JPH02252374A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To obtain accurate focus information, and to realize accurate focus adjustment by sample-holding a picture signal, and extracting an outline component. CONSTITUTION:A clamp circuit 19 is fixed at reference voltage every other picture element in conformity to a clamp pulse from a timing circuit 18, and besides, sampling data is stored, and difference between data of adjacent points is obtained and becomes a focusing evaluation value. In an A/D converting means 24, it is converted into a digital signal every time a pulse signal for A/D conversion is inputted, and is outputted to a control circuit 21. Since this focusing evaluation value is obtained by the clamp circuit 19 by serial- differential-calculating a signal which is sample-held by a sample-hold circuit 16 and corresponds to a luminance level, the output signal of magnitude corresponding to the rate of change of the output of the sample-hold circuit 16 is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an automatic focusing device used in a video camera or the like, which controls a lens system based on focus information obtained from an image signal.

(Prior Art) As an automatic focus adjustment device for video cameras, etc., instead of the conventional triangulation method using infrared rays,
A system has been proposed in which a lens system is controlled using focus information obtained from an image signal (video signal).

In this method, focus information is obtained by extracting a component (hereinafter referred to as a contour component) corresponding to an outline of a subject from an image signal. That is, in a focused state, the above-mentioned outline portion becomes clear, and the image signals corresponding to this portion have a large difference in brightness. On the other hand, in an out-of-focus state, the outline portion is blurred and no large difference in brightness occurs in the image signal. Therefore, the lens system may be controlled so that a large difference in brightness occurs in the contour portion of the image signal.

As a method for extracting the above contour components, JP-A-60-2
There is a device using a delay circuit as shown in Japanese Patent No. 56278. In this method, for the contour in the horizontal direction, the difference between the current image signal and a signal obtained by delaying the image signal by a certain short period of time is calculated, and for the contour in the vertical direction, the difference is obtained by delaying the image signal by one horizontal scanning period. The difference between the signal and the current image signal is taken, the focus state is determined from the magnitude of these differences, and the lens system is controlled in the direction in which the focus is aligned (in the direction in which the difference increases).

(Problem to be Solved by the Invention) The method using the delay circuit described above can basically detect contours in only one direction (horizontal or vertical direction), and uses the best point of a two-dimensional image as the contour detection point. Unable to select and detect. Therefore, the objects to be detected are limited to objects that have an outline in the horizontal direction, objects that have an outline in the vertical direction, and the like.

The purpose of the present invention is not limited to the horizontal or vertical direction.
An object of the present invention is to provide an automatic focus adjustment device that can extract contour components of a subject and perform accurate focus adjustment for any subject.

[Structure of the invention]

(Means for Solving the Problems) An automatic focus adjustment device according to the present invention has a sample hold circuit that samples an image signal corresponding to a subject image and outputs sample data according to the brightness level of this image signal. . Further, a timing circuit is provided which is synchronized with the horizontal and vertical directions of the image signal, determines sampling points and sampling intervals by the sample and hold circuit, and sequentially performs sampling operations. Further, a differential means is provided for determining the difference between adjacent point data from the sample data sequentially output from the sample hold circuit, and the lens system is controlled so that the difference determined by the differential means exhibits a maximum value. A control means is provided.

(Function) In the present invention, a minute object portion can be selected by sequentially sampling and holding image signals in synchronization with the horizontal and vertical directions according to the sampling points and sampling intervals determined by the timing circuit. Further, by determining the difference between adjacent point data of these sample data, the outline component of the subject can be reliably extracted, and the focus can be adjusted accurately in response to changes in focus.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 11 denotes a lens system of a video camera. A subject image formed on an imaging surface by this lens system 11 is converted into an electrical signal by an image sensor 12, and further amplified by a preamplifier 13.

The output signal of this front field tfi13 includes the process circuit 1
4, various processes are added to the signal and it becomes a television signal.

16 is a first sample-and-hold circuit, and 7 is a second sample-and-hold circuit, each of which samples the output signal of the preamplifier 13, that is, an image signal corresponding to a subject image (not shown), and samples this image signal. Output sample data according to the brightness level.

18 is a timing circuit that synchronizes with the horizontal and vertical directions of the image signal and synchronizes each sample and hold circuit 16,
1? In this method, sampling points and sampling intervals are determined and the sampling operations are performed sequentially. Further, the second sample and hold circuit 17 is configured to have a period delayed by one pixel with respect to the first sample and hold circuit 16.

Reference numeral 19 denotes a differential means for determining the difference between adjacent point data on the imaging surface. For this purpose, the respective output signals of the first sample and hold circuit 16 and the second sample and hold circuit 17 are inputted, and a differential operation thereof is performed. The differential output from this differential means 19 is applied to a control circuit 21 via a peak value detection circuit 20. The control circuit 21 controls the lens system 11 using the motor 22 so that the differential output, that is, the difference between adjacent point data on the imaging surface is maximized.

Next, the operation will be explained using FIG. FIG. 2 shows the relationship between the image captured by the image sensor 12 shown in FIG. 1 and the signal waveforms ■ to ■ of each part in FIG.
and out-of-focus state (b).

In the figure, if the image is composed of white and black as shown, the brightness level of the output signal of the preamplifier 13, that is, the image signal ■, will be steep as shown in the figure if it is in the focused state (1). In the out-of-focus state (b), it falls gently. Each sample and hold circuit 16, 17 samples the image signal (2) according to the sampling pulse (2) from the timing circuit 18.

The timing circuit 18 includes a sample hold circuit 16
．． A sampling operation is performed on the image signal (2) in synchronization with the horizontal and vertical directions so that the sampling point No. 17 moves diagonally on the imaging plane as shown. Furthermore, the interval between these sampling points can also be set to any value.

Here, the phase of the second sample and hold circuit 17 is 1 relative to the first sample and hold circuit 16 as described above.
Since they are delayed by a pixel, the phases of the sampling data (■), which are these output signals, are shifted by one pixel as shown in the figure, and the differential means 19 provides these differential outputs (2). This differential output ■ has a maximum amplitude in the focused state (1).

On the other hand, in the out-of-focus state (b), the fall of the image signal itself is gentle, so the amplitude of the differential output ■ is shallow.

The control circuit 21 inputs the differential output ■ through the peak value detection circuit 20, and controls the motor 22 so that the differential output ■, that is, the difference between adjacent point data on the imaging surface shows a maximum. and controls the lens system 11 to bring it into focus.

In this way, since the image signal (2) is sampled and held, the extraction position of the contour component on the screen can be selected. Therefore, even if there is no object in the center of the screen, it is possible to select the optimal position and bring it into focus.

Further, the interval between sampling points can be changed by the timing circuit 18 according to the spatial frequency of the object. In other words, the sampling point interval can be set finely for images with high spatial frequency, and conversely, the sampling point interval can be set coarsely for images with low spatial frequency, thereby obtaining correct focus information. be able to.

The embodiment shown in FIG. 3 uses one sample and hold circuit 16 to sample and hold the image signal, and also serves as a differential means 19 for determining the difference between adjacent point data on the imaging surface. , a clamp circuit is used to hold sample data at a reference value. Furthermore, this clamp circuit! The output signal of 9, that is, the focus evaluation value ■^
A ^/D conversion means 24 for /D conversion is provided, and the output signal ■ is applied to the control circuit 21.

Of course, the timing circuit 18 is synchronized with the horizontal and vertical directions of the image signal, and the sample and hold circuit 18 is synchronized with the image signal in the horizontal and vertical directions.
It has the function of determining sampling points and sampling intervals according to No. 6 and sequentially performing sampling operations. In addition,
It also has a function of controlling the operation timing of the clamp circuit 19 and the ^/D conversion means 24.

Next, the operation will be explained using FIG. FIG. 4 shows the relationship between the signal waveforms (1) to (2) of each part in FIG. 3 for the in-focus state (1) and the out-of-focus state (b), respectively.

In the figure, it is assumed that the image consists of black and white, as in the previous embodiment. In this case, as mentioned above, the output signal of the preamplifier 13, that is, the brightness level of the image signal
In the out-of-focus state (b), the light falls gently. The sample and hold circuit 16 samples the image signal (2) according to the sampling pulse (2) from the timing circuit 18, and obtains sampling data (2).

The clamp circuit 19 fixes every other pixel to the reference voltage in accordance with the clamp pulse (2) (double the period of the sampling pulse (2)) from the timing circuit 18. Further, the sampling data (2) is stored in a capacitor (not shown). Then, since serial differential calculation is performed at the next point, the difference between the adjacent point data described above is obtained, and this becomes the focus evaluation value (■). This focus evaluation value ■ is the A/D
In the conversion means 24, the ^/ from the timing circuit 18
Every time the D-conversion pulse signal is input, it is converted into a digital signal (2) and output to the control circuit 21.

This focus evaluation value ■ is obtained in the clamp circuit 19 by serial differential calculation of the signal corresponding to the luminance level sampled and held by the sample and hold circuit 16, and is obtained by serial differential calculation of the signal corresponding to the luminance level sampled and held by the sample and hold circuit 16.
It is produced as an output signal whose magnitude depends on the rate of change. That is, in the in-focus state, the brightness level of the image signal (2) falls sharply, resulting in an output signal with a large amplitude. On the other hand, in the blurred state, the luminance level of the image signal (2) falls slowly, so the amplitude of the output signal becomes small.

The control circuit 21 inputs the above output signal, that is, the digital signal ■ corresponding to the focus evaluation value ■, and drives the motor 22 so that the digital signal corresponds to the maximum value, thereby controlling the lens system 11. Through this operation, the lens system 11 is brought into focus on a subject (not shown).

In the present invention, by changing the timing of the sampling pulse, the slope of the sampling link pixel row can be changed as shown in FIG. It is also possible to sample the periphery of the screen.

Furthermore, by utilizing the fact that a television image is composed of an even field and an odd field, it is also possible to form the sampling pixel array into an O or x shape. That is, in FIG. 6, if the left semicircle is sampled in the odd field and the right semicircle is sampled in the even field, a pseudo circular contour component can be extracted.

〔Effect of the invention〕

As described above, according to the present invention, by sample-holding image signals and extracting contour components, it is possible to accurately obtain focus information even for minute images and to bring the image into focus correctly.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic focus control device according to the present invention, FIG. 2 is a time chart explaining the operation using signal waveforms of each part shown in FIG. 1, and FIG. FIG. 4 is a time chart illustrating the operation using signal waveforms of each part shown in FIG. 3, and FIGS. 5 and 6 are diagrams showing sampling pixel arrays. 11.-lens system, 16..sample hold circuit, 1
8. Timing circuit, 19. Differential means, 21. Fist control circuit. ■ Trout - ] - 11) 2 - Figure

Claims (1)

[Claims] (1) Sampling the image signal corresponding to the subject image,
A sample hold circuit outputs sample data according to the brightness level of the image signal, and the sample hold circuit synchronizes with the horizontal and vertical directions of the image signal, determines sampling points and sampling intervals by the sample hold circuit, and performs sampling operations sequentially. a timing circuit; a differential means for determining the difference between adjacent point data from sample data sequentially output from the sample and hold circuit; and controlling a lens system so that the difference determined by the differential means reaches a maximum. An automatic focus adjustment device comprising: a control circuit for controlling the focus;