JPH04158322A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To improve the precision of the automatic tracking function by extracting the intensity distribution of each block in a focus area as the feature quantity of a photographed object, detecting the movement of the feature quantity between frames, and changing the focus area. CONSTITUTION:The image signal outputted from an image pickup section 1 is converted into a digital signal and stored in a frame memory 3, and it is further compressed and coded by a signal process section 4 and recorded by a record section 5 as the image data. The output of the process section 4 is fed to a DCT section 6, and the DCT coefficient obtained here is fed to an arithmetic section 7. The arithmetic section 7 notices a specific coefficient in the DCT coefficient and outputs the control signal corresponding to the change of the coefficient indicating the intensity. A focus control section 8 receives the control signal and drives a motor in the image pickup section 1 to move the position of a lens. The position of the lens is adjusted, and the position where the specific coefficient becomes the maximum value is judged as the focused position. An automatic focus adjusting device with the automatic tracking function to precisely follow a moving object to be photographed is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention detects the focal position of a lens from frequency components contained in a video signal from a video camera, still camera, etc.
The present invention relates to an automatic focus adjustment device that automatically adjusts the focus of a camera, and particularly relates to an automatic focus adjustment device that has an automatic tracking function that automatically tracks and adjusts the focus of a subject moving relative to the camera.

[Conventional technology]

The camera's automatic focus adjustment device extracts a specific high-frequency component from the video signal obtained from the imaging unit, and adjusts the focus by moving the lens position so that the amplitude value of this high-frequency component is maximized. The device is known (e.g.
``NHK Technical Research'' Volume 17, No. 1, ``Automatic focus adjustment device for television cameras using mountain-climbing servo method'').

This device considers the lens system as a kind of low-pass filter,
Focusing on the fact that the equivalent bandwidth for a subject at a certain distance changes when the focus is adjusted, the definition of the screen is detected by detecting the amplitude change of the high frequency component of the video signal near the cutoff frequency, and the focus position of the lens is determined. It is something to seek.

In this case, the amplitude value of the high frequency component near the cutoff frequency has a mountain-shaped characteristic that is maximum at the best imaging position and decreases as the focal point shifts back and forth. in particular,
A signal of a specific high frequency component (for example, IMH2) is extracted from the video signal obtained by scanning the image in the horizontal direction using a band pass filter, and the position of the lens is adjusted so that the amplitude value of this high frequency component is maximized. The focus is adjusted. However, with this device, the focus area is fixed at the center of the shooting screen, so if the subject you want to focus on moves, other subjects will come into focus, leaving the target subject out of focus. There is.

Therefore, as a device that automatically tracks the focus position according to the movement of the subject, for example, Japanese Patent Laid-Open No. 60-254107
(name: ``Automatic tracking device for cameras'') has been proposed. This device detects changes in color difference signals within a specific tracking field of the tracked subject, detects the presence or absence of movement of the tracked subject and the direction of movement, moves the focus area to follow the movement of the tracked subject, At this moved position, focus detection or focus adjustment is performed using known means such as the aforementioned hill-climbing servo system.

[Problem to be solved by the invention]

However, in the conventional example described above, the movement of the tracked subject is recognized from the color difference signal, so if the color of the target subject is close to the background color, the movement of the tracked subject is recognized. The disadvantage is that it cannot be detected. This is because the accuracy of identifying the subject cannot be improved due to the ambiguity of color information.

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic focus adjustment device having an automatic tracking function that can accurately recognize the movement of a subject.

[Means to solve the problem]

The automatic focus adjustment device according to the present invention converts the subject image formed on the imaging surface into a digital image signal, calculates the average value of the luminance distribution within the focus area from this digital image signal, and moves this average value. The camera is configured to detect the movement of the subject image, move the focus area, and detect the in-focus position 1 of the subject image within the moved focus area.

[For production]

In the configuration of the present invention, the luminance distribution within the focus area of the subject image formed on the imaging plane is detected, and the average value (center of gravity) of this luminance distribution is taken as the feature amount of the subject. Then, the movement of the subject is detected by comparing the feature amount in a certain frame with the feature amount one frame later. Next, the focus area is moved following this movement, and the in-focus position of the subject is detected within this new focus area. By doing this, it is possible to accurately recognize and track a moving subject and keep it in focus.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of an automatic focus adjustment device according to the present invention.

This device consists of an imaging unit 1 consisting of a solid-state imaging device such as a CCD that converts a subject image formed through a lens into an electrical signal.
The video signal outputted from the imaging section 1 is converted into a digital signal by the AD conversion section 2, and then stored in the frame memory 3.
is temporarily stored. The digital signal stored in the frame memory 3 is compressed and encoded by the signal processing section 4, and recorded in the recording section 5 as digital image data. Also,
The output of the signal processing section 4 is supplied to the DCT section 6.

The DCT unit 6 converts the image data in the focus area FE shown in FIG. 2 into one block of n×n pixels, for example, 8×8
Divide into multiple blocks consisting of pixels, and 2 blocks for each block.
Dimensional Discrete Cosine Transform (DCT)
Co51ne Transformation+) is applied. D
CT is a type of orthogonal transformation in the frequency domain, and the resulting nXn DCT coefficients FuV (u+V=0+1+...
'+n-1) is one block of image data fij(i
, j=0.1. ..., n-1), however, C
-=1 frame (2(w=0) =1 (W≠0). Each DCT coefficient Fuv represents a component obtained by decomposing one block of image data into spatial frequencies,
The coefficient FOO is a value proportional to the average value of image data fij (
The higher the variables u and v become, the higher the frequency component (alternating current component) is. FIG. 3 shows an 8×8 matrix of DCT coefficients Fuv. In the figure, the coefficient FOO at the top left represents the magnitude of the DC component included in the image, the coefficients below it represent the magnitude of the high frequency component of longitudinal waves, and the coefficients to the right represent the magnitude of the high frequency component of transverse waves. It represents. Therefore, by observing the DCT coefficient Fuv, it is possible to simultaneously detect the magnitudes of longitudinal waves, transverse waves, and their composite waves included in the image in the block.

The DCT coefficients obtained by the DCT section 6 are supplied to the calculation section 7. The arithmetic unit 7 focuses on a specific coefficient among the DCT coefficients and outputs a control signal according to the amount of change in that coefficient. The focus control section 8 receives this control signal and drives the motor within the imaging section 1 to move the position of the lens. In this way, the imaging section 1. AD conversion section 2. Frame memory 3. Signal processing section 4゜DCT section 6. Arithmetic unit 7. The position of the lens is adjusted by a closed loop formed by the focus control unit 8, and the position where a specific coefficient has the maximum value is determined to be the in-focus position. In addition, the calculation unit 7 stores the maximum value of the specific coefficient detected in this way, and if the input specific coefficient changes by more than a certain value, it determines that the content of the subject has changed and performs the calculation again. Redo the focusing action.

Next, the operation of detecting the moving amount and moving direction of the subject in the calculation unit 7 will be explained.

As mentioned above, the two-dimensional DCT coefficient Fuν represents the frequency distribution for each block, and the coefficient FOO in the upper left shaded area in FIG. 3 represents the DC component of the block, that is, the average value of luminance. There is.

Therefore, the distribution of the average value of luminance of each block within the focus area FE can be viewed as the feature amount of the subject.

This feature value is based on the shape of the subject and the focus area FE.
It changes depending on the position occupied within the image, so if the same subject is captured in two frames before and after, the movement of the subject can be detected from the difference in the distribution.

FIG. 4 shows a conceptual diagram of subject motion detection in the calculation unit 7. In the figure, subject A represents the distribution of DC components of each block within the focus area EF in a certain frame, and subject B is the same. It represents the distribution of DC components (luminance) of each block within the focus area EF one frame after the image. In reality, the background other than the object to be tracked is captured within the focus area FE, but this does not change and is therefore canceled out in subsequent processing (the shaded area in FIG. 4). First, the center of gravity G of the DC component of all blocks in the focus area FH when the subject A is photographed is determined, and is taken as the characteristic sound of this frame. Next, the center of gravity H of the DC component of the next frame is found in the same manner. Actually, the center of gravity G is calculated as the center of gravity including all the hatched areas, but since the center of gravity G is included in the same way when calculating the center of gravity H of the next frame, it can be ignored. Therefore, the amount and direction by which the center of gravity G moves toward the center of gravity H is considered to be the movement vector between one frame of the characteristic sound in this area. By moving the focus area within the field of view based on this movement vector, it is possible to follow the subject to be tracked.

The focus control section 8 changes the focus area FE based on this information from the calculation section 7, and redoes the focusing operation. In this way, it is possible to maintain focus while automatically tracking the subject.

[Effects of the Invention] According to the present invention, the luminance distribution of each block within the focus area is extracted as the characteristic sound of the subject, and the movement of this characteristic sound between frames is detected to change the focus area. Therefore, it is possible to provide an automatic focus adjustment device having an automatic tracking function that accurately follows a moving subject.

This relieves the photographer from the trouble of keeping the subject always within the focus area, and improves the operability of the camera. Furthermore, in recent years, systems that detect and follow movements have been required in various industrial fields, for example, in the eye Φ parts of microscopes and various robots, and the present invention can be applied to these systems as well.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic focus adjustment device according to the present invention, FIG. 2 is a diagram showing block division within a focus area, FIG. 3 is a diagram showing a matrix of two-dimensional DCT coefficients, and FIG. The figure is a conceptual diagram of subject motion detection. DESCRIPTION OF SYMBOLS 1... Imaging unit, 2... AD conversion unit, 3... Frame memory, 4... Signal processing unit, 5... Recording unit, 6...
...DCT section, 7... Calculation section, 8... Focus control section.

Claims (3)

[Claims] (1) Convert the subject image formed on the imaging surface into a digital image signal, calculate the average value of the luminance distribution within the focus area from this digital image signal, and calculate the movement of the subject image based on the movement of the average value. An automatic focus adjustment device characterized in that the focus area is moved by detecting the focus area, and the in-focus position of the subject image is detected within the moved focus area. (2) an imaging device that converts a subject image formed through a lens on the imaging surface of an imaging device into an electrical signal; and an AD conversion device that converts the converted electrical signal into a digital image signal; orthogonal transformation means for dividing an image signal within a focus area into a plurality of blocks each consisting of a plurality of n×n pixels, and performing two-dimensional orthogonal transformation in the frequency domain for each block to obtain a plurality of n×n transform coefficients; , detecting the focal position of the lens from a specific first transform coefficient among the transform coefficients, and detecting the distribution of the luminance signal from the distribution of the specific second transform coefficient of each block within the focus area. and a calculation means for detecting the amount and direction of movement of the subject from changes in the distribution of the luminance signal, and a focus control means for moving the position of the lens and the focus area based on the detection signal from the calculation means. An automatic focus adjustment device comprising: (3) Detection of the distribution of the luminance signal in the calculation means:
3. The automatic focus adjustment device according to claim 2, wherein the automatic focus adjustment is performed by determining the center of gravity of the distribution of the specific second transformation coefficient of each block within the focus area.