JPH09331537A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the color reproducibility using automatic white balance by correcting a white color detection range for white balance adjustment based on a flicker ratio into a range around a white color temperature of lighting so as to avoid a possibility in which a colored object is judged in mistake under an indoor lighting to be a white color. SOLUTION: A flicker caused by a difference between a frequency of a fluorescent light flicker and a video field frequency of a camera of the NTSC system is used to allow a user to recognize the image pickup under an indoor fluorescent light. That is, an output of a luminance signal processing means 53 is applied to a flicker detection means 11, which detects a flicker due to a luminance change caused for each of three video image fields. A microcomputer 60 generates data of a white color detection range by the fluorescent lighting based on the flicker to apply the data to white balance control means 56, 57, in which the usual white color detection range is switched into a range around a white color temperature of a fluorescent light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus for automatically performing white (white) balance adjustment (hereinafter referred to as auto white balance or AWB), and particularly to an object under illumination using a commercial AC power source. Of A
The present invention relates to an imaging device that performs WB.

[0002]

2. Description of the Related Art Conventional electronic image pickup devices (hereinafter referred to as "cameras") are equipped with an automatic electronic shutter, an automatic gain control, and Various automatic control means such as auto focus, auto flicker reduction, and AWB are adopted. Further, as these control means become smaller and lighter, the shooting environment of the camera expands so that the camera can be used both indoors and outdoors. Adaptive automatic control is required.

The AWB in these automatic control means needs to be controlled so as to follow the color temperature representing the energy distribution of visible light. This color temperature is generally expressed in Kelvin (K). The smaller the value, the more "red", and the larger the value, the more "blue". For example, the light of "candle" is about 1,500
K, fluorescent lamp is about 4,100K, blue sky is about 10,000K
However, it is about 3,500K to 6,000 for human eyes.
The subject can be recognized as white in conformity with the color temperature of K. However, a white subject may become “red” or “blue” depending on the color temperature due to the spectral characteristics of the color filters of the camera. Therefore, as shown in FIG. 4, a specific range on the white locus in the color temperature is set (the range indicated by the dotted line in the figure), and the color indicating the color temperature in that range is “white”. The white balance is adjusted by letting you judge that there is.

Next, A which has been concretely practiced in the past
An example of WB will be described with reference to FIG. A video signal which is picked up by the image pickup element 51 and photoelectrically changed is sampled by the sample hold circuit 52 and separated into a luminance signal component (Y) and a color signal component (C). The luminance signal component (Y) is signal-processed by the luminance signal processing means 53 and applied to the encoder 54. The color signal component (C) separated by the sample and hold circuit 52 is separated by the color signal separation circuit 55 into primary color signal components of red (R), green (G), and blue (B), among which red The (R) signal component and the blue (B) signal component are applied to the white balance control means 56 and 57, respectively, and the outputs of the white balance control means 56 and 57 are applied to the color signal processing means 58. The green (G) signal component from the color signal separation circuit 55 is directly applied to the color signal processing means 58. This color signal processing means 5
The red (R), green (G), and blue (B) signals are processed at 8 and a predetermined color signal is supplied to the encoder 54. The output of the luminance signal processing means 53 is applied to the white balance detecting means 59, and the white balance detecting means 59 processes the RY signal and the BY signal obtained by being processed by the color signal processing means 58. Is being applied. The degree of deviation from white is measured by measuring a red (R) component and a blue (B) component from the RY and BY by using a counter (not shown). The signal processed by the white balance detecting means 59 is sent to the microcomputer 60.
To the red (R) signal component and blue (B)
The control data signal for controlling the gain of the signal component is the white balance control means 56 for the red (R) signal component.
And a color signal processing means 58 (dotted line) for inputting to the white balance control means 57 for the blue (B) signal component, a white balance detection means 59, a microcomputer 60, and white balance control means 56, 57 form a loop,
The color signal is being corrected. The control data signal from the microcomputer 60 is also input to the white balance detecting means 59 (dotted line) and used as a detection level feedback signal.

The detailed structure of the white balance detecting means 59 described with reference to FIG. 5 will be described with reference to FIG. The luminance signal (Y) from the luminance signal processing means 53 and the RY and BY signals from the color signal processing means 58 are input to the gate pulse generation circuit 61, and the RY signal is a logical product. The BY signal is input to the circuit 62 and is input to the AND circuit 63. In the gate pulse generation circuit 61, a pulse in the range for detecting white as shown by the dotted line in FIG. 4 is generated, this pulse is supplied to the microcomputer 60 via the multiplier 64, and the logical product is obtained. Circuits 62 and 6
It is also input to 3. The logical product circuits 62 and 63 obtain a logical product from the RY and BY signals and the pulse from the gate path generation circuit 61, and the logical product is white information and is output as micro information via multipliers 65 and 66. Computer 60
Is taken into. The microcomputer 60 calculates red (R) and blue (B) gains from the pulse and each information of RY and BY, and controls them by the white balance control means 56 and 57 and the white balance detection means 59. It is supplied as data.

[0006]

In the conventional automatic white balance adjustment of a camera, when the white detection range (dotted line) shown in FIG. 4 is enlarged, there is an advantage that the tracking range of the color temperature is widened. There was a problem that the subject was mistakenly judged to be white (other than white). Also, if the white detection range (dotted line) is made smaller, the color temperature tracking range becomes narrower, and the error of judging a colored (non-white) subject as white is reduced, but the color temperature tracking range becomes narrower.
There was a problem in practice. In particular, the setting of the white detection range due to the difference in the light source and the illumination between the outdoors and the indoors has been a major issue for camera manufacturers.

[0007]

According to the present invention, in auto white balance adjustment of a video camera, if it is possible to determine that the temperature is below a specific color temperature even if the color temperature range for white detection is increased, the white detection range is reduced. Focusing on the point that good color reproducibility is possible, the white detection range is centered on the color temperature of the fluorescent lamp, especially using the flicker phenomenon that occurs under indoor fluorescent lamp illumination. The flicker detection means that is caused by the difference between the frequency due to the illumination of the fluorescent lamp that is lit by the commercial power supply (AC) of the luminance signal component of the video signal captured by the image sensor and the field frequency of the image sensor. A means for storing a luminance signal component of a predetermined number of fields detected by the flicker detecting means, and an average of the luminance signal components of the predetermined number of fields. Whitening range based on the information compared by the leveling means, the comparing means for comparing the luminance signal component of each of the predetermined fields with the luminance signal component averaged by the averaging means, A white detection range data generating means for generating data, and an image pickup apparatus for controlling the white balance detecting and adjusting means with the data generated by the white detection range data generating means.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the electronic image pickup device (camera) is often used both indoors and outdoors. Especially when used indoors, there are cases where fluorescent lighting is used. The color temperature of the fluorescent lamp is about 4,100K as described above. The present invention detects that it is under this fluorescent lamp, and by setting the white range to the color temperature of the fluorescent lamp, the white detection range can be reduced to a specific range, and good control of color reproducibility is possible. It focuses on. For example, when a photograph is taken under a fluorescent lamp that is lit by a commercial power source of 50 Hz, a flicker phenomenon occurs due to a difference between the blinking frequency of the fluorescent lamp and the video field frequency of an NTSC camera. The inventor has noticed that the use of this flicker phenomenon can be used to perform white adjustment (white balance) of the camera by recognizing that the image is taken under illumination by a fluorescent lamp indoors.

The flicker phenomenon is caused, for example, by taking a picture under a fluorescent lamp which is lit at a commercial power frequency of 50 Hz.
Fluorescent lamp blinks 100 times / Sec, whereas NTS
Since the field frequency of the C-type camera is 60 times / Sec (one screen in two fields), this light and dark interfere and feel as a flicker. In particular,
As shown in FIG. 1, the fluorescent lamp is 50 Hz /
When the light is turned on with a commercial power source having a Sec frequency, the light is turned on at the positive and negative of the frequency.
Blinking with / Sec. On the other hand, as shown in FIG. 1B, the camera is configured such that the video field frequency of the television receiver is 60 Hz / Sec (in the case of NTSC system), and the video camera has one field image every 16.66 mSec. Become. The brightness, which is the lightness and darkness of the image for each field of the camera, differs as shown in FIG. 1C, for example, and this is perceived by human eyes as flicker. This flicker is because the start of blinking of the fluorescent lamp and the start of the video field of the video camera are the same for every three fields of the video signal. It occurs and appears as a flicker of 3 fields (about 20 Hz) when the captured image is reproduced.

The present invention will be described in detail with reference to FIG. In the description, those having the same functions as those of the above-described conventional auto white balance having the same functions as those in FIG. A video signal captured by the image sensor 51 is processed by a brightness signal processing means 53 through a sample hold circuit 52 to process a brightness signal component (Y) in the video signal, and the brightness signal is processed by an encoder 54 and a white balance detecting means. Although applied to 59, the output of the brightness signal processing means 53 is applied to the flicker detection means 11. The flicker detecting means 11 detects the flicker caused by the change in the brightness generated for each of the three video fields, and outputs it to the microcomputer 60. The microcomputer 60 generates data of the white detection range by the illumination of the fluorescent lamp based on the flicker that has been taken in and supplies it to the white balance adjusting means 56 and 57 so that the white detection range becomes normal. The range (range determined from the outdoor white temperature range) is switched to the white detection range centered on the white temperature of the fluorescent lamp.

Next, the structure of the flicker detecting means 11 will be described with reference to FIG. The output from the luminance signal processing means 53 is applied to the integrating circuit 12. This integration circuit 1
2 has a time constant sufficiently shorter than the one video field period (about 60 Hz) described above. The signal for each video field integrated by the integration circuit 12 is passed through the switch 13 to the three memories 14a of the memory 14,
14b and 14c are stored for each video field.
Further, the output of the switch 13 is input to the averaging circuit 15 for each of the three video field signals.

The output of the memory 14 is the switch 16
Is input to the comparison circuit 17 and the output of the averaging circuit 15 is also input to the comparison circuit 17. The switch 13 is switched by the vertical synchronizing signal (V, Sync) for switching the video field to output the luminance signal of the first field in FIG. 1 to the memory 14a and also to the averaging circuit 15. The switch 13 is switched so that the luminance signal of the second field is output to the memory 14b and the averaging circuit by the next vertical synchronization signal (V, Sync), and is changed to the third by the next vertical synchronization signal (V, Sync). The switch 13 is controlled so as to output the luminance signal of the second field to the memory 14c and the averaging circuit 15. Switch 1
6 is a vertical synchronizing signal (V, S) similar to the switch 13.
sync) to switch each memory 14a, 14b, 14
Switching is controlled so that the luminance signals of the first to third fields stored in c are sequentially output to the comparison circuit 17. The comparison circuit 17 compares the integrated value for each field stored in the memory 14 with the average value of the luminance signals of the three fields in the averaging circuit 15 to obtain the difference. The signal of the difference obtained by the comparison circuit 17 is fetched as data into the microcomputer 60 of FIG. 2, and the minimum and maximum values (min
/ Max) ratio, and the occurrence of flicker is detected using the ratio. When flicker occurs, the fluctuation of the brightness of the cycle of the above three fields occurs, so the ratio of the minimum value and the maximum value of the brightness signal is smaller than 1 (ratio <1), and a certain constant value. Will approach. After detection is performed a plurality of times, the occurrence of flicker is recognized with this value (identified as an image picked up under a fluorescent lamp), and data preset in the microcomputer 60 is extracted. By applying to the white balance control means 56 and 57, the white detection range is corrected to the white detection range centered on the color temperature of the fluorescent lamp, and the indoor white adjustment (auto white balance) can be easily performed. It is a thing. It should be noted that images taken outdoors do not show periodic flicker due to such a brightness change in each field,
The luminance signals of the three video fields detected by the flicker detection circuit 11 and integrated by the integration circuit 12 and the averaging circuit 15
Since the ratio with the luminance signal of the video field averaged by 1 is 1, it is possible to control the automatic white balance in the state of the predetermined white detection range.

In the above description, the video field frequency is 60 Hz / Sec and the commercial power supply frequency is 50 Hz / Sc.
Although the case of e is used, for example, when the video field frequency of the PAL (PAL) and SECAM (SECAM) system of color television broadcasting is 50 Hz / Sec and the commercial power supply frequency is 60 Hz / Sec, every 5 video fields. Flicker occurs. In this case, by providing five memories so as to store the memory 14 shown in FIG. 3 in accordance with the luminance signals of the five video fields,
Obviously, the same automatic white balance adjustment is possible. Furthermore, it is obvious that the present invention can be modified in many ways without departing from the spirit of the invention.

[0014]

As described above, the present invention detects flicker caused by the difference between the video field frequency of the camera and the commercial power supply frequency for lighting the illumination, and adjusts the white balance based on the flicker ratio. By correcting the white detection range of the object to a range centered on the white temperature of the lighting, it eliminates the risk of erroneously determining a subject with colors other than white under indoor lighting as white, and It is possible to provide an imaging device that has excellent color reproducibility due to white balance and that enables white balance adjustment in a short time.

[Brief description of drawings]

FIG. 1 is a waveform diagram showing a blinking frequency of a fluorescent lamp or the like used for automatic white balance adjustment of an image pickup apparatus of the present invention, a video field frequency of a camera, and a change in luminance for each video field of a video camera.

FIG. 2 is a block diagram showing a configuration of automatic white balance adjustment used in the image pickup apparatus of the present invention.

FIG. 3 is a circuit configuration diagram of a flicker detection unit used for automatic white balance adjustment of the image pickup apparatus of the present invention.

FIG. 4 is a graph showing a color temperature in a white detection range of a camera.

FIG. 5 is a block diagram showing a configuration of automatic white balance adjustment of a conventional image pickup apparatus.

FIG. 6 is a block diagram showing a detailed configuration of automatic white balance adjustment of a conventional image pickup apparatus.

[Explanation of symbols]

 11 ... Flicker detecting means 12 ... Integrating circuit 13 ... Switch 14 ... Memory 15 ... Averaging circuit 16 ... Switch 17 ... Comparison circuit 53 ... Luminance signal processing means 56, 57 ... White balance control means 60 ... Microcomputer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuo Sakurai 3-3-9 Shimbashi, Minato-ku, Tokyo Toshiba Abu E. Co., Ltd. (72) Inventor Masayoshi Sato 3-3 Shinbashi, Minato-ku, Tokyo No. 9 Toshiba Abu E Co., Ltd.

Claims (4)

[Claims] 1. Illumination light lit at a first frequency, an imaging device for converting an image illuminated by the illumination light into a video signal of a second field frequency, and a color component and a luminance component from the video signal. A circuit for generating the color component, a white balance control unit having a white detection range setting unit to which the color component is input, and a white balance detection unit for detecting a deviation from white based on the color component output from the white balance control unit. A signal based on the detected deviation from the white color is fed back, and the white balance control means for correcting the color component output according to this signal; and the first frequency and the second frequency from the luminance component. Flicker detection means for detecting flicker due to frequency resonance and outputting a flicker detection signal, and a white detection range according to the flicker detection signal. Imaging apparatus being characterized in that a said white balance control means being set. 2. Illumination light turned on at a first frequency, an image pickup device for converting an image illuminated by the illumination light into a video signal of a second field frequency, and a color component and a luminance component from the video signal. A circuit for generating, a circuit for generating a three-primary-color signal from the color components, at least two colors of the three-primary-color signals are respectively input, and a plurality of white balance control means each having a white-detection range setting means, White balance detection means for detecting deviation from white based on the primary color signals respectively output from the plurality of white balance control means, and a signal based on the detected deviation from white color is fed back and output according to this signal. The white balance control means for correcting at least two of the three primary colors; and the first frequency from the luminance component. A flicker detection unit that detects flicker due to resonance of the second frequency and outputs a flicker detection signal, and a plurality of white balance control units that set a white detection range according to the flicker detection signal are provided. An imaging device characterized by the above. 3. A flicker detecting means for storing each luminance signal for each field of the number of fields of the video signal in the resonance cycle of the flicker, and the flicker detecting means for storing each field, and the luminance signal stored for each field. The image pickup apparatus according to claim 1 or 2, further comprising: a calculation unit that compares the values, and a white balance control unit that sets a white detection range based on the comparison result. 4. The image pickup apparatus according to claim 3, wherein the flicker detection and the calculation are performed a plurality of times.