JPH0695764B2 - Imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image pickup apparatus using an image pickup device, particularly to a white balance method.

[Prior art]

Conventionally, there are two types of white balance adjustment methods in this type of image pickup apparatus. 1-A and 2-B show schematic block diagrams of respective circuits.

In the system shown in FIG. 1-A, the optical information of the subject is converted into an electric signal by the image pickup device, and 3 from the white subject image at this time is converted.
This is a method in which the gains of the gain controllers 20 and 30 are feed-back controlled so that the primary color signal / red, green, and blue signal output levels are the same. 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 of FIG. 1-B is independent of the image sensor,
It has a spectral characteristic similar to that of the image sensor, or is equipped with a colorimetric sensor 70 for detecting the color temperature of an external light source, and controls the levels of the output three primary color signals of the image sensor from the output signal of the color temperature detector 80. In this method, a white balance adjustment is performed by generating a control voltage for controlling the gain controllers 20 and 30. In the figure, 90 is the control voltage generation system described above,
The same (corresponding) configurations as in FIG. In addition, R, B,
G is the red, blue, and green output signals from the imaging system 10, and Y is the output luminance signal from the process circuit 40.

Each of the above two methods has advantages and disadvantages.
That is, in the first method (FIG. 1-A), a white subject is imaged, or if there is a portion corresponding to white, correct white balance adjustment can be performed, but the operability is extremely poor. There is a drawback that. That is, in order to surely perform the optimum white balance adjustment, it is necessary to image a white subject, which may cause a loss time, or this operation is extremely troublesome for the photographer. Its biggest drawback is that it is not suitable for electronic still cameras that take advantage of one-chance.

The second method (FIG. 1-B) is usually called an auto-tracking white balance, and the advantage of this method is that the colorimetric sensor 70 is provided independently of the image pickup system. There is an advantage that the white balance can be adjusted in a short time and the photographer does not need to perform the white balance operation.

However, a drawback is that the white balance is less accurate than the first method, and that the white balance is deviated in an object with high saturation, for example. Now, let us consider a case of a detection method using red and blue colorimetric diodes for the colorimetric sensor 70. For example, when the background of the photographed subject is blue sky or the sunset, the output of the blue colorimetric sensor is considerably larger than the output of the red colorimetric sensor in the former case, so the light source color temperature is lower than it actually is. Is also determined to be high, and the blue signal of the image sensor is controlled to be small in the end, so that the photographic screen becomes reddish. Similarly, in the latter case, the shooting screen will be bluish.

Furthermore, the second method has the following drawbacks. As shown in FIG. 1-B, since the colorimetric sensor system, that is, the control voltage generation system 90 and the image pickup signal system 10 are independent, considerable accuracy is required for adjustment of both systems and temperature change. That is. By the way, in the first method, since the feedback system is constructed, such a problem hardly occurs.

A further problem in the second method is that the gain control circuit 2
The linearity characteristic is required for 0 and 30. The linearity of a normal gain control circuit is 6 to 7 dB even if the accuracy is a little low.
It is a degree. However, when the color temperature of the light source changes from 2,000 to 10,000K, the gain control range of the red signal needs to be about 10 dB. Therefore, the difference of 3 to 4 dB causes a problem that the circuit needs to be corrected by complicating it.

〔Purpose〕

The present invention has been made in view of the above various problems, and the gain control circuit can be switched by a plurality of means, and the colorimetric sensor output signal is feedback-controlled through an imaging signal system. By doing so, it is intended to eliminate the above-mentioned drawbacks.

〔Example〕

The present invention will be described below with reference to the drawings. FIG. 2 is a block diagram of the circuit configuration of the image pickup apparatus according to the embodiment of the present invention. In the figure, the same (corresponding) configurations as those of the above-mentioned conventional example shown in FIG.

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 of the output signal of the image pickup system 10 are led to the process circuit 40 which performs the video signal processing together with the green G signal through the gain controllers 20 and 30 whose signal amplitudes are controlled. An output signal (luminance signal, color difference signal) of the process circuit 40 is converted into an NTSC signal by an encoder 50.

By the way, each of the gain controllers 20 and 30 is controlled by the switch circuits 100A and 100B by selecting a control voltage from a system computer (hereinafter referred to as syscon) 120. The control voltage generation sources in this embodiment are an automatic tracking white balance system and a feed back type white balance system. However, the control voltage generation source is not limited to this. For example, when a strobe is used, 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 described. First, the automatic tracking system is an R, B or R, G, B colorimetric sensor.
Performs logarithmic amplification of photocurrent from 70, and color temperature detector
In 80, R / B or R / B, B / G, detects the color temperature of the light source than the value of such R / G, from the detection signal, the control voltage V _'R of the R signals and B signals in the color temperature , V ′ _B is generated in the control voltage generation system 90. The control voltage V _'R,
V _'B, the switches 1000A, is led to 100B, the system controller 12
Selected with 0.

The determination circuit 85 is a circuit that determines whether or not the color temperature detection system 80 detects an accurate color temperature. When a highly saturated subject is imaged, the B signal or R signal level becomes extremely large, 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 the color temperature detection / judgment circuit, in which the above-mentioned state is judged by the low level detection comparator 85L and the high level detection comparator 85H shown in FIG.
Send the results to (Fig.). As a result, if the automatic tracking system determines that the color temperature is not accurate, the gain controller 20, 30
The switches 100A and 100B switch the control voltages V _R and V _B to feed back system V ″ _R and V ″ _B. Therefore, in this case, white balance is performed using the color signals obtained from the image pickup system 10.

The color signals R, G, B from the imaging system 10 are input to the process circuit 40 via the gain controllers 20 and 30. The R, G, B signals of the process output are controlled by the control voltage V ″
_R , V ″ _B is output, and the gain controller 2
Control 0,30. Therefore, if a white subject is imaged during this time, the white balance adjustment can be performed correctly. Here, the white balance circuit 60, the gain controllers 20 and 30, and the 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 described. In order to detect only the signals R, G, B corresponding to a white object in the output signal of the process circuit 40, the peak hold 61, Then, the peak hold signals of B and G are sent to the signal B by the comparator 63, the up-down counter 64 and the DA converter 65 in the next stage.
The gain controller 30 is controlled by being converted into a DC signal corresponding to the output difference between G and G. This operation is performed until the peak hold signal levels of the signals R and B become almost the same.

With the above, an accurate white balance was obtained,
If the peak hold systems 61 and 62 have long time constants, they are not suitable for one-shot electronic still cameras. Therefore, when used as an electronic camera, it is necessary to switch to a short time constant and to fix the control voltage of the gain controller while recording the video signal in the recording system.
This can be achieved by providing the peak hold circuits 61 and 62 with a plurality of time constant circuits and controlling the DA converter 65 and the like by the syscon 120.

Furthermore, when it is used as a video camera, the color constant can be prevented from abruptly changing by switching the time constant to a longer one.

[Other Examples]

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

In this embodiment, the output signals r, g, b of the colorimetric sensor 70 are subjected to signal processing through a video signal system so that the white balance adjustment operation can be performed quickly and accurately. That is, the signals r, g, b of the colorimetric sensor 70 are subjected to blanking processing in the blanking processing circuit 130,
The level is adjusted at the same time as the synchronization timing of the imaging system 10. And only when white balance is measured
By guiding the signal of 70 to the white balance control means through the switch circuit 140 or the like, the above-described feed back type white balance operation is performed. When the white balance operation is completed, the switch circuit 140 is switched to the image pickup signal system by the syscon 120 and the clock 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, and 137 is a level adjusting circuit.

Although only the output processing circuit system of the R sensor for detecting red color is shown in the figure, the output processing circuit system of the B sensor for detecting blue color or the output processing circuit system of the G sensor for detecting green color is similar. It can be configured.

The output of each colorimetric sensor 70 is non-linearly compressed by the logarithmic compression amplifier 131 and suppressed within a predetermined signal level range.
Next, in the mixer 132, the signal Vos from the level adjustment circuit
Is mixed with and input to the base of the transistor 133. The signal corresponding to the pace input is guided to the amplifier 136 and amplified.

The level adjusting circuit 137 changes the signal level Vos applied to the mixer 132 according to the average value of each color signal of the colorimetric sensor 70. Specifically, if the level of the average value becomes higher, the signal level Vos is made smaller, so that the output level of the mixer 132 is adjusted to fall within a predetermined signal level range.

Inverter 135 from clock system 5 Is input, the transistor 134 is turned on at a timing synchronized with the horizontal / vertical scanning of the imaging system 10, and the collector of the transistor 133 is grounded. Therefore, the output level of the amplifier 136 in the horizontal blanking period becomes zero level, and the black level period is formed. Here, this black level period corresponds to the clamp timing in the subsequent process circuit 40 and the like.

The output of each colorimetric sensor is thus the blanking processing circuit.
After the black level period is formed at a predetermined timing in 130, the gain controller 20, 30, through the switch circuit 140,
It is input to the process circuit 40 and the like, and is subjected to white balance control in the same manner as the video signal from the image pickup system 10.

At this time, in the present invention, as described above, since the black level period is added to the output of each colorimetric sensor, the white balance control means common to the signal from the image pickup system can be used and the configuration is simplified. It is possible to control the white balance properly.

In addition, the level adjustment circuit 137 adjusts the output level of the colorimetric sensor according to the brightness of the subject so that the output level falls within a substantially constant range. Correct white balance control is possible with a simple configuration when used.

Next, FIG. 7 is a diagram showing another configuration example of the blanking processing circuit 130 of FIG. 5, in which 150 is an integrator and 141 is an integrator 150.
Reset circuit to generate the reset timing signal of the
2 is a blanking circuit for adding a blanking pulse to the output of the integrator 150. Is input via the inverter 144. Reference numeral 143 is a black level clip circuit for setting the black level potential during the period in which the blanking pulse is added.

Further, the reset circuit 141 shortens the reset cycle of the integrator 150 as the output average value of the colorimetric sensor for each color increases, so that the output of the integrator 150 falls within a substantially predetermined signal level range. It is for control.

As described above, also in this embodiment, since the black level period corresponding to the clamp timing in the process circuit 40 and the like is added, the white balance means common to the image pickup system can be used.

〔effect〕

As described above with reference to the embodiments, according to the present invention, since the output of the image pickup system or the colorimetric sensor can be selectively input to the white balance control means of the image pickup apparatus, the signal processing is performed. The temperature characteristics between the system and the colorimetric system, and the linearity of the gain controller were no longer an issue.

In addition, the colorimetric sensor system can immediately obtain an optical signal as a photocurrent instead of periodically performing charge accumulation and charge transfer as in an image pickup system, and thus has an advantage of good white balance response. can get.

[Brief description of drawings]

FIGS. 1-A and 1-B are block diagrams of the conventional two-system circuit arrangement for white balance adjustment, and FIG. 2 is a block diagram of the circuit configuration of the image pickup apparatus of the first embodiment of the present invention. FIG. 3 is a block diagram of the color temperature detection determination circuit of FIG. 2, FIG. 4 is a block diagram of the internal circuit configuration of the white balance circuit of FIG. 2, and FIG. 5 is a circuit of the second embodiment of the present invention. Configuration block diagrams, FIGS. 6 and 7 are block diagrams of the configurations of the blanking processing circuit according to the first and second embodiments, respectively. 10 …… Imaging system 20, 30 …… Gain controller 60 …… White balance circuit 70 …… Color measurement sensor 85 …… Judgment circuit 90 …… Control voltage generation system 100A, 100B, 140 …… Switch circuit 130 …… Ranking processing circuit

Claims (1)

[Claims] 1. A color image pickup means for converting an optical image into a plurality of electric color signals, a gain control means for adjusting a gain balance between the plurality of electric color signals, and a subject provided separately from the color image pickup means. A colorimetric sensor for detecting the color temperature of the, a first detecting means for detecting a color signal portion corresponding to a white subject in the color signal via the gain control means, and a color temperature sensor for detecting Second detection means for detecting whether or not the color temperature is within a predetermined range; and the electric color signal by the gain control means so that the color signal portion detected by the first detection means becomes white. A first mode for feedback-adjusting the gain balance between the electric color signals and the gain control means for adjusting the gain balance between the electric color signals according to the color temperature detected by the colorimetric sensor. And a second mode, the first detection mode is selected when the second detection means detects that the color temperature is not within a predetermined range, and the second detection means is selected. The white balance control means for selecting the second mode when the previous color temperature is detected to be within a predetermined range by the image pickup apparatus.