JP4933347B2 - IMAGING DEVICE, ITS CONTROL METHOD, PROGRAM, AND STORAGE MEDIUM - Google Patents

Description

  The present invention relates to an image pickup apparatus such as a digital camera using an image pickup element capable of reading an image at high speed such as a CMOS sensor.

  Conventionally, in an automatic focusing apparatus called a TV-AF method, a focus component is detected based on a captured image signal so that the contrast is maximized. At this time, by displaying the captured image signal on the screen, it is possible to perform an automatic focusing operation (autofocus operation) while confirming the subject on the screen. It is also possible to record a moving image by recording a captured image.

  Since the frame rate at the time of the above display or moving image recording is usually determined to be a certain rate such as 30 frames per second, for example, the rate of detection of the focusing signal is also determined by this rate.

  In order to detect the in-focus position with higher accuracy, the method for further increasing the detection rate of the in-focus signal is to read out the image at a rate faster than the display rate, and to output the in-focus signal using the fast rate signal. There is a method of using an image thinned out for display for creation and display.

For example, in the method described in Patent Document 1, reading of an image is performed four times in total, ie, once for display image acquisition and three times for automatic focusing image acquisition during a display period of one frame. This provides an imaging apparatus capable of performing display at a constant cycle while increasing data acquisition for automatic focusing.
JP 2002-247443 A

  However, in the above-described conventional example, when the focusing operation is performed while displaying an image or recording a moving image, the focus change is directly displayed on the screen or recorded as a moving image. For this reason, for example, a wobbling focus that repeats focusing or blurring in the vicinity of the in-focus position occurs, and the quality of the display image or the recorded image is lowered.

  Accordingly, the present invention has been made in view of the above-described problems, and an object of the present invention is to eliminate the fluctuation of the focus of the display image near the in-focus position when automatically focusing during image display or moving image recording. It is to improve the quality of a display image or a recorded image.

In order to solve the above-described problems and achieve the object, an imaging apparatus according to the present invention displays an image signal and an imaging element that photoelectrically converts a subject image formed by an imaging optical system to generate an image signal. Display means, focus detection means for detecting a focus evaluation signal corresponding to the contrast of a subject based on an image signal generated at a first time interval by the imaging device, and the display means displaying the image signal. Selection for selecting one of the image signals generated by the image sensor at the first time interval for each second time interval that is a period of time and is longer than the first time interval. and means, and a display control means for displaying on the display means a selected image signal in the second time interval by said selecting means, said selecting means, looking for a focus position of the imaging optical system In the state where the image signal generated by the imaging device is sequentially selected at every second time interval, and the in-focus position of the imaging optical system is captured, the imaging Among the image signals generated by the element, an image signal having a larger detected focus evaluation signal is selected .

The image pickup apparatus control method according to the present invention includes an image pickup device that generates an image signal by photoelectrically converting a subject image formed by an image pickup optical system, a display unit that displays the image signal, and the image pickup device. And a focus detection unit that detects a focus evaluation signal corresponding to the contrast of the subject based on the image signal generated at the first time interval, and the display unit controls the image signal. For each second time interval that is longer than the first time interval and is selected from the image signals generated by the imaging device at the first time interval. comprises a selection step, and a display control step of displaying on the display means a selected image signal in the second time interval at said selection step of, in said selecting step, said imaging In the state where the in-focus position of the academic system is being searched, the image signal generated by the image sensor is sequentially selected every second time interval, and the in-focus position of the imaging optical system is captured. In the case of the state, the image signal having a larger detected focus evaluation signal is selected from among the image signals generated by the image sensor .

  According to the present invention, it is possible to improve the quality of a display image or a recorded image by eliminating the fluctuation of the focus of the display image near the in-focus position when automatically focusing during image display or moving image recording. .

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing a schematic configuration of a digital camera which is a first embodiment of an imaging apparatus of the present invention.

  The digital camera according to the present embodiment includes an imaging optical system 1 in which a focus lens (focus adjustment lens) 2 is disposed, and generates an image signal by photoelectrically converting a subject image formed by the imaging lens 3 using an imaging element 3. To do. Then, the signal processing circuit 8 converts the digitized signal through the pre-processing circuit 4 and the A / D converter 5 having a CDS circuit and an amplifier circuit for removing output noise into an image signal.

  The autofocus operation (focus detection operation, automatic focus adjustment operation) is controlled by the control unit 12. First, the focus lens 2 is driven to move along the optical axis of the imaging optical system 1 via the focus lens drive circuit 13. Then, the AF evaluation value calculation circuit 14 calculates an AF evaluation value corresponding to the contrast of the subject in the distance measuring frame from the image signal captured during the movement of the focus lens 2 (detects the in-focus state), and performs AF evaluation. The focus lens 2 is driven to the peak position of the value. More details will be described later.

  Further, when the switch SW11 linked to the release button is pressed, an image is recorded on the recording medium 9.

  Also, an image stored in the display image memory 7 is displayed on the EVF (electronic viewfinder) 10 via the memory controller 6. At this time, AF evaluation values of images picked up by a method described later are sequentially compared, and an image closer to the in-focus state is selected by the image selection unit 15 and stored in the display image memory 7. This makes it possible to display a focused image.

  Next, an operation of selecting and displaying an image close to the focused state during the focusing operation will be described using the flow of FIG.

  First, in step S1, movement driving of the focus lens 2 along the optical axis of the imaging optical system 1 is started. It is assumed that the focus lens 2 is driven by a normal hill-climbing method as described in steps S2 to S4 below. An image of the operation is shown in FIG.

  First, in step S2, an AF evaluation value (a value indicating the contrast height of the image) is acquired from the image signal output from the image sensor 3. In step S3, it is determined whether to reverse the moving direction of the focus lens 2 based on the AF evaluation value. For example, it is reversed when the peak of the AF evaluation value is detected as in B and C of FIG. 3, or is reversed when the evaluation value continues to decrease. When reversing the moving direction of the focus lens 2, the driving direction of the focus lens 2 is reversed in step S4, and the process returns to step S2. If not reversed, the process returns to step S2.

  On the other hand, in step S5, the previously stored AF evaluation value is compared with the current AF evaluation value. If the current time is larger, it is determined that the in-focus state is closer, and in step S6, the image stored in the display image memory 7 is replaced with the current image. At this time, the larger AF evaluation value is stored and used for comparison with the next AF evaluation value. If the current value is smaller, the stored image is not replaced and the process proceeds to step S7.

  In step S7, it is determined whether or not the number of AF evaluation values acquired is a predetermined value. If the predetermined value is reached, the image displayed on the EVF is updated with the stored image in step S8. Also, the number of AF evaluation values acquired is cleared. As a result, it is possible to update the display image using the images stored so far in a certain cycle.

  In the above description, the display of the image is described. However, the same applies to the moving image recording of the image, and the stored image may be recorded at a predetermined cycle.

  Next, FIG. 4 shows an example of the relationship between the display update period and the acquired AF evaluation value in the above operation.

  FIG. 4 shows that images are acquired for AF evaluation five times within one display update period (second time interval, for example, 1/30 second when an image of 30 frames per second is displayed on the EVF). The image acquisition is performed at the time interval of FIG. Then, an image corresponding to the AF evaluation value indicated by the arrow is displayed (display controlled) on the screen of the EVF 10. Note that, by combining the display update period and the focus reciprocation period as shown in FIG. 4, it is possible to always display an image in focus.

  In addition, since the images are sequentially selected and stored, the stored memory can be minimized.

  According to the first embodiment described above, it is possible to provide an imaging device capable of displaying a high-quality image or recording a moving image with a minimum memory and which does not fluctuate.

(Second Embodiment)
Next, a second embodiment will be described. In the present embodiment, a configuration is described in which an image to be displayed can be selected and displayed in an out-of-focus state and an in-focus state by changing the selection method of an image to be displayed based on the operation state of the autofocus operation To do.

  The external configuration of the digital camera is the same as that of FIG. 1 showing the first embodiment, and only the operation is different.

  First, the autofocus operation will be described.

  The autofocus operation has two modes, a wobbling mode and a hill-climbing mode.

  The wobbling mode is a focusing operation mode that is selected when close to the in-focus state, and the in-focus state is achieved even when the subject is moving slightly by reciprocating the focus lens 2 in a minute section centered on the peak position. Can be maintained.

  The hill-climbing mode is a focusing operation mode that is selected when no AF evaluation value peak is found. The focus lens is driven at a higher speed than the wobbling operation, and the focus lens is moved in one direction until the AF evaluation value peak is found. To drive. If it is not found in one direction, it is possible to detect the in-focus position from all the focus areas at high speed by driving in the reverse direction. By switching between the two modes, a fast and stable focus operation is performed.

  The above operation corresponds to steps S11 to S14 in the flowchart of FIG.

  In step S11, a wobbling operation is performed. In step S12, it is determined whether or not there is a peak of the AF evaluation value, that is, whether or not it is in focus. If it is in focus, the process returns to step S11 and continues. Perform wobbling action. If not in focus, a hill climbing operation is performed in step S13. In step S14, it is determined whether or not the peak of the AF evaluation value has been found. If not found, the process returns to step S13 to continue the hill climbing operation. If the peak is found and it is determined that the mountain climbing is finished, the process returns to step S11 to start the wobbling operation.

  Next, an operation for changing a method for selecting an image to be displayed according to an operation state of the autofocus operation will be described.

  Steps S15 to S18 in FIG. 5 illustrate selection of a display image during the wobbling operation. Similar to the first embodiment, the selection of an image close to the in-focus state will be omitted, and a description thereof will be omitted.

  Step S19 shows selection of a display image during hill-climbing operation. During the climbing operation, an in-focus image cannot be obtained, so an image closer to the display timing is selected. That is, the latest image is selected and stored in the display image memory 7 in order to reduce the delay in time until display.

  As described above, during the wobbling operation in which the in-focus state is captured, an image in the in-focus state can be selected and displayed. In addition, the latest image with a small time delay is selected during the hill-climbing operation for searching for the in-focus state. As a result, a more appropriate display image can be obtained according to the operation state of the autofocus operation.

(Other embodiments)
The object of each embodiment is also achieved by the following method. That is, a storage medium (or recording medium) in which a program code of software that realizes the functions of the above-described embodiments is recorded is supplied to the system or apparatus. Then, the computer (or CPU or MPU) of the system or apparatus reads and executes the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but the present invention includes the following cases. That is, based on the instruction of the program code, an operating system (OS) running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  Furthermore, the following cases are also included in the present invention. That is, the program code read from the storage medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer. Thereafter, based on the instruction of the program code, the CPU or the like provided in the function expansion card or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  When the present invention is applied to the above storage medium, the storage medium stores program codes corresponding to the procedure described above.

1 is a block diagram illustrating a configuration of a digital camera according to a first embodiment of the present invention. It is a flowchart which shows the image selection operation | movement at the time of the focusing operation | movement in 1st Embodiment. It is a figure explaining the focusing operation | movement in 1st Embodiment. It is a figure explaining the display update period and AF evaluation value obtained in 1st Embodiment. It is a flowchart which shows the image selection operation | movement at the time of the focusing operation | movement in 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image pick-up optical system 2 Focus lens 3 Image pick-up element 4 Pre-processing circuit 5 A / D converter 6 Memory controller 7 Image memory for display 8 Signal processing circuit 9 Recording medium 10 EVF
DESCRIPTION OF SYMBOLS 11 Switch 12 Control part 13 Focus lens drive circuit 14 AF evaluation value calculation circuit 15 Image selection part

Claims (9)

An image sensor that photoelectrically converts a subject image formed by an imaging optical system to generate an image signal;
Display means for displaying image signals;
Focus detection means for detecting a focus evaluation signal corresponding to the contrast of the subject based on an image signal generated at a first time interval by the imaging device;
Generated at the first time interval by the imaging device at each second time interval that is a cycle in which the display means displays the image signal and is a time interval longer than the first time interval. A selection means for selecting one of the image signals;
Display control means for causing the display means to display the image signal selected by the selection means at the second time interval ,
The selection means sequentially selects the image signal generated by the imaging element at every second time interval in a state where the in-focus position of the imaging optical system is being searched. An image pickup apparatus characterized by selecting an image signal having a larger focus evaluation signal detected from among image signals generated by the image pickup element in a state where the in-focus position is captured . Said selecting means, when in a state of looking for a focus position of the imaging optical system, you select the latest image signal of said first image signal generated at time intervals by the image pickup device The imaging apparatus according to claim 1 . If the state entrapping focus position of the imaging optical system, to claim 1 or 2, characterized in that reciprocates the imaging optical system along the optical axis around the focus position The imaging device described. The imaging apparatus according to claim 3, wherein the imaging optical system performs a reciprocating operation at a period in which a focus position can be detected based on an image signal acquired within the second time interval. 5. The imaging apparatus according to claim 3 , wherein a period of a reciprocating operation of the imaging optical system is matched with the second time interval.   The imaging apparatus according to claim 1, further comprising a recording unit that records the image signal selected by the selection unit at the second time interval. An image sensor that photoelectrically converts a subject image formed by the imaging optical system to generate an image signal, a display unit that displays the image signal, and an image signal that is generated at a first time interval by the image sensor A method of controlling an imaging apparatus comprising: a focus detection unit that detects a focus evaluation signal corresponding to a contrast of an object based on
Generated at the first time interval by the imaging device at each second time interval that is a cycle in which the display means displays the image signal and is a time interval longer than the first time interval. A selection step of selecting one from the image signals;
A display control step of causing the display means to display the image signal selected in the selection step at the second time interval ,
In the selection step, in a state where the in-focus position of the imaging optical system is being searched, the image signal generated by the imaging element is sequentially selected every second time interval, and the imaging optical system In a state where the in-focus position is captured, an image signal with a larger detected focus evaluation signal is selected from among the image signals generated by the image sensor, and the control method of the imaging apparatus .   A program for causing a computer to execute the control method according to claim 7.   A computer-readable storage medium storing the program according to claim 8.

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