JP4313766B2 - Imaging device - Google Patents

Description

  The present invention relates to a photographing apparatus such as a digital camera or a mobile phone with a built-in camera, which includes a release button and performs still image photographing by pressing the release button.

  In recent years, digital cameras for obtaining image data representing a subject imaged on an image pickup device such as a CCD image pickup device have been widely used in place of a conventional type of camera for taking a photograph on a photographic film. Mobile phones incorporating various types of cameras have also become widespread. Here, the description will be continued under the name of a digital camera, generically or representatively.

  In recent years, the sensitivity of digital cameras has increased, and digital cameras compatible with ISO 1600 have become rare. Further, with the progress of noise reduction processing technology year by year, it has become possible to shoot with low noise even if it is equivalent to ISO 1600.

  However, as the sensitivity increases, the linearity of the signal level read from the image sensor with respect to the amount of light irradiated on the image sensor has become a problem.

  FIG. 6 is a diagram illustrating an example of the linearity of the CCD image sensor.

  The horizontal axis in FIG. 6 indicates the amount of light irradiated on the CCD image sensor, and the vertical axis indicates the level of the signal read from the CCD.

  In the case of shooting at a sensitivity equivalent to ISO 200, almost all of the light amount region shown in FIG. 6 is used for shooting. As the sensitivity increases, the amount of light applied to the CCD image sensor decreases and is read from the CCD image sensor. This is dealt with by increasing the gain of the amplifier that amplifies the image signal after being processed.

  Here, the relationship between the amount of light applied to the CCD image sensor in FIG. 6 and the level of the output signal from the CCD image sensor is poor in linearity mainly in a region where the amount of light is small (region indicated by a circle R in FIG. 6). It has become. For this reason, in the case of the low sensitivity setting, the region where the linearity is poor remains in a part of the entire region. However, in the case of the high sensitivity setting, the region where the linearity is poor is mainly used.

Here, in general, the imaging device does not have a sufficient dynamic range, and therefore, as shown in Patent Document 1, photometry is performed in a plurality of times. However, a photometric error becomes large at each photometric connection portion, and eventually the exposure in still image shooting is deviated from the proper exposure.
JP-A-6-130462

  In view of the above circumstances, an object of the present invention is to provide an imaging device that can reduce the influence of the poor linearity of an image sensor on the exposure calculation and can perform still image shooting with high-precision exposure.

The photographing apparatus of the present invention that achieves the above object provides:
Photographing means for providing a release button and taking a still image by pressing the release button;
Photometric means for performing photometry for still images prior to taking a still image;
A sensitivity selection means for selecting the shooting sensitivity,
The photometric means performs photometry over the entire field luminance range by multiple times of photometry that divides each partial luminance range when the predetermined field luminance range is divided into a plurality of partial luminance ranges,
When the predetermined high sensitivity is selected as the shooting sensitivity, the above-mentioned field luminance range is divided into a relatively large number of partial luminance ranges compared to the case where a shooting sensitivity lower than the high sensitivity is selected. Thus, photometry of the entire range of the field luminance range is performed by relatively many times of photometry sharing the partial luminance ranges.

  According to the photographing apparatus of the present invention, when the high sensitivity is set, the object luminance range to be measured is divided into a relatively large number of partial luminance ranges compared to when the low sensitivity is set. Therefore, even when high sensitivity is set, high-precision photometry is performed, and still image shooting is performed with high-precision exposure. Also, instead of dividing the brightness into the same partial luminance range when high sensitivity is set for all sensitivities, metering is performed with dividing into a small number of partial luminance ranges when low sensitivity is set. As a result, the time required for photometry as a whole can be shortened.

  Embodiments of the present invention will be described below.

  FIG. 1 is an external perspective view of a digital camera, which is an embodiment of a photographing apparatus of the present invention, seen from the front and obliquely above.

  A zoom lens barrel 12 having a photographing lens 11 including an optical zoom lens therein is provided at the center of the front surface of the digital camera 10 shown in FIG. Further, a flash light emitting device 13 that emits flash light in synchronization with photographing and an optical viewfinder objective window 14 are provided on the upper front of the digital camera 10.

  A slide-type power switch 15 is provided on the left side of the front surface of the digital camera 10.

  Further, a release button 16 is provided on the upper surface of the digital camera 10.

  FIG. 2 is a block diagram showing a circuit configuration of the digital camera shown in FIG.

  The digital camera 10 includes a zoom lens 21 and a focus lens 22 constituting the photographing lens 11, an iris 23 whose aperture diameter can be adjusted in multiple stages, a photographing lens (the zoom lens 21 and the focus lens 22), and an iris. A CCD image pickup device (hereinafter referred to as “CCD”) 24 that receives an object image formed through the image sensor 23 and generates an analog signal, and the object light incident through the imaging lens and the iris 23. A mechanical shutter 25 for limiting the irradiation time to the CCD 24 is provided.

  The digital camera 10 also includes a timing generator that controls the timing of the electronic shutter of the CCD 24 and the timing of reading of the image signal, an A / D conversion circuit that generates an analog signal read from the CCD 24, and a digital image signal. Read circuit 26, an image input controller 27 for transmitting a digital image signal from the read circuit 26 to the bus line 50, and a digital image signal input via the bus line 50 as luminance (Y) and color. An image signal processing circuit 28 for converting into a YC signal represented by (C) is provided.

  Further, the digital camera 10 includes a compression processing circuit 29 that compresses a YC signal input via the bus line 50, and an NTSC (National TV Standards Committee) signal that converts the YC signal input via the bus line 50. There is provided a video encoder 30 for converting into a video. The NTSC signal output from the video encoder 30 is supplied to a liquid crystal monitor (hereinafter referred to as “LCD”) 31 and an image is displayed on the LCD 31.

  The digital camera 10 includes a CPU 32 that controls the entire digital camera 10, motor drivers 33 to 36 that drive the zoom lens 21, the iris 23, the focus lens 22, and the mechanical shutter 25, respectively, and FIG. Two switches S1 and S2 which are turned on when a release button 16 shown in FIG. One of the two switches S1, S2 is a switch that is turned on when the release button 16 is half-pressed, and the other switch S2 is turned on when the release button 16 is fully pressed. This is a switch. Therefore, hereinafter, the state where the release button 16 is half-pressed may be referred to as “S1 state”, and the state after the release button 16 is fully pressed may be referred to as “S2 state”. A state in which the power of the digital camera 10 is on and the camera is in the shooting mode but the release button 16 has not been pressed may be referred to as an “S0 state”.

  Further, the digital camera 10 includes a timer 37 for measuring various times, an AF detection circuit 38 for detecting a focus position by contrast detection based on a digital image signal, and a field luminance based on the digital image signal. And an AE & AWB detection circuit 39 for detecting white balance, a memory (SDRAM) 40 for temporarily storing digital image signals, and a recording medium 100 which is a portable recording medium for the image signals compressed by the compression processing circuit 29 A media controller 41 for recording is provided.

  Further, the digital camera 10 has a photographing mode for photographing in response to pressing of the release button 16 and a reproduction mode for reading a photographed image recorded on the recording medium 100 from the recording medium 100 and displaying it on the liquid crystal monitor 31. , A switch group 42 including various switches for switching various modes and sensitivities in the shooting mode, extending the zoom lens, and the like, the power switch 15 shown in FIG. A power supply circuit 43 that is controlled by turning off / off and supplies power to each part, a battery 44 as a power source that supplies power to the power supply circuit 43, and a flash light emitting device 13 that also emits flash in synchronization with photographing, as shown in FIG. Is provided.

  FIG. 3 is a diagram showing a general photographing sequence of the digital camera shown in FIGS. 1 and 2.

  When the power is turned on (ON), the taking lens is extended and the LCD 31 (see FIG. 2) is turned on. Thereafter, a through image that is a moving image for display is displayed on the LCD 31. Thereafter, when the release button is pressed halfway to shift to the S1 state, photometry (AE) and focus position detection (AF) are performed for determining still image exposure. The screen is displayed. In this state, when the release button is fully pressed (S2 state), the timing clock supplied to the CCD 24 by the readout circuit 26 in the block diagram shown in FIG. 2 is changed to a timing clock for still images. Exposure is performed, exposure is performed immediately after completion of exposure preparation, an image signal is read out from the CCD 24, and the timing clock supplied to the CCD 24 is changed to a timing clock for a through image after the reading is completed. Preparation for through image display is made, and then the release button for the next shooting can be pressed.

  In the still image AE of the still images AE and AF shown in FIG. 3, photometry for the still image is performed as follows.

  FIG. 4 is a diagram showing a normal photometric diagram used in the digital camera of the present embodiment.

  In the digital camera of the present embodiment, the sensitivity can be set to any one of ISO100, ISO200, ISO400, ISO800, and ISO1600. FIG. 4 shows any sensitivity within the range of ISO100 to ISO800 excluding ISO1600. FIG. 7 is a photometric diagram that is employed when is set.

  Here, the field luminance range of EV3 to EV18 is measured in three steps as shown by (1), (2), and (3) in FIG.

  In (1), exposure is performed by adjusting the iris aperture diameter, the shutter speed of the electronic shutter, and the like so that the EV8 has a proper exposure, and each of the fields when the object field is divided into a plurality of (for example, 128) regions. Photometry is performed for the area within the partial luminance range of EV3 to EV9.5 of the area. In (2), the iris aperture diameter, the shutter speed of the electronic shutter, and the like are adjusted so that the EV12 has proper exposure. Exposure is performed, and photometry is performed on a region within the partial luminance range of EV 9.5 to EV 13.5. In (3), the iris aperture diameter, the shutter speed of the electronic shutter, etc. are set so that the EV 16 has proper exposure. Is adjusted and exposure is performed, and photometry is performed on an area within the partial luminance range of EV13.5 to EV18. Thereby, photometry is performed for the entire field luminance range EV3 to EV18. In this way, photometry is performed over a wide luminance range by sharing three times, and AE calculation for still images is performed based on the photometry results for these three, and the exposure during still image shooting is determined. The Here, photometry is performed in a range of EV3 to EV18, but exposure is adjusted in a range of EV4 to EV17.

  As shown in FIG. 4, as a result of the photometry performed by sharing the partial luminance ranges, there is a problem as to whether or not the shared photometric connection portions are well connected. In the case of the digital camera of this embodiment, there is almost no problem in ISO 100 to ISO 800, but if the photometric diagram of FIG. 4 is applied to ISO 1600 as it is, the linearity with reference to FIG. For a certain area, the photometry in (1) is determined to be overexposed (better than EV 9.5), and the photometry in that area is left to the photometry in (2). In the photometry in (2), The same area is determined to be an exposure under (darker than EV 9.5), so that correct photometry of the area may not be performed, and exposure determination for still image shooting may not be performed accurately. .

  FIG. 5 is a photometric diagram at the time of high sensitivity employed in the digital camera of the present embodiment.

  This photometric diagram is a photometric diagram adopted when ISO 1600 is set. Here, the range of EV3 to EV18 is divided into four times and the photometry is performed.

  That is, in (1), when the exposure is performed by adjusting the iris aperture diameter, the shutter speed of the electronic shutter, etc. so as to achieve proper exposure in EV7, the field is divided into a plurality of (for example, 128) areas. Photometry is performed for the area within the partial luminance range of EV3 to EV8.5, and in (2), the iris aperture diameter, the shutter speed of the electronic shutter, and the like are adjusted so that the EV10 can be properly exposed. Then, exposure is performed, and photometry is performed on a region within the partial luminance range of EV 8.5 to EV 11.5. In (3), the iris aperture diameter and shutter of the electronic shutter are adjusted so that EV 13 can achieve proper exposure. Exposure is performed with the speed and the like adjusted, and photometry is performed for an area within the partial luminance range of EV11.5 to EV14.5. In (4), Shutter speed, etc. of the iris diaphragm diameter and an electronic shutter so that proper exposure is performed is adjusted exposure at V16, photometry is performed for the area inside portion luminance range of EV14.5～EV18. By performing the photometry four times, photometry is performed for the entire field luminance range EV3 to EV18.

  In this way, photometry is performed over a wide range of brightness divided over four times, and AE calculation for still images is performed based on the photometry results for these four times, and the exposure during still image shooting is determined. .

  As described with reference to FIG. 6, ISO 1600 uses a region with poor linearity, but here, as shown in FIG. 5, the photometry is divided into four times, so that one photometry is shared. The partial luminance range to be used can be narrow, and the occurrence of contradictions in the photometric results of the photometry sharing the adjacent partial luminance ranges described above can be sufficiently reduced, and high-precision exposure calculation for still images can be performed. Done.

  Here, the photometric chart shown in FIG. 4 is adopted for ISO 100 to ISO 800, and the photometric chart shown in FIG. 5 is adopted only for ISO 1600, but the photometric chart shown in FIG. For ISO ISO and ISO 1600, ISO 800 and ISO 1600 may employ a photometric diagram as shown in FIG.

  In addition, here, the photometry is divided into four times for high sensitivity, and the photometry is divided into three times when the sensitivity is lower than that. However, this is only an example, and the entire field luminance range to be measured is measured. Depending on the size of the image sensor, the degree of linearity of the image sensor, etc., photometry may be performed by sharing the number of times different from the example shown here.

  Although the digital camera having the appearance shown in FIG. 1 has been described here, the present invention is not only applied to a photographing apparatus having an appearance as a “camera”, but is also applied to, for example, a camera with a built-in mobile phone. can do.

It is the external appearance perspective view which looked at the digital camera which is one Embodiment of the imaging device of this invention from the front diagonally upward. It is a block diagram which shows the circuit structure of the digital camera shown in FIG. It is a figure which shows the general imaging | photography sequence of the digital camera shown in FIG. 1, FIG. It is a figure which shows the normal photometry figure currently used with the digital camera of this embodiment. It is a photometric diagram at the time of high sensitivity employed in the digital camera of the present embodiment. It is the figure which showed an example of the linearity of a CCD image pick-up element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Digital camera 11 Shooting lens 12 Zoom lens barrel 13 Flash light-emitting device 14 Optical viewfinder objective window 15 Power switch 16 Shutter button 21 Zoom lens 22 Focus lens 23 Iris 24 CCD
25 Mechanical shutter 26 Reading circuit 27 Image input controller 28 Image signal processing circuit 29 Compression processing circuit 30 Video encoder 31 LCD
32 CPU
33, 34, 35, 36 Motor driver 37 Timer 38 AF detection circuit 39 Detection circuit 40 Memory (SDRAM)
41 Media Controller 42 Switch Group 50 Bus 100 Recording Media

Claims (1)

A photographing means having a release button for taking a still image by pressing the release button;
Photometric means for performing photometry for still images prior to taking a still image;
A sensitivity selection means for selecting the shooting sensitivity,
The photometry means performs photometry over the entire field luminance range by a plurality of times of photometry sharing each partial luminance range when the predetermined field luminance range is divided into a plurality of partial luminance ranges,
When a predetermined high sensitivity is selected as the shooting sensitivity, the field luminance range is divided into a relatively large number of partial luminance ranges compared to a case where a shooting sensitivity lower than the high sensitivity is selected. An imaging device characterized in that photometry is performed over the entire field luminance range by relatively many times of photometry sharing each partial luminance range.

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