JPH04240990A - Color image pickup device - Google Patents

Abstract

PURPOSE:To obtain the color image pickup device in which proper white balance is adjusted even when a fluorescent light of low frequency lighting and high frequency lighting is employed for a light source. CONSTITUTION:A difference between an output of a buffer 11 and an output of an integration device 12 is amplified by a differential amplifier 13 to obtain a ripple component of an external light and when a difference between a maximum value and a minimum value exceeds a prescribed value, it is detected by a comparator 16 to detect flicker of an external light. Then an output of a white balance control voltage introduction circuit 10 is corrected to adjust white balance for a fluorescent light.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to color imaging devices such as electronic still cameras and video cameras, and particularly to white balance adjustment thereof.

0002

2. Description of the Related Art Conventionally, various white balance (hereinafter referred to as WB) methods have been proposed for color imaging devices such as video cameras in order to remove the influence of external light and obtain good color reproduction. In particular, WB under fluorescent lighting is different from W outdoors.
The tendency is different from B and requires special treatment. For example, the one described in JP-A-59-141888 is one of them.
This is an example.

FIG. 6 is a block diagram showing a conventional example of the above-mentioned WB system, in which 1 is an image sensor that converts a subject image into an electrical signal, 2 and 3 are amplifiers whose gain is variable according to a control voltage, and 4
is a process circuit that derives Y (luminance), R-Y, B-Y signals by inputting R (red), G (green), and B (blue) signals, 5
is NTSC (nation) from Y, R-Y, B-Y signals.
al television system com
6 is a colorimetric sensor that outputs a photocurrent proportional to the red and blue components of the external light source light, and 7 and 8 are logarithmic compression circuits that convert the input current into a logarithmic compression voltage. , 9 is a differential amplifier, and 10 is a WB control voltage derivation circuit that estimates the color temperature from the logarithmically compressed value of the red-blue ratio of external light and outputs appropriate gain control voltages for red and blue signals. . 14 is a minimum value clamp circuit that uses the minimum level of the input value as a reference voltage value;
5 is a maximum value detection circuit that peak-holds the maximum value of the input signal, 16 is a comparator that compares the magnitude with an internal reference voltage value, and 31 is a band pass filter (BPF) that passes only a specific frequency band.

The operation of the conventional example will be explained below. In the image sensor 1, R, B, and G signals corresponding to the red, blue, and green components of the photoelectrically converted subject light are obtained, and the R and B signals are transmitted through an R signal amplifier 2 and a B signal amplifier 3.
The G signal is sent as it is to the process circuit 4 and the encode circuit 5, and finally to the NT
It is converted into a predetermined signal such as an SC signal.

On the other hand, the colorimetric sensor 6 outputs a photocurrent IR equivalent to the red component of the light source illuminating the object and a photocurrent IB equivalent to the blue component of the light source light, which are respectively output by logarithmic compressors 7 and 8. Logarithmically compressed. Logarithmically compressed signal LOG(IR),
LOG(IB) is subtracted by the differential amplifier 9, and LOG(IB) is subtracted by the differential amplifier 9.
R/IB). The WB control voltage derivation circuit 10 to which LOG (IR/IB) is input derives the voltage for controlling the gain of the signal amplifiers 2 and 3, and calculates the color temperature of the light source light estimated from the value of LOG (IR/IB). It is set at a reasonable profit.

[0006] Furthermore, the output of the differential amplifier 9 is transmitted through the BPF 31
A frequency component around 100 Hz to 120 Hz is extracted, and the minimum potential of the AC component is fixed at a constant potential by a minimum value clamp circuit 14. Further, a maximum value detection circuit 15 detects the maximum potential of the AC component, and a comparator 16 compares the level with a constant value E0. As a result of comparison, if it is large, it is 100Hz ~
It is determined that the 120Hz AC component is large, and it is determined that the light source has a large flicker, such as a fluorescent light, and that information is transmitted to the WB.
It is sent to the control voltage derivation circuit 10. Based on this information, the circuit 10 uses color correction (R,
B. Increase the gain and relatively weaken the green component). This makes it possible to appropriately correct the color of light sources such as fluorescent lamps, which have a greenish tinge, unlike general light. Furthermore, the amount of ripple can be detected by sampling a waveform containing ripples at regular intervals and deriving the difference between the maximum value, minimum value, or average value of the sampled values, and the fluorescent lamp correction can be performed.

[0007]

[Problems to be Solved by the Invention] However, in the conventional example, it is difficult to detect ripple components (several KHz or more) due to flicker for inverter type high frequency lighting type fluorescent lamp light sources that have recently become common. is not possible, and therefore it is not possible to correct the greenish tendency of fluorescent lamps. In particular, in an example where a waveform containing ripples is sampled at a constant cycle, depending on the sample cycle, aliasing distortion occurs due to high frequency ripples, resulting in detection errors (for example, if the ripple cycle and sample cycle match, the ripple is Although it is possible to prevent aliasing by shortening the sampling period, shortening the sampling period causes many other problems (such as an increase in the hardware and software load on the control means).

The present invention was made in view of these problems, and an object of the present invention is to provide a color imaging device that can perform proper WB regardless of whether the light source is a low-frequency lighting or high-frequency lighting fluorescent lamp. It is something to do.

[0009]

Means for Solving the Problems In the present invention, in order to achieve the above object, a color imaging device is configured as shown in (1) and (2) below. (1) external light measuring means for measuring the brightness or color of external light;
an integrating means for obtaining an integral value of the output of the external light measuring means; a flicker detecting means for detecting flicker of external light based on at least the output of the integrating means; and a white balance adjustment according to the output of the flicker detecting means. A color imaging device comprising a color correction means for performing correction.

(2) The color imaging device according to (1) above, further comprising means for rectifying the input before the integrating means.

[0011]

[Operation] With the configurations (1) and (2) above, the brightness or color of external light is measured, the integral value of the external light measurement output is obtained, and flicker of external light is detected from this, and the white balance is Correct the adjustment. In the configuration (2) above, in particular, the output of the external light measuring means is rectified to extract the ripple component.

0012

[Examples] The present invention will be explained in detail below using examples. FIG. 1 is a block diagram of a "color imaging device" which is a first embodiment of the present invention. In the figure, 1-10, 14-16
The blocks shown in FIG. 6 have the same functions as the same-sign part of the conventional example shown in FIG.
is a differential amplifier.

The operation of this embodiment will be explained below with reference to FIG. First, the operation of the block from the colorimetric sensor 6 to the differential amplifier 9 is the same as the conventional example shown in FIG. differential amplifier 13
The difference component is amplified to obtain the integral value of the ripple component. With this method, it is possible to detect flicker components even for high-frequency flicker. Furthermore, by deriving the difference between the buffer output and the integrator output, the flicker component can be amplified to a greater extent. The operations of other blocks 1 to 10 and 14 to 16 are shown in Figure 6.
This is the same as the conventional example. Note that the colorimetric sensor 6 functions as a brightness measuring means for detecting flicker of external light.

The first embodiment described above has more components than the conventional example shown in FIG. 6, which may lead to an increase in cost. In addition, changes in outside light other than fluorescent light flicker, for example,
When a single large amount of light is momentarily incident (e.g. strobe light)
As with the conventional example, there is a possibility that flicker may be mistakenly detected. In order to solve these problems, a second embodiment of the present invention shown in FIG. 2 attempts to efficiently detect continuous ripples at a constant period.

In FIG. 2, 1 to 5 are the same blocks as in the first embodiment, 17 is a photometric sensor for measuring the brightness of external light, 18 is a buffer, 19 is a capacitor, 20 is a diode, 21 is a resistor, 22 , 23, 24, 25 are integrators,
26 is an A/D (analog-digital) converter, 27 is a microcomputer (hereinafter referred to as microcomputer), 28 is a memory, and 29 is a D/A (digital-analog) converter.

FIG. 3 is a waveform diagram of the main part of this embodiment, and FIG. 4 is a flowchart showing the operation of this embodiment. The operation of this embodiment will be described below with reference to FIGS. 2, 3, and 4. Blocks 1 to 5 perform the same operations as in the first embodiment, but
Luminance signal Y of the output of the process circuit 4, color difference signal RY,
B-Y is averaged over at least one screen (1V) by integrators 23, 24, and 25, and is input to an A/D converter 26. On the other hand, the brightness of external light is measured by the photometric sensor 17 and sent to the capacitor 19 via the buffer 18, where the DC component is cut off. In other words, the level of line AA' in FIG. 3(a) becomes the ground level. Next, the alternating current waveform in Figure (A) is half-wave rectified by the diode 20 and the resistor 21 whose other end is grounded, as shown in Figure (B), and a part of the ripple component is extracted.

By integrating this half-wave rectified waveform by an integrator 22, a DC level Va is obtained. This Va becomes a level representing the ripple amount of the flicker light source. The output of the integrator 22 is input to an A/D converter 26. From each input of the A/D converter 26, calculations shown in the flowchart of FIG. 4 are performed to generate control voltage digital values for the R and B signal amplifiers 2 and 3, and sent to the D/A converter 29.

This operation will be explained in more detail. As shown in S1 of FIG. 4, the memory 28 connected to the microcomputer 27 has initial values a, b, c, d, e, f, g, h,
j is memorized. In S2, the A/D converter 26 outputs the output Va of the integrator 22, the output RY (integral value) of the integrator 23,
24 output B-Y (integral value), 25 output Y (integral value)
Enter the value converted to a digital value. In addition, in FIG. 4, the integral value is indicated by an overline. In S3, R, G,
Derive the B value. Furthermore, in S4, Va is compared with the constant a, and if Va > a (S4 YES), it is determined that the light source is a fluorescent lamp because the flicker ripple component is large, and in S5 VRD=b×G/ R+c, VBD=d×G
The control voltage is derived from /B+e. In other words, the G component is also adjusted to perform WB correction and fluorescent lamp correction. On the other hand, S
4, if Va≦a (S4 NO), it is determined that the light source is a non-fluorescent light source because the flicker ripple component is small.
VRD=f×B/R+g, VBD=h×R/B at S6
The control voltage is derived from +j. That is, the color temperature is estimated from the ratio of the R signal and the B signal, ignoring the G component, and signals VRD and VBD suitable for the color temperature are derived. Then, in S7, the signals VRD and VBD obtained in the above manner are
is converted into an analog value by the D/A converter 29, and the amplifiers 2 and 3
The control voltage shall be

As described above, according to this embodiment, the number of components of the flicker ripple component detection means can be reduced compared to the first embodiment, and the instantaneous light change as shown in FIG. The influence of disturbance caused by this can also be reduced compared to the conventional example and the first embodiment.

FIG. 5 is a block diagram showing a third embodiment of the present invention, and blocks 1 to 29 have the same functions as the blocks with the same symbols in FIG. Further, 30 is an integrator. In this embodiment, the operations of blocks 1 to 5, 23 to 29 are almost the same as in the second embodiment, and in particular, the operations of blocks 1 to 5, 23 to 29 are
The explanation will focus on the ripple component detection portions 22 and 30.

The output of the photometric sensor 17 is distributed to a buffer 18 and an integrator 30, and is connected to a diode 20 and a resistor 2.
1, it is half-wave rectified. At this time, the level of the output of the buffer 18 corresponding to line AA' in FIG. Therefore, at the input of the integrator 22, as shown in FIG.
The level corresponding to line BB' is also V30. The output of (b) becomes V30+Va at the integrator 22, and A
/D converter 26. In microcontroller 27, V3
Va is derived from the difference between 0 and V30+Va, and control voltages for the R signal amplifier 2 and the B signal amplifier 3 are derived in the same manner as in the second embodiment. Further, at this time, information on the brightness (luminance) of external light is taken in from V30, and the accuracy of fluorescent lamp discrimination can be increased based on the brightness information. In other words,
If the brightness is within the range of the original fluorescent light, reduce the value of the constant a, and conversely, if the brightness is non-fluorescent light (similar to outside light), increase the value of a to avoid judgment errors. do.

In each of the embodiments described above, the outputs of the photometric sensor and colorimetric sensor are used not only for simple ripple component detection, but also for AE (automatic exposure adjustment) and AWB (automatic white balance) adjustment, respectively. In this case, if each sensor output is amplified and used at the same amplification factor for ripple component detection, AE, and AWB, the ripple component detection accuracy may not improve. Therefore, by making the amplifier gain of each sensor higher when detecting the ripple component than when adjusting AE and AWB, detection accuracy can be further improved and malfunctions can be prevented. Furthermore, in the second and third embodiments,
Although a half-wave rectifying element is used to detect the ripple component, it may also be constituted by a full-wave rectifying element. Further, in each of the embodiments, an integrator is used to detect the ripple component, but this integrator integrates the input signal over a predetermined time, and its output is proportional to the average value of the input signal. Therefore, instead of an integrator, it is possible to use a smoothing circuit, a low-pass filter, etc., and "integration" in the present invention includes "average".

[0023]Furthermore, an optical sensor other than the colorimetric sensor or the photometric sensor, for example, a light receiving element for AF (automatic focus adjustment) may be used for ripple component detection.

[0024]

[Effects of the Invention] As explained above, according to the present invention,
By detecting a wide range of ripple components from the light source, from low frequencies to high frequencies, it is possible to detect flicker even for high-frequency lighting type fluorescent light sources, and prevents images from becoming greenish even when shooting under fluorescent light sources. It becomes possible to make corrections.

[Brief explanation of the drawing]

[Figure 1] Block diagram of the first embodiment

[Figure 2] Block diagram of the second embodiment

[Figure 3] Waveform diagrams of main parts of the second and third embodiments

[Figure 4] Flowchart of the second embodiment

[Figure 5] Third
Example block diagram

[Figure 6] Block diagram of conventional example

[Explanation of symbols]

6 Colorimetric sensor 10 WB control voltage derivation circuit 11 Buffer 12 Integrator 13 Differential amplifier 14 Minimum value clamp circuit 15 Maximum value detection circuit 16 Comparator

Claims (2)

[Claims] 1. An external light measuring means for measuring the brightness or color of external light, an integrating means for obtaining an integral value of the output of the external light measuring means, and at least a flicker of the external light based on the output of the integrating means. A color imaging device comprising: flicker detection means for detecting flicker; and color correction means for correcting white balance adjustment according to the output of the flicker detection means. 2. The color imaging device according to claim 1, further comprising means for rectifying the input before the integrating means.