JPH0576836B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an imaging apparatus using an imaging device, particularly to a white balance method.

[Prior art]

Conventionally, there are two methods for white balance adjustment in this type of imaging device. Figures 1-A and 2-B show respective schematic circuit configuration block diagrams.

The method shown in Figure 1-A uses an image sensor to convert the optical information of the subject into electrical signals, and at this time, the signal output level of the three primary color signals red, green, and blue from the white subject image is the same. Gain controller 20, 3
This method is performed by performing feedback control on a gain of 0. In the figure, 10 is an imaging system, 40 is a process circuit, 50 is an encoder, 60 is a white balance circuit, and 5 is a clock system.

Another method shown in Figure 1-B is independent of the image sensor and has the same spectral characteristics as the image sensor, or
Alternatively, the control includes a colorimetric sensor 70 that detects the color temperature of an external light source, and controls the gain controllers 20 and 30 that control the levels of the three primary color signals output from the image sensor based on the output signal of the color temperature detector 80. This method generates a voltage to adjust white balance. In the figure, reference numeral 90 denotes the control voltage generation system, and other components that are the same (equivalent) to those in FIG. 1-A are designated by the same reference numerals. Note that R, B, and G are red, blue, and green output signals from the imaging system 10, respectively, and Y is an output luminance signal from the process circuit 40.

The above two methods each have advantages and disadvantages. In other words, in the first method (Figure 1-A), correct white balance adjustment can be performed if a white subject is imaged or if there is a portion corresponding to white, but the operability is extremely poor. There is a drawback. In other words, to ensure optimal white balance adjustment, it is necessary to image a white subject, which may result in loss of time or
Moreover, this operation is extremely troublesome for the photographer, and the biggest drawback of this method is that it is not suitable for electronic still cameras that take advantage of one-chance shooting.

The second method (Figure 1-B) is usually called automatic tracking white balance, and the advantage of this method is that the colorimetric sensor 7 is independent of the imaging system.
0, it is possible to adjust the white balance in a short time, and there is an advantage that the photographer does not need to perform a white balance operation.

However, the drawback is that the accuracy of white balance is lower than that of the first method, and for example, the white balance may shift when photographing a subject with high chroma. Now, let us consider a detection method using red and blue colorimetric diodes as the colorimetric sensor 70. For example, if the background of the subject is a blue sky or a sunset, the colorimetric sensor output for blue will be much larger than the colorimetric sensor output for red, so the light source color temperature will be lower than the actual color temperature. Since the green signal of the image sensor is determined to be high and the green signal of the image sensor is controlled to become small, the image pickup screen becomes reddish.
Similarly, in the latter case, the captured screen will have a bluish tint.

Furthermore, this second method has the following drawbacks. As shown in Figure 1-B, since the colorimetric sensor system, that is, the control voltage generation system 90, and the imaging signal system 10 are independent, considerable precision is required for adjustment of both systems and for temperature changes, etc. That's true. Incidentally, in the first method, since a feedback system is configured, such problems hardly occur.

A further problem with the second method is that the gain control circuits 20 and 30 are required to have linearity characteristics. The linearity of a normal gain control circuit is about 6 to 7 dB, even if the accuracy is considered somewhat low. However, when the color temperature of the light source changes from, for example, 2000K to 1000K, the gain control range for the red light is approximately
10dB is required. Therefore, when the difference is in the range of 3 to 4 dB, there is a problem in that the circuit needs to be complicated and corrected.

〔the purpose〕

The present invention has been made in view of the various problems described above, and it consists of configuring the output signal of a colorimetric sensor provided independently of the imaging system to perform white balance through the video signal system. Therefore, it is an attempt to eliminate the above-mentioned drawbacks.

〔Example〕

The present invention will be explained below based on the drawings. Second
The figure shows a circuit configuration block diagram of an imaging device illustrating the principle according to the present invention. In the figure, components that are the same (corresponding) to those in FIG. 1 of the prior art example described above are indicated by the same reference numerals, and redundant explanation will be omitted.

An imaging system 10 controlled or driven by the clock system 5 is composed of an optical system, an imaging device, and the like. The red R and blue B signals output from the imaging system 10 pass through gain controllers 20 and 30 whose signal amplitudes are controlled, respectively, and are led together with the green G signal to a process circuit 40 that performs video signal processing.
The output signal (luminance signal, color difference signal) of this process circuit 40 is converted into an NTSC signal by an encoder 50.

By the way, each gain controller 20, 30 is controlled by a control voltage selected from a system computer (hereinafter referred to as system computer) 120 by switch circuits 100A, 100B, respectively. The control voltage generation sources in this embodiment are an automatic tracking white balance system and a feedback white balance system. However, the control voltage generation source is not limited to this. For example, when using a strobe, a control voltage generation source that outputs a fixed value that matches the color temperature of the strobe may be selected depending on whether or not the strobe is used.

Next, the white balance system 60 will be explained. First, the automatic tracking system logarithmically amplifies the photocurrent from the R, B or R, G, B colorimetric sensor 70, and then, in the color temperature detector 80,
The color temperature of the light source is detected from the value of R/B or R/B, B/G, R/G, etc., and from this detection signal, the control voltage of the R signal and B signal at that color temperature is determined.
V' _R and V' _B are generated in a control voltage generation system 90. These control voltages V' _R and V' _B are applied to the switch 10.
It is guided to 0A and 100B and selected by the system controller 120.

The determination circuit 85 is a circuit that determines whether the color temperature detection system 80 is detecting accurate color temperature. When an object with high saturation is imaged, the B signal or R signal level becomes extremely high, so that the color temperature detection signals V' _R and V' _B become low level or high level. FIG. 3 is a block diagram of a color temperature detection/determination circuit, in which the above-mentioned state is determined by the low level detection comparator 85 and high level detection comparator 85H shown in the figure, and the results are sent to the system controller 120 (FIG. 2). send. As a result, if the automatic tracking system determines that the color temperature is not accurate, the gain controllers 20 and 30
By 00A and 100B, the control voltages _V'R and _V'B are switched to feedback system _V''R and _V''B . Therefore, in this case, the color signal obtained from the imaging system 10 is used to perform white balance.

Color signals R, G, and B from the imaging system 10 are input to a process circuit 40 via gain controllers 20 and 30. The R, G, and B signals of the process output are applied to control voltages V″ _R ,
V″ _B is output, and this voltage controls the gain controllers 20 and 30. Therefore, if a white subject is imaged during this time, white balance adjustment can be performed correctly. 60, gain controllers 20 and 30, and process circuit 40 constitute white balance control means.

FIG. 4 shows a block diagram of the internal circuit configuration of the white balance circuit 60. Here, only the V″ _B system is shown. This drawing will be briefly explained. Among the output signals of the process circuit 40, in order to detect only the signals R, G, and B corresponding to a white object, the peak hold 61, 62.The B and G peak hold signals are then passed to the next stage comparator 63, up/down counter 64, and DA converter 6.
5, it is converted into a DC signal corresponding to the output difference between signals B and G to control the gain controller 30. This operation is performed until the peak hold signal levels of signals R and B become approximately the same.

Accurate white balance has been achieved in the above manner, but if the peak hold systems 61 and 62 have long time constants, they are unsuitable for a one-shot electronic still camera. Therefore, when using it as an electronic camera, it is necessary to switch to a short time constant, and it is necessary to fix the control voltage of the gain controller while recording the video signal in the recording system. this is,
A plurality of time constant circuits may be provided in the peak hold circuits 61 and 62, and the DA converter 65 and the like may be controlled by the system controller 120.

Furthermore, when used as a video camera, by switching the time constant to a longer value, sudden color changes can be prevented.

FIG. 5 shows a circuit configuration block diagram of an embodiment of the present invention, and the same (corresponding) configurations as in FIG. 2 are designated by the same reference numerals.

In this embodiment, the output signal r of the colorimetric sensor 70,
By processing signals g and b through a video signal system, the white balance adjustment operation is performed quickly and accurately. That is, the signals r, g, and b from the colorimetric sensor 70 are subjected to blanking processing in the blanking processing circuit 130 to match the synchronization timing of the imaging system 10 and to match the levels. Then, only during white balance, the signal from the colorimetric sensor 70 is transferred to the switch circuit 1.
40 or the like to the white balance control means, the above-mentioned feedback type white balance operation is performed. When the white balance operation is completed, the switch circuit 140 is switched to the imaging signal system by the system controller 120 and the lock system 5.

FIG. 6 is a diagram showing a first embodiment of the configuration of the blanking processing circuit 130, in which 131 is a logarithmic compression amplifier, 132 is a mixer, 133 and 134 are transistors, 135 is an inverter, 136 is an amplifier,
137 is a level adjustment circuit.

Although the figure shows only the output processing circuit system of the R sensor that detects red color, the output processing circuit system of the B sensor that detects blue color or the output processing circuit system of G sensor that detects green color is also similar. It can be configured as follows.

The output of the colorimetric sensor 70 is sent to the logarithmic compression amplifier 131.
The signal is compressed non-linearly and kept within a predetermined signal level range. Next, it is mixed with the signal V _ps from the level adjustment circuit in mixer 132 and input to the base of transistor 133 . A signal corresponding to this base input is led to an amplifier 136 and amplified.

The level adjustment circuit 137 changes the signal level V _ps applied to the mixer 132 according to the average value of each color signal from the colorimetric sensor 70 . Specifically, when the level of the average value becomes high, the signal level V _ps is decreased, thereby adjusting the level so that the output level of the mixer 132 falls within a predetermined signal level range.

A composite blanking signal from the clock system 5 is input to the inverter 135, and
Transistor 134 is turned on at a timing synchronized with the horizontal and vertical scanning of 0, and the collector of transistor 133 is grounded. Therefore, the output level of the amplifier 136 during the horizontal blanking period becomes zero level, forming a black level period.

Here, this black level period corresponds to the clamp timing in the subsequent process circuit 40 and the like.

In this way, the output of each colorimetric sensor is outputted to the blanking processing circuit 130 to form a black level period at a predetermined timing.
etc., and undergoes white balance control in the same way as the video signal from the imaging system 10.

At this time, in the present invention, as described above, a black level period is added to the output of each colorimetric sensor, so a common white balance control means can be used for the signal from the imaging system, and the configuration can be simplified. Moreover, it is possible to perform correct white balance control.

In addition, since the level adjustment circuit 137 adjusts the output level of the colorimetric sensor to be within a substantially constant range according to the brightness of the subject, the same white balance control means as the signal from the imaging system is used. When using it, you can control the correct white balance with a simple configuration.

Next, FIG. 7 shows the blanking processing circuit 1 of FIG.
In the figure, 150 is an integrator, 141 is a reset circuit for forming a reset timing signal for the integrator 150, and 142 is an integrator 1.
A blanking circuit for adding blanking pulses to the output of clock system 5 outputs a composite blanking signal from clock system 5 to inverter 14.
It is input via 4. Reference numeral 143 is a black level clip circuit for making the period to which the blanking pulse is added to a black level potential.

Further, the reset circuit 141 resets the integrator 15 as the average value of the outputs of the colorimetric sensors for each color increases.
This is to shorten the 0 reset period, thereby controlling the output of the integrator 150 so that it falls approximately within a predetermined signal level range.

In this way, also in this embodiment, since the black level period corresponding to the clamp timing in the process circuit 40 etc. is added, it is possible to use the same white balance means as the imaging system.

〔effect〕

As described above using the embodiments, according to the present invention, the level ratio of a plurality of color signals in the output signal of the colorimetric sensor provided independently of the imaging system of the imaging device is set to a predetermined ratio. Since white balance control is performed, adjustment between the signal processing system and the colorimetric system is easy, and temperature characteristics and gain controller linearity are no longer a problem.

In addition, the colorimetric sensor system does not periodically perform charge accumulation and charge transfer like an imaging system, but can immediately obtain an optical signal as a photocurrent, which has the advantage of a good white balance response. can get.

[Brief explanation of the drawing]

1-A and 1-B are circuit configuration block diagrams of two conventional white balance adjustment methods, respectively. FIG. 2 is a circuit configuration block diagram of an imaging device showing the principle according to the present invention. The figure is a block diagram of the color temperature detection and determination circuit in Figure 2, Figure 4 is a block diagram of the internal circuit configuration of the white balance circuit in Figure 2, and Figure 5 is a block diagram of the circuit configuration of an embodiment of the present invention. , FIG. 6, and FIG. 7 are block diagrams of a first embodiment and a second embodiment of the configuration of the blanking processing circuit, respectively. 10... Imaging system, 20, 30... Gain controller, 60... White balance circuit, 70... Colorimetric sensor, 85... Judgment circuit, 90... Control voltage generation system, 100A, 100B, 140... Switch circuit, 130...Blanking processing circuit.

Claims (1)

[Scope of Claims] 1. Imaging means 10 for converting subject light into a plurality of color signals; and color signal gain adjustment means 20, 30 for adjusting the gains of the plurality of color signals obtained from the imaging means.
and a colorimetric means 70 that is provided separately from the imaging means and forms a plurality of color signals, and the color signal gain is adjusted while the output of the colorimetric means is supplied to the input side of the color signal gain adjuster. a first mode in which the white balance is controlled by feedback controlling the gain of the color signal gain adjustment means using the output of the image pickup means; An imaging device comprising: a control means 140 for switching between a second mode and a second mode supplied to an input side.