JP5804693B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus that performs imaging using flash assist light.

  In a conventional imaging device, when shooting a subject image using flash auxiliary light, so-called pre-flash is performed before shooting in order to determine the flash emission amount at the time of shooting, and the reflected light from the subject at the time of pre-flash Many systems are used to determine the amount of light emitted during photo shooting.

  In the electronic still camera described in Patent Document 1, the reflected light from the subject at the time of pre-emission is measured by a photometric element different from the image sensor, and an appropriate light emission amount is determined using the value. In the imaging apparatus described in Patent Document 2, reflected light from a subject at the time of pre-emission that has passed through a photographing lens is received by an imaging element, and an appropriate light emission amount is determined using the output of the imaging element. If the subject is at a short distance during pre-flash and the output of the image sensor exceeds a predetermined value, the pre-emission is performed again by reducing the aperture of the photographic lens, and the light emission amount is determined from the output of the appropriate image sensor. Yes.

JP 200387652 A Japanese Patent Laid-Open No. 2001-21961

  However, in the electronic still camera described in Patent Document 1 described above, since the photometric element is provided separately from the imaging element for photographing the subject image, the mechanism becomes complicated and the cost increases. In addition, in a system that performs predetermined processing on the output of the image sensor and displays it on a display to perform framing, a photometric optical system that is different from the imaging optical system must be provided, which further increases the complexity and cost of the mechanism. Invite up. Further, a photometric error due to parallax between the imaging optical system and the photometric optical system occurs.

  In addition, since the image pickup apparatus described in Patent Document 2 performs photometry at the time of pre-emission using an image pickup element, the problems caused in Patent Document 1 are avoided. However, depending on the shooting conditions, since the aperture value is changed and multiple pre-flashes are required, the shutter time lag is increased.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to make it possible to appropriately determine the amount of light emitted at the time of main light emission by one pre-light emission without causing a complicated mechanism. It is.

An image pickup apparatus according to the present invention is an image pickup element for converting a subject image formed by a photographing optical system into an electric signal, and includes a normal sensitivity pixel for image acquisition having a predetermined sensitivity, and the normal sensitivity pixel. And an image sensor having low-sensitivity pixels for photometry that are not used for image acquisition, which are discretely arranged between them and have a smaller aperture and lower sensitivity than the normal sensitivity pixels, and an object using a strobe auxiliary light device When shooting, the strobe auxiliary light device is pre-flashed before the main shooting, and the strobe assist in the main shooting is based on the result of converting the reflected light from the subject into an electrical signal by the image sensor. Control means for controlling the amount of light emitted from the optical device, and the control means, when the strobe auxiliary light device is pre-lighted, when the signal level of the normal sensitivity pixel is equal to or lower than a predetermined level. The amount of light emitted by the strobe auxiliary light device in the main photographing is controlled based on the signal of the normal sensitivity pixel, and when the level of the signal of the normal sensitivity pixel exceeds the predetermined level, the low sensitivity pixel The light emission amount of the strobe auxiliary light device in the main photographing is controlled based on a signal obtained by multiplying a signal by a coefficient that compensates a sensitivity ratio with the normal sensitivity pixel.

  According to the present invention, it is possible to appropriately determine the amount of light emitted at the time of the main light emission by one pre-light emission without causing a complicated mechanism.

1 is a block diagram showing a configuration of an imaging apparatus according to a first embodiment of the present invention. FIG. 3 is a diagram illustrating an arrangement of pixels of the image sensor according to the first embodiment. The figure which shows the saturation characteristic of a normal sensitivity pixel and a low sensitivity pixel. 6 is a flowchart showing the pre-light emission operation of the first embodiment. 6 is a flowchart illustrating an image evaluation operation according to the first embodiment. The figure which shows the saturation characteristic of a normal sensitivity pixel and a low sensitivity pixel. The block diagram which shows the structure of the imaging device concerning the 2nd Embodiment of this invention. The figure which shows arrangement | positioning of the pixel of the image pick-up element of 2nd Embodiment. The top view and sectional drawing of the pixel for an imaging of the image pick-up element of 2nd Embodiment. The top view and sectional drawing of the focus detection pixel of the image sensor of 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a block diagram showing a configuration of an imaging apparatus according to the first embodiment of the present invention. In FIG. 1, 101 is a lens, 102 is a diaphragm built in the lens 101, 103 is an image sensor such as a CMOS sensor, 104 is a signal processing circuit, 105 is a control device, and 106 is a shutter button. 107 is a liquid crystal display device such as a TFT, 108 is a removable memory card, and 109 is a strobe auxiliary light device.

  Hereinafter, the operation of the imaging apparatus configured as described above will be described.

  In the present embodiment, the strobe auxiliary light device 109 emits light with a predetermined light amount during pre-flash of the strobe, and reflected light from a subject (not shown) is imaged on the image sensor 103 by the lens 101 and converted into an electric signal. It will be read later. From the image sensor 103, the signal of the low sensitivity pixel as well as the signal of the normal sensitivity pixel for image acquisition are simultaneously read out and input to the signal processing circuit 104.

  The signal processing circuit 104 performs predetermined processing separately for the normal sensitivity pixel for image acquisition and the low sensitivity pixel, and obtains the result of the intensity of the reflected light from the subject in each area in the screen. The control device 105 determines the flash emission amount at the time of actual photographing from the intensity of the reflected light at the time of pre-emission obtained by the signal processing circuit 104.

  At the time of actual photographing, the strobe auxiliary light device 109 emits light with a strobe emission amount determined from the intensity of reflected light at the time of pre-emission, and a subject image (not shown) illuminated by the strobe auxiliary light is connected to the image sensor 103 by the lens 101. Imaged and converted into an electrical signal. At this time, the aperture 102 is set to an appropriate aperture size according to the imaging conditions, and a light flux having an appropriate amount of light for image capturing reaches the image sensor 103.

  An image signal of a subject image subjected to photoelectric conversion is read from the image sensor 103. At this time, the low-sensitivity pixel signal is simultaneously read out together with the normal-sensitivity pixel signal for image acquisition and is input to the signal processing circuit 104.

  The signals of the normal sensitivity pixel and the low sensitivity pixel for image acquisition are subjected to predetermined processing, converted into image data, recorded on the memory card 108 and displayed on the liquid crystal display device 107.

  FIG. 2 is a diagram illustrating a state of arrangement of pixels of the image sensor 103. In FIG. 2, as the normal sensitivity pixel 201 for image acquisition, an R pixel 201R in which an R filter that transmits red light is stacked, a G pixel 201G in which a G filter that transmits green light is stacked, and a B filter that transmits blue light. The stacked B pixel 201B is arranged. In addition to the normal sensitivity pixel 201, a low sensitivity pixel 202 is disposed. The low-sensitivity pixel 202 has a smaller opening area than the R pixel 201R, the G pixel 201G, and the B pixel 201B, and the amount of light incident on the photoelectric conversion unit in the pixel is limited. The sensitivity is, for example, 1/10.

  FIG. 3 shows the output of the normal sensitivity pixel 201 and the low sensitivity pixel 202 according to the subject distance when a pre-flash operation for determining the light emission amount at the time of flash photography is performed in an imaging device using the image sensor 103. It is the graph which showed the mode of. Here, the pixel saturation output is normalized to 1, and the subject distance is normalized with the distance of the main subject determined by an autofocus mechanism (not shown) as 1.

  At the time of pre-emission, the pixel output of the normal sensitivity pixel 201 is about 1/10 of the saturation charge amount when there is an object with 18% reflectance that is the average reflectance of the subject at the position of the main subject distance described above. In addition, the light emission amount of the strobe auxiliary light device 109 is controlled. The intensity of reflected light from the subject is inversely proportional to the square of the subject distance, which is the distance between the camera equipped with the strobe light emitting unit and the subject. For this reason, even with an 18% reflectance object, the output of the normal sensitivity pixel 201 is saturated when it is closer than about 0.32 times the main subject distance (in the case of a short distance). Further, in the case of a white object having a reflectance of 90%, the output of the normal sensitivity pixel 201 is saturated when it is closer than 0.71 times the main subject distance.

  On the other hand, since the sensitivity of the low-sensitivity pixel 202 is, for example, 1/10 of that of a normal pixel, the distance at which the reflected light of an object having 18% reflectance is saturated is approximately 0.1 times the main subject distance, and 90% reflection is performed. Even if the ratio is, the pixel output that is not saturated can be obtained up to 0.22 times the main subject distance.

  FIG. 4 is a flowchart for explaining the entire pre-light emission operation of the present embodiment. When the pre-flash operation is started (S401), acquisition of main subject distance information determined by the autofocus mechanism (S402) and exposure information by ambient stationary light before pre-flash is acquired (S403).

  Of the main subject distance information and exposure information, the pre-emission amount is determined from the ISO sensitivity setting and the aperture value information (S404), and pre-emission is performed (S405). The subject light illuminated by the ambient stationary light and the strobe pre-emission is imaged on the image sensor 103, photoelectrically converted and read out as a video signal (S406). Then, the read video signal is evaluated in a state where the screen area is divided (S407).

  At this time, the intensity of the reflected light from the pre-emission is extracted by comparing with the pre-emission video signal illuminated only by the ambient steady-state light, and the amount of the main emission is determined in consideration of the state of the ambient steady-state light. (S408), and the pre-flash operation is terminated (S409).

  FIG. 5 is a flowchart illustrating in more detail step S407 during the pre-light emission operation. When the video evaluation is started (S501), the luminance level of the video signal is evaluated for each small area divided in the screen. At this time, it is determined whether or not the signal level of the normal pixel sensitivity 201 is equal to or lower than the saturation level of the image sensor (S502). If the signal level is equal to or lower than the saturation level (S502-YES), the normal sensitivity pixel 201 in the divided small area is determined. Is subjected to predetermined processing to obtain a luminance signal (S503).

  On the other hand, when the saturation level has been reached (S502-NO), the signal of the low sensitivity pixel 202 in the small region is multiplied by a coefficient that compensates for the sensitivity ratio of the normal sensitivity pixel 201 and the low sensitivity pixel 202 to obtain a luminance signal. Obtain (S504). The video evaluation is completed by obtaining an appropriate luminance signal according to the signal level of the normal sensitivity pixel 201 or the low sensitivity pixel 202 (S505).

  FIG. 6 is a diagram showing how the luminance signal extracted in the procedure of FIG. 5 changes according to the subject distance. The horizontal axis represents the subject distance normalized by the main subject distance as in FIG. 3, and the vertical axis represents the luminance signal levels of the normal sensitivity pixel 201 and the low sensitivity pixel 202 after the sensitivity of the low sensitivity pixel 202 is corrected. As is apparent from the figure, an appropriate signal can be obtained by using the output of the low sensitivity pixel 202 even in a region where the subject distance is short and the output of the normal sensitivity pixel 201 is saturated. It is possible to obtain an appropriate amount of flash emission at the time of shooting.

(Second Embodiment)
FIG. 7 is a block diagram showing a configuration of an imaging apparatus according to the second embodiment of the present invention. The same members as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. Reference numeral 703 denotes an image sensor having a phase difference detection function.

  In the second embodiment of the present invention, the basic operation at the time of pre-emission is the same as that of the first embodiment. However, in the present embodiment, the low-sensitivity pixel 202 is replaced with a phase difference detection pixel (hereinafter, referred to as a phase difference detection pixel). 802) (also referred to as focus detection pixels) is used.

  FIG. 8 is a diagram illustrating a state of arrangement of pixels of the image sensor 703. A normal sensitivity pixel for image acquisition (hereinafter also referred to as an imaging pixel) 801 is the same as the normal sensitivity pixel 201 of the first embodiment. Further, a phase difference detection pixel 802 is disposed on the image sensor 703. The phase difference detection pixel 802 has a slit-like opening at a position offset left and right in the pixel region, and the sensitivity ratio between the normal sensitivity pixel 801 and the phase difference detection pixel 802 is the same as that of the first embodiment. The sensitivity ratio between the normal sensitivity pixel 201 and the low sensitivity pixel 202 in FIG.

  9 and 10 are diagrams for explaining the structures of the imaging pixels (normal sensitivity pixels) and the focus detection pixels (phase difference detection pixels). In the present embodiment, a plurality of focus detection pixels that receive light passing through a partial region (a region where a part is shielded) of the exit pupil of the photographing optical system are provided. In the present embodiment, G (green) is applied to 2 diagonal pixels out of 4 pixels of 2 rows × 2 columns (hereinafter, row = X, column = Y, for example, 2 rows × 2 columns are represented as 2 × 2). A Bayer arrangement is employed in which pixels having a spectral sensitivity of 1 are arranged and one pixel having a spectral sensitivity of R (red) and B (blue) is arranged for each of the other two pixels. In addition, focus detection pixels having a structure to be described later are distributed between the Bayer arrays.

  FIG. 9 shows the arrangement and structure of the imaging pixels. FIG. 9A is a plan view of 2 × 2 imaging pixels. As is well known, in the Bayer array, G pixels are arranged diagonally, R and B pixels are arranged in the other two pixels, and a 2 × 2 structure is repeatedly arranged. FIG.9 (b) is AA sectional drawing of Fig.9 (a). ML is an on-chip microlens arranged on the forefront of each pixel. CFR is an R (red) color filter. CFG is a G (green) color filter. PD (PhotoDiode) schematically shows a photoelectric conversion unit of a CMOS sensor. CL (Contact Layer) is a wiring layer for forming signal lines for transmitting various signals in the CMOS sensor. TL (TakingLens) schematically shows a photographing optical system.

  The on-chip microlens ML and the photoelectric conversion unit PD of the imaging pixel are configured to capture the light beam that has passed through the photographing optical system TL as effectively as possible. The exit pupil EP (ExitPupil) of the photographing optical system TL and the photoelectric conversion unit PD are in a conjugate relationship by the on-chip microlens ML, and the effective area of the photoelectric conversion unit PD is designed to be large. In FIG. 9B, the incident light beam of the R pixel has been described, but the G pixel and the B (blue) pixel have the same structure. Accordingly, the exit pupil EP corresponding to each of the RGB pixels for imaging has a large aperture, and the light flux from the subject is efficiently taken in to improve the S / N of the image signal. As described above, each of the plurality of imaging pixels receives light passing through the entire area of the exit pupil EP and generates an image of the subject.

  FIG. 10 is a diagram showing the arrangement and structure of focus detection pixels for performing pupil division in the horizontal direction (lateral direction) of the imaging optical system TL. Here, the horizontal direction or the horizontal direction is perpendicular to the optical axis and extends in the horizontal direction when the imaging apparatus is set so that the optical axis of the imaging optical system and the long side of the imaging screen are parallel to the ground. The direction along a straight line. Further, the pupil division direction in FIG. 10 is the horizontal direction. FIG. 10A is a plan view of pixels of 2 rows × 2 columns including focus detection pixels. When obtaining an image signal for recording or viewing, the main component of luminance information is acquired by G pixels. Since human image recognition characteristics are sensitive to luminance information, image quality degradation is easily recognized when G pixels are lost. On the other hand, the R pixel or the B pixel is a pixel that acquires color information (color difference information). However, since human visual characteristics are insensitive to color information, the pixel that acquires color information has some defects. However, image quality degradation is difficult to recognize. Therefore, in the present embodiment, among the pixels of 2 rows × 2 columns, the G pixel is left as an imaging pixel, and the R pixel and the B pixel are replaced with focus detection pixels. The focus detection pixels are denoted as SHA and SHB in FIG.

  FIG. 10B is a cross-sectional view taken along the line AA in FIG. In FIG. 10B, the diameter of the exit pupil EP of the photographic optical system TL indicates a state in which the phase difference can be detected.

  The microlens ML and the photoelectric conversion element PD have the same structure as the imaging pixel shown in FIG. In the present embodiment, since the signal of the focus detection pixel is not used for image generation, a transparent film CFW (white) is disposed instead of the color separation color filter. Moreover, since pupil division is performed by the image sensor, the opening of the wiring layer CL is biased in one direction with respect to the center line of the microlens ML. Specifically, since the opening OPHA of the pixel SHA is biased to the right side, the light beam that has passed through the left exit pupil EPHA of the imaging optical system TL is received. Similarly, since the opening OPHB of the pixel SHB is biased to the left side, the light beam that has passed through the right exit pupil EPHB of the imaging optical system TL is received. Therefore, the pixels SHA are regularly arranged in the horizontal direction, and the subject image acquired by these pixel groups is defined as an A image. In addition, the pixels SHB are also regularly arranged in the horizontal direction, and the subject image acquired by these pixel groups is a B image. By detecting the relative positions of the A image and the B image, the amount of focus shift ( Defocus amount) can be detected.

  In the pixels SHA and SHB, focus detection is possible for an object having a luminance distribution in the horizontal direction of the shooting screen, for example, a vertical line, but focus detection is not possible for a horizontal line having a luminance distribution in the vertical direction. Therefore, in this embodiment, the latter is also provided with pixels that perform pupil division in the vertical direction (longitudinal direction) of the photographing optical system so that the focus state can be detected.

  Further, since the focus detection pixel is a defective pixel on the captured image, the image signal at the position of the focus detection pixel is interpolated using the signals of the surrounding imaging pixels.

  In the present embodiment, when the strobe is pre-flashed, the output of the phase difference detection pixel 802 is read out together with the output of the normal sensitivity pixel 801 from the image sensor 703, and appropriate measures are taken to perform the same once as in the first embodiment. It is possible to obtain an appropriate amount of strobe light emission with the pre-flash. Also, it is possible to obtain focus information in the screen at the time of pre-emission at the same time.

Claims (3)

An image sensor for converting a subject image formed by a photographing optical system into an electrical signal, and is discretely arranged between normal sensitivity pixels for image acquisition having a predetermined sensitivity and the normal sensitivity pixels. An image sensor comprising a low-sensitivity pixel for photometry that is not used for image acquisition with a smaller aperture and lower sensitivity than the normal sensitivity pixel;
When illuminating the subject using a strobe auxiliary light device and taking a picture, the strobe auxiliary light device is pre-flashed before the main photographing, and the reflected light from the subject is converted into an electrical signal by the image sensor. Control means for controlling the light emission amount of the strobe auxiliary light device in the main photographing based on,
When the strobe auxiliary light device pre-lights and the level of the signal of the normal sensitivity pixel is equal to or lower than a predetermined level, the control means is configured to use the strobe in the main photographing based on the signal of the normal sensitivity pixel. The amount of light emitted from the auxiliary light device is controlled, and when the signal level of the normal sensitivity pixel exceeds the predetermined level, the signal of the low sensitivity pixel is multiplied by a coefficient that compensates for the sensitivity ratio with the normal sensitivity pixel. An image pickup apparatus that controls a light emission amount of the strobe auxiliary light device in the main photographing based on the received signal.   The imaging device according to claim 1, wherein the sensitivity lower than the normal sensitivity pixel is about 1/10 the sensitivity of the normal sensitivity pixel.   The normal sensitivity pixel is an imaging pixel that receives a light beam that has passed through an exit pupil of the photographing optical system, and the low sensitivity pixel receives a light beam in which a part of the exit pupil of the photographing optical system is shielded. The imaging apparatus according to claim 1, wherein the imaging apparatus is a focus detection pixel.

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