KR20010037684A - Apparatus for correlating of exposure automatically of a digital still camera and method for performing the same - Google Patents

Abstract

PURPOSE: A method and a device for automatically correcting exposure of a digital still camera are provided to reduce an error of an exposure correction according to a luminance level difference between a subject and a background by dividing an image into areas in consideration of arrangements of a subject and a background and extracting an exact subject area from divided areas. CONSTITUTION: A CCD photographing section(100) includes an electronic shutter(130) adjusts amount of input light of a subject and a CCD pickup section(120) for picking up the input light of the subject and outputting a corresponding image signal. An analog/digital converter(200) converts the image signal form the CCD photographing section(100) into a digital image data. An exposure controller(300) extracts a subject area to be photographed among an image of one frame and calculates a luminance level distribution of the subject area. The exposure controller(300) controls an exposure correction of the extracted data of the electronic shutter(130) through a histogram analysis with respect to the luminance level.

Description

Apparatus for correlating of exposure automatically of a digital still camera and method for performing the same}

The present invention relates to an exposure compensation device and method of a digital still camera, and more particularly, to an exposure compensation device and method capable of accurately correcting the exposure of an electronic shutter using edge detection of image data in a digital still camera. will be.

It is the field of image sensor that is most practically applied to the application of the charge-coupled device (CCD) technology, which was invented by Bell et al., Boyle et al. Image sensors are used in a wide range of fields such as video cameras, surveillance cameras, medical cameras, industrial instrumentation, facsimile, image scanners, bar code readers, and the like.

Moreover, recently, CCD image sensors with optimized structures for digital still cameras have also emerged.

As such, the sharpness of image quality and the removal of color noise are essential in all optical devices using a CCD. In particular, the importance of image quality is further emphasized because a digital image recording device such as a digital still camera is used to preserve still images.

Exposure control of such a digital still camera may have various methods, but the following two methods are most frequently used.

The first method is mainly used in an optical camera. The image input through the lens is divided into regions and then the luminance level value in the effective area is controlled to an appropriate luminance level value.

The second method extracts a histogram of the luminance level of the input image and controls the data in the saturated region at a constant rate.

According to the first method, the performance varies according to the arrangement of the divided regions, and the accuracy of the exposure compensation of the corrected image is deteriorated because the average of the luminance level values is controlled in the effective region. That is, in the case of performing exposure compensation with the average value of the brightness levels, since the consideration of the brightness level distribution of the image data is not included in the exposure compensation process, the corrected data may include a light quantity shortage or a saturated region.

In addition, according to the second method, since the histogram of the image data is analyzed to always control the saturation region of the image to a predetermined ratio or less, accurate exposure compensation is achieved in the entire image in consideration of the luminance level distribution of the image data. Since there is no consideration of a region to be mainly focused on, there is a problem that inappropriate exposure compensation is performed when the luminance level difference between the background and the subject is large in the image.

Camera exposure calculation device dependent on type of scene, filed on August 28, 1992, by Daiko and Japan of Japan, and patented on August 24, 1993. to be photographed; USPN No. 5,239,333) is a photometric sensor that is segmented with this information when a photographer inputs information about the type of image to be photographed, for example, close-up, person, or landscape. Exposure control suitable for the image to be captured is performed with the input light amount information.

However, the invention of US Pat. No. 5,239,333 has a problem that a user has to input a kind of image to be photographed one by one.

In addition, an exposure calculation device for camera (USPN No. 5,319,416) filed on October 10, 1991, issued by Takada and Japan in Japan, and licensed on June 7, 1994, A photometric sensor is arranged for each area to control proper exposure through boundary extraction. According to US Pat. No. 5,319,416, which is designed on the premise of application in the proposed camera, the photometric sensor is exclusively arranged for exposure control.

There are a plurality of photometric sensors arranged in this way, but there are limitations on the number, and each photometric sensor displays the average value of the amount of light in a specific area instead of the luminance level value of one pixel, so that the correct exposure compensation for the entire image is performed. There is a problem that is not made.

SUMMARY OF THE INVENTION The present invention has been made to solve the conventional problems, and an object of the present invention is to provide an exposure compensation device capable of accurately performing exposure compensation centering on a subject area during automatic exposure control of a digital still camera. It is.

Another object of the present invention is to provide an exposure compensation method capable of accurately performing exposure compensation centering on a subject area during automatic exposure control of a digital still camera.

1 is a block diagram of an exposure compensation apparatus of a digital still camera according to an embodiment of the present invention.

2 is a flowchart illustrating an exposure compensation method of a digital still camera according to an embodiment of the present invention.

<Description of the code | symbol about the principal part of drawing>

100: CCD photographing unit 110: photographing lens

120: CCD imager 130: electronic shutter

200: analog to digital conversion unit 300: exposure control unit

400: digital control unit 500: LCD unit

600: memory unit 700: system control unit

An exposure compensation apparatus of a digital still camera according to one aspect for realizing the object of the present invention converts an image signal photographed by a CCD photographing unit into a digital image signal and performs exposure correction on the basis of this. In the exposure compensation device of a digital still camera,

A CCD photographing unit including an electronic shutter configured to perform an open / close operation to adjust a light amount of incident light, and a CCD imaging device configured to photograph a subject light incident through the electronic shutter and output a corresponding image signal;

An analog to digital converter converting the image signal output from the CCD photographing unit into digital image data; And

The subject image is extracted from the image of one frame photographed by processing the digital image data, the luminance level distribution of the subject region is calculated, and the extracted data is analyzed by the histogram of the luminance level. An exposure control unit for controlling the exposure compensation of the.

In addition, the exposure compensation method of the digital still camera according to one aspect for realizing another object of the present invention, converts the image signal photographed by the CCD photographing unit into a digital image signal based on this exposure of the CCD photographing unit In the exposure compensation method of the digital still camera performing the correction,

Extracting luminance level data from a center photometric region of the picked-up image;

Extracting a subject boundary value from the extracted luminance level data;

Extracting a histogram from the extracted object boundary value; And

And a fourth step of inputting an image after calculating a ratio of the saturation region according to the histogram extracted in the third step and the center photometric region of the image extracted in the first step, performing exposure compensation accordingly.

According to the exposure compensation device and method of the digital still camera, when effective exposure extraction of the subject is possible within the central metering area during automatic exposure control in the digital still camera, the subject area is extracted, and the luminance of the data in the extracted area is extracted. A histogram according to the level can be obtained and analyzed, and appropriate exposure compensation can be automatically performed centering on the subject area.

Then, embodiments will be described so that those skilled in the art can easily implement the present invention.

1 is a block diagram of an exposure compensation apparatus of a digital still camera according to an embodiment of the present invention.

As shown in FIG. 1, an exposure compensation apparatus of a digital still camera according to an exemplary embodiment of the present invention includes a CCD photographing unit 100, an analog-digital converting unit 200, an exposure control unit 300, and digital control processing. A unit 400, an LCD unit 500, a memory unit 600, and a system controller 700 are included.

The CCD photographing unit 100 controls a photographing lens 110 for converting an incident image into a predetermined size, a CCD photographing unit 120 for capturing an image converted in size by the photographing lens 110, and an amount of incident light. Including the electronic shutter 130, the image taken by the imaging lens 110 in response to the control of the system control unit 700 is taken according to the shutter speed of the electronic shutter 130, and the captured image is analog Output to the digital conversion unit 200.

The analog-to-digital converter 200 receives an analog-type image signal from the CCD photographing unit 100 and converts the analog-type image signal into digital-type image data, and then converts the digital image data into the exposure controller 300 and the digital controller 400, respectively. Output

The exposure controller 300 includes a subject region extractor 310, a boundary region extractor 320, an electronic shutter controller 330, and a histogram extractor 340. The subject region to be photographed is extracted through edge detection of the image data, and the exposure compensation of the electronic shutter 130 is performed by analyzing the extracted data by histogram of the luminance level.

In more detail, the subject region extracting unit 310 extracts the subject region from the entire region of the image data. In general, the camera user captures a subject to be photographed by matching it to the center of the screen. Thus, the extraction of the subject region may extract the subject region by excluding a background part from the center block of the screen.

The boundary region extractor 320 accurately extracts the boundary region of the subject using an edge detection algorithm from the subject region extracted by the subject region extractor 310, that is, the subject region extracted from the center of the screen. In general, an edge detection algorithm is an algorithm for detecting edge components of an image signal by differentiating an original image signal that can be used in a manner of detecting an outline of an image signal.

The histogram extractor 330 extracts a histogram according to the luminance level distribution in the extracted subject boundary region. The reason for extracting such a histogram is that edge detection algorithms generally have difficulty in extracting an accurate boundary depending on the shape or arrangement of the subject in the area. Therefore, if the boundary area extracted by the boundary area extraction unit 320 is not valid, the center metering is performed. This is to prevent the exposure compensation error due to the failure of the boundary value extraction by extracting the histogram with respect to the luminance distribution value of the entire region.

The electronic shutter controller 340 controls the shutter speed of the electronic shutter 130 of the CCD photographing unit 100 to obtain a ratio of the saturated region from the extracted histogram and maintains the ratio at an appropriate level. The method of obtaining is an arithmetic mean of the extracted histogram within a certain range.

More specifically, the electronic shutter controller 340 controls to reduce the exposure time of the electronic shutter 130 when the saturation region is larger than the arithmetic mean of the saturation region, and when the saturation region is smaller than the arithmetic mean of the saturation region. The exposure time of the electronic shutter 130 is controlled to increase the exposure.

That is, when the saturated area is larger than the arithmetic mean value of the saturated area, the luminance level of the subject is brighter than the background screen, so that the limit value of the range that the digital still camera allows to reduce the exposure of the electronic shutter 130, for example, 1 If the exposure is corrected so that the exposure time of the electronic shutter 130 is shortened by / 1000 seconds, and the saturated area is smaller than the arithmetic mean of the saturated area, the luminance level of the subject is darker than the background screen. Exposure compensation is performed such that the exposure time of the electronic shutter 130 is extended by a limit of a range allowed by the digital still camera, for example, 1/8 second, to increase the exposure.

The digital controller 400 outputs the digital image data provided from the analog-to-digital converter 200 to the LCD unit 500 and the memory unit 600 under the control of the system controller 700.

The LCD unit 500 displays the digital image data provided from the digital control unit 400, and the memory unit 600 receives and stores the digital image data from the digital control unit 400 under the control of the system control unit 700. do.

The system controller 700 outputs control signals for capturing a picture of one picture to the CCD unit 100, the digital controller 400, and the memory unit 600, respectively.

2 is a flowchart illustrating an exposure compensation method of a digital still camera according to an embodiment of the present invention.

As shown in Figs. 1 and 2, the power of the digital still camera is turned on (step S10), and the image signal captured by the CCD unit 100 is received and converted into digital image data (step S20).

Subsequently, luminance level data is extracted from the center metering area of the digital image data converted in step S20 (step S30).

Subsequently, a subject boundary value is extracted from the luminance level data extracted in step S30 (step S40), and a histogram is extracted from the extracted subject boundary value (step S50).

Next, the ratio between the saturation region according to the histogram extracted in step S50 and the center metering region of the extracted image is calculated (step S60), and when the saturation region is the same as the center metering region multiplied by a predetermined coefficient, the image is input as it is ( Step S80). At this time, the constant coefficient is any one of 0.01 to 0.99 and can be set by the user.

If the saturation region is larger than the central metering region multiplied by a predetermined coefficient in step S60, the shutter speed of the electronic shutter is controlled to reduce the exposure (step S70), thereby inputting an image (step S80). In this case, the degree of exposure reduction is defined by the user, and can be specified up to a value allowed by the digital still camera itself, for example, within 1/1000 second.

In addition, if the saturation region is smaller than the central metering region multiplied by any one of coefficients, for example, 0.01 to 0.99 in step S60, the shutter speed of the electronic shutter 130 is controlled to increase the exposure (step S90). An image is input (step S80). In this case, the degree of exposure increase is defined by the user and can be specified within a value allowed by the digital still camera itself, for example, within 1/8 second.

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. It will be appreciated.

As described above, the present invention divides a region in consideration of an arrangement of a subject and a background in an image to be photographed, and extracts an accurate subject region from the subject region by using an edge detection algorithm, thereby making background correction during exposure. The error of exposure compensation due to the difference between the brightness level of the camera and the subject can be reduced.

In addition, a histogram according to the luminance level is obtained for the data in the extracted area to always control the ratio of saturated pixels to a predetermined level or less, thereby avoiding inaccurate exposure control according to the average value control of the effective area, and focusing on the subject in the effective area. An optimized exposure control image can be obtained.

Claims (5)

An exposure compensation apparatus of a digital still camera, which converts an image signal photographed by a CCD photographing unit into a digital image signal and performs exposure correction on the CCD photographing unit based on the same. A CCD photographing unit including an electronic shutter configured to perform an open / close operation to adjust a light amount of incident light, and a CCD imaging device configured to photograph a subject light incident through the electronic shutter and output a corresponding image signal; An analog-digital converter for converting the image signal output from the CCD photographing unit into digital image data; And The subject image is extracted from the image of one frame photographed by processing the digital image data, the luminance level distribution of the subject region is calculated, and the extracted data is analyzed by the histogram of the luminance level. Automatic exposure compensation device for a digital still camera comprising an exposure control unit for controlling the exposure compensation. The method of claim 1, wherein the exposure control unit A subject region extracting unit which extracts a subject region from all regions of the digital image data; A boundary region extracting unit which extracts a boundary region of the subject from the extracted subject region according to an edge detection algorithm; A histogram extractor configured to extract a histogram according to the luminance level distribution in the extracted object boundary region; And And an electronic shutter controller which controls the electronic shutter speed of the CCD photographing unit so as to obtain a ratio of the saturated region from the extracted histogram and maintain the ratio at an appropriate level. In the exposure compensation method of the digital still camera which converts the image signal photographed by the CCD photographing unit into a digital image signal and performs the exposure correction on the basis of the CCD imager, Extracting luminance level data from a center photometric region of the picked-up image; Extracting a subject boundary value from the extracted luminance level data; Extracting a histogram from the extracted object boundary value; And And a fourth step of inputting an image after calculating a ratio of the saturation region according to the histogram extracted in the third step and the center metering region of the image extracted in the first step, performing exposure compensation accordingly. Automatic exposure compensation method for still cameras. 4. The automatic exposure of a digital still camera according to claim 3, wherein the ratio between the saturation region according to the histogram and the center metering region of the image in the fourth step is a value obtained by subtracting the center metering region multiplied by a predetermined factor from the saturation region. Calibration method. The method of claim 4, wherein the fourth step Reducing the exposure and inputting an image when the saturation region is larger than the center metering region multiplied by a predetermined coefficient; Inputting an image by increasing the exposure when the saturation region is smaller than the center metering region multiplied by a predetermined coefficient; And And inputting an image when the saturation region is the same as the center metering region multiplied by a predetermined coefficient.