JP2004221650A - Electronic camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic camera capable of attaining a high speed automatic focusing (AF) control and properly displaying a preview at the AF control. <P>SOLUTION: A CCD (charge couple device) imaging device for a digital camera 1 can select either a draft mode wherein comparatively many pixels are read and an automatic focusing mode wherein the pixels are read at a comparatively high speed. The digital camera 1 attains high speed AF by performing AF control on the basis of an image Gf read in the automatic focusing mode, detects the moving amount (vector) M of an object by utilizing the image Gf read in the automatic focusing mode, generates a display image Gh on the basis of the moving amount and an image Gb which has been read in the draft mode before the transition to the automatic focusing mode, and allows an LCD (liquid crystal display) or the like to display the display image Gh. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electronic camera having an autofocus (hereinafter, also simply referred to as AF) control function and a display function of displaying an image on a liquid crystal display or the like.
[0002]
[Prior art]
A digital camera (electronic camera) generally has a display unit (display means) such as a liquid crystal display (hereinafter, also referred to as LCD). Then, on this LCD, a live view image for preview before actual shooting is updated and displayed at predetermined time intervals. Such image display for preview (hereinafter, also referred to as preview display) is very useful for grasping the photographing situation of a subject when photographing with a digital camera.
[0003]
Some digital cameras adopt a hill-climbing method using an image signal from a CCD image pickup device of the digital camera as an autofocus control method. The “hill-climbing method” is a focus control method in which the lens position at which the focus evaluation value such as the contrast of an image obtained by the CCD image pickup device is the largest is specified as the lens position in the focused state. This hill-climbing method has the advantage that it is not necessary to separately provide a distance measuring sensor for measuring the distance to the subject, and is therefore adopted in many digital cameras.
[0004]
By the way, in the CCD image pickup device, a read mode for live view (also referred to as a draft mode) for reading an image over a relatively wide range, and an image read at a higher speed by reading a part of the image in the draft mode. There is an AF reading mode (also referred to as an automatic focusing mode).
[0005]
In a digital camera having the above-described auto focus control function and display function, it is expected that the speed of the auto focus control will be increased by using such a readout mode for AF (automatic focusing mode). Is done.
[0006]
As such a technique, there is a technique described in Patent Document 1 below. In this prior art, a reading mode in a CCD image pickup device is selected according to a setting as to whether or not an image is to be displayed on a display unit during photographing. Then, only when it is set that the image is not to be preview-displayed on the display unit, the image is read in a read mode (corresponding to an automatic focusing mode) in which a part of the image is read to read out the image at a relatively high speed. On the other hand, when the preview display of the image is set on the display unit, the image is read in a read mode (corresponding to a draft mode) for reading an image over a relatively wide range, and the read image is displayed on the display unit.
[0007]
[Patent Document 1]
JP 2001-318307 A
[0008]
[Problems to be solved by the invention]
However, in the above-described conventional technique, when the preview display of the image is set on the display unit, the image is read out in the draft mode which is slower than the automatic focusing mode. There is a problem that can not be.
[0009]
On the other hand, in a case where the image is read while the image is previewed on the display unit and the image is read in the automatic focusing mode, if the image read in the automatic focusing mode is used only, the image is read in the automatic focusing mode. An image corresponding to an area larger than the output image cannot be displayed. This is because an image read in the automatic focusing mode corresponds only to an area smaller than that in the draft mode.
[0010]
In order to cope with such a situation, an image immediately before the start of the autofocus control is continuously displayed on the display unit during the autofocus control, and the updating of the screen display on the display unit is stopped. However, in this case, the live view display is not updated at all during the auto focus control, and the image stops, so that when changing the composition in shooting, the position of the subject on the screen cannot be confirmed. Inconvenience will occur.
[0011]
In view of the above problems, an object of the present invention is to provide an electronic camera capable of speeding up autofocus control and optimizing preview display during autofocus control.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 is an electronic camera, comprising: an imaging element that converts a subject image into an image signal by photoelectric conversion; a display unit that displays an image based on the image signal; Display control means for controlling a display operation in the means, focus control means for performing autofocus control based on the image signal, and read control means for controlling a read operation of the image signal from the image sensor. The readout control unit may be configured to read out image signals corresponding to a predetermined number of pixels among all pixels in the image sensor at a time point before the autofocus control by the focus control unit. An image signal is read from the image sensor, and at the time of the autofocus control, an image signal corresponding to a smaller number of pixels than the predetermined number of pixels among all the pixels is read. The image signal is read from the image sensor in a second mode in which a plurality of images are read at high speed, and the focusing control unit performs the autofocus control based on the image signal read in the second mode, and The control means detects the movement amount of the subject using the image signal read in the second mode during the autofocus control, and detects the movement amount and the movement amount in the first mode before shifting to the second mode. A display image is generated based on the first image based on the read image signal, and the display image is displayed on the display unit.
[0013]
According to a second aspect of the present invention, in the electronic camera according to the first aspect of the present invention, the display control means generates, as the display image, an image whose center position is shifted from the center position of the first image by the moving amount. It is characterized by the following.
[0014]
According to a third aspect of the present invention, in the electronic camera according to the first or second aspect, the display image is obtained as an image obtained by extracting a partial region of the first image.
[0015]
According to a fourth aspect of the present invention, in the electronic camera according to the first or second aspect, the display image is an image obtained as an image obtained by extracting a partial region of the first image. The control means performs the display control on condition that an enlarged display mode for enlarging and displaying the partial area of the first image is selected by an operator at a time before the time of the autofocus control. And
[0016]
According to a fifth aspect of the present invention, in the electronic camera according to any one of the first to third aspects, the display control means changes a preview display on the display means in response to an operation of pressing a shutter button by an operator. The display is changed to a preview display by the display control.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0018]
<Schematic configuration>
FIGS. 1, 2 and 3 are views showing the external configuration of a digital camera 1 (electronic camera or imaging device) according to an embodiment of the present invention. FIG. 1 is a front view, FIG. Corresponds to the rear view. These drawings do not always conform to the triangular projection, and the main purpose is to exemplify the appearance of the digital camera 1.
[0019]
A photographing lens 2 is provided on the front side of the digital camera 1. The photographing lens 2 has a zoom function, and is configured so that the photographing magnification can be changed by manually rotating the zoom ring 2a.
[0020]
Further, a shutter button (release button) 9 is provided on the upper surface of the digital camera 1, and the shutter button 9 is a two-stage push-in switch capable of distinguishing between a half-pressed state and a fully-pressed state by the user. When the automatic focusing mode is set, the automatic focusing control (also referred to as autofocus control) is started when the shutter button is half-pressed, and a book for photographing a recording image when the shutter button is fully pressed. Start the shooting operation.
[0021]
On the upper surface of the digital camera 1, there is provided a mode switching dial 3 for switching between "shooting mode", "reproduction mode" and "communication mode". The shooting mode is a mode in which a subject is shot to generate image data, and the shooting mode is further divided into a still image shooting mode and a moving image shooting mode. The reproduction mode is a mode in which image data recorded on the memory card 90 is reproduced and displayed on a liquid crystal display (hereinafter, referred to as LCD) 5 provided on the back side of the digital camera 1. Further, the communication mode is a mode in which data is transferred to an external computer 91 or the like via the external connection interface 38 provided on the side of the digital camera 1.
[0022]
On the rear surface of the digital camera 1, an LCD 5 for performing live view display and playback display of a recorded image and the like before an actual photographing operation, and an electronic viewfinder (hereinafter, referred to as EVF) 4 are provided. The LCD 5 and the EVF 4 each display a color image. In the following description, a case where the LCD 5 has a display pixel number of 320 × 240 is exemplified.
[0023]
Further, a menu button 6 is provided on the back of the digital camera 1, and when the menu button 6 is pressed, various menu screens are displayed on the LCD 5. Further, on the back of the digital camera 1, there is provided a control button 7 including a cross cursor button 7a for moving a display cursor on the LCD 5 in four directions and an enter button 7e provided at the center of the cross cursor button. . Using the menu button 6 and the control button 7, an operation for setting various shooting parameters is performed. The setting states of various shooting parameters are displayed on a data panel 8 arranged on the upper surface side of the digital camera 1. Various operation buttons such as an enlarge button 35a are arranged on the back of the digital camera 1 in addition to the above.
[0024]
Further, on the side of the digital camera 1, an insertion mounting portion for a memory card 90, which is a detachable recording medium, is provided, and image data obtained by actual shooting is stored in the memory card 90 set in the insertion mounting portion. Be recorded.
[0025]
<Internal configuration>
Next, the internal configuration of the digital camera 1 will be described.
[0026]
FIG. 4 is a block diagram illustrating internal functions of the digital camera 1.
[0027]
The photographing lens 2 is driven by a lens driving unit 31 and is configured to change the focus state of an image formed on the CCD image sensor 10. At the time of automatic focusing (autofocus) setting, the overall control unit 20 automatically determines the lens driving amount of the photographing lens 2 from the image, and the photographing lens 2 is driven based on this lens driving amount. At the time of manual focusing (manual focus) setting, the lens driving amount is determined according to the operation amount of the control button 7 by the user, and the photographing lens 2 is driven based on this lens driving amount.
[0028]
The CCD imaging device 10 functions as an imaging unit that captures a subject image and generates an electronic image signal, has 2560 × 1920 pixels, and has a light image of the subject formed by the imaging lens 2. (Subject image) is photoelectrically converted into an image signal of R (red), G (green), and B (blue) color components (a signal composed of a signal sequence of pixel signals received by each pixel) for each pixel. Output. The timing generator 32 generates various timing pulses for controlling the driving of the CCD imaging device 10. The operation of reading the image signal from the CCD image sensor 10 is controlled by the overall control unit 20 and the timing generator 32.
[0029]
The driving method (readout mode) of the CCD imaging device 10 includes three modes: a “draft mode”, an “autofocus mode”, and a “real shooting mode”. Switching control between these three modes is performed by the overall control unit 20 and the timing generator 32.
[0030]
Among these three modes, the “draft mode” is a readout mode for generating an image for preview (also referred to as live view) before actual shooting. In short, the draft mode is a mode in which image signals are thinned out and read in order to generate a preview image.
[0031]
Generally, signal reading from a CCD image pickup device is performed for each horizontal line. For this reason, in the draft mode, when reading out pixel signals for each horizontal line from the CCD image pickup device 10 having 2560 pixels in the horizontal direction and 1920 pixels in the vertical direction, the CCD image pickup device 10 is driven so as to read out one line out of eight lines. You. That is, in the draft mode, the 1920 horizontal lines are read out in a state where they are thinned out by 1/8. As a result, the image G1 output from the CCD image pickup device in the draft mode has 2560 × 240 pixels as shown in FIG. The draft mode can also be expressed as a mode in which image signals corresponding to a predetermined number of pixels among all pixels in the image sensor are read.
[0032]
The “auto focus mode” (hereinafter, also referred to as AF mode) is a mode in which a plurality of images are read at high speed by reading image signals corresponding to a smaller number of pixels than in the draft mode (and the main shooting mode). is there. This automatic focusing mode is applied at the time of automatic focusing control (automatic focusing control). In the automatic focusing mode, some horizontal lines (for example, 80 lines located at the center) of the 240 lines read in the draft mode are read. As a result, the image G2 output from the CCD image pickup device in the automatic focusing mode is composed of 2560 × 80 pixels as shown in FIG. Note that the broken line in FIG. 6 shows the image G1 in the draft mode.
[0033]
In the “autofocus mode”, image signals corresponding to a smaller number of horizontal lines than the “draft mode” (in other words, image signals corresponding to a smaller number of pixels than the “draft mode”) are read. Therefore, reading of frame images is speeded up, and a plurality of images are read at high speed. Specifically, the lines other than the 80 horizontal lines do not need to be read out as pixel signals from the CCD image sensor 10, and are discharged from the vertical transfer lines of the CCD image sensor 10 by high-speed driving using short-period drive pulses to achieve high-speed driving. , The speed of the image signal from the CCD imaging device 10 can be increased. For example, when the reading speed of the frame image in the draft mode is a maximum of 30 FPS (frames per second), the reading speed of 60 FPS is possible according to the automatic focusing mode.
[0034]
Comparing the above two read modes, the draft mode can be expressed as a mode for reading a relatively large number of pixels, and the automatic focusing mode can be expressed as a mode capable of a relatively high-speed read.
[0035]
Further, the “main photographing mode” is a mode in which an image signal is read out with respect to the entire frame image, that is, all pixels of 2560 × 1920. Then, the timing generator 32 drives the CCD imaging device 10 based on the designated one of these read modes.
[0036]
An image signal obtained from the CCD image pickup device 10 is supplied to a signal processing circuit 11 (FIG. 4), and the signal processing circuit 11 performs predetermined analog signal processing on the image signal (analog signal). The signal processing circuit 11 has a correlated double sampling circuit (CDS) and an automatic gain control circuit (AGC). The signal processing circuit 11 performs noise reduction processing of the image signal by the correlated double sampling circuit, and controls the gain by the auto gain control circuit. By performing the adjustment, the level of the image signal is adjusted.
[0037]
The A / D converter 12 converts each pixel signal of the image signal into a 12-bit digital signal. The A / D converter 12 converts each pixel signal (analog signal) into a 12-bit digital signal based on an A / D conversion clock input from the overall control unit 20.
[0038]
The WB (white balance) circuit 13 performs level conversion of each of R, G, and B color components. The WB circuit 13 converts the levels of the R, G, and B color components using the level conversion table stored in the overall control unit 20. The parameters (gradients of the characteristics) of each color component of the level conversion table are set by the general control unit 20 automatically or manually for each captured image. The γ correction circuit 14 corrects the gradation of the pixel data.
[0039]
The color correction unit 15 performs color correction on the image data input from the γ correction circuit 14 based on parameters related to color correction set by the user, and converts color information expressed in the RGB color space into a YCrCb color space. Is converted to the color information represented by. By this color system conversion, a luminance component value Y is obtained for all pixels.
[0040]
The resolution conversion unit 16 performs a predetermined resolution conversion on the image data obtained from the CCD image pickup device 10 and cuts out an area.
[0041]
For example, at the time of live view display, the resolution conversion unit 16 performs predetermined resolution conversion on image data obtained by driving the CCD imaging device 10 in the draft mode, and obtains image data having an image size suitable for the number of display pixels of the LCD 5. (320 × 240 pixels) is generated. That is, at the time of live view display, the resolution conversion unit 16 performs 1/8 thinning-out only in the horizontal direction of the image G1 shown in FIG. 5 to generate a live view image Gb having 320 × 240 pixels.
[0042]
Further, at the time of automatic focusing, the resolution conversion unit 16 converts an image corresponding to an automatic focusing evaluation area (also referred to as an AF evaluation area or AF area) based on an image signal read in the “automatic focusing mode”. Generate. Specifically, the resolution conversion unit 16 extracts an image Gf corresponding to the AF evaluation area. The image Gf is extracted from the image G2 without performing the thinning process at a predetermined pixel number interval in the horizontal direction. Specifically, the image Gf of the AF evaluation area is composed of an image component having 640 × 80 pixels, and is located at a central portion of an image G2 obtained from the CCD image sensor 10 at the time of automatic focusing as shown in FIG. It is extracted by cutting out the located 640 × 80 pixel image component. The image Gf is input to the AF image memory 17b (see FIG. 7) in the AF evaluation value calculation unit 17, and is used for calculating the AF evaluation value.
[0043]
Further, the digital camera 1 performs live view display not only when the autofocus control (autofocus control) is not performed but also during the autofocus control. That is, the digital camera 1 performs live view display regardless of whether or not autofocus control (autofocus control) is being performed.
[0044]
Therefore, the display control unit 33 displays the image Gb for live view on the LCD 5 or the like except during the autofocus control, generates the image Gh for live view display also during the autofocus control, and displays the image Gh on the LCD 5. And so on. The image Gh is an image extracted (more specifically, extracted as a part of the image Gb) from the image Gb already acquired at the time before the autofocus control. The image Gh will be described later in detail.
[0045]
Hereinafter, the live view display based on the image read in the automatic focusing mode is also referred to as “AF live view display”. In this embodiment, this AF live view display is used as a live view display during auto focus control. In addition, to distinguish from the “AF live view display”, a live view display based on only the image read in the draft mode is referred to as a “draft live view display” for convenience. In this embodiment, the “draft live view display” is used as the live view display when the auto focus control is not performed.
[0046]
Further, at the time of actual photographing, the resolution conversion unit 16 outputs the image data obtained from the color correction unit 15 to the overall control unit 20 without performing the resolution conversion process. Then, the image data obtained at the time of the main photographing is stored in the image memory 34.
[0047]
The image data having been subjected to the predetermined resolution conversion by the resolution conversion unit 16 is provided to the display control unit 33 via the overall control unit 20, and the live view image is displayed on the LCD 5 and the EVF 4, It is also provided to the photometric calculation unit 18 to calculate an evaluation value for automatic exposure (AE) control. At the time of the automatic focusing control, the image data subjected to the predetermined resolution conversion by the resolution conversion unit 16 is also given to the AF evaluation value calculation unit 17, and the evaluation value for the automatic focusing control (for the automatic focusing control) is obtained. Is calculated.
[0048]
The AF evaluation value calculation unit 17 functions when the user presses the shutter button 9 to the half-pressed state S1, and performs an evaluation value calculation operation for performing automatic focusing control of a contrast method. Here, based on the image Gf (FIG. 6) of the AF evaluation area obtained from the resolution conversion unit 16, the sum of absolute differences between two horizontally adjacent pixels is calculated as an AF evaluation value. The AF evaluation value calculated by the AF evaluation value calculation unit 17 is output to the overall control unit 20.
[0049]
The photometry operation unit 18 divides the image data of 320 × 240 pixels output from the resolution conversion unit 16 in the draft mode into, for example, 300 (20 × 15) blocks, and evaluates the AE evaluation value based on the representative luminance value of each block. Is calculated. The AE evaluation value calculated by the photometry calculation unit 18 is output to the overall control unit 20.
[0050]
The image memory 34 is a memory for temporarily storing image data obtained by the CCD image pickup device 10 and subjected to the above-described image processing. The image memory 34 has a storage capacity of at least one frame. When a recording instruction is given by the user, the image data is transferred from the image memory 34 to the memory card 90, and the image data is recorded and stored.
[0051]
The card interface (card I / F) 37 is an interface for writing and reading image data to and from the memory card 90 mounted on the insertion mounting portion on the side of the digital camera 1. When reading / writing image data from / to the memory card 90, the compression / expansion unit 36 performs a compression process or an expansion process on the image data by, for example, the JPEG method. An external connection interface (external connection I / F) 38 is an interface for enabling communication with an external computer 91 via a communication cable or the like, and is realized by, for example, a communication interface conforming to the USB standard. Via the card I / F 37 and the external connection I / F 38, a control program recorded on a recording medium such as a CD-ROM set in the memory card 90 or the external computer 91 is stored in the RAM 20a or the ROM 20b of the overall control unit 20. Can be captured.
[0052]
The operation unit 35 is an operation unit including the mode switching dial 3, the menu button 6, the control button 7, the shutter button 9, the enlargement button 35a, and the like, and is a member for the user to operate the settings of the digital camera 1.
[0053]
The overall control unit 20 is configured by a microcomputer including a RAM 20a and a ROM 20b therein. The microcomputer executes a predetermined program, and functions as a control unit that controls the above units in an integrated manner.
[0054]
The overall control unit 20 has different functions when the digital camera 1 is in the shooting mode and when the digital camera 1 is in the playback mode.
[0055]
In the photographing mode, the overall control unit 20 instructs a timing generator to drive the CCD imaging device 10 to the timing generator. Specifically, the CCD image sensor 10 is set to the draft mode during live view display (except during automatic focusing), and the CCD image sensor 10 is set to the automatic focusing mode during automatic focusing (AF). At the time of the main photographing operation, the CCD image pickup device 10 is set to the main photographing mode.
[0056]
<Display overview>
Next, an outline of a display state during the autofocus control will be described.
[0057]
FIG. 7 is a block diagram showing main functions of the digital camera 1 at the time of live view display in the shooting mode. FIG. 7 also shows detailed functional blocks in the display control unit 33. The display control unit 33 displays a live view image on the LCD 5 (or the EVF 4) by cooperating with the overall control unit 20.
[0058]
FIG. 8 is a diagram showing the correspondence between the position of the display image Gh displayed on the LCD 5 during the autofocus control and the position of the image Gb displayed on the LCD 5 at a time before that. In other words, FIG. 8 shows the positional relationship between the images Gb and Gh when the image Gh is extracted from the image Gb.
[0059]
As shown in FIG. 8, the center position Ch of the image Gh is an image shifted from the center position Cb of the image Gb by a movement amount M (described later). This movement amount M is calculated using at least one image Gf read in the automatic focusing mode, as described later. In other words, the image Gh is extracted in a state where the position corresponding to the original image Gb is shifted according to the movement amount M.
[0060]
The image Gh is an image corresponding to an area smaller than the image Gb by the maximum movement amount Mmax in each of the vertical and horizontal directions. The maximum movement amount Mmax is a value that is predetermined as an allowable maximum value of the composition change amount (or the object movement amount), and is also referred to as an allowable movement amount or an allowable deviation amount.
[0061]
Note that the image Gg shown in FIG. 8 corresponds to the extracted image Gh when the movement amount M is zero.
[0062]
FIG. 9 is a diagram showing a state where image Gh is displayed on LCD 5. The image Gh is an image having a smaller pixel size than the LCD 5 (or the image Gb), and is displayed on a part of the LCD 5. FIG. 9 shows a case where the center position Ch of the image Gh is always displayed so as to be aligned with the center position Cb of the LCD 5.
[0063]
However, the display state is not limited to this. For example, as shown in the positional relationship with the original image Gb shown in FIG. The image Gh may be displayed in a shifted state.
[0064]
Further, here, the case where the image Gh is displayed on the LCD 5 with the pixel size as it is without performing the resolution conversion on the pixel size of the image Gh is exemplified, but the present invention is not limited to this. For example, as shown in FIG. 10, the image Gh is subjected to resolution conversion (enlargement processing) having the same image size as the image Gb (LCD 5), and the image Gk obtained by the conversion is displayed on the LCD 5. You may do so.
[0065]
As shown in FIG. 7, the display control unit 33 includes a display image generation unit 41, a movement amount detection unit 42, a VRAM 44, and a switching unit 45. Control operation is realized.
[0066]
Among them, the movement amount detection unit 42 has a function of detecting the movement amount of the subject (in other words, the amount of change in composition) by comparing a plurality of images Gf read and acquired in the automatic focusing mode. Have.
[0067]
In addition, during the autofocus control, the display image generation unit 41 extracts a partial area from the image Gb and performs a display position designation process (and / or a scaling process) to perform a display image Gh (or a zoom process). Gk). Note that the display image generation unit 41 transfers the image Gb as it is to the VRAM 44 and displays the image Gb as a live view image except during the autofocus control.
[0068]
Further, the VRAM 44 is an image memory for video output, and temporarily stores the composite image output from the display image generation unit 41.
[0069]
Further, the switching unit 45 has a function of selecting a display unit of an output destination, and an image from the VRAM 44 is output to the selected display unit. The switching unit 45 outputs an image in the VRAM 44 to one of the LCD 5 and the EVF 4 or both the LCD 5 and the EVF 4. Here, the case where the present invention is applied to the image output to the LCD 5 will be mainly described, but the present invention may be applied to the image output to the EVF 4.
[0070]
Such display control enables display output in a mode such as that shown in FIG. The detailed operation of each unit will be described later.
[0071]
<Detailed operation>
Next, this display operation will be described in more detail.
[0072]
Here, a case will be described in which AF live view display is performed when the shutter button 9 is half-pressed (also referred to as state S1). In the AF live view display, the autofocus control is performed using the image Gf read out from the CCD image pickup device 10 in the automatic focusing mode and generated, and in the draft mode before shifting to the automatic focusing mode. AF live view display is performed using the image Gh read and generated.
[0073]
FIG. 11 is a timing chart showing an operation in the digital camera 1, and FIG. 12 is a conceptual diagram showing a reading operation from the CCD image sensor 10.
[0074]
As shown in FIG. 11, in the CCD imaging device 10, after the exposure operation is performed, one cycle (here, 1/30 second or 1/60 second) is delayed and each pixel in the CCD imaging device 10 is delayed. The stored charge is read as an image signal. This read operation is performed according to the command pulses VD and VT.
[0075]
Here, the command pulse VD is a pulse for instructing all the photodiodes in the CCD image sensor 10 to output the respective accumulated charges to the vertical register in the CCD image sensor 10. The command pulse VT is a pulse for commanding a vertical transfer register in the CCD 10 to transfer. An image signal corresponding to each horizontal line is output by repeatedly sending the command pulse VT at a fixed minute cycle. Specifically, an image signal corresponding to each horizontal line from the upper side to the lower side is transmitted according to each command pulse VT.
[0076]
As shown in FIG. 12, in the draft mode, an image signal including 240 horizontal lines is read according to the command pulses VD and VT. The image signal read in the draft mode corresponds to the image G1. On the other hand, in the automatic focusing mode, an image signal including 80 horizontal lines is read according to the command pulses VD and VT. The image signal read in the automatic focusing mode corresponds to the image G2.
[0077]
Further, when the reading mode of the CCD imaging device 10 is changed from the draft mode to the automatic focusing mode, the reading interval is shortened, and high-speed reading becomes possible. This is because, in the draft mode, 240 horizontal lines are read out, whereas in the automatic focusing mode, 80 horizontal lines need to be read out. By reducing the number of pixels read at a normal speed, the speed of reading pixels can be increased. In FIG. 12, portions denoted by symbols W1 and W2 indicate portions that perform an operation of reading unnecessary image signals at high speed.
[0078]
In the following, the photographing operation of the digital camera 1 will be roughly described in two periods T1 and T2 with reference to FIG.
[0079]
When the “photographing mode” is selected by operating the mode switching dial 3, a live view display (draft live view display) is performed on a predetermined display unit (the LCD 5 in this case) in the period T1. During this period T1, the auto focus control has not been performed yet.
[0080]
Then, in this period T1, an image signal is read from the CCD image sensor 10 in the draft mode. Specifically, an image signal corresponding to an image G1 (FIG. 5) having a pixel size of 2560 × 240 is read from the CCD imaging device 10. Then, an image Gb for a live view having a pixel size of 320 × 240 generated by the resolution converter 16 or the like based on the image signal is displayed on the LCD 5.
[0081]
More specifically, as shown in FIG. 7, the live view image Gb generated by the resolution conversion unit 16 is temporarily stored in the image memory 34, and thereafter, the display image generation unit 41, the VRAM 44, and the switching unit The image is displayed on the LCD 5 through 45. Here, the image Gb is not subjected to any special processing by the display image generation unit 41, and is passed through to the VRAM 44 as it is. Further, the switching unit 45 selects the LCD 5 as the display unit of the output destination. Thereby, the image Gb is displayed on the LCD 5 as a live view image. In the live view display (draft live view display) during this period T1, the display image is updated at a speed of 30 FPS.
[0082]
Thereafter, when the shutter button 9 is pressed down to the half-pressed state S1 by the operator, the reading mode of the CCD imaging device 10 is changed to the automatic focusing mode, and the period T2 starts. Specifically, the overall control unit 20 uses the timing generator 32 to control the CCD image sensor 10 to read out image signals in the automatic focusing mode. During this period T2, auto focus control is performed and live view display (AF live view display) is performed.
[0083]
In this period T2, an image signal is read from the CCD image sensor 10 in the automatic focusing mode. Specifically, an image signal corresponding to an image G2 (FIG. 6) having a pixel size of 2560 × 80 is read from the CCD imaging device 10. Then, the resolution conversion unit 16 generates an image Gf of the AF evaluation area having a pixel size of 640 × 80 based on the image signal.
[0084]
The AF evaluation value calculation unit 17 calculates an AF evaluation value based on the pixel value of each pixel in the image Gf in the AF evaluation area. Then, auto focus control is performed based on the AF evaluation value. As a control method, a so-called “contrast method (hill climbing method)” is adopted. This “contrast method” calculates an AF evaluation value (such as a contrast value of an image) for each lens position while driving a lens, obtains a lens position P (not shown) at which the AF evaluation value becomes maximum, This is a control method in which the subject is brought into a focused state by moving the photographing lens 2 to the position P. During this autofocus control, an image signal is read from the CCD image sensor 10 at a high frame rate (here, at 60 FPS) in the autofocus mode, so that the autofocus control can be speeded up.
[0085]
Further, the moving amount M of the subject is obtained using the image Gf. The movement amount M is expressed as a vector. Here, in principle, the moving amount of the subject is calculated by comparing two consecutive images Gf that are sequentially photographed. When the first image Gf after the transition to the automatic focusing mode is acquired, there is no other image Gf to be compared, so that the first image Gf is compared with the image Gb taken immediately before. Then, the movement amount of the subject is calculated.
[0086]
Then, based on the movement amount M, an image Gh as shown in FIGS. 8 and 9 is generated. The image Gh may be newly generated each time the image Gf is newly acquired, or may be newly generated at a timing required for the display update rate. FIG. 11 shows a case where a new image Gh is generated every four frames.
[0087]
Specifically, the image Gb obtained in the draft mode at the end of the period T1 remains in the image memory 34 (FIG. 7) without being updated after the transition to the period T2, and is stored in the image memory 34 (FIG. 7). The image is input to the image generator 41.
[0088]
The image Gf from the AF evaluation value calculation unit 17 is updated at a high frame rate (here, at 60 FPS) and input to the movement amount detection unit 42. The moving amount detector 42 calculates the moving amount M using the sequentially input images Gfi (i = 1, 2,...).
[0089]
More specifically, first, the moving amount ΔM1 is obtained by comparing the photographed image Gb immediately before the shift to the readout mode and the first image Gf1 after the shift to the readout mode. Next, the movement amount ΔM2 is obtained by comparing the first image Gf1 and the second image Gf2. Similarly, the moving amount ΔM3 is obtained by comparing the second image Gf2 and the third image Gf3, and the moving amount ΔM4 is obtained by comparing the third image Gf3 and the fourth image Gf4. . In each image comparison operation, the shift amount between the two images may be obtained as the movement amount ΔMi by using a technique such as pattern matching. The movement amounts ΔM1 to ΔM4 are expressed as vectors, like the movement amount M.
[0090]
Then, by summing the movement amounts ΔM1 to ΔM4, the movement amount M is obtained (M = ΔM1 + ΔM2 + ΔM3 + ΔM4).
[0091]
Thereafter, the display image generation unit 41 extracts an image Gh having a smaller size than the image Gb from the image Gb. In the image Gh, the center position is shifted by the moving amount M from the center position of the image Gb.
[0092]
The image Gh generated by the display image generation unit 41 is transferred to the VRAM 44 together with designation of the display position, and output to the LCD 5 selected as the display destination by the switching unit 45. By repeating such an operation at a predetermined cycle, AF live view display can be realized.
[0093]
In the live view display (AF live view display) during the period T2, the display image Gh is updated at a frame rate of 15 FPS (= 60/4). However, it is not necessary to update at this frame rate, and the image display may be updated at the same frame rate (30 FPS) as the period T1 in the period T2 by generating the image Gh every two frames. .
[0094]
When the subject is brought into a focused state by the autofocus control operation in the period T2, the autofocus control ends, and the mode returns to the draft mode. After returning to the draft mode, the same operation as in the period T1 is performed.
[0095]
Thereafter, when the operator presses the shutter button 9 down to the fully pressed state S2, the reading mode of the CCD imaging device 10 is changed to the main shooting mode. Specifically, the overall control unit 20 uses the timing generator 32 to control the CCD image sensor 10 to read out image signals in the main shooting mode.
[0096]
Then, after an exposure operation for a time corresponding to a predetermined shutter speed (for example, 1/15 second), an image signal is read from the CCD image sensor 10 in the main photographing mode. Specifically, an image signal corresponding to a pixel size of 2560 × 1920, that is, an image signal of the size of the entire frame is read. Further, when predetermined image processing such as compression processing is performed on the obtained image signal, an image file in a predetermined format is generated as image data. The generated image file is recorded on the memory card 90. In addition, at the time of the main shooting, the live view display is temporarily interrupted.
[0097]
When the recording operation on the memory card 90 ends, the mode returns to the draft mode again. After returning to the draft mode, the same operation as in the period T1 is performed. Thereafter, the same operation is repeated.
[0098]
FIG. 13 and FIG. 14 are flowcharts showing the above operation. This operation will now be described with reference to the flowcharts of FIGS.
[0099]
First, in step SP1, the digital camera 1 acquires the image Gb acquired immediately before shifting to the draft mode.
[0100]
Next, in step SP2, after the reading mode from the CCD image pickup device 10 is changed, the first image Gf1 after the mode change is obtained.
[0101]
In step SP3, the image Gb and the image Gf1 are compared to determine whether or not the two images match. The images Gb and Gf1 have different numbers of pixels, but the corresponding positions may be compared.
[0102]
When they match, the movement amount ΔM1 is regarded as zero (vector), and the process proceeds to step SP9.
[0103]
On the other hand, if they do not match, the process proceeds to step SP4, and the movement amount ΔM1 is calculated. Further, it is determined whether a calculation error has occurred, whether the movement amount has exceeded a specified amount, and the like (steps SP5 and SP6).
[0104]
If it is determined in step SP5 that the movement amount ΔM1 has not been properly calculated for some reason, the process proceeds to step SP9. In step SP6, it is determined whether each component of the movement amount (vector) M does not exceed the allowable movement amount Mmax. If any component of the movement amount (vector) M exceeds the allowable movement amount Mmax, the excess component of the movement amount M is set to the maximum allowable value Mmax (step SP7). Thereby, the movement amount M is adjusted so that the extraction area at the time of generating the image Gh in step SP24 falls within the image Gb.
[0105]
The calculated movement amount M is temporarily stored in the memory (step SP8).
[0106]
At step SP9, the value of the counter i is set to 2.
[0107]
After that, in step SP12, the i-th image (here, the second image) Gfi after the change of the reading mode is obtained.
[0108]
In step SP13, the two images Gf (here, the images Gf1 and Gf2) of the (i-1) -th and i-th images are compared with each other, and it is determined whether or not the two images match. .
[0109]
If they match, the movement amount ΔMi (here, ΔM2) is regarded as zero (vector), and the process proceeds to step SP19.
[0110]
On the other hand, if they do not match, the process proceeds to step SP14, the movement amount ΔM2 is calculated, and the movement amount M is updated by adding the ΔM2 to ΔM1. Further, it is determined whether a calculation error has occurred, whether the movement amount has exceeded a specified amount, and the like (steps SP15 and SP16).
[0111]
If it is determined in step SP15 that the movement amount ΔM2 has not been properly calculated for some reason, the process proceeds to step SP19. In step SP16, it is determined whether each component of the movement amount (vector) M does not exceed the allowable movement amount Mmax. If any component of the movement amount (vector) M exceeds the allowable movement amount Mmax, the excess component of the movement amount M is set to the allowable movement amount Mmax (step SP17). Thereby, the movement amount M is adjusted so that the extraction area at the time of generating the image Gh in step SP24 falls within the image Gb.
[0112]
The calculated movement amount M is temporarily stored in the memory (step SP18), and it is determined whether or not all the images Gf to be acquired have been acquired (step SP19).
[0113]
When an unacquired image Gfi remains, the counter i is incremented by one (step SP21), the process returns to step SP12, and the same operation is repeated.
[0114]
As a result, ΔM3 and ΔM4 are calculated, and the total movement amount M = ΔM1 + ΔM2 + ΔM3 + ΔM4 is calculated.
[0115]
Thereafter, if it is determined in step SP22 that the movement amount M has been properly acquired, the process proceeds to step SP23, where the above-described image Gh is generated, and the image Gh is displayed on the LCD 5. If it is determined in step SP22 that the movement amount M has not been properly acquired, the image previously displayed on the LCD 5 is determined as the next display image.
[0116]
Thereafter, by repeating the same operation, the live view display at the time of the auto focus control is performed.
[0117]
As described above, according to the digital camera 1 of this embodiment, at the time of the autofocus control, the reading from the CCD image pickup device 10 is performed in the automatic focusing mode, so that the speed of the autofocus control can be increased. it can. Also, at the time of the auto focus control, the moving amount of the subject is detected using the image signal read in the automatic focusing mode, and the moving amount and the moving amount of the subject are read out in the draft mode before shifting to the automatic focusing mode. A display image is generated based on the image Gb, and the display image is displayed on the LCD 5 or the like. Therefore, it is possible to perform the framing operation while considering the moving amount of the subject (in other words, the change in the composition) while displaying an image larger than the image read in the automatic focusing mode. That is, the preview display during the auto focus control can be optimized.
[0118]
Further, the display image generation unit 41 generates an image Gh whose center position Ch is shifted by the moving amount M from the center position Cb of the image Gb as a display image, and the generated display image is displayed on the LCD 5 or the like. Therefore, it is possible to more accurately indicate a change in composition.
[0119]
Furthermore, since the preview display image Gh is obtained as an image obtained by extracting a partial area of the image Gb (in other words, a partial image of the image Gb), it is possible to prevent the preview area from being lost. More specifically, since the image Gh is extracted as an image having a size obtained by subtracting an allowable movement amount (allowable shift amount) Mmax from the image Gb in advance, a preview image among the regions to be displayed as a shooting target region is displayed. Can be prevented from occurring (that is, the preview area is missing). Further, in the above description, since the movement amount M is adjusted in step SP17 and the like so that the extraction area of the image Gh falls within the image Gb, even if the composition change exceeds the allowable deviation amount, the preview area may be omitted. It is possible to prevent. When the movement amount M becomes larger than the allowable movement amount Mmax, a warning operation may be performed. For example, a display for notifying the operator that "the preview display is not always accurate because the deviation amount exceeds the allowable value" may be performed.
[0120]
Further, in the above, in response to the operation of pressing the shutter button 9 by the operator (more specifically, the operation of pressing the shutter button 9 to the half-pressed state S1), the AF process is started and the preview display is displayed on the image Gb. Is changed to the image Gh, the discomfort due to the change in the preview display can be reduced as compared with the case where the preview display is changed regardless of the operation of the operator.
[0121]
<Modified examples>
The embodiments of the present invention have been described above, but the present invention is not limited to the above-described contents.
[0122]
For example, in the above embodiment, the case where the image signal is read at 60 FPS in the automatic focusing mode has been described. However, the present invention is not limited to this, and the image signal may be read at various reading speeds in the automatic focusing mode. . For example, the image signal may be read at 120 FPS in the automatic focusing mode.
[0123]
Further, in the above-described embodiment, the case where the same value is used as the allowable movement amount Mmax in any of the upper, lower, left, and right directions has been described, but the present invention is not limited to this. For example, different values may be used in the vertical direction and the horizontal direction.
[0124]
Further, in the above embodiment, the case where the movement amount M is adjusted so that the extraction area of the image Gh falls within the image Gb (step SP17 and the like) is illustrated, but the invention is not limited thereto. For example, even when the movement amount M exceeds the allowable movement amount Mmax, the image Gh may be extracted from a position corresponding to the calculated movement amount M without performing such adjustment.
[0125]
Further, in the above embodiment, at the time before the autofocus control, the entire area of the image Gb read in the draft mode is displayed as a preview image, and at the time of the autofocus control, one area of the image Gb is displayed. Although the case where the partial area is displayed as the preview image has been described as an example, the present invention is not limited to this.
[0126]
For example, on the condition that the operator has selected the enlarged display mode for enlarging and displaying a partial area of the shooting target area (corresponding to the entire area of the image Gb) even before the time of the autofocus control. Such a preview display control may be performed. Examples of the magnified display mode include a magnified display mode at the time of digital zoom shooting, a magnified display mode at the time of checking a focused state, and the like. Further, the setting as to which of the enlarged display mode and the normal preview display (displaying the entire region of the photographing target region) is selected as the preview display at the time of photographing is made by the operator using the magnifying button 35a (FIG. It is changed in response to the pressing of 3) or the like. Accordingly, the display control unit 33 sets one of the above-described enlarged display modes (such as the enlarged display mode at the time of digital zoom shooting and the confirmation of the in-focus state) to the preview display mode in response to the depression of the enlargement button 35a. The above-mentioned image Gh may be displayed on the LCD 5 or the like on the condition that the setting of the image Gh is detected.
[0127]
Here, as a situation in which the operator selects the enlarged display mode, a situation on the assumption that the movement of the subject is small is assumed. Therefore, by performing the above-described preview display control when the enlarged display mode is selected by the operator, there is a possibility that the preview display can be more appropriately displayed by the partial area extracted from the image Gb. Can be enhanced. More specifically, when the enlargement display mode is selected, the movement of the subject is small, and the possibility that the movement amount of the subject is equal to or less than the allowable movement amount (allowable deviation amount) Mmax increases. The possibility that the preview image Gh can be generated can be increased.
[0128]
For the same reason, the above-described preview display control is applied when the one-shot AF (one-shot method) is adopted as the AF mode instead of when the continuous AF (continuous method) is adopted as the AF mode. Is preferred. Here, the “continuous mode” is a mode in which the auto focus control is continuously performed while the shutter button 9 is half-pressed, and the “one-shot mode” is one time after the shutter button 9 is half-pressed. This is a method in which the AF operation is performed and the lens position is not changed once the lens is in focus. The one-shot method is often applied to a subject with less movement than the continuous method. Therefore, by performing the above-described preview display control on the condition that the one-shot method is selected as the AF mode, it is possible to more appropriately display the preview display using an image obtained by extracting a partial area of the image Gb. Can be enhanced.
[0129]
Further, in the above embodiment, the case where the preview display is changed from the image Gb to the display by the image Gh in response to the operator pressing the shutter button 9 to the half-pressed state S1 has been exemplified. It is not limited to. For example, the preview display may be changed from the image Gb display to the image Gh display in response to the operator pressing the shutter button 9 to the fully pressed state S2.
[0130]
Specifically, when the AF speed is changed in two stages according to the degree of pressing of the shutter button, display control is performed to display the image Gh as a preview display image when performing relatively high-speed AF control. It may be. More specifically, when the shutter button 9 is pressed down to the half-pressed state S1, relatively slow AF control is performed using the image Gb read in the draft mode, and the shutter button 9 is pressed down to the fully pressed state S2. When it is performed, relatively high-speed AF control is performed using the image Gf read in the automatic focusing mode. Then, in response to the operator pressing the shutter button 9 to the fully pressed state S2, the display control unit 33 changes the preview display on the LCD 5 or the like from the display by the image Gb to the display by the image Gh. do it. According to this, it is also possible to optimize the display at the time of the high-speed AF after shifting to the state S2 while changing the AF speed stepwise as necessary. Further, since the preview display is changed in response to the operation of pressing the shutter button 9 by the operator, the sense of incongruity due to the change in the preview display is reduced as compared with the case where the preview display is changed regardless of the operation of the operator. It is also possible.
[0131]
The specific embodiments described above include inventions having the following configurations.
[0132]
(1) In the electronic camera according to any one of claims 1 to 5,
The electronic camera according to claim 1, wherein the display control unit detects a movement amount of the subject image using the first image and at least one image based on an image signal read in the second mode.
[0133]
(2) In the electronic camera according to any one of claims 1 to 5,
The electronic camera according to claim 1, wherein the display control unit detects a moving amount of the subject image using a plurality of images based on the image signals read in the second mode.
[0134]
【The invention's effect】
As described above, according to the first to fifth aspects of the present invention, at the time of autofocus control, reading from the image sensor is performed in the second mode, so that the speed of the autofocus control is increased. Can be. Also, at the time of the auto focus control, the moving amount of the subject is detected using the image signal read in the second mode, and the moving amount and the moving amount of the subject are read in the first mode before shifting to the second mode. A display image is generated based on the image and the display image is displayed on the display unit. Therefore, it is possible to perform the framing operation while displaying an image larger than the image read in the second mode. That is, the preview display during the auto focus control can be optimized.
[0135]
In particular, according to the second aspect of the present invention, the display image is generated as an image whose center position is shifted from the center position of the first image by the movement amount calculated by the display control means. The change can be shown more accurately.
[0136]
According to the third aspect of the present invention, the display image is obtained as an image obtained by extracting a partial area of the image, so that the preview area can be prevented from being lost.
[0137]
Further, according to the invention described in claim 4, when the enlarged display mode is selected by the operator, by performing the display control of claim 1, the preview display is more appropriately performed. Possibilities can be increased.
[0138]
According to the invention described in claim 5, the preview display is changed in response to the operator pressing the shutter button. Therefore, the sense of incongruity due to the change in the preview display can be reduced as compared with the case where the preview display is changed regardless of the operation of the operator.
[Brief description of the drawings]
FIG. 1 is a front view showing an external configuration of a digital camera.
FIG. 2 is a top view illustrating an external configuration of the digital camera.
FIG. 3 is a rear view illustrating an external configuration of the digital camera.
FIG. 4 is a block diagram showing internal functions of the digital camera.
FIG. 5 is a diagram illustrating a concept of image reading in a draft mode.
FIG. 6 is a diagram illustrating a concept of image reading in an automatic focusing mode.
FIG. 7 is a block diagram showing main functions at the time of live view display.
FIG. 8 is a diagram showing a positional relationship between an image Gb and an image Gh extracted from the image Gb.
FIG. 9 is a diagram showing a display state of an image Gh on an LCD 5;
FIG. 10 is a diagram showing a state where an enlarged image Gk of the image Gh is displayed on the LCD 5.
FIG. 11 is a timing chart showing an operation in the digital camera.
FIG. 12 is a conceptual diagram showing a read operation from a CCD image sensor.
FIG. 13 is a flowchart showing an operation in the digital camera.
FIG. 14 is a flowchart showing an operation in the digital camera.
[Explanation of symbols]
1 Digital camera
4 EVF
5 LCD
9 Shutter button
10 CCD image sensor
Mmax Maximum travel distance
M Movement amount (vector)
Gb image (taken in draft mode)
Gf image (acquired in autofocus mode)
Gh display image
Cb Center position of image Gb
Ch Image Gh center position

Claims (5)

An electronic camera,
An image sensor that converts a subject image into an image signal by photoelectric conversion,
Display means for displaying an image based on the image signal,
Display control means for controlling a display operation in the display means,
Focusing control means for performing autofocus control based on the image signal,
Reading control means for controlling a reading operation of the image signal from the image sensor,
With
The readout control unit is configured to read out the image signal in a first mode for reading out image signals corresponding to a predetermined number of pixels among all the pixels in the image pickup device at a time before the autofocus control by the focus control unit. Reading an image signal from an element, and in the autofocus control, reading out a plurality of images at a high speed by reading out image signals corresponding to a smaller number of pixels than the predetermined number of pixels among the all pixels. Read out the image signal from the image sensor,
The focusing control unit performs the autofocus control based on the image signal read in the second mode,
The display control means detects an amount of movement of the subject using an image signal read in the second mode during the autofocus control, and detects the amount of movement of the subject and the first amount before shifting to the second mode. An electronic camera, wherein a display image is generated based on a first image based on an image signal read in a mode, and the display image is displayed on the display unit. The electronic camera according to claim 1,
The electronic camera according to claim 1, wherein the display control unit generates an image whose center position is shifted from the center position of the first image by the moving amount as the display image. The electronic camera according to claim 1 or 2,
The electronic camera according to claim 1, wherein the display image is obtained as an image obtained by extracting a partial area of the first image. The electronic camera according to claim 1 or 2,
The display image is an image obtained as an image obtained by extracting a partial region of the first image,
The display control means performs the display control on condition that an enlarged display mode for enlarging and displaying a partial area of the first image is selected by an operator at a time before the time of the autofocus control. An electronic camera characterized by the following. The electronic camera according to any one of claims 1 to 3,
An electronic camera, wherein the display control means changes a preview display on the display means to a preview display by the display control in response to an operation of pressing a shutter button by an operator.

Images