JPH026473B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a color video camera equipped with white balance adjustment means.

[Prior art]

Color video cameras are provided with white balance adjustment means to prevent deterioration of color reproducibility due to changes in color temperature of light source light.

The white balance adjustment means used in color video cameras can be roughly divided into two types: a manual method and a semi-automatic method.

The manual white balance adjustment means uses an adjustment knob to control the gain of a variable gain amplification circuit for white balance adjustment built into the camera body, and each time the color temperature of the light source changes, The user can take an image of a white subject, capture light equivalent to the light source, and adjust it with the adjustment knob to achieve white balance.

In addition, the semi-automatic white balance adjustment means includes a variable gain amplification circuit for white balance adjustment within the camera body, a removable white filter in front of the image sensor, and a one-button switch for white balance adjustment. By pressing , a white filter is inserted in front of the image sensor, and the gain of the white balance adjustment variable gain amplification circuit is controlled. When pressed, the white balance is automatically adjusted.

As a recent trend, semi-automatic white balance adjustment means are becoming mainstream as emphasis is placed on ease of operation of color video cameras.

FIG. 1 is a block diagram showing an example of a conventional color video camera equipped with such a white balance adjustment means, in which 1 is an optical lens system, 2 is a white filter, 3 is an image sensor, and 4 is a white balance adjustment switch. , 5, 6 and 7 are amplifier circuits, 8 and 9 are variable gain amplifier circuits, 10 is a signal processing circuit, 11 and 12 are detection circuits, 13 is an encoder, 14 is an output terminal, 15
is a subject, and 16 is a light source.

To explain the operation of this prior art, when the white balance adjustment switch 4 is not operated, the white filter 2 is located away from the front of the image sensor 3 as shown by the dotted line, and the light source light from the light source 16 is reflected by the subject 15. and enters the image sensor 3 through the optical lens system 1. Therefore, the image sensor 3
5, a red signal (hereinafter referred to as R signal),
A green signal (hereinafter referred to as G signal) and a blue signal (hereinafter referred to as B signal) are generated.

The R and B signals are amplified by amplifier circuits 5 and 7, respectively.
Signal processing circuit 1 through variable gain amplifier circuits 8 and 9
0, and the G signal is amplified by the amplifier circuit 6 and supplied to the signal processing circuit 10. The signal processing circuit 10 has a matrix circuit, and has R, B, S
The signals include a luminance signal (hereinafter referred to as Y signal) 17, a color difference signal R-Y signal 18, and B-Y signal 19.
occurs. These signals are supplied to an encoder 13 and a color video signal is obtained at an output terminal 14.

On the other hand, when the white balance adjustment switch 4 is pressed, the white filter 2 is
As shown by the solid line, the optical lens system 1 and the image sensor 3
, and the detection circuits 11 and 12 are put into operation.

Therefore, white light equivalent to the light source light is incident on the image sensor 3, and the R-Y signal 1 for the white light is input to the image sensor 3.
8 is detected by the detection circuit 11, and the BY signal 19 is detected by the detection circuit 12. By the way, in the signal processing circuit 10, the Y signal 17 is generated in the relationship of Y=1/3 (R+G+B), and when the white balance is maintained, the levels of the R, G, and B signals are equal. Therefore, when the white balance is maintained, both the RY signal 18 and the BY signal 19 are zero, and the output signals of the detection circuits 11 and 12 are zero.

However, when the white balance is not maintained,
From the detection circuits 11 and 12, R-Y signals 18,
Output signals corresponding to the level of the B-Y signal 19 are obtained, and these output signals are supplied as control signals to the variable gain amplifier circuits 8 and 9.
9, the gain is controlled so that the RY signal 18 and the BY signal 19 are zero.

When the white balance adjustment is completed and the white balance adjustment switch 4 is released, the white filter 2 moves to the position shown by the dotted line, the detection circuits 11 and 12 become inactive, and the variable gain amplifier circuits 8 and 9 is held at the controlled gain above.

In this way, the semi-automatic white balance adjustment means can automatically adjust the white balance simply by pressing the white balance adjustment switch, so it is more effective than the manual white balance adjustment means. It is very easy to operate.

However, the semi-automatic white balance adjustment means is no different from the manual white balance adjustment means in that it is left to the user to determine whether there is a change in the color temperature of the light source. In general, color temperature is a vague concept for users, and they often forget to adjust the white balance, and even under the same light source, color temperature varies slightly depending on the type of subject. It is virtually impossible for even non-general users to adjust the white balance in accordance with such subtle changes in color temperature. Therefore, in the past, it was not possible to fully utilize the white balance means, and the operation was sometimes troublesome.

Furthermore, color video cameras are used together with video tape recorders, and since it is common for the video tape recorder to record images while the color video camera is capturing images, recording must be temporarily stopped each time the white balance is adjusted, or If you do not stop recording, a white image will be recorded,
This may result in missed imaging opportunities.

As described above, although the conventional white balance means has been made easier through semi-automation, it has had various practical problems.

[Purpose of the invention]

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned prior art,
White balance adjustment is performed independently of the imaging operation,
To provide a color video camera that does not require any manual operation for white balance adjustment.

A further object of the present invention is to provide a color video camera in which the color temperature of light source light is accurately detected and the accuracy of white balance adjustment is improved.

[Summary of the invention]

In order to achieve this object, the present invention detects a red light component and a blue light component from light within the visibility region using two sensors, and calculates the color temperature of the light source light from the level ratio of the output signals of the sensors. The present invention is characterized in that a color temperature signal representing the color temperature is obtained, and the gains of the variable gain amplifier circuits for the R and B signals are controlled based on the color temperature signal.

Furthermore, the present invention is characterized in that the output signals of the respective sensors are logarithmically compressed with different time constants to compensate for differences in response characteristics between the sensors.

[Example of the present invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of a color video camera according to the present invention, in which 20 and 21 are optical filters, 22 and 23 are sensors, 24 is a color temperature signal generation circuit, 25 is a control signal generation circuit, 26
is a process encoder, and parts corresponding to those in FIG. 1 are given the same reference numerals, and some explanations will be omitted.

In FIG. 2, the optical filter 20 is an infrared cut filter, which limits the spectral sensitivity characteristics of the image sensor to the visual sensitivity range of about 400 to 700 nm, making it possible to obtain good color reproducibility. . The optical filter 21 also has the same light transmittance as the optical filter 20, and removes incident light with a wavelength of 700 nm or more, such as an infrared cut filter or a heat ray absorption filter.

The sensor 22 is a light receiving element such as a photodiode that is sensitive to red light, and the sensor 23 is sensitive to blue light. Since the optical filter 21 is provided in front of the sensors 22 and 23, the sensors 22 and 23
Similar to the light received by the image sensor 3, the light received by the image sensor 3 is within the visibility range, and the spectral sensitivity characteristics of the sensors 22 and 23 are limited to the visibility range.

The color temperature signal generation circuit 24 divides the output signals of the sensors 22 and 23 to generate a signal 27 representing the ratio thereof.
occurs. The output signal of the sensor 22 is a signal representing the intensity of the received red light, and the output signal of the sensor 23 is a signal representing the intensity of the received blue light, and the color temperature of the light source light is determined by the red light component and the blue light. The output signal 27 of the color temperature signal generation circuit 24 is a signal representing the color temperature of the light source light. This color temperature signal 27 is supplied to a control signal generation circuit 25, and control signals 28 and 28 for controlling the gains of variable gain amplifier circuits 8 and 9,
29 is generated. These gains are controlled by control signals 28 and 29 so that white balance is always maintained.

Note that the process encoder 26 includes a circuit corresponding to the signal processing circuit 10 and encoder 13 in FIG.
A Y signal is formed, encoded, and a color video signal is output to the output terminal 14.

Next, the operation of this embodiment will be explained.

In FIG. 2, light from a subject 15 passes through an optical lens system 1, and an infrared cut filter 20 cuts off an infrared component to become light within the visibility range, and the light is incident on an image pickup device 3. Therefore, the image sensor 3
images the subject 15 through light within the visibility range and generates R, G, and B signals. The R, G, and B signals are amplified by amplifier circuits 5, 6, and 7, respectively, and the R and B signals are supplied to the process encoder 26 through variable gain amplifier circuits 8 and 9, respectively, and a color video signal is obtained at the output terminal 14. It will be done.

Meanwhile, at the same time, the light source light from the light source 16 is turned into light within the visibility range by the optical filter 21 and is irradiated onto the sensors 22, 23.
3 generates output signals of levels corresponding to the red light and blue light of the irradiated lights, respectively. These output signals are supplied to the color temperature signal generation circuit 24 to obtain a color temperature signal 27 representing the color temperature of the light source, and this color temperature signal 27 is supplied to the control signal generation circuit 2.
5 to generate control signals 28 and 29. The control signal 28 controls the gain of the variable gain amplifier circuit 8 in accordance with the color temperature of the light source light, and the control signal 29 similarly controls the gain of the variable gain amplifier circuit 9. Therefore, the variable gain amplifier circuits 8 and 9 have a gain corresponding to the color temperature of the light source light, and the reproduced image based on the color video signal obtained at the output terminal 14 is white-balanced.

As described above, in this embodiment, the color temperature of the light source light is constantly monitored and the white balance is adjusted, and there is no need for manual judgment of color temperature changes or any manual operation for white balance adjustment. First, white balance adjustment is performed reliably and good color reproducibility is always obtained.

FIG. 3 is a block diagram showing another embodiment of the color video camera according to the present invention.
is a logarithmic compression circuit, 32 is a diode, 33, 34
35 is a capacitor, and 35 is a diode. Parts corresponding to those in FIG. 2 are given the same reference numerals, and some explanations will be omitted.

In FIG. 3, the output signal of the sensor 22 is logarithmically compressed by a logarithmic compression circuit 30, and the output signal of the sensor 23 is
The output signals are logarithmically compressed by a logarithmic compression circuit 31 and supplied to the color temperature signal generation circuit 24, respectively. The illuminance of the light source light varies by four orders of magnitude, from several tens of lx to several hundred thousand lx, and it is necessary to make the dynamic range of the sensors 22 and 23 the same for this illuminance range, and the logarithmic compression circuits 30 and 31 It was established for this purpose.

That is, when the sensors 22 and 23 are photodiodes, the photodiodes can obtain an output current without an external power source while being irradiated with light due to their self-bias function. The time constant until the output current reaches a steady state depends on the amount of irradiation light. By the way, photodiodes generally have higher sensitivity on the long wavelength side (red light side) and weaker sensitivity on the shorter wavelength side (blue light side), so the photodiodes 22 and 23 have a time constant for their output signals to reach a steady state. will be different, and an unstable transient period will occur in the color temperature signal 27. For this reason, at medium illuminance or above, the absolute value of the time constants of the photodiodes 22 and 23 is small, and the difference in these time constants is not a particular problem, but at low illuminance, the absolute value of the time constants is small. The time constant at which the color temperature signal obtained by the output signals of the photodiodes 22 and 23 reaches a steady state is determined by the time constant of the photodiode 23, which is sensitive to blue light, and the transient response time becomes longer and becomes unstable. actions will be taken.

The logarithmic compression circuit 30 includes a diode 32 and a capacitor 33, and the logarithmic compression circuit 31 includes a capacitor 34 and a diode 35. capacitor 3
3 reduces the time constant of the photodiode 22,
In addition, the capacitor 34 reduces the time constant of the photodiode 23, but the capacitance of each capacitance is made different, so that the time constant of the photodiode 23 is made smaller and the time constants of the photodiodes 22 and 23 are made equal. ing.

Furthermore, the diodes 32 and 35 are conductive when the output levels of the photodiodes 22 and 23 are above a certain value, respectively, and short-circuit the capacitors 33 and 34, respectively. The characteristics of the diodes 32 and 35 are set so that the diodes 32 and 35 become conductive when the illuminance is medium or higher.

With such a configuration, in this embodiment, when the color temperature of the light source light changes, the sensor 23 quickly responds to the change, no ripples occur during transients, and the transient response time of the color temperature signal 27 is extremely short, resulting in a change in the color temperature of the light source. Balance adjustment is always performed accurately by rapidly following changes in the color temperature of the light source.

〔Effect of the invention〕

As described above, according to the present invention, the color temperature of the light source light is constantly monitored and white balance adjustment is performed even during the imaging operation, so that there is no problem with the imaging operation, and there is no need to worry about the white balance adjustment. No manual operation is required, white balance adjustment is performed reliably, and good color reproducibility is always obtained.
It has been significantly improved in practical terms, and there is no unstable transient operation of white balance adjustment that can be detected by changes in color temperature, and the accuracy of white balance adjustment has been improved. We can provide color video cameras with different functions.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a conventional color video camera, FIG. 2 is a block diagram showing an embodiment of a color video camera according to the present invention, and FIG. 3 is a block diagram showing another embodiment of a color video camera according to the present invention. FIG. 3...Image sensor, 8, 9...Variable gain amplifier circuit, 20, 21...Optical filter, 22, 23...
...Sensor, 24...Color temperature signal generation circuit, 25...
...control signal generation circuit, 30, 31...logarithmic compression circuit.

Claims (1)

[Claims] 1. The first layer has light transmission characteristics in the visibility region on the front surface.
A color video camera in which a red signal and a blue signal from an image sensor provided with an optical filter are respectively supplied to a variable gain amplifier circuit, and white balance is adjusted by controlling the gain of the variable gain amplifier circuit. a second optical filter having light transmission characteristics in the visibility region; and one receiving the transmitted light of the second optical filter, one having spectral sensitivity characteristics for red light and the other having spectral sensitivity characteristics for blue light. a first logarithmic compression circuit to which the output signal of the first sensor is supplied; and a second logarithmic compression circuit to which the output signal of the second sensor is supplied. , a color temperature signal generation circuit that generates a color temperature signal by dividing the output signals of the first and second logarithmic compression circuits, and a control that generates a gain control signal for each of the variable gain amplifier circuits based on the color temperature signal. a signal generation circuit, the first and second logarithmic compression circuits have different time constants to make the response characteristics of the first and second sensors approximately equal, and constantly detect the color temperature of the light source light. A color video camera characterized by being configured such that white balance can be set at all times.