KR20100098119A - Digital camera and controlling method thereof - Google Patents

Abstract

PURPOSE: A digital camera and a method for controlling the same are provided to refer brightness distribution within a screen and calculates white balance gain from an area satisfying a achromatic color, thereby adjusting more accurate white balance. CONSTITUTION: An achromatic color area calculator(151) searches an area satisfying achromatic color conditions among whole screen area. A brightness difference calculator(153) calculates the brightness difference between luminance of whole screen area and luminance of achromatic color area. If the luminance difference is bigger or the same as threshold value, a WB(White Balance gain calculator)(155) calculates a gain value form the achromatic color area. If the luminance difference is smaller than the threshold value, the WB calculates a gain value form the whole screen area.

Description

Digital camera and controlling method

The present invention relates to a digital camera and a control method thereof. More specifically, a digital camera capable of performing a more accurate white balance adjustment by calculating a white balance gain from an area satisfying an achromatic condition with reference to a luminance distribution in a screen. And a control method thereof.

In general, the human eye detects white color under any light source, but when viewed through the camera, the human eye may appear red or blue depending on sunlight, fluorescent light, or incandescent light. This is due to the color temperature of the light source. If the color temperature is high, the color is blue. If the color temperature is low, the color is red. When affected by the color temperature in this way, the correct color cannot be reproduced in the output of the image. Accordingly, the white balance adjustment is performed so that a white subject is reproduced white under a light source so that not only white but also other colors are correctly reproduced.

Conventionally, auto white balance (AWB) is performed with reference to the entire screen area. In this case, the luminance distribution is greatly affected. That is, in the image where both shade and sunny are simultaneously taken on a very clear day, the shade has a very low signal value, while the sunny has a very high signal value, so the average value tends to be skewed toward the sun. However, in practice, sunny data is saturated or near-saturated data, and although white balance is a case where the data on the shade side should be intensively referred to, the white balance error is caused by referring to the data skewed toward the sunny side.

Disclosure of Invention An object of the present invention is to provide a digital camera and a method of controlling the same, which can reduce white balance errors in shade in images taken with sunny days and shades on a sunny day.

Another object of the present invention is to provide a digital camera capable of precise white balance adjustment and a control method thereof by calculating a white balance gain from an area satisfying an achromatic condition with reference to a luminance distribution within a screen.

A digital camera of the present invention for achieving the above and other objects, the achromatic region detection unit for finding a region that satisfies the achromatic condition in the entire screen region;

A luminance difference calculator for calculating a luminance difference Br1-Br2 between the luminance Br1 of the entire screen region and the luminance Br2 of the achromatic region; And

i) If the luminance difference Br1-Br2 ≥ the threshold Cr, the gain value is calculated from the achromatic region, and ii) if the luminance difference Br1-Br2 <the threshold Cr, the gain value is calculated from the entire screen region. And a white balance gain calculator.

Preferably, the achromatic region detector divides the entire screen region into a plurality of image blocks and determines whether the achromatic condition is satisfied in units of image blocks.

For example, the achromatic region detection unit may set an achromatic condition as to whether the mixing ratio of the R, G, and B color signals detected in each image block falls within a set range.

Preferably, the digital camera further includes a white balance adjusting unit having a gain value calculated by the white balance gain calculating unit and correcting R, G and B color signals of each pixel constituting the screen.

On the other hand, the control method of the digital camera according to another aspect of the present invention,

An achromatic region detection step of finding an achromatic region that satisfies an achromatic condition from the entire screen region;

Calculating a luminance difference Br1-Br2 from the luminance Br1 of the entire screen region and the luminance Br2 of the achromatic region; And

If luminance difference Br1-Br2 ≥ threshold Cr, a gain value is calculated from an achromatic region, and if luminance difference Br1-Br2 <threshold Cr, a white balance gain is calculated that calculates a gain value from the entire screen region. It includes; step.

Preferably, the method for controlling the digital camera further includes dividing the entire screen area into a plurality of image blocks.

In the achromatic region detection step, it is determined whether an achromatic condition is satisfied in units of image blocks.

For example, in the achromatic region detection step, it may be an achromatic condition as to whether the mixing ratio of the R, G, and B color signals detected in each image block falls within a set range.

Preferably, the control method of the digital camera further includes a white balance adjusting step having a gain value calculated in the white balance gain calculating step and correcting R, G, and B color signals of each pixel constituting the screen.

According to the digital camera of the present invention and the control method thereof, the white balance gain can be calculated from the region satisfying the achromatic condition by referring to the luminance distribution in the screen, so that the white balance can be adjusted more precisely and the subject region where the sun and shade coexist. White balance errors in the shade can be reduced.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. Through this specification, a digital camera is a mobile device having an appropriate photographing function, and does not simply mean a negotiated camera classified based on a morphological feature called a camera, and combines portability and shooting functions such as a camcorder, a mobile phone, a PDA, and the like. It is used in a broad sense to encompass all devices.

1 schematically shows the overall configuration of a digital camera according to one embodiment of the present invention. Referring to the drawings, the digital camera includes a plurality of optical lenses and an optical unit 110 for forming an image of a subject on an image pickup surface, and an image of the subject via the optical unit 110 as an electrical image signal. An image pickup device 120 for conversion, an analog front end circuit 130 for converting an output signal of the image pickup device 120 to a quantized digital video signal, and an operation for signal processing A buffer memory 140 that temporarily stores an image signal to provide an area, a recording medium 170 in which image data of a subject is stored in the form of a still image or a moving image file, and collectively controlling the overall data flow and each component. Digital signal processor 150 is included. In addition, the digital camera is an input / output device that includes a user input unit 190 having a plurality of input mechanisms for detecting a user's manipulation, and an image output unit for receiving image signals from the digital signal processor 150 and displaying them on the screen. 180) may be further included.

The optical unit 110 includes a zoom lens 112 for changing the focal length while moving back and forth along the optical axis direction, a shutter 114 and an aperture 116 for adjusting an exposure time and an incident light amount to the imaging device 120, And a focus lens 118 that adjusts the focus of the subject image formed on the imaging device 120. The photographing operation of the optical unit 110 may be controlled by the digital signal processor 150 via the driver 111.

The imaging device 120 is, for example, a Charged Coupled Device (CCD) or a Complementary Metal Oxide Semiconductor (CMOS) image sensor, and converts an image of a subject incident through the optical unit 111 into an electrical image signal. do. The operation of the image pickup device 120 may be controlled by the digital signal processor 150 via a timing generator 121 (TG).

The analog front-end circuit 130 (AFE circuit) performs an analog image signal output from the imaging device 120 by performing a correlated double sampling (CDS) process and an analog digital conversion (ADC) process on the output signal of the imaging device. To convert the digital video signal. The digital video signal is transmitted to the encoder / decoder 160, and is converted into encoded data according to a prescribed compression scheme and stored in the recording medium 170. The buffer memory 140 is a volatile memory that provides a work area for processing various data, and may be configured as a DRAM (Dynamic Random Access Memory or SDRAM), and the encoder / decoder 160 and the digital signal processor 150 Provides a work area for data processing.

The digital signal processor 150 executes a program recorded in an EEPROM (145, Electronically Erasable and Programmable ROM) to control the overall operation of the digital camera regarding image capturing and processing of image data. In particular, the digital signal processor 150 adjusts the gains for the R, G, and B color signals constituting the digital image signal, thereby excluding the influence of light source types (eg, sunlight, incandescent lamps, fluorescent lamps) and correcting colors. Perform White Balance adjustment to reproduce. The digital signal processor 150 finds an area (hereinafter referred to as an achromatic region) that satisfies an achromatic condition from the entire screen region, and according to the magnitude relationship between the luminance Br1 of the entire screen region and the luminance Br2 of the achromatic region. Perform white balance adjustment in different ways. That is, when the luminance difference Br1-Br2 between the two regions is smaller than the threshold value Cr, the WB gain value is calculated by combining the R, G, and B color signals of the entire screen region. However, when the luminance difference Br1-Br2 between the two regions is larger than the threshold value Cr, the WB gain value is collected by collecting only the R, G, and B color signals in the achromatic region without calculating the WB gain value from the entire screen region. Calculate. Finally, the digital signal processor 150 generates a white balanced color signal by correcting the R, G, and B color signals of each pixel signal according to the calculated WB gain.

In relation to the white balance adjustment operation, the digital signal processor 150 includes an achromatic region detector 151, a luminance difference detector 153, a WB gain calculator 155, and a WB adjuster 157. The achromatic region detection unit 151 finds an area satisfying the achromatic condition among the entire screens. More specifically, the achromatic region detection unit 151 determines whether an achromatic condition is satisfied in units of image blocks, and recognizes the block as an achromatic region according to the determination result. For example, the achromatic region detection unit 151 divides one screen into a plurality of image blocks, calculates a representative value (ex. Average value) of R, G, and B color signals in each image block, and compares it with the achromatic condition. Done. For example, the achromatic condition may be set to a mixing ratio of the R, G, and B color signals (eg, the ratio of the R / G color signal and the ratio of the B / G color signal), and these range from 1 ± α. Once inside, it can be recognized as an achromatic region. As an example, if 1-α ≦ R / G ≦ 1 + α and 1-α ≦ B / G ≦ 1 + α, the corresponding image block may be recognized as an achromatic region.

The luminance difference detector 153 extracts the luminance Br1 of the entire screen and the luminance Br2 of the region recognized as achromatic color and calculates the luminance difference Br1-Br2 between the two regions. For example, the luminance difference detector 153 calculates the luminance Br1 of the entire screen by averaging the luminance values of the entire screen, and calculates the luminance Br2 by averaging the luminance values of the achromatic region. Then, the magnitude relation is determined by comparing the luminance difference Br1-Br2 between the two regions and the preset threshold value Cr.

The WB gain calculator 155 calculates the WB gain value from the achromatic region when the luminance difference Br1-Br2> the threshold value Cr, and when the luminance difference Br1-Br2 <the threshold value Cr, the entire screen area. The WB gain value is calculated from

i) If the luminance difference (Br1-Br2) ≥ the threshold value (Cr), the luminance deviation is severe within one screen, and it is likely that the image of the subject image where sunny and sunny areas coexist in a sunny day is captured. At this time, since the sunny data has a very high signal level, the sunny data has a very low signal level, and if the average of these is calculated to calculate the WB gain value from the entire screen, the sunny data tends to be skewed toward the sunny side. Since sunny data is saturated data of chromatic color series, accurate white balance adjustment can be performed by calculating WB gain value from achromatic color tone data. More specifically, the WB gain calculation unit 155 is configured such that the representative values (ex. Average values) of the R, G, and B color signals calculated in the achromatic region constitute a mixing ratio of 1: 1: 1. The WB gain value for the B color signal can be calculated. For example, the WB gain for the R signal may be the representative of the G signal divided by the representative of the R signal, and the WB gain for the B signal may be the representative of the G signal divided by the representative of the B signal.

2) If the luminance difference Br1-Br2 < the threshold value Cr, it is judged that there is no luminance deviation to consider the error of the white balance, so that the WB gain value is calculated from the entire screen. For example, the WB gain calculator 155 may calculate a WB gain value such that the R, G, and B color signals of the entire screen form a 1: 1: 1 mixing ratio.

The WB adjusting unit 157 has a calculated WB gain value and adjusts gains for R, G, and B color signals of each pixel. For example, the WB adjusting unit multiplies the WB gain value with respect to each of the R, G, and B color signals of each pixel to generate a white balance balanced R, G, and B color signal to perform white balance adjustment.

2 is a view for explaining a control method of a digital camera according to another aspect of the present invention, which is a flowchart illustrating a series of control steps performed for white balance adjustment. First, the digital signal processor 150 divides one screen into a plurality of image blocks (S10), finds image blocks satisfying an achromatic condition, and recognizes the image blocks as an achromatic region (S11). For example, since a combination of lights (ex. 1: 1: 1) in which R, G, and B color components are equally mixed can be defined as achromatic color, representative values of R, G, and B color signals from each image block are defined. (e.g., average value), and incorporate an image block whose mixing ratio (e.g. R / G color signal ratio, B / G color signal ratio) of R, G and B color signals close to 1 into the achromatic region. Can be. For example, if 1-α ≦ R / G ≦ 1 + α and 1-α ≦ B / G ≦ 1 + α, the corresponding image block may be incorporated into the achromatic region.

Next, the luminance Br1 of the entire screen is calculated (S12). More specifically, the digital signal processor 150 may calculate the luminance Br1 of the entire screen by extracting and averaging the luminance signals of each pixel constituting one screen. Next, the luminance Br2 of the achromatic region is calculated (S13). More specifically, the digital signal processor 150 may calculate the luminance Br2 of the achromatic region by extracting the luminance signal of each pixel constituting the achromatic region and averaging them. Then, the luminance difference Br1-Br2 between the entire screen and the achromatic region is calculated and compared with the threshold value Cr (S14, S15). The digital signal processor 150 calculates the WB gain value from the achromatic region if the luminance difference Br1-Br2 ≥ the threshold Cr (S16), and if the luminance difference Br1-Br2 <the threshold Cr, the whole The WB gain value is calculated from the screen area (S17).

1) If the luminance difference (Br1-Br2) ≥ the threshold value (Cr), the luminance deviation is severe within one screen, and it may be an image in which both sunny and negative regions are captured together on a very clear day. At this time, since the sunny data has a very high signal level, the sunny data has a very low signal level, and if the average of these is calculated to calculate the WB gain value from the entire screen, the sunny data tends to be skewed toward the sunny side. However, since the sunny data is saturated data of chromatic color series, accurate white balance adjustment can be performed by calculating the WB gain value from the chromatic color tone data. For example, the digital signal processor 150 may calculate a WB gain value so that the ratio of the R, G, and B color signals in the achromatic region may be 1: 1: 1.

2) If the luminance difference Br1-Br2 < the threshold value Cr, it is determined that there is no luminance variation enough to cause an error in the white balance, and thus WB gain value is calculated from the entire screen. For example, the digital signal processor 150 may calculate a WB gain value so that the R, G, and B color signals of the entire screen may have a ratio of 1: 1: 1.

Next, with the WB gain value calculated from the achromatic region or the entire screen region, the gain for the R, G, and B color signals of each pixel is adjusted (S18). For example, the digital signal processor performs a white balance adjustment by generating a balanced R, G, B color signal by multiplying the WB gain value for each of the R, G, B color signals of each pixel.

Although the present invention has been described with reference to the embodiments illustrated in the accompanying drawings, it is merely exemplary, and various modifications and equivalent other embodiments are possible from those skilled in the art to which the present invention pertains. You will understand the point. Therefore, the true scope of protection of the present invention should be defined by the appended claims.

1 is a block diagram showing the overall configuration of a digital camera according to a preferred embodiment of the present invention.

2 is a view for explaining a control method of a digital camera according to another aspect of the present invention, which is a flowchart illustrating a series of control steps performed for white balance adjustment.

<Explanation of symbols for the main parts of the drawings>

110: optical unit 111: driver

112: zoom lens 114: shutter

116: aperture 118: focus lens

120: imaging device 121: timing generator

130: analog front end circuit (AFE circuit)

140: buffer memory 145: EEPROM

150: digital signal processor 151: achromatic region detection unit

153: luminance difference detection unit 155: WB gain calculation unit

157: WB adjusting unit 160: encoder / decoder

170: recording medium 180: video output unit

190: user input unit

Claims (8)

An achromatic region detection unit for finding a region satisfying an achromatic condition among all screen regions; A luminance difference calculator for calculating a luminance difference Br1-Br2 between the luminance Br1 of the entire screen region and the luminance Br2 of the achromatic region; And i) If the luminance difference Br1-Br2 ≥ the threshold Cr, the gain value is calculated from the achromatic region, and ii) if the luminance difference Br1-Br2 <the threshold Cr, the gain value is calculated from the entire screen region. White balance gain calculation unit; Digital camera comprising a. The method of claim 1, The achromatic region detection unit divides the entire screen region into a plurality of image blocks, and determines whether the achromatic condition is satisfied in units of image blocks. The method of claim 2, And wherein the achromatic region detection unit sets an achromatic condition as to whether a mixing ratio of the R, G, and B color signals detected in each image block falls within a set range. The method of claim 1, And a white balance adjusting unit having a gain value calculated by the white balance gain calculating unit and correcting R, G and B color signals of each pixel constituting the screen. An achromatic region detection step of finding an achromatic region that satisfies an achromatic condition from the entire screen region; Calculating a luminance difference Br1-Br2 from the luminance Br1 of the entire screen region and the luminance Br2 of the achromatic region; And If luminance difference Br1-Br2 ≥ threshold Cr, a gain value is calculated from an achromatic region, and if luminance difference Br1-Br2 <threshold Cr, a white balance gain is calculated that calculates a gain value from the entire screen region. Control method of a digital camera comprising a. The method of claim 5, Dividing the entire screen area into a plurality of image blocks; In the achromatic region detection step, it is determined whether the achromatic condition is satisfied in units of image blocks. The method of claim 6, In the achromatic region detection step, the achromatic condition is set as whether the mixing ratio of the R, G, and B color signals detected in each image block falls within a set range. The method of claim 5, And a white balance adjustment step of correcting the R, G, and B color signals of each pixel constituting the screen, having the gain value calculated in the white balance gain calculation step.

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