JP2007006243A - Digital camera and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital camera capable of increasing a frame rate of a motion image even if an area image sensor does not have a structure for a high-speed draft mode, and to provide a control method thereof. <P>SOLUTION: Electric charges are accumulated in a photodiode of a CCD area image sensor. The electric charges, to be accumulated in the photodiode, of different fields forming one frame are time-divided so that the electric charges corresponding to one color component can be transferred for each vertical CCD, and are transferred to the vertical CCD. The electric charges of each cell of the vertical CCD are transferred for each field to a horizontal CCD. The electric charges of a plurality of cells of the vertical CCD are accumulated for each field in each of cells of the horizontal CCD. The electric charges of each of cells of the horizontal CCD are transferred for each field to a detector. Pixel signals corresponding to the electric charges transferred to the detector are generated for each field. The pixel signals are used for each field to generate a plurality of consecutive frames, and motion image display and still image display are executed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a digital camera and a control method thereof, and more particularly to a digital camera using an area image sensor having no structure for a high-speed draft mode and a control method thereof.

  Conventionally, CCD area image sensors that transfer charges accumulated in a photodiode by dividing them into a plurality of fields are known (see, for example, Patent Documents 1 and 2). By dividing and transferring the charge accumulated in the photodiode into a plurality of fields, the area of the vertical CCD can be reduced. As a result, the area of the photodiode can be increased, which is advantageous in that the saturation signal amount can be increased. A digital camera equipped with an electronic viewfinder is equipped with a function that selectively reads out a plurality of photodiodes arranged along a vertical CCD at regular intervals in order to increase the frame rate of moving images displayed on the electronic viewfinder. In many cases, a CCD area image sensor corresponding to the draft mode is mounted. The CCD area image sensor compatible with the high-speed draft mode has an electrode structure for thinning out the charges accumulated in the photodiodes according to a rule capable of forming a color image and reading them out to the vertical CCD at a time. The pixels in the vertical direction can be thinned and read out. As a result, it is possible to read a coarse image representing the entire image, that is, an image with a low resolution, so that the frame rate of a moving image can be increased by reading the coarse image in a short time.

JP-A-8-18875 Patent No. 3009041

  An object of the present invention is to provide a digital camera that can increase the frame rate of a moving image and a control method thereof even when the area image sensor does not have a structure for a high-speed draft mode.

(1) According to the digital camera control method for achieving the above object, the charge is accumulated in the photodiode of the CCD area image sensor, and the charge corresponding to one color component is transferred for each vertical CCD. Charges in different fields constituting one frame stored in the photodiode are time-divided and transferred to the vertical CCD, and charges in each cell of the vertical CCD are transferred to the horizontal CCD for each field. The charge of a plurality of cells is accumulated in each cell of the horizontal CCD for each field, the charge of each cell of the horizontal CCD is transferred to the detection unit for each field, and a pixel signal corresponding to the charge transferred to the detection unit is obtained. It is generated for each field, and each frame of the moving image is displayed on the screen while using the pixel signal for each field to generate a plurality of continuous frames. Charges are accumulated in the photodiode, and charges in different fields constituting one frame are time-divisionally transferred to the vertical CCD, and stored in the photodiode. The charge is transferred to the horizontal CCD for each field, the charge of one cell of the vertical CCD is accumulated in each cell of the horizontal CCD for each field, and the charge of each cell of the horizontal CCD is transferred to the detection unit for each field. A still image recording step of generating a pixel signal corresponding to the charge transferred to the detection unit for each field, generating a still image based on the pixel signals of a plurality of fields, and storing the still image in a recording medium; Receiving a still image recording instruction, and transitioning from the moving image display step to the still image recording step.
This is a case where the area image sensor does not have a structure for the high-speed draft mode by using the pixel signal of one field for generating a plurality of continuous frames, that is, by overlapping the pixel signal of one field with a plurality of frames. However, the frame rate of the moving image of the digital camera can be increased. Further, by storing charges for a plurality of cells of the vertical CCD in each cell of the horizontal CCD and transferring the charges of each cell of the horizontal CCD to the detection unit, the number of times of transfer of charges by the horizontal CCD can be reduced. As a result, the frame rate of the moving image of the digital camera can be further increased. When the charge accumulated in the photodiode is time-divided and transferred to the vertical CCD, the vertical CCD is divided into each cell of the horizontal CCD by dividing the charge corresponding to one color component for each vertical CCD. Even if charges for a plurality of cells are accumulated, charges corresponding to different color components are not mixed in each cell of the horizontal CCD. On the other hand, when recording a still image, a high-resolution still image can be recorded by transferring the charge of one cell of the vertical CCD to each cell of the horizontal CCD.

  (2) In the moving image display step, the brightness of the moving image may be adjusted by amplifying the pixel signal with a gain corresponding to the pixel signal.

(3) The control method of the digital camera may further include a setting step of setting an exposure period according to the number of cells of the vertical CCD in which charges are accumulated in each cell of the horizontal CCD based on the pixel signal. Good. In the still image recording step, charges may be accumulated in the photodiode by exposing the photodiode to the exposure period.
By setting the exposure period according to the number of vertical CCD cells in which charges are stored in each horizontal CCD cell, even if charges in a plurality of vertical CCD cells are stored in horizontal CCD cells, And an accurate exposure period can be set.

(4) In the moving image display step, the resolution of the frame may be reduced by generating the pixel signal thinned out in the horizontal direction.
By generating pixel signals by thinning out in the horizontal direction, the processing amount for displaying a moving image can be reduced.

(5) In the moving image display step, the resolution of the frame may be reduced by generating the pixel signal added in the horizontal direction.
By generating pixel signals added in the horizontal direction, the processing amount for displaying a moving image can be reduced. Further, when the pixel signal of the field is generated by adding in the horizontal direction, the S / N can be improved as compared with the case of generating the pixel signal of the field thinned out in the horizontal direction.

(6) A digital camera that achieves the above object is connected to a photodiode, a vertical CCD connected to the plurality of photodiodes, a horizontal CCD connected to the plurality of vertical CCDs, and the horizontal CCD. Charge is repeatedly accumulated in the photodiode, the charges in different fields constituting one frame accumulated in the photodiode are time-divisionally transferred to the vertical CCD, The charge of each cell is transferred to the horizontal CCD for each field, the charges of a plurality of cells of the vertical CCD are stored for each field in the cells of the horizontal CCD, and the charge of each cell of the horizontal CCD is stored for each field. The pixel signal corresponding to the charge transferred to the detection unit is generated for each field, and the previous signal is generated for each field. A moving image display unit that displays each frame of a moving image on a screen while using a pixel signal to generate a plurality of continuous frames, an instruction receiving unit that receives a still image recording instruction, and a photodiode that responds to the still image recording instruction. Charges are accumulated, and charges in different fields constituting one frame, which are accumulated in the photodiode, are time-divided and transferred to the vertical CCD, and the charge of each cell of the vertical CCD is transferred to the horizontal CCD for each field. The charge of one cell of the vertical CCD is accumulated in each cell of the horizontal CCD for each field, the charge of each cell of the horizontal CCD is transferred to the detection unit for each field, and transferred to the detection unit A still image recording unit that generates a still image based on charges in a plurality of fields and stores the still image in a recording medium.
A digital camera uses an area image sensor for high-speed draft mode by using a pixel signal of one field to generate pixel signals of a plurality of continuous frames, that is, by overlapping a pixel signal of one field into a plurality of frames. Even if it does not have a structure, the frame rate of the moving image can be increased. Further, the digital camera accumulates charges for a plurality of cells of the vertical CCD in each cell of the horizontal CCD, and transfers the charges of each cell of the horizontal CCD to the detection unit, thereby transferring the charges for one field by the horizontal CCD. The number of times can be reduced. As a result, the frame rate of the moving image of the digital camera can be further increased. On the other hand, when recording a still image, the digital camera can record a high-resolution still image by transferring the charge of one cell of the vertical CCD to each cell of the horizontal CCD.

  It should be noted that the order of each operation of the method described in the claims is not limited to the order of description as long as there is no technical obstruction factor, and may be executed in any order, or may be executed simultaneously. Also good. In addition, each function of the plurality of units provided in the present invention is realized by hardware resources whose functions are specified by the configuration itself, hardware resources whose functions are specified by a program, or a combination thereof. Further, the functions of the plurality of units are not limited to those realized by hardware resources that are physically independent of each other. Further, the present invention can be specified as an invention of a program as well as an invention of a recording medium on which the program is recorded.

Embodiments of the present invention will be described below based on a plurality of examples. In each of the embodiments, the component having the same reference sign corresponds to the component of the other embodiment having the reference sign.
(First Example)
1A, 1B, 1C, and 2A are views showing the appearance of a digital still camera (DSC) 1 according to the first embodiment of the present invention. FIG. 2B is a diagram showing an external appearance of the DSC 1 with the interchangeable lens unit 2 attached thereto. FIG. 3 is a block diagram showing DSC1. The DSC 1 may be a compact camera type or a single-lens reflex camera type.

  The DSC 1 can mount a plurality of types of interchangeable lens units 2 on the mount 28. A focus adjustment dial 58 and an aperture adjustment dial 56 are provided outside the lens barrel of the lens unit 2. When the focus adjustment dial 58 rotates, the lenses 60 and 64 move in the optical axis direction. By rotating the focus adjustment dial 58, the focus can be adjusted. When the aperture adjustment dial 56 rotates, the aperture of the aperture 62 increases or decreases. The aperture can be adjusted by rotating the aperture adjustment dial 56.

  The first shutter curtain 30 and the second shutter curtain 32 constitute an electrically controlled focal plane shutter. The first shutter curtain 30 and the second shutter curtain 32 become operable by rotating the winding lever 14, and the mechanical opening operation and blocking operation are electrically controlled by the shutter driving unit 70. That is, when the shutter operation starts, the first shutter curtain 30 operates first, and the light projected through the lens in the interchangeable lens unit 2 is released, so that the exposure of the image sensor 72 is started, and the second Exposure is continued until the shutter curtain 32 operates. Then, since the light projected through the lens is blocked again with the completion of the operation of the second shutter curtain 32, the exposure is completed. The configuration of the shutter is not particularly limited, and it may be one that does not use electrical control for the operation of the shutter curtain, or the charge accumulation time of the image sensor 72 can be set to the substrate voltage without using the shutter curtain. You may control by what is called electronic shutter.

  The internal illuminance meter 66 is an optical sensor that measures the illuminance of reflected light from the shutter curtain. Since the illuminance of light incident on the internal illuminance meter 66 changes according to the aperture of the aperture 62, the output value of the internal illuminance meter 66 also changes when the aperture adjustment dial 56 rotates. The amount of light projected through the lens in the interchangeable lens unit 2 can be measured according to the output of the internal illuminance meter 66 that measures the illuminance of the reflected light of the shutter curtain. This measurement result is used to calculate the shutter speed, that is, the exposure period of the image sensor 72 by the DSC 1.

  Here, the surface of the shutter curtain in the shooting preparation state is not a simple black or white coating, but is painted so that the reflectance is about 18%. As a result, the illuminance of the light projected through the lens unit 2 can be accurately measured by the internal illuminance meter 66. Also, the internal illuminance meter 66 cannot accurately measure the illuminance of the light when the reflected light from the shutter curtain is incident. In this case, since it is not possible to calculate an appropriate exposure period, it is not possible to photograph with appropriate exposure. Therefore, by forming a rough textured surface on the surface of the shutter curtain, the light incident on the shutter curtain is softly diffused on the surface of the shutter curtain. As a result, light diffused softly on the surface of the shutter curtain is incident on the internal illuminance meter 66, so that the internal illuminance meter 66 can accurately measure the illuminance of the incident light.

  In DSC1, the reflectance on the surface is changed between the central part and the peripheral part of the shutter curtain so that the center-weighted exposure photography is possible. Specifically, for example, by coating the shutter curtain in a darker color toward the peripheral portion so that the reflectance on the surface decreases from the central portion to the peripheral portion of the shutter curtain, the reflection amount of the shutter curtain Is adjusted. The internal illuminance meter 66 is adjusted so as to output accurate illuminance when the reflectance of the lens unit 2 in the optical path direction by the shutter curtain is about 18%. If the shutter curtain is not used, the image sensor 72 can directly detect the illuminance of the light that has passed through the lens unit 2, or the internal illuminometer 66 can indirectly detect the reflected light of the half mirror.

FIG. 4 is a schematic diagram of the image sensor 72. FIG. 5 is a schematic diagram for explaining a reading method of the image sensor 72.
The image sensor 72 is a so-called CCD color area image sensor including photodiodes 720, vertical CCDs 721, horizontal CCDs 722, detection units 723, and the like that are discretely arranged in a two-dimensional space. The image sensor 72 includes R, G, and B color filters that are arranged in a Bayer array for each photodiode 720, and accumulates signal charges indicating the gray level of one of the RGB channels for each pixel in the photodiode 720. In addition, although the image sensor 72 in which the photodiodes 720 are arranged in a square lattice is illustrated, the photodiodes 720 of the image sensor 72 may be arranged in a honeycomb. Further, the color filters of the image sensor 72 may be arranged in stripes.

  The vertical CCD 721 includes four transfer electrodes for inputting vertical drive signals V1, V2, V3, and V4 for each cell 721a. By sequentially applying vertical drive signals V1, V2, V3, and V4 having different phases to the four transfer electrodes in a stepwise manner, a potential well is formed in the vertical CCD 721 for each cell 721a, and the potential well of each cell 721a is formed. The constrained charges sequentially move to the potential wells of the adjacent cells 721a one after another. The signal charges transferred from the photodiode 720 to each cell 721a in this way are transferred to the horizontal CCD 722. Hereinafter, the signal charge transfer by the vertical CCD 721 is referred to as “vertical CCD transfer”.

  The horizontal CCD 722 includes two transfer electrodes for inputting horizontal drive signals Vh1 and Vh2 for each cell 722a. In the horizontal CCD 722, different potential wells are formed in the cell 722a. In addition, by applying horizontal drive signals Vh1 and Vh2 having phases different by 180 degrees to the two transfer electrodes, a potential well is formed for each cell 722a. The charges bound to the potential wells of the cells 722a sequentially move to the potential wells of the adjacent cells 722a one after another. The signal charges transferred to each cell 722 a by the vertical CCD 721 in this way are sequentially transferred to the detection unit 723. Specifically, a vertical signal line 724 and a horizontal signal line 725 are connected to transfer electrodes (not shown) of the vertical CCD 721 and the horizontal CCD 722, respectively. The vertical CCD 721 and the horizontal CCD 722 are driven by a vertical drive signal (see V1 to V4 in FIG. 8) and a horizontal drive signal (see Vh1 and Vh2 in FIG. 8) respectively applied to the signal lines by the imaging controller 76. The signal charge is transferred.

  The detection unit 723 converts the charge transferred by the horizontal CCD 722 into a pixel signal. Specifically, for example, the detection unit 723 is a floating diffusion amplifier, and converts a signal charge into a voltage value as a pixel signal by its capacitance. Although the vertical CCD 721 is exemplified by the four-phase drive type image sensor 72, the vertical CCD 721 of the image sensor 72 may be any number of phase drive CCDs. Further, although the horizontal CCD 722 is exemplified by the image sensor 72 of the two-phase driving method, the horizontal CCD 722 of the image sensor 72 may be a CCD of any phase driving. The detection unit 723 may be a floating gate amplifier.

  As shown in FIG. 5, the image sensor 72 is a so-called frame readout type area image sensor that reads out pixel signals of one frame in two fields. In the area image sensor of the frame readout method, the vertical CCD for readout is used for both the first field and the second field, so that the area of the vertical CCD can be reduced. As a result, the size of the photodiode 720 can be increased, and the size of the cell 721a (see FIG. 4) of the vertical CCD 721 can be increased. Therefore, the frame readout type area image sensor is advantageous in that the saturation signal charge amount can be increased. is there. The image sensor 72 includes a shift electrode for controlling the transfer of signal charges from the photodiode 720 to the vertical CCD 721 between the photodiode 720 and the vertical CCD 721. A shift signal line 726 and a shift signal line 727 are connected to the shift electrode so that a charge signal indicating the gray level of the same channel is transferred to the vertical CCD 721 of each column in the readout of each field. Specifically, for example, in an image sensor 72 including a Bayer color filter, shift signal lines 726 and shift signal lines 727 are alternately connected to successive shift electrodes. In this case, in the image sensor 72, at the time of reading the first field, a signal charge indicating the density level of the G channel or the B channel is transferred from the photodiode 720 to the vertical CCD 721 of each column (see FIG. 5A). At the time of reading two fields, signal charges indicating the light and dark levels of the R channel or G channel are transferred (see FIG. 5B).

  As described above, the image sensor 72 reads out the signal signals of one frame in two fields by time-dividing and transferring the signal charges in different fields to the vertical CCD 721. The image sensor 72 has been described as one pixel signal read out in two fields, but may be an area image sensor that reads out one frame pixel signals in three or more fields.

  Here, the image sensor 72 does not include a shift signal line for selectively transferring signal charges from a plurality of photodiodes 720 arranged along the vertical CCD 721, for example, a structure for a high-speed draft mode. Therefore, in the image sensor 72, the size of the photodiode 72 can be increased, and the size of the vertical CCD 721 can be increased, so that the saturation signal charge amount can be increased. Further, since the area of the light receiving surface of the photodiode 720 can be increased, it is advantageous in terms of sensitivity and the like. However, in the image sensor 72, the number of signal charges transferred by the horizontal CCD 722 necessary for displaying one frame is obtained by thinning out the signal charges accumulated in the photodiode 720 and transferring them to the vertical CCD 721 as in the high-speed draft mode. Can not be reduced.

  For example, when reading out all the pixels of a 6 million pixel area image sensor (3008 pixels in the horizontal direction and 2000 pixels in the vertical direction) with a conventional frame readout method and a readout speed of 25 MHz, a readout time of 0.04 μs per pixel Therefore, reading of one field requires a reading time of at least 120.32 ms (= 0.04 μs × 3008 × 1000). Therefore, reading of one frame requires a reading time of 240.64 ms including at least two fields. That is, when displaying continuous images (hereinafter referred to as “through image readout”) using a 6 million pixel area image sensor that does not support the high-speed draft mode, only four frames per second can be read out. Here, the through image is a moving image series obtained by imaging a subject at a predetermined time interval. In addition, this is a time for reading all the pixels of 3008 pixels in the horizontal direction and 2000 pixels in the vertical direction. Usually, the time for reading the optical black pixels arranged around the image sensor 72 is Other processing time for driving, high-speed discharge transfer time for noise discharge, exposure time of subject, etc. are also required, so it is practically possible to read out only two or three frames per second. In other words, it is impossible to read a moving image of the subject moving substantially.

  Therefore, DSC 1 devises the reading method based on the idea that it is not necessary to have a high resolution as an image to be displayed as a moving image, and it is better to have a high frame rate even with a low resolution. First, after exposure for a predetermined time, the signal charge is first moved to the vertical CCD 721 by the shift signal. Thereafter, each signal charge is transferred by the vertical CCD 721. At this time, signal charges for a plurality of cells of the vertical CCD 721 are accumulated in each cell 722a of the horizontal CCD 722 to perform analog addition accumulation of the signal charges for the plurality of cells in the vertical direction. The number of additions may be for 2 cells or 3 cells. Then, signal charges for a plurality of cells of the vertical CCD 721 are transferred by the horizontal CCD 722. In this way, by adding the signal charges for a plurality of cells of the vertical CCD 721, the number of readout lines of the pixel lines in the vertical direction is reduced (for example, if the addition is for 2 cells, the number of readout lines is halved and 4 cells are obtained. In the case of addition of minutes, the number of readout lines can be reduced by a factor of four.) In order to display one frame of a through image as a moving image without having a structure for a high-speed draft mode. The number of signal charges transferred by the horizontal CCD 722 can be reduced. At this time, for example, if 2 cells are added and 4 cells are added, the number of signal charge transfers can be reduced to 1/2 or 1/4, respectively, and the frame rate is increased by 2 or 4 respectively. be able to. In addition, since the apparent sensitivity of the image sensor 72 is increased by adding the signal charges, the exposure period of the image sensor 72 during live view display is shortened according to the number of additions (for example, 2 for the addition of 2 cells). Since the addition of one-fourth and four-cells can be reduced to one-fourth), the frame rate can be further improved. As a result, the DSC 1 can display a through image at high speed even using the image sensor 72 having a large number of pixels that can shoot a high-resolution still image. Further, by adding signal charges for a plurality of cells of the vertical CCD 721, the signal charge SN ratio can be improved. The moving image may be a moving image recorded by the moving image shooting function of the DSC 1. The number of signal charges to be added may be 2 cells, 3 cells, 4 cells, or may be changed automatically or manually. Hereinafter, “adding the signal charges for n cells of the vertical CCD 721 in each column in each cell 722a of the horizontal CCD 722” is referred to as “n times pixel addition”.

  On the other hand, when taking a still image, the DSC 1 drives the image sensor 72 by a general driving method, that is, accumulates signal charges for one cell of the vertical CCD 721 in each cell 722 a of the horizontal CCD 722, and the horizontal CCD 722. The pixel signal is read by transferring the signal charge of one cell of the vertical CCD 721 by one cell 722a. As a result, a high-resolution still image can be recorded.

The imaging controller 76 shown in FIG. 3 applies a vertical drive signal, a horizontal drive signal, and a shift signal to the transfer electrode of the vertical CCD 721, the transfer electrode of the horizontal CCD 722, and the shift electrode, respectively, a vertical signal line 724, a horizontal signal line 725, and a shift signal. Application is performed via signal lines 726 and 727.
The analog front end (AFE) 74 includes a correlated double sampling (CDS) circuit 740, an amplifier 742, an analog / digital (A / D) converter 744, and an analog black level reproduction circuit (not shown) (optical in the image sensor 72). And a circuit that reproduces the optical black reference voltage by determining the black signal level using the masked pixels. The CDS circuit 740 is a circuit that removes reset noise included in the pixel signal output from the image sensor 72. The amplifier 742 is a circuit for amplifying the pixel signal with a gain corresponding to the brightness of the subject in cooperation with the control unit 80, and is a so-called variable gain amplifier. The A / D converter 744 performs A / D conversion on the pixel signal to generate a digital pixel signal (hereinafter referred to as pixel data). Pixel data output from the AFE 74 is stored in the RAM 100 by the image processing controller 98.

The image processing controller 98 performs various image processing on the pixel data output from the AFE 74 in cooperation with a RAM (Random Access Memory) 100, a color processing unit 102, a resolution conversion unit 104, and a compression / decompression unit 106. Apply.
The RAM 100 is a volatile memory that temporarily stores pixel data and the like.
The color processing unit 102 cooperates with the image processing controller 98 to perform image development processing on the pixel data output from the AFE 74. The development processing is performed for each pixel by demosaic processing for interpolating the gray level of each pixel of pixel data corresponding to the signal charge of each photodiode 720 on the image sensor 72 between neighboring pixels, white balance correction, and gradation correction. Is a process of forming frame data having three levels of RGB light and gray levels, and finally reproducing it in the form of an image.
The resolution converter 104 cooperates with the image processing controller 98 to convert the resolution of the frame data (total number of pixels) to a predetermined resolution. Specifically, for example, the resolution conversion unit 104 converts the frame data to a resolution corresponding to an imaging condition set by the user before imaging, or converts the frame data to a resolution corresponding to the screen size of the LCD 36.

The compression / decompression unit 106 cooperates with the image processing controller 98 to compress the frame data and decompress the compressed frame data (for example, compress the image data into JPEG format image data, Decompress compressed data). The frame data can be stored in the removable memory 92 without being compressed.
The graphic controller 94 cooperates with the image processing controller 98 to display the image represented by the frame data on the LCD 36 on the screen.
The functions of the image processing controller 98, the color processing unit 102, the resolution conversion unit 104, the compression / decompression unit 106, and the graphic controller 94 described above may be realized by a dedicated circuit such as an ASIC or DSP, or the control unit 80 may. You may implement | achieve by running a specific program.

The operation unit 84 includes a power switch 52, a release button 10, a shutter speed dial 12, buttons 40, 42, 44, 46, 48, 50 for setting shooting conditions and the jog dial 22.
The external interface controller 86 connects the DSC 1 and an external system (not shown) such as a personal computer (PC) so that they can communicate with each other. The removable memory controller 88 is an input / output mechanism that transfers data stored in the RAM 81 to a removable memory 92 connected to the card connector 90.
The flash memory 82 is a non-volatile memory that stores an image processing program executed by the control unit 80. An image processing program and various data necessary for the DSC 1 to operate can be stored in the flash memory 82 by downloading from a predetermined server via a network, reading from the removable memory 92, or the like.

  The control unit 80 includes a CPU 78, a RAM 81, and a flash memory 82. The control unit 80 controls each unit of the DSC 1 by executing a control program stored in the flash memory 82. The RAM 81 is a volatile memory that temporarily stores control programs and various data.

FIG. 6 is a flowchart showing the flow of processing in the through image shooting mode of DSC1. The process shown in FIG. 6 is activated when the DSC 1 transitions to the through image capturing mode, and is repeated until the DSC 1 transitions from the through image capturing mode to a mode other than the through image capturing mode.
First, the control unit 80 opens the first shutter curtain 30 and the second shutter curtain 32 in cooperation with the shutter driving unit 70 (see step S100). Hereinafter, “opening the first shutter curtain 30 and the second shutter curtain 32” is referred to as “opening the shutter curtain”.

  In step S102, the control unit 80 displays the through image on the LCD 36. Specifically, the control unit 80 causes the photodiode 720 to accumulate signal charges for a predetermined exposure period using an electronic shutter while the shutter curtain is open, and reads out a pixel signal based on the signal charges from the image sensor 72. Then, the control unit 80 generates frame data from the read pixel signal, performs pixel-specific pixel interpolation processing, white balance processing, color reproduction processing, gamma correction processing, vertical and horizontal size reduction processing, and the like on the frame data, An image for one frame represented by the frame data after various processes is displayed on the LCD 36. The controller 80 displays the through image on the LCD 36 as a moving image by repeating these series of processes. Details will be described later.

In step S104, the control unit 80 determines whether or not the release button 10 has been pressed. When the release button 10 is pressed, the control unit 80 executes processing for capturing a still image of the subject (see Step S106 to Step S118). This process corresponds to the “transition stage” described in the claims, and the control unit 80 and the release button 10 function as the “instruction receiving unit” described in the claims in this process.
In step S106, the first shutter curtain 30 and the second shutter curtain 32 are closed in cooperation with the control unit 80 and the shutter driving unit 70 (hereinafter referred to as “closing the shutter curtain”), and the shutter for the next shutter operation. Charging, preparation of the image sensor 72 for the next shooting, and the like.
In step S108, the control unit 80 detects the illuminance of the screen surface reflected light by the first shutter curtain 30 or the second shutter curtain 32. Specifically, the control unit 80 reads the output signal of the internal illuminance meter 66 to detect the illuminance of the light that passes through the aperture 62 of the lens unit 2 and is reflected by the shutter curtain.

In step S110, the control unit 80 sets an exposure period (appropriate time during which the shutter curtain should be opened) that is optimal for the shooting conditions at that time in accordance with the illuminance of the curtain surface reflected light. Specifically, for example, the control unit 80 sets the exposure period based on the output signal of the internal illuminance meter 66.
In steps S112 to S114, the controller 80 opens the shutter curtain for the exposure period set in step S110. Specifically, the control unit 80 prepares for exposure of the image sensor 72 prior to opening the shutter curtain (for example, discharge processing of charges accumulated in the photodiodes 720 of the image sensor 72, and the vertical CCD 721 and horizontal CCD 722. The remaining charge is discharged). When the image sensor 72 is ready for exposure, the control unit 80 cooperates with the shutter driving unit 70 to open the shutter curtain (see step S112), and the exposure period set after the shutter curtain is opened. After the elapse, the shutter curtain is closed (see step S114). As a result, the image sensor 72 is exposed to light from the subject for the exposure period.

  In step S116 to step S118, the control unit 80 generates a still image. Specifically, the controller 80 sequentially discharges the electric charges remaining in the vertical CCD 721 and the horizontal CCD 722 of the image sensor 72 and then drives the image sensor 72 by the general driving method described above, thereby sequentially starting from the image sensor 72. The pixel signal of one field and the pixel signal of the second field are read (see step S116). The control unit 80 cooperates with the color processing unit 102 to perform development processing on the read pixel signal of the first field and the pixel signal of the second field so that the pixel signal of the first field Frame data is generated from the pixel signal of the field. Further, the control unit 80 cooperates with the resolution conversion unit 104, the compression / decompression unit 106, the image processing controller 98, and the removable memory controller 88 to perform resolution conversion and compression processing (for example, compression conforming to the JPEG standard) for frame data. The frame data is stored in the removable memory 92 or the like as a still image (for example, a JPEG format still image) (see step S118). The processing from step S106 to step S118 corresponds to the “still image recording stage” recited in the claims, and each part of the DSC 1 that operates in this processing corresponds to the “still image recording unit” recited in the claims.

  FIG. 7 is a schematic diagram showing the operation of the image sensor 72 in the through image display process. FIG. 8 is a schematic diagram illustrating a drive signal output by the imaging controller 76 in the through image display process. (A1) to (A4) in FIG. 7 show states of the image sensor 72 from t1 to t4 in FIG. 8, respectively. FIG. 9 is a schematic diagram illustrating a process of generating frame data from pixel signals in the through image display process. Specific processing for reading out the first-field pixel signal from the image sensor 72 and generating one frame of frame data from the read-out first-field pixel signal and the previously-read-out second-field pixel signal will be described below. The through image display process will be described with reference to FIG.

  First, the control unit 80 transfers the signal charge of the first field from the corresponding photodiode 720 to each cell 721a of the vertical CCD 721 (see FIG. 7A1, the waveform of Vsh at t1 shown in FIG. 8). At this time, all the cells 721a of the vertical CCDs 721 in each column correspond to signal charges indicating the gray level of the same channel, specifically, signal charges indicating the gray level of the G channel or signal charges indicating the gray level of the B channel. Is transferred from the photodiode 720.

  Next, the control unit 80 adds signal charges for a plurality of cells of the vertical CCD 721 in each column in each cell 722 a of the horizontal CCD 722. Specifically, for example, when adding the signal charges for two cells of the vertical CCD 721, the control unit 80 does not drive the horizontal CCD 722 (see the waveform of Vh from t1 to t5 shown in FIG. 8), and the vertical CCD 721 The signal charge for two cells of the CCD 721 is transferred to each cell 722 a of the horizontal CCD 722. Waveforms V1 to V4 from t1 to t3 shown in FIGS. 7A2 and 7A3 and FIG. 8 indicate vertical drive signals for transferring the signal charge of the first cell, and FIG. 7A4 and FIG. Waveforms V1 to V4 from t4 to t5 shown in FIG. 4 indicate vertical drive signals for transferring the signal charge of the second cell. As a result, signal charges for two cells of the vertical CCD 721 in each column are accumulated in each cell 722 a of the horizontal CCD 722. As described above, since the signal charges indicating the gray level of the same channel are transferred to the vertical CCDs 721 in each column, the signal charges indicating the gray level of different channels are mixed in each cell 722a of the horizontal CCD 722 by pixel addition. It will never be done.

  Next, the control unit 80 causes the horizontal CCD 722 to transfer the signal charge after pixel addition to the detection unit 723 (see the waveform of Vh from t5 to t6 shown in FIG. 8), and the detection unit 723 converts the signal charge into a pixel signal. Let That is, the horizontal CCD 722 wipes out the charge only once each time the charge of two cells of the vertical CCD is accumulated in each cell. In DSC1, by reducing the number of signal charges transferred by the horizontal CCD 722 in this way, the number of signal charges transferred by the vertical CCD 721 required to display one frame can be reduced. Specifically, the number of signal charges transferred by the vertical CCD 721 required to display one frame is reduced to 1 / n by n-times pixel addition. As a result, pixel signals necessary for displaying one frame can be output from the image sensor 72 at high speed. When the detection unit 723 is a floating diffusion amplifier, the control unit 80 transfers the signal charges for a plurality of cells of the horizontal CCD 722 to the detection unit 723, and adds the signal charges in the detection unit 723, and then detects the signal charges. The signal charge may be converted into a pixel signal by the unit 723.

  The pixel signal read from the image sensor 72 is subjected to processing such as noise removal, brightness adjustment, and A / D conversion by the AFE 74. Specifically, the brightness adjustment is performed by the control unit 80 controlling the gain of the amplifier 742 in accordance with the brightness of the subject. For example, the control unit 80 determines the brightness of the subject from the pixel signal read before the pixel signal to be subjected to brightness adjustment. That is, the control unit 80 performs feedback control of the pixel signal by the amplifier 742. Note that the brightness of the through image may be adjusted by setting a multiple of pixel addition for each field and each frame according to the brightness of the subject in a state where the exposure period is constant. When the above-described brightness adjustment by the amplifier 724 and brightness adjustment by pixel addition are used together, the pixel signal subjected to pixel addition indicates that the subject is brighter than the actual subject brightness. It is necessary to consider a multiple of pixel addition in determining the brightness of the image. Further, the brightness of the subject may be determined based on the pixel signal before the brightness adjustment by the amplifier 724.

  Next, the control unit 80 stores the pixel data output from the AFE 74 in the RAM 100 in cooperation with the image processing controller 98. Here, the vertical resolution of the frame represented by the pixel data output from the AFE 74 is reduced in the vertical direction by adding signal charges. Therefore, the control unit 80 thins out the pixels of the pixel data in the horizontal direction according to the number of additions of the signal charges in the vertical direction or adds pixel values that are continuous in the horizontal direction, thereby representing the frame represented by the pixel data output from the AFE 74. Reduce the vertical resolution. As a result, the distortion of the frame represented by the pixel data output from the AFE 74 is corrected and the resolution of the frame is reduced. By reducing the information amount of the pixel data in this way, it is possible to reduce the amount of processing performed on the image data thereafter.

  Next, the control unit 80 cooperates with the color processing unit 102 to read pixel data of the second field read last time (see F2 (n-1) shown in FIG. 9) and pixel data of the first field read this time. (See F1 (n) shown in FIG. 9), frame data for one frame (see the first frame shown in FIG. 9) is generated. The control unit 80 displays the frame represented by the frame data converted into the resolution corresponding to the screen size of the LCD 36 on the LCD 36 in cooperation with the resolution conversion unit 104, the image processing controller 98, and the graphic controller 94. By the way, the pixel data of the first field read this time is the next frame data (second data shown in FIG. 9) together with the pixel data of the second field to be read next time (see F2 (n + 1) shown in FIG. 9). Used to generate a frame reference).

  As described above, by using the pixel data read from the image sensor 72 to generate frame data for two consecutive frames, that is, by overlapping pixel data of one field into two frames, as shown in FIG. Compared to the case where pixel data is used to generate frame data for one frame, the frame rate of the through image display can be increased. When the image sensor 72 is an image sensor that reads a pixel signal by dividing one frame into a plurality of fields of three or more fields, the pixel data read from the image sensor 72 is stored for a plurality of consecutive frames according to the number of fields. It may be used to generate the frame data. The DSC 1 may switch the frame generation mode shown in FIG. 9 and the frame generation mode shown in FIG. 10 automatically or manually. The through image display process described above corresponds to the “moving image display stage” recited in the claims. Moreover, each part of DSC1 which operate | moves in a through image display process is equivalent to the "moving image display unit" as described in a claim.

(Second embodiment)
The DSC according to the second embodiment is substantially the same as the DSC 1 according to the first embodiment, except that the internal illuminance meter 66 according to the first embodiment is not provided.
Since the DSC according to the second embodiment does not include the internal illuminance meter 66, the exposure period at the time of still image shooting cannot be calculated using the screen reflection light unlike the DSC1 according to the first embodiment. Therefore, the DSC according to the second embodiment sets the exposure period during still image shooting according to the luminance value indicated by the pixel signal read from the image sensor 72 during the through image display processing.

  Here, in the DSC according to the second embodiment, the brightness adjustment by the pixel addition described in the first embodiment and the brightness adjustment by the amplifier 742 are performed on the pixel signal. Therefore, the pixel signal after brightness adjustment indicates that the subject is brighter than the actual brightness of the subject. Therefore, in the DSC according to the second embodiment, an exposure period corresponding to the multiple of pixel addition and the gain of the amplifier 742 is set based on the pixel signal. For example, when n-fold pixel addition is performed, the DSC according to the second embodiment corrects the exposure period acquired based on the pixel signal by multiplying by n, and the corrected exposure period is the exposure period during still image shooting. Set as.

  By setting the exposure period according to the pixel addition multiple and the gain of the amplifier 742 based on the pixel signal, the DSC that does not include the internal illuminance meter 66 can be optimally adapted to the brightness of the subject. A still image can be taken during the exposure period. In the DSC according to the second embodiment, the exposure period may be set based on the pixel signal before the brightness adjustment by the amplifier 742. The process of setting the exposure period described above corresponds to a “setting stage” described in the claims.

The figure which shows the external appearance of the digital still camera by this invention. The figure which shows the external appearance of the digital still camera by this invention. 1 is a block diagram of a digital still camera according to the present invention. 1 is a schematic diagram of an image sensor according to the present invention. FIG. 3 is a schematic diagram for explaining a reading method of the image sensor according to the present invention. The flowchart which shows the flow of the process in imaging | photography mode. The schematic diagram which shows the action | operation of the image sensor in a through image display process. The schematic diagram which shows the drive signal of the image sensor in a through image display process. The schematic diagram for demonstrating the process which produces | generates frame data from a pixel signal. The schematic diagram for demonstrating the process which produces | generates frame data from a pixel signal.

Explanation of symbols

72 image sensor (CCD area image sensor), 76 imaging controller (moving image display unit, still image recording unit), 80 control unit (moving image display unit, instruction receiving unit, still image recording unit), 94 graphic controller (moving image display unit) 98 image processing controller 98 (moving image display unit, still image recording unit), 102 color processing unit (moving image display unit, still image recording unit), 104 resolution conversion unit (moving image display unit, still image recording unit), 106 compression / compression Expansion unit (still image recording unit), 720 photodiode, 721 vertical CCD, 721a cell (vertical CCD cell), 722 horizontal CCD, 723 detection unit

Claims (6)

Charges are accumulated in the photodiodes of the CCD area image sensor, and charges in different fields constituting one frame accumulated in the photodiodes are transferred so that charges corresponding to one color component are transferred for each vertical CCD. The time-division is transferred to the vertical CCD, the charge of each cell of the vertical CCD is transferred to the horizontal CCD for each field, and the charge of the plurality of cells of the vertical CCD is stored for each field in each cell of the horizontal CCD. , Transferring the charge of each cell of the horizontal CCD to the detection unit for each field, generating a pixel signal corresponding to the charge transferred to the detection unit for each field, and continuing the pixel signal for each field in a plurality of frames A video display stage for displaying each frame of the video on the screen while using
Charges are accumulated in the photodiode, charges in different fields constituting one frame accumulated in the photodiode are time-divided and transferred to the vertical CCD, and charges in each cell of the vertical CCD are transferred for each field. The charge of one cell of the vertical CCD is accumulated in each cell of the horizontal CCD for each field, the charge of each cell of the horizontal CCD is transferred to the detection unit for each field, and the detection unit Generating a pixel signal corresponding to the charge transferred to each field, generating a still image based on the pixel signals of a plurality of fields, and storing the still image in a recording medium; and
Accepting a still image recording instruction, a transition stage to shift from the moving image display stage to the still image recording stage,
A method for controlling a digital camera including:   The digital camera control method according to claim 1, wherein in the moving image display step, the brightness of the moving image is adjusted by amplifying the pixel signal with a gain corresponding to the pixel signal. A setting step of setting an exposure period according to the number of cells of the vertical CCD in which charges are accumulated in each cell of the horizontal CCD based on the pixel signal;
3. The digital camera control method according to claim 1, wherein in the still image recording step, charges are accumulated in the photodiode by exposing the photodiode to the exposure period.   4. The digital camera control method according to claim 1, wherein the resolution of the frame is reduced by generating the pixel signal thinned out in a horizontal direction in the moving image display step.   4. The digital camera control method according to claim 1, wherein the resolution of the frame is reduced by generating the pixel signal added in the horizontal direction in the moving image display stage. A photodiode;
A vertical CCD connected to a plurality of the photodiodes;
A horizontal CCD connected to the plurality of vertical CCDs;
A detection unit connected to the horizontal CCD;
Charges are repeatedly accumulated in the photodiode, and charges in different fields constituting one frame accumulated in the photodiode are time-divided and transferred to the vertical CCD, and the charge of each cell of the vertical CCD is field Transfer to the horizontal CCD every time, accumulate the charge of the cells of the vertical CCD in each cell of the horizontal CCD for each field, transfer the charge of each cell of the horizontal CCD to the detection unit for each field, A moving image display unit that generates a pixel signal corresponding to the electric charge transferred to the detection unit for each field, and displays each frame of the moving image on the screen while using the pixel signal for each field to generate a plurality of continuous frames;
An instruction receiving unit for receiving a still image recording instruction;
In accordance with the still image recording instruction, charges are accumulated in the photodiode, and charges in different fields constituting one frame accumulated in the photodiode are time-divided and transferred to the vertical CCD, and the vertical CCD The charge of each cell of the CCD is transferred to the horizontal CCD for each field, the charge of one cell of the vertical CCD is accumulated in each cell of the horizontal CCD for each field, and the charge of each cell of the horizontal CCD is stored for each field. A still image recording unit that transfers to the detection unit, generates a still image based on the charges of the plurality of fields transferred to the detection unit, and stores the still image in a recording medium;
Digital camera equipped with.

Images