JP5011625B2 - Imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a camera distance detection apparatus.
[0002]
[Prior art]
A so-called phase difference detection type distance measuring device is known as a camera distance detecting device. This distance measuring device has a pair of line sensors provided corresponding to the focus detection areas, and determines the distance to the subject based on the interval between a pair of subject images formed through lenses on each line sensor. To detect. The distance between the subject images is close to each other in the so-called front pin state in which the lens connects the sharp image of the subject in front of the planned focal plane (subject side), and in the so-called rear pin state in which the sharp image of the subject is connected after the planned focal plane. Move away from each other. Therefore, the subject image is photoelectrically converted by a line sensor to be converted into an electrical signal, and these signals are processed to obtain the relative distance between the pair of subject images, thereby obtaining the distance to the subject corresponding to the focus detection area. It is done. As the line sensor, a charge storage type light receiving element such as a CCD is used. In the charge storage type light receiving element, the charge storage time is controlled according to the subject brightness. When the subject luminance is high, the charge accumulation time is shortened, and when the subject luminance is low, the charge accumulation time is lengthened.
[0003]
[Problems to be solved by the invention]
If the subject brightness is too low, the signal level of the charge accumulation signal output from the light receiving element after charge accumulation cannot be sufficiently increased even if the charge accumulation time is lengthened, making it difficult to correctly perform distance detection calculation. It is.
[0005]
An image pickup apparatus according to the present invention intercepts an imaging unit that enters a light beam from a subject through a photographic lens and outputs an imaging signal, and a passing state in which an infrared light component included in the light beam passes in an optical path to the imaging unit. Filter means for switching between the cut-off state, an extraction means for extracting a human face from an image pickup signal output from the image pickup means when the filter means is in a passing state, and a size of the face extracted by the extraction means on the photographing screen. Refer to the size detection means to be detected, storage means for storing in advance information indicating the relationship between the size of the face detected by at least the size detection means and the distance to the subject, and information stored in the storage means And distance calculating means for calculating a distance used for the focus adjustment processing based on the size of the face detected by the size detecting means.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing an outline of an electronic still camera according to an embodiment of the present invention. In FIG. 1, an electronic still camera includes a photographing lens 11, an optical filter 12, a CCD 13, an A / D conversion circuit 14, an image processing circuit 15, a buffer memory 16, a CPU 17, a frame memory 18, and an LCD. The display unit 19 includes a distance measuring / focusing circuit 30, a lens driving unit 35, an optical filter driving unit 40, and an operation member 50. The operation member 50 includes a release button and each switch described later. When the operation member 50 is operated, an operation signal from the operated release button and switch is sent to the CPU 17. The electronic still camera is provided with a detachable recording medium 60.
[0007]
When a power switch (not shown) of the electronic still camera is turned on, the CPU 17 starts a control program by performing a predetermined on operation of the electronic still camera. The CPU 17 controls the operation timing for charge accumulation and accumulated charge readout for the CCD 13 constituting the image sensor. When a release operation signal is input to the CPU 17 from a release button (not shown), the CPU 17 starts a photographing operation. A subject image is formed on the imaging surface of the CCD 13 by the photographing lens 11, and the CCD 13 accumulates signal charges according to the brightness of the subject light.
[0008]
The optical filter 12 is an infrared light blocking filter and removes an infrared light component contained in the subject light. The optical filter drive unit 40 drives the optical filter 12 according to a command from the CPU 17. The optical filter 12 is inserted on the optical path at the time of photographing, and is retracted from the optical path at the time of distance measurement before photographing.
[0009]
The signal charge accumulated in the CCD 13 is discharged by a timing signal from the CPU 17 and converted from an analog imaging signal to a digital signal by the A / D conversion circuit 14. The digitally converted signal is guided to the image processing circuit 15, subjected to predetermined image processing such as contour processing, gamma correction, and color temperature adjustment (white balance), and is temporarily stored in the buffer memory 16.
[0010]
The image data after image processing is processed into image data for display by the image processing circuit 15 and stored in the frame memory 18. The display data stored in the frame memory 18 is displayed as a photographing result on an external monitor such as the LCD display unit 19. The image processing circuit 15 further performs processing for compressing the image data after the image processing in the buffer memory 16 to a predetermined ratio by a recording method such as JPEG. The image data subjected to the data compression is given a predetermined file name by the CPU 17 and recorded on the recording medium 60.
[0011]
The ranging / focusing circuit 30 extracts an imaging signal based on a human face from among the imaging signals output from the CCD 13, and determines the main subject (this object) according to the size of the image (face) based on the extracted imaging signal on the shooting screen. In this case, the distance to the person having the extracted face) is calculated. The distance measuring / focusing circuit 30 sends a lens driving instruction to the lens driving unit 35 so that the subject light flux from the calculated distance is imaged on the imaging surface of the CCD 13. As a result, a focus lens (not shown) constituting the photographing lens 11 is driven to the in-focus position in the optical axis direction.
[0012]
The present invention is characterized in that a subject whose approximate size is known in advance, such as a human face, is used, and ranging calculation is performed from the size of the subject image to be captured. In this embodiment, the optical filter 12 is retracted from the optical path during distance measurement to capture an image of infrared light with the CCD 13, and the image signal from the CCD 13 having a high signal level is determined by the human face image. Considered as an imaging signal.
[0013]
The flow of the focusing control process performed by the CPU 17 of the electronic still camera according to the present embodiment will be described with reference to the flowchart of FIG. The processing shown in FIG. 2 is started when a release button (not shown) is half-pressed and a half-press operation signal is input to the CPU 17. In step S11, the CPU 17 issues a command to the optical filter drive unit 40, retracts the optical filter 12 from the optical path, and proceeds to step S12. In step S12, the CPU 17 issues a command to the distance measuring / focusing circuit 30 to extract a target image (here, a human face). The distance measuring / focusing circuit 30 receives a command from the CPU 17 and extracts a signal having a high luminance from the imaging signals output from the CCD 13.
[0014]
FIG. 3 is a diagram illustrating an example of a screen in which a person is imaged in a state where infrared light is incident on the CCD 13 by retracting the optical filter 12 from the optical path. Generally, since infrared light is radiated from the human skin, when the infrared light is exposed, the brightness of the portion where the skin is exposed increases. For this reason, the image signal from the CCD 13 has a signal level corresponding to the portion 31 where the skin is exposed, such as the face, higher than the other portions of the photographing screen. At this time, the charge accumulation time for the CCD 13 is controlled by the CPU 17 so as not to saturate the signal level of the imaging signal in the portion with high luminance.
[0015]
The distance measuring / focusing circuit 30 regards the target image as a target image when two or more pixels adjacent to each other have an image signal whose signal level is a predetermined value or higher, and notifies the CPU 17 that the target has been extracted. In step S13, the CPU 17 issues a command to the distance measuring / focusing circuit 30 to perform image measurement. The distance measuring / focusing circuit 30 counts how many pixels the image signal having a signal level equal to or higher than a predetermined value is adjacent, and sends the count result to the CPU 17. In step S14, the CPU 17 detects the focal length of the photographic lens 11, sends information indicating the detected focal length to the distance measuring / focusing circuit 30, and proceeds to step S15. The focal length of the photographic lens 11 is detected by a lens information detection circuit (not shown), and the detection result is sent to the CPU 17.
[0016]
When the focal length information is sent from the CPU 17 in step S15, the distance measuring / focusing circuit 30 refers to a conversion table stored in a memory (not shown) in the distance measuring / focusing circuit 30 to reach the target. Convert to distance. FIG. 4 is a conversion table showing an example of the relationship between the count number and the distance to the target when the focal length of the photographic lens 11 is 38 mm. For example, when the number of pixels of the CCD 13 is 2048 dots in the horizontal direction of the shooting screen and 1536 dots in the vertical direction of the shooting screen, it indicates how many pixels the face of the person who is the target subject is composed of image signals. Yes. That is, the count number corresponds to the size occupied by the subject image on the shooting screen.
[0017]
In step S16, the distance measuring / focusing circuit 30 converts the converted distance to the target into information indicating the focus position of the focus lens, and drives the focus lens to the focus position with respect to the lens drive unit 35. Instruct. The relationship between the distance to the target and the focus position is stored in the distance measuring / focusing circuit 30. As a result, the lens driving unit 35 drives the focus lens, and focus control is performed on the target subject. When the lens driving instruction is given to the lens driving unit 35, the distance measuring / focusing circuit 30 sends a signal notifying the end of the focusing process to the CPU 17.
[0018]
In step S17, the CPU 17 determines whether or not the release button has been fully pressed. The CPU 17 makes an affirmative determination in step S17 when a full-press operation signal is input, and proceeds to step S18. If the full-press operation signal is not input, the CPU 17 makes a negative determination and returns to step S12. In step S18, the CPU 17 issues a command to the optical filter drive unit 40, causes the optical filter 12 to be inserted on the optical path, and proceeds to step S19. In step S19, the CPU 17 starts the above-described photographing operation, and ends the process shown in FIG.
[0019]
The taking lens 11 may be a zoom lens. When the photographing lens 11 is a zoom lens, the table value shown in FIG. 4 is changed according to the change of the focal length. Specifically, the face size (dots) value shown in FIG. 4 is multiplied by (38 / focal length (unit: mm)). For example, when the focal length is 75 mm, the value of the face size (dots) according to FIG. 4 may be multiplied by (38/75) = about 1/2. It is assumed that the focal length set for the zoom lens is detected by a lens information detection circuit (not shown), and the detection result is sent to the CPU 17.
[0020]
Generally, there are individual differences in the size of a person's face, and the size of the face varies depending on whether the subject is an adult or a child. Accordingly, when the size of the face of the person who is the subject is different from the size of the face of the person who is the model of the table shown in FIG. 4, an error occurs in the distance measurement result. In actual shooting, there is a range in focus distance depending on the depth of field, so even if there is an error in the distance converted by the table in FIG. 4, in many cases the subject (person with the face to be extracted) Focus on. In particular, when a wide-angle lens is used, it is easy to focus on the subject because a deep depth of field is obtained.
[0021]
According to the embodiment described above, the following operational effects can be obtained.
(1) The size (number of pixels) occupied by a subject (here, a human face) whose size is known on the shooting screen is obtained in advance for each distance to the subject and tabulated. A human face is extracted from the image pickup signal at the time of distance measurement, the number of pixels corresponding to the extracted image pickup signal is counted, and the subject distance is obtained from the table. Therefore, for example, unlike conventional techniques such as hill-climbing method and phase difference detection method, even when the shooting screen does not include a subject with high contrast or when the subject brightness is low and sufficient contrast cannot be obtained, Ranging can be performed by referring to the table.
(2) Since the optical filter 12 that removes infrared light during distance measurement is retracted out of the optical path, an image of infrared light is picked up by the CCD 13. As a result, human skin with high luminance in the infrared light region is imaged, so that even when the luminance in the visible light region is low, an imaging signal with a level sufficient to extract a human face is obtained, and distance measurement is performed. It can be carried out.
(3) Since the optical filter 12 is inserted on the optical path at the time of photographing after distance measurement, a visible light image can be photographed without being affected by infrared light.
[0022]
In the above-described embodiment, a person's face is extracted and distance measurement is performed at the time of distance measurement. However, the distance measurement method may be switched depending on the shooting environment. For example, when the luminance by visible light is equal to or higher than a predetermined value, distance measurement is performed by a known hill-climbing method or phase difference detection method, and when the luminance by visible light is lower than the predetermined value, a human face is extracted as described above. To measure the distance.
[0023]
In the above description, the optical filter 12 is retracted at the time of distance measurement, and an infrared image is taken to extract a human face. Instead of this, an image of visible light may be captured without retracting the optical filter 12, and a human face may be extracted from the captured image signal. In this case, if the ratio of the R color component, the G color component, and the B color component of the imaging signal satisfies a predetermined ratio, it is regarded as a skin color, and an image of a human face that has a predetermined number or more adjacent to these imaging signals It is considered.
[0024]
In step S12 described above, the distance measuring / focusing circuit 30 is regarded as an image of a human face when image signals having a signal level of a predetermined value or more are adjacent to each other by 2 pixels or more. Instead, the photographer operates a cross switch (not shown) included in the operation member 50 while the imaging screen (through image) before the release button is fully pressed is displayed on the LCD display unit 19. An image based on a human face may be designated. In this case, the distance measuring / focusing circuit 30 regards the image signal corresponding to the designated position as an image of a human face.
In the above description, information indicating the focus position of the focus lens is obtained using the distance detected by the distance measuring / focusing circuit 30, and automatic focus adjustment (autofocus) that instructs the lens drive unit 35 to drive the focus lens. ) The device has been described. In addition to performing focus adjustment, camera control may be performed using the distance detected by the distance measuring / focusing circuit 30. For example, the distance measurement result is used for edge enhancement processing for enhancing the outline of an image photographed by an electronic still camera. In this case, the edge enhancement is weakly performed when the distance measured is shorter than a predetermined distance, and the edge enhancement is performed strongly when the distance measured is longer than a predetermined distance. As a result, the outline of a distant subject can be emphasized and expressed clearly.
[0026]
Further, the white balance processing may be changed using the distance detected by the distance measuring / focusing circuit 30. For example, white balance adjustment using color information of the subject extracted when the distance measured is shorter than a predetermined distance, and the entire shooting screen including colors other than the subject extracted when the distance measured is longer than a predetermined distance White balance adjustment is performed using the color information.
[0027]
Furthermore, the light control processing at the time of photographing using a flash device (not shown) may be changed using the distance detected by the distance measuring / focusing circuit 30. For example, when the distance measured is shorter than a predetermined distance, the main subject is prevented from being whitened by suppressing the amount of light emitted to the flash device or by narrowing the aperture during shooting. When the measured distance is longer than a predetermined distance, the main subject is prevented from sinking black by increasing the amount of light emitted to the flash device or opening the aperture during shooting.
[0029]
【Effect of the invention】
As described in detail above, according to the present invention, for example, distance detection calculation can be performed correctly even in a low luminance state.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an outline of an electronic still camera according to an embodiment of the present invention.
FIG. 2 is a flowchart for explaining a flow of focusing control processing performed by a CPU of the electronic still camera.
FIG. 3 is a diagram illustrating an example of a screen on which a person is imaged in a state where infrared light is incident on a CCD.
FIG. 4 is a diagram of a conversion table showing a relationship example between a count number and a distance to a target.
[Explanation of symbols]
11 ... Photography lens, 12 Optical filter,
13 ... CCD, 15 ... Image processing circuit,
17 ... CPU, 19 ... LCD display,
30 ... Ranging / focusing circuit, 35 ... Lens drive unit,
40 ... Optical filter drive unit, 50 ... Operation member

Claims (4)

Imaging means for entering a light flux from a subject through a photographing lens and outputting an imaging signal;
Filter means for switching between a passing state for passing an infrared light component included in the light flux and a blocking state for blocking in an optical path to the imaging means;
An extracting means for extracting a human face from an imaging signal output from the imaging means when the filter means is in the passing state;
A size detecting means for detecting the size of the face extracted by the extracting means on the photographing screen;
Storage means for storing in advance information indicating the relationship between at least the size of the face detected by the size detection means and the distance to the subject;
A distance calculation unit that refers to the information stored in the storage unit and calculates a distance used for focus adjustment processing based on the size of the face detected by the size detection unit;
An imaging apparatus comprising: The imaging device according to claim 1,
An imaging apparatus, further comprising: a control unit that starts an imaging operation based on an imaging signal output from the imaging unit after the filter unit is switched to the cutoff state. The imaging device according to claim 1 or 2,
The image pickup apparatus characterized in that the filter means switches to the passing state when the luminance by the visible light component is less than a predetermined value. In the imaging device according to any one of claims 1 to 3,
The taking lens is a zoom lens;
The storage means stores the information for each focal length of the photographing lens,
The distance calculating means calculates a distance used for the focus adjustment according to a focal length set for the photographing lens.

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