KR20110079310A

KR20110079310A - Auto white balance image processing method

Info

Publication number: KR20110079310A
Application number: KR1020090136328A
Authority: KR
Inventors: 천복기
Original assignee: 주식회사 동부하이텍
Priority date: 2009-12-31
Filing date: 2009-12-31
Publication date: 2011-07-07

Abstract

AWB image processing method according to an embodiment comprises the steps of analyzing the histogram of the pixels constituting the image; Determining whether more pixels than the reference value are overexposed as a result of the histogram analysis; If more pixels than the reference value are overexposed, reducing the current exposure time by the ratio of total pixels to overexposed pixels; And extracting color (B / G, R / G) values of pixels constituting the image, and selecting only pixels belonging to a white point region among the extracted color values as white pixels.

According to the exemplary embodiment, more effective data, ie, white pixels, may be selected among pixels constituting the image by adjusting the exposure time, thereby obtaining AWB information as close as possible to the light source.

Description

AF image processing method {Auto White Balance image processing method}

Embodiments relate to AWB image processing methods.

In the case of natural light, the color temperature is changed by factors such as visual difference, climate, lighting conditions, shadows, etc. Therefore, the white balance should be adjusted according to the change of light conditions.

In the case of the camera module, AWB (Auto White Balance) is processed through image processing.

The AWB refers to a process in which an image processor stores a white balance value in a reference environment, and compensates for the color value of light according to the stored white balance value when light is incident from the outside.

Conventional image processing sets the exposure time to a relatively large value in order to adjust the overall brightness, whereby the homeostasis of the ratio (B / G, R / G) of the element values (R, G, B) of the white point pixel is broken. It cannot be used as valid data for AWB execution.

As such, when AWB is performed with a small number of valid data by excluding over-exposed pixels, a loss of information and a deterioration of an image may occur.

The embodiment improves the conventional processing method of performing AWB with a small number of valid data by excluding over-exposed pixels, thereby selecting more white pixels among the pixels constituting the image to obtain AWB information as close as possible to the light source. Provides AWB image processing method to obtain.

According to the embodiment, the following effects are obtained.

First, more effective data, ie, white pixels, may be selected among pixels constituting the image by adjusting the exposure time, and the AWB information as close as possible to the light source may be obtained.

Second, the AWB information can be obtained as much as possible by moving the overexposed pixel to the measurable effective range by adjusting the exposure time, and the image degradation can be prevented due to the improved AWB performance.

AWB image processing method according to an embodiment will be described in detail with reference to the accompanying drawings.

Hereinafter, in describing the embodiments, detailed descriptions of related known functions or configurations are considered to unnecessarily obscure the subject matter of the present invention, and thus only the core configurations directly related to the technical spirit of the present invention will be referred to.

The embodiment relates to an AWB image sensing method of increasing effective data used as white pixels when performing AWB (Auto White Balance) by adjusting an exposure time of an image sensor.

First, the AWB will be briefly described as follows.

1 is a diagram illustrating a Bayer image and an AWB processed image, and FIG. 2 is a graph illustrating the coordinates of an AWB white pixel.

First, color (B / G, R / G) values of all pixels are extracted from a Bayer image as shown in FIG. 1A, and the extracted color values are displayed in coordinates of the AWB white pixel as shown in FIG.

Second, R and B gains to be compensated for are calculated by selecting only pixels belonging to a white point region, which is a reference of AWB.

In this case, the selected pixel is referred to as a "white pixel".

The white pixels are pixels belonging to the first to sixth patches of the Macbeth Chart A of FIG. 1.

The white pixel informs the current temperature of the light source, and is represented by a histogram having a scattering point concentrated at a predetermined coordinate point as shown in the region “B” of FIG. 2.

Third, when the R and B gains are calculated, AWB is completed as shown in FIG.

As such, the white pixel is selected not only for all pixels on the screen but only for pixels belonging to the white point area, and thus performs AWB. If more white pixels exist, more accurate information closer to a light source can be obtained. .

3 and 4 are graphs showing the effective range of the white pixel according to the color value (code) level and the patch number.

3 shows that the exposure time is set to 300 ms. Patches 5 and 6 are overexposed so that linearity (see the white pixel line in FIG. 2) is collapsed between the R, G, and B pixels. It goes beyond and is not selected as useful data, ie white pixels.

On the other hand, Figure 4 is a case where the exposure time is set to 100ms, patches 1 to 6 are all within the effective range can be selected as a white pixel.

As such, reducing the exposure time increases the probability that all patches are selected as the white pixel.

Hereinafter, an AWB image sensing method according to an embodiment will be described.

5 is a graph illustrating a result of analyzing a histogram of pixels.

(A) of FIG. 5 shows the number of pixels for each pixel brightness level present within the effective range of the histogram during overexposure, and (b) shows the number of pixels for each pixel brightness level present within the effective range of the histogram during proper exposure. It is.

First, the histogram of the pixels forming the image is analyzed.

Second, as a result of histogram analysis, it is determined whether more pixels than the reference value are overexposed.

Third, if more pixels than the reference value are excessively exposed as shown in (a) of FIG. 5, the current exposure time is reduced by the ratio of the total pixels to the overexposed pixels.

For example, according to the experimental results of FIGS. 3 and 4, it is possible to reduce the current exposure time by 1/3 to make an overexposed pixel a valid pixel.

Fourth, color (B / G, R / G) values of pixels constituting the image are extracted, and only pixels belonging to a white point region of the extracted color values are selected as white pixels.

Fifth, an R and B gain to be applied to the compensation is calculated based on the selected white pixel.

Sixth, after returning to the past exposure time, the calculated R and B gains are applied to the image to process the compensation process.

The AWB image processing method according to this embodiment is assumed to be performed once in a still capture mode.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood that various modifications and applications other than those described above are possible. For example, each component specifically shown in the embodiments of the present invention can be modified and implemented. And differences relating to such modifications and applications will have to be construed as being included in the scope of the invention defined in the appended claims.

1 illustrates a Bayer image and an AWB processed image.

2 is a graph illustrating the coordinates of an AWB white pixel.

3 and 4 are graphs showing effective ranges of white pixels according to color value (code) levels and patch numbers.

5 is a graph showing a result of analyzing a histogram of pixels.

Claims

Analyzing a histogram of pixels forming an image;

Determining whether more pixels than the reference value are overexposed as a result of the histogram analysis;

If more pixels than the reference value are overexposed, reducing the current exposure time by the ratio of total pixels to overexposed pixels; And

AWB image processing comprising extracting color (B / G, R / G) values of pixels constituting the image and selecting only pixels belonging to a white point region among the extracted color values as white pixels Way.

The method of claim 1,

If fewer pixels than the reference value are overexposed, the current exposure time is maintained within the white point area of the extracted color values while maintaining the current exposure time without reducing the current exposure time by the ratio of the total pixels to the overexposed pixels. And selecting only pixels as white pixels.

The method of claim 1, wherein after selecting the white pixel:

And calculating R and B gains to be applied to the compensation based on the selected white pixels.

The method of claim 3, wherein after calculating the R and B gains,

AWB image processing method further comprising the step of returning to the past exposure time.

5. The method of claim 4,

And processing the compensation process by applying the calculated R and B gains to the image.

The method of claim 1, wherein reducing the current exposure time by the ratio of total pixels to overexposed pixels

AWB image processing method characterized by reducing the current exposure time by 1/3.

5. The method of claim 4,

Analyzing the histogram of the pixels constituting the image, and returning to the past exposure time, is performed in a still capture mode.

The method of claim 7, wherein

Analyzing the histogram of the pixels constituting the image to returning to the past exposure time is performed once in a still capture mode.