KR20040042004A - Controlling apparatus and method of auto focus for digital camcoder - Google Patents

Abstract

PURPOSE: An apparatus and a method for controlling auto-focus of a digital camcorder are provided to allow a user to photograph an image even in a dark place. CONSTITUTION: A digital camcorder includes a lens unit(100), a charge coupled device (CCD)(110), an automatic gain controller(120), an analog-digital converter(130), a digital signal processor(140), a microcomputer(150), and a focus lens motor driver(160). The CCD converts an optical signal of a object, received through the lens unit, into a video signal. The automatic gain controller samples the video signal and controls the gain of the video signal. The analog-digital converter converts the video signal into a digital signal. The digital signal processor encodes the digital signal and processes the digital signal into color and luminance signals. The focus motor driver drives a focus lens in response to a focusing control signal received from the microcomputer to bring an object to a focus.

Description

Control apparatus and method of auto focus for digital photographing apparatus {Controlling apparatus and method of auto focus for digital camcoder}

The present invention relates to an auto focus control apparatus and a control method of a photographing apparatus such as a camcorder, particularly when shooting in a normal auto focus state in various situations, such as when there is a spot light in a low illuminance state. The present invention relates to an auto focus control apparatus and a control method.

In general, a camcorder (CAMCORDER) is a video and audio signal processing apparatus capable of recording video and audio signals on a provided recording medium and reproducing the recorded signals. In other words, the camcorder not only has the functions of a general camera but also has a function of a recorder capable of recording a photographed subject. By using such a camcorder, a user can photograph and record a desired subject, and then check the photographed subject again.

FIG. 1 is a diagram illustrating a characteristic change of auto focus data amount when a subject is photographed in a normal auto focus state, and FIG. 2 is a diagram illustrating a characteristic change of auto focus data amount when spot light is photographed. It is. 1 and 2, the horizontal axis represents the position of the focus lens, and the vertical axis represents the autofocus data amount (hereinafter referred to as AF data amount) accordingly. In the conventional camcorder, when photographing a subject in a normal autofocus state, it is recognized that focus is achieved at a position A where the amount of AF data is the largest as shown in FIG. 1. The reason for this is that when defocusing in the normal state, the shape of the subject becomes clumped and the distinction of contrast is unclear, so the amount of AF data decreases, and when the focus is achieved, the distinction of contrast is clear. This is because the amount of AF data increases as shown in FIG.

On the other hand, if you are shooting an actor who is illuminated on a theater stage, or if you are shooting a subject with a car headlight, that is, if you are shooting a dark spot light in the surroundings, look at the AF data amount and the position of the focus lens. As shown in 2. That is, in comparison with reference to the focused positions A and B in FIGS. 1 and 2, the amount of AF data in autofocus control in a normal state and autofocus control in a spot light is almost in inverse relationship. can see. Therefore, in the conventional camcorder, when the normal autofocus is performed in the spot light state, the subject is defocused by focusing on the position where the amount of AF data is the highest.

In order to overcome this problem, Korean Patent Laid-Open Publication No. 1997-031236 discloses a function of performing normal autofocus in consideration of a spot light. That is, when photographing a subject in which a spot light exists, the amount of autofocus data becomes larger when the focus is slightly out of focus than in a precisely focused state, but the luminance component above the threshold is also increased. Using this fact, if it was determined that spot light photography was taken, the focus lens was driven in accordance with the amount of clip data obtained by luminance data, and the focus lens was stopped at the clip data position of the lowest value to focus on the subject.

However, when a brightly colored subject is projected in a very dark situation, the amount of autofocus data becomes larger when the focus is slightly out of focus than when the spot is lit. However, in the case of clip data, there is a tendency to decrease as opposed to when there is a spot light. Therefore, when the subject is a bright color in a very dark situation, it is determined that the spot light exists, and when the subject is focused by stopping the focus lens at the lowest clip data position, there is a problem in that the focus is not correct.

The present invention has been made to solve the above problems, an object of the present invention is to always focus correctly even when shooting a dark place in the normal autofocus state, the spotlight is present, or a brightly colored subject It is to provide an auto focus control method so that the user can be adjusted so that the user does not have inconvenience in shooting in a dark place.

1 is a characteristic diagram of AF data amount change when photographing a general subject in normal autofocus;

2 is a characteristic diagram of AF data amount change during spot light shooting;

3 is a characteristic diagram of change in relative ratio of AF data during spot light shooting;

4 is a block diagram showing an auto focus control apparatus according to the present invention; and

5 is a flowchart illustrating an auto focus control method by the auto focus control apparatus illustrated in FIG. 4.

A digital photographing apparatus according to the present invention for achieving the above object is a DSP for encoding a digitized captured image signal, outputting the AF data obtained by converting the contrast data from the captured image signal, the position of the focus lens to focus the subject And a microcomputer for calculating a relative ratio of output signals having different frequencies constituting AF data, and outputting a focusing control signal so that the focus lens is positioned at a position where the relative ratio becomes a peak. It is done.

On the other hand, according to the present invention, the step of reading the AF data output by converting the contrast data from the digitized captured image signal of the digital photographing device, calculating the relative ratio of the output signal having a different frequency constituting the AF data, spot Determining whether to take light or not; and if the spot light is determined in the determining step, adjusting the position of the focus lens so that the focus lens is positioned at a position where the relative ratio becomes a peak. A focus control method is provided.

The determining may include determining spot light imaging when the relative ratio decreases when the AF data increases.

The adjusting of the position may include moving the focus lens in a direction in which the relative ratio increases when it is determined that the spot light is photographed, and stopping the focus lens at a position before the decrease start point when it is determined that the relative ratio starts to decrease. It is characterized by.

As a result, even when the spot light is photographed, the subject to be photographed can be accurately focused.

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

4 is a block diagram showing a schematic configuration of a camcorder which is a digital photographing apparatus. As illustrated, the digital photographing apparatus includes a lens unit 100, a CCD 110, an auto gain controller (AGC) 120, an analog-to-digital converter (ADC) 130, a digital signal processor (DSP) 140, The microcomputer 150 and the focus lens motor driver 160 are included.

The lens unit 100 includes a focus lens, a zoom lens and an aperture for controlling the amount of light while zooming in and out of a subject while moving forward and backward in the optical axis direction and receiving an image of the subject.

The CCD 110 operates an optical signal of a subject that is enlarged and reduced through the lens unit 100 according to horizontal and vertical imaging driving pulses generated by a timing generator (not shown). Is converted into a captured image signal and output. AGC (Auto Gain Control) samples the image signal captured by the CCD 110, and gains and outputs it. The analog-to-digital converter (ADC) 130 converts the captured image signal of one field, which is gain-adjusted by the AGC 120, into a digital signal.

The digital signal processor (DSP) 140 encodes the digitized captured image signal for one field, processes it as a color or luminance signal in NTSC or PAL format, and outputs it to a VCR (not shown). The DSP 140 outputs AF (Auto Focus) data obtained by converting contrast of the captured image signal to the microcomputer 150. The AF data is output as two signals having different frequencies, such as f1 and f2 shown in FIGS. 1 and 2.

The microcomputer 150 controls the overall operation of the camcorder by embedding a memory in which a control program according to an embodiment of the present invention is stored. In addition, the microcomputer 150 calculates a relative ratio f2 / f1 of the AF data f1 and f2 input from the DSP 140 and outputs a focusing control signal according to the relative ratio f2 / f1.

The focus motor driver 160 drives the focus lens in response to the focusing control signal input from the microcomputer 150 to focus the subject.

When a general subject is photographed in the normal autofocus state using the camcorder configured as described above, the AF data amount change characteristic as shown in FIG. 1 is shown. In spot light imaging, the AF data amount change characteristic as shown in FIG. 2 is shown. 1 and 2, the horizontal axis represents the position of the focus lens, and the vertical axis represents the amount of AF data according to the position of the focus lens. Two signals f1 and f2 are output according to the frequency of the output signal.

As shown in FIG. 1, when the defocus is performed in the normal state without considering the spot light, the shape of the subject becomes clumped and the contrast is unclear, so the amount of AF data is reduced. As the focus is focused, the shape of the subject becomes clearer, and the distinction of the contrast becomes clear. According to such a change characteristic of the amount of AF data, in the case of normal autofocus, the focus lens is stopped at a position where the AF data amount becomes a peak.

As shown in Fig. 2, during spot light imaging, the change characteristic of the AF data amount is almost inversely proportional to that in the normal state. However, FIG. 3 is a graph showing the relative ratios f2 / f1 of the AF data f1 and f2 during spot light photographing. As shown in FIG. 3, the relative ratio increases as the subject is focused even when spot light photographing is performed.

The present invention controls the autofocus by using the change characteristic of the relative ratio.

Hereinafter, an autofocus control process for spot light photographing according to an exemplary embodiment of the present invention will be described with reference to FIG. 5.

First, the microcomputer 150 checks whether the current camcorder mode is the camera mode in step 200 and proceeds to step 210 in the camera mode. In operation 210, the microcomputer 150 reads AF data input through the DSP 140 and calculates a relative ratio f2 / f1 of AF data input at two frequencies f1 and f2.

In operation 220, the microcomputer 150 determines whether spot light is photographed. In the determination method, if the AF data decreases when the relative ratio f2 / f1 increases, it is determined that spot light imaging is performed. If it is determined in step 220 that the specific subject is being shot with the spot light, the microcomputer 150 proceeds to step 230 and outputs a control signal to the focus lens motor driver 160 to move the focus lens in a direction in which the relative ratio increases. The peak point while driving is examined in step 240.

If the relative ratio f2 / f1 of the AF data f1 and f2 continuously increases and decreases in step 240, it is determined that the peak of the relative ratio is determined, and the microcomputer 150 proceeds to step 250 in a position where the relative ratio is peaked. After stopping the focus lens, the auto focus control process at the time of spot light shooting according to the embodiment of the present invention is terminated. As a result, the subject to be photographed can be accurately focused even during spot light shooting.

Meanwhile, in the embodiment of the present invention, the position of the focus lens having the highest relative ratio f2 / f1 is searched while driving the focus lens in the direction in which the relative ratio f2 / f1 increases. However, if it is determined that the spot light is photographed, the AF lens f1 and f2 are automatically stored by sequentially driving the focus lens to the entire region where the focus lens can be driven, and the relative ratio f2 / f1 of f1 and f2 is automatically stored. ), The subject may be focused by reading the highest value among the calculated relative ratios f2 / f1 and stopping the focus lens at a position corresponding thereto.

In addition, although the preferred embodiment of the present invention has been shown and described above, the present invention is not limited to the above-described specific embodiment, the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Of course, various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or prospect of the present invention.

As described above, the present invention uses the property that the subject imaged by the spot light is focused at the peak of the relative ratio of the AF data, thereby stopping the focus lens at a position where the relative ratio of the AF data is peak, thereby subjecting the subject to spot light shooting. It is possible to focus precisely and to focus accurately even when photographing a brightly colored subject in a dark place.

Claims (4)

In a digital photographing apparatus, A DSP for encoding the digitized captured image signal and outputting AF data obtained by converting contrast data from the captured image signal; A focus motor driver for adjusting a position of the focus lens to focus on the subject; And a microcomputer that calculates a relative ratio of output signals having different frequencies constituting the AF data, and outputs a focusing control signal so that the focus lens is positioned at a position where the relative ratio becomes a peak. Auto focus control. Reading the AF data output by converting the contrast data from the digitized captured image signal of the digital photographing apparatus; Calculating a relative ratio of output signals having different frequencies constituting the AF data; Determining whether to take a spot light; And And adjusting the position of the focus lens such that the focus lens is positioned at a position where the relative ratio becomes a peak when it is determined that the spot light is photographed in the spot light photographing determination step. Control method. The method of claim 2, And in the spot light photographing determination step, determine that spot light photographing is performed when the relative ratio decreases when the AF data is increased. The method of claim 2, In the adjusting of the position of the focus lens, if it is determined that the spot light is photographed, the focus lens is moved in a direction in which the relative ratio increases, and if it is determined that the decrease of the relative ratio starts, the focus is at the position before the decrease start point. An auto focus control method for a digital photographing apparatus, characterized by stopping a lens.