JP2000032332A - Electronic camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to obtain a through picture excellent in movement without damaging picture quality of a capture picture by setting an driving frequency of an image sensor high during a display period of the through picture and setting the driving frequency short during a capture period. SOLUTION: A cycle of driving signals (Vs, Hs) outputted from a timing generator 33 is synchronized with a first clock signal CKH having a first frequency of high cycle for a through period and is synchronized with a second clock signal CKL having a second frequency on a low cycle side during a capture period. Thus, during the through period, the cycle of the driving signals (Vs, Hs) becomes shorter, while the cycle of the driving signals (Vs, Hs) becomes longer during the capture period. As a result, the through picture excellent in movement can be obtained without damaging picture quality of the capture picture by shortening a transfer time of a CCD 31 during a display period of the through picture and lengthening the transfer time of a CCD 31 during the capture period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic camera, and more particularly, to an electronic camera provided with an image sensor having a high pixel count.

[0002]

2. Description of the Related Art Electronic cameras use a two-dimensional image sensor (generally, a CCD: char)
This is converted into a video signal by a ge coupled device, and the video signal is displayed on a liquid crystal display or stored in a nonvolatile semiconductor memory. This camera has many features not found in conventional film cameras, such as the ability to play images on the spot and transfer images to remote locations, and is widely used in various fields, both public and private. In recent years, with the advent of inexpensive CCDs with more than 1 million pixels, many devices capable of recording extremely high-definition images have been circulating, and have reached a level comparable to the image quality of conventional cameras. .

FIG. 8 is a plan layout diagram of a CCD.
The CCD has a large number of photoelectric conversion elements (generally, photodiodes) 100 regularly arranged on a plane, and
00, a charge storage unit 101 and a vertical charge transfer unit 102 are arranged for each column, and a horizontal charge transfer unit 103 is arranged at the output end of each charge transfer unit 102. The portion surrounded by the broken line in the figure is one pixel. The electric charge corresponding to the light intensity generated by the photoelectric conversion element 100 is sent out to the electric charge transfer section 102 in the vertical direction via the electric charge accumulation section 101, and the vertical drive pulse Vs
And sequentially transferred to the horizontal charge transfer section 103 in synchronization with the horizontal drive pulse Hs, and is output to the outside in a time series (serial) in synchronization with the horizontal drive pulse Hs.

An electronic camera, especially an electronic camera with a liquid crystal display, takes a picture by setting a recording mode by operating a predetermined key switch, pointing a photographic lens at the object, and displaying an image of the subject (through-the-lens) displayed on the liquid crystal display. Image), adjust the composition, and when the desired composition is obtained, press the shutter key halfway to fix the exposure and focus and then press the shutter key fully. .

[0005]

The CCD outputs (transfers) information of all effective pixels serially in synchronization with a predetermined drive signal. Assuming that the number is N, the transfer of one image requires at least “N × T” time. Since it is obvious that the transfer time increases in proportion to the number of pixels, the effect of the transfer time cannot be ignored, especially in a CCD having a very large number of pixels. That is, in the electronic camera described above, a through image is displayed on the liquid crystal display, and this through image is a moving image that is sequentially updated in units of several tens of frames per second, that is, a “moving image”. An increase in the time causes a reduction in the number of frames, and a longer update interval of the live view image results in a jerky movement, which impairs the quality of the live view image.

On the other hand, the above problem can be solved by minimizing the transfer time by shortening the driving cycle of the CCD as much as possible. However, on the other hand, reading of pixel information fails due to variations in CCD characteristics. Or image sampling after reading pixel information may fail,
In this case, there is a new problem that the quality of an image (hereinafter, referred to as “captured image”) recorded in the nonvolatile semiconductor memory is impaired.

Accordingly, an object of the present invention is to obtain a through image with good motion without deteriorating the image quality of a captured image.

[0008]

According to the first aspect of the present invention,
An image sensor that outputs a video signal of a subject in synchronization with a predetermined drive signal, display means for displaying the video signal as a through image, and capture means for capturing the video signal in response to a predetermined key operation; Frequency setting means for setting the frequency of the drive signal high during the display period of the live view image and setting the frequency low during the capture period. Claim 2
The described invention has an exposure function for automatically or manually setting an exposure time, an image sensor for outputting a video signal of a subject in synchronization with a predetermined drive signal, and a frequency of the drive signal when the exposure time is short. Frequency setting means for setting the frequency to be high and setting the frequency to be low when the exposure time is long. The invention according to claim 3 is the invention according to claim 2, further comprising: display means for displaying the video signal as a through image; and capture means for capturing the video signal in response to a predetermined key operation. The frequency setting means executes the setting processing during a display period of the live view image. According to a fourth aspect of the present invention, there is provided an exposure function for automatically or manually setting an exposure time, an image sensor for outputting a video signal of a subject in synchronization with a predetermined drive signal, and a display for displaying the video signal as a through image. Means, capture means for capturing the video signal in response to a predetermined key operation, and setting the frequency of the drive signal high during the display period of the through image and setting the frequency low during the capture period Frequency setting means for setting the frequency to a higher frequency side when the exposure time is short, and setting the frequency to a lower frequency side when the exposure time is long.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings, taking an electronic camera equipped with a high-pixel CCD and having an automatic exposure and automatic focus function as an example.
FIG. 1 is an external view of an electronic camera according to the present embodiment. Although not particularly limited, the electronic camera 10 is divided into a main body portion 11 and a camera portion 12 rotatably attached to the main body portion 11, and is illustrated on a front surface (a back surface side in the drawing) of the camera portion 12. The photographic lens is omitted. Behind the photographic lens, a CCD of high pixels (for convenience, 1 million pixel class), which is also not shown, is attached. The image can be converted into a video signal to generate a high-resolution frame image.

On the other hand, the main body 11 has a flat display device for checking an image (through image or captured image),
For example, a liquid crystal display 13 (display means) is attached, and various operation keys such as a shutter key 14 are attached at appropriate positions. The types and names of operation keys vary depending on the manufacturer and model, and cannot be uniquely specified.
Minus key 16, Menu key 17, Power switch 1
8, display key 19, recording mode key 20, self-timer key 21, strobe mode key 22, REC
/ PLAY key 23 and the like, and the functions (roles) of these keys are as follows.

(1) Shutter key 14: In the recording mode, as the name implies, it is a key that functions as a "shutter key" (fixing exposure and focus by half-pressing and capturing an image by full-pressing). When the menu key 17 is pressed in a playback mode (a mode in which a captured image is played back or output to another device), a YES key for confirming various selection items displayed on the liquid crystal display 13 is pressed. It is a multi-function key that also works. (2) Plus key 15: a key used to select a reproduced image and various system settings. “Plus” means the selection direction, which is the direction of the latest image in the case of image selection, and the scanning direction of the liquid crystal display 13 in the case of system setting selection. (3) Minus key 16: Same function as the plus key except that the direction is reversed.

(4) Menu key 17: A key for performing various system settings. In the recording mode, various items (definition of recorded image, auto focus on / off, etc.) necessary for recording an image are displayed on the liquid crystal display 13, or in the reproduction mode, a delete mode (image erasing mode) is displayed. The first various items are displayed on the liquid crystal display 13. (5) Power switch 18: A switch for turning on and off the power of the camera. (6) Display key 19: A key for overlappingly displaying various information on an image displayed on the liquid crystal display 13. For example, in the recording mode, the remaining number of shootable images and the shooting mode (normal shooting, panoramic shooting, etc.) ) Are displayed in an overlapped manner, and in the playback mode, the attribute information (page number, definition, etc.) of the playback image is overlapped and displayed.

(7) Recording mode key 20: A key which can be used only in the recording mode. Select normal shooting or panoramic shooting. (8) Self-timer key 21: A key for turning on / off the self-timer function. (9) Strobe mode key 22: This key is used for various settings related to the strobe, for example, for forcibly emitting light, prohibiting light emission, and preventing red-eye. (10) REC / PLAY key 23 This is a key for switching between a recording mode and a reproduction mode. In this example, the switch is a slide switch. When the switch is slid up, the recording mode is set, and when the switch is slid down, the playback mode is set.

FIG. 2 is a block diagram of the electronic camera according to the present embodiment. The electronic camera according to the present embodiment has an automatic exposure function and an automatic focus function, and includes elements unique to these functions (for example, a light amount measurement sensor, a distance measurement sensor, an auto focus driving mechanism, and control of these elements). And the like, but are not shown in the block diagram for simplicity of illustration. In FIG. 2, reference numeral 30 denotes a photographic lens, 31 denotes a CCD (image sensor), 32 denotes a horizontal / vertical driver, and 33 denotes a timing generator (TG: Timi).
ng Generator), 34 is a sample and hold circuit, 35 is an analog-to-digital converter, 36 is a color process circuit, 37 is a DMA controller, 38 is a DRAM interface, 39 is a DRAM, 40 is a flash memory (capture means), 41 is a CPU ( Display means, capture means), 42 is a JPEG circuit, 43 is VRAM
(Display means), 44 is a VRAM controller (display means), 45 is a digital video encoder (display means), 46 is a key input unit, and 47 is a bus.

The functions of these components are generally as follows. (A) Photo lens 30: This is for forming an image of a subject on the light receiving surface of the CCD 31, and has a focusing mechanism for an automatic focusing function. Note that a zoom function may be provided, or a retractable type may be provided. (B) CCD 31: a solid-state imaging device that transfers electric charges in an array. Also called a charge-coupled device. Although some are used for analog delay lines and the like, this specification particularly refers to a so-called solid-state image sensor that converts two-dimensional optical information into a time-series (serial) electric signal.

In general, a CCD has a photoelectric conversion section in which a number of photoelectric conversion elements (see reference numeral 100 in FIG. 8) are arranged in an array, and a charge storage section (see reference numeral 101 in FIG. 8) for storing output charges of the photoelectric conversion elements. ) And a charge reading unit (reference numerals 102, 10 in FIG.
3), and each of the photoelectric conversion elements becomes a pixel. For example, in a CCD having one million effective pixels, at least one million cells in the array are arranged. Hereinafter, for convenience of explanation, the illustrated CCD
The number of effective pixels of 31 is 1280 × 960. That is, 1280 in the row direction (horizontal direction) and the column direction (vertical direction)
Has an array structure of 1280 columns.times.960 rows composed of 960 pixels.

In general, CCDs can be classified into two types according to a charge reading method. First
Is a type of "interlaced readout method" in which pixels are skipped one by one when reading out signals, and a second type is a "full-scale readout method" in which all pixels are read out in order.
The first type is a camera integrated VTR (video tape rec)
order), and the mainstream of electronic cameras is the second type. Hereinafter, CC in the present embodiment
D31 is also of the second type, but is not limited to this.

(C) Horizontal / vertical driver 32 and timing generator 33: This is a part for generating a drive signal necessary for reading the CCD 31, and the CCD 31 of the present embodiment is
Since it is assumed that the entire surface is read out, a drive signal capable of transferring (reading out) pixel information in units of rows while designating each column of the CCD 31 one after another, in other words, 12
Horizontal and vertical drive signals (hereinafter referred to as “horizontal drive pulse”) for serially reading out pixel information in a direction from the upper left to the lower right of the array structure of 80 columns × 960 rows (this direction is similar to the scanning direction of the television). Hs, vertical drive pulse Vs ”). (D) Sampling and holding circuit 34: samples a time-series signal (an analog signal at this stage) read from the CCD 31 at a frequency suitable for the driving frequency (read speed) of the CCD 31 (for example, correlated double sampling). ). Note that automatic gain adjustment (AGC) may be performed after sampling. (E) Analog-to-digital converter 35: Converts a sampled signal into a digital signal.

(F) Color process circuit 36: A part for generating a luminance / color difference multiplex signal (hereinafter, referred to as a YUV signal) from the output of the analog / digital converter 35. The reason for generating the YUV signal is as follows. The output of the analog-to-digital converter 35 substantially corresponds to the output of the CCD 31 on a one-to-one basis except for the difference between analog and digital and errors in sampling and digital conversion, and is the light primary color data (RGB data) itself. However, this data is large in size, causing disadvantages in terms of limited memory resource utilization and processing time. Therefore,
It is necessary to reduce the amount of data to some extent by some method. In general, each component data (R data, G data, and B data) of RGB data can be represented by three color difference signals GY, RY, and BY with respect to the luminance signal Y. If the redundancy of these three color difference signals is removed, GY need not be transferred, and GY = α (R−
Y) -β (BY), which is a kind of data amount reduction signal based on the principle that the signal can be reproduced. here,
α and β are synthesis coefficients.

The YUV signal is converted to a YCbCr signal (Cb
And Cr may be referred to as BY and RY, respectively, but in this specification, they are unified to YUV signals. The signal format of the YUV signal is composed of three fixed-length blocks called "components" each independently including a luminance signal and two color difference signals, and has a length (number of bits) of each component. The ratio is called the component ratio. Although the component ratio of the YUV signal immediately after the conversion is 1: 1: 1, the two components of the color difference signal are shortened, that is, 1: x: x (where,
By setting x <1), the data amount can also be reduced.
This utilizes the fact that human visual characteristics are less sensitive to color difference signals than luminance signals.

(G) DMA controller 37: Data transfer between the color process circuit 36 and the DRAM 39 (more precisely, the DRAM interface 38) is performed without the intervention of the CPU 41, and is called a direct memory transfer (DMA). memory access). It may be abbreviated as DMAC. Generally, DMAC
In small computer systems, CPUs and I / Os
It controls data transfer between memory and memory or between memory and I / O instead of the O processor. It generates a source address and a destination address necessary for data transfer, and reads a source read cycle and a destination. The CPU or the I / O processor sets the initial address, cycle type, transfer size, and the like to the DMAC, and then transfers control to the DMAC. Data transfer is
It starts after receiving a DMA transfer request signal from an I / O device or an I / O processor. (H) DRAM interface 38: a signal interface between the DRAM 39 and the DMA controller 37;
And a signal interface between the DRAM 39 and the bus 47.

(I) DRAM 39: a kind of rewritable semiconductor memory. Generally, a DRAM is a static RAM (SRA) in that data is dynamically rewritten (refreshed) in order to retain stored contents.
Although different from M), although the writing and reading speeds are inferior to those of the SRAM, it is particularly suitable for an electronic camera because the unit cost per bit is low and a large-capacity temporary storage can be formed at a low cost. However, the present invention is not limited to a DRAM. Any rewritable semiconductor memory may be used.

Here, the storage capacity of the DRAM 39 must satisfy the following conditions. The first condition is CP
The point is that a work space of a sufficient size necessary for U41 must be secured. The size of the work space depends on the CPU 41
Architecture and OS (operating system)
In addition, since it is determined by various application programs executed under the management of the OS, it is sufficient to consider these specifications and make them appropriate and appropriate. Second
Is that a temporary storage space for captured images must be secured. This storage space may be a part of the work space, but at least information of a high-definition image (1280 ×
It must be large enough to store 960 pixel image information and a YUV signal having a 1: 1: 1 component ratio.

(J) Flash memory 40: rewritable read-only memory (PROM: programmable area)
d only memory) that can be electrically rewritten by erasing the contents of all bits (or blocks). Flash EEPROM (flash electrically era
sablePROM). The flash memory 40 in the present embodiment may be a fixed type that cannot be removed from the camera body, or may be a removable type such as a card type or a package type. The flash memory 40, whether built-in or removable, must be initialized (formatted) in a predetermined format. In the initialized flash memory 40, the number of images corresponding to the storage capacity can be recorded.

(K) CPU 41: centrally controls the operation of the camera by executing a predetermined program. The program is written in, for example, an instruction ROM in the CPU 41. In the recording mode, a program for the mode is stored. In the reproduction mode, a program for the mode is stored in the instruction ROM.
The program is loaded into the RAM inside the PU 41 and executed. (L) JPEG circuit 42: A part that performs JPEG compression and decompression. JPEG compression parameters are provided from the CPU 41 each time compression processing is performed. The JPEG circuit 4
2 should be dedicated hardware in terms of processing speed, but it can also be performed by the CPU 41 in software.

It should be noted that JPEG stands for joint photographic.
An abbreviation of experts group, an international coding standard for color still images (full-color or grayscale still images that do not include binary or moving images). In JPEG, lossless encoding that can completely restore compressed data,
Two methods of irreversible coding that cannot be undone are defined, but in most cases, the latter irreversible coding with a high compression ratio is used. The ease of use of JPEG lies in the fact that the degree of image quality degradation accompanying encoding can be freely changed by adjusting parameters used for compression (compression parameters). That is, on the encoding side, an appropriate compression parameter can be selected from the trade-off between image quality and file size, or on the decoding side, the decoding speed is increased at the expense of some quality, or it takes time. Is easy to use because you can choose to play it at the highest quality. The practical compression ratio of JPEG is about 10: 1 to 50: 1 for lossy codes. Generally, if the ratio is from 10: 1 to 20: 1, visual deterioration does not occur, but if some deterioration is allowed, even from 30: 1 to 50: 1 can be used sufficiently. Incidentally, the compression ratio of another encoding system is, for example, GIF (graphics interchange format).
In the case of (1), since the ratio is only about 5: 1, the superiority of JPEG is apparent.

(M) VRAM 43: so-called video RA
M, and when a through image or a reproduced image is written in the VRAM 43, the image is sent to the liquid crystal display 13 via the digital video encoder 45 and displayed. Some video RAMs have two ports for writing and reading, and can write and read an image simultaneously and in parallel. The VRAM 43 of the present embodiment also has this type of port. Video RA
M may be used. (N) VRAM controller 44: A part for controlling data transfer between the VRAM 43 and the bus 47 and between the VRAM 43 and the digital video encoder 45. In short, writing of an image for display to the VRAM 43 and reading of the same image from the VRAM 43 Is the part that controls If a dual port type video RAM is used,
The VRAM controller 44 may be unnecessary or simplified.

(O) Digital video encoder 45:
The digital value display image read from the VRAM 43 is converted into an analog voltage and is sequentially output at a timing according to the scanning method of the liquid crystal display 13. (P) Key input unit 46: A unit for generating operation signals for various key switches provided on the camera body. (Q) Bus 47: A data (and address) transfer path shared among the above-described units. Although not shown in the figure, necessary control lines (control lines) are also provided between the units.

<Structure Specific to Embodiment> FIG.
FIG. 3 is a detailed diagram including a D31, a horizontal / vertical driver 32, and a timing generator (TG) 33. The difference from FIG. 2 is that a clock selection unit 50 as a frequency setting unit is provided. The clock selection unit 50 includes the timing generator 3
In this embodiment, a first clock signal CK _H having a _first frequency f ₁ and a second clock signal CK _H having a lower frequency than the first frequency f ₁ are generated. It is one that generates a second clock signal CK _L having a frequency f _2, and the logic of the two clock signals CK _H, the CK _L, a predetermined signal (hereinafter referred to as "through-capture signal") , And the basic clock signal CK of the timing generator 33 is used.

The through capture signal means "one logic" while a through image is displayed in the recording mode.
Is an arbitrary signal that becomes “another logic” while capturing an image. The one logic and the other logic correspond to “1” and “0” (or “high level” and “low level”) in binary logic. The clock selector 50 selects the first clock signal CK _H on the high frequency side when the through capture signal is at one logic, and selects the first clock signal CK _H on the low frequency side when the through capture signal is at another logic. In other words, the clock selection unit 50 selects the second clock signal CK _{L. In} short, the clock selection unit 50 selects CK _H during the display period of the live view image and sets CK = CK _H, and selects CK _L during the capture period. And CK = CK _L
It is assumed that. Here, the above-mentioned sample and hold circuit 34 performs image sampling at a high frequency based on the first clock signal CK _H during the display period of the live view image, and at a low frequency based on the second clock signal CK during the capture period. Image sampling is performed.

Next, the operation will be described. First, an outline of recording and reproduction of an image will be described. <Recording mode> CC arranged behind the photographic lens 30
D31 is a signal (Vs, H) from the horizontal / vertical driver 32.
Driven in s), the video collected by the photographic lens 30 is photoelectrically converted at regular intervals, and a video signal for one screen is output. Then, the video signal is sampled by a sampling and holding circuit 34 and converted into a digital signal by an analog-to-digital converter 35, and then a YUV signal is generated by a color process circuit 36. This YUV signal is transferred to the DRAM 39 via the DMA controller 37 and the DRAM interface 38,
9 is read by the CPU 41 after the transfer to
The data is sent to the liquid crystal display 13 via the VRAM controller 44 and the digital video encoder 45 and displayed.

When the direction of the camera is changed in this state, the composition of the image displayed on the liquid crystal display 13 changes, and the shutter key 14 is "half-pressed" at an appropriate time (when a desired composition is obtained). After the exposure and focus are set and “full press”, the YUV signal stored in the DRAM 39 is fixed at the current YUV signal,
Further, the image displayed on the liquid crystal display 13 is also fixed to the image at the same time. And at that time, DRAM3
9 is sent to the JPEG circuit 42 via the DRAM interface 38, and the Y, C
Each of the components b and Cr is JPEG-encoded in a unit called a basic block of 8 × 8 pixels, written into the flash memory 40, and recorded as a captured image for one screen.

<Reproduction Mode> From CCD 31 to DRAM 3
9 is stopped and, for example, in the single display mode, the latest captured image is read from the flash memory 40 and the liquid crystal display 13
Is displayed, and the desired image is displayed by pressing the plus key 15 or the minus key 16.

<Operation at the Time of Reproduction Specific to Embodiment> Here, the procedure of image recording in the present embodiment is set to the recording mode by operating the function switch 23 as in the conventional example, and the photographic lens is set. Point the camera at the subject and adjust the composition while viewing the image (through image) of the subject displayed on the liquid crystal display 13. When the desired composition is obtained, press the shutter key 14 "half-press" to fix the exposure and focus. After that, the shutter key 14 is pressed "fully". However, as described above, the "through capture signal" becomes one logic during the display period of the through image, and during the capture period, as described above. Since it is a signal of other logic, if up to the display period of the through image and from to the capture period,
The basic clock signal CK of the timing generator 33 is CK _H from CK to CK _L from CK.

Therefore, the period of the drive signal (Vs, Hs) output from the timing generator 33 is synchronized with the first clock signal CK _H having the first frequency f ₂ on the high frequency side during the period from to. in addition, it becomes possible to synchronize the second clock signal CK _L having a second frequency f ₁ in the period of the low-frequency side from to, after all, is in a period or through period from to the drive signals (Vs, H
While the period of s) is shortened, an effect is obtained that the period of the drive signal (Vs, Hs) becomes longer during the period from to, that is, during the capture period.

As a result, during the display period of the through image, C
The transfer time of the CD 31 can be shortened to ensure smooth movement of the through image, and further, during the capture period, the transfer time of the CCD 31 can be lengthened to ensure reading of pixel information and sampling of the image. In particular, it is possible to obtain a special effect in accordance with the object of the present invention (obtaining a through image with a good motion without deteriorating the image quality of a captured image).

Incidentally, the shortening of the transfer time during the display period of the live view image may possibly fail in information transfer (readout) of some pixels or sampling of some images. Also, CCD
Liquid crystal display 13 with far fewer pixels than 31
Since there is no particular problem with the display of, and there is almost no inconvenience in practical use, some transfer errors or sampling errors can be ignored.

<Another Embodiment> FIG. 4 is a block diagram of another embodiment, in which a clock signal is selected using an automatic exposure function. Here, "exposure" refers to the brightness of a photograph, and the proper exposure is the light coming through a photographic lens, the sensitivity of the film to be used (ASA sensitivity), and the brightness of the lens in the case of a film camera. (Also referred to as exposure time: generally F value) and shutter speed. The automatic exposure function is for automatically determining the "F value". For example, shutter key 14
When the button is pressed halfway, the amount of light that has passed through the photographic lens 30 at that time is measured by a sensor, and arithmetic control with a preset film sensitivity (the sensitivity of an image sensor in the case of an electronic camera) is performed to perform an F value ( And shutter speed).

In the example of FIG. 4, the basic clock signal CK of the clock generator 33 is set to CK _H on the high frequency side or CK on the low frequency side according to the F value (exposure time) determined by the automatic exposure function. A selection signal generator 51 as a frequency setting means for generating a selection signal SEL for determining whether to make _L
It has. When the exposure time is short, the selection signal SEL output from the selection signal generator 51 is CK = CK _H
When the exposure time is long, C becomes
This is a signal of another logic for setting K = CK _{L. In} short, when the exposure time is short, the transfer time of the CCD 31 is shortened, and when the exposure time is long, the transfer time of the CCD 31 is lengthened. It embodies the function and is based on the following concept.

When the driving frequency (frequency of Vs or Hs) of the CCD 31 is increased, the transfer time of the CCD 31 is shortened.
Conversely, as the frequency is lowered, the transfer time becomes longer, as described above. FIG. 5 shows an actual CCD (1
For example, when the driving frequency is set to 30 MHz and when the driving frequency is set to 10 MHz, the transfer time changes three times from 41 ms (millisecond) to 123 ms. When the number of frames of the through image is converted into 24 frames per second, which is 8 frames, it is clear that the quality of the through image can be improved (improved in smoothness) by increasing the frequency.

On the other hand, FIG. 6 is a view showing the exposure time of the same CCD, in the case of a sufficiently bright subject (33 ms).
If the subject is dark enough to require a strobe (2
00 ms). In FIG. 6, 33
ms is equivalent to 30 frames / sec, 50 ms is equivalent to 20 frames / sec, 100 ms is equivalent to 10 frames / sec, and 167
ms corresponds to 6 frames / sec, and 200 ms corresponds to 5 frames / sec. According to these two figures (FIGS. 5 and 6), for example, when the exposure time is 33 ms, if the driving frequency is 20 MHz, the transfer time is 61 ms, and as a result, the dead time (28 ms) is subtracted. Or the charge accumulating section in the CCD 31).
For example, if the exposure time is 100 ms and the drive frequency is 20 MHz, the transfer time is 61 ms, and eventually a 39 ms wasted time (CCD 31
It can be understood that the charge transfer section and the sample and hold circuit 34 during the idle time are generated. Therefore,
To eliminate such wasted time, adjust the exposure time according to CC
It is important to change the drive frequency (frequency of Vs, Hs) of D31, and the "selection signal generator 5" in FIG.
"1" is provided in accordance with such a concept. Note that, in the example of FIG.
Although the drive frequency (frequency of Vs, Hs) of D31 is changed, it is not limited to this. For example, the “through capture signal” used in the above embodiment may be used together. Also in this case, when the through capture signal is at one logic (that is, during the display period of the through image), the drive frequency is shifted to the high frequency side, and when it is at another logic (that is, during the capture period), the drive frequency is changed. The idea of swinging to the lower frequency side is the same as in the above embodiment. This is for obtaining a through image with good motion without deteriorating the image quality of the captured image.

In the above example, the clock signal CK is changed to two high and low frequencies (f ₁ , f ₂ ) in accordance with the exposure time.
, Which is only the simplest example. For example, as shown in FIG. 7, a linear (non-linear) change characteristic 6 between the exposure time and the clock frequency is obtained.
0, or a multi-step change characteristic 6 of two or more steps.
One may be provided. An appropriate method may be selected in consideration of required performance and cost.

[0043]

According to the first aspect of the invention, the driving frequency of the image sensor is set high during the display period of the live view image, while the drive frequency is set low during the capture period. In the middle, the transfer time of the image sensor can be shortened and the movement of the through image can be smoothed,
Further, during the capture period, the transfer time of the image sensor can be lengthened to avoid a transfer error of the pixel information. Therefore, it is possible to obtain a through image with good motion without deteriorating the image quality of the captured image. According to the second aspect of the present invention, when the exposure time is short, the drive frequency of the image sensor is set high, while when the exposure time is long, the frequency is set low, so that the transfer time of the image sensor is set to the exposure time. Accordingly, the transfer efficiency or the image quality can be improved by reducing the unnecessary downtime of the image sensor. According to the third aspect of the present invention, in the second aspect of the present invention, the frequency setting means executes the setting process during a display period of the live view image, so that a smooth movement of the live view image is ensured. Can be. According to the invention described in claim 4, the driving frequency of the image sensor is changed in accordance with the exposure time, and the frequency is further changed during the display period of the live view image and during the capture period. In addition to improving the transfer efficiency or the image quality by reducing the useless pause time, it is also possible to obtain a through image with a good motion without deteriorating the image quality of the captured image.

[Brief description of the drawings]

FIG. 1 is an external view of an electronic camera.

FIG. 2 is a block diagram of the electronic camera.

FIG. 3 is a main block diagram of the embodiment.

FIG. 4 is a main part block diagram of another embodiment.

FIG. 5 is a diagram showing a correspondence between a driving frequency, a transfer time, and a timing of a through image.

FIG. 6 is a diagram showing a correspondence between an exposure time and a timing of a through image.

FIG. 7 is a characteristic diagram of a clock frequency and an exposure time.

FIG. 8 is a plan layout diagram of a CCD.

[Explanation of symbols]

 Hs Horizontal drive pulse (drive signal) Vs Vertical drive pulse (drive signal) 10 Electronic camera 13 Liquid crystal display (display means) 31 CCD (image sensor) 40 Flash memory (capture means) 41 CPU (display means, capture means) 43 VRAM (Display means) 44 VRAM controller (Display means) 45 Digital video encoder (Display means) 50 Clock selection section (Frequency setting means) 51 Selection signal generation section (Frequency setting means)

Claims (4)

[Claims] 1. An image sensor for outputting a video signal of a subject in synchronization with a predetermined drive signal, a display means for displaying the video signal as a through image, and capturing the video signal in response to a predetermined key operation An electronic camera, comprising: capture means for setting the frequency of the drive signal high during the display period of the live view image, and frequency setting means for setting the frequency low during the capture period. 2. An exposure function for automatically or manually setting an exposure time; an image sensor for outputting a video signal of a subject in synchronization with a predetermined drive signal; and a frequency of the drive signal when the exposure time is short. An electronic camera, comprising: frequency setting means for setting the frequency to be high and setting the frequency to be low when the exposure time is long. 3. A display unit for displaying the video signal as a through image, and a capture unit for capturing the video signal in response to a predetermined key operation, wherein the frequency setting unit includes a display period for displaying the through image. 3. The electronic camera according to claim 2, wherein the setting process is performed during the operation. 4. An exposure function for automatically or manually setting an exposure time, an image sensor for outputting a video signal of a subject in synchronization with a predetermined drive signal, and display means for displaying the video signal as a through image. Capture means for capturing the video signal in response to a predetermined key operation; and setting the frequency of the drive signal high during the display period of the live view image, setting the frequency low during the capture period, and setting the exposure time. An electronic camera comprising: frequency setting means for setting the frequency to a higher frequency side when is shorter and setting the frequency to a lower frequency side when the exposure time is long.