JPH04267210A - Automatic focussing device - Google Patents

Abstract

PURPOSE:To provide a automatic focussing device which can rapidly detect a position to be focused even though no object having a high contrast is present in a designated area. CONSTITUTION:In an automatic focusing device comprising a pick-up lens 1 driven mainly by a motor 8, an image pick-up element 2, an image processing circuit 3 and a BPF circuit 5 for extracting a contrast value of an object to be picked up, an area having a high contrast value, adjacent to a designated area to be focused from which a peak value of contrast values cannot be detected, is automatically selected, instead of the a designated area.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device, and more particularly to an automatic focusing device that is less likely to be unable to focus.

0002

2. Description of the Related Art Conventionally, automatic focusing devices for video cameras, still cameras, etc. detect contrast information as sharpness information of a photographed screen from high frequency components in a video signal. A so-called hill-climbing automatic focusing device is known that controls the lens position so that the contrast value obtained by integrating components is maximized. Note that in this case, the lens extension position where the contrast value is maximum corresponds to the in-focus position.

[0003] Furthermore, an automatic focusing technique for automatically switching the focusing area is also known in the mountain climbing method. A device applying this technology, for example, divides the screen frame into multiple focusing areas, focuses on a certain arbitrary area, and if it is determined that focusing is impossible due to the condition of the subject, expands the AF area. Then, the mountain climbing focus position detection is performed again. Examples of systems that provide the plurality of AF areas include a focus detection device disclosed in Japanese Patent Application Laid-Open No. 62-267713 and an automatic focus adjustment device disclosed in Japanese Patent Application Laid-Open No. 63-193133.

0004

[Problems to be Solved by the Invention] However, according to the automatic focusing device that automatically widens the focusing area, the original A
If there is no contrasting subject within the F-area, even if you enlarge the AF area, there is a possibility that there is no subject even within this enlarged area. In some cases, the in-focus position could not be detected and photography had to be stopped.

[0005] The purpose of the present invention is to solve the above-mentioned problems,
To provide an automatic focusing device capable of quickly detecting a focusing position even when a subject exists outside a designated AF area, and hardly causing an inability to focus.

[0006]

[Means for Solving the Problems] The automatic focusing device of the present invention includes a first means for extracting and retaining image sharpness information from each of a plurality of focus target areas set within a field of view; Focus adjustment is performed by gradually driving the focusing means in a direction in which the sharpness information indicates higher sharpness based on the sharpness information regarding one area among the sharpness information of each focus target area obtained by the first means. A predetermined focus state is achieved depending on the second means for performing the operation and the initial focus adjustment operation performed by the second means on an area previously set as the initial focus target area among the respective focus target areas. and a third means for reselecting one of the respective focus target areas to perform the next focus adjustment operation by the second means when the focus target area cannot be obtained. It is characterized by

[0007]

[Operation] When the predetermined in-focus state cannot be obtained by the initial adjustment operation for the area set as the above-mentioned initial focus target area, one of the above-mentioned focus target areas is selected. Then, perform the next focusing adjustment operation.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on embodiments shown in the drawings. FIG. 1 is a main block configuration diagram of an imaging device incorporating an automatic focusing device according to an embodiment of the present invention. As shown in this figure, the imaging device incorporating the above-mentioned focusing device mainly includes a photographic lens 1, an imaging element 2, an imaging processing circuit 3 that performs imaging signal amplification and sample hold processing, and an image processing circuit 3 that performs image signal amplification and sample hold processing. A finder 10 for displaying the AF area, a video signal output terminal section 4, and a bandpass filter B. for extracting a contrast value, which is contrast information as sharpness information, from an imaging signal. P. F. Circuit 5 (first means)
, an A/D conversion circuit 6 (first means) for analog/digital conversion, an arithmetic processing circuit 7 (incorporating the first, second, and third means) composed of a CPU, ROM, RAM, etc.; AF that provides an AF start area switching signal to the arithmetic processing circuit 7
It is composed of a start area changeover switch 11, a motor 8 for driving the photographing lens 1, a motor drive circuit 9 for the motor 8, and a video recording and reproducing system (not shown). The above-mentioned areas are areas in which the screen is divided into predetermined areas such as areas A, B, to I on the photographing screen g shown in FIG. 3, and the focus detection process is performed from within these areas. It is assumed that a focus target area is selected.

[0009] The operation of the above-mentioned imaging device having the above configuration is as follows: First, subject light is taken in through the photographing lens 1;
An image of the subject is formed on the image sensor 2. The output signal from the image sensor 2 is sampled and held in the image processing circuit 3, and sent as an image signal to the output terminal section 4, the finder 10, and the B. P. F. It is output to circuit 5. Then, it is output as a video signal from the output terminal section 4 to the recording/reproducing circuit, and the finder 11 displays the video imaged on the image sensor and a mask of the AF area where the AF processing is being performed by the arithmetic processing circuit 7. A' is displayed (see Figure 3). In addition, the above B. P. F. In the circuit 5, a predetermined high frequency component of the image of the area is extracted as a contrast value,
Furthermore, it is converted into a digital value by the A/D conversion circuit 6,
This is taken into the RAM of the arithmetic processing circuit 7 as sharpness information. This arithmetic processing circuit 7 includes a circuit that detects the peak point of the contrast value in the area designated by the AF start area changeover switch 11 or another selected area using the mountain climbing method, and performs focus determination. In addition to the second and third means, it also has means for outputting a signal for displaying the currently selected AF area on the finder 10. Note that the AF processing area is cut out in memory,
This is performed based on horizontal and vertical synchronization pulses from the imaging processing circuit 3. Further, the arithmetic processing circuit 7 controls the focus detection operation and drives the motor 8 via the motor drive circuit 9 during the focusing operation to move the photographing lens 1 to a predetermined position.

[0010] The focusing process of this automatic focusing device detects the contrast value of a specified area among the areas divided into a predetermined number, and if the maximum value cannot be detected,
For example, the maximum value of the contrast value of an area of another adjacent area is detected, and the position corresponding to the maximum value is processed as the in-focus position. Therefore, the memory capacity of the device,
The input section is smaller than the conventional one, and the processing speed can be relatively high. In other words, with conventional hill-climbing focusing devices, if the maximum contrast value does not exist in the designated area, it is necessary to enlarge the area to be processed and detect the focus position.
Therefore, it is necessary to obtain a large amount of contrast information, and it is also necessary to widen the dynamic range of the input section such as a comparator that compares contrast values, which inevitably increases the size of the hardware, but these problems is solved in this embodiment. In addition, in conventional systems, when processing is done digitally, the number of bits of the contrast value increases, which may complicate the calculation process and increase the processing time; however, this embodiment has the advantage of this. You can also expect

Next, the processing operations of the automatic focusing device of this embodiment, including the above-mentioned focusing processing, will be explained using the flowchart of FIG. 2, the viewfinder image shown in FIG. 3, and the contrast characteristic diagram shown in FIG. 4. Note that in this focusing device, the screen g is divided into areas A to I, as shown in the finder image of FIG. 3, and area A is the designated focus detection area. Also,
It is assumed that the subject has contrast value characteristics with respect to the number of feeding steps n for each of the areas A to I, as shown in FIG. In the process, first, in step S01, the number of extension stages n is set to 0, the current lens extension position is returned to the infinite distance ∞ position, and in step S02, the contrast value An at the number of stages n in area A (n=0 in this case) is determined. Read and write to the memory of the arithmetic processing circuit. Then, in step S03, the motor 8 is driven in one step forward rotation,
Extend photographing lens 1. Then, the contrast value An+1 at the stage number n+1 of the lens extension position is taken into the memory of the arithmetic processing circuit 7 (step S04).
. Further, the contrast value An for the previous stage number and the contrast value An+1 for the current stage number are compared, and if the value An is larger, it is determined that the maximum value has been detected, and the process proceeds to step S06. If the value An+1 is larger, it is determined that the contrast value is increasing, and the process jumps to step S07.

In step S06, the subroutine "AF processing (A)" is called, and the photographing lens 1 is moved to the step number position where the contrast value is maximum, and the main focusing processing is ended. Note that in this process, it is also possible to drive the lens 1 to the above-mentioned in-focus position, taking into account the backlash of the drive system. On the other hand, if the process jumps to step S07, it is determined whether or not the current drive stage number has reached the final nmax. If it has not reached it, the process jumps to step S08, increments the stage number n, and returns to step S03. When the final number of steps is reached, that is, when the contrast value peak cannot be detected in the entire driving range as in the contrast characteristic of area A in FIG. Switch the focus target area. The area to be switched here is the area where the contrast value is the maximum at the final number of steps reached or the current number of steps reached, and is an area adjacent to area A, for example, area H in the case of FIG. 4.

Next, the process proceeds to step S10, where the drive motor 8 is reversed by one stage. In step S11, the contrast value Hn of the area is read. And step S
In step S12, the contrast value Hn+1 of the previous stage is compared, and if the value Hn+1 is larger, it is determined that the maximum value has been detected, and the process proceeds to step S13. If the value Hn is larger, it is determined that the contrast value is increasing, and the process proceeds to step S1.
Jump to 4.

In step S13, the subroutine "AF processing (B)" is called, the photographing lens 1 is moved to the step number position where the contrast value is maximum, and the main focusing processing is ended. If the process jumps to step S14, it is determined whether or not the current drive stage number n has reached the position of 0. If it has not reached the position, the process jumps to step S16, decrements the stage number n, and returns to step S10. When the number of stages n reaches the 0 position, that is, when the contrast value peak is not detected in the entire driving range, the process advances to step S15, and the subroutine "error processing" is called. In this error processing, another area close to another area A, which has the next highest contrast value, may be adopted as the AF processing area. Furthermore, the same AF target area as described above may be selected. Then, the AF process may be performed again. Here, the photographing lens 1 may be stopped at the time when the error processing routine is executed (in this case, at the infinite position). In addition, the photographing lens 1 is placed in the position
You may play out.

In the above embodiment, the AF area of the screen was divided into nine equal parts as shown in FIG. The central area may be circular and the area around it may be divided into four, or the surrounding divided areas B to E may be set to overlap the central area A as shown in FIG. Furthermore, as shown in FIG. 7, it is also possible to set each area at a predetermined location on the screen so that they do not touch each other. It should be noted that the present invention can be applied not only to electronic cameras but also to movie cameras and silver halide cameras.

[0016]

Effects of the Invention As described above, the automatic focusing device of the present invention has a first
a second means for performing a focus adjustment operation, and a second means for selecting one of the focus target areas when a predetermined in-focus state cannot be obtained by the initial focus adjustment operation; Therefore, the present invention can be used even when a subject exists outside the focus area and focus detection cannot be performed in the initially designated area, or when This is especially true when taking macro shots, but it is especially effective when the subject is in a pattern with uniform contrast. In that case, focus detection is performed based on image information from other adjacent areas. , it has remarkable effects such as making it possible to automatically and quickly detect the in-focus position without performing a trigger operation again.

[Brief explanation of the drawing]

FIG. 1 is a main block configuration diagram of an imaging device incorporating an automatic focusing device according to an embodiment of the present invention.

FIG. 2 is a flowchart of focusing processing by the automatic focusing device shown in FIG. 1;

FIG. 3 is a diagram of a finder image showing a focus target area of the automatic focusing device shown in FIG. 1;

4 is a contrast characteristic diagram of the subject in each area of the finder image in FIG. 3; FIG.

FIG. 5 is a focusing area screen showing a modified example of the focusing target area of the automatic focusing device shown in FIG. 1;

FIG. 6 is a focusing area screen showing another modification of the focusing area of the automatic focusing device shown in FIG. 1;

7 is a focusing area screen showing still another modification of the focusing area of the automatic focusing device shown in FIG. 1; FIG.

[Explanation of symbols]

Claims (1)

[Claims] 1. A first means for extracting and retaining image sharpness information from each of a plurality of focus target areas set within a visual field; and sharpness information of each focus target area by the first means. a second means for performing a focus adjustment operation by gradually driving the focusing means in a direction in which the sharpness information indicates a higher sharpness with respect to sharpness information regarding one of the areas; If a predetermined focusing state cannot be obtained by the initial focus adjustment operation by the second means performed on the area previously set as the initial focus target area within each of the focus target areas, an automatic focusing device comprising: a third means for reselecting one focus target area and causing the second means to perform the next focus adjustment operation.