JP2874192B2 - Backlight correction device - Google Patents

Description

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

[Summary of the Invention]

According to the present invention, in a backlight correction device, an iris control unit, an AGC amplifier to which an imaging signal is supplied, a unit for averaging an output signal of the AGC amplifier, and a relatively bright region in an output signal of the AGC amplifier Means for detecting the ratio of a bright area among a plurality of divided screens obtained by dividing the imaging screen, determining whether the light is normal or backlit by a comparison output, and generating a reference signal based on the determination output. With this arrangement, the backlight correction for obtaining a sufficient correction effect can be automatically performed.

[Conventional technology]

FIG. 6 shows an example of a conventional backlight correction device. Conventionally, in this type of device, an imaging signal is maintained at a predetermined signal level by controlling the gain of an iris and an AGC amplifier.

In the configuration of FIG. 6, an image of a desired subject is formed on the light receiving surface of the solid-state imaging device 54 via the iris 52 by the lens 53.

The solid-state imaging device 54 has a complementary color filter on the light receiving surface, and an output signal obtained from each pixel is output via the sample and hold circuit 55 at the timing of raster scanning.
The above output signal is supplied to the detection circuit 56 and the AGC amplifier 57.

When an output signal Ss of the sample and hold circuit 55 (hereinafter, referred to as an imaging signal) Ss is supplied to the detection circuit 56, the imaging signal Ss
The amount of incident light of the solid-state imaging device 54 is detected based on the level of the solid-state image sensor 54, and an output signal corresponding to the amount of incident light is supplied to the comparison circuit 58.

In the switch 59, one of the backlight correction reference power supply Vref1 and the standard reference power supply Vref2 is selectively connected. Switching between the reference power supplies Vref1 and Vref2 is performed by manual operation of the switch 59. Then, the connected reference power supply Verf1 or Vref2 is supplied to the comparison circuit 58. The detection circuit 56 and one of the reference power supplies Vref1 and Vref2 are compared by a comparison circuit 58, and the iris 52 is controlled based on the comparison result.

As a result, in standard time, the amount of incident light on the solid-state imaging device 54 is limited to a predetermined value or less, and the imaging signal Ss output from the sample and hold circuit 55 is suppressed to a predetermined signal level or less. Also, at the time of backlight correction, the iris 52 is widely opened compared to the standard time.

On the other hand, the above-mentioned imaging signal Ss is
After being amplified, it is supplied to the detection circuit 60.

The output signals supplied from both the detection circuit 60 and the reference power supply Vref3 are compared by a comparison circuit 61, and the gain of the AGC amplifier 57 is controlled based on the comparison result.

Thus, even when the iris 52 is fully opened, the gain of the AGC amplifier 57 is controlled to be large when the brightness of the subject is low and the amount of light is insufficient.

Thus, in the standard time, the control of the iris 52 and the AGC
By controlling the gain of the amplifier 57, the signal level of the imaging signal Ss output from the AGC amplifier 57 is maintained at a predetermined level. Also, at the time of backlight correction, the control of the iris 52 and the control of the gain of the AGC amplifier 57 cause the signal level to be closer to the saturation level than the standard time, and the imaging signal Ss set to a higher level.
Output from the AGC amplifier 57.

[Problems to be solved by the invention]

The conventional general backlight correction is performed by changing the reference power supply or lowering the level of the output signal of the detection circuit 56 by manually operating the switch 59 by the user.

However, in the manual, it is desirable to be able to automatically perform backlight correction in consideration of the case where the user must operate the switch himself and forgets to operate the switch.

On the other hand, in the conventional automatic backlight correction, it is determined whether or not there is backlight based on a comparison between the average value and the peak value of the brightness on the imaging screen. If it is determined that there is backlight, the reference power source is changed, and the above-described backlight correction is performed.

However, backlight correction in the automatic mode cannot perform sufficient backlight correction as compared with the manual mode, and there is a problem that the correction effect cannot be expected much.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a backlight correction device capable of automatically performing backlight correction with a sufficient correction effect.

[Means for solving the problem]

According to the present invention, in a backlight correction device that compares an imaging signal with a reference value and controls an iris and an amplifier according to a magnitude relationship between an average level of the imaging signal and the reference value, an iris control unit includes: AGC amplifier to which an imaging signal is supplied, means for averaging the output signal of the AGC amplifier, and AGC
The output signal of the amplifier detects a relatively bright area, compares the ratio of the bright area among a plurality of divided screens obtained by dividing the imaging screen, and determines whether the light is normal or backlight by the comparison output. Means for generating a reference signal based on the output.

[Action]

The output signal of the AGC amplifier is, on the one hand, averaged. On the other hand, for each of a plurality of divided screens formed by dividing the imaging screen, based on the output signal of the AGC amplifier,
The bright area is detected, and the area of the bright area is obtained.

Then, the ratio of the occupied area of the bright area is compared between the divided screens, and a judgment of normal light or back light is made. Based on this determination, a reference signal indicating whether the light is normal or backlight is formed.

Based on this reference signal, the iris control means and the AGC
The amplifier and the amplifier are controlled, whereby the backlight correction with a sufficient correction effect can be automatically performed.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. In this embodiment, the present invention is applied to a video camera.

In the configuration shown in FIG. 1, the optical system 1 mainly includes a lens 2 and an iris 3.
An image of a desired subject is formed on the light receiving surface of the solid-state imaging device 4 such as a CCD via the.

The solid-state imaging device 4 has a complementary color filter on the light receiving surface. An output signal obtained from each pixel of the solid-state imaging device 4 is supplied to an AGC amplifier 6 for each pixel at a raster scanning timing via a sample and hold circuit 5.

The output signal Ss of the sample-and-hold circuit 5 (hereinafter, referred to as an image signal) is amplified by an AGC amplifier 6 and then output from a terminal 7 on the one hand, and by an A / D converter 8 on the other hand, for example, Each pixel is an 8-bit digital signal DS. This digital signal DS for each pixel
Are supplied to the integrating circuit 9 and the comparing circuit 10, respectively.

The level of the digital signal DS is compared with the level of the reference digital signal DSref supplied from the reference digital signal generation circuit 11 by the comparison circuit 10. The level of the reference digital signal DSref is set to about twice the desired level Lo (for example, a level of 80 in analog value) shown in FIG.

A signal S1 is set to a high level when the level of the imaging signal Ss shown in FIG. 2 exceeds the level of the reference digital signal DSref, and is set to a low level when the level does not exceed the level of the reference digital signal DSref. 12 terminals 12a
Supplied to In FIG. 2, DMAX is the maximum value of the dynamic range.

The vertical synchronizing signal SV is supplied to the terminal 14 of the pulse generating circuit 13, and the horizontal synchronizing signal SH is supplied to the terminal 15. In this pulse generation circuit 13, in order to divide the imaging screen A shown in FIG. 3 and FIG. 4 into a plurality of regions, for example, two regions AR1 and AR2 as shown in FIG. 3 and FIG. Switch circuit
A switching control signal for controlling the switching of 12 is formed based on the vertical synchronization signal SV and the horizontal synchronization signal SH, and the switching control signal is supplied to the switch circuit 12. Therefore,
In the switch circuit 12, the terminals 12a and 12b are connected in the area AR1, and the terminals 12a and 12c are connected in the area AR2.

The high-level signal S1 supplied from the comparison circuit 10 via the switch circuit 12 is used for one vertical cycle for the integration circuits 16, 17
Are counted respectively. In the integrating circuit 16, the frequency of the high-level signal S1 in the area AR1 is counted, and a count value C1 is obtained. By obtaining the count value C1, the level of the digital signal DS in the area AR1 is changed to the reference digital signal DSref.
The number of pixels of a portion that is at least twice as large, that is, the area is obtained.

Similarly, in the integrating circuit 17, the frequency of the high-level signal S1 in the area AR2 is counted, and a count value C2 is obtained. By obtaining the count value C2, the level of the digital signal DS in the area AR2 is changed to the reference digital signal DSre.
The number of pixels in a portion that is at least twice as large as f, that is, the area is obtained. The count values C1 and C2 are supplied to the comparison circuit 24.

The comparison circuit 24 determines whether the light is direct or backlight based on the count values C1 and C2 described above.

As shown in FIG. 3, the subject B is located in the central area AR2.
Is arranged, and in a composition in which the sun 18 is arranged behind the subject B in the outer area AR1, the light is clearly backlit. In this case, the count value C1 in the area AR1 is
Is larger than the count value C2 in [C1> C2]. Therefore,
If C1> C2, the comparison circuit 24 determines that the subject is backlit,
The backlight correction control signal E1 is supplied to the switch circuits 25 and 29, respectively.

Further, as shown in FIG. 4, the subject B is arranged in the central area AR2, another subject M is arranged behind the subject B in the outer area AR1, and the subject B, M If the composition does not have the sun 18, the light will be clear. In this case, the count value C1 in the area AR1 is smaller than the count value C2 in the area AR2 [C2> C1]. Therefore, C2
If> C1, the comparison circuit 24 determines that the light is direct light, and the control signal E2 for the standard time is supplied to the switch circuits 25 and 29, respectively.

The reference signal generating circuit 20 forms an AGC amplifier reference signal DAref for backlight correction, and the reference signal generating circuit 21 forms a standard time AGC amplifier reference signal DAref. The reference signal generating circuit 22 forms an iris reference signal DIref for backlight correction, and the reference signal generating circuit 23 forms an iris reference signal DIref for standard time.

The above-described reference signal generation circuits 20 and 21 are respectively switch circuits.
25 reference terminals 25b and 25c
22 and 23 are connected to terminals 29b and 29c of the switch circuit 29, respectively.

If the control signal E1 for backlight correction is output from the switch circuit 25,
When supplied to the terminal 29, the terminals 25a and 25b and the terminals 29a and 29b are connected respectively, and the AGC amplifier reference signal DAref for backlight correction
Then, the iris reference signal DIref for backlight correction is selected. As a result, the reference signal D for the AGC amplifier for backlight correction
Aref is supplied to a subtraction circuit 27, and an iris reference signal DIref for backlight correction is supplied to the subtraction circuit 26.

The control signal E2 for the standard time is output from the switch circuits 25 and 29.
, The terminals 25a and 25c and the terminals 29a and 29c are respectively connected to select the standard time AGC amplifier reference signal DAref and the standard time iris reference signal DIref. As a result, the reference signal DAref for the AGC amplifier for the standard time is
, And the standard time iris reference signal DIref is supplied to the subtraction circuit 26.

On the other hand, the digital signal D supplied from the A / D converter 8
S is supplied to the integration circuit 9 for one vertical cycle. In the integrating circuit 9, the brightness level in the image screen A represented by the digital signal DS is integrated and averaged for each field, and the integrated value EO is supplied to the subtracting circuits 26 and 27, respectively.
Supplied. The reset signal RS supplied to the terminal 28
Is supplied to the integrating circuits 16 and 17 and the integrating circuit 9 and each value is reset every vertical cycle, that is, every field.

The subtraction circuit 26 subtracts the integral value EO and the iris reference signal DIref for each field, and this subtraction value is
Through a digital low-pass filter 31 having a time constant in a field unit and a D / A converter 32, a control signal SIR
Is supplied to the iris 3.

In the subtraction circuit 27, the integral value EO and the AGC amplifier reference signal DAref are subtracted every field, and the subtracted value is used as the digital low-pass filter 33 and the D / A converter 34.
Is supplied to the AGC amplifier 6 as a control signal SAG.

The iris 3 is controlled by the above-described control signal SIR. Accordingly, in the standard time, the amount of incident light on the solid-state imaging device 4 is limited to a predetermined value or less, and the imaging signal Ss output from the sample hold circuit 5 is suppressed to a predetermined signal level or less.

In the AGC amplifier 6, the gain is adjusted by the control signal SAG. Thus, in the standard time, even if the iris 3 is fully opened, the gain of the AGC amplifier 6 is controlled to be large when the brightness of the subject is low and the amount of light is insufficient.

In this way, at the standard time, the imaging signal Ss output from the AGC amplifier 6 is maintained at a predetermined signal level.

Also, at the time of backlight correction, the iris 3 is widely opened compared to the standard time. Then, by controlling the iris 3 and controlling the gain of the AGC amplifier 6, the image signal Ss whose signal level is closer to the saturation level than the standard time and which has a higher level is obtained.
Output from the AGC amplifier 6.

This makes it possible to automatically perform backlight correction with a sufficient correction effect.

 FIG. 5 shows a modification of this embodiment.

In this modification, the imaging screen A is divided into four areas AR1 to AR4, count values C1 to C4 are obtained for each of the areas AR1 to AR4, and the direct light and the backlight are based on the magnitude relation of the count values C1 to C4. Is to control the iris 3 and the AGC amplifier 6.

In this case, four integrating circuits are required corresponding to the four areas AR1 to AR4, and the switch circuit 12 is required to be capable of sequentially switching and connecting four terminals corresponding to the four integrating circuits. Become. Then, an adder circuit or the like for adding the count values C1 to C4 is required. Further, a multiplying circuit and a coefficient may be provided in consideration of a case where it is necessary to perform weighting on the count values C1 to C4 of each area.

On the other hand, in response to this, a switch circuit capable of sequentially switching and connecting the four terminals is provided on the A / D converter 8 side of the integrating circuit 9, and the above-mentioned is provided on the subtracting circuits 26 and 27 side of the integrating circuit 9. It is necessary to provide a weighting and adding circuit including such a multiplying circuit, a coefficient, and an adding circuit.

Other configurations and operations are the same as those of the above-described embodiment, and a duplicate description will be omitted.

According to this embodiment, an example is shown in which backlight control is performed by controlling both the iris 2 and the AGC amplifier 6, but the present invention is not limited to this.
One of the AGC amplifiers 6 may be fixed and the other may be controlled.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to the backlight correction apparatus concerning this invention, there exists an effect that the backlight correction which can acquire sufficient correction effect can be performed automatically.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is an explanatory diagram showing a level change of an image pickup signal, and FIGS.
FIG. 5 is an explanatory view showing an area of an image pickup screen, FIG. 5 is an explanatory view showing a modification, and FIG. 6 is a block diagram showing a conventional backlight correction device. Description of main symbols in the drawings 3, 52: iris, 6, 57: AGC amplifier, 9: integrating circuit, 1
0, 24: comparison circuit, 16, 17: integration circuit, 26, 27: subtraction circuit,
Ss: imaging signal, DSref: reference digital signal, A: imaging screen, A
R1 to AR4: area, C1 to C2: count value, E O: integral value, SAG,
SIR, E1, E2: control signal, DIref: iris reference signal, D
Aref: Reference signal for AGC amplifier.

Claims (1)

(57) [Claims] An iris control apparatus comprising: an iris control device that compares an image signal with a reference value and controls an iris and an amplifier according to a magnitude relationship between the average level of the image signal and the reference value. Means, an AGC amplifier to which an imaging signal is supplied, means for averaging the output signal of the AGC amplifier, and a comparatively bright area detected by the output signal of the AGC amplifier to divide an imaging screen. Means for comparing the ratio of the bright area occupied among a plurality of divided screens, determining whether the light is normal or backlight based on the comparison output, and generating a reference signal based on the determination output. Backlight correction device.