KR101128517B1 - AF method for digital image processing device - Google Patents

Abstract

The automatic focus adjustment method of the digital image processing apparatus according to the present invention comprises the steps of: determining whether the backlight conditions; Storing automatic exposure adjustment information when it is determined that the backlighting condition is performed; Performing autoexposure adjustment for auto focus by adjusting the brightness of the subject portion to a reference brightness; Performing auto focus; And reducing the stored automatic exposure adjustment information.

According to the automatic focusing method of the digital image processing apparatus of the present invention, accurate automatic focusing can be performed even in backlight conditions.

Description

Automatic focusing method of digital image processing device {AF method for digital image processing device}

1 is a block diagram illustrating a configuration of an exemplary digital camera to which the concept of the present invention can be applied.

2 is a flowchart for explaining an automatic focus adjusting method of a digital image processing apparatus according to an exemplary embodiment of the present invention.

3 is a diagram illustrating an example of a rear surface of a digital camera as an example of a digital image processing apparatus to which the automatic focus adjustment method of the present invention may be applied.

4 is a preview image displayed on the LCD monitor of FIG. 3.

5 is a preview image of automatic exposure control for accurate autofocus control in backlight conditions.

6 illustrates a multi-field metering window for determining backlight conditions.

7 is a graph showing the result of AF performed by the prior art under backlight conditions.

8 is a graph showing the result of performing AF according to the present invention under backlight conditions.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital image processing apparatus, such as a digital camera, and more particularly to an automatic focusing method of a digital image processing apparatus.

In the digital camera, auto exposure (AE) control is a function for making the optimum amount of light incident to an image pickup device such as a charge coupled device (CCD) through a lens.

On the other hand, the backlight condition refers to a case in which a ray of light is shining toward the camera from the back of the subject. In the backlight condition, the luminance difference is large in the screen. Therefore, in the conventional digital camera, when shooting under backlight conditions, the surroundings of the subject are very bright and the subject portion is darkened.

Especially in auto focus (AF) of TTL (through the lens) method, focus value data is extracted based on contrast ratio, which focuses on dark areas with low contrast ratio. The value data is inaccurate. Therefore, AF is incorrectly performed because the subject part is dark under backlight conditions.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide an automatic focus adjustment method of a digital image processing apparatus capable of performing accurate automatic focus adjustment even in a back light condition.

According to an aspect of the present invention, there is provided a method for automatically focusing a digital image processing apparatus, the method including: (a) determining whether a backlight condition is applied; (b) storing the automatic exposure adjustment information when it is determined that the backlighting condition is performed; (c) performing autoexposure adjustment for auto focus by adjusting the brightness of the subject portion to the reference brightness; (d) determining that it is not a backlight condition or performing autofocus adjustment after step (c); And (e) reducing the stored automatic exposure adjustment information.

In the step (a), the backlighting condition may be determined using the multi-field metering information.

In the step (c), the automatic exposure adjustment for the automatic focus adjustment may be performed by adjusting the AGC gain of the photoelectric conversion signal to a predetermined value or more.

In the step (c), the automatic exposure adjustment for the automatic focus adjustment may be performed by adjusting the exposure time to a predetermined period or more.

Hereinafter, the configuration and operation of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote components that perform the same function.

1 is a block diagram illustrating a configuration of an exemplary digital camera to which the concept of the present invention can be applied.

The optical system OPS including the lens unit and the filter unit optically processes light from a subject. The lens unit in the optical system OPS includes a zoom lens, a focus lens, and a compensation lens.

A photoelectric conversion unit (OEC) of a charge coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS) converts light from an optical system (OPS) into an electrical analog signal. Here, the digital signal processor 7 controls the timing circuit 2 to control the operation of the photoelectric converter OEC and the analog-to-digital converter 1. The CDS-ADC (Correlation Double Sampler and Analog-to-Digital Converter) element 1 as an analog-to-digital converter processes the analog signal from the photoelectric converter (OEC), removes the high frequency noise, and adjusts the amplitude. (auto gain control, AGC) and then convert to a digital signal. The digital signal processor 7 processes the digital signal from the CDS-ADC element 1 to generate a digital image signal classified into luminance and chroma signals.

The DRAM (Dynamic Random Access Memory) 4 temporarily stores digital image signals and other temporary processing data from the digital signal processor 7.

The EEPROM (Electrically Erasable Programmable Read Only Memory) 5 stores algorithms and setting data necessary for the operation of the digital signal processor 7. The memory card of the user is attached to and detached from the memory card interface 6.

The digital image signal from the digital signal processor 7 is input to the LCD driver 14, whereby the image is displayed on the color LCD panel 17.

On the other hand, the digital image signal from the digital signal processor 7 can be transmitted by serial communication via the USB (Universal Serial Bus) connection 18 or the RS232C interface 8 and its connection 19, and the video filter ( 9) and through the video output unit 20 can be transmitted as a video signal.

The audio processor 13 outputs the audio signal from the microphone MIC to the digital signal processor 7 or the speaker SP, and outputs the audio signal from the digital signal processor 7 to the speaker SP.

The user input unit INP may include a shutter button, a mode selection button, a function selection button, a zoom button, a direction movement button, and the like. The user input unit INP is operated by the user to generate a command for performing each function according to the user's instruction.

The microcontroller 12 controls the lens driver 10, whereby the zoom motor M _Z , the focus motor M _F , and the aperture motor M _A are zoom lenses in the optical system OPS, The focus lens and the aperture are driven respectively. The light emitting unit LAMP driven by the microcontroller 12 may include a self-timer lamp, an auto-focus lamp, a flash standby lamp, and the like. On the other hand, the microcontroller 12 drives the flash 15 by controlling the operation of the flash controller 11 in accordance with the signal from the flash-light amount sensor 16.

The digital camera to which the present invention can be applied does not have to include all the components of FIG. 1, and those skilled in the art may delete some of the components, add another component, or modify some components according to the specification. I will understand.

2 is a flowchart for explaining an automatic focus adjusting method of a digital image processing apparatus according to an exemplary embodiment of the present invention.

The shutter input operation performed by the user includes a first shutter S1 for performing auto exposure (AE) adjustment and an auto focus (AF) adjustment, and a second shutter S2 for photographing and storing an image. There is).

First, the first shutter (S1) is input to determine whether the backlight condition (S100).

If it is determined that the backlight conditions, the current AE information is stored (S102).

AE adjustment for AF is performed by adjusting the subject brightness to the reference brightness (S104).

The backlight condition refers to a case in which a ray of light is shining toward the camera from the back of the subject. In the backlight condition, the luminance difference is large in the screen between the divided windows. Therefore, in the conventional digital camera, the photographing is performed under backlight conditions without any additional correction. Thus, the surroundings of the subject are very bright and the subject portion is darkened as shown in FIG. 4. FIG. 4 is a preview image displayed on the LCD monitor of FIG. 3, in which the background is very high brightness under backlight conditions, while the AE control is performed with low brightness.

In TTL AF, the focus evaluation value is extracted based on the contrast ratio, and the focus position is determined as the focus position. When the contrast ratio of the subject part is low in backlight conditions, the focus evaluation data is shown in FIG. 7. There is a problem that becomes incorrect. This will be described again with reference to FIG. 7.

Accordingly, the present invention is characterized by separately performing AE adjustment for accurate AF by adjusting the luminance of the subject portion to the reference luminance.

AF is performed after step S104 (S106). If it is not a backlight condition, AF is performed without performing steps S102 and S104. AF can be performed, for example, by the so-called high frequency climbing method of the TTL method. The AF of the TTL method determines the position where the high frequency component of the subject image is maximized as the focus position.

After the step S106 is reduced to the stored AE information (S108). In the present invention, step S104 is a step for performing accurate AF. After AF is performed in step S106, the step S104 should be reduced to the previous AE state. In step S104, the luminance of the subject portion is forcibly increased to perform distorted AE for accurate AF. Therefore, the camera returns to the previous AE state to capture the appropriate brightness.

When the second shutter S2 is input by the user's operation after step S108, the camera performs shooting and stores the image.

Hereinafter, a method for determining backlight conditions performed in step S100 will be described in detail. In step S100, the backlighting condition may be determined using, for example, multi-part metering information.

In multi-part metering, each area of the screen divided into several parts can be individually metered, the average value can be calculated to adjust the exposure, and the exposure difference of each part can be examined and the exposure can be automatically adjusted.

The backlight condition refers to a case in which a ray of light is shining toward the camera from the back of the subject. In the backlight condition, the luminance difference is large in the screen between the divided windows.

The determination of such backlight conditions is performed by using a window used in AF and a window used in AE. That is, in determining the backlight condition, information on the total luminance is obtained using the full multi-segment window used in the AE, and luminance information on the subject is obtained using the center window used in the AF.

FIG. 6 shows a multi-sided metering window for determining backlight conditions, in which five windows hatched at the center are used for AF.

In FIG. 6, the image grating is composed of 7 × 5 gratings horizontally and vertically. Therefore, the luminance value of each divided window may be represented by K (1,1), K (1,2), ..., K (7,5).

Backlight conditions determination method using the exemplary multi-splitting window of Figure 6 will be described by the following equations (1) to (3).

First, the overall luminance level can be expressed by, for example, Equation 1 below.

The luminance level of the subject portion by the AF window may be expressed by, for example, Equation 2 below.

In operation S100, when the following Equation 3 is satisfied using Equations 1 and 2, it may be determined as a backlight condition.

Equation 3 means that it is determined that the backlighting condition is different if the difference between the exposure values of the five central windows of the subject portion and the other windows is a predetermined value, for example, 2EV or more.

3 is a diagram illustrating an example of a rear surface of a digital camera as an example of a digital image processing apparatus to which the automatic focus adjustment method of the present invention may be applied.

At the rear of the digital camera of Fig. 3, the viewfinder 100, autofocus lamp 101, flash status lamp 102, mode dial 103, wide-angle zoom button 104, telephoto zoom button 105, 5 Function button 106, speaker 107, external output terminal 108, DC power input terminal 109, playback mode button 110, LCD monitor 111, display the currently set shooting information on the monitor or LCD monitor An LCD button 112, a manual focus button 113, a pause button 114 and the like are provided to turn off / turn on.

Here, the five function button 106 is provided with a menu entry / confirmation button and up, down, left, and right buttons at the center. When the menu is displayed on the monitor, the up, down, left and right buttons can function as special function buttons instead of directional movement.

The various function buttons shown in FIG. 3 may be provided to perform two or more complex functions in addition to the functions shown in the names.

Light incident through the digital camera optical system (OPS in FIG. 1) is photoelectrically converted in the photoelectric conversion unit (OEC in FIG. 1), AGC gain adjustment and digital signal in the CDS-ADC (1 in FIG. 1), and DSP It is displayed as a preview on the LCD monitor 111 through the AE control (7 of FIG. 1).

In the case where the digital camera displays an image of 30 frames per second in the preview, the exposure time of the preview image is about 30 msec maximum. If the preview image is dark even when the exposure time is maximized in the dark, the preview image is brightly corrected by adjusting the AGC gain.

The image displayed on the LCD monitor 111 of FIG. 3 is an image of a typical backlight condition in which the subject is facing the sun.

Under such backlight conditions, since the luminance of the entire image is high, the exposure time is reduced to, for example, 10 msec or less in the preview state. In this case, the luminance of the subject becomes relatively low.

FIG. 4 is a preview image displayed on the LCD monitor of FIG. 3, in which the background is very high brightness under backlight conditions, while the AE control is performed with low brightness.

FIG. 5 is a preview image subjected to AE control for accurate AF under backlight conditions in step S104. Compared to FIG. 4, the subject is not only a background but also a subject part having high luminance, so that accurate AF may be performed. After AF is performed in the state of FIG. 5 (S106 in FIG. 2), the AF is restored to the original AE state again (S108).

Hereinafter, embodiments of performing autoexposure adjustment for adjusting the brightness of the subject part for autofocus adjustment in step S104 will be described in detail.

In step S104, the luminance of the subject portion may be increased by, for example, adjusting the AGC gain of the photoelectric conversion signal to a predetermined value or more and adjusting the exposure time to a predetermined period or more.

First, a method of increasing the AGC gain of the photoelectric conversion signal output from the photoelectric conversion unit (1 in FIG. 1) will be described as an embodiment of step S104.

In this method, the exposure time and the AGC gain are determined by the total brightness incident through the camera's optical system (OPS in FIG. 1), thereby fixing the exposure time in an environment in which a certain level of brightness is maintained. In addition, the AGC gain is compensated for acquiring only the luminance information of the subject portion (T of Equation 2) to maintain the luminance of the subject portion above a predetermined level. That is, the reference is made to the overall luminance S of Equation 1 described above under backlight conditions. After fixing the exposure time, the AGC gain is increased in order to adjust the luminance T of the subject portion to the reference luminance S level, whereby the luminance difference between the reference luminance S and the subject portion T (Equation 3). ΔEV).

Next, as another embodiment of step S104, a method of lengthening an exposure time is first performed by determining an exposure time and an AGC gain by a total brightness incident through an optical system of the camera (OPS of FIG. 1). Lock the AGC gain under conditions that maintain brightness. Then, only the luminance information of the subject portion (T in Equation 2) is obtained to compensate the exposure time in order to maintain the luminance of the subject portion above a predetermined level. That is, the reference is made to the overall luminance S of Equation 1 described above under backlight conditions. After fixing the AGC gain, the exposure time is lengthened to adjust the luminance T of the subject portion to the reference luminance S level, whereby the luminance difference between the reference luminance S and the subject portion T (Equation 3). ΔEV).

7 is a graph showing the result of AF performed by the prior art under backlight conditions. Each graph represents the focus estimate in five central windows for AF. 7 is a result of performing AF in the state of FIG.

In the TTL-type AF, the point where the high frequency component of the image of the subject input, that is, the focus evaluation value, is maximized while the focus lens is moved is determined as the focus position. When the lens is in the focus position, the contour of the subject image is sharpest, so the high frequency component is maximized. The focus evaluation value tends to increase as the lens approaches the focus position, and the focus evaluation value tends to decrease as the lens passes through the focus position and moves away from the focus position. In this way, the position inverting from the tendency of increasing the focus value to the decreasing tendency, that is, the maximum vertex position of the focus evaluation value is detected as the focus position.

Referring to FIG. 7, it can be seen that the maximum value of the focus evaluation value is not properly detected in each AF window.

The inaccurate focus evaluation data under such backlight conditions is caused by the TTL AF to extract the focus evaluation data based on the contrast ratio. In other words, AF is incorrectly performed because the subject part is dark under backlight conditions.

8 is a graph illustrating a result of AF performed after adjusting luminance of a subject part under backlight conditions. Each graph represents the focus estimate in five central windows for AF. 8 is a result of performing AF in the state of FIG.

Referring to FIG. 8, it can be seen that the maximum value of the focus evaluation value in each AF window is formed at the focus lens FP position, so that the focus position can be accurately detected even in a back light condition.

The above embodiments have been described with reference to a digital camera as an example of a digital image processing apparatus to which the present invention can be applied, but are not limited thereto. Those skilled in the art will appreciate that the present invention is applicable to mobile phones, personal digital assistants (PDAs), etc., which have built-in digital camera functions to perform AE and AF functions when capturing images. In addition, the present invention can be applied to a portable multimedia player (PMP), which has recently been in the spotlight. PMP is a portable, next-generation multimedia player with complex functions such as music playback, broadcast reception, games, electronic dictionary, video playback, and digital camera such as MP3. As described above, the concept of the present invention may be applied to a PMP in which an image capturing function is built in a digital camera.

The best embodiments have been disclosed in the drawings and specification above. Although specific terms have been used herein, they are used only for the purpose of describing the present invention and are not used to limit the scope of the present invention as defined in the meaning or claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, according to the automatic focusing method of the digital image processing apparatus of the present invention, accurate automatic focusing can be performed even in a back light condition.

The invention is not limited to the examples described above and represented in the drawings. Those skilled in the art taught by the above-described embodiments, many modifications to the above-described embodiments are possible by substitution, erasure, merging, etc. within the scope and object of the present invention described in the following claims.

Claims (4)

(a) determining whether it is a backlight condition; (b) storing the automatic exposure adjustment information when it is determined that the backlighting condition is performed; (c) performing autoexposure adjustment for auto focus by adjusting the brightness of the subject portion to the reference brightness; (d) determining that it is not a backlight condition or performing autofocus adjustment after step (c); And and (e) reducing the stored autoexposure adjustment information to the digital image processing apparatus. The method of claim 1, wherein step (a) A method for autofocusing a digital image processing apparatus, comprising: determining backlighting conditions using multi-part metering information. The method of claim 1, wherein step (c) A method for autofocusing a digital image processing apparatus, characterized by performing autoexposure adjustment for autofocusing by adjusting the AGC gain of the photoelectric conversion signal to a predetermined value or more. The method of claim 1, wherein step (c) An autofocus adjustment method of a digital image processing apparatus, characterized by performing autoexposure adjustment for autofocus adjustment by adjusting an exposure time to a predetermined period or more.

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