JP2000101904A - Electronic still camera - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce the size of an AF unit, thereby reducing cost and improving the degree of freedom of design, and shortening the base line length and suppressing parallax. SOLUTION: Irradiating means for irradiating a light beam toward a subject, image acquiring means for acquiring an image signal when no light ray is irradiated and an image signal when a light ray is irradiated, and calculating a difference between two images And a calculating means for calculating the position of the center of gravity of the difference in the image, and a control means for controlling the focus position of the photographic lens based on the position of the center of gravity. An autofocus light receiving system can be configured using an imaging system, and there is no need to provide a light receiving system dedicated to autofocus as in the related art.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electronic still camera, and more particularly, to an electronic still camera having an active type automatic focusing device using infrared rays.

[0002]

2. Description of the Related Art In general, cameras including electronic still cameras are equipped with various automatic mechanisms for taking clear pictures regardless of the skill of the user. An auto-focusing device (AF: also called auto-focusing) is a typical example. AF is roughly classified into an active method using infrared rays or ultrasonic waves, and a passive method using only light from a subject, and the latter method is often used in popular electronic still cameras.

FIG. 7 is an external view of a conventional electronic still camera equipped with an active AF using infrared rays. A camera body 1 has various key switches 2 to 10 including a shutter key 2 (for details, see FIG. 7). In addition, a strobe 11, a photographic lens 12, a finder 13, an AF unit 14 and the like are provided on the front surface thereof. As shown schematically in the drawing, the AF unit 14 includes an infrared light emitting diode 16 that emits infrared light 15, and an optical axis of the infrared light 15 output from the infrared light emitting diode 16. Lens 17 for irradiating light in the direction, and lens 20 for focusing the optical axis of infrared light 18 reflected by the subject and forming an image on the light receiving surface of light receiving sensor 19
In addition to the above, although not shown, the light emitting operation of the infrared light emitting diode 16 is turned on in response to “half-pressing” of the shutter key 2 (operation of stopping halfway without fully pushing down),
Further, a control unit is provided which calculates a light receiving position of the infrared light 18 on the light receiving surface of the light receiving sensor 19 at that time to obtain a focus shift amount, and drives a focusing mechanism of the photographic lens 12 to perform a series of controls for focusing. .

The light receiving sensor 19 is, as described above,
It can output a signal capable of calculating the light receiving position on the light receiving surface. For example, a line type CCD (Charge Cou
pledDevice) and PSD (Position Sensitive Device)
Are used.

[0005]

However, in the above-described conventional electronic still camera, there are two optical systems, a light emitting system including an infrared light emitting diode 16 and a lens 17, and a light receiving system including a light receiving sensor 19 and a lens 20. Since the system is provided with a system, the cost is high, and the enlargement of the AF unit section 14 is unavoidable, so that there is a problem that the degree of freedom in layout design is hindered and the design of the camera is affected. , AF unit section 14 and photographic lens 12
However, there is a problem in that the so-called parallax (also referred to as parallax), which causes a shift between the images, cannot be avoided because the distance (that is, the base line length) of the image must be long.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to reduce the size of the AF unit, thereby reducing costs and improving the degree of freedom of design, and shortening the base line length and suppressing parallax.

[0007]

According to the first aspect of the present invention,
An electronic still camera that converts an image of a subject passing through a photographic lens into an image signal by an imaging system including a two-dimensional image sensor and displays the image signal on a display unit or stores the image signal in a storage unit. Irradiating means for irradiating a light beam toward a subject, and image acquiring means for acquiring the image signal when the light is not radiated from the irradiating means and the image signal when the light is radiated from the irradiating means, Calculating means for calculating the difference between the two images obtained by the image obtaining means and calculating the position of the center of gravity of the difference in the image; and focusing on the photographic lens based on the position of the center of gravity calculated by the calculating means. Control means for controlling the position. Claim 2
The invention described in the electronic still camera according to claim 1, wherein the irradiating means irradiates an infrared ray to a subject, and the imaging system also includes an infrared signal component included in the subject. It has a characteristic that it can be converted into an image signal. The invention described in claim 3 is the invention according to claim 1.
In the electronic still camera described above, the irradiating means irradiates a light beam in a visible light range to the subject. According to a fourth aspect of the present invention, in the electronic still camera according to the first aspect, the calculating means calculates a difference between a luminance signal and a color signal of the two images.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. An electronic still camera converts an image of a subject through a photographic lens into a video signal using a two-dimensional image sensor (generally a CCD: charge coupled device), displays the video signal on a liquid crystal display, and uses a nonvolatile semiconductor memory. Or to memorize it. 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. 1 is an external view of an electronic still camera. The illustrated electronic still camera 30 includes various key switches 33 to 4 including a shutter key 32 on a camera body 31.
1 (details will be described later), a strobe 42, a photographic lens 43, a finder 44, an AF unit 45 and the like are provided on the front surface thereof, and a liquid crystal display 46 (display means) is provided on the back surface thereof. . The AF unit 45 includes an infrared light emitting diode 4 that emits infrared light 47 as schematically shown in the drawing.
8 (irradiation means) and a lens 49 (irradiation means) for narrowing the optical axis of the infrared light 47 output from the infrared light emitting diode 48 and irradiating the object direction. (See light emitting diode 16 and lens 17)
However, the difference is in the mechanism for obtaining the amount of focus shift. That is, in the present embodiment, the light emitting operation of the infrared light emitting diode 47 is turned on and the infrared light emitting diode 47 is turned on in response to the "half press" of the shutter key 32, which will be described in detail later. Two CCD images taken immediately before and during the ON period,
In short, a CCD that does not include infrared light reflected by the subject
An image (hereinafter referred to as "image A") and a CCD containing infrared light
An image (hereinafter, referred to as “image B”) is obtained, and the amount of focus shift is obtained based on these two CCD images. Therefore, the light receiving system (see FIG. There is a structural difference in that no light receiving sensor 19 and lens 20 are provided.

One of the key switches 33 to 41 is the shutter key 33 as described above.
For example, a plus key 33, a minus key 34, a power switch 35, a menu key 36, a display key 37,
A recording mode key 38, a self-timer key 39, a strobe mode key 40, a REC / PLAY key 41, and the like, and the functions (roles) of these keys are as follows. (1) Shutter key 32: In the recording mode, as the name implies, it functions as a "shutter key" (exposure and focus are fixed by half-pressing, and an image is captured by full-pressing). When the menu key 36 is pressed at the time of (a mode for reproducing a captured image or outputting to another device), it also functions as a YES key for understanding various selection items displayed on the liquid crystal display 46. Multi-function key. (2) Plus key 33: 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 46 in the case of system setting selection. (3) Minus key 34: Same function as the plus key except that the direction is reversed.

(4) Menu key 36: A key for performing various system settings. In the reproduction mode, various items such as a delete mode (image erasing mode) are displayed on the liquid crystal display 46. In the recording mode, for example, the definition of the recorded image, such as the definition of the image and the autofocus, are required. The selection items such as ON / OFF are displayed on the liquid crystal display 46. (5) Power switch 35: A switch for turning on / off the power of the camera. (6) Display key 37: A key for overlappingly displaying various information on an image displayed on the liquid crystal display 46. 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 38: A key which can be used only in the recording mode. Select normal shooting or panoramic shooting. (8) Self-timer key 39: A key for turning on / off the self-timer function. (9) Strobe mode key 40: A key for various settings related to the strobe, for example, for forcibly emitting light, prohibiting light emission, and preventing red-eye. (10) REC / PLAY key 41 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 still camera according to the present embodiment. 2, reference numeral 43 denotes a photographic lens; 50, an OLPF (optical low-pass filter); 51, a CCD (image sensor);
Vertical driver, 53 is a timing generator (TG: Timing)
Generator), 54 is a sample and hold circuit, 55 is an analog-to-digital converter, 56 is a color process circuit,
57 is a DMA controller, 58 is a DRAM interface, 59 is a DRAM, 60 is a flash memory (storage means), 61 is a CPU (image acquisition means, calculation means, control means), 62 is a JPEG circuit, 63 is a VRAM, 64
Is a VRAM controller, 65 is a digital video encoder, 66 is a key input unit, 67 is a bus, and 68 is a drive circuit for an infrared light emitting diode (infrared light emitting diode) 48.

The functions of these units are generally as follows. (A) Photo lens 43: This is for forming an image of a subject on the light receiving surface of the CCD 51, 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. However, in the case where the zoom function is provided, each time the zoom ratio is changed, the focal length at that time is read, and the focal length is calculated by a later-described calculation process (the process of FIG. 4; particularly, the drive amount calculation process of focusing in step S8). ) Must be reflected. (B) OLPF 50: As will be described later, in an electronic still camera capable of taking a color photograph, a color filter array is attached to the front of the CCD 51 to obtain RGB signals (also referred to as three-color signals). Since an actual image pickup signal contains various frequency components, for example, when a signal of a frequency component corresponding to the pitch of the color filter array enters, the signal is detected as a false color signal, and the image is taken. The color image deteriorates significantly. OLF
P50 is for removing unnecessary frequency components such as the false color signal. A lenticular in which minute cylindrical lenses are arranged, a phase filter in which a transparent thin film is formed in a striped shape by vapor deposition, or a quartz filter using birefringence of artificial quartz are used.

The principle of a quartz filter utilizing the birefringence of artificial quartz is as follows. When the artificial quartz is cut so as to include the optical axis and light is incident from the cut surface, the incident light vibrates in a plane that vibrates in a plane including the optical axis (called ordinary ray) and in a plane perpendicular to the optical axis. It is divided into rays (called extraordinary rays). The refractive index of each n _o, and n _e, and the thickness of the quartz plate and t, the separation width d is be expressed by _{d = t × [(n e} 2 -n o 2) / 2n o n e] It can be, at a wavelength of 5893 Å, n _o is 1.54425, n _e is next 1.55336, by choosing the thickness t of the quartz plate suitably, any separation width d is obtained. Since the separation width d is also related to the cutoff frequency, an OLPF having an arbitrary cutoff characteristic can be obtained depending on the value of the thickness t. In general, in a solid-state imaging device such as a CCD, since pixels are discrete and independent, it is necessary to blur a spatial frequency of a subject corresponding to a pixel pitch. Use different quartz plates in a stack.

Here, as shown in FIG. 3, a general OL
The passband of the PF corresponds to the spectral sensitivity of the human eye,
And it is about 400 to 650 nm in the visible light region that does not include the above-described unnecessary frequency components, and further has a so-called infrared cut coat surface to prevent the passage of the infrared frequency components. OLPF of this embodiment
The component 50 optimizes the design of the infrared cut coat surface 50a so that even if the frequency is in the infrared region, the component in the specific frequency region corresponding to the emission wavelength of the infrared light emitting diode 48 (about 93).
(In the vicinity of 0 nm) is transmitted with a low loss similar to that in the visible light region. (C) CCD 51: a solid-state imaging device that transfers electric charges in an array. Also called a charge-coupled device. Some are used for analog delay lines, etc., but in this specification,
In particular, it refers to a solid-state image sensor that converts two-dimensional optical information into a time-series (serial array) electric signal.

In general, a CCD has a photoelectric conversion section in which a large number of photoelectric conversion elements are arranged in an array, a charge accumulation section for accumulating output charges of the photoelectric conversion elements, and a charge readout for reading out the charges of the charge accumulation section in a predetermined manner. 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 number of effective pixels of the illustrated CCD 51 is 1280 × 96.
Set to 0. That is, 1280 in the row direction (lateral direction),
12 pixels composed of 960 pixels in the column direction (vertical direction)
Assume that it has an array structure of 80 columns × 960 rows. Note that the CCD 51 of the present embodiment is a color CCD.
Generally, since the pixel information itself of a CCD does not have color information, a color filter array (a primary color filter using three primary colors of light or a complementary color filter using three primary colors of colors) is mounted on the front surface of a color CCD. In addition, CCDs can be divided into two types according to a charge reading method. The first type is a "jump-out readout method" (also referred to as an interlaced CCD) in which pixels are skipped one by one when reading out a signal. Say) type. Although the second type is frequently used in electronic still cameras, the first type may be used in recent megapixel-class electronic still cameras exceeding one million pixels. Hereinafter, for convenience of explanation, the CCD 51 of the present embodiment is of a second type (full-surface reading system).

(D) Horizontal / vertical driver 52 and timing generator 53: a part for generating a drive signal necessary for reading the CCD 51. The CCD 51 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 a row unit while designating each column of the CCD 51 one after another.
It generates horizontal and vertical drive signals for serially reading out pixel information in the direction from the upper left to the lower right of the array structure of 80 columns × 960 rows (this direction is similar to the television scanning direction). . (E) Sampling and holding circuit 54: Sampling (for example, correlated double sampling) a time-series signal (which is an analog signal at this stage) read from the CCD 51 at a frequency suitable for the resolution of the CCD 51. . Note that automatic gain adjustment (AGC) may be performed after sampling. (F) Analog-to-digital converter 55: Converts a sampled signal into a digital signal.

(G) Color process circuit 56: A portion for generating a luminance / color difference multiplex signal (hereinafter, referred to as a YUV signal) from the output of the analog / digital converter 55. The reason for generating the YUV signal is as follows. The output of the analog-to-digital converter 55 substantially corresponds to the output of the CCD 51 one-to-one 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 x
<1) can also reduce the data amount. This utilizes the fact that human visual characteristics are less sensitive to color difference signals than luminance signals.

(H) DMA controller 57: A data transfer between the color process circuit 56 and the DRAM 59 (to be precise, the DRAM interface 58) without the intervention of the CPU 61, 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. (I) DRAM interface 58: a signal interface between the DRAM 59 and the DMA controller 57;
And a signal interface between the DRAM 59 and the bus 67.

(J) DRAM 59: 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 still camera because the unit price per bit is low and a large-capacity temporary storage can be configured at 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 59 must satisfy the following conditions. The first condition is that the capacity is such that a temporary storage space for a captured image can be secured. This storage space stores at least "two images" of high-definition image information (1280 × 960 pixel image information and a YUV signal having a component ratio of 1: 1: 1) generated by the color process circuit 56. Must be as large as possible. The second condition is that the capacity is sufficient to secure a sufficient work space required for the CPU 61. The size of the work space is determined by the architecture of the CPU 61, the OS (Operating System) and various application programs executed under the control of the OS. I just need. (K) Flash memory 60: rewritable read only memory (PROM: programmable read only memor)
y) means that the contents of all bits (or blocks) can be electrically erased and rewritten. Flash EEPROM (flash electrically erasable PRO)
M). The flash memory 60 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. Note that the flash memory 60
, Whether built-in or removable, must be initialized (formatted) in a predetermined format. The number of images corresponding to the storage capacity can be recorded in the initialized flash memory 60.

(L) CPU 61: centrally controls the operation of the camera by executing a predetermined program. The program is stored in the instruction ROM inside the CPU 61.
In the recording mode, the program for the mode is written. In the reproduction mode, the program for the mode is written from the instruction ROM to the CPU 61.
Is loaded into the internal RAM and executed. (M) JPEG circuit 62: A part that performs JPEG compression and decompression. JPEG compression parameters are provided from the CPU 61 each time compression processing is performed. The JPEG circuit 6
2 should be dedicated hardware in terms of processing speed, but it can also be performed by the CPU 61 in software. JPEG is a joint photographic experts group
And an international coding standard for color still images (full-color or grayscale still images that do not include binary images or moving images). In JPEG, two schemes are defined: lossless encoding that can completely restore compressed data and irreversible encoding that cannot be restored. In most cases, the latter scheme has a high compression rate. Lossy coding 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. JPE
The practical compression ratio of G is approximately 1 for lossy codes.
It is about 0: 1 to 50: 1. 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. By the way, the compression rate of other encoding methods is, for example,
5 in case of GIF (graphics interchange format)
Since it is only about 1, the superiority of JPEG is apparent.

(N) VRAM 63: so-called video RA
M, and when a through image or a reproduced image is written in the VRAM 63, the image is sent to the liquid crystal display 46 via the digital video encoder 65 and displayed.

Some video RAMs have two ports for writing and reading, and can write and read an image simultaneously and in parallel. However, the VRAM 63 of this embodiment also has Video RAM of this type
May be used. (O) VRAM controller 64: a part for controlling data transfer between the VRAM 63 and the bus 67 and between the VRAM 63 and the digital video encoder 65. In short, writing a display image to the VRAM 63 and reading the same image from the VRAM 63 Is the part that controls If a dual port type video RAM is used,
The VRAM controller 64 can be unnecessary or simplified.

(P) Digital video encoder 65:
The digital value display image read from the VRAM 63 is converted into an analog voltage, and is sequentially output at a timing according to the scanning method of the liquid crystal display 46. (Q) Key input section 66: A section for generating operation signals for various key switches provided on the camera body. (R) Bus 67: A data (and address) transfer path shared among the above components. Although not shown in the figure, necessary control lines (control lines) are also provided between the units. (S) Drive circuit 68: The drive circuit 68 drives the infrared light emitting diode 48 when the control signal 69 from the CPU 61 is active.
During this drive, the photographic lens 43
Irradiate the infrared ray 47 to the subject in the front direction.

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 43
D51 is driven by a signal from the horizontal / vertical driver 52, and the video collected by the photographic lens 43 is photoelectrically converted at regular intervals to output a video signal for one image. Then, the video signal is sampled by the sampling and holding circuit 34 and converted into a digital signal by the analog-to-digital converter 55, and then a YUV signal is generated by the color process circuit 56. The YUV signal is transferred to the DRAM 59 via the DMA controller 57 and the DRAM interface 58. After the transfer to the DRAM 59 is completed, the YUV signal is read by the CPU 61 and sent to the liquid crystal display 46 via the VRAM controller 64 and the digital video encoder 65. Is displayed.

When the direction of the camera is changed in this state, the composition of the image displayed on the liquid crystal display 46 changes, and the shutter key 32 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 59 is fixed at the current YUV signal,
Further, the image displayed on the liquid crystal display 46 is also fixed to the image at the same point. Then, at that time, the DRAM 5
9 is sent to the JPEG circuit 62 via the DRAM interface 58 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 60, and recorded as one captured image.

<Reproduction Mode> From CCD 51 to DRAM 5
9 is stopped and, for example, in the single display mode, the latest captured image is read from the flash memory 60 and the liquid crystal display 46 is displayed.
And displays the desired image by pressing the plus key 33 or the minus key 34.

<Auto Focus Process> The auto focus process (AF process) in the present embodiment is performed according to a flowchart shown in FIG. In this flowchart, first, in the recording mode, when "half press" of the shutter key 32 is detected (YES determination in S1), the output of the CCD 51 at that time (more precisely, the color process circuit 5)
6 is captured as an "image A" and stored in the DRAM 59 (S2). Next, the control signal 69 is activated to turn on the infrared light emitting diode 48 (S3). (Accurately, the YUV signal appearing at the output of the color process circuit 56) is fetched as "image B" and stored in the DRAM 59 (S4), and then the control signal 69 is made inactive to turn off the infrared light emitting diode 48. (S3) Preceding part 70
Following the former part 70, two images (images A and B) stored in the DRAM 59 are subjected to pixel calculation to generate a difference image (S6), and then the center of gravity of the difference image is calculated. The calculation (S7) is performed and the photographic lens 4 is
After calculating the driving amount of the focusing of No. 3 (S8) and driving the photographic lens 43 by the focusing driving mechanism not shown (S9), the shutter key 32 is fully pressed.
(S11: See the description of the recording mode described above) in response to the operation (S10: push-down operation to the end).

Here, the "center of gravity" is a peak position P of a luminance signal in a difference image (image A-image B) between image A and image B, as shown in FIG. Let Lp be the center of the optical axis of
If the distance to the object is d, the distance to the subject can be represented by the distance d. Now, as shown in FIG. 6, the distance (namely, the base line length) from the mounting position of the infrared light emitting diode 48 to the optical axis center (Lp) of the photographic lens 43 is D, the focal length of the photographic lens 43 is f, Assuming that the distance to L is L, the front principal point (Note 1) of the photographic lens 43 is H, and the rear principal point (Note 2) of the photographic lens 43 is H ', a similar relationship (Note 3) is obtained. D = f / d is satisfied, and this equation is modified to obtain L = (D / d) × f. Accordingly, the distance L from the peak position P of the luminance signal in the difference image between the image A and the image B (image A-image B) to the subject can be obtained, and the photographic lens 43 is focused according to the distance L. Can be.

Note 1, Note 2: The principal point is an imaginary point serving as a base point when measuring the focal length in a photographic lens or the like. The front principal point is a reference point on the subject side, and the rear principal point is a reference point on the imaging plane side. Light rays incident on the front principal point have the property of exiting at the same angle from the rear principal point. In an actual photographic lens or the like, the position of the principal point depends entirely on the structure of the lens. For example, FIG. 6 illustrates that the front principal point H is located inside the front surface 43a of the photographic lens 43 and the rear principal point H ′ is located outside the rear surface 43b of the photographic lens 43. These positional relationships are merely examples of an electronic still camera.

Note 3: Similarity refers to the fact that in the nature of the principal point described above, the ray 72 incident on the front principal point H from the subject exits from the rear principal point H 'at the same angle and becomes a ray 73. Based on the above, the similarity of two right-angled triangles in which the lengths of these two rays 72 and 73 (in the case of the ray 73, the length from the rear principal point H 'to the imaging plane) are the respective hypotenuse lengths Is to say. That is, the first right triangle has the length of the light ray 72 as the hypotenuse, and the lengths of the other two sides as D and L.
In the second right triangle, the length of the light ray 73 is the length of the hypotenuse, and the lengths of the other two sides are d and f. , 73 are parallel, the two right triangles are clearly analogous.

As described above, according to the present embodiment, the light receiving system for autofocus is configured by using the image pickup system including the photographic lens 43 and the CCD 51. (The light receiving sensor 19 and the lens 20 in FIG. 7) is not required, so that the AF unit 45 can be reduced in size and the cost can be reduced and the degree of freedom in design can be improved. With the downsizing of the AF unit section 45, the distance (base line length) between the AF unit section 45 and the photographic lens 43 can be reduced, and parallax (parallax) can be suppressed to improve the accuracy of autofocus. Is obtained.

In the present embodiment, since the photographic lens 43 is included in the light receiving system of the autofocus, the CCD 51 is determined by the difference between the current focus position and the object position for the following reason (Note 4). There is a possibility that the image on the imaging surface will be blurred. However, considering the center of gravity of the light intensity distribution of the blurred image, the photographic lens 43 is almost telecentric (Note 5) on the image side. The positional accuracy does not deteriorate much, and even if deterioration is a problem,
By increasing the telecentricity of the photographic lens 43, a sufficient measure can be taken.

Note 4: In general, the refractive index of glass changes depending on the wavelength of transmitted light, and the optical glass used for a photographic lens is no exception. Therefore, when various light beams having different wavelengths are passed through a photographic lens made of optical glass, the imaging point is slightly shifted for each light beam, and so-called longitudinal chromatic aberration occurs. Generally, in an electronic still camera, the visible light range (4
Although the photographic lens structure is optimally designed so that the longitudinal chromatic aberration is within a practically acceptable level in a wavelength range of from 00 to 650 nm), for the ultraviolet light and infrared light other than the visible light range, for example, Since the light is attenuated or cut before reaching the CCD, it is not considered in the structural design of the photographic lens. For this reason, the infrared light having a wavelength longer than the visible light causes a shift in the optical axis direction, and when viewed on the image plane of the visible light, the image due to the infrared light is slightly blurred.

Note 5: Telecentricity of a photographic lens is an optical term meaning that it is parallel to the optical axis.
In the electronic still camera, it is necessary to design the principal ray of the light beam emitted from the final surface of the photographic lens (see reference numeral 43b in FIG. 6) almost telecentrically (actually, at an angle of about 0 to 10 degrees regardless of the focal length). There). This is because light rays need to be perpendicularly incident on the OLPF, infrared cut surface, microlenses on the CCD chip, and the like on the rear side of the photographic lens. Here, the chief ray is simply the middle ray of the light beam for forming an image at one point. If the image side of the photographic lens is completely telecentric, the optical axis and the principal ray of the luminous flux corresponding to any image point will be parallel. The distance between the position and the optical axis does not change. After all, by increasing the telecentricity,
This can prevent the positional accuracy from deteriorating.

<Modifications of Embodiment> The present invention is not limited to the above-described embodiment, and various modifications are possible within the intended range. Hereinafter, the modified examples are listed. First, in the above embodiment, an image A containing no infrared light from a subject is captured first, and then an image B containing infrared light is captured.
The point is that two images, one containing infrared light and the other containing infrared light, need only be captured with as little time as possible, and the order is not particularly essential. Alternatively, both or one of the image A and the image B may be an average image of a plurality of images. In this case, the change in the image in the time axis direction can be canceled, which is preferable.

Further, in the above embodiment, the two images A and B are both stored in the DRAM 59, but the image B to be captured second is not necessarily stored in the DRAM 59. This is because the difference from the image A can be calculated while capturing the image B. In the above embodiment, C
Although two full-size images A and B corresponding to the number of effective pixels of the CD 51 are taken in, the distance measurement area for focusing is generally limited to a predetermined area near the center of the full-size image. , B may be adjusted to the predetermined area. The processing speed can be improved without wasting memory.

In the above-described embodiment, the photographic lens is driven to a predetermined position immediately after calculating the driving amount. However, the present invention is not limited to this. For example, the photographic lens may be driven in response to a full press of a shutter key. You may. Further, in the above embodiment, the difference between the “luminance signals” between the image A and the image B is used. In addition, the difference between the “color signals” between the image A and the image B may be used. In this way, two images A,
Even when the luminance signal changes due to the change of the light state of the subject while capturing B, there is almost no difference in the color signal, so that an error due to the change in the light state can be suppressed. The method of using the color signal is, for example, to calculate the difference between the images A and B for each of the RGB color signals, and set the image ratio close to the ratio of the color of the infrared light emitting diode to be used as the imaging position of the infrared light emitting diode. What is necessary is just to obtain the position of the center of gravity. It is needless to say that not only the luminance signal but also the color signal alone can provide a corresponding effect.

In the above embodiment, an infrared light emitting diode is used, but a light emitter in the visible light range can be used instead of the infrared light emitting diode. When a light emitter in the visible light range is used, it is not necessary to change the spectral sensitivity characteristics of the infrared cut coat surface of the OLPF. For example, a general infrared absorbing glass can be used, which is convenient. Since the distance can be visually checked, there is also an effect that the distance measurement can be confirmed on a viewfinder or a monitor.

[0042]

According to the first aspect of the present invention, an image of a subject passing through a photographic lens is converted into an image signal by an imaging system including a two-dimensional image sensor, and the image signal is displayed on a display means. And an irradiating means for irradiating the object with a light beam, the image signal when the irradiating means does not irradiate the light, and irradiating the light from the irradiating means. Image acquisition means for acquiring the image signal when the image processing is performed, computing means for computing the difference between the two images acquired by the image acquisition means, and computing the position of the center of gravity of the difference in the image, Control means for controlling the focus position of the photographic lens based on the position of the center of gravity calculated by the means, so that an imaging system including a photographic lens and an image sensor is used. It is possible to configure a light receiving system of auto focus Te. Therefore, there is no need to provide a light receiving system (light receiving sensor 19 and lens 20 in FIG. 7) dedicated to auto focus as in the related art, and the AF unit can be reduced in size accordingly, reducing costs and increasing design flexibility. In addition to the special effect that it can be improved,
With the miniaturization of the unit, the distance (base line length) between the AF unit and the photographic lens can be shortened, resulting in parallax (parallax).
, And a special effect that the accuracy of autofocus can be improved. According to the second aspect of the present invention, in the electronic still camera according to the first aspect,
The irradiating means irradiates an infrared ray to a subject, and the imaging system has a characteristic that an infrared signal component included in the subject can be converted into an image signal. The existing light emitting system (the infrared light emitting diode 16 and the lens 1 shown in FIG. 7) included in the AF unit of the camera is used.
7) can be diverted, and the merit that significant renovation of the AF unit is not required can be obtained. According to the third aspect of the present invention, in the electronic still camera according to the first aspect, since the irradiating unit irradiates a subject with a light beam in a visible light range,
Although the existing light emitting system included in the AF unit unit of the electronic still camera cannot be used, it is not necessary to modify the imaging system, particularly the infrared cut surface of the OLPF, and the influence on the image quality can be minimized. There is an advantage.
According to the fourth aspect of the present invention, in the electronic still camera according to the first aspect, the calculating means calculates a difference between a luminance signal and a color signal of the two images. (Or when used with a luminance signal)
Is advantageous in that even if the state of the light beam of the subject changes during the acquisition of two images, it is less likely to be affected by the change, so that it is possible to avoid deterioration in the accuracy of focusing.

[Brief description of the drawings]

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

FIG. 2 is a block diagram of an electronic still camera.

FIG. 3 is a diagram showing a spectral transmittance of an infrared cut coat.

FIG. 4 is a flowchart of an autofocus process.

FIG. 5 is a conceptual diagram of images A and B and their difference images.

FIG. 6 is a conceptual diagram showing a positional relationship between main components.

FIG. 7 is an external view of a conventional example.

[Explanation of symbols]

 Reference Signs List 30 electronic still camera 43 photographic lens 46 liquid crystal display (display means) 47 infrared light emitting diode (irradiation means) 49 lens (irradiation means) 51 CCD (image sensor) 60 flash memory (storage means) 61 CPU (image acquisition means, calculation) Means, control means)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 9/79 H04N 9/79 G F term (Reference) 2H011 AA01 BA34 BB03 BB06 DA08 2H051 AA01 BA47 BA70 CC03 CE14 DA15 DA16 5C022 AA13 AA15 AB15 AB24 AB28 AC00 AC03 5C053 FA08 GB36 KA04 5C055 AA06 BA06 CA07 EA02 EA04 FA22 HA31

Claims (4)

[Claims] 1. An image of a subject passing through a photographic lens is converted into an image signal by an imaging system including a two-dimensional image sensor.
An electronic still camera that displays the image signal on a display unit or stores the image signal in a storage unit, wherein the irradiation unit irradiates a light beam toward the subject; and the image when the light beam is not irradiated from the irradiation unit. A signal and an image acquisition unit for acquiring the image signal when light is emitted from the irradiation unit; and calculating a difference between the two images acquired by the image acquisition unit, and a center of gravity of the difference in the image. An electronic still camera, comprising: arithmetic means for calculating the following; and control means for controlling the focus position of the photographic lens based on the position of the center of gravity calculated by the arithmetic means. 2. The irradiating means irradiates an infrared ray to a subject, and the imaging system has a characteristic capable of converting an infrared signal component contained in the subject into an image signal. The electronic still camera according to claim 1, wherein 3. The electronic still camera according to claim 1, wherein said irradiating means irradiates a light beam in a visible light range to a subject. 4. The electronic still camera according to claim 1, wherein the calculating means calculates a difference between a luminance signal and a color signal of the two images.