JPH04172078A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To adjust a photographing optical system to a focusing state in a short time by reading out the picture sample data of each lens position written in a memory, and retrieving the position of a focusing lens to become the focusing state then driving. CONSTITUTION:A memory means 18 storing the sample data of a picture signal by a photoelectric converting means for an image pickup at each step position of the moving area of the focusing lens, and arithmetic means 42-52 obtaining a prescribed arithmetic value corresponding to the level of a high frequency component in each screen from the picture sample data to be stored are equipped. And the step position of the focusing lens where the arithmetic value becomes maximum is found, and the focusing lens is driven at the step position. Therefore, since it is sufficient the movement of a mechanical movable part is simple and one direction, a time necessary for a focal point detection can be shortened. Thus, it is possible to shorten the time until adjusting at the focal point.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an automatic focus adjustment device in an imaging device, that is, an electronic camera, equipped with a photoelectric conversion means for imaging.

[Prior Art] In the conventional example of the electronic camera mentioned above, for example, an electronic still camera that records an image signal from an image sensor on a magnetic disk called a still video floppy, the high frequency component of the output signal of the image sensor is the largest. Automatic focus adjustment is performed by controlling the position of the focusing lens.

For example, there are three types of bandpass filters (B P F): wide band, medium band, and narrow band, and these BP
A selection switch that selects the output of F, an A/D converter that digitizes the output of the switch, and the output data of the A/D converter on one screen (or a predetermined focus detection area)
We prepared an integration circuit that integrated within the
, compare the integrated value of the broadband BPF output within one screen (or focus detection area) before and after moving the focusing lens by a minute distance, and move the focusing lens in the direction that increases the BPF output. . And B
When the PF output exceeds a predetermined value, the selection switch
By replacing the BPF in use with one with a narrower band, the focusing lens can be controlled to be in focus even when the imaging state of the photographic optical system is significantly deviated from the subject.

[Problems to be Solved by the Invention] In such a conventional example, processing is performed to detect high frequency components from the output signal of the image sensor by driving the image sensor while moving the focusing lens. The burden on the microcomputer that performs overall control becomes heavy, making it difficult to perform other processing. Therefore, there is a drawback that it takes time to perform the main exposure (and record on the recording medium) while adjusting the focus. That is, in electronic still cameras, there is a long time lag between the operation of the record release button and the execution of recording, resulting in a poor operational feel during use.

Therefore, it is an object of the present invention to provide an automatic focus adjustment device that can adjust the photographing optical system to a focused state in such a short time.

[Means for Solving the Problems] An automatic focus adjustment device according to the present invention is an automatic focus adjustment device for an imaging device equipped with a photoelectric conversion means for imaging, and the automatic focus adjustment device is an automatic focus adjustment device for an imaging device equipped with a photoelectric conversion means for imaging, and in which A memory means for storing sample data of the image signal produced by the imaging archetype conversion means, and a predetermined calculated value corresponding to the level of the high frequency component on each screen is determined from the image sample data stored in the memory means. The present invention is characterized by comprising a calculation means, and a control means for determining a step position of the focusing lens at which the value calculated by the calculation means is maximum, and driving the focusing lens to the step position.

[Operation] By the above means, necessary image data can be obtained in the process of moving the focusing lens in the position direction, and after that, the predetermined calculated value according to the level of the high frequency component by the above calculation means is the maximum. All you have to do is find the lens position where the value becomes and move the focusing lens to that lens position.

In other words, since the movement of the mechanically movable part is simple and unidirectional, the time required to detect the in-focus point can be shortened, and therefore the time required to adjust to the in-focus point can be shortened.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of the present invention applied to an electronic still camera. Reference numeral 610 is a photographic lens unit having a zoom function, and is internally provided with an aperture and a shutter. 12 is a solid-state image sensor that converts an optical image into an electrical signal; 14 is an image processing circuit that converts the output signal of the image sensor 12 into a video signal; 16 is an A/D converter; 18
20 is a memory control circuit that controls writing and reading of the memory 18; 22 is a D/A converter; 24 is a D/A converter;
A recording processing circuit that converts the analog video signal output from the A converter 22 into a recording signal; 26 is a magnetic head; 28 is a magnetic disk that is a recording medium; 30 is a spindle motor that rotates the magnetic disk 28; 32 is a motor drive circuit that drives the spindle motor 32; 34 is a motor drive circuit that drives the spindle motor 32;
This is a head drive circuit that sends the magnetic head 26 to a designated radial position on the magnetic disk 28, that is, to a designated track.

36 is a lens drive circuit that drives the zooming lens and focusing lens of the photographic lens unit 10, 38 is an aperture drive circuit that drives the aperture of the photographic lens unit 10, and 40 is a shutter of the photographic lens unit 10. This is a shutter drive circuit.

42 is a low-pass filter (LPF), 44 is a band-pass filter (BPF) for extracting high-frequency components, and 46 is a BPF whose band is narrower than that of BPF 44.

48 is a switch that selects the outputs of LPF 42, BPF 44, and BPF 46; 50 is an A/D converter that digitizes the output of switch 48; and 52 is an integration circuit that integrates the output data of A/D converter 50 for one screen. It is.

54 is a microcomputer that performs predetermined calculations and controls the entire system; 56 is an operating device that includes keys, switches, etc. for inputting predetermined instructions to the calculation control circuit 54; and 58 is a display that displays the operating status, etc. It is a display device that

To make it easier to understand, first, we will briefly explain the recording operation of a photographed image after focus adjustment is completed. The optical image produced by the photographic lens unit 10 is converted into an electrical signal by the image sensor 12, and the output signal of the image sensor 12 is sent to the image processing circuit 1.
4 is converted into a video signal. The output of the image processing circuit 14 is digitized by the A/D converter 16 and temporarily stored in the memory 18 via the memory control circuit 20.

The video signal stored in the memory 18 is read out and applied to the D/A converter 22 via the memory control circuit 18.
converted back to an analog video signal.

The recording processing circuit 24 performs recording processing on the output signal of the D/A converter 22 and converts it into a signal for recording. Recording processing circuit 24
The output is recorded on the magnetic disk 28 by the magnetic head 26.

The magnetic disk 28 is rotated at a predetermined speed by a spindle motor 30 driven by a motor drive circuit 32, and the magnetic head 26 is sent to a designated track on the magnetic disk 28 by a head drive circuit 34.

FIG. 2 shows a flowchart of the main routine for focus adjustment in this embodiment. First, the focusing lens is moved in steps from an infinite distance position to a close distance position, and the image output by the image sensor 12 at each position is shown in FIG.
Any of the sample patterns shown in a) to (f) is written into the memory 18 (Sl). Figure 3 (a) shows a sample pattern that is uniform across the screen, (b) shows a center-weighted sample pattern, and (c) shows a diagonal sample pattern.
pattern, (d) is a sample pattern in the vertical and horizontal directions,
(e) shows a sample pattern with emphasis on the periphery, and (f) shows a horizontally upward sample pattern. Weighting can be adjusted depending on the density of sample points.

The image sample data for each lens position written in the memory 18 in this way is read out, and the position of the focusing lens that will be in focus is searched for by the circuits 42 to 52 (details will be described later) (S2). The focusing lens is driven to the determined lens position (S3), and the focus adjustment operation is completed by displaying that the focus has been achieved (S4).

FIG. 4 shows a detailed flowchart of the image capture routine 81 of FIG. First, the focusing lens is moved to the infinite position (S11), the step movement amount counter n is set to 1 (512), and the output of the image sensor 12 exposed for a certain period of time is sent to the image processing circuit 14 and the A/D converter. 16 and the memory control circuit 20, and the image data of any sample point of the sample pattern as shown in FIGS. 3(a) to 3(f) is written into the memory 18 (S 13).

Check whether the counter n is equal to N for the total number of steps N of the focusing lens from infinity to close range (S14), and if not, move the focusing lens one step toward close range. Let me (S
15), the counter n is incremented 816), and the output image of the image sensor 12 is stored in the memory 18 again in a predetermined sample pattern.

When the counter n becomes equal to the total number of steps N, the memory 1
8 finishes importing the image data.

As a result of the above, in the moving range of the focusing lens,
Image data of a predetermined sample pattern will be stored in the memory 18.

FIG. 5 shows a detailed flowchart of the focused point search routine 82 in FIG. I want to set 1 to counter n 5
21) Read the n-th sample data from the memory 18 to the memory control circuit 20. 522) The D/A converter 22 converts it into an analog signal, and the BPF 44 or 46 extracts the high frequency component. The outputs of the BPFs 44 and 46 selected by the switch 48 are digitized by the A/D converter 50 and integrated by the integrating circuit 52. The integration result of the integration circuit 52 is applied to the arithmetic control circuit 54 (S23).

For all step positions of the focusing lens, calculate the integral value of the high frequency component of the sample data of each screen (
822-25). That is, until n becomes equal to N (S
24), n is incremented 525), and sample data is read out from the memory 18 for each n to determine the integral value of the high frequency component (S22, 23).

After obtaining the integral values for all steps (S24), the step position of the focusing lens where the integral value becomes the maximum is searched, and this routine is ended (S26).

BPF46 has a narrower band than BPF44. Therefore, normally, the switch 48 is set so that either the BPF 44 or the BPF 46 is selected, and for example, depending on the BPF 44 or the BPF 46 selected in the process shown in FIG. If the determination cannot be made, the switch 48 may be used to select another BPF 46 or 44.

Instead of FIG. 5, the step position of the in-focus point may be searched by the routine shown in FIG. According to the routine shown in FIG. 6, the search time can be shortened.

In Figure 6, first set the counter n to 5.
31) Read the n-th image sample data from the memory 18 (S 32), convert it into analog data by the D/A converter 22, and send it to the BPF 44 or 46, the switch 48,
The A/D converter 50 and the integrating circuit 52 calculate the integrated value of the high frequency component, and the arithmetic control circuit 54 stores the integrated value (S33).

Until the counter n becomes larger than N-4 for the total number of steps N (S34), n is increased by 4 (S35),
Calculate the integral value of the high frequency component of the screen at each step position (S
32.33).

When n becomes larger than N-4 (S34), the step position of the focusing lens where the integral value obtained in S33 is maximized is determined, and this step position is set as M (S36).
).

Set another counter m to M537) and read the m-th image sample data from the memory 1853
8) Similarly to S33, the integrated value of the high frequency component is taken into the calculation control circuit 54 (S39).

Until m becomes M+4 (S40), m is incremented (S41), and the integral value of the high frequency component of each screen is determined and stored (838, 39).

When m becomes equal to M+4 (S40), the step position of the focusing lens at which the integral value determined in S39 is maximized is determined (S42). The step position determined here corresponds to the focal point.

In the method shown in FIG. 6, first, a lens position where the high-frequency integral value is maximum is roughly searched, and then a precise search is performed around the roughly searched lens position. Therefore, search time can be shortened.

In this embodiment, the focusing lens is moved from an infinite distance to a close distance when image data is loaded into the memory 18, but the opposite may of course be used. In FIG. 6, the coarse search is performed in units of 4 steps, but of course other number of steps may be used.

Although the explanation has been given using an example of an electronic still camera that uses a magnetic disk as a recording medium, it can also be applied to electronic cameras that use a solid-state memory device as a recording medium, and furthermore, it can be applied to video cameras and TVs.
It can also be applied to left camera exposure control. In an apparatus not equipped with a memory having a capacity equivalent to the memory 18, a gate circuit for extracting samples of the pattern shown in FIG. 3 may be provided.

[Effects of the Invention] As can be easily understood from the above description, according to the present invention, the time required to detect a focused point can be shortened, and the time lag for focus adjustment can be shortened.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the configuration of an embodiment of the present invention, and FIG.
is a flowchart of the main focus adjustment routine, FIG. 3 is a diagram showing sample patterns, FIG. 4 is a detailed flowchart of 81 in FIG. 2, FIG. 5 is a detailed flowchart of 82 in FIG. 2, and FIG. The figure is another flowchart of 82 in FIG. 10: Photographic lens unit 12: Solid-state image sensor 1
4: Imaging processing circuit 16: A/D converter 18: Memory 20: Memory control circuit 22: D/A converter 24
: Recording processing circuit 26: Magnetic head 28: Magnetic disk 30 Spindle motor 32: Motor drive circuit 34: Head drive circuit 36: Lens drive circuit 38
: Aperture drive circuit 40: Shutter drive circuit 42 :
LPF44.46: BPF 48: Switch 50:
A/D converter 52: Integrating circuit 54: Arithmetic control circuit
56: Operating device 58: Display device

Claims (1)

[Claims] An automatic focusing device for an imaging apparatus equipped with an imaging photoelectric conversion means, the memory means storing sample data of an image signal produced by the imaging photoelectric conversion means at each step position in a predetermined movement range of a focusing lens; , a calculation means for calculating a predetermined calculation value according to the level of high-frequency components for each screen from the image sample data stored in the memory means, and a step position of the focusing lens where the calculation value by the calculation means is maximized. 1. An automatic focusing device comprising: control means for determining the step position and driving the focusing lens to the step position.