JP2006050031A - Imaging device - Google Patents

Abstract

【Task】
To obtain high-quality still images by suppressing fluctuations in video signals during still image shooting.
[Solution]
In order to solve the above-mentioned problem, operation is performed in a monitoring mode in which continuous shooting is performed before a still image shooting mode in which still image shooting is performed, and a change in the video signal is detected in the monitoring mode, and a still image is detected based on the detected change The fluctuation of the video signal in the shooting mode is predicted, and the fluctuation of the video signal in the predicted still image mode is suppressed. As described above, according to the present invention, it is possible to suppress the fluctuation of the video signal in the still image mode, so that a high-quality still image can be obtained.
[Selection] Figure 1

Description

  The present invention relates to a photographing apparatus that photographs a moving image and a still image using an image sensor.

  As background art in this technical field, for example, there is JP-A-2003-134392 (Patent Document 1). The publication describes that “the present invention relates to an imaging device and a method for controlling the imaging device, and is applied to, for example, a television camera so that flicker can be reliably prevented”. . Further, as a solution, “the present invention obtains a predicted value of the incident light amount when detecting the luminance level DY of the imaging result and prevents flicker by feedback control, and determines the gain of the amplifier circuit 6 based on this predicted value. It also describes that a signal component based on a flicker cycle is extracted from the luminance level, and the signal level of the imaging result is corrected by the signal level of this signal component.

JP 2003-134392 A

  It is well known that the image quality of so-called movie cameras has improved due to the advancement of imaging devices and signal processing technologies. For example, fluorescent lamp flicker under fluorescent lamp illumination is suppressed during movie shooting (for example, Patent Document 1 above). ). On the other hand, when shooting and recording still images with a so-called digital still camera, the change was recorded as it was, even though the change in the video signal due to the change in illuminance occurred under the fluorescent lamp illumination. There has been a problem that the image quality of the photographed image is significantly deteriorated.

  An object of the present invention is to obtain a high-quality still image.

  In order to solve the above-mentioned problem, operation is performed in a monitoring mode in which continuous shooting is performed before a still image shooting mode in which still image shooting is performed, and a change in the video signal is detected in the monitoring mode, and a still image is detected based on the detected change. The fluctuation of the video signal in the shooting mode is predicted, and the fluctuation of the video signal in the predicted still image mode is suppressed.

  According to the present invention, a high-quality still image can be obtained.

  Hereinafter, the present invention will be described using examples.

FIG. 1 shows a configuration example of a photographing apparatus of the present invention. In the figure, 1 is an aperture, 2 is an image sensor, 3 is a pre-signal processing unit, 4 is a gain variable unit, 5 is a signal processing unit, 6 is a detection unit, 7 is a control unit, 8 is a driver, and 9 is a drive unit. It is. Although the amplification unit 5 and the signal processing unit 6 are illustrated as separate blocks in the figure, the amplification unit 5 and the signal processing unit 6 may be integrated. An image of a subject (not shown) under a certain illumination is formed on an image sensor 2 through an optical system (not shown) and a diaphragm 1, and the formed subject image is formed by the image sensor 2 with a predetermined exposure time. Only the photoelectric conversion is performed and read out, and the pre-signal processing unit 3 outputs it as a photographing signal. The photographic signal is processed by the variable gain 4 and the signal processing unit 5 and output as a video signal such as an RGB signal or a YC signal, or is encoded by an encoding unit (not shown) and is recorded (not shown). To be recorded. On the other hand, the detection unit 6 detects the imaging signal to detect the signal amount, and based on the detected signal amount, the control unit 7 performs at least one of the following controls (1) to (3). Do. That is,
(1) Control the signal gain of the gain variable section 4.
(2) The driver 8 is controlled to control the aperture value of the aperture 1. Alternatively, FIG. 1 shows an example in which the diaphragm 1 is used, but liquid crystal may be used in place of the diaphragm 1 to control the transmittance of the liquid crystal.
(3) The drive unit 9 is controlled to control the exposure time or exposure timing of the image sensor 1.

  FIG. 2 shows an embodiment of the operation. As operation modes, there are moving image shooting and still image shooting, and a still image shooting preparation mode for preparing for still image shooting is arranged between the two shooting modes. Hereinafter, the moving image shooting mode is referred to as a monitoring mode. In the monitoring mode, the drive unit 9 drives the image sensor 1 based on the control of the control unit 7, detects the imaging signal continuously output by the video drive by the detection unit 6, and based on the detection result. In addition, the control unit 7 detects the brightness variation of the video signal, that is, the phase or amount of the brightness variation. In the still image shooting preparation mode, the control unit 7 estimates the phase or amount of luminance fluctuation that occurs in the still image shooting mode. Further, in the still image shooting mode, the control unit 7 controls the aperture value of the diaphragm 1 or the exposure time of the image sensor 1 based on the estimated luminance variation phase or luminance variation amount to control the exposure amount of the still image, Alternatively, the signal gain of the gain variable unit 4 is controlled.

  FIG. 3 shows an example of exposure amount control and signal gain control. In the figure, an example is shown in which an image pickup device in which the exposure times of two-dimensionally arranged pixel groups are almost uniform, such as a well-known CCD type image pickup device, is used as the image pickup device 1. In addition, as an example of the illumination condition, a video signal having a field period of 60 Hz is generated by fluorescent lamp (100 Hz blinking period) illumination using a commercial power supply of 50 Hz. As an example of the exposure time Tzm in the monitoring mode, two cases of Tzm (1) in the case of 1/60 second equal to the field period and Tzm (2) in 1/100 second are shown. The shooting signal level in the case of is shown by Sm (1) and Sm (2). Strictly speaking, there is a time delay of one field period between the exposure timing and the signal output timing. However, for the sake of easy understanding, FIG. 3 shows the exposure timing and the signal output timing in coincidence. When the exposure time is Tzm (1), the photographic signal level fluctuates at the least common multiple of 1/20 second of the illuminance change period 1/100 second and the field period 1/60 second. That is, it fluctuates so that the signal level a, the signal level b, and the signal level c are repeated with a three field period as one period. In this case, if the timing of the still image shooting mode is the timing shown in FIG. 3, it can be estimated that the shooting signal level Ss (1) of the still image becomes the signal level b by the exposure time Tzs (1). Here, the period of the still image shooting mode is set longer, but this is because it is assumed that more pixel signals are read out in the still image shooting mode than in the monitoring mode, and the same number in both modes. When the pixel signal is read out, it is not necessary to lengthen the period of the still image shooting mode. Further, during the period of reading out the pixel signal, the aperture 1 is closed or the mechanical shutter (not shown) is closed so that the still image exposure period becomes a period as shown in FIG. On the other hand, when the exposure time is Tzm (2), the illuminance change period coincides, so the shooting signal level Sm (2) is a constant value d, and the signal level is the exposure time Tzs (2) even in the still image shooting mode. Ss (2) can be estimated as the signal level d.

  When the signal level b is lower than the desired signal level e, the shadow portion of the subject is crushed, or when the signal level b is higher than the desired signal level e, the bright portion of the subject is overexposed. The image quality is significantly impaired.

  If the signal gain G (3) of the gain variable section 4 in the monitoring mode is set to Ga, Gb, Gc as shown in FIG. 3 and the video signal level So (3) is set to the level e, the signal level is set in the still image shooting mode. Since b can be estimated as b, by setting the signal gain G (3) of the gain variable section 4 to Gb, the signal level in the still image shooting mode can be set to the desired level e.

  Further, the exposure time Tzs (3) in the still image shooting mode may be α times (α = e / b) the exposure time Tzm (1) in the monitoring mode. In this case, since the dynamic range of the image sensor 1 can be used effectively, an image with a good SN ratio can be obtained.

  Further, if the aperture value F (3) of the aperture 1 is Fm in the monitoring mode, the aperture value Fs = βFm (β = (e / b) 1/2) in the still image shooting mode. Also good. In this case, since the dynamic range of the image sensor 1 can be used effectively, an image with a good SN ratio can be obtained. Instead of the diaphragm 1, a liquid crystal capable of controlling the transmittance may be used, and the transmittance may be controlled similarly.

  FIG. 4 shows another example of exposure amount control and signal gain control. In the figure, an example in which an image sensor in which the exposure time of a two-dimensionally arranged pixel group is sequentially different in units of pixels is used as the image sensor 1 as in a known CMOS image sensor. Show. In addition, as an example of the illumination condition, a video signal having a field period of 60 Hz is generated by fluorescent lamp (100 Hz blinking period) illumination using a commercial power supply of 50 Hz. As an example of the exposure time Tzm in the monitoring mode, two cases of Tzm (1) in the case of 1/60 second equal to the field period and Tzm (2) in 1/100 second are shown. The shooting signal level in the case of is shown by Sm (1) and Sm (2). Strictly speaking, although there is a time delay of one field period between the exposure timing and the signal output timing, in order to make it easy to understand, in FIG. 4, the exposure timing and the signal output timing are shown to be coincident. When the exposure time is Tzm (1), different periods of illuminance that change with a period of 1/100 seconds are integrated in each pixel, so the minimum of the illuminance change period of 1/100 seconds and the field period of 1/60 seconds is minimum. Taking the common multiple of 1/20 second as a unit, the photographing signal level fluctuates five times within the unit. That is, the signal level fluctuates so as to have 5 peaks and valleys, with 3 field periods as one period. In this case, if it is detected that the change in the shooting signal level in the monitoring mode is as shown in FIG. 4, the change in the shooting signal level when the subsequent shooting is performed is as indicated by the broken line in FIG. 4Sm (1). It can be estimated that Therefore, if the timing of the still image shooting mode is the timing shown in FIG. 4, it can be estimated that the shooting signal level Ss (1) of the still image is as shown in FIG. Here, the period of the still image shooting mode is set longer, but this is because it is assumed that more pixel signals are read out in the still image shooting mode than in the monitoring mode, and the same number in both modes. When the pixel signal is read out, it is not necessary to lengthen the period of the still image shooting mode. On the other hand, when the exposure time is Tzm (2), the illuminance change period coincides, so the shooting signal level Sm (2) is a constant value d, and the signal level is the exposure time Tzs (2) even in the still image shooting mode. Ss (2) can be estimated as the signal level d.

  If the signal level Ss (1) of the still image has peaks and valleys as shown in FIG. 4, the image becomes a still image with horizontal lines in the image, and the image quality is significantly impaired.

  If it can be estimated that the signal level is Ss (1) in the still image shooting mode, the signal gain G (3) of the gain variable section 4 in the still image shooting mode is set as shown in FIG. The signal level in the mode can be set to a desired level e.

  In the monitoring mode, if the signal gain of the gain variable section 4 is controlled as shown in FIG. 4, a constant video signal level can be obtained even in the monitoring mode.

  Further, the aperture value of the diaphragm 1 or the transmittance of a material such as liquid crystal disposed instead of the diaphragm 1 may be controlled as indicated by G (3) in FIG. In this case, since the dynamic range of the image sensor 1 can be used effectively, an image with a good SN ratio can be obtained.

  In the above embodiments, illumination with a blinking period of 100 Hz and a video signal with a field period of 60 Hz are taken as an example. However, even when the blinking period and field period of illumination are different from the above conditions, the above method is used similarly. Obviously you can.

  According to the above embodiment, generally, the illumination condition does not change greatly between the monitoring mode and the still image shooting mode, so that the fluctuation of the video signal in the still image shooting can be suppressed.

  INDUSTRIAL APPLICABILITY The present invention can be used for an imaging device that captures moving images and still images using an image sensor.

Configuration example of the present invention Example of operation of the present invention Timing chart showing operation examples and effects of the present invention Timing chart showing another operation example and effect of the present invention

Explanation of symbols

1 is an aperture, 2 is an image sensor, 3 is a front signal processing unit, 4 is a gain variable unit, 5 is a signal processing unit, 6 is a detection unit, 7 is a control unit, 8 is a driver, and 9 is a driving unit.

Claims (6)

An imaging device that captures videos and still images,
Photographing means for photoelectrically converting a subject image and outputting a photographing signal;
Signal processing means for processing the photographing signal and outputting a video signal;
Control means for controlling the aperture value and exposure time of the photographing means and the signal gain of the signal processing means;
With
The control means detects a change in the shooting signal or video signal during moving image shooting, predicts a change in the shooting signal or video signal during still image shooting based on the detected change, and Controlling one or more of the aperture value and exposure time of the imaging means and the signal gain of the signal processing means to suppress the predicted variation;
An imaging device characterized by the above.   An imaging device having a signal processing unit for processing a video signal output from the imaging device, and having a still image shooting mode for taking a still image and a monitoring mode for performing continuous shooting prior to the still image shooting Detecting a change in the video signal in the monitoring mode, predicting a change in the video signal in the still image shooting mode based on the detected change, and detecting the change in the video signal in the predicted still image mode. An imaging apparatus characterized by suppressing.   In the imaging device, the exposure time of the pixel groups arranged in a two-dimensional manner is substantially uniform, and the variation of the video signal in the predicted still image mode varies in units of scanning planes of the imaging device. The imaging device according to claim 2.   In the image pickup device, the exposure time of a pixel group arranged in a two-dimensional manner differs in units of pixels or in units of a plurality of pixels, and the fluctuation of the video signal in the predicted still image mode is determined by the scanning plane of the image pickup device. The photographing apparatus according to claim 2, wherein the photographing apparatus varies in a smaller unit.   4. The photographing apparatus according to claim 2, wherein the fluctuation of the video signal is suppressed by controlling an exposure time of the image sensor in a still image photographing mode. 6. The photographing apparatus according to claim 2, wherein the fluctuation of the video signal is suppressed by controlling a signal gain of the signal processing unit in a still image photographing mode.

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