KR101533282B1 - Digital camera and controlling method thereof - Google Patents

Abstract

A digital camera and a control method thereof are disclosed in the present invention. The digital camera includes an achromatic area detection unit for detecting an area satisfying an achromatic color condition in a full screen area, a luminance calculating unit for calculating a luminance (Br1-Br2) between the luminance Br1 of the entire screen area and the luminance Br2 of the achromatic area And calculates a gain value from the achromatic area if the luminance difference Br1-Br2 is equal to or greater than the threshold value Cr, and ii) if the luminance difference Br1-Br2 is smaller than the threshold value Cr, And a white balance gain calculating unit for calculating a gain value.

According to the present invention, a digital camera and its control method capable of performing more accurate white balance adjustment can be provided by calculating a white balance gain from an area satisfying an achromatic color condition by referring to a luminance distribution in a screen.

Description

[0001] Digital camera and controlling method thereof [0002]

The present invention relates to a digital camera and a control method thereof. More particularly, the present invention relates to a digital camera and a control method thereof that calculate a white balance gain from an area satisfying an achromatic color condition by referring to a luminance distribution in a screen, And a control method thereof.

Generally, the human eye will detect white as white under any light source, but when viewed through a camera, it looks red or green depending on sunlight, fluorescent light, and incandescent light. This is due to the color temperature of the light source. If the color temperature is high, it becomes the color of the blue color system. If the color temperature is low, it becomes the color of the red color system. If the color temperature is affected by this, the correct color can not be reproduced when the image is outputted. This is called white balance adjustment so that white objects as well as other colors can be reproduced correctly by adjusting white subjects under whatever light source to reproduce white.

Conventionally, the auto white balance (AWB) is performed by referring to the entire screen area. In this case, the luminance distribution is greatly influenced. That is, in an image in which shade and sunshine are simultaneously shot on a very clear day, the shade has a very low signal value, whereas the sunshine has a very high signal value, so that the average value tends to be shifted toward the sunny side. However, in practice, the on-site data is close to saturation or saturation, and the white balance refers to data that is shifted to the sunny side, even though the shaded data should be referred to.

An object of the present invention is to provide a digital camera and a control method thereof that can reduce a white balance error in a shade in an image shot together with a sunny day and a shade on a clear day.

Another object of the present invention is to provide a digital camera and a control method thereof that can accurately adjust white balance by calculating a white balance gain from an area satisfying an achromatic color condition by referring to a luminance distribution in a screen.

According to another aspect of the present invention, there is provided a digital camera including: an achromatic region detection unit for detecting an area satisfying an achromatic color condition in a full screen area;

A luminance difference calculating unit for calculating a luminance difference (Br1 - Br2) between the luminance (Br1) of the full screen area and the luminance (Br2) of the achromatic area; And

(i) a gain value is calculated from the achromatic area if the luminance difference Br1-Br2 is equal to or greater than the threshold value Cr, and ii) if the luminance difference Br1-Br2 is smaller than the threshold value Cr, And a white balance gain calculator.

Preferably, the achromatic area detecting unit divides the entire screen area into a plurality of image blocks, and determines whether or not the achromatic color condition is satisfied for each of the image blocks.

For example, the achromatic region detecting unit may determine whether the blending 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 adjustment unit having a gain value calculated by the white balance gain calculation unit and correcting the R, G, and B color signals of the pixels constituting the screen.

According to another aspect of the present invention, there is provided a method of controlling a digital camera,

An achromatic region detection step of detecting an achromatic region satisfying an achromatic color condition from a full screen region;

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

The gain value is calculated from the achromatic area if the luminance difference Br1-Br2 is equal to or greater than the threshold value Cr and the white balance gain is calculated from the entire screen area if the luminance difference Br1- Step.

Preferably, the control method of 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 the achromatic color condition is satisfied in units of image blocks.

For example, in the achromatic region detection step, whether or not the mixing ratio of the R, G, and B color signals detected in each image block falls within a set range can be regarded as achromatic condition.

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

According to the digital camera and its control method of the present invention, by calculating the white balance gain from an area that satisfies the achromatic color condition with reference to the luminance distribution in the screen, more accurate white balance adjustment can be performed. In the subject area in which sunshine and shade coexist White balance errors in the shade can be reduced.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings attached hereto. Throughout the present specification, a digital camera is not limited to a camera of a consultation classified on the basis of a morphological characteristic of a camera as a mobile device having an appropriate photographing function, and is not limited to a camera having a portable function and a photographing function such as a camcorder, It is used in a broad sense to cover all devices.

Fig. 1 schematically shows an overall configuration of a digital camera according to an embodiment of the present invention. Referring to the drawings, the digital camera includes an optical unit 110 including a plurality of optical lenses to image an object image with respect to an image sensing plane, and an image sensor (not shown) An analog front end circuit 130 (Analog Front End: AFE circuit) for converting an output signal of the image pickup element 120 into a quantized digital image signal, an operation for signal processing A buffer memory 140 for temporarily storing a video signal to provide an image 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 a recording medium 170 for collectively controlling the overall data flow and respective constituent parts And a digital signal processor 150. The digital camera includes a user input unit 190 having a plurality of input mechanisms for detecting a user's operation as an input and output device, a video output unit (not shown) for receiving a video signal from the digital signal processor 150 180).

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

The image pickup device 120 is a CCD (Charged Coupled Device) or CMOS (Comple Metal Oxide Semiconductor) image sensor. The image pickup device 120 converts an image of an object incident via the optical unit 111 into an electrical image signal do. The operation of the imaging element 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 CDS (Correlated Double Sampling) processing and ADC (Analog Digital Conversion) processing on the output signal of the image pickup device, Into a digital video signal. The digital video signal is transmitted to the encoder / decoder 160, converted into encoded data according to a prescribed compression method, and then stored in the recording medium 170. The buffer memory 140 is a volatile memory that provides a work area for various types of data processing and may be configured as a DRAM (Dynamic Random Access Memory or SDRAM). The encoder / decoder 160 and the digital signal processor 150 Provides a work area for data processing.

The digital signal processor 150 controls the operation of the entire digital camera related to image capturing and processing of image data by executing a program recorded in an EEPROM 145 (Electronically Erasable and Programmable ROM). In particular, the digital signal processor 150 eliminates the influence of a light source type (e.g., sunlight, incandescent lamp, and fluorescent lamp) by adjusting the gains of the R, G, and B color signals forming the digital video signal, Perform white balance adjustment so that it is reproduced. The digital signal processor 150 finds an area satisfying the achromatic color condition from the entire screen area (hereinafter referred to as an achromatic area), and according to the magnitude relationship between the luminance Br1 of the entire screen area and the luminance Br2 of the achromatic area Perform white balance adjustment in different ways. That is, when the luminance difference (Br1-Br2) between the two areas is smaller than the threshold value (Cr), the R, G, and B color signals of the entire screen area are collected to calculate the WB gain value. However, when the luminance difference (Br1-Br2) between both areas is larger than the threshold value (Cr), the WB gain value is not calculated from the entire screen area and only the R, G and B color signals of the achromatic area are collected, . Finally, the digital signal processor 150 corrects the R, G, and B color signals of each pixel signal according to the calculated WB gain to generate a white balanced color signal.

The digital signal processor 150 includes an achromatic area detecting unit 151, a luminance difference detecting unit 153, a WB gain calculating unit 155, and a WB adjusting unit 157. [ The achromatic area detecting unit 151 finds an area in the entire screen that satisfies the achromatic color condition. More specifically, the achromatic area detecting unit 151 determines whether or not the achromatic color condition is satisfied in units of image blocks, and recognizes the corresponding block as an achromatic color area according to the determination result. For example, the achromatic area detection unit 151 divides one screen into a plurality of image blocks, calculates representative values (e.g., average values) of the R, G, and B color signals in each of the image blocks, . For example, the achromatic condition may be set as a blending ratio of the R, G, and B color signals (ex. Ratio of R / G color signal, ratio of B / G color signal) It can be recognized as an achromatic region. For example, if 1-α ≦ R / G ≦ 1 + α and 1-α ≦ B / G ≦ 1 + α, the corresponding image block can be recognized as achromatic region.

The luminance difference detector 153 extracts the luminance Br1 of the entire screen and the luminance Br2 of the area recognized as achromatic color and calculates the luminance difference Br1 to Br2 between the two areas. 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 area. Then, the brightness difference (Br1-Br2) between the two areas is compared with a preset threshold value Cr to determine the magnitude relationship.

The WB gain calculator 155 calculates the WB gain value from the achromatic area if the luminance difference Br1-Br2 is equal to or greater than the threshold value Cr and if the luminance difference Br1-Br2 is smaller than the threshold value Cr, The WB gain value is calculated.

i) When luminance difference (Br1-Br2) ≥ threshold value (Cr), there is a large luminance deviation in one screen, and there is a high possibility that a subject image in which sunny and shade coexist on a clear day is captured. At this time, the sunny place data has a very high signal level, whereas the shade data has a very low signal level. Therefore, if the WB gain value is calculated from the whole screen by averaging the values, the sunbeam data tends to be shifted toward the sunny side. Since the on-the-spot data is the saturated data of the chromatic system, accurate white balance adjustment can be performed by calculating the WB gain value from the achromatic series of sound data. More specifically, the WB gain calculating unit 155 calculates the WB gain of each of the R, G, and B color signals so that the representative value (average value) of the R, G, and B color signals calculated in the achromatic region is 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 value of the G signal divided by the representative value of the R signal, and the WB gain for the B signal may be the representative value of the G signal divided by the representative value of the B signal.

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

The WB adjusting unit 157 adjusts the gains for the R, G, and B color signals of the respective pixels with the calculated WB gain values. For example, the WB adjuster adjusts the white balance by generating R, G, and B color signals in which the white balance is balanced by multiplying the R, G, and B color signals of the pixels by the WB gain values.

FIG. 2 is a flowchart illustrating a control method of a digital camera according to another aspect of the present invention, 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 the achromatic condition, and recognizes the image blocks as an achromatic area (S11). For example, a combination of lights (1: 1: 1) in which R, G, and B color components are mixed together can be defined as an achromatic color. (ex. average value), and the image block having a mixture ratio of R, G, B color signals (ex. ratio of R / G color signal and ratio of B / G color signal) . For example, if 1-α ≤ R / G ≤ 1 + α, 1-α ≤ B / G ≤ 1 + α, then the corresponding image block can be incorporated into the achromatic region.

Next, the brightness Br1 of the entire screen is calculated (S12). More specifically, the digital signal processor 150 can calculate the luminance Br1 of the entire screen by extracting and averaging the luminance signals of the pixels constituting one screen. Next, the luminance Br2 of the achromatic area is calculated (S13). More specifically, the digital signal processor 150 can calculate the luminance Br2 of the achromatic area by extracting the luminance signals of the pixels constituting the achromatic area and averaging the luminance signals. Then, the luminance difference Br1-Br2 between the entire screen and the achromatic area is calculated and compared with the threshold value Cr (S14, S15). The digital signal processor 150 calculates a WB gain value from the achromatic area if the luminance difference Br1-Br2 is equal to or greater than the threshold value Cr in step S16. If the luminance difference Br1-Br2 is smaller than the threshold value Cr, 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 large in one screen, and it can be an image in which sunny and shade are captured together on a very clear day. At this time, the sunny place data has a very high signal level, whereas the shade data has a very low signal level. Therefore, if the WB gain value is calculated from the whole screen by averaging the values, the sunbeam data tends to be shifted toward the sunny side. However, since the on-site data is the saturated data of the chromatic color series, accurate white balance adjustment can be performed by calculating the WB gain value from the achromatic series of sound data. For example, the digital signal processor 150 may calculate the WB gain value so that the R, G, and B color signals of the achromatic region may form a ratio of 1: 1: 1.

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

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

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, You will understand the point. Accordingly, the true scope of protection of the present invention should be determined by the appended claims.

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

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

Description of the Related Art

110: Optical unit 111: Driver

112: zoom lens 114: shutter

116: aperture 118: focus lens

120: Imaging element 121: Timing generator

130: Analog front end circuit (AFE circuit)

140: buffer memory 145: EEPROM

150: digital signal processor 151: achromatic area detection unit

153: luminance difference detector 155: WB gain calculator

157: WB adjuster 160: Encoder / decoder

170: recording medium 180: video output unit

190: user input

Claims (8)

An achromatic area detection unit for detecting an area satisfying an achromatic color condition among the entire screen areas; A luminance difference calculating unit for calculating a luminance difference (Br1 - Br2) between the luminance (Br1) of the full screen area and the luminance (Br2) of the achromatic area; And (i) a gain value is calculated from the achromatic area if the luminance difference Br1-Br2 is equal to or greater than the threshold value Cr, and ii) if the luminance difference Br1-Br2 is smaller than the threshold value Cr, And a white balance gain calculating unit. The method according to claim 1, Wherein the achromatic area detection unit divides the entire screen area into a plurality of image blocks and determines whether or not an achromatic color condition is satisfied in units of image blocks. 3. The method of claim 2, Wherein the achromatic region detection unit determines whether or not the blending ratio of the R, G, B color signals detected in each image block falls within a set range. The method according to claim 1, Further comprising a white balance adjusting unit having a gain value calculated by the white balance gain calculating unit and correcting the R, G, B color signals of the pixels constituting the screen. An achromatic region detection step of detecting an achromatic region satisfying an achromatic color condition from a full screen region; Calculating a luminance difference (Br1-Br2) from the luminance (Br1) of the entire screen area and the luminance (Br2) of the achromatic area; And The gain value is calculated from the achromatic area if the luminance difference Br1-Br2 is equal to or greater than the threshold value Cr and the white balance gain is calculated from the entire screen area if the luminance difference Br1- The method comprising the steps of: 6. The method of claim 5, Further comprising dividing the full screen area into a plurality of video blocks, Wherein the step of detecting an achromatic region determines whether an achromatic color condition is satisfied in units of image blocks. The method according to claim 6, Wherein the achromatic region detection step determines whether the blending ratio of the R, G, and B color signals detected in each image block falls within a predetermined range. 6. The method of claim 5, Further comprising a white balance adjusting step of correcting the R, G, and B color signals of the pixels constituting the screen with the gain value calculated in the white balance gain calculating step.

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