JPS61224796A - Color temperature information forming device and image pickup device - Google Patents

Abstract

PURPOSE:To eliminate the influence due to the flickering of a light source in a short time and to obtain the color temperature information of an object by calculating the output of plural color sensors to detect the color component with a different object light concerning the period of the integer times of 1/2 of the prescribed light source. CONSTITUTION:By an R sensor 2 and a B sensor 3 having the same spectral light sensitibity as the image pickup element, an R component and a B component of the light from the object under the light source are respectively detected, and output signals iR and iB are logarithm-compressed by logarithm compressing circuits 4 and 5 and l o g i R and l o g i B are outputted. A ratio l o g i R/iB of the signals lo g i R and iB are obtained by a differential amplifier 6 of a calculating block 14, and added through an LPF 16 to an A/D converter 10. The converter 10 and a microcomputer 11 to calculate and process the output are controlled by the signal from a synchronizing circuit 15 which synchronizes with the control of an element 1, and control values CRD and CBD are outputted from the computer 11. The control values CRD and CBD are D/A converted and the white balance of the image pickup signal from the element 1 is adjusted by R and B signal amplifiers.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an improved color temperature information forming device and imaging device.

[Prior Art] When an image capturing device such as an electronic camera captures an image of a subject, a phenomenon occurs in which a white subject is reproduced as colored depending on the spectral sensitivity of the illumination light source. Conventionally,
In order to prevent this phenomenon, an automatic tracking white balance adjustment device has been proposed that measures the color temperature of the light source and automatically adjusts the white balance in the imaging device based on the information.

FIG. 1 is a block diagram showing an example of a conventional automatic tracking white balance adjustment device. 2 is an R sensor, and 3 is a B sensor, which have the same red and blue spectral sensitivities as the image sensor 1, and detect the Rr& component and B component of light from an object under a light source, respectively. Since the output signals iR and ilB from each sensor 2 and 3 have a very wide variation range, they are logarithmically compressed by logarithmic compression circuits 4 and 5 to obtain signals representing logiR and iogig, respectively.

The signals indicating logiH and Iogig are connected to differential amplifier B.
This is converted into a signal indicating the difference log(iR/ie), and thereby the ratio of the R component to the daylight component in the subject light is obtained. 7 is a control voltage derivation circuit which inputs a signal indicating log(iR/iB) from the differential amplifier 8, and calculates the input value, that is, the R component and the B component.
Amplifiers 7 and 8 that determine the color temperature of the light source based on the ratio of the color temperature of the light source and derive a control voltage, and use the derived control voltage to amplify the signal indicating the R component and the signal indicating the B component from the imaging device 1. The amplification degree is controlled, thus performing white balance adjustment, and the white balance adjusted signal is modulated and multiplexed in the signal processing circuit 13 and converted into a standard TV signal (for example, NTSC).

However, with special (blinking) light sources such as fluorescent lamps, flickering of light occurs. This flicker
occurs at a frequency twice the frequency of the commercial power supply, and each color component has roughly different strengths. Therefore, the output signal of the differential amplifier 8 indicating log(iR/is) also changes in magnitude at a period twice the commercial power supply frequency. Although flicker is not so noticeable to the human eye under a fluorescent light source, a color sensor accurately detects the periodic color change of a subject caused by the flicker of the light source.

As a countermeasure against flicker, an analog low-pass filter is inserted between the differential amplifier B and the control voltage calculation circuit 7 in the video camera, thereby preventing the adverse effects of flicker. However, in devices such as electronic cameras that require white balance adjustment within a short time after the power is turned on, the frequency of the signal component that must be removed is as low as 100 Hz, so analog low-pass A filter has a large time constant and is inappropriate.

Also, for example, as shown in Fig. 1, as a color sensor, R(
In an imaging device using two types of sensors, red) and B (blue), information on the G (green) component of the light source cannot be obtained. Conventionally, black body radiation, which is close to sunlight, is used as the standard. In this case, when the ratio of the Rm component and the B component is determined, the ratio between these and the G component is also determined, so the G component is determined from the R and B component ratio. We were able to predict the ratio of

However, since light sources such as fluorescent lamps have a unique spectrum, it is difficult to predict the ratio of the G component from the R and 8 component output ratios as in the case of black body radiation. The G component cannot be corrected accurately, and the reproduced image becomes greenish.

[Objective] The object of the present invention is to eliminate the drawbacks of the prior art as described above,
Even under flickering light sources such as fluorescent lights, color temperature information can be formed in a short time without being affected by color flickering.
Furthermore, it is an object of the present invention to provide a color temperature information forming device capable of forming appropriate color temperature information including a G (green) component even when using two types of sensors, for example, R and B. .

Another object of the present invention is to provide an imaging device that can obtain a proper color image even under a flickering light source as described above.

[Embodiment] FIG. 2 is a configuration diagram showing an embodiment of an imaging device including the color temperature information forming device of the present invention. In FIG. 2, 2 is an R sensor, and 3 is a B sensor, which have the same red and blue spectral sensitivities as the image sensor in the imaging device 1, and have the R and B components of light from the subject under the light source. Detect each. Since the output signals iR and 1B from each sensor 2 and 3 have a very wide range of variation, they are logarithmically compressed by logarithmic compression@paths 4 and 5 to obtain signals representing logiR and iogiB, respectively. The signals indicating logiR and iogie are converted by the differential amplifier 8 into a signal indicating the difference log(iR/in), thereby obtaining the ratio of the R component and the B component in the subject light.

The output of the differential amplifier 6, which indicates the ratio of the R component to the B component in the subject light, is passed through the low-pass filter 1B and then sent to the A/D.
In the converter 10, discontinuous sampling is performed by converting into a digital signal in synchronization with the output of a synchronization circuit 15 that forms a synchronization signal for driving the imaging device l. Here, the sampling synchronization is selected with respect to the commercial power supply frequency fs as follows.

That is, since the flicker component depends on the absolute value of the polarity of the power supply, the frequency is 2 fs. Furthermore, in order to sample this 2fs component, a sampling frequency of 4fs or more is required according to Nyquist's sampling theorem. Therefore, the sampling period needs to be smaller than (1/4) fs. In reality, as will be explained later, the flicker component spreads to the vicinity of the 4th harmonic (1/1B) fs
The signal from the A/D converter IO is preferably processed in the microcomputer 11 in synchronization with the output from the synchronous circuit 15.
Derive digital control values ctta and ceD. The microcomputer 11 has a CPU, a RAM, and a ROM that stores procedures as shown in FIG.

A signal indicating the derived digital control value is inputted from the microcomputer 11 to the input/A converter 12, and converted by this D/^ converter into analog control values CR and ce, which are respectively sent to the R signal amplifier 8.
and input to the B signal amplifier 3. The signal from the image sensor 1 (
The amplification degrees of the amplifiers 8 and S that amplify the R and B components of the subject light are controlled, and the white balance is adjusted. Note that 14 is a calculation block as a color temperature information forming means.

The microcomputer 11 performs the following calculations (1) and (2).

(1) Remove the periodic variation in the output of the differential amplifier 6, which indicates the ratio of the R component to the B component in the subject light.

(2) Measure the magnitude of the change (amplitude) and correct the control signal accordingly.

Regarding (1), the following calculation is performed.

In this case, the frequency component of the periodic variation of the differential amplifier output is set to twice the commercial power supply frequency (2fs) as the fundamental wave,
It consists only of the first, second, third, fourth, etc. high frequencies. Therefore, it can be seen that the variation can be removed by averaging the differential amplifier output during a period of (1/:fs) [seconds]. By the way, the commercial power frequency is 5 in the Kanto region.
Since it is divided into 0Hz and 130Hz in the Kansai region, the period (1/2fs) [seconds] is (17100) seconds in the Kanto region and 1/120 seconds in the Kansai region, as shown in Figure 3.
seconds, and the two do not match.In this case, if you calculate the average over a period of (1/120) seconds for the differential amplifier output, for example, in the Kansai region, the average will be obtained accurately, and the periodic changes in the differential amplifier output will be calculated. It can be removed, but in the Kanto region, the fundamental wave 1
This is not possible because the cycle has not finished, so if we take the average over a period of (1/20) seconds, this is 5 cycles of the fundamental wave in the Kanto region and 6 cycles of the fundamental wave in the Kansai region.
The cycle is completed in (1/20) seconds in both cases. Therefore, an accurate value can be obtained by taking the average over that period (1/20 second). Like this (1
Since the periodic changes in the differential amplifier output can be removed in /20) seconds, or 50 S, the control signal from which the changes have been removed can be generated in a shorter time than in the conventional example using an analog low-pass filter. You will get it.

Next, regarding (2) above, the amplitude of the periodic change in the output of the differential amplifier is determined, and the signal from the imaging device l (in the video signal) is calculated using the amplitude value as a function.
The relative amplification degree of the G component with respect to the amplification degree of R and BfIt is determined, and the control signal is corrected so that the relative amplification degree of the G component becomes the determined value. That is, when the amplitude of the periodic change in the output of the differential amplifier is large, it is considered that, for example, only a fluorescent lamp is the light source, so the proportion of the G component in the video signal is reduced. Furthermore, when the same amplitude is small, it is determined that sunlight or the like without flicker is the light source, and the proportion of the G component in the video signal is increased.

Furthermore, under a light source where a fluorescent lamp and sunlight exist simultaneously, the amplitude of the periodic change in the output of the differential amplifier corresponds to the ratio of the amount of light from the fluorescent lamp to the amount of sunlight, so it is a function of the amplitude value. As a result, the ratio of the G component to the R and day components in the video signal is adjusted.

FIG. 4 shows a flowchart actually executed by the microcomputer 11. In this FIG.
The /D and D/A converters and microcomputer are assumed to be 8-bit processing.

As shown in wS4 figure, step S! Predetermined areas A, B, N and E of RAM in the microcomputer in
, the initial value is static 0. B 255. N −0 and! −
Set to 0. Then, in step S2, the differential amplifier output is sampled by the A/D converter. Then, in step S3, R in the microcomputer
A) Set the digital value of the sampled differential amplifier output in region C of II.
and A (initial value is 0), and if C is larger than A, proceed to step S5 and replace A with C (that is, A indicates the maximum value of the sampled output). If A is larger than C, proceed to step SS. In step S8, compare the sizes of C and B (initial value is 255), and if C is smaller than B, proceed to step S7 and exchange B to C. (In other words, B indicates the minimum value of the sampled output.) If B is smaller than C, proceed to step S8. If N (initial value is 0) is smaller than the constant value j in step S8, proceed to step S9. The sum of E (initial value is 0) and C is set to E, and the process proceeds to step S10, where N is increased by 1.
Then, the process returns to step S2 and the differential amplifier output is sampled again. Steps S2-S8 and S9. SIO
is repeated until N becomes larger than j, that is, if N)j is reached in step S8, step Sll is repeated.
Then, it is determined whether N-j+1, and if so, the process proceeds to step 312 to check the difference (D-A-B) between the maximum value and the minimum value of the sampled output. Next, the process proceeds to step S13, where it is determined whether this D is smaller than a constant value a. If D is smaller than a, it is judged that there is no periodic variation in the output of the differential amplifier, and the process proceeds to step S14, where the microcomputer A constant value is set in area I of RAM in the RAM, a constant value C is set in area G of the same RAM, and then the process proceeds to step S15, where the control voltage is set as a light source that does not require green correction such as sunlight. Cuo and CB
, is determined based on CR-F+dxC and CB=G+eXC (C is the most recently sampled differential amplifier output), and then proceeds to step S1B, where the determined control voltage supply is output to the C8 D/A converter, Return to step S2.

By the way, regarding the value of j, this is because the amplitude of the periodic change in the differential amplifier output must be found by N-j (by repeating steps S2 to SIO).
The value of J must be applied to the timing that indicates the passage of one period of the fundamental wave.

Therefore, the frequency of the sampling clock in the A/B converter is set to IKHz, and the commercial power supply frequency is set to 115
In the case of 0 c/s, the number of times sampling must be performed is 1/100g÷1/1000g=10 times, and j=8.

Now, in step S13, if the amplitude of the periodic variation of the differential amplifier output sampled by 10rjiJ is equal to or larger than the fixed value a, the process proceeds to step S8, where C is roughly added to E, and the process proceeds to step SIO, where N is increased by 1. Then, the process returns to step S2 and the differential amplifier output is sampled again.

Then, step S8 to step S1! Nissumi, N
is greater than or equal to j+1, so proceed to step S17, and N-
Determine if K. That is, until N becomes K (1/2
Set the sampling period to 1kHz until 0 seconds have elapsed. , et al., K-1/2G+ 1/1000-1-49)
Repeat the sampling and add C to E (repeat steps S2 to S8.S17.S9 and SIO in this order).When tK is reached in step S17, proceed to step S1B and add E to +1. By dividing, the average value of the differential amplifier output, that is, the value with periodic changes removed, is obtained. Next, the process proceeds to step S19 to further obtain the amplitude D-A-B at that time, and then proceeds to step 920 to determine whether the value (D) is greater than or equal to 1 constant value f.
If so, it is determined that the light source is only a fluorescent lamp, and the process proceeds to step S21.
Then, the G component in the video signal is weakened relative to the R and B components. That is, for example, in an imaging device having an R and day component processing circuit, there is no circuit that changes the gain of the G component, so F-f (constant value) is and G=g (a constant value), and after setting C, proceed to step S15. On the other hand, if D(f) in step S20, proceed to step S22 to determine whether D(a). If so, the process proceeds to step S14 and corrects the control voltage assuming that the light source is sunlight as described above.Also, if D)a, it is determined that the light source is a mixture of the sun and a fluorescent lamp, and the process proceeds to step S923. Let's take the linear function of its amplitude as F-b+D Xh(
Calculate Gsc+D Xl (constant value),
The control voltage C to IC8D is determined as 0 or more, which proceeds to step S15.

In addition to the above-mentioned methods, several other methods can be considered as means for removing the periodic variation from the output of the differential amplifier. In the above example, sampling was performed for (1/20) seconds so that an accurate average could be taken in both the Kanto and Kansai regions. However, if the sampling frequency period is (1/1200) seconds, for example, in the Kanto region, The 12th sampling constitutes one cycle and becomes equal to the first sampling value, and in the Kansai region, the 10th sampling is the same. Therefore, compare the 10th sampling value and the 1st sampling value, and if they are equal, the Kansai region is determined and the average of the differential amplifier output is taken at that point. If they are different, the Kanto region is sampled two more times and the 12 Take the average of the times.

In this way, it is possible to remove the variation in the output of the differential amplifier by 50%.
In the Kansai region, it takes 17,120 seconds to adjust the white balance, whereas in the Kanto region, it takes 17,100 seconds to adjust the white balance.

Since there is a possibility that harmonic high-frequency components (for example, components of 450 Hz or higher) may be aliased, the high-frequency components are dropped using an analog low-pass filter 16 with a small time constant before sampling, which reduces noise and is effective. It is true. Note that this low-pass filter 18 functions as a band-limiting means, and a similar effect can be obtained by using a band-pass filter or a trap circuit.

Incidentally, since the image pickup device and the image pickup tube that constitute a part of the image pickup device are also affected by flicker, the image pickup signal itself will have color flicker. In the case of an image sensor, such as a COD, since charge is accumulated for a certain period of time, flickering can be effectively reduced with the same effect as averaging the output of the differential amplifier described above, but this can be effectively reduced by using a shutter. When used in an electronic camera, the storage time on the CCD may be shortened by the shutter.
In such a case, even if the flicker is corrected only by the white balance adjustment device, flicker will appear in the image signal and it will be meaningless. Therefore, the differential amplifier output in the white balance adjustment device Flickering can be effectively corrected by synchronizing the averaging period with the charge accumulation time in the CCD. In this embodiment, taking this into consideration, the sampling timing l and the drive scanning timing of the image sensor tl are set. Another feature is that it is synchronized.

Also, as a method for correcting green components in video signals.

R component and BIi! guided by R sensor and B sensor! It is possible to predict the type of light source from the ratio of i and min0. For example, if R/B is 1.5 or more, it is determined that it is an indoor fluorescent light, and the proportion of green component is reduced, and the R/B
If it is 2.5 or more, it is determined that it is a tungsten light source, and if it is 1.5 or less, it is considered as outdoor sunlight and the green component is corrected.

In the above embodiments, the color temperature information forming device is used as a part of the white balance adjustment device, but the color temperature information forming device of the present invention is merely for displaying color temperature information or giving a warning. It may be.

Further, although the color temperature information forming means in the embodiment forms color temperature information by subtracting the logarithm compression values of the R sensor and the B sensor, it is also possible to simply calculate the ratio of the outputs of both sensors. good.

[Effects] As described above, according to the present invention, appropriate color temperature information can be obtained in a short time even under flickering light sources such as fluorescent lamps and under a mixture of these and sunlight.

2 is a block diagram showing an embodiment of the present invention, FIG. 3 is a schematic diagram of a flicker to explain how to average the differential amplifier output, and FIG. 4 is a block diagram showing an embodiment of the present invention. It is a flowchart for actual operation in an example.

2...R sensor, 3...B sensor, lO...A/D converter, 11...Microcomputer, 12...D/A converter.

Figure 1

Claims (1)

[Claims] 1) A plurality of color sensors each detecting different color components from subject light, and outputs of the plurality of color sensors are set to 1/1 of the blinking cycle of a predetermined light source.
A color temperature information forming device comprising: color temperature information forming means for forming color temperature information of a subject by calculating for a period that is an integral multiple of 2. 2) A plurality of color sensors each detecting different color components from the subject light, and the output of the plurality of color sensors is set to 1/2 of the blinking cycle of a predetermined light source.
color temperature information forming means for forming color temperature information of a subject by performing calculations over a period that is an integer multiple of the color temperature information forming means; a color imaging means for controlling white balance in accordance with the output of the color temperature information forming means; An imaging device having: