JPH0783485B2 - Color temperature information forming device and imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improved color temperature information forming apparatus and image pickup apparatus.

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

FIG. 1 is a block diagram showing an example of a conventional automatic tracking type white balance adjusting apparatus. Reference numeral 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 R and B components of the light from the subject under the light source, respectively. Since the output signals i _R and i _B from the respective sensors 2 and 3 have a very wide range of variation, they are logarithmically compressed by the logarithmic compression circuits 4 and 5 to obtain lo
Signals representing gi _R and iogi _B are obtained. logi _R and log
the difference by the differential amplifier 6 signals indicating a i _B log (i _R /
i _B ), which gives the ratio of the R and B components in the subject light. Reference numeral 7 denotes a control voltage derivation circuit, which is a log (i
_R / i _B ), and input this value, that is, R
An amplifier 7 that determines the color temperature of the light source based on the ratio of the component and the B component, derives the control voltage, and amplifies the signal indicating the R component and the signal indicating the B component from the imaging device 1 by the derived control voltage. The gains of 8 and 8 are controlled, and thus white balance adjustment is performed. The signal subjected to the white balance adjustment is modulated and multiplexed in the signal processing circuit 13 and converted into a standard TV signal (for example, MTSC).

By the way, in a special (flashing) light source such as a fluorescent lamp, light flicker occurs. This flicker occurs at a cycle twice as high as the frequency of the commercial power supply, and the color components have different intensities from each other. for that reason
The magnitude of the output signal of the differential amplifier 6 indicating log (i _R / i _B ) also changes at a cycle twice the frequency of the commercial power supply.
Under the fluorescent light source, flicker is not noticeable to human eyes, but the color sensor accurately detects the periodical color change of the subject caused by the flicker of the light source.

As a measure against flicker, in the video camera, an analog low-pass filter is inserted between the differential amplifier 6 and the controller voltage calculation circuit 7 to prevent an adverse effect due to flicker. However, in devices such as electronic cameras that require white balance adjustment in a short time after power is turned on, the frequency of the signal component that must be removed is a low frequency of about 100 Hz, so analog low-pass The filter has a large time constant and is inappropriate.

Further, for example, as a color sensor as shown in FIG.
In an image pickup apparatus using two types of sensors (red) and B (blue), information on the G (green) component of the light source cannot be obtained. The standard is black body radiation close to that of conventional sunlight, and in this case, if the ratio of the R component and the B component is determined, the ratio of these and the G component is also determined. Could be predicted. However, since a light source such as a fluorescent lamp has a unique spectrum, it is difficult to predict the ratio of the G component from the R and B component output ratio as in the case of black body radiation.
Therefore, the G component cannot be accurately corrected for the fluorescent light source, 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 a flicker light source such as a fluorescent lamp, it is possible to form color temperature information that is not affected by color flicker in a short time.
It is another object of the present invention to provide a color temperature information forming apparatus capable of forming appropriate color temperature information including the G (green) component even when two types of sensors, R and B, are used. .

Another object of the present invention is to provide an image pickup apparatus capable of obtaining a proper color image even under the light source having the flicker as described above.

[Embodiment] FIG. 2 is a block diagram showing an embodiment of an image pickup apparatus including the color temperature information forming apparatus 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 image pickup apparatus 1, and the R and B components of the light from the subject under the light source. Are detected respectively. Since the output signals i _R and i _B from the respective sensors 2 and 3 have a very wide range of variation, they are logarithmically compressed by the logarithmic compression circuits 4 and 5 to obtain signals indicating logi _R and iogi _B , respectively. The signal indicating logi _R and iogi _B is converted into a signal indicating the difference log (i _R / i _B ) by the differential amplifier 6, and the ratio of the R component and the B component in the subject light is obtained by this.

The output of the differential amplifier 6 indicating the ratio of the R component to the B component in the subject light is passed through the low pass filter 16 and then of the synchronizing circuit 15 that forms a synchronizing signal for driving the image pickup apparatus 1 in the A / D converter 10. Discontinuous sampling is performed by converting to a digital signal in synchronization with the output. Here, sampling synchronization is selected as follows for the commercial power frequency fs. That is, since the flicker component depends on the absolute value of the polarity of the power source, the frequency is 2fs. Also, in order to sample this 2fs component, a sampling frequency of 4fs or more is required according to the Nyquist sampling theorem. Therefore, the sampling period must be smaller than (1/4) fs. Actually, as will be described later, since the flicker component extends to the vicinity of the fourth harmonic, it is desirable that the period is shorter than (1/16) fs. The signal from the A / D converter 10 is also processed in the microcomputer 11 in synchronization with the output from the synchronizing circuit 15, and the digital control value is output.
_Derive C _RD and C _BD . Microcomputer 11 is CP
It has a U, a RAM and a ROM storing the procedure as shown in FIG. The signal indicating the derived digital control value is input from the microcomputer 11 to the D / A converter 12,
This D / A converter enables analog control value C _R
And C _B to convert to R signal amplifiers 8 and B, respectively.
Input to the signal amplifier 9. Input control value C _R
And C _B control the amplification degree of amplifiers 8 and 9 for amplifying the signals (representing the R component and the B component of the subject light, respectively) from the image sensor 1 to perform white balance adjustment. Incidentally, reference numeral 14 is a calculation block as a color temperature information forming means.

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

(1) The periodic change in the output of the differential amplifier 6 which indicates the ratio of the R component to the B component in the subject light is removed.

(2) The magnitude (amplitude) of the change is measured, and the control signal is corrected accordingly.

Regarding (1), the following calculation is performed.

In this case, the frequency component of the cyclical change of the output of the differential amplifier consists of only the following first, second, third, fourth ... . Therefore, it can be seen that if the average of the differential amplifier output in the period of (1/2 fs) [seconds] is taken, the change can be removed. By the way, since the commercial power frequency is divided into 50Hz in the Kanto region and 60Hz in the Kansai region, the cycle (1 / 2fs) [seconds] is (1/100) seconds in the Kanto region and in the Kansai region as shown in Fig. 3. It becomes 1/20 second and both do not match. At this time, regarding the differential amplifier output, for example, if the average of the period of (1/120) seconds is obtained, the average can be accurately obtained in the Kansai region, and the periodic change of the differential amplifier output can be removed. I can't do that because one cycle of the wave isn't over.
Therefore, if we take the average of the period of (1/20) seconds, this will be 5 cycles of the fundamental wave in the Kanto region and 6 cycles of the fundamental wave in the Kansai region, and both will have a period of 1/20 seconds. Complete. Therefore, an accurate value can be obtained by taking the average of that period (1/20 seconds). In this way, since it is possible to remove the periodic change of the differential amplifier output in (1/20) seconds, that is, 50 ms, the change can be removed in a shorter time than the conventional example using the analog low-pass filter. A control signal will be obtained.

Next, regarding (2) above, regarding this, the signal from the image pickup apparatus 1 (in the video signal) is obtained by obtaining the amplitude of the periodical change in the output of the differential amplifier and using the amplitude value as a function.
The relative amplification of the G component with respect to the amplifications of the R and B components is determined, and the control signal is corrected so that the relative amplification of the G component becomes the determined value. That is, when the amplitude of the periodical change in the output of the differential amplifier is large, only the fluorescent lamp is considered to be the light source, for example, so that the proportion of the G component in the video signal is reduced. Further, when the amplitude is small, it is determined that sunlight or the like without flicker is the light source to increase the ratio of the G component in the video signal, and further, a light source in which a fluorescent lamp and sunlight simultaneously exist. Below, the amplitude of the cyclical change in the output of the operational amplifier corresponds to the ratio of the amount of light from the fluorescent lamp and the amount of sunlight, so the ratio of the G component to the R and B components in the video signal as a function of the amplitude value. Will be adjusted.

FIG. 4 shows a flowchart actually executed by the microcomputer 11. In this Figure 4, the A / D
8bi for D / A converter and microcomputer
t processing.

As shown in FIG. 4, in step S1, predetermined values A = 0, B = 255, N = 0 and E = 0 are set in predetermined areas A, B, N and E of the RAM in the microcomputer. Then, in step S2, the differential amplifier output is sampled by the A / D converter. Then, in step S3, the sampled digital value of the differential amplifier output is set in the area C of the RAM in the microcomputer. Next, in step S4, the sizes of C and A (initial value is 0) are compared. If C is larger than A, the process proceeds to step S5 and A
Replace C with C (ie A will represent the maximum value of the sampled output). If A is larger than C, step
Proceed to S6. In step S6, C and B (initial value is 25
Compared with 5), if C is smaller than B, proceed to step S7 and replace B with C (that is, B indicates the maximum value of the sampled output). If B is smaller than C, proceed to step S8. N in step S8
If (initial value is 0) is smaller than the constant value j, step S9
Then add E (initial value is 0) and C to E
And proceed to step S10 to increase N by 1,
Then, returning to step S2, the differential amplifier output is sampled again. As described above, in the embodiment of the present invention, the colorimetric information output of the plurality of color sensors is sampled at a cycle shorter than 1/4 cycle of the commercial power supply, and the signals obtained by the sampling are added to obtain E. You're getting value. Repeat steps S2-S8 and S9, S10 until N is greater than j. That is, in step S8, N
If> J, proceed to step S11, where N =
j + 1, and if so, the process proceeds to step S12 and the difference between the maximum value and the minimum value of the sampled output (D = A-
Examine B). Next, in step S13, it is determined whether or not this D is smaller than a constant value a. If D is smaller than a, it is determined that there is no periodic change in the output of the differential amplifier, and in step S14, the microcomputer RAM in
The constant value b is set in the area F of the above, the constant value c is set in the area G of the same RAM, and the process proceeds to step S15, where the control voltage C _RD and C _BD is C _R = F + d × C and C _B = G + e × C
(C is the most recently sampled differential amplifier output). Then, the process proceeds to step S16, the obtained control voltages C _RD and C _BD are output to the D / A converter, and the process returns to step S2.

By the way, it is the value of j. This is because the amplitude of the periodical change in the output of the differential amplifier must be obtained by N = j (by repeating Steps S2 to S10). Must be applied to the timing indicating the time point after one cycle of. Therefore, if the sampling clock frequency in the A / D converter is 1 KHz and the commercial power supply frequency is 1/50 c / s, the number of times sampling must be performed is 1/100 s ÷ 1/1000 s = 10 times, and j = 8 Becomes

If the amplitude of the cyclical change of the differential amplifier output sampled 10 times in step S13 is equal to or greater than the constant value a, the process proceeds to step S9, C is further added to E, and N is incremented by 1 in step S10. Return to step S2,
The differential amplifier output is sampled again.

Then, from step S8 to step S11, N is j
Since it is +1 or more, the process proceeds to step S17, and it is determined whether N = K. In other words, until N becomes K (until 1/20 seconds elapse, if the sampling period is 1 kHz, K = 1/20 ÷
(1 / 1000-1 = 49) Repeat sampling and add C to E (steps S2 to S8, S17, S9 and S10 are repeated in this order). As described above, in the present invention, the sampling values are added until N = K. In step S17, N
When K = K, the process proceeds to step S18 and E is divided by K + 1 to obtain the average value of the differential amplifier output, that is, the value obtained by removing the periodic change. Then proceed to step S19 to find the amplitude D = A-B at that time, then step
Proceed to S20 to determine if the value (D) is greater than or equal to one constant value f. If D> f, determine that the light source is only a fluorescent lamp, and proceed to step S21 to set the G component in the video signal to R and B. Try to weaken relative to the ingredients. That is, for example, in an image pickup apparatus having an R and B component processing circuit, there is no circuit that changes the gain of the G component, so R
So that the ratio of B component to G component is increased,
After setting F = f (constant value) and G = g (constant value) and C, the process proceeds to step S15. On the other hand, step S20
If D <f in step S22, the process proceeds to step S22 and D <a
To judge. If D <a, the process proceeds to step S14 and the control voltage is corrected if the light source is sunlight as described above. If D> a, it is determined that the sun and the fluorescent lamp are mixed as the light source, and the process proceeds to step S23, where F = b + D × h (constant value), G as a linear function of the amplitude D.
= C + D × i (constant value) is calculated, and the process proceeds to step S15. The control voltages C _RD and C _BD are obtained as described above.

It should be noted that some means other than the above can be considered as means for removing the periodic change from the output of the differential amplifier. In the above example, sampling was performed for (1/20) seconds so that the average can be taken accurately in both the Kanto and Kansai regions. For example, if the sampling frequency period is (1/1200) seconds, in the Kanto region At the 12th sampling, it becomes one cycle and becomes equal to the sampling value at the 1st sampling, and the same for the 10th sampling in the Kansai region. Therefore, the 10th sampling value and the 1st sampling value are compared, and if both are equal, the Kansai region is taken. At that time, the differential amplifier output is averaged, and if they are different, the Kanto region is sampled twice.
Take the average of 12 times.

By doing this, it takes 50 ms to remove the change in the differential amplifier output.
It takes only 1/120 seconds in the Kansai region and 1/100 seconds in the Kanto region, so white balance adjustment can be done in a shorter time.

Further, in this embodiment, the sampling frequency is low (for example,
Since the high frequency component of the 1 / 2fs harmonic of the differential amplifier output (for example, the component of 450Hz or more) may fold back from 900Hz), drop the high frequency component with the analog low-pass filter 16 with a small time constant. It is effective because there is little noise because it is sampled from. The low-pass filter 16 functions as a band limiting means, and the same effect can be obtained by a band-pass filter or a trap circuit.

By the way, the image pickup device and the image pickup tube forming a part of the image pickup apparatus should be affected by the flicker, so that the image pickup signal itself has color flicker. In the case of an image pickup device such as a CCD, electric charge is accumulated for one constant time, so that flicker can be effectively reduced with the same effect as that of averaging the outputs of the differential amplifiers described above, but this has a shutter. When used in an electronic camera, the storage time in the CCD may be shortened due to the shutter.In such a case, even if the flicker is corrected by the white balance adjustment device alone, the image signal will flicker. Comes out and becomes meaningless. Therefore, the period for averaging the outputs of the differential amplifier in the white balance adjustment device
The flicker can be effectively corrected by synchronizing with the charge accumulation time in the CCD. The present embodiment is also characterized in that the sampling timing and the driving scanning timing of the image pickup device 1 are synchronized in consideration of such a situation.

Further, as a method of correcting the green component in the video signal, it is possible to predict the type of the light source from the ratio of the R component and the B component introduced by the R sensor and the B sensor.
For example, if the R / B is 1.5 or more, it is determined to be an indoor fluorescent lamp and the ratio of the green component is reduced.If the R / B is 2.5 or more, it is determined to be the tungsten light source, and if the R / B is 1.5 or less, the outdoor sunlight is corrected to correct the green component. To do.

In the above embodiment, the color temperature information forming device is used as a part of the white balance adjusting device, but the color temperature information forming device of the present invention is for merely displaying the color temperature information and giving a warning. May be

Further, although the color temperature information is formed by subtracting the logarithmic compression values of the R sensor and the B sensor of the color temperature information forming means of the embodiment, for example, the ratio of both sensor outputs may be simply calculated. .

[Effects] As described above, according to the present invention, it is possible to obtain appropriate color temperature information in a short time even under a light source with flicker such as a fluorescent lamp and when these and sunlight are mixed.

[Brief description of drawings]

FIG. 1 is a block diagram of a conventional automatic tracking white balance adjusting device, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is a diagram for explaining how to average the outputs of differential amplifiers. FIG. 4 is a schematic diagram of flicker, and FIG. 4 is a flowchart for actual operation in the embodiment of the present invention. 2 ... R sensor, 3 ... B sensor, 10 ... A / D converter, 11 ... Microcomputer, 12 ... D / A converter.

Claims (4)

[Claims] 1. A plurality of color sensors that form colorimetric information by detecting different color components from a subject, and the colorimetric information output from the plurality of color sensors is output from a quarter of the cycle of a commercial power source. And a color temperature information forming unit that forms color temperature information by adding signals obtained by the sampling at a short cycle and a color temperature information forming apparatus. 2. The color temperature information forming apparatus according to claim 1, further comprising band limiting means for removing high frequency components of the colorimetric information. 3. A plurality of color sensors that form color measurement information by detecting different color components from a subject, and the color measurement information output of the plurality of color sensors is output from a quarter of the cycle of the commercial power source. A color temperature information forming means for forming color temperature information by sampling at a short cycle and adding signals obtained by the sampling, and a color imaging means for controlling a white balance state based on the color temperature information, An imaging device having a. 4. The image pickup apparatus according to claim 3, wherein the sampling timing and the scanning timing of the color image pickup means are synchronized with each other.