JPH031771A - Backlight correction device - Google Patents

Abstract

PURPOSE:To attain backlight correction obtaining sufficient correction effect automatically by comparing a ratio shared by a light area in plural split sections, discriminating a backlight depending on the comparison output and generating a reference signal. CONSTITUTION:An output signal from an AGC amplifier 6 is averaged by an integration circuit 9 on one hand and a comparatively light area is detected based on an output signal of the AGC amplifier 6 for each of plural split patterns formed by splitting pickup pattern with a pulse generating circuit 13 on the other hand and an area of the light area is obtained. Then the ratio of the light area between split patterns is compared by a comparator circuit 24 to discriminate rear light and reference signal 20-23 representing whether or not backlight exists are formed based on the discrimination. Based on the reference signal, the control means of an iris 3 and the AGC amplifier 6 are controlled. Then backlight correction obtaining sufficient correction effect is implemented automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a backlight correction device, and particularly to a backlight correction device suitable for a video camera.

[Summary of the invention]

In this invention, in the backlight correction device, an iris control means, an AGC amplifier to which an imaging signal is supplied, a means for averaging the output signal of the AGC amplifier, and an output signal of the AGC amplifier are used to control a relatively bright area. Detects and compares the ratio of the bright N range between multiple divided screens formed by dividing the imaging screen, determines whether it is front lighting or backlighting based on the comparison output, and generates a reference signal based on the determination output. By providing this means, it is possible to automatically perform backlight correction that provides a sufficient correction effect.

[Conventional technology]

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

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

The solid-state image sensor 54 has a complementary color filter on its light-receiving surface, and output signals obtained from each pixel are outputted via a sample-hold circuit 55 at the timing of rask scanning. The above output signal is transmitted to the detection circuit 56 and the AGC amplifier 57.
supplied to

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

The switch 59 selectively connects either the backlight correction reference power source Vref1 or the standard reference power source Vref2. Switching between the reference power sources VrefL and Vref2 is performed by manually operating the switch 59. Then, the connected reference power supply Vrefl or Vref2
is supplied to the comparison circuit 58. The above-mentioned detection circuit 56 and either the reference power source Vrefl or Vref2 are compared in a comparison circuit 58, and the iris 52 is controlled based on the comparison result.

As a result, the amount of light incident on the solid-state image sensor 54 is limited to a predetermined value or less during standard time, and the image pickup signal Ss output from the sample hold circuit 55 is suppressed to a predetermined signal level or less. Furthermore, during backlight correction, the iris 52 is opened wider than during standard time.

On the other hand, the above-described image signal Ss is amplified in the AGC amplifier 57 and then supplied to the detection circuit 60.

The output signals supplied from both the above-mentioned detection circuit 60 and reference power supply V ref3 are compared by a comparison circuit 61, and the gain of the AGC amplifier 57 is controlled based on the comparison result.

As a result, even if the iris 52 is fully opened, when the brightness of the subject is dark and the amount of light is insufficient, the AGC amplifier 5
The gain of 7 is controlled to be large.

In this way, standard time is controlled by the control of the iris 52 and the AG
By controlling the gain of the C amplifier 57, the AGC amplifier 57
The signal level of the image pickup signal Ss outputted from the camera is maintained at a predetermined level. Further, during backlight correction, by controlling the iris 52 and controlling the gain of the AGC amplifier 57, the AGC amplifier 57 outputs an imaging signal Ss whose signal level is closer to the saturation level than in the standard time and is set at a higher level.

[Problem to be solved by the invention]

Conventional general backlight correction was performed by a user manually operating a switch 59 to change the reference power source or to lower the level of the output signal of the detection circuit 56.

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

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

However, backlight correction in the automatic mode has the problem that sufficient backlight correction cannot be performed in the manual mode, and the correction effect cannot be expected to be very effective.

Therefore, an object of the present invention is to provide a backlight correction device that can automatically perform backlight correction that provides a sufficient correction effect.

[Means for Solving the Problems] The present invention provides a backlight correction device that compares an imaging signal with a reference value and controls an iris and an amplifier according to the magnitude relationship between the average level of the imaging signal and the reference value. In the
an iris control means, an AGC amplifier to which the imaging signal is supplied, a means for averaging the output signals of the AGC amplifier;
A relatively bright area is detected using the output signal of the GC amplifier, the proportion of the bright area is compared between multiple split screens formed by dividing the imaging screen, and front-lighting or back-lighting is determined based on the comparison output. and means for generating a reference signal based on the judgment output.

[Effect]

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

Then, the ratio of bright areas between the split screens is compared, and a determination is made as to whether the screen is frontlit or backlit. Based on this determination, a reference signal indicating whether it is front lighting or back lighting is generated.

Based on this reference signal, the iris control means and the AGC
The amplifier is controlled, so that backlight correction that provides 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 l is mainly composed of a lens 2 and an iris 3, and the lens 2 is used to capture a desired object onto the light receiving surface of a solid-state image sensor 4 such as a CCD through the iris 3. An image is formed.

The solid-state image sensor 4 has a complementary color filter on its light receiving surface. The output signal obtained from each pixel of the solid-state image sensor 4 is
The signal is supplied to the AGC amplifier 6 pixel by pixel via the sample hold circuit 5 at the timing of the rask scan.

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

In the comparison circuit 10, the digital signal O5 is converted into a reference digital signal DS supplied from the reference digital signal generation circuit 11.
The level is compared with ref. This reference digital signal DS
The level of ref is the desired level Lo shown in FIG.
(For example, the analog level is set to about twice the level of 80).

The signal S1 shown in FIG. 2 is set to high level when it exceeds the level of reference digital signal DSref, and set to low level when it does not exceed the level of reference digital signal DSref. 12
is supplied to the terminal 12a of the terminal 12a. Note that in FIG. 2, DMAχ is the maximum value of the dynamic range.

A vertical synchronizing signal S■ is supplied to a terminal 14 of the pulse generating circuit 13, and a horizontal synchronizing signal SH is supplied to a terminal 15 thereof. This pulse generating circuit 13 is designed to divide the imaging screen A shown in FIGS. 3 and 4 into a plurality of areas, for example, two areas AR1 and eight R2 as shown in FIGS. 3 and 4. , a switching control signal that controls switching of the switch circuit 12 is formed based on the vertical synchronization signal SV and the horizontal synchronization signal SH, and this switching control signal controls the switching of the switch circuit 12.
2. Therefore, in the switch circuit 12, the terminals 12a and 12b are connected in the area API, and the terminals 12a and 12b are connected in the area AR.
2, the terminals 12a and 12c are connected.

A high level signal 31 supplied from the comparison circuit 10 via the switch circuit 12 is applied to the integration circuit 1 for one vertical period.
6.17 respectively. In the integration circuit 16, the area A
The frequency of the high level signal 31 at PI is counted to obtain a count value C1. By obtaining this count value CI, the number of pixels, that is, the area, of the portion in the area ARI where the level of the digital signal O8 is twice or more than the reference digital signal DSref is determined.

Similarly, the integration circuit 17 counts the frequency of the high level signal S1 in the area AR2 and obtains a count value C2.
is obtained. By obtaining this count value C2, the number of pixels, that is, the area, of the portion in the area AR2 where the level of the digital signal O3 is twice or more than the reference digital signal DSref is determined. Each count value C1, C2 is supplied to a comparison circuit 24.

The comparison circuit 24 determines whether the light is in front light or back light based on the above-mentioned count values CI and C2.

As shown in FIG. 3, the subject B is located in the central area AR2.
If the composition is such that the sun 18 is placed behind the subject B in the outer region ARI, the subject B will clearly be backlit. In this case, the count value C1 in the area ARI is larger than the count value C2 in the area AR2 (CI
>C2). Therefore, when CI>C2, the comparison circuit 24 determines that there is backlight, and the control signal E1 for backlight correction is supplied to the switch circuits 25 and 29, respectively.

Furthermore, as shown in Fig. 4, subject B is placed in the central area ^R2, another subject M is placed behind subject B in the outer area API, and If the composition is such that there is no sun in the direction, it will clearly be frontlit. In this case, the count value C1 in the area ARI is
It is smaller than the count value C2 in the area AR2 (C2>
CI). Therefore, when C2>C1, the comparator circuit 24 determines that it is front light, and the standard time control signal E2 is supplied to the switch circuits 25 and 29, respectively.

In the reference signal generation circuit 20, an AGC amplifier reference signal DAref for backlight correction is generated.
1, an AGC amplifier reference signal DAref for standard time is formed. Further, the reference signal generation circuit 22 generates an iris reference signal Dlref for backlight correction, and the reference signal generation circuit 23 generates an iris reference signal Dlref for standard time.
Iref is formed.

The reference signal generation circuits 20 and 21 described above are connected to terminals 25b and 25c of the switch circuit 25, respectively, and the reference signal generation circuits 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
．． 29, terminals 25a, 25b, terminal 29
a and 29b are connected, and the AGC amplifier reference signal DAref for backlight correction and the iris reference signal Dlref for backlight correction are selected. As a result, the AGC amplifier reference signal DAref for backlight correction is generated by the subtraction circuit 2.
7 and is supplied to the iris reference signal Dl for backlight correction.
ref is supplied to subtraction circuit 26.

Further, the control signal E2 for standard time is transmitted to the switch circuit 25.
29, terminals 25a, 25C1 terminal 29a
, 29c are connected to the AGC amplifier reference signal DAref for standard time and the iris reference signal D for standard time.
lref is selected.

As a result, the standard time AGC amplifier reference signal DAre
f is supplied to a subtraction circuit 27, and an iris reference signal Dlref for standard time is supplied to a subtraction circuit 26.

On the other hand, the digital signal OS supplied from the A/D converter 8 is supplied to the integrating circuit 9 for one vertical period. In this integration circuit 9, the brightness level within the image capture screen A represented by the digital signal DS is integrated and averaged for each field, and the integrated value EO is calculated by the subtraction circuit 26.2.
7, respectively. The reset signal RS supplied to the terminal 28 is supplied to the integration circuits 16 and 17 and the integration circuit 9, and is reset every vertical period, that is, every field.

In the subtraction circuit 26, the integral value EO is subtracted from the iris reference signal Dlref for every l field, and this subtraction value is used to filter the digital low-pass filter 31 having a time constant for each field and the D/A converter 32. is supplied to the iris 3 as a control signal SIR.

In the subtraction circuit 27, the integral values EO and AG are calculated for each field.
Subtraction with the C amplifier reference signal DAref is performed, and the subtracted value is supplied to the AGC amplifier 6 as a control signal SAG via the digital low-pass filter 33 and the D/A converter 34.

Iris 3 is controlled by the above-mentioned control signal SIR. As a result, during standard time, the amount of light incident on the solid-state image sensor 4 is limited to a predetermined value or less, and the image pickup signal Ss output from the sample hold circuit 5 is suppressed to a predetermined signal level or less.

Further, in the AGC amplifier 6, gain adjustment is performed using the above-mentioned control signal SAG. As a result, standard time is
Even if the iris 3 is fully opened, when the brightness of the subject is dark and the amount of light is insufficient, the gain of the AGC amplifier 6 is controlled to be large.

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

Furthermore, during backlight correction, the iris 3 is opened wider than during 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 and higher than the standard time is set.
is output from the AGC amplifier 6.

As a result, backlight correction with sufficient correction effect can be automatically performed.

FIG. 5 shows a modification of this embodiment.

In this modification, the imaging screen A is divided into four areas ARI to AR.
Divide into 4, count values 01 to C for each area ARI to AR4
Iris 3 and AG
This is intended to control the C amplifier 6.

In this case, the integration circuit has four areas AI? 1~AR4
In addition, the switch circuit 12 must be able to sequentially switch and connect four terminals corresponding to the four integrating circuits. And count values C1 to C
Addition circuits and the like for adding 4 are required respectively. Further, a multiplication circuit and a coefficient may be provided in consideration of the case where it becomes necessary to weight the count values 01 to C4 of each area.

On the other hand, in response to this, a switch circuit that can sequentially switch and connect four terminals is arranged on the A/D converter 8 side of the integrating circuit 9.
For weighting, it is necessary to arrange an adder circuit on the 7 side for weighting, which consists of the multiplier circuit, coefficients, and adder circuit as described above.

Other configurations and operations are the same as those of the above-described embodiments, and therefore redundant explanations will be omitted.

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

〔Effect of the invention〕

According to the backlight correction device according to the present invention, there is an advantage that backlight correction with sufficient correction effect can be automatically performed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing level changes of an imaging signal, and FIGS.
5 is an explanatory diagram showing a modified example, and FIG. 6 is a block diagram showing a conventional backlight correction device. DLref near iris reference signal, DAref:A
GC amplifier standard reference signal engineer

Claims (1)

[Claims] A backlight correction device that compares an imaging signal with a reference value and controls an iris and an amplifier according to the magnitude relationship between the average level of the imaging signal and the reference value, comprising: a control means, an AGC amplifier to which an imaging signal is supplied, a means for averaging the output signal of the AGC amplifier, and a means for detecting a relatively bright area using the output signal of the AGC amplifier and dividing the imaging screen. The apparatus is characterized by comprising means for comparing the percentage occupied by the bright area between a plurality of divided screens, determining front lighting or backlighting based on the comparison output, and generating a reference signal based on the determination output. Backlight correction device.