KR100641354B1 - Image Focus Detection Device and Image Focus Detection Method - Google Patents

Abstract

A device and a method for detecting a focus of an image are provided to adjust a focus of camera by calculating a focal distance from an inputted image to a subject in real time without an additional focus control device or a burden of large calculation. A camera(110) takes a photograph of a subject by selecting an accurate focal distance to the subject among unaccurate focal distances while a position of a lens is changing to the subject. An image signal processing circuit(120) processes each image signal photographed from the camera according to the various focal distances to generate digital image frame signals of the subject and a focal distance signal according to each frame signal. A dynamic thresholding circuit(130) processes dynamic thresholding to image frames inputted from the image signal processing circuit to obtain images to which dynamic thresholding is applied. A pixel calculator(140) counts the number of pixels of images processed by dynamic thresholding. A motor driving unit(150) adjusts the position of the lens for controlling the focal distance. A focal distance controller(160) transmits a control signal for a motor to the motor driving unit by considering a pixel number signal of each image frame transmitted from the pixel calculator and a focal distance signal corresponding to each image frame transmitted from the image signal processing circuit.

Description

Image Focus Detection Device and Image Focus Detection Method {IMAGE FOCUS DECTECTING METHOD AND DEVICE USING DYINAMIC THRESHOLDING METHOD}

1 is a block diagram schematically illustrating an image focus detection apparatus according to the present invention for automatically detecting a focus based on an image to which dynamic thresholding is applied;

2 is a view schematically showing a state in which a focal length is adjusted according to an adjustment of a lens;

3 is a non-focal distance image,

4 is a diagram illustrating a dynamic threshold value applied to an image of FIG. 3 in which a focal length is not correct;

5 is an image having a focal length,

FIG. 6 illustrates an image of applying a dynamic threshold value to the image of FIG. 5 having a focal length; FIG.

7 is a diagram schematically illustrating a general image frame.

[Description of Reference Code]

110- camera, 120- video signal processing circuit,

130-dynamic thresholding circuit, 140-pixel calculator,

150-motor drive, 160-focal length adjuster.

The present invention relates to an image focus detecting apparatus and an image focus detecting method for adjusting focus using a dynamic thresholding technique.

The image frame is composed of a plurality of pixels, for example, in a frame composed of 3x3 pixels, the center pixel has eight neighboring pixels surrounding itself. Here, in order to compare the eight neighboring pixels with the center pixel, an average of eight neighboring pixels, for example, a gray level value, is obtained. The average value is called a threshold value, and the threshold value and the gray level of the center pixel are calculated. Comparing the values, for example, except for the average value or less, extracting the center pixel representing the average value or more into pixels is referred to as the thresholding technique.

For example, as shown in FIG. 7, in a 3x3 image frame, the gray level of the center pixel 22 is, for example, 10, and the average value (thresholding value or threshold value) of the gray level of the peripheral pixel of the peripheral pixel is 11 days. In this case, the center pixel 22 may be represented by the digital value 0. When the gray level of the center pixel is, for example, 15, the center pixel 22 may be represented by the digital value 1 because the center pixel 22 is larger than the threshold value 11. . In FIG. 7, the threshold value for the pixel 21 can be obtained by averaging the gray level values of the peripheral pixels, for example, (11, 12, 11, 32, 31).

On the other hand, in an image frame composed of a plurality of pixels, for example, 1024x1024 pixels, the threshold value applied to each of the plurality of center pixels is determined by the neighboring pixels surrounding the pixel, and thus the threshold values for all the pixels forming the image frame. May be different from each other, and successively obtained threshold values for each of the plurality of center pixels are called dynamic threshold values. Therefore, applying dynamic thresholding to an image frame means comparing the dynamic threshold value calculated for all pixels in the image frame with the gray level value of the corresponding center pixel, and then extracting the threshold value or more as a pixel as described above. Means that.

On the other hand, the image obtained by the camera is affected by the focal length at the time of shooting. When taking a picture using a camera, if the focus (focal length) is set closer or farther, the image of the subject is blurred and taken (see FIG. 3). In this case, the focus is out of focus. That is, since the difference between the gray level values with the neighboring pixels is small, the gray level value change of the image is smoothly continued.

On the other hand, if the focal length is adjusted according to the position of the subject, an accurate image of the subject may be obtained (see FIG. 5). In this case, it is said that the focus is well achieved and the photographing is performed without the image of the subject being blurred. That is, since the difference between the gray level values with the neighboring pixels is large, the gray level value change of the image changes abruptly over the entire image frame.

On the other hand, when the target subject is photographed without blurring the image, it means that high frequency components appear mainly in the subject part, and when the image is blurry, it is interpreted that low frequency components appear mainly on the subject and its surroundings. Various methods for detecting a focal length using these characteristics have been disclosed. However, in such a method, a process such as Fourier transform is required to obtain low frequency and high frequency components directly from an image. This needs to be added, and since a plurality of processes are added according to the addition of a plurality of components, there is a problem in that real-time processing of the image becomes difficult.

The present invention is to solve the above problems, the cost of the device configuration and increase in the volume of the device is reduced as a number of hardware configuration is not required, and in real time through a simple process accompanying a simple configuration An object of the present invention is to provide an image focus detecting apparatus and an image focus detecting method for adjusting a focal length by using dynamic thresholding capable of setting an optimal focal length for a subject.

In order to achieve the above object, the present invention is to select the correct focal length (r) for the subject that can be one of a plurality of inaccurate focal length (r ') while the lens is shifted with respect to the subject A camera for capturing an image and each image signal photographed from the camera according to the various focal lengths r 'are processed to obtain a digital image frame signal of the subject and a focal length r' signal corresponding to each frame signal. A dynamic thresholding circuit for performing a dynamic thresholding process on a plurality of image frames inputted from the processing circuit by using a generated video signal processing circuit and a dynamic thresholding technique, wherein the dynamic thresholding circuit obtains an image to which dynamic thresholding is applied; A pixel calculator that counts the number of pixels of a dynamic thresholded image, and adjusts the position of the lens of the camera Motor for controlling a focal length r ', a pixel number signal for each image frame transmitted from the pixel calculator, and a focal length r' signal corresponding to each image frame transmitted from the image signal processing circuit. In consideration of this, it provides a video focus detection device comprising a focal length adjuster for transmitting a control signal of the motor to the motor driver.

The focal length adjuster of the present invention compares the count signal input from the calculator, selects an image frame having the largest number of pixels, and selects one of the focal lengths r 'corresponding to each frame input from the image signal processing circuit. The focal length r that matches the image frame having the largest number of pixels selected in the comparison process is selected, and the selected focal length r signal is transmitted to the motor driver.

According to another embodiment of the present invention, in the camera to shoot the image of the subject by selecting the optimal focal length (r) of the inaccurate focal length while adjusting the inaccurate focal length (r ') for the subject, the subject Detecting a plurality of subjects for each of a plurality of incorrect focal lengths and collecting a plurality of subjects images; and digitally converting the collected images of the plurality of subjects, the plurality of incorrect focal length signals and image frame signals for each focal length. Generating a number of pixels; applying dynamic thresholding to the plurality of digitally converted image frames; counting the number of pixels in the plurality of image frames to which dynamic thresholding is applied; Selecting an image frame having a maximum focal length when collecting the image frame having the largest number of pixels and (r) determining the optimal focal length (r). .

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

1 is a block diagram of an image focus detection apparatus according to the present invention for automatically detecting a focus based on an image to which dynamic thresholding is applied, a camera 110, an image signal processing circuit 120, a dynamic thresholding circuit, and a pixel. The calculator 140, the focal length adjuster 160, and the motor driver 150 are shown.

Here, the camera 110 is a device for capturing an image of the subject, and according to the operation of the motor, not shown, as shown in FIG. 2, for example, the lens 20 is moved toward the subject 10 (in the A direction). Selecting the correct focal length r for the subject 10, which may be one of a number of incorrect focal lengths r 'while reversing.

In Fig. 2, the lens 20 is adjusted to show that the focal length f is at the B position, with the focal length r being set correctly, and inaccurate when the focal f 'is not at the B position. It is shown in the state set to one focal length r '. On the other hand, for example, the forward and backward operation of the lens 20 is performed under the control of the motor driver 150.

Here, each analog image signal photographed from the camera 110 according to the various focal lengths r 'is input to the image signal processing circuit unit 120 performing A / D conversion or other signal processing. A digital image frame of the subject 10 and a focal length r 'signal corresponding to each frame signal are generated.

Meanwhile, the dynamic thresholding circuit 130 performs a dynamic thresholding process on a plurality of image frames (or all pixels of the frame) input from the processing circuit 120 by using the dynamic thresholding technique described above. An image to which dynamic thresholding is applied, in which only a predetermined number of pixels, for example, a pixel having a threshold value or more, is displayed among all pixels in each frame, is obtained.

Here, FIG. 4 is an image in which dynamic thresholding is applied to an experimental image frame in which the focal length shown in FIG. 3 is not correct. Since the focal length r 'is not correct, the value of each pixel in the image frame is, for example, the value of the neighboring pixel. It becomes less than the dynamic threshold value calculated | required as the average of gray level value (for example, represented by the digital value 0), and shows the state where relatively few pixels were detected when the dynamic thresholding technique was applied.

In addition, FIG. 6 is an image in which dynamic thresholding is applied to an image frame in which the focal length r shown in FIG. 5 is correct. Since the focal length r is well fitted, the value of each pixel in the image frame is, for example, the neighboring pixel. When the dynamic thresholding method is equal to or greater than the dynamic threshold value calculated as an average of gray level values of (e.g., denoted by the digital value 1), a relatively large number of pixels are detected in comparison with FIG.

Meanwhile, the pixel calculator 140 calculates (counts) the number of pixels of the dynamic thresholding image, and the motor driver 150 adjusts the position of the lens 20 of the camera to focal length r. Adjust ').

In addition, the focal length adjuster 160 is a pixel number signal for each image frame transmitted from the pixel calculator 140, for example, detected at each focal length, and each image transmitted from the image signal processing circuit 120. In consideration of each focal length r 'signal for a frame, the motor driver 150 transmits a focal length r signal of an image frame having a maximum number of pixels.

Hereinafter, referring to a specific operation of the apparatus for detecting an image focus according to the present invention, first, when the camera 110 is operated to photograph the subject 10, the motor driving unit 150 is located at the position A of the first lens 20. The camera 110 detects an image signal of the subject at various focal lengths r 'and transmits the image signal to the processing circuit unit 120 at the focal length r'.

For example, as the lens is moved from the initial focal length of the camera, the focal length r 'is changed to 2, 3, 4, mm to detect an image frame according to each changed focal length.

In this case, when the focal length r is correct, for example, when the focal length r is 3 mm, the digital image frame generated by the processing circuit unit 120 does not bleed the image of the subject 10 as shown in FIG. 5. When the focal length r 'is not correct, for example, when the focal length r' is 2 or 3 mm, the image is blurred as shown in FIG. 3.

Each of the image frames according to the focal lengths digitally processed by the processing circuit unit 120 is subjected to the dynamic thresholding process as described with reference to FIG. 7 in the dynamic thresholding circuit unit 130, and focuses the respective image frames. Distance information (eg, 2, 3, 4 mm) is transmitted to the focal length adjuster 160. In this case, the pixel calculator 140 counts the number of pixels for each of the thresholded image frames (for example, counts the number of pixels having a digital value of 1), and the count signal is input to the focal length adjuster 160. do.

Here, the focal length controller 160 compares the count signal input from the calculator 140 to select an image frame having the largest number of pixels, and according to each frame input from the image signal processing circuit 120. Among the focal lengths r ', a focal length r, for example, 3 mm, that matches an image frame having the largest number of pixels selected in the comparison process is selected. Since the selected focal length r 3 mm is transmitted to the motor driver 150, and the motor driver 150 currently has a focal length of 4 mm, the lens 20 of the camera 110 is driven by driving the motor. ) Is advanced by 1 mm so that it is adjusted to an optimal focal length r, for example 3 mm.

As described above, according to the automatic focus detection apparatus using the dynamic thresholding according to the present invention, the camera focuses by calculating the focal length from the input image itself to the subject in real time without a separate focusing device or a large calculation load. And, accordingly, it can be simply implemented in hardware, and there is an effect of adjusting the focus or focal length with the subject in real time.

The technical idea according to the present invention can be variously applied to a device such as a video camera, a digital camera, a camera mobile phone.

Claims (4)

Taking an image of the subject by selecting the correct focal length r for the subject 10, which may be one of a plurality of inaccurate focal lengths r 'as the lens 20 is shifted with respect to the subject 10 Camera 110, Image signals generated by the camera 110 according to the various focal lengths r 'to generate digital image frame signals of the subject and focal length r' signals according to the frame signals. Processing circuit 120, Dynamic thresholding circuit unit 130 to perform a dynamic thresholding process for a plurality of image frames input from the processing circuit unit 120 by using a dynamic thresholding technique, to obtain an image to which dynamic thresholding is applied; A pixel calculator 140 for counting the number of pixels of the dynamic thresholding image; A motor driver 150 for adjusting a focal length r 'by adjusting the position of the lens 20 of the camera;  In consideration of the pixel number signal for each image frame transmitted from the pixel calculator 140 and the focal length r 'signal corresponding to each image frame transmitted from the image signal processing circuit 120, the motor driving unit ( And a focal length adjuster (160) for transmitting a control signal of the motor to the motor (150). The apparatus of claim 1, wherein the focal length adjuster 160 selects an image frame having the largest number of pixels by comparing the count signal input from the calculator 140, and inputs the image signal from the image signal processing circuit 120. The focal length r corresponding to the image frame having the largest number of pixels selected in the comparison process among the focal lengths r 'for each frame is selected, and the selected focal length r signal is transferred to the motor driver 150. Image focus detection apparatus characterized in that the transmission to. The method of claim 2, wherein the motor driver 150 adjusts the lens 20 of the camera 110 according to the focal length r signal transmitted from the focal length adjuster 160 so that the camera is optimal. An image focus detection apparatus, characterized in that for adjusting the focal length (r). In the camera that shoots the image of the subject by selecting the optimal focal length (r) of the inaccurate focal length while adjusting the inaccurate focal length (r ') with respect to the subject 10, Collecting a plurality of subject images by detecting images of the subject at a plurality of inaccurate focal lengths; Digitally converting the collected images of the plurality of subjects to generate the plurality of incorrect focal length signals and image frame signals for each focal length; Applying dynamic thresholding to a plurality of digitally converted image frames; Counting the number of pixels in the plurality of image frames to which dynamic thresholding is applied, Selecting an image frame having the largest number of pixels among the plurality of image frames; And setting the focal length (r) at the time of collecting the image frame having the largest number of pixels as the optimum focal length (r).

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