JP2010135904A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow live view display of high quality and an AF of high precision to be performed regardless of a posture of an imaging apparatus. <P>SOLUTION: An imaging element 120 includes a rectangular image area, pixels are arranged so that the number of pixel columns arranged in a long side direction may exceed the number of pixel rows arranged in a short side direction, thinning read in a plurality of thinning read modes differing in combination of a long side direction thinning ratio to be thinning ratio in the long side direction and short side direction thinning ratio to be thinning ratio in the short side direction is allowed. A thinning read mode selection portion 102 selects any mode from among the plurality of thinning read modes of the imaging element 120 in accordance with a photography posture of a horizontal position and a vertical position detected by a photography posture detection portion 154 in performing thinning read by the imaging element 120. Thus, resolution in the direction along the horizontal direction of a subject in an image signal to be obtained becomes almost stable regardless of a photography posture. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging apparatus having an imaging element having a plurality of thinning readout modes.

  In order to meet the increasing needs for high-definition images, the number of pixels of image sensors is increasing. An image sensor having a number of pixels exceeding 10 million pixels and 20 million pixels is used in an imaging apparatus such as a digital camera. From such a high-pixel image sensor, a high-pixel image signal can be obtained.

  On the other hand, image signals are read from the image sensor at a relatively high frame rate, such as 30 frames per second and 60 frames per second (30 fps, 60 fps), and a moving image is displayed on a liquid crystal display device or the like. Processing for adjusting the focus or recording a moving image is performed. When reading, processing, displaying, and recording an image signal at such a relatively high frame rate, the image signal having the number of pixels exceeding 10 million pixels and 20 million pixels is read and processed as it is. Is not practical in an imaging apparatus used by general users. This is because the processing power required for the processing unit that processes the image signal is increased, and this may lead to an increase in product cost due to the high performance of the processing unit and may shorten the battery life. Because there is. In addition, at the time of displaying and recording moving images, a high number of pixels such as the 10 million pixels and 20 million pixels described above are not required for consumer products.

  For the reasons described above, when an image signal is read from the image sensor at a relatively high frame rate, processing for reducing the amount of information when reading the image signal from the image sensor is performed by so-called pixel thinning readout.

  Incidentally, an image obtained from a general imaging device such as a digital still camera or a movie camera has a horizontally long rectangular shape. With respect to the aspect ratio, for example, an image with an aspect ratio of 4: 3, 3: 2, 16: 9 can be obtained from a digital still camera, and an image with an aspect ratio of 4: 3, 16: 9 can be obtained from a movie camera. Can be obtained. In addition, in an imaging device incorporated in a mobile phone or the like, a vertically long image is often obtained, and its aspect ratio is set to, for example, 3: 4.

  Hereinafter, in order to simplify the description, it is assumed that the imaging apparatus includes an imaging element capable of outputting an image having a horizontally long aspect ratio in which the dimension along the horizontal direction of the screen is longer than the dimension along the vertical direction. In other words, when taking an image with the imaging device in a posture in which the top surface of the imaging device is located on the upper side in the vertical direction and the bottom surface is located on the lower side in the vertical direction (hereinafter, this posture is referred to as horizontal position) It is assumed that an image that is longer in the left-right direction than the direction (hereinafter referred to as a horizontally long image) is obtained. Further, the image pickup apparatus is placed sideways while facing the subject and the image pickup apparatus is photographed in a posture in which the upper surface of the image pickup device faces the right or left side of the photographer (hereinafter, this posture is referred to as a vertical position). In this case, it is assumed that an image longer in the vertical direction than the horizontal direction (hereinafter referred to as a vertically long image) is obtained.

  When shooting a subject, the user takes a picture in a horizontal position or a vertical position according to the shape of the subject and the intention of drawing. Many of the imaging devices include a display device using a color liquid crystal display element or the like and an electronic viewfinder device (EVF) (hereinafter simply referred to as a display device). The photographer changes the posture of the imaging device while viewing the live view image displayed on the display device, and obtains a desired composition. At this time, the image signal from which the amount of information has been reduced by the above-described pixel thinning or pixel addition is read from the image sensor at a relatively high frame rate, and a moving image is displayed on the display device.

  By the way, when performing the above-described pixel thinning or pixel addition in order to reduce the amount of information of the image signal output from the image sensor, the resolution in the vertical direction of the screen is more greatly reduced than the resolution in the horizontal direction of the screen. It was generally done.

  When pixel thinning or pixel addition is performed as described above, two problems described below may occur. That is, one is a deterioration in image quality of the live view image, and the other is a decrease in accuracy of contrast AF (AF: Auto Focus = automatic focus adjustment).

  First, image quality degradation of a live view image will be described. For example, consider a case where a user faces an object having a relatively fine vertical stripe while holding the imaging device in a horizontal position. In this case, the live view image maintains a relatively high number of pixels in the direction along the horizontal direction of the horizontally long screen. Accordingly, since the resolution in the direction along the horizontal direction in the horizontally long screen (horizontal resolution) is relatively high, the vertical stripes can be reproduced relatively well. Therefore, interference fringes such as moire are difficult to occur, and the image of vertical stripes in the displayed live view image is relatively good.

  Next, consider a case where the user faces the subject having the vertical stripes while holding the imaging device in the vertical position. In this case, the resolution in the direction along the horizontal direction of the vertically long screen (horizontal resolution) is greatly reduced by the pixel thinning or pixel addition. As a result, the sampling spatial frequency of the image sensor is substantially lowered, and moire is likely to occur in a portion having a periodic pattern (portion of vertical stripes) present in the subject image. As a result, the image quality of the displayed live view image may be lowered depending on the posture of the imaging apparatus, even though the same subject is faced.

  Described below is a decrease in accuracy of contrast AF. Contrast AF is a type of AF that repeats the process of obtaining the contrast evaluation value of the subject image from the image signal output from the image sensor while moving the focusing lens in the photographic lens little by little along the optical axis direction of the photographic lens. It is. The contrast evaluation value is a value obtained by quantitatively determining how much contrast the subject image has. Then, the in-focus position is searched from the moving direction of the focusing lens and the increase / decrease tendency of the contrast evaluation value, and the focusing lens position when the contrast evaluation value reaches the peak value (maximum value) is set as the in-focus position. At this time, in order to increase the AF speed, it is necessary to repeat the above processing at shorter time intervals. Therefore, it is possible to obtain a contrast evaluation value using an image signal read from the image sensor for live view image display. It is common.

  A subject such as a building, a plant, or an upright person generally has many contours or edges extending in a direction in which gravity acts, that is, in a vertical direction. When performing contrast AF, it is possible to obtain good AF accuracy by obtaining a contrast evaluation value from the image of the edge.

  Assume that an image of a subject having an edge extending in the vertical direction is formed on the image area of the image sensor. In such a situation, in order to obtain the contrast evaluation value by extracting the image of the edge extending in the vertical direction, the image is orthogonal to the image of the edge extending in the vertical direction formed on the image area of the image sensor. It is efficient to process an image signal obtained from a plurality of pixels lined up linearly along the direction of the image. This is because the contrast evaluation value can be obtained from the one-dimensional data string, and the processing time can be reduced.

  Here, “a plurality of pixels lined up linearly along a direction orthogonal to the image of the edge extending in the vertical direction” will be considered. Depending on the orientation (horizontal position, vertical position) of the imaging device, the arrangement direction of the plurality of pixels differs as described below. For example, an image pickup apparatus in which an image pickup device having a horizontally long aspect ratio is incorporated and a horizontally long image can be obtained when shooting in a horizontal position will be described as an example.

  In the above example, when the image pickup apparatus is held in a horizontal position, in the image pickup device in which the pixels are two-dimensionally arranged in the vertical and horizontal directions, a plurality of pixels lined up linearly along the horizontal direction (long side direction) “A plurality of pixels lined up linearly along a direction orthogonal to the image of the edge extending in the vertical direction”. On the other hand, when the imaging device is held in a vertical position, a plurality of pixels arranged linearly along the vertical direction (short side direction) in the imaging device in which the pixels are two-dimensionally arranged in the vertical and horizontal directions are A plurality of pixels lined up linearly along a direction orthogonal to the image of the edge in the vertical direction.

  Therefore, when the orientation of the imaging device is detected and the imaging device is held in a horizontal position, the image signal obtained from a plurality of pixels arranged directly along the long side direction of the imaging element is processed, and the vertical position It is conceivable to process image signals obtained from a plurality of pixels arranged linearly along the short side direction of the image sensor.

  That is, in the two-dimensional image signal output from the image pickup device for live view image display, when the image pickup apparatus is set in the horizontal position, from a plurality of pixels lined up linearly along the long side direction of the image pickup device. The contrast evaluation value may be obtained using the image signal. On the other hand, when the imaging apparatus is held in the vertical position, the contrast evaluation value may be obtained using image signals from a plurality of pixels linearly arranged along the short side direction of the imaging element.

  However, the two-dimensional image signal output from the image sensor for live view image display includes relatively high spatial frequency information in the long side direction of the image sensor, whereas in the short side direction of the image sensor. For the reasons described above, it is difficult to include relatively high spatial frequency information.

  Therefore, the contrast evaluation value obtained when the imaging apparatus can change the direction in which the contrast evaluation value is obtained in accordance with the detected posture and is held in the vertical position does not necessarily accurately indicate the imaging state of the subject image. It is no longer a reflection. For this reason, the accuracy of AF can be reduced. That is, there is a possibility that the AF accuracy obtained for the same subject differs between when the image is taken in the horizontal position and when the image is taken in the vertical position.

  Japanese Patent Application Laid-Open No. 2004-133867 discloses a technique for dealing with a change in the image quality of an image obtained and displayed by pixel thinning or pixel addition depending on the attitude of the imaging apparatus. This technique is applied when displaying a moving image obtained from an imaging device by performing pixel thinning on a PC or a TV monitor (hereinafter referred to as a TV monitor) connected to the imaging device.

  In the above-mentioned Patent Document 1, as a first embodiment, when shooting in the horizontal position, an image based on the horizontally long (horizontal 2,560 pixels, vertical 480 pixels) image data obtained in the first thinning mode is horizontally long. Displayed on the TV monitor. On the other hand, when the posture of the imaging device is the vertical position, an image based on the vertically long (960 pixels wide, 2,560 pixels long) image data obtained in the second thinning mode is displayed on the horizontally long TV monitor. In both the first and second thinning modes, pixel thinning is not performed in the long side direction of the imaging element having a horizontally long aspect ratio, but pixel thinning is performed in the short side direction. Then, compared with the thinning rate in the first thinning mode corresponding to the shooting at the horizontal position, the thinning rate in the second thinning mode corresponding to the shooting at the vertical position is halved. As a result, when an image obtained by photographing in the vertical position is displayed on the TV monitor so as to be vertically long, a sufficient resolution is obtained in the horizontal direction of the displayed image.

  In Patent Document 1, as a second embodiment, in the first thinning mode corresponding to the shooting in the horizontal position, the short of the image sensor (long side: 2,560 pixels, short side: 1,920 pixels). An example in which pixel thinning is performed only in the side direction and pixel thinning is performed in both the long side direction and the short side direction of the image sensor in the second thinning mode corresponding to shooting in the vertical position is also disclosed. The size of the image obtained by this thinning-out readout is 2560 pixels on the long side when shooting in the horizontal position and 640 pixels on the short side, and 1 on the long side when shooting in the vertical position. , 920 pixels and 853 pixels of image data on the short side are obtained.

An image obtained by photographing in the horizontal position is displayed horizontally on the horizontally long TV monitor, while an image obtained by photographing in the vertical position is displayed vertically on the horizontally long TV monitor. Since the horizontal display resolution of the TV monitor is 720, the number of pixels in the horizontal direction of the horizontal image obtained by shooting at the horizontal position is 2,560 pixels, and the horizontal direction of the vertical image obtained by shooting at the vertical position. The number of pixels of 853 exceeds the display resolution. Therefore, an image with a resolution exceeding the display performance can be obtained both in the horizontal position and in the vertical position, so that a reduction in the horizontal resolution can be suppressed.
JP 2007-208742 A

  As described above, according to the technique disclosed in Patent Document 1, the decimation rate at the time of pixel decimation readout is changed according to the horizontal position shooting and the vertical position shooting, thereby reducing the horizontal resolution of the displayed image. Can be suppressed. However, if the image processing for contrast AF is performed based on the image data obtained by the thinning readout as described above, the following problems may occur.

  That is, in Patent Document 1, the number of pixels in the horizontal direction obtained by thinning-out readout at the time of horizontal position shooting and vertical position shooting is 2,560 pixels and 960 pixels, respectively, in the first embodiment. The form is 2,560 pixels and 853 pixels, respectively. That is, the number of pixels in the horizontal direction at the time of vertical position shooting is 960 pixels in the first embodiment, 853 pixels in the second embodiment, and the number of horizontal pixels at the time of horizontal position shooting (2,560 pixels). ) Significantly reduced. This means that the focus adjustment accuracy can be reduced when performing autofocusing by performing contrast detection from a one-dimensional image data sequence obtained from a pixel sequence aligned in the horizontal direction on a vertically long screen during vertical position shooting. To do.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of obtaining a display image with stable contrast AF accuracy and stable quality regardless of the shooting posture.

The present invention is applied to an imaging device having an imaging device, a shooting posture detection unit, and a thinning readout mode selection unit,
The imaging element has a rectangular image area, and the number of pixels arranged in a long side direction that is a direction along the long side of the rectangle is in a short side direction that is a direction along the short side of the rectangle. Pixels are arranged to exceed the number of arranged pixels, and a combination of a long side direction thinning rate that is the thinning rate in the long side direction and a short side direction thinning rate that is the thinning rate in the short side direction is a combination It is configured to enable decimation readout in different decimation readout modes,
The photographing posture detection unit is configured to be able to detect that the photographing posture of the imaging device is set in a horizontal position or a vertical position,
The thinning-out reading mode selection unit is one of the plurality of thinning-out reading modes of the image sensor according to the photographing posture detected by the photographing posture detection unit when the thinning readout is performed by the imaging device. By selecting, the above-described problem is solved by making the resolution in the direction along the horizontal direction of the subject image in the obtained image signal substantially constant regardless of the photographing posture.

  In the present invention, the imaging device has a rectangular image area, and the number of pixels arranged in the long side direction is larger than the number of pixels arranged in the short side direction. Thinning readout is possible in a plurality of thinning readout modes in which the combination of the thinning rate in the long side direction and the thinning rate in the short side direction is different. Then, the thinning readout mode selection unit selects a thinning readout mode according to the photographing posture detected by the photographing posture detection unit, and thereby in the direction along the horizontal direction of the subject image in the image obtained by the thinning readout. By making the resolution of the image approximately constant regardless of the shooting posture, the edge extending in the vertical direction in the subject image is detected and autofocus calculation is performed, and the accuracy when detecting the focus is set to the shooting posture. Regardless, it can be maintained substantially constant. In addition, when performing live view display, the horizontal resolution (display resolution) of the displayed image can be kept substantially constant, and when viewed in a horizontal position as in a conventional imaging device, the live view is displayed. Although moire does not occur in the image, it is possible to suppress a problem such that moire occurs when the image is held in the vertical position.

  1 and 2 are diagrams schematically showing an appearance of an imaging apparatus according to an embodiment of the present invention. The present invention can be applied to any type of imaging device such as a so-called compact digital still camera with a fixed imaging lens, a lens interchangeable camera, a single-lens reflex camera, and a camera having an electronic viewfinder. The present invention is also applicable to digital movie cameras. The imaging device 10 may also be incorporated in a mobile phone or a personal digital assistant (PDA).

  In the following description, it is assumed that the imaging device 10 is a compact digital still camera with a fixed imaging lens. The imaging apparatus 10 includes a photographing lens 110, a flash light emitting unit 142, a grip unit G, an operation unit 150 including a release switch 150R and a zoom switch 150Z, a display unit 130, and the like.

  The image pickup apparatus 10 has an image pickup element having a horizontally long aspect ratio (details of the image pickup element will be described later), and is taken with the upper surface T of the image pickup apparatus 10 facing upward in the vertical direction, that is, the horizontal position. It is assumed that a horizontally long image is obtained when shooting with. In addition, it is assumed that a vertically long image is obtained when shooting is performed with the grip portion G positioned above or below the vertical direction, that is, when shooting is performed in a vertical position.

  The display unit 130 includes a color liquid crystal display element, an organic EL display element, and the like. The display unit 130 can display a live view image during a shooting preparation operation, that is, when the user holds the imaging device 10 toward the subject and presses the release switch 150R. The display unit 130 is also configured to reproduce and display images (moving images and still images) obtained by shooting. The image area of the image sensor has a horizontally long aspect ratio as described above. That is, the image area has a horizontally long rectangular shape. The display unit 130 may have an aspect ratio that is substantially the same as the aspect ratio of the image area of the image sensor. In the embodiment of the present invention, the display unit 130 has a display resolution of 800 pixels in the long side direction and 600 pixels in the short side direction.

  FIG. 2 shows a state in which a horizontally long live view image is displayed on the display unit 130 when the imaging apparatus 10 is held in a horizontal position. In the example of FIG. 2, the horizontal line H in the subject image is substantially parallel to the direction in which the long side of the display unit 130 extends.

  FIG. 3 is a block diagram illustrating a schematic configuration of the imaging apparatus 10 according to the embodiment of the present invention. The imaging apparatus 10 includes a system controller 100, an AF processing unit 108, a photographing lens 110, an aperture 112, a shutter 114, an AF mechanism 116, an imaging element 120, an imaging circuit 122, an image processing unit 124, A memory 126, a shift mechanism 128, and a display unit 130 are included. The imaging apparatus 10 further includes a flash control circuit 140, a flash light emitting unit 142, an operation unit 150, various sensors 152 such as a shake sensor, a brightness sensor, and a temperature sensor, a shooting posture detection unit 154, and a memory card. Interface 162. The recording medium 160 can be a flash memory card or a small hard disk unit configured to be detachable from the imaging apparatus 10.

  The system controller 100 can be composed of an ASIC (application specific integrated circuit), CPU, hardware logic, or the like, and has a thinning readout mode selection unit 102, a contrast AF control unit 104, and a display control unit 106 therein.

  The aperture 112 is for adjusting the amount of subject light transmitted through the photographing lens 110, and the opening state thereof is controlled by the system controller 100. The shutter 114 is controlled to be opened and closed by the system controller 100. The AF mechanism 116 moves the focusing lens in the photographing lens 110 along the optical axis direction of the photographing lens 110 so that the subject image is focused on the image area of the image sensor 120.

  The image sensor 120 can be composed of a CCD or a CMOS image sensor. In this embodiment, the image sensor 120 will be described as an XY address scanning type CMOS image sensor capable of dot sequential reading.

  Here, the image sensor 120 will be described in detail with reference to FIGS. 4, 5, and 6. FIG. 4 is a diagram conceptually illustrating a state in which a plurality of pixels are provided on the image area of the image sensor 120. The image area of the image sensor 120 has a dimension of W in the long side direction and H in the short side direction, and its aspect ratio W: H is 4: 3. In the following description, the imaging device 120 has a pixel size of 4,000 pixels in the long side direction and 3,000 pixels in the short side direction for the purpose of simplifying the explanation and facilitating understanding of the invention. . That is, the ratio of the number of pixels arranged in the short side direction to the number of pixels arranged in the long side direction (4,000: 3,000) is equal to the aspect ratio (4: 3) of the image area. To do. The image pickup device 120 has a so-called Bayer array on-chip color filter. In FIG. 4, Gr and Gb are green, R is red, and B is a blue on-chip color filter formed on each pixel.

  The image sensor 120 has an all-pixel readout mode, a first thinning readout mode, and a second thinning readout mode as image readout modes. Of course, other decimation readout modes may be provided. However, in order to simplify the description, the image sensor 120 has first and second decimation readout modes as the decimation readout mode.

  In the all-pixel readout mode, for example, an image signal for 4,000 pixels in a row labeled 1 in FIG. 4 (hereinafter simply referred to as “first row”) is output, and then labeled 2 The image signal for 4,000 pixels in the row, that is, the second row is output, and the image signal for 4,000 pixels in the row denoted by reference numeral 3000, that is, the 3,000th row is output. As described above, the image signal can be read out by the raster scan method. In the present specification, reading an image signal as described above is referred to as “scanning in the long side direction and reading the image signal”.

  The first decimation readout mode and the second decimation readout mode will be described with reference to FIGS. In both the first and second thinning readout modes, the image signal is read out by the raster scan method as in the all-pixel readout mode.

  FIGS. 5A and 5B are diagrams conceptually illustrating the first decimation readout mode. FIG. 5A is an enlarged view of the entire image sensor 120, and FIG. 5B is an enlarged view of a portion P of the image area shown in FIG. Show. Further, (c) shows a target pixel to be read and a scanning direction in the first thinning-out reading mode. FIG. 5C shows that an image signal is read out from a pixel indicating the color (Gr, Gb, R, B) of the on-chip color filter.

  The first thinning readout mode is a thinning readout mode that is selected when the imaging apparatus 10 is held in the horizontal position. That is, corresponding to the case where the imaging apparatus 10 is set in a state where the horizontal line (horizontal direction) in the subject image formed on the image area of the imaging element 120 is substantially parallel to the long side of the imaging element 120. This is the selected thinning readout mode.

  As shown in FIG. 5, in the first thinning readout mode, the scanning direction is parallel to the long side direction of the image area of the image sensor 120. The thinning rate is set to 3 in the long side direction and 12 in the short side direction. In the example shown in FIG. 5 (c), in the first row, columns with symbols 1, 4, 7,..., 1 + 3 × n,..., 4000 (n is a natural number including 0; the same applies hereinafter) Hereinafter, an image signal is read out from the pixels of “first column, fourth column,...”). Next, in the fourteenth row, an image signal is read from the pixels in the above column. Further, in the 25th row, the image signals are read out to the second and 990th rows from the pixels in the above-mentioned column. The reason why the row read out after the first row is not the thirteenth row even though the thinning rate is 12 is that the arrangement of the on-chip color filters is the same in the first row and the thirteenth row. is there. That is, if thinning readout is performed as in the first row, the 13th row, the 25th row, and the 37th row, it is impossible to obtain blue color information from the obtained image signal. Therefore, thinning readout is performed in the first row, the 14th row, the 25th row, the 38th row, the 49th row, and so on.

  With the first decimation readout mode described above, an image signal composed of 1,333 pixels in the long side direction and 250 pixels in the short side direction of the image sensor 120 can be obtained. In this way, the total number of pixels of the image obtained by performing decimation readout in the first decimation readout mode is 1,333 × 250 = 333,250 (pixels).

  6A and 6B are diagrams conceptually illustrating the second thinning readout mode. FIG. 6A is an enlarged view of the entire image sensor 120, and FIG. 6B is an enlarged view of a portion P of the image area shown in FIG. Show. Further, (c) shows a pixel to be read out and a scanning direction in the second thinning readout mode. FIG. 6C shows that an image signal is read out from a pixel indicating the color (Gr, Gb, R, B) of the on-chip color filter.

  The second thinning readout mode is a thinning readout mode selected when the imaging device 10 is held in the vertical position. That is, corresponding to the case where the imaging apparatus 10 is set in a state where the horizontal line (horizontal direction) in the subject image formed on the image area of the imaging element 120 is substantially parallel to the short side of the imaging element 120. This is the selected thinning readout mode.

  As shown in FIG. 6, the scanning direction in the second thinning readout mode is a direction parallel to the short side direction of the image area of the image sensor 120. The thinning rate is set to 3 in the short side direction and 12 in the long side direction. In the example shown in (c) of FIG. 6, image signals are output from the pixels in the first column, the first row, the fourth row, the seventh row,..., The (1 + 3 × n) row,. Read out. Next, in the fourteenth column, an image signal is read from the pixels in the above row. Further, although not displayed due to space limitations, in the 25th row, the 38th column, the 49th column,..., Image signals are read from the pixels in the above row. In the example of FIG. 6, the column read out after the first column is not the thirteenth column but the fourteenth column because the arrangement of the on-chip color filters is the same in the first column and the thirteenth column. Because there is. That is, if thinning readout is performed as in the first column, the thirteenth column, the twenty-fifth column, and the thirty-seventh column, red color information cannot be obtained from the obtained image signal.

  With the second thinning readout mode described above, an image signal composed of 333 pixels in the long side direction and 1,000 pixels in the short side direction of the image sensor 120 can be obtained. In this way, the total number of pixels of the image obtained by performing decimation readout in the second decimation readout mode is 333 × 1,000 = 333,000 (pixels).

  With reference to FIG. 3 again, other components of the imaging device 10 will be described. The imaging circuit 122 performs processing such as CDS (correlated double sampling), amplification, and A / D conversion on the analog image signal read from the imaging device 120 to generate a digital image signal. The data is output to the processing unit 124. Note that the imaging circuit 122 may be configured integrally with the imaging element 120.

  The AF processing unit 108 inputs a part of the digital image signal output from the imaging circuit 122, extracts an image signal having a high spatial frequency component by auto-focus calculation processing (for example, high-pass filter processing, and calculates a contrast value) And the processing result is output to the system controller 100. The AF processing unit 108 has a line buffer, and a digital image signal is temporarily stored in the line buffer. Since the autofocus calculation is performed on the one-dimensional array of digital image signal values read from the line buffer, the autofocus calculation process can be performed at a relatively high speed.

  At this time, when the image sensor 120 is set to the first decimation readout mode, a one-dimensional array of image signal values obtained by reading from a predetermined row is stored in the line buffer and autofocusing is performed. Arithmetic processing is performed. When the image sensor 120 is set to the second decimation readout mode, an image signal of a one-dimensional array obtained by reading from a predetermined column is stored in the line buffer and autofocus calculation processing is performed. Is done. Therefore, it is possible to perform autofocus calculation using the image signal read from the contrast detection target pixel during the reading of the image signal for one frame from the image sensor 120, and to speed up the autofocus processing. Is possible.

  Note that the number of rows or columns to be read into the line buffer may be one or plural. Further, the row or column to be read into the line buffer may be determined in advance or may be determined dynamically according to the state of the subject. In any case, the AF processing unit 108 only needs to process the image signal stored in the line buffer among the digital image signals continuously output from the imaging circuit 122, so that the autofocus calculation process can be performed at high speed. Can be done.

  The image processing unit 124 is configured by an ASIC or the like, and generates digital image data by performing demosaic, white balance, black level adjustment, γ adjustment, correction processing of defective pixels, and the like on the digital image signal output from the imaging circuit 122. To do. Note that in this specification, data generated by processing by the image processing unit 124 is referred to as image data, and data processed in a stage before the image processing unit 124 is referred to as an image signal.

  The memory 126 includes a flash memory and an SDRAM having a relatively high access speed. The flash memory stores a program executed by the system controller 100, control parameters of the imaging device 10, and the like. The SDRAM is configured to be accessible from both the image processing unit 124 and the system controller 100. The image processing unit 124 and the system controller 100 are used as buffers (work areas) when performing various processes.

  The flash light emitting unit 142 includes a xenon tube, a reflector, a diffuser, and the like. The flash control circuit 140 includes a booster circuit, a capacitor for storing energy for light emission, a dimming circuit, and the like, and controls the light emission of the flash light emission unit 142 in response to the light emission command signal output from the system controller 100 To do. The flash light emitting unit 142 and the flash control circuit 140 may be configured using high-intensity LEDs. In that case, a booster circuit or the like can be omitted.

  The operation unit 150 includes a release switch 150R, a zoom switch 150Z (FIG. 2), a mode switch, and the like, and a signal corresponding to a user operation is output to the system controller 100.

  The various sensors 152 include a camera shake sensor, a brightness sensor, a temperature sensor, and the like of the imaging device 10 during the imaging operation. Hereinafter, these sensors are collectively referred to as a sensor 152.

  The photographing posture detection unit 154 is configured to be able to output a signal corresponding to the posture of the imaging device 10 and can use an inclination sensor using a weight, a magnet, a Hall element, or the like, a MEMS sensor, or the like. The photographing posture detection unit 154 may be capable of detecting only whether the posture of the imaging device 10 is the horizontal position or the vertical position. For example, the signal corresponding to the inclination angle with respect to the horizontal position. (Information) may be configured to be output.

  The shift mechanism 128 is for shifting the image sensor 120 along two axes orthogonal to each other in a plane parallel to the image area. Vibration of the imaging device 10 is detected by a hand shake sensor in the sensor 152. Camera shake can be reduced by shifting the image sensor 120 by the shift mechanism 128 in a direction and a stroke in which image blur caused by the vibration is canceled. The shift mechanism 128 is controlled by the system controller 100.

  The thinning readout mode selection unit 102, contrast AF control unit 104, and display control unit 106, which are functional blocks in the system controller 100, will be described. These functional blocks can be implemented when the system controller 100 executes a program stored in the memory 126.

  The thinning readout mode selection unit 102 reads out the image signal from the image sensor 120 in the thinning readout mode, in accordance with the photographing posture detected by the photographing posture detection unit 154, the first and second thinning readout modes described above. Select one of them.

  The contrast AF control unit 104 monitors the autofocus calculation result output from the AF processing unit 108. Then, the focusing lens in the photographing lens 110 is driven via the AF mechanism 116 so that the subject image formed in the image area of the image sensor 120 becomes sharper.

  The display control unit 106 performs processing for displaying an image based on the image data read and generated from the image sensor 120 in the first or second thinning readout mode on the display unit 130.

  FIG. 7 conceptually illustrates how the image is displayed on the display unit 130 based on the image signal read from the image sensor 120 in the first decimation readout mode in the imaging device 10 held in the horizontal position. It is a thing. (A) shows a horizontally long image of 4,000 pixels in the long side direction and 3,000 pixels in the short side direction, which is obtained by reading out all pixels from the image sensor 120. (B) shows the image data generated from the image signal read out by the first decimation readout with the decimation rate set to 3 in the long side direction and 12 in the short side direction. This image data has a pixel size of 1,333 pixels in the long side direction of the image sensor 120 and 250 pixels in the short side direction.

  When the image based on the image data is displayed on the display unit 130, the display control unit 106 issues a control signal to the image processing unit 124 so as to perform the pixel number conversion process (scaling process) described below. Since the image processing unit 124 has 1,333 pixels that exceed 800 pixels, which is the display resolution of the display unit 130, in the long side direction of the image sensor 120 during the pixel number conversion process, the image processing unit 124 performs a thinning process. On the other hand, the short side direction of the image sensor has only 250 pixels lower than 600 pixels, which is the display resolution of the display unit 130. Therefore, processing for increasing the number of pixels to 600 pixels is performed by interpolation processing. As a result, display image data having 800 pixels in the long side direction and 600 pixels in the short side direction as shown in (c) is generated. The display control unit 106 outputs the display image data to the display unit 130. Note that the scaling process may be performed by the display control unit 106.

  FIG. 8 conceptually illustrates a state in which an image is displayed on the display unit 130 based on an image signal read from the image sensor 120 in the second decimation readout mode in the imaging device 10 held in the vertical position. It is a thing. (A) shows a vertically long image of 4,000 pixels in the long side direction and 3,000 pixels in the short side direction, which is obtained by reading all pixels from the image sensor 120. (B) shows the image data generated from the image signal read out by the second thinning-out readout with the thinning-out rate set to 12 in the long side direction and 3 in the short side direction. This image data has a pixel size of 333 pixels in the long side direction of the image sensor 120 and 1,000 pixels in the short side direction.

  When the image based on the image data is displayed on the display unit 130, the display control unit 106 issues a control signal to the image processing unit 124 so as to perform the pixel number conversion process (scaling process) described below. Since the image processing unit 124 has only 333 pixels lower than 800 pixels, which is the display resolution of the display unit 130, in the long side direction of the image sensor 120 during the pixel number conversion process, the number of pixels is set to 800 pixels by interpolation processing. Increase the process. On the other hand, in the short side direction of the image sensor, the display unit 130 has 1,000 pixels that exceed the display resolution of 600 pixels. Therefore, a process of reducing the number of pixels to 600 pixels by a thinning process is performed. As a result, display image data having 600 pixels in the short side direction and 800 pixels in the long side direction as shown in FIG. The display control unit 106 outputs the display image data to the display unit 130. Note that the scaling process may be performed by the display control unit 106.

  Here, with reference to FIG. 9, a description will be given of an autofocus calculation process performed on the image signal read from the image sensor 120 in the first and second decimation readout modes and stored in the line buffer. In FIG. 9A, the image pickup apparatus 10 is held in the horizontal position, the first decimation readout mode is selected, and the image signal read by scanning in the long side direction of the image sensor 120 is the line buffer LB. It shows how it is memorized. In (b), the imaging device 10 is held in the vertical position, the second thinning readout mode is selected, and the image signal read by scanning in the short side direction of the imaging device 120 is stored in the line buffer LB. It shows how it is done.

  As a premise for the following description, in FIGS. 9A and 9B, the imaging conditions differ only in composition, and all other conditions are the same. That is, the shooting distance, the focal length of the shooting lens 110, and the focus adjustment position are all the same.

FIGS. 9A and 9B show a state in which a subject image (an inverted inverted image) is formed on the image area of the image sensor 120 as viewed from the front side of the imaging device 10. . In (a), the number of pixels in the direction along the horizontal direction H in the subject image of the image signal read from the image sensor 120 in the first decimation readout mode is 1,333. In (b), the number of pixels in the direction along the horizontal direction H in the subject image of the image signal read from the image sensor 120 in the second decimation readout mode is 1,000. Comparing the ratio of these number of pixels (1,333 pixels, 1,000 pixels) with the aspect ratio (4: 3) of the image sensor 120,
1333 ÷ 1000 = 1.333
4 ÷ 3 ≒ 1.333
Is almost equal. That is, the resolutions of the image signals read in the first and second thinning readout modes and stored in the line buffer LB are substantially equal.

  This resolution can be considered as the ability to identify two points present in the subject image at a distance D as two points. With the configuration described above, when the image signal is read out in the first and second thinning readout modes, the pitch of the thinning readout target pixels arranged in the direction along the horizontal direction H in the subject image is the horizontal position and the vertical position shooting. It is almost constant regardless of the posture. Therefore, the image signals obtained from these readout target pixels have substantially the same resolution. 9A and 9B show the spatial frequencies obtained from the image signals read out from the same position in the subject image and stored in the line buffer LB in the first and second decimation readout modes. Is shown by a graph drawn schematically.

  Note that the image signals to be stored in the line buffer LB need not be all for 1,333 pixels and 1,000 pixels. That is, only a part of the continuous image signals are stored in the line buffer LB, such as 50 continuous pixels or 100 continuous pixels from the image signals continuously read out from the image sensor 120. May be. In addition, the image signal of a plurality of portions such as the left portion, the center portion, and the right portion in the shooting screen may be sequentially stored in the line buffer LB and the autofocus calculation may be performed. In this way, so-called multipoint focus detection can be performed.

  The processing procedure performed by the system controller 100 to read the image signal from the image sensor 120 in the thinning readout mode according to the posture (horizontal position, vertical position) of the imaging apparatus 10 described above and perform display or autofocus calculation. Will be described with reference to FIGS.

  The processing procedures shown in the flowcharts of FIGS. 10 to 13 are performed when the system controller 100 reads out the program stored in the memory 126 and interprets and executes it. More specifically, the program may be stored in the flash memory in the memory 126 as firmware. Normally, this program is stored in the flash memory during the manufacturing process of the imaging apparatus 10. Alternatively, a new program obtained by the user of the imaging apparatus 10 via the Internet or a storage medium such as a magnetic disk, an optical disk, or a memory card can be stored in the flash memory. The program stored in the flash memory is transferred to the RAM in the memory 126, and the system controller 100 sequentially reads and interprets and executes it.

  When a battery is mounted in the imaging device 10, the battery cover is closed, and a reset signal is issued, execution of the processing shown in the flowcharts of FIGS. 10 to 13 is started. In S1000, the system controller 100 performs an initial setting process. The initial setting processing includes exposure mode, setting ISO sensitivity of the image sensor 120, white balance mode (tungsten light, fluorescent light, clear sky, cloudy, automatic, manual, etc.), photometry mode, AF mode, number of recorded pixels, image This is a process of setting the data compression rate, the thinning-out reading mode, and the like at the time of recording data to initial values (default setting or setting previously selected by the user). In the embodiment of the present invention, when the thinning readout mode is set to an initial value, the first thinning readout mode is selected.

  In S1002, the system controller 100 determines whether or not the power switch of the imaging apparatus 10 is turned on. While this determination is denied, the determination of S1002 is repeated and the system controller 100 waits for the power switch to be turned on. On the other hand, if the determination in S1002 is affirmed, the system controller 100 performs a setting mode determination process in S1004. The setting mode determination process is a process of determining the operation mode of the imaging apparatus 10 set by the user.

  If it is determined in the determination process of S1004 that an operation mode other than the recording mode is set, the process proceeds to S1010, a process corresponding to the set mode is performed, and then the process returns to S1002. As an operation mode other than the recording mode, a reproduction mode is typical. On the other hand, if it is determined in S1004 that the recording mode is set, the process proceeds to S1006, and the contents currently set (the contents initially set in S1000 and the operation mode determined in S1004). Process to display.

  In S1008, the system controller 100 determines whether or not the live view display is set to OFF, and if this determination is affirmed (determined that the live view display is OFF), the process proceeds to S1012 and will be described below. Controls the recording mode operation without live view display. If the determination in S1008 is negative (it is determined that live view display is on), the process proceeds to S1100 in FIG.

  In S1012, which is a branch destination when the determination in S1008 is affirmed, the system controller 100 determines whether or not half-pressing of the release switch 150R (FIGS. 1 and 2) is ON, and this determination is denied. Then, the process returns to S1002. If the determination in S1012 is affirmative (determined that half-press is on), the process proceeds to S1014, and the system controller 100 uses the brightness (the amount of light incident on the image area of the image sensor 120) as a reference. It is determined whether or not the value is exceeded.

  This reference value is determined as described below. That is, when the field luminance is relatively dark, the amount of subject light incident on the image area of the image sensor 120 decreases and noise increases. In such a case, processing for reducing noise is performed by lowering the frame rate and extending the accumulation time, or by further increasing the thinning rate during thinning readout and performing pixel addition processing.

  The reference value corresponds to determining whether the noise needs to be reduced. If the brightness exceeds the reference value, the noise reduction processing is not performed, and AF control corresponding to the shooting posture is performed in S1016. As a result, the focus of the photographic lens 110 is adjusted, and a sharp image of the subject is formed on the image area of the image sensor 120. Details of the processing performed in S1014 will be described later in detail with reference to the flowchart of FIG.

  On the other hand, if it is determined in S1014 that the brightness does not exceed the reference value, AF control including processing for reducing the noise is performed in S1024. After AF control in S1016 or S1024 is performed, the process proceeds to S1018.

  In step S1018, the system controller 100 performs a shooting preparation operation. That is, the image pickup necessary for correcting camera shake by inputting information such as the camera shake amount and brightness obtained from the sensor 152 (FIG. 3) and the focal length, F value, and shooting distance set by the taking lens 110. The shift direction and shift amount of the element 120 (FIG. 3) are determined, the exposure amount is determined, and the image sensor shift control and the exposure amount control are performed based on these determined amounts.

  In S1020, the system controller 100 determines whether or not the release switch 150R is fully pressed, and returns to S1012 if the determination is negative. If the determination in S1020 is affirmative (determined that full-press is on), the process proceeds to S1022, and shooting (all pixel readout processing from the image sensor 120), image processing, image data compression, and compressed image are performed. Processing for recording data on the recording medium 160 (FIG. 3) is performed. Thereafter, the system controller 100 returns to the process of S1002.

  A process performed when the determination in S1008 is negative (live view display is determined to be on) will be described with reference to FIG.

  In S1100, the system controller 100 performs a camera shake reduction operation. That is, the image sensor 120 (FIG. 3) necessary for correcting the camera shake by inputting information such as the camera shake amount obtained from the sensor 152 (FIG. 3), the focal length set by the photographing lens 110, and the photographing distance. The shift direction and the shift amount are determined, and the image sensor shift is controlled based on the determined amount.

  In step S1102, the system controller 100 performs live view display processing with default settings. In the embodiment of the present invention, the live view display with the default setting is the live view display corresponding to the case where the imaging apparatus 10 is held in the horizontal position described with reference to FIGS. That is, the thinning readout mode is set to the first thinning readout mode, scanning is performed in the long side direction of the image sensor 100, and the display unit has 1,333 pixels in the long side direction and 250 pixels in the short side direction. Image data is generated. The image data is displayed by performing thinning / interpolation so that the display unit has 800 pixels in the long side direction and 600 pixels in the short side direction.

  In step S1104, the system controller 100 performs processing for updating the live view display condition. The process for updating the live view display condition is a process for updating conditions such as a frame rate (frame / second) and resolution when the image sensor 120 performs pixel thinning readout in response to a change in the field luminance or the like. It is. That is, when the field luminance is relatively dark, the amount of subject light incident on the image area of the image sensor 120 decreases and noise increases. As a result, the live view image displayed on the display unit 130 is rough and difficult to see. When such a situation is expected, processing for reducing noise is performed by lowering the frame rate to increase the accumulation time, or further increasing the thinning rate at the time of thinning readout and performing pixel addition processing.

  In S1106, the system controller 100 determines whether or not the half-press of the release switch 150R (FIGS. 1 and 2) is ON. If this determination is negative, the process returns to S1002 (branch C). On the other hand, if the determination in S1106 is affirmative (determining that half-pressing is on), the process proceeds to S1108, and the system controller 100 determines brightness (amount of light incident on the image area of the image sensor 120). It is determined whether or not exceeds the reference value. In order to suppress the increase in noise described above, this reference value needs to be processed such as lowering the frame rate and extending the accumulation time, or further increasing the thinning rate during thinning readout and performing pixel addition processing. It corresponds to determining whether or not.

  When the determination in S1108 is affirmative, that is, in S1110, which is a branch destination when it is determined that it is not necessary to reduce the noise, autofocus control corresponding to the shooting posture is performed. Adjustments are made. As a result, a sharp image of the subject is formed on the image area of the image sensor 120. The processing performed in S1110 will be described later with reference to the flowchart of FIG.

  In subsequent S1112, the system controller 100 performs display control processing corresponding to the shooting posture. The display control process corresponding to the shooting posture will be described later with reference to the flowchart of FIG.

  When the determination in S1108 is negative, that is, in S1118, which is a branch destination when it is determined that the noise needs to be reduced, the system controller 100 performs low-brightness autofocus control. That is, when the amount of subject light incident on the image area of the image sensor 120 is small, it may be difficult to perform accurate autofocus calculation due to noise. In such a case, as described above, the frame rate is lowered to extend the accumulation time, or the pixel addition processing is performed by further increasing the thinning rate during thinning readout. Then, autofocus calculation processing is performed using the image signal with reduced noise, and the position of the focusing lens is controlled based on the result.

  Subsequently, the system controller 100 performs display control during low luminance in S1120. That is, when the amount of subject light incident on the image area of the image sensor 120 is small, the live view image displayed on the display unit 130 may be unsightly due to noise. In such a case, as described above, the frame rate is lowered to extend the accumulation time, or the pixel addition processing is performed by further increasing the thinning rate during thinning readout. Then, live view display is performed using the image signal with reduced noise. In this case, the frame rate of the live view image is lowered and the resolution may appear to be lowered, but the noise of the displayed image is reduced.

  In the low-brightness autofocus control in S1118 and the low-brightness display control in S1120 described above, the main point is to reduce noise. For this reason, the autofocus control and display control corresponding to the shooting posture, which are performed in S1110 and S1112, are not performed. If the number of pixels of the image signal obtained by performing the above-described processing for reducing noise still exceeds the number of pixels of the display unit 130, the shooting posture as performed in S1110 and S1112 is set. The corresponding autofocus control and display control may be performed in S1118 and S1120.

  In S1114 following the process of S1112 or S1120, the system controller 100 determines whether or not the full press of the release switch 150R is ON. If this determination is negative, the process returns to S1104. If the determination in S1114 is affirmative (determined that full-press is on), the process proceeds to S1116, and imaging (all pixel readout processing from the image sensor 120), image processing, image data compression, and compressed image are performed. Processing for recording data on the recording medium 160 (FIG. 3) is performed. Thereafter, the system controller 100 returns to the process of S1104.

  The AF control corresponding to the shooting posture executed by the system controller 100 will be described with reference to the flowchart of FIG.

  In S1200, the system controller 100 inputs information related to the posture (tilt angle) of the imaging device 10 from the sensor 152 (FIG. 3). The sensor 152 outputs a binary type (only whether the shooting posture is a horizontal position / vertical position) and a multi-value (a value corresponding to the tilt angle of the imaging device 10). There are some possible types. In the embodiment of the present invention, the sensor 152 is described as being capable of outputting multiple values.

  In step S1202, the system controller 100 performs processing for determining a shooting posture. That is, based on the information output from the sensor 152, the horizontal direction of the subject image formed on the image area of the image sensor 120 (hereinafter referred to as “the horizontal direction of the subject image”) is the long side direction of the image sensor 120. And a process of determining which one of the short side directions is angularly close. When it is determined that the horizontal direction of the subject image is angularly closer to the long side direction than the short side direction of the image sensor 120, the shooting posture is determined to be a horizontal position. Conversely, when it is determined that the horizontal direction of the subject image is angularly closer to the short side direction of the image sensor 120 than the long side direction, the shooting posture is determined to be the vertical position. When the horizontal direction of the subject image is exactly halfway between the short side direction and the long side direction of the image sensor 120, it may be determined as the horizontal position.

  In S1202, which is a branch destination when it is determined in S1202 that the imaging posture of the imaging apparatus 10 is the horizontal position, the system controller 100 reads the image sensor 120 and the imaging circuit so that the image signal is read out in the first decimation readout mode. 122 is set. With this setting, an image signal is output from the image sensor 120 in the first decimation readout mode.

  In step S1206, the system controller 100 performs first autofocus calculation processing. That is, as described with reference to FIG. 9A, from the image sensor 120 in the scanning direction closer to the angle along the horizontal direction of the subject image (in this case, the long side direction of the image sensor). High-pass filter processing is performed on the one-dimensional array of image data based on a continuous portion in the read image signal. A contrast evaluation value is obtained from the result obtained by the high-pass filter processing.

  In S1208, which is a branch destination when it is determined in S1202 that the shooting posture of the imaging apparatus 10 is the vertical position, the system controller 100 reads the image signal 120 and the imaging circuit so that the image signal is read in the second thinning readout mode. 122 is set. With this setting, an image signal is output from the image sensor 120 in the second thinning readout mode.

  In step S1210, the system controller 100 performs a second autofocus calculation process. That is, as described with reference to FIG. 9B, from the image sensor 120 in the scanning direction in the direction closer to the angle along the horizontal direction of the subject image (in this case, the short side direction of the image sensor). High-pass filter processing is performed on the one-dimensional array of image data based on a continuous portion in the read image signal. A contrast evaluation value is detected from the result obtained by the high-pass filter processing.

  When the processing in S1206 or S1210 is completed, the system controller 100 determines in S1212 whether or not the contrast evaluation value obtained in S1206 or S1210 is a maximum. That is, a change in contrast evaluation value is monitored while moving the focusing lens by a so-called hill-climbing AF method, and it is determined whether or not a peak evaluation value or a contrast evaluation value close to the peak value can be obtained at the current focusing lens position.

  If the determination in S1212 is positive, the system controller 100 returns. On the other hand, if the determination in S1212 is negative, the process branches to S1214 to perform processing for moving the focusing lens, and returns to S1200. In the flowchart of FIG. 12, for the processing in the case where the contrast evaluation value obtained in S1206 or S1210 is too low and it is difficult to determine whether the focus is in focus or not, it is easy to understand the present invention. Omitted for purposes.

  With reference to the flowchart of FIG. 13, display control corresponding to the shooting posture executed by the system controller 100 will be described.

  In S1300, the system controller 100 inputs information related to the posture (tilt angle) of the imaging device 10 from the sensor 152 (FIG. 3). As described above, in the embodiment of the present invention, the sensor 152 will be described as being capable of outputting multiple values.

  In step S1302, the system controller 100 performs processing for determining a shooting posture. That is, based on the information output from the sensor 152, a process is performed to determine which of the long side direction and the short side direction of the image sensor 120 is angularly close to the horizontal direction of the subject image. When it is determined that the horizontal direction of the subject image is angularly closer to the long side direction than the short side direction of the image sensor 120, the shooting posture is determined to be a horizontal position. Conversely, if it is determined that the horizontal direction of the subject image is angularly closer to the short side direction than the long side direction of the image sensor 120, the shooting posture is determined to be the vertical position. When the horizontal direction of the subject image is exactly halfway between the short side direction and the long side direction of the image sensor 120, it may be determined as the horizontal position.

  In S1304, which is a branch destination when it is determined in S1302 that the imaging posture of the imaging apparatus 10 is the horizontal position, the system controller 100 reads the image signal in the first decimation readout mode and the imaging circuit 120 so that the image signal is read out. 122 is set. With this setting, an image signal (an image signal of 1,333 pixels in the long side direction and 250 pixels in the short side direction) is output from the image sensor 120 in the first decimation readout mode.

  In step S1306, the system controller 100 performs a first image display process. That is, as described with reference to FIG. 7, thinning / interpolation processing is performed on image data having 1,333 pixels in the long side direction and 250 pixels in the short side direction of the image sensor 120 to obtain 800 pixels and 600 pixels, respectively. A control signal is issued to the image processing unit 124 so as to generate pixel display image data. An image based on the display image data is displayed on the display unit 130.

  In S1308, which is a branch destination when it is determined in S1302 that the shooting posture of the imaging apparatus 10 is the vertical position, the system controller 100 reads the image sensor 120 and the imaging circuit so that the image signal is read in the second thinning readout mode. 122 is set. With this setting, an image signal (an image signal having 333 pixels in the long side direction and 1,000 pixels in the short side direction) is output from the image sensor 120 in the second thinning readout mode.

  In step S1310, the system controller 100 performs a second image display process. That is, as described with reference to FIG. 8, thinning / interpolation processing is performed on image data having 333 pixels in the long side direction and 1,000 pixels in the short side direction of the image sensor 120 to obtain 800 pixels and 600 pixels, respectively. A control signal is issued to the image processing unit 124 so as to generate pixel display image data. An image based on the display image data is displayed on the display unit 130.

  The display control process according to the shooting posture described above is completed, and the system controller returns.

  As described above, in the imaging device 10 according to the embodiment of the present invention, the imaging element 120 has a plurality of thinning readout modes in which combinations of thinning rates in the long side direction and the short side direction of the image area are different. Then, a thinning readout mode corresponding to the detected photographing posture is selected, whereby the resolution in the direction along the horizontal direction of the subject image is substantially constant regardless of the photographing posture in the image signal obtained by the thinning readout. To be.

  By doing this, it is possible to detect the edge extending in the vertical direction in the subject image, perform autofocus calculation, and maintain the accuracy when detecting the focus substantially constant regardless of the shooting posture. Become. In addition, when performing live view display, the horizontal resolution (display resolution) of the displayed image can be kept substantially constant, and when viewed in a horizontal position as in a conventional imaging device, the live view is displayed. Although moire does not occur in the image, it is possible to suppress a problem such that moire occurs when the image is held in the vertical position.

  Further, when switching the thinning readout mode according to the shooting posture, the short side direction thinning rate is longer in the horizontal position than the long side direction thinning rate in terms of the long side direction thinning rate and the short side direction thinning rate. In the vertical position, the thinning rate in the long side direction is set to be larger than the thinning rate in the short side direction. By doing so, it is possible to suppress a large change in the capacity (number of pixels) of the image signal read by switching the thinning readout mode when the photographing posture is changed. In this way, it is possible to suppress changes in throughput during reading and processing of image signals.

  In addition, the resolution in the horizontal direction of the subject image is always kept high by reducing the thinning rate in the long side direction at the horizontal position and decreasing the thinning rate in the short side direction at the vertical position. It becomes possible to do. This is effective in increasing the accuracy of autofocus by detecting vertical edges that are included in the subject image in a relatively large amount.

  Although the case where the image sensor 120 is an XY address scanning type CMOS image sensor has been described above as an example, the image sensor 120 may be a CCD or the like. Note that it is difficult for a CCD to read an image signal by an XY address scanning method because of the principle of reading the image signal. This will be described with reference to FIG. 14 (a) showing the principle of image signal readout from the CCD.

  In general, the CCD moves the charge accumulated in each pixel to the vertical transfer path V, then moves the image signal for one row to the horizontal transfer path H, and outputs the image signal pixel by pixel from the horizontal transfer path H. It has a configuration for reading. Therefore, the scanning direction at the time of scanning by the raster scanning method is only a direction parallel to the left-right direction in FIG. FIG. 14A shows an example in which the thinning rate in the long side direction is set to 2 and the thinning rate in the short side direction is set to 3.

  Now, as shown in FIG. 14B, it is assumed that shooting is performed in the vertical position, and autofocus calculation processing is performed based on the image signal of the region S. In this case, as shown in FIG. 14 (c), the image signals of the pixels corresponding to the region S from the image signals of D1, D2, D3,. ) Can be sequentially stored in the line buffer LB. When the necessary image signals are stored in the line buffer LB, the autofocus calculation process can be performed on the image signals in the line buffer LB.

  The image signal to be stored in the line buffer LB is determined by the contrast AF control unit 104 according to the detected photographing posture, and the control signal is output to the AF processing unit 108. The AF processing unit 108 is configured to extract a necessary image signal from image signals sequentially output from the imaging circuit 122 based on the control signal output from the contrast AF control unit 104 and store the extracted image signal in the line buffer LB. Is done.

  The example in which the imaging apparatus 10 according to the embodiment of the present invention has the line buffer LB for AF processing has been described above. However, the present invention is not limited to this, and may have a buffer capable of storing two-dimensionally arranged image signals (hereinafter referred to as an area buffer). This area buffer may be capable of recording all image signals for one frame read from the image sensor 120 by thinning-out reading, or may be capable of recording a part of image signals. Hereinafter, an example in which the imaging apparatus 10 includes an area buffer will be described with reference to FIGS. 15 and 16.

  FIGS. 15A and 15B are diagrams for explaining the second thinning readout when the imaging apparatus 10 has an area buffer. FIG. 15A shows the scanning direction, FIG. 15B shows the arrangement of on-chip color filters, and FIG. 2 shows a pixel to be read in thinning-out reading of 2.

  When the imaging apparatus 10 includes an area buffer, the second thinning readout is different from that illustrated in FIG. 6 as described below. The first decimation readout is the same as that described above with reference to FIG.

  The second decimation readout in the case where the imaging apparatus 10 has an area buffer will be described with reference to FIG. 15, focusing on the difference from that shown in FIG. The scanning direction in the second thinning readout mode shown in FIG. 15 is a direction parallel to the long side direction of the image area of the image sensor 120, as in the first thinning readout mode shown in FIG. It is different from 6.

  On the other hand, the thinning rate is set to 3 in the short side direction and 12 in the long side direction, which is the same as that shown in FIG. As a result, as shown in FIG. 15C, in the first column, the first row, the 14th row, the 25th row, the 38th row, the 49th row,..., The (1 + 24 × n) row, Image signals are read out from the pixels in the (14 + 24 × n) th row,..., The 3985th row, and the 3998th row. Similarly, an image signal is read out from the pixels in the above row in the fourth column, the seventh column,..., The (1 + 3 × n) column,.

  In the example of FIG. 15, the row read next to the first row is not the thirteenth row but the fourteenth row. The first row and the thirteenth row have the same arrangement of on-chip color filters. Because there is. That is, if thinning readout is performed as in the first row, the 13th row, the 25th row, the 37th row, and the 49th row, red color information cannot be obtained from the obtained image signal.

  With the second decimation readout mode described above, an image signal composed of 333 (4000 ÷ 12) pixels in the long side direction and 1,000 (3000 ÷ 3) pixels in the short side direction can be obtained. It becomes. That is, an image signal composed of 333,000 pixels of 1,000 pixels in the direction closer to the horizontal direction of the subject image formed on the image sensor 120 and 333 pixels in the direction closer to the angle in the vertical direction. Can be obtained by the second thinning readout described above with reference to FIG.

  The resulting image signal is the same as that shown in FIG. As described above, the reason for performing thinning readout in a constant scanning direction regardless of the photographing position is that even if the scanning direction is changed, it is difficult to cause a difference in the time until the two-dimensional array image signal is stored in the area buffer. Because there are many. That is, when the image signal is stored in the line buffer LB, as is apparent from FIG. 9B, changing the scanning direction is effective in shortening the time from the start to the completion of the image signal storage. It is. However, when a two-dimensional array of image signals is stored in the area buffer, a difference in scanning direction often does not easily cause a difference in time required from the start to completion of image signal storage in the area buffer.

  However, in the case of storing only a part of the two-dimensional array image signal in the image signal obtained by thinning-out reading in the area buffer, depending on what partial area is cut out and stored, the shape of the partial area In some cases, changing the scanning direction is effective in reducing the time. In such a case, the second thinning readout may be performed by any one of the thinning readouts described with reference to FIGS. 6 and 15. Hereinafter, it is assumed that the thinning-out reading described with reference to FIG. 15 is performed in the second thinning-out reading.

  FIG. 16 shows an autofocus operation performed on an image signal read from the image sensor 120 in the first and second thinning readout modes and stored in the area buffer when the imaging apparatus 10 has an area buffer. It is a figure explaining a process. In FIG. 16A, the image pickup apparatus 10 is held in the horizontal position, the first thinning readout mode is selected, and the image signal read by scanning in the long side direction of the image sensor 120 is the area buffer AB. It shows how it is memorized. (B) shows an image signal (first decimation readout mode that is read out by scanning the image sensor 120 in the long side direction when the imaging apparatus 10 is held in a vertical position, the second decimation readout mode is selected, and the image sensor 120 is scanned. (It should be noted that the thinning rate in the long side direction and the short side direction is different from that in the case of FIG. 3).

  As a premise for the following description, in FIGS. 16A and 16B, it is assumed that the shooting conditions differ only in composition, and all other conditions are the same. That is, the shooting distance, the focal length of the shooting lens 110, and the focus adjustment position are all the same.

FIGS. 16A and 16B show a state in which a subject image (an inverted inverted image) is formed on the image area of the image sensor 120 as viewed from the front side of the imaging device 10. . In (a), the number of pixels in the direction along the horizontal direction H in the subject image of the image signal read from the image sensor 120 in the first decimation readout mode is 1,333. In (b), the number of pixels in the direction along the horizontal direction H in the subject image of the image signal read from the image sensor 120 in the second decimation readout mode is 1,000. Comparing the ratio of these number of pixels (1,333 pixels, 1,000 pixels) with the aspect ratio (4: 3) of the image sensor 120,
1333 ÷ 1000 = 1.333
4 ÷ 3 ≒ 1.333
Is almost equal. That is, the resolution in the direction along the horizontal direction H in the subject image among the image signals read out in the first and second thinning-out reading modes and stored in the area buffer LB is substantially equal.

  With the configuration described above, when the image signal is read out in the first and second thinning readout modes, the pitch of the thinning readout target pixels arranged in the direction along the horizontal direction H in the subject image is the horizontal position and the vertical position shooting. It is almost constant regardless of the posture.

  The AF calculation process performed on the image signal in the area buffer AB will be described. The AF calculation processing can perform high-pass filter processing in any direction in the two-dimensional array of image signals stored in the area buffer AB. However, in the imaging device 10 according to the embodiment of the present invention, as described above, the two-dimensional image signal in the area buffer AB has a relatively high resolution in the direction along the horizontal direction H in the subject image. It is configured. Accordingly, it is desirable to perform high-pass filter processing on one-dimensional array image data based on a continuous portion in the direction along the horizontal direction H in the subject image. In other words, the AF calculation process is performed so as to detect the vertical edge in the subject image, and the AF calculation is performed so as to effectively use the relatively high resolution in the direction along the horizontal direction in the subject image. It is desirable for obtaining high AF accuracy.

  From the above viewpoint, when the imaging apparatus 10 includes the area buffer AB, the AF processing unit 108 (FIG. 3) performs high-pass filter processing on the image signal stored in the area buffer AB according to the shooting posture. The direction when performing the process is the direction along the arrows marked with L and T in FIGS. 16A and 16B, and the contrast evaluation value is detected from the obtained result.

  16 (a) and 16 (b) correspond to substantially the same position in the subject image obtained by horizontal / vertical position shooting in the two-dimensional image signal stored in the line buffer LB as described above. A state in which the spatial frequencies obtained from the one-dimensional image signal of the part to be substantially equal is shown by a graph drawn schematically.

  As described above, it is not necessary to store all of the image signals obtained by the thinning-out reading in the area buffer AB. That is, it may be configured such that only a part of the continuous image signals are stored in the area buffer LB from the image signals continuously read out from the image sensor 120. Further, the photographing screen is divided into a plurality of areas, and image signals of a plurality of portions corresponding to the respective divided regions are stored in the area buffer AB, and the above-described autofocus calculation is performed for each of the plurality of portions. It may be configured to be In this way, so-called multipoint focus detection can be performed.

  Even in the case where the imaging device 10 has the area buffer AB, the processing procedure of the system controller 100 when the image signal is read out from the imaging device 120 in the thinning readout mode according to the attitude of the imaging device 10 and display or AF calculation is performed is as follows. 10 to FIG. 13 is substantially the same except for the parts described below.

  In S2104 in FIG. 12 and S1304 in FIG. 13, the first decimation readout described with reference to FIG. 5 is performed. Similarly, in S1208 and S1308, the second thinning readout described with reference to FIG. 15 is performed.

  In the first AF calculation process performed in S1206, as shown in FIG. 16A, the two-dimensional image signals stored in the area buffer AB are arranged in a direction along the long side direction of the image sensor 120. A high pass filter process is performed on the signal to obtain a contrast evaluation value. That is, in FIG. 16A, the high-pass filter process is performed in the direction of the arrow with the symbol L, and the contrast evaluation value is obtained.

  Further, in the second AF calculation process performed in S1210, as shown in FIG. 16B, in the two-dimensional image signal stored in the area buffer AB, in the direction along the short side direction of the image sensor 120. High-pass filter processing is performed on the aligned signals, and a contrast evaluation value is obtained. That is, in FIG. 16B, a high-pass filter process is performed in the direction of the arrow labeled T, and a contrast evaluation value is obtained.

  In the above, the image signal having the number of pixels reduced from the number of pixels obtained by reading all pixels from the image sensor 120 (4,000 pixels in the long side direction and 3,000 pixels in the short side direction). An example in which thinning-out reading is performed when reading is described. However, the present invention is not limited to this, and the number of pixels of the image signal to be read out may be reduced using a so-called pixel addition technique.

  The imaging apparatus according to the present invention can be a photographic lens fixed or interchangeable still camera or movie camera. Further, the present invention can be applied to a camera incorporated in a mobile phone, a personal digital assistant (PDA), a notebook PC, or the like.

1 is a perspective view schematically showing a front side appearance of an imaging apparatus according to an embodiment of the present invention. It is a perspective view showing roughly the back side appearance of the imaging device concerning an embodiment of the invention. 1 is a block diagram schematically showing an internal configuration of an imaging apparatus according to an embodiment of the present invention. It is a figure which shows the example of an arrangement | sequence of the pixel of an image pick-up element. FIG. 6 is a diagram for explaining first thinning readout, where (a) shows a scanning direction, (b) shows an array of on-chip color filters, and (c) shows a pixel to be read in the first thinning readout. FIG. 6 is a diagram for explaining second thinning readout, where (a) shows a scanning direction, (b) shows an array of on-chip color filters, and (c) shows a pixel to be read in second thinning readout. It is a figure explaining a mode that a live view display is performed based on the image data produced | generated from the image signal read in 1st thinning-out readout mode, (a) is an image obtained by carrying out all pixel readout, (B) is the thinned-out read image data generated from the image signal read in the first thinned-out read mode, and (c) is the long side of the display image obtained by performing the scaling process on the thinned-out read image data. Display image data having 800 pixels in the direction and 600 pixels in the short side direction is shown. It is a figure explaining a mode that a live view display is performed based on the image data produced | generated from the image signal read by 2nd thinning-out readout mode, (a) is an image obtained by carrying out all pixel readout, (B) is the thinned-out read image data generated from the image signal read in the second thinned-out read mode, and (c) is the long side of the display image obtained by performing the scaling process on the thinned-out read image data. Display image data having 800 pixels in the direction and 600 pixels in the short side direction is shown. A state in which a part of continuous image signals among the image signals read in the first and second thinning readout modes is stored in the line buffer is shown in FIG. (B) shows an example in which thinning readout is performed in the second thinning readout mode. It is a flowchart which illustrates roughly the process sequence of the live view display and autofocus calculation performed with the system controller in the imaging device which concerns on embodiment of this invention. It is a flowchart explaining the process sequence following the process of the flowchart shown in FIG. 6 is a flowchart for schematically explaining a processing procedure of AF control corresponding to a photographing posture, which is executed by a system controller in the imaging apparatus according to the embodiment of the present invention. It is a flowchart which illustrates roughly the process sequence of the display control corresponding to a photography attitude | position performed with the system controller in the imaging device which concerns on embodiment of this invention. It is a figure which shows notionally the process of AF control corresponding to an imaging | photography attitude | position in case an image pick-up element is CCD, (a) is the operation principle of the image signal reading performed by CCD, (b) is vertical position imaging | photography. (C) shows how the image signal extracted from the image signal read from the CCD is stored in the line buffer. It is a figure explaining the 2nd thinning-out reading applicable when it has an area buffer as a buffer for AF processing, (a) is a scanning direction, (b) is an arrangement of an on-chip color filter, (c) Indicates a pixel to be read out in the first decimation readout. When an area buffer is provided as an AF processing buffer, a part or all of the image signals read out in the first and second thinning-out reading modes are stored in the area buffer. a) shows an example in the case where thinning-out reading is performed in the first thinning-out reading mode, and (b) shows an example in which thinning-out reading is performed in the second thinning-out reading mode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Imaging device 100 ... System controller 102 ... Thinning-out reading mode selection part 104 ... Contrast AF control part 106 ... Display control part 108 ... AF process part 110 ... Shooting lens 112 ... Aperture 114 ... Shutter 116 ... AF mechanism 120 ... Imaging element 122 Image pickup circuit 124 Image processing unit 126 Memory 130 Display unit 140 Flash control circuit 142 Flash light emitting unit 150 Operation unit 152 Sensor 154 Shooting posture detection unit 160 Memory card 162 Memory card interface LB Line buffer

Claims (10)

An imaging device having an imaging element, a shooting posture detection unit, and a thinning readout mode selection unit,
The imaging element has a rectangular image area, and the number of pixels arranged in a long side direction that is a direction along the long side of the rectangle is in a short side direction that is a direction along the short side of the rectangle. Pixels are arranged to exceed the number of arranged pixels, and a combination of a long side direction thinning rate that is the thinning rate in the long side direction and a short side direction thinning rate that is the thinning rate in the short side direction is a combination It is configured to enable decimation readout in different decimation readout modes,
The photographing posture detection unit is configured to be able to detect that the photographing posture of the imaging device is set in a horizontal position or a vertical position,
The decimation readout mode selection unit selects any one of the plurality of decimation readout modes of the image sensor according to the imaging orientation detected by the imaging orientation detection unit when performing the decimation readout with the image sensor. The image pickup apparatus is characterized in that, in the obtained image signal, the resolution in the direction along the horizontal direction of the subject image becomes substantially constant regardless of the shooting posture.   The combination of the long side direction thinning rate and the short side direction thinning rate in the thinning readout mode selected corresponding to each of the case where the photographing posture of the imaging device is a horizontal position and a vertical position is a horizontal position photographing posture. In the decimation readout mode selected corresponding to the other, the other decimation rate is set to be larger than the decimation rate in one, and in the decimation readout mode selected in accordance with the shooting posture in the vertical position, the other decimation rate is set. The imaging apparatus according to claim 1, wherein the one thinning rate is set to be larger than the thinning rate.   The combination of the long side direction thinning rate and the short side direction thinning rate in the thinning readout mode selected corresponding to each of the case where the photographing posture of the imaging device is the horizontal position and the vertical position is the long side direction Of the short side directions, the thinning rate in the direction that is angularly close to the horizontal direction of the subject image formed in the image area of the image sensor is thinned in the direction that is angularly close to the vertical direction of the subject image. The imaging apparatus according to claim 2, wherein the imaging apparatus is set to be smaller than a rate. An image display unit;
A display processing unit for displaying on the image display unit an image obtained by imaging with the imaging element;
The display processing unit calculates the number of pixels of the image data generated by processing the image signal read from the image sensor in the thinning readout mode selected according to the shooting posture detected by the shooting posture detection unit. The imaging apparatus according to claim 1, wherein the imaging apparatus is configured to perform scaling processing so as to match a number of display pixels when displayed on the image display unit. An AF processing unit for processing an image signal read from the image sensor and performing an autofocus operation;
The AF processing unit is arranged in the long side direction according to the shooting posture detected by the shooting posture detection unit in a two-dimensional array of image signals obtained corresponding to pixels two-dimensionally arranged on the image area. The autofocus calculation is performed on image data based on image signals obtained from pixels arranged in the direction closer to the horizontal direction of the subject image formed on the image area in the short side direction. The imaging apparatus according to claim 4, wherein the imaging apparatus is configured as described above. The image sensor is an XY address scanning type capable of dot-sequential readout along any direction of the long side direction and the short side direction,
A scanning direction switching unit that switches a scanning direction at the time of reading an image signal from the image sensor by a raster scanning method to the long side direction or the short side direction;
The scanning direction switching unit is a direction along a horizontal direction of a subject image formed on the image area, out of the long side direction and the short side direction, according to the photographing posture detected by the photographing posture detecting unit. The imaging apparatus according to claim 5, wherein the imaging apparatus is configured to switch in a scanning direction that is closer to the angle.   The AF processing unit is based on a continuous portion in the image signal read from the image sensor in the scanning direction switched by the scanning direction switching unit according to the photographing posture detected by the photographing posture detection unit. The imaging apparatus according to claim 6, wherein the imaging apparatus is configured to perform the autofocus operation on one-dimensional array image data. A brightness determination unit that determines the brightness of the subject or the brightness of light incident on the image area through the photographing lens;
The thinning readout mode selection unit, based on the detection result of the brightness determination unit, the imaging according to the shooting posture detected by the shooting posture detection unit when the brightness is equal to or lower than a predetermined brightness. The imaging apparatus according to claim 1, wherein the imaging apparatus is configured not to perform a process of selecting any one of the plurality of thinning readout modes of the element.   9. The predetermined brightness corresponds to a brightness at which execution of noise reduction processing is started in response to a decrease in the amount of subject light incident on the image area. The imaging device described in 1. A release operation member;
The thinning readout mode selection unit is configured to select one of the plurality of thinning readout modes of the image sensor according to the photographing posture detected by the photographing posture detector when the release operation member is half-pressed. The imaging apparatus according to claim 1, wherein the imaging apparatus is configured to start execution of a process for selecting the mode.

Images