JP5595167B2 - Imaging apparatus and control method thereof - Google Patents

Description

  The present invention relates to a technique for realizing high image quality of a still image acquired during zoom driving of an optical lens.

Recent digital single-lens reflex cameras and digital still cameras can shoot moving images, and digital video cameras can also shoot still images. As described above, an imaging apparatus having a shooting mode other than the main target mode is known. In particular, digital video cameras are equipped with a function for capturing and recording still images simultaneously during moving image recording, that is, a so-called still image simultaneous recording function. On the other hand, when the zoom mechanism of the optical lens is operating at the time of capturing a still image, radial blur may occur in the still image at the time of capture depending on the zoom speed or shutter speed, and there is a risk of significant image quality degradation. This is because the angle of view changes due to the zoom operation performed during the exposure period of the image sensor, and the change causes blurring.
Therefore, if the electronic zoom is regularly used instead of the optical zoom, the optical zoom operation does not occur and the angle of view of the subject image received by the image sensor does not change, so that radial blur does not occur. However, in the high-magnification processing by electronic zoom, a part of the screen is cut out and enlarged by image processing, which causes image quality degradation. That is, the number of pixels is smaller than the image quality with the number of pixels of the original image sensor.
In a conventional imaging device, when acquiring a still image during the zoom operation of the optical lens, a method of acquiring a still image by temporarily stopping the zoom operation and a method of acquiring a still image when the zoom operation ends Is adopted. However, the former method has a problem that the zoom operation becomes unnatural during moving image recording. Further, since the latter method cannot record an image at the moment when a still image is to be acquired, there is a possibility that an image contrary to the photographer's intention is recorded.
Japanese Patent Application Laid-Open No. 2004-228561 discloses a method of capturing still images continuously during zoom operation and capturing still images using the start and end of zoom operations as triggers.

JP 2007-316471 A

In the related art, there is a problem that, when acquiring a still image during a zoom operation, sufficient measures are not taken to capture an image at the moment intended by the photographer without causing radial blur. For this reason, radial blur causes degradation of image quality, and convenience is impaired when a still image unintended by the photographer is acquired.
An object of the present invention is to improve convenience by capturing an image according to a photographer's intention while minimizing image quality degradation in still image shooting during a zoom operation.

In order to solve the above problems, an apparatus according to the present invention is an image pickup apparatus having a function of an optical zoom performed by driving an optical lens having a zoom mechanism, and an electronic zoom function performed by enlargement and reduction processing of image data obtained by an image pickup device. An operation means for instructing acquisition of a still image, an image processing means for enlarging a part of the image data from the image sensor or reducing the image data, and image data processed by the image processing means are recorded. The recording means, and when the operation means receives a still image acquisition instruction during the optical zoom operation, the optical zoom operation is stopped and the electronic zoom is temporarily switched to the still image image. Control means for causing the recording means to record data is provided. The control means changes the electronic zoom magnification as time elapses in a transition period from recording the still image data to the recording means to restarting the optical zoom operation to return to the original operation speed. Then, control is performed so as to return to the original magnification before stopping the operation of the optical zoom.

  According to the present invention, it is possible to acquire a still image according to a photographer's intention while minimizing image quality degradation.

It is a block diagram showing an example of composition of an imaging device concerning one embodiment of the present invention. It is a flowchart which shows the process example of the still image recording which concerns on 1st Embodiment of this invention. It is a figure explaining the example of switching control of an optical zoom and an electronic zoom. It is a flowchart which shows the process example of the still image recording which concerns on 2nd Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram illustrating a configuration example of an imaging apparatus according to an embodiment of the present invention. The imaging apparatus has an optical zoom function that is optically performed by driving a lens and an electronic zoom function that is electronically performed by image enlargement and reduction processing.
An optical lens and an optical LPF (low-pass filter) 1 take in light from a subject and form an image on the image sensor 2. The optical lens and the optical LPF 1 include a focus mechanism that adjusts the position of the focus surface, a zoom mechanism that changes the focal length, an iris mechanism that changes the aperture amount of the lens, and the like. In general, the imaging apparatus has a manual mode in which the photographer can freely set and change these, and an auto mode in which the system control unit 6 to be described later automatically controls. Recently, the main subject (face of a person, etc.) is detected, and the zoom control is automatically performed to keep the main subject at a certain size as well as adjusting the focus and iris according to the main subject. Has also been proposed.

  The imaging device 2 receives incident light from the optical lens and the optical LPF 1 and converts it into an electrical signal, and then outputs the signal. Representative examples of the image pickup device 2 include a CCD (charge coupled device) image sensor and a CMOS (complementary metal oxide semiconductor) image sensor. An analog electrical signal output from the image sensor 2 is converted into a digital signal by an AFE (analog front end) 3. In addition to a device that directly outputs an analog video signal, the image sensor 2 includes a device that performs AD (analog-digital) conversion processing inside the image sensor 2 and outputs digital data such as LVDS. LVDS is an abbreviation for “Low Voltage Differential Signaling”. The AFE 3 converts an analog electric signal from the image sensor 2 into a digital signal and sends it to the image processing unit 4 as data such as LVDS. is there.

The image processing unit 4 performs various image processing such as gamma correction, knee correction, and noise reduction on the digitized video signal. For example, when the image pickup device 2 is a CMOS image sensor, the image processing unit 4 performs removal of fixed pattern noise unique to the CMOS image sensor, black level clamp processing, and the like. The image processing unit 4 has an electronic zoom processing function, cuts out a necessary shooting range from a shot image, performs an enlargement process, and changes the zoom magnification by performing an image reduction process. The image processing unit 4 includes a storage circuit for storing set value data necessary for each correction and image processing.
The system control unit 6 controls each unit of the imaging apparatus. For example, the system control unit 6 controls the focus mechanism, zoom mechanism, and iris mechanism in the optical lens and the optical LPF 1 to perform focus adjustment and exposure operation, and controls the image processing unit 4 to perform electronic zoom, development processing, and recording processing. And so on. The still image acquisition key 7 sends a still image acquisition instruction signal to the system control unit 6. That is, the key constitutes a part of the operation unit, and is an operation means for issuing a still image acquisition instruction to the imaging apparatus. The photographer can instruct the system control unit 6 to acquire a still image by pressing the still image acquisition key 7 at the moment when the user wants to acquire the still image.
The video signal subjected to various image processing by the image processing unit 4 is sent from the signal output unit 5 to an image display unit such as a monitor (not shown). That is, the signal output unit 5 outputs the video signal after the image processing from the image processing unit 4 to a predetermined external monitor, or outputs it to an image display unit attached to the imaging apparatus to display an image on the display screen.
The recording unit 8 records the image data from the image processing unit 4 on a recording medium (not shown) in accordance with a command from the system control unit 6. The recording unit 8 outputs image data read from the recording medium to the image processing unit 4 in accordance with a command from the system control unit 6.

Next, the operation of the imaging apparatus will be described using the flowchart of FIG. The following processing is realized according to a program that is interpreted and executed by the central processing unit that constitutes the system control unit 6.
First, when the photographer operates the still image acquisition key 7 in S1, the system control unit 6 receives a still image acquisition instruction command and instructs the image processing unit 4 to start acquisition of a still image. In S2, the system control unit 6 determines whether or not the current mode is a moving image priority mode, that is, a mode in which the imaging apparatus prioritizes the acquisition of moving images. If the current mode is the moving image priority mode, the process proceeds to S3. If the current mode is a mode that prioritizes the acquisition of still images, the process proceeds to S8.
In S3, the system control unit 6 determines whether or not the optical zoom is operating based on the lens information of the optical lens and the optical LPF1. If the optical zoom operation is being performed, the process proceeds to S4. If the optical zoom operation is not being performed, the process proceeds to S7. In S4, the system control unit 6 temporarily stops the optical zoom operation and switches to the electronic zoom. When switching to the electronic zoom, the field angle of the subject image received by the image sensor 2 does not change, and thus radial blurring does not occur. Switching of the electronic zoom is performed by the image processing unit 4 under the control of the system control unit 6. In the next step S5, a still image data acquisition process is performed, and the recording unit 8 records the image data on a recording medium (not shown). Thereafter, the process proceeds to S6. Here, switching to the optical zoom that has been temporarily stopped is performed smoothly, and the operation of the zoom mechanism is resumed.
On the other hand, when the process proceeds from S3 to S7, a still image data acquisition process is executed, the recording unit 8 records the image data on a recording medium (not shown), and the series of processes ends. When the process proceeds from S2 to S8, the system control unit 6 determines whether or not the optical zoom is in operation. If the optical zoom operation is being performed, the process proceeds to S9. If the optical zoom operation is not being performed, the process proceeds to S7 and still image recording is executed. In S9, the system control unit 6 temporarily stops the optical zoom operation, and then acquires still image data and records it on a recording medium (not shown) (S10). Thereafter, the optical zoom operation is resumed (S11).

Next, the switching process between the optical zoom and the electronic zoom will be described in detail with reference to FIG.
FIG. 3A illustrates a case in which switching to the electronic zoom is temporarily performed while the zoom-in operation is being performed from the wide side to the tele side in the optical zoom. The horizontal axis is a time axis, and the time when the zoom operation starts is t0, and the time when the photographer operates the still image acquisition key 7 is t1. The vertical axis represents the zoom magnification. A graph line indicated by a solid line in the drawing represents a temporal change in the optical zoom magnification, and a graph line indicated by a dotted line represents a temporal change in the electronic zoom magnification. The time change rate of the optical zoom magnification corresponds to the operation speed of the optical zoom.
After the optical zoom magnification increases from time t0, the optical zoom operation stops at time t1, and the optical zoom magnification shows a constant value during the period up to time t2. The electronic zoom is switched to at time t1, and during the period from t1 to t2, the electronic zoom magnification is increased and still image recording is performed during this period. The electronic zoom magnification that has been increased until then starts decreasing at time t2, and switching from electronic zoom to optical zoom is performed during a period from time t2 to time t3. During this transition period, the system control unit 6 sends a control signal to the image processing unit 4 to decrease the electronic zoom magnification over time, and the optical zoom magnification changes with time so as to cancel out the decrease in electronic zoom. Increase the rate. That is, the time change rate of the magnification obtained by combining the optical zoom magnification and the electronic zoom magnification from time t2 to time t3 is equal to the time change rate of the optical zoom from time t0 to time t1. This is to prevent the photographer from feeling unnaturalness due to switching from electronic zoom to optical zoom.
When the electronic zoom magnification returns to the magnification at time t1 at time t3, the operation speed of the optical zoom returns to the original, and the time change rate of the optical zoom magnification becomes the same value as the time change rate in the period from time t0 to t1. Become. By such switching control, zooming can be performed with as little unnaturalness as possible to the photographer.

  FIG. 3B illustrates a case where the electronic zoom is temporarily switched while the zoom-out operation is being performed from the tele side to the wide side in the optical zoom. In this example, when the optical zoom magnification decreases from time t0, and when the optical zoom magnification becomes a constant value and switches to electronic zoom at time t1, the electronic zoom magnification decreases compared to the magnification during the period from time t0 to time t1. Go. From time t2, the electronic zoom magnification starts to increase, and the optical zoom magnification decreases with time so that the increase in electronic zoom is offset. When the electronic zoom magnification returns to the magnification at time t1 at time t3, the time change rate of the optical zoom magnification becomes the same value as the time change rate during the period from time t0 to time t1. The difference from the zoom-in shown in FIG. 3A is that the zoom-out changes in a direction in which the electronic zoom magnification decreases, so that the pixel area wider than the pixel area used by the image sensor 2 for normal shooting. Is to use. That is, in the case of image reduction, it is necessary to mount an image sensor having an effective pixel area larger than the pixel area that is actually output so as not to reduce the resolution.

  According to the first embodiment, the operation signal of the still image acquisition key 7 is used as a trigger to switch from optical zoom to electronic zoom when acquiring a still image, and the acquired image data is recorded. As a result, the photographer can take a still image with no radial blur and with minimal deterioration in image quality, without being aware that the zoom operation is being performed by the optical lens.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. The configuration of the imaging apparatus according to the second embodiment is the same as that in the first embodiment. In the following, differences from the first embodiment will be described, and the same components will not be described in detail by using the reference numerals already used.
The still image acquisition process will be described with reference to the flowchart of FIG. In this process, radial blurring is reduced by setting the electronic shutter at a high speed when acquiring a still image. The difference from FIG. 2 is the processing of S20 following S3 and S21 following S5.
When it is determined in S3 that the optical zoom operation is being performed, in S20, the system control unit 6 controls the image pickup device 2 to set the electronic shutter speed to a value larger than the value at the time of normal moving image shooting and sets the exposure amount. adjust. That is, in the second embodiment, instead of the electronic zoom, the exposure time of the image sensor 2 is reduced by temporarily increasing the speed of the electronic shutter, and still image acquisition and recording are performed in a state where radial blur is reduced. (S5). Since the exposure time is reduced, the system control unit 6 increases the gain at the time of image processing, that is, the gain value of the AFE 3 or the image processing unit 4. Thereby, the brightness equivalent to that before the change of the electronic shutter speed is obtained. In S21, the system control unit 6 adjusts the exposure amount by returning the electronic shutter speed value and the gain value of the AFE 3 or the image processing unit 4 to their original values.

  In the second embodiment, when the still image is acquired, the speed value of the electronic shutter is increased to shorten the exposure time, and the gain of the AFE 3 or the image processing unit 4 is changed accordingly, thereby recording the acquired image data. Processing is performed. As a result, even if the device does not have an electronic zoom function, the photographer can shoot still images with no radial blur and with minimal degradation of image quality, without being aware that the optical lens is being zoomed. . In the second embodiment, the method of changing the exposure time by electronic shutter speed control and compensating the exposure amount by changing the gain of the AFE 3 or the image processing unit 4 is exemplified. However, the exposure time and the exposure amount control method are imaged. Various methods can be adopted according to the specifications of the apparatus.

1 Optical lens and optical LPF
2 Image sensor 3 AFE
4 Image processing unit 5 Signal output unit 6 System control unit 7 Still image acquisition key 8 Recording unit

Claims (5)

An image pickup apparatus having a function of an optical zoom performed by driving an optical lens having a zoom mechanism and an electronic zoom function performed by an enlargement and reduction process of image data obtained by an image sensor,
Operation means for instructing acquisition of a still image;
Image processing means for enlarging a part of the image data from the image sensor or reducing the image data;
Recording means for recording image data processed by the image processing means;
When receiving an instruction to acquire a still image from the operation means during the operation of the optical zoom, the operation of the optical zoom is stopped and the electronic zoom is temporarily switched to the image data of the still image. Control means for recording ,
The control means changes the electronic zoom magnification as time elapses in a transition period from recording the still image data to the recording means to restarting the optical zoom operation to return to the original operation speed. The image pickup apparatus is controlled to return to the original magnification before stopping the operation of the optical zoom . When the control means receives a still image acquisition instruction from the operation means in the middle of changing the optical zoom magnification, the control means temporarily stops the optical zoom operation to set the optical zoom magnification to a constant value, and the electronic zoom magnification. The imaging apparatus according to claim 1 , wherein the image data of the still image acquired while increasing or decreasing the image is recorded in the recording unit. The control means, so that the time rate of change of magnification by combining the electronic zoom magnification with the optical zoom magnification in the transition period, equal to the time rate of change of the front of the optical zoom magnification to stop the operation of the optical zoom The imaging apparatus according to claim 1, wherein the optical zoom magnification and the electronic zoom magnification are changed. And have a function of an electronic shutter by driving control of the imaging element,
When the electronic zoom is not used, the control means temporarily increases the speed value of the electronic shutter when receiving a still image acquisition instruction from the operation means during the optical zoom operation, and the image the image pickup apparatus according to image data of a still image obtained by increasing the gain value of the processing means to claim 1, characterized in that Ru is recorded in the recording means. A control method executed by an imaging device having a function of optical zoom performed by driving an optical lens having a zoom mechanism and electronic zoom performed by enlargement and reduction processing of image data obtained by an image sensor,
Receiving an instruction to acquire a still image during the operation of the optical zoom;
When receiving an instruction to acquire a still image in the step, the control unit stops the operation of the optical zoom and temporarily switches to the electronic zoom;
Performing an enlargement or reduction process on the image data obtained from the image sensor and recording it in a recording means ;
In the transition period from when the control means records the still image data to the recording means to when the operation of the optical zoom is resumed to return to the original operation speed, the electronic zoom magnification is changed as time elapses. And a step of controlling to return to the original magnification before stopping the operation of the optical zoom .

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