JP3294319B2 - Still image pickup device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a still image pickup apparatus having an automatic focusing (hereinafter abbreviated as AF) function.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of an electronic still camera with an automatic focusing function having a function of detecting a blur amount of an image from an output of a solid-state imaging device for imaging a subject and automatically focusing. 4, reference numeral 1 denotes a lens unit, 2 denotes a lens drive motor, 3 denotes an aperture, and 4 denotes an aperture drive circuit. Reference numeral 5 denotes a solid-state imaging device that converts a subject image into an electric signal, and reference numeral 6 denotes a solid-state imaging device driving circuit for driving the solid-state imaging device 5. Reference numeral 7 denotes an A / D output of the solid-state imaging device 5.
An A / D conversion circuit for conversion. 8 is an A / D conversion circuit 7
Is a memory for storing the output of Reference numeral 9 denotes an ES filter that calculates an ES value (described later) that represents a blur amount.
Reference numeral 10 denotes a system control circuit for controlling the entire system, including a CPU, a ROM storing a procedure for executing an operation sequence as shown in FIG. 6 by the CPU, and a RAM having a work area and the like. Reference numeral 11 denotes an imaging signal processing circuit that performs processing such as γ conversion and band limitation on the output of the memory 8. 12 is an imaging signal processing circuit 11
Is a D / A conversion circuit that performs D / A conversion on the output of the D / A converter. Reference numeral 13 denotes an FM modulation circuit that performs FM modulation on the output of the D / A conversion circuit 12. Reference numeral 14 denotes a REC amplifier that current-amplifies the output of the FM modulation circuit 13. 15 is a magnetic head, 16 is a magnetic sheet as a recording medium, 17 is a motor for rotating the magnetic sheet 16, and 18 is a motor servo circuit for stabilizing the rotation of the motor 17. 19 is a photometric element for measuring the brightness of the subject. Reference numeral 20 denotes a release switch, and a series of photographing operations is started when the release switch is turned on.

FIG. 5 shows an interline transfer type solid-state imaging device often used as a solid-state imaging device. In FIG. 5, reference numeral 501 denotes an interline transfer type solid-state imaging device. Reference numeral 502 denotes a photodiode which converts light into electric charges and accumulates them, and reference numeral 503 denotes a vertical CCD which transfers electric charges generated by the photodiodes in a vertical direction. V1 to V4 are
This is a transfer electrode of the vertical CCD 503, and V1 also serves as a transfer gate for transferring charges of odd rows of the photodiode. Similarly, V3 also serves as a transfer gate for transferring charges of the even-numbered rows of the photodiode. Vertical CCD 503
Are driven by four-phase transfer pulses. 504 is a vertical C
This is a horizontal CCD that transfers charges transferred from the CD 503 in the horizontal direction. H1 and H2 are horizontal CCD5
A transfer electrode 04 is driven by a two-phase transfer pulse. An output amplifier 505 converts charges from the horizontal CCD 504 into a voltage and outputs the voltage. Reference numeral 506 denotes a top drain for sweeping away unnecessary charges by reverse transfer. Reference numeral 507 denotes a bottom drain for sweeping away unnecessary charges by forward transfer.

FIG. 6 is a diagram showing an operation sequence of an electronic still camera with an automatic focusing function. When the release switch 20 is turned on at time TO, a series of photographing sequences is started. Optimal aperture value Av based on the output of photometric element 19
And an optimal shutter speed Tv. The aperture is set to open between T1 and T2, and between T2 and T3, the lens unit 1 is moved to the focus position from infinity to the nearest by n steps or the lens driving motor 2
And a series of operations such as sweeping out unnecessary charges, exposing, and reading out signal charges, that is, an AF operation, and calculating the amount of blurring from the output of the solid-state imaging device 5 in n times of reading out signal charges. A position with a small amount, that is, an optimum focus position is calculated. Between T3 and T4, the aperture value is set to Av, and at the same time the lens unit 1 is set to the focusing lens position. T4
Then, a clear operation of sweeping unnecessary charges to the top drain 506 by reverse transfer is performed, and thereafter, main exposure is performed. Next, the signal charges are read from T5, and the processing signals are recorded on the magnetic sheet 16.

FIG. 7 shows one of the methods for detecting the amount of blur.
FIG. 2 is a diagram for explaining one ES method. The ES method is disclosed in U.S. Pat. No. 4,804,831 and will be described only briefly. In the same figure, (a) is a video signal, and the edge stands when in focus, and the edge falls when out of focus. (B)
Is the absolute value D of the differential waveform of the video signal. (C),
(D) shows delay signals DL1 and DL2 of the differential waveform D, respectively.
(E) is the integral waveform I (I = D + DL1 + DL
2), which indicates the contrast at the edge of the video signal. By dividing D by I as shown in (f), the ES value indicating the sharpness of the edge is represented.

FIG. 8 shows an example of the configuration of the ES filter 9 which performs the processing shown in FIG. 8, reference numeral 801 denotes a differentiating circuit, 802 denotes an absolute value circuit, 803 denotes a delay circuit, 804 denotes an integrating circuit, and 805 denotes a division circuit. Reference numeral 806 denotes a peak hold circuit which determines the value of the image information having the highest ES value as the ES location of the subject and outputs the determined value.

FIG. 9 is a diagram showing changes in the lens position and the ES value when performing the AF operation for obtaining the in-focus position.
The lens feed is continuously sent from the minimum position to the maximum position,
In the meantime, image information is accumulated in the solid-state imaging device 5 every one vertical scanning period (abbreviated as 1 V), the signal is read out, the ES value is obtained from the image, and the position where the ES value is the largest is set as the focus position. A curve having a peak at the in-focus position drawn when the lens feed amount is plotted on the horizontal axis and the focus signal (in this case, the ES value) is plotted on the vertical axis is called a hill-climbing curve. The accuracy of focus detection is good.

[0008]

However, in the conventional AF operation, the lens needs to be moved n steps or continuously to a focus position from infinity to a close range and the AF operation needs to be performed n times. There is a problem that it takes 60 seconds.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a still image pickup apparatus which solves the above problems.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a first focus detection means for determining a focus direction based on an image signal from an image pickup device for picking up a subject image via a lens. And specifying a range for detecting a signal indicating the degree of focus based on an image signal from the image sensor in the focus direction determined by the first focus detection means, and moving the lens within the specified range. A signal indicating the degree of focus is detected based on the image signal from the image sensor at a plurality of predetermined positions by moving, and a signal having the highest degree of focus among the detected signals indicating the degree of focus is obtained. Moving the lens to a given position
And a still image pickup device having the in-focus detection means.

[0011]

[0012]

FIG. 1 is a block diagram of an electronic still camera with an automatic focusing function according to the present invention. In FIG. 1, the same components as those in FIG. 4 are denoted by the same reference numerals, and description thereof is omitted. Reference numeral 101 denotes a high-pass filter for detecting a high-frequency component of an image. The cutoff frequency of this filter 101 is set low so that the lens moving direction can be calculated even when the image is out of focus, especially when the image is largely blurred, and the hill-climbing curve is gentle. The output of this filter is C
U value.

FIG. 2 shows an operation sequence of the electronic still camera according to the present invention. FIG. 3 is a diagram showing changes in the lens position, the CU value, and the ES value when the focus lens position is obtained in the present invention.

The focusing operation of the present invention will be described with reference to FIGS. 1, 2 and 3. Release switch 20 at time T0
Is input, a series of photographing sequences is started. The optimum aperture value Av and the optimum shutter speed Tv are calculated from the output of the photometric element 19. The aperture is set to open between T1 and T2, and at T2, the lens unit 1 is moved by the lens drive motor 2 to near the center (M-1) of the lens position at infinity and the closest lens position, and the CU value (CU [M-
1]) is calculated. After that, the lens is moved one step, and the time T
In step 3, the CU value (CU [M]) when the lens position is M is calculated. Similarly, the CU when the lens position is M + 1 at time T4
The value (CU [M + 1]) is calculated. The calculated three points C
The moving direction of the lens unit 1 is determined from the U value. For example, when CU [M-1] ≦ CU [M] <CU [M + 1], as shown in FIG. 3, the lens unit 1 is moved from time T4 to T5 to M, and at time T5 from M to infinity. A series of operations such as sweeping out unnecessary charges, exposing, and reading out signal charges, ie, AF, while moving the lens unit 1 in steps of k steps or continuously to a distant lens position
Performs the operation to read the signal charge
By calculating the amount of blur from the output of (1), the position with the least amount of blur, that is, the focusing lens position (P) is calculated.
Since the movement amount of the lens during the AF operation is １ ／ compared to the related art, the time required for focusing is also reduced to １ ／. The lens unit 1 is set while the aperture value is set to Av between T6 and T7.
Is set to the focusing lens position (P). From T7, a clear operation of sweeping out unnecessary charges to the top drain 506 by reverse phase is performed, and thereafter, main exposure is performed. Next, signal charges are read out from T8, and processing signals are recorded on the magnetic sheet 16.

Similarly, CU [M-1]> CU [M] ≧ C
In the case of U [M + 1], as shown in FIG.
The lens unit 1 is moved to M during this time, and then the lens unit 1 is moved to the closest lens position until T6.) In the case of CU [M-1] <CU [M] ≦ CU [M + 1], FIG. (The lens unit 1 is moved to M + m between T4 and T5, and then the lens unit 1 is moved to M-m from T6) to calculate the focusing lens position (P) and perform photographing.

In this embodiment, when the lens unit 1 is moved to the focusing lens position (P) at the time of photographing, the lens unit 1 is moved directly from the AF operation end point.
It is also possible to temporarily move to the AF operation start point and move to the point P from the same direction as in the AF operation. The filter for detecting the blur amount is not limited to the ES filter, and may be, for example, a high-pass filter or a band-pass filter. Further, the filter for determining the lens moving direction may be a band-pass filter. Furthermore, in this embodiment, the focus detection means is constituted only by a digital filter, but it goes without saying that the focus detection means may be carried out in an analog manner.

[0017]

As described above, according to the present invention, quick and accurate focusing information can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electronic still camera with an automatic focusing function according to the present invention.

FIG. 2 is a diagram showing an operation sequence of the electronic still camera of the present invention.

FIG. 3 illustrates a lens position and C when a focus position is obtained in the present invention.
It is a figure showing change of U value and ES value.

FIG. 4 is a block diagram of a conventional electronic still camera with an automatic focusing function.

FIG. 5 is a configuration diagram of an interline transfer type solid-state imaging device.

FIG. 6 is a diagram showing an operation sequence of a conventional electronic still camera with an automatic focusing function.

FIG. 7 is a diagram illustrating an ES method.

FIG. 8 is a configuration diagram of an ES filter.

FIG. 9 is a diagram illustrating changes in a lens position and an ES value when performing an AF operation.

FIG. 10 is a diagram showing another example of a change in a lens position, a CU value, and an ES value when a focus position is obtained in the present invention.

FIG. 11 is a diagram showing another example of a change in a lens position, a CU value, and an ES value when a focus position is obtained in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lens 2 Lens drive motor 10 System control circuit 101 High pass filter

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/225-5/247

Claims (1)

(57) [Claims] A first focus detection unit that determines a focus direction based on an image signal from an image sensor that captures a subject image via a lens; and a first focus detection unit that determines a focus direction. Specify a range for detecting a signal indicating the degree of focus based on an image signal from the image sensor in the focusing direction, and move the lens in the specified range to set the image sensor at a plurality of predetermined positions. A second focus that detects a signal indicating the degree of focus based on the image signal from the camera, and moves the lens to a position where the signal with the highest focus is obtained from the signals indicating the detected focus. A still image pickup device comprising: a detection unit.