JP2006352422A - Drive method of area image sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drive method of an area image sensor capable of attaining a high frame rate even when the area image sensor has no structure for a high speed draft mode. <P>SOLUTION: The drive method stores electric charges to photodiodes, transfers the electric charges stored in the photodiodes to vertical CCDs, transfers the electric charges in each cell of the vertical CCDs to a horizontal CCD to store electric charges by the cells of the vertical CCDs to each cell of the horizontal CCD, transfers the electric charges of each cell of the horizontal CCD to a detection section, and detects the electric charges transferred to the detection section. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  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). Since the charge accumulated in the photodiode is divided into a plurality of fields and transferred, the area of the vertical CCD can be reduced. As a result, the area of the photodiode can be increased, which is advantageous in terms of the saturation signal charge amount. A digital camera equipped with an electronic viewfinder has a function of selectively reading out a plurality of photodiodes arranged along a vertical CCD at regular intervals in order to increase the frame rate of a moving image displayed on the electronic viewfinder. In many cases, a CCD area image sensor corresponding to the mounted high-speed draft mode is mounted. The CCD area image sensor that supports 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 out 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 an area image sensor driving method capable of increasing the frame rate even in an area image sensor having no structure for a high-speed draft mode.

(1) The area image sensor driving method for achieving the above object is to store charges in a photodiode, transfer the charges stored in the photodiode to a vertical CCD, and charge each cell of the vertical CCD. Transfer to the horizontal CCD, accumulate the charge of a plurality of cells of the vertical CCD in each cell of the horizontal CCD, transfer the charge of each cell of the horizontal CCD to the detection unit, and transfer the charge transferred to the detection unit To detect.
The number of charges transferred by the horizontal CCD required to display one frame by accumulating 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 Can be reduced. As a result, signals necessary for displaying one frame can be output from the area image sensor at high speed.

(2) When accumulating charges in the photodiode, charges in different fields constituting one frame are time-divided and transferred to the vertical CCD, and when transferring the charges to the horizontal CCD, When the charge of each cell is transferred to the horizontal CCD for each field and the charge is transferred to the detection unit, the charge of each cell of the horizontal CCD is transferred to the detection unit for each field and the charge is detected. At this time, the charge transferred to the detection unit may be detected for each field.
By transferring the charges in different fields from the photodiode to the vertical CCD in a time-sharing manner, the size of the vertical CCD cell can be increased, which is advantageous in terms of saturation signal amount.
(3) When transferring a charge to the vertical CCD, a charge corresponding to one color component may be transferred for each vertical CCD.
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.
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.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1A, 1B, 1C, and 2A are views showing the appearance of a digital still camera (DSC) 1 according to 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 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. 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. In this way, in the horizontal CCD 722, the signal charges transferred to each cell 722 a by the vertical CCD 721 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. Further, when the image sensor 72 includes a color filter having a stripe arrangement, an all-pixel readout method may be used.

  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”.

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. Apply via lines 726, 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 types of image processing on the pixel data output from the AFE 74 in cooperation with the RAM 100, the color processing unit 102, the resolution conversion unit 104, and the compression / decompression unit 106.
A RAM (Random Access Memory) 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 a 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 100 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).
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. The control unit 80 stores a function of the exposure period using the signal level of the output signal of the internal illuminance meter 66 as a variable in the flash memory 82 and the like, and calculates the exposure period from the function and the output signal of the internal illuminance meter 66. By doing so, the exposure period may be set.

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, after discharging the electric charge remaining in the vertical CCD 721 and the horizontal CCD 722 of the image sensor 72, the control unit 80 reads the first field pixel signal and the second field pixel signal from the image sensor 72 (step S116). reference). 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).

  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. However, when signal charges indicating the gray levels of different channels may be mixed in pixel addition, for example, when displaying a monotone through image, the signal charges indicating the gray levels of different channels are applied to the vertical CCDs 721 of each column. It may be transferred.

  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. 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.

  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, in cooperation with the color processing unit 102, the control unit 80 generates frame data for one frame from the pixel data of the second field read last time and the pixel data read this time (see FIG. 9). 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 read this time is used to generate the next frame data together with the pixel data to be read next time as shown in FIG. That is, the DSC 1 displays the through image on the LCD 36 while using the pixel data read from the image sensor 72 to generate frame data for two consecutive frames.

  By using the pixel data read out from the image sensor 72 for generating frame data for two consecutive frames, the through image is compared with the case where the pixel data is used for generating frame data for one frame (see FIG. 10). The frame rate of 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. In addition, the DSC 1 may control to switch between the frame generation mode illustrated in FIG. 9 and the frame generation mode illustrated in FIG.

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. 6 is a flowchart showing a flow of processing in a through image shooting 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 (area image sensor), 720 photodiode, 721 vertical CCD, 721a cell (vertical CCD cell), 722 horizontal CCD, 722a cell (horizontal CCD cell) 723 detector

Claims (3)

Accumulates charge in the photodiode,
Transferring the charge accumulated in the photodiode to a vertical CCD;
Transfer the charge of each cell of the vertical CCD to the horizontal CCD,
The charge for a plurality of cells of the vertical CCD is accumulated in each cell of the horizontal CCD,
Transfer the charge of each cell of the horizontal CCD to the detection unit,
Detecting the charge transferred to the detection unit;
Driving method of area image sensor. When accumulating charges in the photodiode, the charges in different fields constituting one frame are time-divided and transferred to the vertical CCD,
When transferring the charge to the horizontal CCD, the charge of each cell of the vertical CCD is transferred to the horizontal CCD field by field,
When transferring the charge to the detection unit, the charge of each cell of the horizontal CCD is transferred to the detection unit for each field,
The area image sensor driving method according to claim 1, wherein when detecting the charge, the charge transferred to the detection unit is detected for each field.   3. The method of driving an area image sensor according to claim 2, wherein when the charge is transferred to the vertical CCD, the charge corresponding to one color component is transferred for each vertical CCD.

Images