JPS62159595A - Automatic white balance device - Google Patents

Abstract

PURPOSE:To reduce the possibility of an erroneous white balance correction by automatically adjusting the white balance by a standard color temperature signal when an illuminance is situated outside a prescribed range (proper illuminance) suitable for the adjustment of the white balance. CONSTITUTION:To the inversion input terminal of a comparator 21, a reference voltage VL corresponding to an excessively low illuminance is supplied and to the non-inversion input terminal of a comparator 22, a reference voltage VH corresponding to an excessively high illuminance is supplied. Accordingly, the comparator 21 outputs the signal of L level during the excessively low illuminance and the signal of H level at the time except the excessively low illuminance and the comparator 22 outputs the signal of L level during the excessively high illuminance and the signal of H level at the time except excessively high illuminance. The output signals of the comparators 21, 22 are supplied to an AND circuit 23 and the AND circuit 23 forms and outputs an illuminance discriminating signal of L level during the excessively high illuminance and during the excessively low illuminance and the illuminance discriminating signal of H level during a proper illuminance.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic white balance device, which automatically adjusts white balance by varying the degree of amplification for a plurality of primary color signals according to the color temperature detected by a sensor. This invention relates to automatic white balance devices for video cameras, etc.

BACKGROUND OF THE INVENTION FIG. 2 shows a block diagram of an example of a video camera using a conventional automatic white balance device. In the figure, light from a subject enters an image sensor 2 via an optical system 1. A signal obtained by photoelectric conversion by the image sensor 2 is supplied to a process circuit 3, where processing such as amplification, single-color demodulation, and gamma correction is performed to obtain primary color signals R, B and a luminance signal Y.

The primary color signals R and B are supplied via amplifiers 4 and 5, and the luminance signal is supplied directly to a video signal processing circuit 6, where matrix calculations and color encoding are performed, for example, in a standard color system such as the NTSC system. The video signal is outputted from the terminal 7 as a video signal.

As shown in FIG. 3, a sensor section 9 is provided on the front surface of the camera body 8 near the optical system 1. A diffusion plate 10 shown in FIG. 2 is disposed on the front surface of the sensor section 9.
0, the subject in front of the camera body 8 and the light surrounding it are integrated and incident on the color temperature sensors 11 and 12, respectively. The color temperature sensors 11 and 12 each have different spectral characteristics and are blue.

It is highly sensitive to red flames, and color temperature sensor 1
Each of the 1.12 output signals is supplied to a color temperature detection circuit 13, where a color temperature detection signal having a level corresponding to the color temperature is generated. This color temperature detection signal is supplied to the white balance correction control circuit 14, and the white balance correction control circuit 14 separates the level of the color temperature detection signal, that is, the level corresponding to the color temperature, for the primary color signal R and for the primary color signal B, respectively. A correction control signal is generated and supplied to each of the amplifiers 4 and 5. The amplifiers 4 and 5 vary their respective gains in accordance with the correction control signals supplied to them, such that, for example, when the color temperature is low, the gain of the primary color signal B is increased and the gain of the primary color signal R is decreased. As a result, the white balance of the standard color video signal output from the terminal 7 is achieved.

Problems to be Solved by the Invention Incidentally, as shown in FIG. 4, a photodiode is used as the color temperature sensor 11, 12, which outputs a signal at a level approximately proportional to illuminance, and the color temperature detection circuit is a logarithmic amplifier 13a. , 13b and a differential amplifier 13c, the output signal level of each color temperature sensor +j11°12 is
, B, a color temperature detection signal with a level of to(+(A/B)) is obtained.

However, the color temperature sensors 11 and 12 become saturated when the illuminance is too high, and when the illuminance is too low, the color temperature sensors 11 and 12 become saturated at signal levels A and B.
is too small, the logarithmic amplifier 13a.

13b cannot maintain the logarithmic relationship between the input level and the output level. Therefore, there is a problem in that incorrect white balance correction is performed when the illuminance is too high or too low.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an automatic white balance device that solves the above problems by using an illuminance discrimination circuit, a color temperature setting circuit, and a switch, or by using these circuits and a color temperature discrimination circuit. .

Means for Solving the Problems In the first invention, the color temperature of the environment in which the imaging device is placed is detected from the output signal of the sensor.

The illuminance determination circuit determines whether the ambient illuminance is within a predetermined range suitable for white balance adjustment based on the output signal of the sensor. The color temperature setting circuit sets and outputs a standard color temperature signal at a level corresponding to the standard color temperature. The switch selects the color temperature detection signal when the environmental illuminance is within a predetermined range based on the determination signal of the illuminance determination circuit, and selects the standard color temperature signal when it is outside the predetermined range. The amplification degree of each of the plurality of primary color signals of the imaging device is varied according to the output signal of this switch, and the white balance is automatically adjusted.

Further, in the second invention, it is determined in which of a plurality of color temperature ranges the color temperature of the environment is located based on the color temperature detection signal, and a color temperature discrimination signal is generated, and the determination signal of the illuminance discrimination circuit is used to generate a color temperature discrimination signal. A color temperature discrimination circuit is added that obtains a color temperature discrimination signal just before the illuminance goes out of a predetermined range, and a standard color temperature setting circuit selects the output color temperature of the color temperature discrimination circuit among the standard color temperature signals for each of multiple color temperature regions. A standard color temperature signal of a level corresponding to the discrimination signal is set and output.

In the first invention, when the illuminance falls outside a predetermined range (appropriate illuminance) suitable for adjusting the white balance, automatic adjustment of the white balance is performed using the standard color temperature signal, thereby eliminating the possibility of incorrect white balance correction. It becomes less.

Further, in the second invention, a standard color temperature signal close to the state immediately before the illuminance falls outside the predetermined range is obtained, and white balance correction when the illuminance falls outside the predetermined range is performed more appropriately.

Embodiment FIG. 1 shows a block system diagram of an embodiment of the essential parts of the apparatus of the present invention. In this figure, the same parts as in FIG. 2 are designated by the same reference numerals, and their explanations will be omitted. In FIG. 1, the output signal of the color temperature sensor 12 is supplied to the color temperature detection circuit 13, and is also supplied to the non-inverting input terminal of the comparator 21 and the inverting input terminal of the comparator 22 of the illuminance discrimination circuit 20.

The inverting input terminal of the comparator 21 is supplied with a reference voltage VL corresponding to insufficient illuminance, and the non-inverting input terminal of the comparator 22 is supplied with a reference voltage ■H corresponding to excessive illuminance. Therefore, the comparator 21 is L when the illuminance is low.
At other times, the comparator 22 outputs a signal at the H level, and outputs a signal at the L level when the illuminance is excessive, and at other times, the signal is at the H level. The output signals of the comparators 21 and 22 are supplied to the AND circuit 23.
generates and outputs an illuminance discrimination signal which is at L level when the illuminance is too high or when the illuminance is too low and is at H level when the illuminance is pressed.

The color temperature detection signal output from the color temperature detection circuit 13 is filtered by a low-pass filter 24 to remove unnecessary high frequency components and delayed, and then sent to terminal a of the switch 25 and comparators 27 and 28 of the color temperature discrimination circuit 26, respectively. is supplied to the non-inverting input terminal of The inverting input terminal of the comparator 27 has a fifth
Threshold voltages VT Hl between the low color temperature region and the medium color temperature region of the color temperature detection signal level shown on the horizontal axis of the figure are supplied, and the comparator 27 is at the L level when the color temperature detection signal level is in the low color temperature region. Then, a D-type flip-flop 29 generates an H-level color temperature discrimination signal in the middle and high color temperature regions.
Supplied to the data input terminal of

Further, the inverting input terminal of the comparator 28 is connected to the threshold voltage VTI- of the medium color temperature region and high color temperature region of the color temperature detection signal.
12 is supplied, and the comparator 28 generates a color temperature discrimination signal in which the color temperature detection signal level is low, the level is 1'' in the medium color temperature region, and the 1'' level is in the high color temperature region, and the signal is output to the D-type flip-flop 30. Supplied to the data input terminal of The output illuminance determination signal of the AND circuit 23 is inverted and supplied to the clock input terminal of each of the flip-flops 29 and 30, and each of the flip-flops 29 and 30 is supplied with the clock input terminal at the time when the output illuminance determination signal of the AND circuit 23 falls, that is. When the illuminance becomes too low or too high, the output color temperature determination signals of the comparators 27 and 28 are latched. Here, since the color temperature detection signal is delayed by the low-pass filter 24, the comparators 27 and 28 latch the color temperature discrimination signal at the appropriate illuminance immediately before the illuminance becomes too low or too high.

The color temperature discrimination signals output from each of the flip-flops 29 and 30 are supplied to the control input terminals of each of the switches 32 and 33 of the standard color temperature setting circuit 31.

The output voltage of the switch 33 is supplied to the terminal a of the switch 32, and the standard color temperature voltage V1 in the low color temperature range shown on the horizontal axis in FIG. When it is at H level, terminal a is selected, and when it is at L level, terminal A is selected.

Further, the terminal a of the switch 32 is supplied with the standard color temperature voltage ■3 in the high color temperature region, the standard color temperature voltage ■2 in the medium color temperature region is supplied to the terminal a, and the switch 33 is supplied with the control input. When is at H level, terminal a is selected, and when is at L level, terminal A is selected. As a result, the standard voltage VI in the low color temperature region, the standard voltage V2 in the medium color temperature region, and the standard voltage l1 in the high color temperature region! A standard color temperature signal at voltage V3 is taken out from switch 32 and supplied to a terminal of switch 25.

The output illuminance discrimination signal of the AND circuit 23 is supplied to the control input terminal of the switch 25, and the switch 25 selects terminal a when this control input is at H level, and selects terminal A when this control input is at L level. Therefore, the switch 25 extracts the color temperature detection signal supplied from the low-pass filter 24 when the illuminance is appropriate (as shown by the solid line ■ in FIG. A standard color temperature signal, which is the standard voltage of the area, is taken out and supplied from the terminal 34 to the white balance correction control circuit 14, which is the same as that shown in FIG.

As a result, when the illuminance is appropriate, white balance is automatically adjusted in the same manner as in the past. Further, even when the illuminance is too low or too high, the appropriate white balance that is closest to the previous color temperature is performed.

Note that when illuminating with a fluorescent lamp or the like, the output signal of the color temperature sensor 12 includes flicker, so a low-pass filter is provided to remove this flicker, and the output signal of the low-pass filter is sent to the comparators 21 and 22. Alternatively, the comparators 21 and 22 may be provided with hysteresis characteristics. In this case, the time constant of the low-pass filter for flicker removal is selected to be smaller than the time constant of the low-pass filter 24.

Note that the color temperature determination circuit 26 is not provided, and the standard color temperature setting circuit 31 directly connects the standard voltage v to the terminal of the switch 25.
2 may be supplied, and is not limited to the above embodiment. In this case as well, it is possible to reduce the possibility that erroneous white balance correction will be performed when the illuminance is too low or too high.

Effects of the Invention As mentioned above, the automatic white balance device, which is the first invention, has the following features:
Since it is equipped with an illuminance discrimination circuit, a color temperature setting circuit, and a switch, there is less risk of incorrect white balance correction being performed even if the illuminance is too high or low, and the white balance can be corrected appropriately. have.

Furthermore, since the automatic white balance device according to the second invention further includes a color temperature discrimination circuit, when the illuminance becomes too high or low, it is possible to perform the appropriate white balance correction closest to the previous color temperature. It has features such as:

[Brief explanation of drawings]

Fig. 1 is a block system diagram of an embodiment of the main part of the device of the present invention, Fig. 2 is a block system diagram of an example of a video camera using the conventional device, and Fig. 3 is a video camera to which the device of the present invention is applied. FIG. 4 is a circuit diagram of an example of a partial circuit of the apparatus shown in FIG. 2, and FIG. 5 is a diagram showing an example of the relationship between output signals of each part shown in FIG. 1. 11.12... Color temperature sensor, 13... Color temperature detection circuit, 14... White balance correction control circuit, 20...
Illuminance discrimination circuit, 24...Low pass filter, 25...Switch, 26...Color temperature discrimination circuit, 31...Standard color temperature setting circuit. Figure 3: Figure 4: EJ-G7Ll? f)0 He, Karebe)n

Claims (2)

[Claims] (1) Obtain a color temperature detection signal according to the color temperature of the environment in which the imaging device is placed from the output signals of multiple sensors with different spectral characteristics, and select the plurality of primary colors of the imaging device according to the color temperature detection signal. In an automatic white balance device that automatically adjusts white balance by varying the degree of amplification for each signal, it is determined from the output signal of the sensor whether the illuminance of the environment is within a predetermined range suitable for white balance adjustment. an illuminance determination circuit; a standard color temperature setting circuit that sets and outputs a standard color temperature signal at a level corresponding to the standard color temperature; and a determination signal from the illuminance determination circuit that determines the color temperature when the illuminance of the environment is within a predetermined range. and a switch that selects the detection signal and selects the standard color temperature signal when the signal is outside a predetermined range, and is configured to vary the amplification degree according to the output signal of the switch. white balance device. (2) A color temperature detection signal corresponding to the color temperature of the environment in which the imaging device is placed is obtained from the output signals of a plurality of sensors having different spectral characteristics, and a plurality of primary colors of the imaging device are detected according to the color temperature detection signal. In an automatic white balance device that automatically adjusts white balance by varying the degree of amplification for each signal, it is determined from the output signal of the sensor whether the illuminance of the environment is within a predetermined range suitable for white balance adjustment. An illuminance determination circuit determines which of a plurality of color temperature ranges the color temperature of the environment is in based on the color temperature detection signal to generate a color temperature determination signal, and determines whether the color temperature of the environment is within a plurality of color temperature ranges based on the determination signal of the illuminance determination circuit. a color temperature discrimination circuit that obtains a color temperature discrimination signal immediately before the illuminance falls outside a predetermined range; and a level corresponding to the output color temperature discrimination signal of the color temperature discrimination circuit among the standard color temperature signals of each of the plurality of color temperature regions. a standard color temperature setting circuit that sets and outputs a standard color temperature signal; and a determination signal from the illuminance determination circuit that selects the color temperature detection signal when the illuminance of the environment is within a predetermined range;
1. An automatic white balance device comprising: a switch for selecting the standard color temperature signal when the standard color temperature signal is outside a predetermined range; and configured to vary the degree of amplification in accordance with the output signal of the switch.