KR100712809B1 - Apparatus for auto white balance control and method for control of auto white balance - Google Patents

Abstract

The present invention is to provide an automatic white balance control device that can prevent the change of the white area in the white balance adjustment process and can represent a white subject in white. To this end, the present invention is to analog-to-digital conversion and color conversion of the analog image signal An analog-digital conversion and interpolation unit for performing interpolation; A digital white balance amplifier for amplifying the interpolated digital image signal by using digital white balance gain; A first color space converter for color space converting the digital image signal to which the white balance gain is applied; A second color space converter for converting the color space without applying a white balance gain to the interpolated digital image signal; A white pixel condition check unit for checking a white pixel condition using a digital image signal in which color balance is not applied and white balance gain is not applied; An average calculating unit for calculating an average of Cr and Cb by using the output of the pixel condition check unit; And an automatic white balance control unit for controlling a white balance for adjusting the digital white balance gain through a feedback loop by using the output of the average calculating unit.

CMOS image sensor, AWB, WBG, WPC.

Description

Automatic white balance control and automatic white adjustment {APPARATUS FOR AUTO WHITE BALANCE CONTROL AND METHOD FOR CONTROL OF AUTO WHITE BALANCE}

1 is a block diagram schematically showing the configuration of a general image sensor according to the prior art.

2 is a flowchart illustrating an edge detection method according to an embodiment of the present invention.

3A and 3B are flowcharts specifically illustrating step S204 of FIG. 2.

4 is an example of interpolating a G intensity value of a pixel having an intensity value in R and B color components using a median filter using pixels having an intensity value in a G color component in a 5 * 5 kernel configured for edge detection. Figure.

FIG. 5 is a diagram showing another example of interpolating G intensity values of pixels having intensity values in color components of R and B using vertical or horizontal line pixel average values. FIG.

6 is a block diagram illustrating an automatic white balance adjustment apparatus of a CMOS image sensor according to another exemplary embodiment of the present invention.

7 is a view showing the results of applying the automatic white balance method of the present invention.

The present invention relates to a CMOS image sensor, and more particularly, to an automatic white balance adjusting device and an automatic white balance adjusting method of a CMOS image sensor.

At present, the image sensor is the mainstream of 1 million pixels, and according to the generalization of digital still cameras, the K-class image sensor having more than 3 million pixels is expected to become common.

Since the image sensor is a device that converts incoming light into an electrical signal, the color of the subject changes depending on the light source. That is, different light sources will have the same color in different colors. In order to correct the subject's color, it is typical to adjust the coefficient of the white subject to the color information, that is, white balance gain (hereinafter referred to as WBG) to make it appear white. (Hereinafter referred to as AWB).

Images through AWB should ideally be natural for the human eye to judge the result of an image taken from a single light source.

1 is a block diagram schematically showing the configuration of a conventional CMOS image sensor.

Referring to FIG. 1, a CMOS image sensor includes a control and external system interface unit 11, a pixel array unit 10, and an analog-to-digital converter unit 12 (hereinafter referred to as an ADC). And a line memory section 13 and an image signal processing section 14.

Hereinafter, the operation of each component of the CMOS image sensor having the above-described configuration will be described in detail.

The pixel array unit 10 is a part that detects information about an image coming from the outside by arranging pixels (Pixel) horizontally and vertically (N, M are integers) in order to maximize the response to light. It is the most essential part of the overall image sensor.

The control and external system interface unit 11 controls the overall operation of the image sensor of the image sensor by using a finite state machine (FSM), and is responsible for the interface operation to the external system, and includes a batch register (not shown). It can be programmed for various internal operations, and it controls the operation of the entire chip according to the programmed information.

On the other hand, although not shown in the figure, the analog line buffer unit serves to sense and store the voltage of the selected one pixel of the row, the analog data stored in the analog line buffer unit is the data value of the column selected by the control of the column decoder is analog It is sent to the variable amplifier via the bus.

The variable amplifier, for example, a programmable gain amplifier (PGA) amplifies the pixel voltage stored in the analog line buffer unit when the pixel voltage is small. Is converted to a digital value through.

The line memory unit 13 stores the digitally converted RGB image signal for each line, and the image signal processor 14 may include error correction, color interpolation, gamma correction, Performs functions such as color space conversion.

Meanwhile, in the image sensor, a fixed pattern noise is generated due to an offset voltage due to a slight difference in the manufacturing process. In order to compensate for the fixed pattern noise, the image sensor reads a reset voltage signal and a data voltage signal from each pixel of the pixel array unit 11 in turn, and outputs the difference. Correlated Double Sampling (hereinafter referred to as CDS).

Since the circuit inside the sensor is difficult to determine whether it is distortion caused by the light source with each incoming data alone, it generally performs white balance under the assumption that the average value of the entire image converges on white.

In this case, when a large number of specific colors are distributed on an image, a phenomenon in which a tone of a specific color approaches gray is caused by incorrect light source correction.

In order to make up for this drawback, recently, a white pixel condition checker (WPC) is used to predict an area where white color may appear due to distortion caused by a light source, and white balance using only corresponding image data. A method of doing this was also developed.

However, this method also produces a phenomenon in which the white area is continuously changed according to the change of WBG, so that the color of the white subject cannot be sent to white and is concentrated in one color.

On the other hand, looks at the above-mentioned conventional problems in detail.

FIG. 2 is a diagram illustrating a white pixel condition checker, FIG. 3 is a block diagram illustrating an automatic white balance adjusting apparatus according to the prior art, and FIG. 4 is a diagram illustrating a conventional problem.

Hereinafter, the prior art will be described with reference to FIGS. 2 to 4.

Referring to FIG. 3, the automatic white balance adjusting device according to the related art uses an amplifier 30 to receive image information output from an ADC and amplify it using a white balance gain, and an output of the amplifier 30. An interpolation / color space conversion unit 31 which performs interpolation and color space conversion, a white pixel determination unit 32 which determines a white pixel using image information which has been subjected to color space conversion, and a pixel determined as white pixel. And an average calculating unit 33 for calculating the average values of Cr and Cb, and a control unit 34 for performing white balance adjustment using the average values of Cr and Cb, and providing the feedback to the amplifier.

In the case of the conventional white AWB, the Cb and Cr axes of FIG. 2 move according to the change of the WBG. As a result of this disadvantage, as shown in FIG. 4, a specific color component continuously enters the white determination region of the WPC predetermined by the designer.

4A illustrates a case where a white subject and a green subject are on an image. In this case, white is distributed in the white determination region defined by the designer, and in the case of green, the white determination region is partially distributed in the white determination region according to the characteristic or color of the sensor such as noise or image distortion caused by the sensor.

Here, the average of the information distributed in the white area is a green area that is invasive, both Cb and Cr have a negative value, and accordingly the algorithm increases the red gain and blue gain values. According to this increase, the image information of the green subject is changed to a color close to gray (R, G, and B have similar values) due to the increase in the R value and the B value. As in b), white is pulled toward purple and green is pulled toward gray.

The present invention proposed to overcome the above problems, to provide an automatic white balance adjustment device and an automatic white balance adjustment method that can prevent the change of the white area in the white balance adjustment process and represent a white subject in white. It is done.

In order to achieve the above object, the present invention provides an analog-to-digital conversion and interpolation unit for analog-to-digital conversion and color interpolation; A digital white balance amplifier for amplifying the interpolated digital image signal by using digital white balance gain; A first color space converter for color space converting the digital image signal to which the white balance gain is applied; A second color space converter for converting the color space without applying a white balance gain to the interpolated digital image signal; A white pixel condition check unit for checking a white pixel condition using a digital image signal in which color balance is not applied and white balance gain is not applied; An average calculating unit for calculating an average of Cr and Cb by using the output of the pixel condition check unit; And an automatic white balance control unit for controlling a white balance for adjusting the digital white balance gain through a feedback loop by using the output of the average calculating unit.

In addition, the present invention in order to achieve the above object, the analog white balance amplifier for amplifying the analog image signal using the analog white balance gain; An analog-digital converter and an interpolator for analog-to-digital conversion and color interpolation of an analog image signal to which analog white balance gain is applied; A first color space converter for color space converting the interpolated digital image signal to which the analog white balance gain is applied; A digital gain compensator for compensating digital gain on the interpolated digital image signal to which analog white balance gain is applied; A second color space converter for color space converting the output of the digital gain compensator; A white pixel condition checker for checking a white pixel condition using an output of the second color space converter; An average calculating unit for calculating an average of Cr and Cb by using the output of the pixel condition check unit; And an automatic white balance control unit for controlling a white balance for adjusting digital white balance gain and digital gain through a feedback loop using the output of the average calculator.

In addition, the present invention, in the block to distinguish the white region, using the image information corresponding to the block to calculate the automatic white balance average, calculate the automatic white balance average, there is a path that is fed back, and distinguish the white region It provides a method for automatic white balance adjustment, characterized in that the building block is separated from the feedback path.

In the present invention, the data path for WBG feedback is calculated and the data path to the WPC for determining the white area is calculated and processed. That is, the information for determining the white region of the subject uses image information not passing through the WBG and is fed back to the WBG using the data passing through the WBG. As a result, the white region may be prevented from being changed during the white balance adjustment process, and the white subject may be expressed in white.

Hereinafter, the most preferred embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art can easily implement the technical idea of the present invention. do.

FIG. 5 is a block diagram illustrating an automatic white balance adjusting device of a CMOS image sensor according to an exemplary embodiment of the present invention.

Referring to FIG. 5, the automatic white balance adjusting device uses an ADC and an interpolator 50 for analog / digital converting an analog image signal and performing color interpolation, and amplifies the digital image signal using digital white balance gain. A digital white balance amplifying unit 51, a first color space converting unit 52 for color space converting a WBG-applied digital image signal, and color space conversion without applying WBG to the interpolated digital image signal. A second color space converter 55 for checking a white pixel condition using a digital image signal that is color space-converted without WBG applied thereto, and a pixel condition checker 56 for checking a white pixel condition. An average calculator 53 for calculating the average of Cr and Cb by using the output of 56) and a digital WBG through a feedback loop using the output of the average calculator 53. And an automatic white balance control unit 54 for controlling the white balance for adjustment.

The automatic white balance circuit having the above-described configuration uses a digital multiplier or a digital signal amplifier as the digital white balance amplifier 51. The WPC path uses information that does not go through the WBG, and the information used to create the average and actual output images uses the information that goes through the WBG, thereby preventing changes in the WPC space due to feedback.

FIG. 6 is a block diagram illustrating an automatic white balance adjustment apparatus of a CMOS image sensor according to another exemplary embodiment of the present invention.

Referring to FIG. 6, the automatic white balance adjusting device performs analog / digital conversion of an analog white balance amplifier 60 for amplifying an analog image signal using analog white balance gain, and an analog image signal to which analog WBG is applied. ADC and interpolation unit 61 for performing color interpolation, a first color space conversion unit 62 for color space conversion of an interpolated digital image signal to which analog WBG is applied, and interpolated digital to which analog WBG is applied A digital gain compensator 65 for compensating digital gain in the image signal, a second color space converter 66 for color space conversion of the output of the digital gain compensator 65, and a second color space converter The average of Cr and Cb is calculated using the output of the white pixel condition check unit 67 and the pixel condition check unit 67 for checking the white pixel condition using the output. An average calculating unit 63 for calculating and an automatic white balance control unit 64 for controlling the white balance for adjusting the digital WBG and the digital gain through a feedback loop using the output of the average calculating unit 63; It is configured by.

The automatic white balance circuit having the above-described configuration uses an analog amplifier as the WBG, and the path of the WPC and the path used to generate the average and actual output image must all go through the analog amplifier. In this case, a circuit for compensating the gain applied to the WBG, that is, the digital gain compensator 65, is inserted in front of the WPC block so that the spatial coordinates of the WPC do not move with the change of the WBG.

7 is a diagram illustrating a result of applying the automatic white balance method of the present invention.

As in the above-described two embodiments, as shown in FIG. 7, the two paths are separated.

In FIG. 4, the pixel entering the white region of the WPC changes according to the change of WBG. However, in FIG. 7, the pixel entering the white region of the WPC does not change regardless of the change of WBG.

7 (a) and 7 (b) show the distribution of pixels in the WPC, and in the present invention, the distribution of pixels in the WPC does not change according to feedback for automatic white balance.

7 (c) and 7 (d) are blocks for calculating an average of feedback of an automatic white balance by calculating an average, and calculating only an average of information of a pixel determined to be a white area in a WPC, thus significantly reducing the phenomenon of tilting. Done.

5 and 6 may be a configuration corresponding to the image signal processor 14 in the CMOS image sensor structure of FIG. 1, and other automatic white balance data processing schemes of the image sensor may be used. When the white region is determined and used, the above-described automatic white balance method of the present invention can be appropriately applied.

According to the present invention as described above, by processing the data path to the WPC that calculates the average and WBG feedback and the WPC to determine the white area, the white area is prevented from being changed during the white balance adjustment process, and the white subject It can be seen through the embodiment that can be expressed in white.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible in the art without departing from the technical spirit of the present invention. It will be clear to those of ordinary knowledge.

The present invention described above has the effect of improving the performance of the image sensor by preventing a change in the white area and expressing a white subject in white during the white balance adjustment process.

Claims (7)

An analog-digital conversion and interpolation unit for performing analog / digital conversion of the analog image signal and color interpolation; A digital white balance amplifier for amplifying the interpolated digital image signal by using digital white balance gain; A first color space converter for color space converting the digital image signal to which the white balance gain is applied; A second color space converter for converting the color space without applying a white balance gain to the interpolated digital image signal; A white pixel condition check unit for checking a white pixel condition using a digital image signal in which color balance is not applied and white balance gain is not applied; An average calculating unit for calculating an average of Cr and Cb by using the output of the pixel condition check unit; And Automatic white balance control unit for controlling the white balance for adjusting the digital white balance gain through a feedback loop using the output of the average calculation unit Automatic white balance adjustment device comprising a. The method of claim 1, And the digital white balance amplifier comprises a digital multiplier or a digital signal amplifier. An analog white balance amplifier for amplifying the analog image signal using analog white balance gain; An analog-digital conversion and interpolation unit for performing analog-to-digital conversion and color interpolation on an analog image signal to which analog white balance gain is applied; A first color space converter for color space converting the interpolated digital image signal to which the analog white balance gain is applied; A digital gain compensator for compensating digital gain on the interpolated digital image signal to which analog white balance gain is applied; A second color space converter for color space converting the output of the digital gain compensator; A white pixel condition checker for checking a white pixel condition using an output of the second color space converter; An average calculating unit for calculating an average of Cr and Cb by using the output of the pixel condition check unit; And Automatic white balance control unit for controlling the digital white balance gain and the white balance for adjusting the digital gain through a feedback loop using the output of the average calculation unit Automatic white balance adjustment device comprising a. In a block separating white areas, an automatic white balance average is calculated using only image information corresponding to the block, A path for calculating an automatic white balance average and being fed back exists, and allowing a block separating the white area to be separated from a feedback path. The method of claim 4, wherein Obtaining said auto white balance average and applying feedback thereof to an analog amplifier. The method of claim 4, wherein Obtaining an average of the automatic white balance and applying the feedback thereof to a digital amplifier. The method of claim 4, wherein Obtaining an average of the automatic white balance and applying the feedback thereof to a digital signal processing apparatus.

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