JPS62182704A - Auto-focus device - Google Patents

Abstract

PURPOSE:To always obtain the in-focus state at the time of video photographing of an object changing the contrast especially by automatically switching plural focus object ranges different in size in accordance with the contrast of the object. CONSTITUTION:If the picture in a selected focus object range A has no contrast, a detection impossibility detecting circuit 17 detects this state to send a range switching signal to a range designating circuit 13, and the range designating circuit 13 sends a range designating signal to the control terminal of a gate circuit 14 so that the luminance signal of a focus object range B wider than the focus object range A passes through the gate circuit 14. Simultaneously, this automatically switched focus object range B is displayed on an EVF 18. If contrast sufficient for focusing cannot be obtained on the picture in the focus object range B, the range switching signal is sent to the range designating circuit 13 from the detection impossibility detecting circuit 17 similarly, and the gate circuit 14 is so controlled that the luminance signal of a focus object range C wider than the focus object range B passes through the circuit 14, and simultaneously, the focus object range C is displayed on the EVF 18 instead of the range B.

Description

[Detailed description of the invention] [Utilization of industry-1-! IIf] The present invention relates to an autofocus device, and more particularly, to an autofocus device that detects a focus state by detecting high frequency components of image information.

[Prior Art] In an autofocus device that detects high-frequency components of image information and determines the in-focus state by contrasting the image based on the level of the same high-frequency components, the main wave object is usually located within the shooting frame. Since it is often located in the center of the image frame, the center of the shooting image frame is used as the focus area and its contrast!・It is designed to detect. However, it is difficult to determine the in-focus state when the subject moves over a wide area of the photographic image frame or when the contrast in the central part is low. Therefore, is it a good idea to focus on a wide range of the photographic image frame and detect its contrast? If the contrast is wide from the beginning, even though the subject is in the center, the background will be in focus. This may cause problems such as

[Problems to be solved by the invention] For these reasons, autofocus devices are already known that have a function of setting the focus range in three stages at the image information processing stage (TV Technology Vol. ,34,
1986.1. (See p. 65).

However, in this conventional device, the photographer manually switches the appropriate focus target range, so for example, the contrast of the selected focus target range is sufficient to override the in-focus state. The decision as to whether the image is correct or not must be made by the photographer or himself/herself, which is inconvenient and
It has been difficult to always maintain focus by following a changing subject during video shooting.

The present invention was made with a view to the two points in mind, and it is an object of the present invention to automatically switch the focus range according to the contrast of the subject and to always obtain the optimal focusing state for the subject situation. 1. To provide an autofocus device that can
target

[Means and effects for solving the problem] The autofocus device of the present invention has one (number of) focus target ranges set within the light receiving area of an image, and one of the focus target ranges is selected. The high frequency component of the selected focusing target range passes through the extraction means No. 11, and the contrast is detected by the same high frequency component to obtain a focusing signal, and the signal extraction means When there are too few high-frequency components passing through and contrast!-detection becomes impossible, this condition is detected and the selected focus range is switched to a larger focus range.

[Example] An example of an autofocus device according to the present invention is configured as shown in FIG. In FIG. 1, a push button 11 is an operation section for selecting a focus target range provided at an easily operated position on the video camera body, and is connected to a control circuit 12. When push button 11 is pressed,
Each time, an operation signal is manually inputted to the control circuit 12, and from the control circuit 12, a preset focus target range is set in a small range within the light receiving area of the photographed image shown in FIG. A, B sequentially from the human range.

A control signal for selecting and switching between C and D is input to the range specifying circuit 13. The range designation circuit 13 is applied with a horizontal synchronization signal H and a vertical synchronization signal V for synchronizing with the image, and based on these synchronization signals H and V, it performs a synchronization according to a control signal from the control circuit 12. Focusing range A-
A range designation signal for designating D is sent to the control end of the gate circuit 14. The control circuit 12 also controls the range designation U path 1.
Since a control signal corresponding to the focus target range specified in step 3 is sent to the electronic viewfinder (hereinafter referred to as EVF) 18, the EVF 18 is supplied with a video signal from an imaging device (not shown). At the same time that the photographed image is displayed, the selected focusing target range is displayed.

Of the video signals taken out from the image sensor, only the luminance signal is manually input to the gate circuit 14, and when the range designation signal from the range designation circuit 13 described in 1- is sent to the control end of the gate circuit 14, , only the luminance signal of the focus target range corresponding to this range designation signal passes through the gate circuit 14 and is sent to the contrast detection circuit 15. The contrast detection circuit 15 extracts a high frequency component from the luminance signal sent from the gate circuit 14 and sends it to the focusing circuit 16, and the focusing circuit 16 is placed at a position where the level of the high frequency component is highest.
That is, a lens drive signal is sent to drive the imaging lens to a position where the contrast is strongest.

The high frequency component detected by the contrast detection circuit 15 is also sent to an undetectable detection circuit 17. and,
This detection circuit 17 detects the minimum contrast necessary for focusing! ! f'i W, and if the contrast i'j is insufficient for focusing, 1; sends a range switching signal to the range specifying circuit 13;

When a range switching signal is sent to the range designation circuit 13, the range designation circuit 13 sends a range designation signal for a focus target range that is one step wider than the focus target range selected by the "-2" push button 11 to the gate circuit 14. It can be switched to

For example, when the photographer operates the pushbutton 11,
The narrowest focusing range A (second
(see figure), this focusing range A is displayed on the EVF 18, and only the luminance signal in the focusing range A passes through the gate circuit 14, and the high frequency components contained therein are converted into contrast. Detection is done by contrast path 15. Therefore, at this time, the photographing lens is driven so as to focus on the image in the L range A by the lens drive signal from the focusing circuit 16 with sufficient contrast for the image in the focus target range A.

-1 U Note: If there is no contrast in the image of the selected focusing target range A, the undetectable detection circuit 17 detects this state and sends a range switching signal to the range specifying circuit 13.
At this time, the range designation circuit 13 sends a range designation signal to its control end so that the luminance signal of the focus range B, which is one step wider than the focus range A, is passed through the gate passage 14. At the same time, this automatically switched focusing target range B is displayed on the EVF 18. If the image in the focus range B has some contrast, the lens is driven so that the image in the focus range B is brought into focus. The contrast sufficient for focusing on the image in the focus target range B is determined by the range specifying circuit 13 similarly by the undetectable detection circuit 17.
A range switching signal is sent to the gate circuit 14, and the gate circuit 14 is controlled to pass the luminance signal of the in-focus target range C which is one step wider than the -1- recorded in-focus target range B, and at the same time, this in-focus target range C is is displayed on the EVF 18 instead of the above range B.

In this way, if the contrast of the image in the selected focus range is not sufficient, it will be automatically expanded to a focus range with sufficient contrast.
When a focused range with contrast is selected, the lens is driven to focus on an image in the same range. Therefore, even if the contrast of the image in the focus range selected by the photographer is low, it will not become impossible to focus at all, and the focus target range in the area including the focus target range selected by the photographer It is possible to obtain an in-focus state by

Note that if sufficient contrast cannot be obtained even when the contrast of the image is detected within the maximum focusing range that is equal to the entire area of the photographic image frame 10, the focusing circuit 16 moves the imaging lens to infinity. A lens drive signal is sent to move the lens to a position intermediate between the far position and the close position, and a compensation operation is performed to minimize the problem of photographing with a completely out of focus position.

[Effects of the Invention] As described in 1-1 above, according to the present invention, the focus range is automatically switched depending on the focus range of m number or the contrast of the limb photograph, so it is possible to set Even if the contrast cannot be obtained in the focused target range, it is possible to focus on the focused target range that has the contrast of
-Can change the state by 11J.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an autofocus device showing an embodiment of the present invention, and FIG. 2 is a photograph showing a plurality of focus target ranges that are automatically switched in the autofocus device shown in FIG. 1 above. FIG. 3 is a plan view of the image frame. 14...Gate circuit (signal extraction means) means for obtaining a focusing signal) 17...Undetectable detection circuit (means for switching to a larger focusing target range) A-D...Focusing Focus range

Claims (1)

[Claims] In an autofocus device that detects a focus state by detecting high frequency components of an image, one of a plurality of predetermined focus target ranges for focusing set within a light receiving area of the image is provided. a means for selecting, a signal extracting means for passing the high frequency component of the selected focusing target range, and a means for detecting the contrast of the image based on the high frequency component passed through the signal extracting means to obtain a focusing signal. and means for detecting the state and switching the selected focus target range to a larger focus target range when the high frequency component passing through the signal extraction means is too small to make contrast detection impossible. Equipped with an autofocus device.