1 although the backlight correction must be performed. Furthermore, as the application of the video camera to which the backlight compensation device is applied,
For example, in the case of a surveillance application, the video camera is installed in a predetermined place, and the user may not be able to operate the switch SW1 depending on the installation place. Further, even if the user can switch the switch SW1 by remote control with respect to the video camera for monitoring, the user does not always monitor the monitor screen. Therefore, the switch SW1 should be switched during backlighting. There are some things you can't do.

Therefore, it is desirable that the backlight compensation device be capable of automatically performing backlight compensation.

On the other hand, conventionally, there is a backlight correction device which can automatically perform backlight correction. In this automatic backlight compensation device, for example, it is determined whether there is backlight based on a comparison between the average value and the peak value of the brightness on the image pickup screen. Specifically, the reference power source is changed to perform the same backlight correction as described above.

However, the back light correction in the automatic type has a problem that the back light correction cannot be performed sufficiently as in the case of the manual type and the correction effect cannot be expected so much. There is also a backlight compensation device having both the automatic backlight compensation function and the manual backlight compensation function, but in this case as well, the same problem as described above occurs.

Therefore, the present invention has been made in view of such a situation, and an object thereof is to provide a backlight correction device capable of automatically performing backlight correction capable of obtaining a sufficient correction effect. .

[0016]

The backlight correction device of the present invention is proposed in order to achieve the above-mentioned object, and an averaging means for averaging the image pickup signals from the solid-state image pickup device, and the averaging means. Dark area detection means for detecting a dark area of the image pickup screen by comparing a reference value that changes according to the average value by the averaging means with the image pickup signal, and an average value by the averaging means and dark by the dark area detection means From the area, the ratio occupied by the area of the dark area in one screen is obtained, and a judgment means for judging whether the light is normal light or backlight based on the average value and the ratio occupied by the area of the dark area is provided. The image pickup signal level obtained from the solid-state image pickup device is controlled based on the determination result of the means.

When the average value is large and the ratio of the area of the dark region is large, the judging means judges that it is a backlight, and when the average value is large and the ratio of the area of the dark region is small, it is judged. Judged as normal light,
When the average value is small and the ratio of the area of the dark region is large, it is determined that the whole is dark by forward light, and when the average value is small and the ratio of the area of the dark region is small, it is determined that the light is normal.

The dark area detecting means detects a dark area by comparing the reference value with the image pickup signal for each divided screen obtained by dividing the image pickup screen at the horizontal scanning frequency, and detects the dark area. The dark area is added for one vertical scanning period to calculate the area of the dark area in one screen.

Further, the backlight correction device of the present invention is provided with an iris for limiting the amount of light incident on the solid-state image pickup device, and controls the aperture amount of the iris based on the judgment result of the judgment means, whereby the solid-state image sensor is controlled. The image pickup signal level obtained from the image pickup device is controlled. Alternatively, the solid-state imaging device includes a charge-sweep-pulse control unit that controls a charge-sweep pulse of the solid-state imaging device, and controls the charge-sweep pulse from the charge-sweep pulse control unit based on the determination result of the determination unit. It is also possible to control the image pickup signal level obtained from the element. Further, the backlight correction device of the present invention can include both the iris and the charge sweep-out pulse control means, and can control each of them based on the determination result of the determination means.

[0020]

According to the present invention, the reference value and the image pickup signal are compared to obtain the dark area in the image pickup screen. The reference value at this time is obtained by averaging the image pickup signals from the solid-state image pickup device. It is supposed to change according to the average value. Therefore, if the ratio of the area occupied by the dark region in the imaging screen is large even though the average value of the entire screen is large, it can be determined that the backlight is present.

[0021]

Embodiments of the present invention will now be described in detail with reference to the drawings.

First, FIG. 1 shows a schematic configuration of a backlight correction device of the present invention.

The backlight compensation device of this embodiment shown in FIG. 1 is installed in, for example, a video camera.

In the structure of FIG. 1, light from a desired subject is condensed on the light receiving surface of the solid-state image pickup device (CCD) 3 through the lens 1 and further through the iris 2. As a result, an image of the subject is formed on the light receiving surface of the solid-state image sensor 3. The solid-state image sensor 3 is provided with a complementary color filter on its light receiving surface.
The output signal obtained from each pixel of the solid-state image sensor 3 is
It is output for each pixel at the timing of raster scanning via the sample hold circuit 4. The output signal Ss ₄ of the sample hold circuit 4 is sent to an AGC (auto gain control) amplifier 5.

Here, in the apparatus of this embodiment, the iris drive circuit 22 for automatically driving and controlling the iris 2 when the user mounts the auto iris lens whose aperture amount is controlled by the iris 2 on the video camera.
CCD iris circuit 21 for controlling the charge sweep pulse of the solid-state image sensor 3 in order to generate an iris control signal IR to be sent to the camera or when a user mounts a fixed aperture manual lens on the video camera.
To generate an iris control signal IR to be sent to the output signal Ss _{4 of the} sample and hold circuit _4.
Is also sent to the following configuration.

That is, the output signal Ss ₄ (the input signal to the AGC amplifier 5) of the sample hold circuit 4 is first sent to the integration circuit 10 and the comparison circuit 14.

The integrating circuit 10 integrates the output signal Ss ₄ within the H rate, which is the horizontal scanning frequency of raster scanning. Here, when as a signal as shown by the solid line in the sample hold circuit 4 outputs signal Ss _4, for example, in FIG. 2 in (a), the integration circuit 10, the H rate or within one horizontal scanning period By integrating the output signal Ss ₄ of the above, the integrated signal i ₁₀ as shown in FIG. 2B is output.

The integrated signal i ₁₀ output from the integrating circuit 10 is sent to the A / D converter 11 at the H rate, which is the horizontal scanning frequency of raster scanning, and the A / D converter 11 outputs an 8-bit digital signal. Converted into a signal and converted to a microcomputer (hereafter referred to as the microcomputer 40)
Taken in.

The digital integrated signal di ₁₀ thus fetched in the microcomputer 40 is sent to the dark level creating arithmetic circuit 12. This dark level creation arithmetic circuit 1
In 2, the above-mentioned H rate integrated signal di ₁₀ is added for one vertical scanning period, that is, for one screen to obtain the average value of the entire screen,
Further, the level of 1 / n of this average value (n is an integer and is set in the arithmetic circuit 12) is used as a reference value for detecting a relatively dark area, and the reference value is used for horizontal scanning in raster scanning. It is sent to the D / A converter 13 at the H rate, which is the frequency. The output from this D / A converter 13 is
The comparison voltage Vco to the comparison circuit 14 is output from the microcomputer 40.

In the comparison circuit 14, the output signal Ss _{4 is} output at the H rate, which is the horizontal scanning frequency of raster scanning.
And the level of the comparison voltage Vco are compared. here,
When the output signal Ss ₄ supplied to the comparison circuit 14 is a signal as shown by the solid line in FIG. 2C, for example, the comparison circuit 14 outputs the H rate, that is, within one horizontal scanning period. deeds level comparison between the comparison voltage Vco indicated by the dotted line in the above output signal Ss ₄ and 2 in (c), if the output signal Ss ₄ is larger than the comparison voltage Vco "H" level ( "1") If it is smaller, the comparison output signal as shown in FIG. 2 (d), which becomes the "L" level ("0"), is output.

The comparison output signal from the comparison circuit 14 is
It is sent to the integrating circuit 15. The integration circuit 15 integrates the comparison output signal to output an integration signal i ₁₅ as shown in (e) of FIG.

What is important here is that both the comparison circuit 14 and the integration circuit 10 perform processing for each horizontal scanning period.

The integrated signal i ₁₅ from the integrating circuit ₁₅ is
A / at the above H rate, which is the horizontal scanning frequency of raster scanning
The A / D converter 16 is sent to the D converter 16.
Is converted into an 8-bit digital signal and taken into the microcomputer 40.

By the way, as described above, the microcomputer 40
The integrated signal i ₁₅ (i.e., the integrated comparison output signal) taken in is output signal Ss in the comparison circuit 14 comparing the output signal Ss ₄ and the comparison voltage Vco.
_{Since 4} corresponds to a portion larger than the comparison voltage Vco, as a result, a relatively non-dark area in the imaging screen is shown.

Therefore, the integrated signal i ₁₅ from the integrating circuit ₁₅ (in the example of FIG. 1, the digitized integrated signal di _15
15 ) is added for one vertical scanning period, that is, for one screen, it is possible to obtain the area of the relatively non-dark area on one screen.

If the comparison output signal of the comparison circuit 14 when the screen is originally uniformly bright is known,
By subtracting the area of the relatively non-dark area on the screen from the known comparison output signal, the area of the relatively dark area on the screen can be obtained.

In this embodiment, the integrated signal di ₁₅ (that is, the comparison circuit 14) obtained by converting the digital signal is obtained.
The signal obtained by integrating and digitally converting the comparison output signal of (1) is sent to the level calculation circuit 17, and the level calculation circuit 17 adds the integration signal di ₁₅ for one vertical scanning period, that is, for one screen, thereby making it relatively dark. The area of the non-dark region on one screen is obtained, and from the one screen consisting of the signals corresponding to the known comparison output signals of the comparison circuit 14 when the screen is uniformly bright, the one screen of the relatively non-dark region By subtracting the area above, the area on one screen of the relatively dark region is obtained.

The signal from the level calculation circuit 17 corresponding to the area on the screen of the relatively dark area is sent to the adder circuit 18. At this time, the adder circuit 18 is also supplied with the reference value (Vref1) from the standard reference value generation circuit 20 that generates the standard (forward light) reference value. Arithmetic circuit 17
A signal obtained by adding the reference value for the standard to the signal from is output. The signal from the adder circuit 18 is supplied to the comparison circuit 19
Sent to

The comparator circuit 19 is also supplied with the integrated signal di ₁₀ digitized by the A / D converter 11. The comparison circuit 19 also adds the integrated signal di ₁₀ for one vertical scanning period, that is, for one screen to obtain the average value of the entire screen. The average value of the entire screen can be supplied from the dark level creating arithmetic circuit 12. Therefore, in the comparison circuit 19, the signal from the adder circuit 18, that is, the signal corresponding to the area on one screen of the comparatively dark region where the reference value for the standard is added, and the average value of the entire screen are Is used to determine whether the light is backlight or forward light under the conditions described below.

1. When the average value is large and the area of the relatively dark area occupies a large amount on one screen, it is determined that the backlight is present.

2. When the average value is large and the ratio of the area of the relatively dark region on one screen is small, it is determined that the light is normal light.

3. When the average value is small and the ratio of the area of the relatively dark region is large on one screen, it is determined that the light is normal and dark.

4. When the average value is small and the area of the relatively dark region occupies a small amount on one screen, it is determined that the light is normal light.

It should be noted that the magnitude of the average value can be determined by the magnitude with respect to the predetermined threshold value for the average value, and the magnitude of the ratio of the area of the dark region can be determined by the magnitude with respect to the predetermined threshold value for the area. .

The comparison circuit (that is, the judging means) 19 judges whether the light is the backlight or the normal light under such conditions, and outputs the iris control signal IR according to the judgment result.

The iris control signal IR is sent to the switch S.
It is sent to the iris drive circuit 22 or the CCD iris circuit 21 via W2. The switch SW2 is switched to send the iris control signal IR to the iris drive circuit 22 when the iris 2 is automatically driven and controlled, and the iris control signal IR is sent to the CCD iris circuit when the fixed aperture is set (manually). It is switched to send to 21. That is, the switch SW2 is connected to the iris drive circuit 22 side when the user mounts the auto iris lens whose diaphragm amount is controlled by the iris 2 on the video camera, and the manual lens of the fixed diaphragm is mounted on the video camera by the user. CC when installed
It can be switched to the D iris circuit 21 side.

The output signal Ss ₄ of the sample-hold circuit 4 is output from the terminal 6 to the subsequent stage configuration as the output signal Ss ₅ amplified by the AGC amplifier 5 and detected by the detection circuit 30. The detection output of the detection circuit 30 is sent to one input terminal of the comparison circuit 31. Further, the reference voltage Vref3 is supplied to the other input terminal of the comparison circuit 31, and therefore,
In the comparison circuit 31, the detection output and the reference voltage Vre
A comparison with f3 is made. The gain of the AGC amplifier 5 is controlled according to the comparison result of the comparison circuit 31.

According to this control loop, even when the iris 2 is fully opened, the gain of the AGC amplifier 5 is controlled to be large when the brightness of the subject is dark and the amount of light is insufficient. Will keep a predetermined level.

As described above, according to the backlight compensation device, in the standard time, the aperture amount control of the iris 2 when the user attaches the auto iris lens whose aperture amount is controlled by the iris 2 to the video camera, or By controlling the charge sweep pulse of the solid-state image pickup device 3 or the gain of the AGC amplifier 5 when the user mounts a fixed aperture manual lens on the video camera,
The signal level of the image pickup signal output from the AGC amplifier 5 is maintained at a predetermined level. As a result, according to the backlight correction device, it is possible to totally correct the light amount from when the subject is bright to when it is entirely dark.

On the other hand, according to the backlight correction device, at the time of backlight correction, the signal level is closer to the saturation level than the standard time and is higher by controlling the aperture amount of the iris 2 or controlling the charge sweep pulse of the solid-state image sensor 3. The leveled imaging signal is output from the AGC amplifier 5. It should be noted that, in the case of the correction at the time of backlighting, the light quantity is not likely to be insufficient, and therefore the gain control of the AGC amplifier 5 is rarely performed as in the normal time, and the aperture amount control of the iris 2 or the solid-state image pickup is performed. Only the control of the charge sweep pulse of the device 3 is sufficient.

That is, according to the backlight correction device of the embodiment of the present invention, the input signal (output signal S
s ₄ ) is averaged by the microcomputer 40 on the one hand, and on the other hand, based on the output signal Ss _{4 for} each H rate obtained by dividing the imaging screen at the H rate of the horizontal scanning frequency of raster scanning and the above-mentioned averaged signal. And a signal (comparison voltage Vco) generated by detecting a relatively dark area is compared,
In this comparison, if the output signal Ss ₄ is higher than the comparison voltage Vco, it is set to "H" level ("1"), and if it is smaller, it is set to "L" level ("0"). By adding up one vertical scanning period, that is, one screen, by integrating the comparison output signal, the area on one screen in a relatively dark area can be obtained. By subtracting the area of the relatively dark area on the screen from the comparison output signal, the area of the relatively dark area on the screen can be obtained. Therefore, it is possible to determine whether the light is backlit or backlit based on the ratio of the area of the relatively dark region on one screen and the average value, and based on this determination, it is indicated whether the light is backlit or backlit. A reference signal (iris control signal IR) is formed, and this reference signal (iris control signal I
The iris 2 and the like are controlled based on R).

As described above, the backlight compensation device of this embodiment can automatically perform backlight compensation with which a sufficient compensation effect can be obtained, and the backlight compensation at this time must comply with the above conditions. Therefore, it is possible to favorably perform the operation regardless of the position of the subject.

[0053]

As is apparent from the above description, in the present invention, the image pickup screen is obtained by comparing the image pickup signal with the reference value which changes according to the average value obtained by averaging the image pickup signals from the solid-state image pickup device. The dark area of is detected, and the ratio of the area of the dark area in one screen is calculated from this average value and the dark area,
From these, it is determined whether the light is normal light or backlight, and based on the result of this judgment, the image pickup signal level obtained from the solid-state image pickup device is controlled. When it is large, it is judged to be backlight, when it is large and the ratio of the area of the dark region is small, it is judged to be normal, and when the average is small and the ratio of the area of the dark region is large, it is judged to be dark by normal light. However, when the average value is small and the ratio of the area occupied by the dark region is small, it is possible to automatically perform the backlight correction by which the sufficient correction effect can be obtained by determining the normal light.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a schematic configuration of a backlight compensation device of an embodiment of the present invention.

FIG. 2 is a diagram used for explaining integration, averaging, and detection of a relatively dark area of an image pickup signal at an H rate in the apparatus of this embodiment.

FIG. 3 is a block circuit diagram showing a schematic configuration of a conventional backlight compensation device.

[Explanation of symbols]

 2 Iris 3 Solid-state image sensor 4 Sample-and-hold circuit 5 AGC amplifier 10, 15 Integrator circuit 11, 16 A / D converter 12 Dark level creation arithmetic circuit 14, 19 Comparison circuit 17 Level arithmetic circuit 18 Adder circuit 20 Standard reference value generation circuit 21 CCD iris circuit 22 Iris drive circuit 40 Microcomputer SW2 switch

Claims (5)

[Claims] 1. A dark area of an image pickup screen by comparing an averaging means for averaging image pickup signals from a solid-state image pickup element with a reference value which changes according to an average value by the averaging means and the image pickup signal. The dark area detection means for detecting, the average value by the averaging means and the dark area by the dark area detection means to obtain the ratio of the area of the dark area in one screen, the average value and the area of the dark area The backlight correction device is characterized in that it has a judging means for judging whether the light is normal light or back light based on the ratio of the . 2. The judging means judges back light when the average value is large and the area ratio of the dark region is large, and when the average value is large and the area ratio of the dark region is small, the judgment means is in order. When the average value is small and the ratio of the area of the dark region is large, it is determined that the whole is dark by the forward light, and when the average value is small and the ratio of the area of the dark region is small, the forward light is determined. The backlight compensation device according to claim 1, wherein the backlight compensation device is determined. 3. The dark region detecting means detects a dark region by comparing the reference value with the image pickup signal for each divided screen obtained by dividing the image pickup screen at a horizontal scanning frequency, and detects the dark region for each divided screen. 3. The backlight correction device according to claim 1, wherein the dark area is added for one vertical scanning period to calculate the area of the dark area in one screen. 4. An image pickup signal level obtained from the solid-state image pickup device, comprising an iris for limiting the amount of light incident on the solid-state image pickup device, and controlling the diaphragm amount of the iris based on the judgment result of the judging means. The backlight correction device according to any one of claims 1 to 3, wherein the backlight compensation device is controlled. 5. A charge sweep pulse control means for controlling a charge sweep pulse of the solid-state imaging device is provided, and the charge sweep pulse from the charge sweep pulse control means is controlled based on the judgment result of the judging means. The backlight correction device according to any one of claims 1 to 3, which controls an image pickup signal level obtained from the solid-state image pickup device.