KR101589493B1 - White ballance control method and apparatus using a flash and digital photographing apparatus using thereof - Google Patents

Abstract

The present invention relates to a method and apparatus for adjusting white balance using a flash, and more particularly, to a method and apparatus for adjusting white balance by calculating color information of a scene to be photographed from two images photographed with flash on / , It is possible to easily solve the inconvenience of the custom white balance mode when it is difficult to perform auto white balance.

White balance, flash, color information

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white balance control method and apparatus using a flash, and a digital photographing apparatus using the same.

The present invention relates to image processing, and more particularly, to a method and apparatus for adjusting white balance using a flash and a digital photographing apparatus using the same.

Generally, white light is white in the human eye under any light source (for example, sunlight, fluorescent light, incandescent light, etc.), but it becomes red or green depending on the light source through the camera image pickup tube. This is due to the color temperature of the light source. If the color temperature is high, it becomes a blue color system. If it is low, it becomes a color of red color system. Therefore, the image processing apparatus generally displays the final desired image by mixing three colors of red, green, and blue (R, G, B). If the color displayed on the screen does not match, the original natural color But a modified color is displayed to obscure human visual characteristics and can be recognized as a serious drawback of quality deterioration of the image output apparatus itself. If you adjust white subjects to whiten under any light source, other colors can be reproduced correctly. This adjustment is called white balance adjustment.

In general, in order to compensate for the same color difference caused by different color temperatures of various light sources, a method called Automatic White Balance (AWB) in digital imaging apparatuses such as cameras, camcorders, Lt; / RTI > The automatic white balance method means that the color average value is assumed to be white and the color average value is shifted to white regardless of the variation of the light source. A conventional AWB (auto white balance) algorithm extracts a point determined as a gray object in an input image, and estimates a color temperature based on the determined color information of the gray object. When the color temperature is estimated, the RGB channel is multiplied by an appropriate gain to adjust the color of the output image accordingly.

For the auto white balance function to work correctly, there should be a gray area on the screen in the preview mode and the gray area judgment must be correct. However, judging whether the R / G / B distortion of the gray area is due to illumination or the original color itself is very insufficient. For example, when there is almost no area assumed to be a gray area in the image to be photographed, it is difficult to perform the AWB algorithm when the color information is not accurate in the night view.

In addition, the white balance was adjusted by adjusting the white balance using the custom white balance mode instead of the auto white balance. For example, if you set the white balance indoors to "Auto," it does not fit well. You adjusted the white balance with a custom white balance with a gray card or white paper, but when you shoot, place a gray card or white paper on the subject There are times when it is difficult to do and it is often troublesome.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a white balance adjustment method capable of solving the inconvenience of manually adjusting the white balance in the case where it is difficult to perform the auto white balance mode or in the custom white balance mode And apparatus.

Another object of the present invention is to provide a digital photographing apparatus using the same.

According to an aspect of the present invention, there is provided a method of adjusting a white balance using a flash, the method comprising: (a) acquiring a first image by shooting the flash and photographing a predetermined object; (b) photographing the subject without bursting the flash to acquire a second image; And (c) extracting respective color information from the acquired first and second images, calculating a reflectance value of the subject using the extracted color information and the color information of the light source of the flash, And calculating a white balance gain value based on the white balance gain value.

Preferably, the step (c) further includes the step of adjusting a white balance of an image to be captured by photographing the subject based on the calculated white balance gain value.

Preferably, the step (c) includes the steps of: comparing the color information of the first image with the color information of the second image; comparing the color information of a portion where the difference of the color information is larger than the first threshold value, And extracts the image from the image.

Preferably, before the step (a), the custom white balance mode is selected by the user.

Preferably, the step (c) calculates the white balance gain value by reflecting the degree of exposure of the acquired first and second images.

According to another aspect of the present invention, there is provided an apparatus for adjusting a white balance using a flash, the apparatus comprising: a control unit for controlling the flash to fire a predetermined subject and photographing the subject without popping the flash; ; The control unit controls the control unit to extract each color information from the first image obtained by shooting the flash and photographing the first image and the second image obtained by photographing without flashing the flash, A video signal processing unit for capturing an image of the subject and adjusting a white balance of an image to be acquired; And a white balance calculation unit for calculating a reflectance value of the subject using the extracted color information and the color information of the light source of the flash, and calculating a white balance gain value based on the reflectance value.

Preferably, the control unit compares the color information of the first image with the color information of the second image, and controls to extract color information of a portion having a large difference in color information from the first image and the second image, And the white balance calculation unit receives the color information of a portion where the difference between the color information from the first image and the second image is larger than the first threshold value, and calculates the white balance gain value based on the received color information.

Preferably, the control unit controls to shoot the first image and the second image when the custom white balance mode is selected.

According to another aspect of the present invention, there is provided a recording medium on which a program for executing the method according to another embodiment of the present invention is recorded.

According to another aspect of the present invention, there is provided a digital photographing apparatus including the apparatus according to another embodiment of the present invention.

According to the embodiment of the present invention, by calculating the color information of the illumination of the scene to be photographed from the two images photographed with the flash on / off, and adjusting the white balance, it is difficult to perform the auto white balance, The inconvenience can be solved simply.

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Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, only parts necessary for understanding the operation according to the present invention will be described, and descriptions of other parts may be omitted so as not to disturb the gist of the present invention.

In addition, terms and words used in the following description and claims should not be construed to be limited to ordinary or dictionary meanings, but are to be construed in a manner consistent with the technical idea of the present invention As well as the concept.

1 is a block diagram of a digital camera according to an embodiment of the digital photographing apparatus of the present invention. 2 is a block diagram for explaining a digital signal processing unit of the digital camera.

1, the digital camera 100 includes an optical section 10, an optical driving section 11, an image pickup element 15, an image pickup element control section 16, a flash 17, an operation section 20, A program storage unit 30, a buffer storage unit 40, a data storage unit 50, a display control unit 60, a data driving unit 61, a scan driving unit 63, a display unit 65 And a digital signal processing unit (DSP) 70.

The optical section 10 receives an optical signal from a subject and provides it to the imaging element 13. [ The optical unit 10 may include at least one lens, such as a zoom lens for controlling the angle of view to be narrowed or widened according to the focal length, and a focus lens for focusing the subject. In addition, the optical unit 10 may further include a diaphragm for adjusting the amount of light.

The optical driver 11 controls the position of the lens, opening and closing of the diaphragm, and the like. The focus can be adjusted by moving the position of the lens. In addition, the amount of light can be adjusted by controlling the opening and closing of the diaphragm. The optical driving unit 11 can control the optical unit 10 according to a control signal automatically generated by a video signal input in real time or a control signal manually input by an operation of a user.

The optical signal transmitted through the optical section 10 reaches the light-receiving surface of the image pickup element 15 to form an image of the object. The image pickup device 15 may be a charge coupled device (CCD) or a complementary metal oxide semiconductor image sensor (CIS) for converting an optical signal into an electric signal. The sensitivity of the image pickup element 15 can be adjusted by the image pickup element controller 16. The image pickup element control unit 16 can also control the image pickup element 15 in accordance with a control signal automatically generated by the video signal inputted in real time or a control signal manually inputted by the user's operation.

The flash 17 is an example of a light source for illuminating a subject brightly at the time of photographing at nighttime outdoors or in a dark place. A flash command is issued from the control section 71 of the DSP 70 to the flash 17 to cause the flash 17 to emit light and the object to be brightened by the emitted light. According to the preferred embodiment of the present invention, when the custom white balance mode is selected, as the user presses the photographing button of the specific subject, the flash is once fired and the subject is photographed, and the subject is photographed without flashing again . Further, in order to perform the white balance calculation, the color information of the flash illumination, that is, the R, G, and B ratios are known.

The operation unit 20 is a place where a control signal from the outside of a user or the like can be input. The operation unit 20 includes a shutter-release button for inputting a shutter-release signal for exposing the image pickup device 15 to light for a predetermined period of time, a power button for inputting power, A wide angle-zoom button and a telephoto-zoom button for widening or narrowing the angle of view, a mode selection such as a character input mode, a shooting mode, and a playback mode, and an exposure setting function selection. The operation unit 20 may have various types of buttons as described above, but the present invention is not limited thereto. The operation unit 20 may be implemented in any form such as a keyboard, a touch pad, a touch screen, and a remote controller.

The white balance mode selection section 21 allows the user to select the auto white balance mode or the custom white balance mode. When the user selects the auto white balance mode through the white balance mode selection unit 21, the above-described AWB algorithm is performed according to the auto white balance mode. The AWB algorithm can not accurately determine the R, G, and B values of the light source because the R, G, and B values of the light reflected from the object are simultaneously affected by the intrinsic reflectivity and the light source of the object. To compensate the R, G, and B values of the light source. Preferably, when the user selects the custom white balance mode, a white balance adjustment algorithm using flash is performed according to a preferred embodiment of the present invention. Although the operation unit 20 and the white balance mode selection unit 21 are described as being separate from each other, it is needless to say that the white balance mode selection function can be integrated in the operation unit 20.

The digital camera 100 further includes a program storage unit 30 for storing programs such as an operating system and an application system for driving the digital camera, a buffer storage unit 40 for temporarily storing data or result data necessary for the operation And a data storage unit 50 for storing various information necessary for a program, including an image file including a video signal.

In addition, the digital camera 100 includes a display control unit 60 for controlling the display of the operation state of the digital camera 100 or the image information photographed by the digital camera 100, a data driving unit 60 for receiving display data input from the display control unit 60, And a display unit 65 for displaying a predetermined image according to a signal input from the scan driver 61, the scan driver 63, the data driver 61, and the scan driver 63. The display unit 65 may include a liquid crystal display panel (LCD), an organic light emitting display panel (OLED), and an electrophoretic display panel (EDD).

The digital camera 100 includes a digital signal processing unit 70 for processing input image signals and controlling the respective components according to the external input signals.

The digital signal processing unit 70 will be described with reference to FIG.

2, the digital signal processing unit 70 includes a control unit 71, a video signal processing unit 72, and a white balance calculation unit 73. In addition, the digital signal processing unit 70 described below and the white balance adjustment device used in the claims should be construed to perform the same function.

The control unit 71 controls the overall operation of the digital signal processing unit 70. According to the preferred embodiment of the present invention, when the custom white balance mode is selected and the shutter release signal is inputted as the user presses the photographing button, the on / off control of the flash 17 is controlled and photographed, Obtain the image. In other words, one shot is captured by shooting the flash, and another shot is captured by taking the shot without popping the flash. In addition, the control unit 71 compares the captured image with the captured image and the color information of the captured image without bursting the flash, that is, the RGB value, and controls the color information of the large difference portion to be extracted.

The image signal processing unit 72 extracts each color information from the image obtained by shooting the flash 17 and obtained by photographing the image obtained by shooting the flash 17 without bursting the flash 17 under the control of the control unit 71. [ Preferably, the RGB information of the portion having a large difference in color information is extracted. Further, the white balance of the image to be acquired is adjusted according to the white balance gain value calculated by the white balance calculation section 72, that is, the ratio of R / G and B / G.

In general, the image signal processing unit 72 converts a video signal input from the image pickup device 15 into a digital signal, and outputs a gamma correction, a color filter array interpolation filter array interpolation, color matrix, color correction, color enhancement, and the like. In addition, the video signal processing unit 72 can perform Auto White Balance or Auto Exposure algorithm when the function is set. Further, the size of the image data is adjusted using a scaler, and the image data is compressed to form an image file of a predetermined format. Conversely, the image file is decompressed. The video signal processor 72 may perform the above-described video signal processes on the video signal input in real-time in the live-view mode before photographing and the video signal input by the shutter-release signal. At this time, different video signal processing may be performed for each of the video signals.

The white balance calculation unit 73 calculates the white balance based on the color information of each of the captured image obtained by flashing the flash inputted from the image signal processing unit 72 and the captured image without flashing the flash and the color information of the light source of the flash 17 Calculate the white balance gain value. Preferably, the white balance gain value may be calculated by reflecting the difference between the exposure time of the image obtained by shooting the flash and the image of the captured image without bursting the flash. Hereinafter, the process of calculating the white balance gain value will be described in detail.

First, define as follows. The ratio of R, G and B of the main illumination of the scene to be photographed is Lr: Lg: Lb, and the ratio of R, G, B of the flash illumination is Lr ': Lg': Lb '. Here, Lr: Lg: Lb is an unknown value, and Lr ': Lg': Lb 'is a known value. Then, the image obtained by comparing the image when the flash is turned on and the image when the image is not popped is extracted, and the color information is extracted, and the color information is referred to as R0, G0, B0 and R1, G1 and B1, respectively. Here, R0, G0, and B0 and R1, G1, and B1 are known values. Rr, Rg, and Rb represent the reflectance of an object or a subject of a scene to be photographed, and the value is unknown.

R0, G0, and B0 values and illumination when the flash is not turned on are shown in Equation (1).

Lr * Rr = fr (R0)

Lg * Rg = fg (G0)

Lb * Rb = fb (Bo)

Here, fr, fg and fb are functions for converting the channel values in the respective channels, that is, the values of R0, G0 and B0 into the amounts of light incident on the pixels.

Similarly, the values of R1, G1, and B1 when the flash is turned on and the illumination are as shown in the following Equation 2.

(Lr + Lr ') * Rr = fr (R1)

(Lg + Lg ') * Rg = fg (G1)

(Lb + Lb ') * Rb = fb (B1)

Here, fr, fg, and fb are functions for converting the channel values in the respective channels, that is, the values of R1, G1, and B1 into the amounts of light incident on the pixels.

The following Equation (3) can be calculated using Equations (1) and (2).

Lr '* Rr: Lg' * Rg: Lb '* Rb

Here, since the value of Lr ': Lg': Lb 'is known, the value of Rr: Rg: Rb can be determined using the above equation (3). That is, the reflectance value of the subject can be obtained.

Therefore, by substituting the reflectance value of the subject calculated in Equation (3) into Equation (1), the values of Lr, Lg, and Lb can be obtained and the R, G, and B values of the illumination can be obtained.

That is, by comparing the color information of the two images, the R, G and B components of the illumination, that is, Lr, Lg and Lb are calculated and the custom white balance value is stored on the basis of the calculated values. Value to perform the white balance function.

In calculating the white balance gain value, the exposure time should be the same when the flash is fired and when it is not fired. Even if the exposure is different, the white balance gain value can be calculated by giving an appropriate weight. For example, if the exposure time when the flash is not turned on is twice as large as that when the flash is turned on, in the above equations (1) and (2), 2Lr is substituted for Lr. The same applies to Lg and Lb.

3 is a flowchart illustrating a white balance adjustment method according to another embodiment of the present invention.

Referring to FIG. 3, in step 300, a custom white balance mode is selected. If the photographing button is pressed by the user in step 302, the flash is fired, the subject is photographed to acquire the first image, and in step 306, the same subject is photographed without popping the flash to acquire the second image do. Here, taking the flash without bursting or popping is irrelevant. In other words, you can shoot the flash without first bursting, then shoot the flash and shoot.

In step 308, the color information of the first image and the second image acquired in steps 304 and 306 are compared. In step 310, the color information of the portion where the difference in color information is large is extracted. In step 312, the white balance gain value is calculated using the extracted color information and the color information of the flash illumination. Here, the calculation of the white balance gain value is as described with reference to Equations 1 to 3 above. That is, the reflectance of the subject is calculated, and the color information and the RGB value of the illumination when the subject is photographed are calculated.

Although the embodiments described above have been described with reference to a digital camera as an example of a digital photographing apparatus to which the present invention can be applied, the present invention is not limited thereto. Those skilled in the art will appreciate that the present invention is also applicable to a camera phone, a personal digital assistant (PDA), and a portable multimedia player (PMP) with a camera function.

Meanwhile, the present invention can be embodied in computer readable code on a computer readable recording medium. A computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored.

Examples of the computer-readable recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device and the like, and also a carrier wave (for example, transmission via the Internet) . In addition, the computer-readable recording medium may be distributed over network-connected computer systems so that computer readable codes can be stored and executed in a distributed manner. In addition, functional programs, codes, and code segments for implementing the present invention can be easily deduced by programmers skilled in the art to which the present invention belongs.

The present invention has been described above with reference to preferred embodiments. It will be understood by those skilled in the art that the present invention may be embodied in various other forms without departing from the spirit or essential characteristics thereof. Therefore, the above-described embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is indicated by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

1 is a schematic block diagram of a digital photographing apparatus 100 according to an embodiment of the present invention.

2 is a schematic block diagram of the digital signal processing unit 70 shown in FIG.

3 is a flowchart illustrating a white balance adjustment method according to another embodiment of the present invention.

Description of the Related Art

17: Flash 21: White balance selection mode

70: digital signal processor 71:

72: video signal processing unit 73: white balance calculation unit

Claims (10)

As a white balance adjustment method using a flash, (a) acquiring a first image by shooting the predetermined subject by exploding the flash; (b) photographing the subject without bursting the flash to acquire a second image; And (c) extracting respective color information from the acquired first and second images, calculating a reflectance value of the subject using the extracted color information and the color information of the light source of the flash, And calculating a white balance gain value based on the white balance gain value. The method according to claim 1, After the step (c) And adjusting a white balance of an image to be acquired by photographing the subject based on the calculated white balance gain value. The method according to claim 1, The step (c) Wherein the color information of the first image and the second image are compared with each other and the color information of the portion where the difference of the color information is larger than the first threshold value is extracted from the first image and the second image, Balance adjustment method. The method according to claim 1, Before the step (a) Further comprising the step of selecting a custom white balance mode by a user's selection. The method according to claim 1, The step (c) Wherein the white balance gain value is calculated by reflecting the degree of exposure of the acquired first and second images. A recording medium on which a program for causing a computer to execute the method according to any one of claims 1 to 5 is recorded. A white balance adjustment device using a flash, A control unit for controlling the flash to shoot a predetermined subject, and to shoot the subject without bursting the flash; The control unit controls the control unit to extract each color information from the first image obtained by shooting the flash and photographing the first image and the second image obtained by photographing without flashing the flash, A video signal processing unit for capturing an image of the subject and adjusting a white balance of an image to be acquired; And And a white balance calculation unit for calculating a reflectance value of the subject using the extracted color information and the color information of the light source of the flash, and calculating a white balance gain value based on the reflectance value. 8. The method of claim 7, Wherein, And controlling the color information of the first image and the second image to be extracted from the first image and the second image, respectively, Wherein the white balance calculation unit comprises: Wherein the white balance adjustment unit calculates the white balance gain value based on the received color information of the portion having a large difference between the color information from the first image and the second image. 8. The method of claim 7, Wherein, And controls to shoot the first image and the second image when the custom white balance mode is selected. A digital photographing apparatus comprising a white balance adjustment device according to any one of claims 7 to 9.

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