KR100860877B1 - Apparatus and method for removing color noise - Google Patents

Abstract

An apparatus and a method for removing color noise are provided to remove color noise even when an image sensor has intensive signal interference or the analog gain of the image sensor increases in a dark place to achieve improve picture quality. An apparatus(210) for removing color noise includes a pre-processor(300) and a filter(310). The pre-processor calculates a difference between a maximum value and a minimum value of color difference signals of input image data. The filter classifies the color difference signals by using the difference calculated by the pre-processor and a predetermined threshold and filters the classified color difference signals by using a weight for adjusting predetermined filtering intensity.

Description

Apparatus and method for removing color noise}

1 is an exemplary diagram for describing color noise generated in a conventional image processing process.

2 is a diagram illustrating a configuration of a color noise removing device according to an embodiment of the present invention.

3 is a diagram illustrating a configuration of a color noise removing unit according to an exemplary embodiment of the present invention.

4 is a diagram illustrating a configuration of a color difference signal that may be used in a preprocessing unit that may be included in a color noise removing unit according to an exemplary embodiment of the present invention.

5 is a view schematically showing the function of the filter unit which may be included in the color noise removing unit according to an embodiment of the present invention.

6 is a flow chart showing the order in which the color noise removal method according to an embodiment of the present invention is performed.

FIG. 7 is a view showing a comparison between an image processed by a conventional image processing process and an image processed by a color noise removing device according to an exemplary embodiment of the present invention. FIG.

The present invention relates to an apparatus and method for removing color noise, and more particularly, to an apparatus and method for removing color noise used in an image processing system.

The image sensor included in the image processing system has a characteristic of high interference between signals or increases the analog gain of the image sensor in a place where the amount of light is insufficient, such as in a dark indoor environment, so that the pixels are lumpy throughout the image. There is a problem in that noise, called visible color noise or color noise, occurs.

1 is an exemplary diagram for describing color noise generated in a conventional image processing process.

In the case of noise due to color interpolation in a typical image processing system, since a component that is not present at a current pixel position is generated by using other components around a pixel, a position having a high frequency component (for example, an edge or Zipper-like noise occurs at the boundary).

However, in the case of color noise generated by increasing the analog gain of the image sensor in a place where the interference between signals has severe characteristics or insufficient light, such as a dark indoor environment, as shown in the example of FIG. It appears regardless of the frequency component in the color image as a whole, the pattern also has a variety of problems.

Therefore, color noise is evaluated as an important problem when evaluating the image quality of an image, and it is required to develop a method of removing such color noise without damaging components at edges or boundaries where high frequency components are many.

In order to solve the conventional problems as described above, the present invention is to increase the analog gain of the image sensor in a place where the image sensor has a characteristic of high interference between signals or there is not enough light such as a dark indoor environment The present invention proposes a color noise removing apparatus and method capable of removing color noise generated accordingly.

In addition, the present invention proposes a color noise removing apparatus and method capable of removing a wide variety of color noise.

Another object of the present invention is to propose a color noise removing apparatus and method capable of removing color noise without damaging a component at an edge or a boundary having a high frequency component.

Still other objects of the present invention will be readily understood through the following description of the embodiments.

In order to achieve the object as described above, according to an aspect of the present invention, there is provided an apparatus for removing color noise.

According to a preferred embodiment of the present invention, a pre-processing unit for calculating a difference value between the maximum value and the minimum value of the color difference signal of the input image data; And classifying the input color difference signals using a difference value calculated by the preprocessor and a preset threshold value, and filtering each of the classified color difference signals by further using a weight value for adjusting a predetermined filtering intensity. An apparatus for removing color noise is provided, including a filter unit for performing filtering.

The preprocessing unit may further calculate a median value and a center average value of the color difference signal of the input image data, and the filter unit may further classify the color difference signal using the median value and the center mean value of the color difference signal calculated by the preprocessor. can do.

The filter unit may further perform classification of the input color difference signal and filtering each of the classified color difference signals by further using a weight value for adjusting a predetermined filtering intensity.

The color noise removing unit may further include a color coordinate converting unit converting the RGB color coordinates of the input image data into a YCbCr color coordinate, and the preprocessor may receive the color difference signal from the color coordinate switching unit.

According to another aspect of the present invention, a method of removing color noise is provided.

According to a preferred embodiment of the present invention, the step of calculating the difference between the maximum value and the minimum value of the color difference signal of the input image data; (B) classifying the input color difference signal using the calculated difference value and a preset threshold value; And (c) performing filtering on each of the classified color difference signals, wherein a weight value for adjusting the filtering intensity preset in any one of the steps (b) and (c) is obtained. There is provided a method for removing color noise, characterized by further using.

The calculating of the difference between the maximum value and the minimum value of the color difference signal of the input image data may further calculate a median value and a center average value of the color difference signal of the input image data. The classifying the input color difference signal using a value may be performed by further using a median value and a center average value of the calculated color difference signal.

Computing a difference value between the maximum value and the minimum value of the color difference signal of the input image data and classifying the input color difference signal using the calculated difference value and a preset threshold value may adjust a preset filtering intensity. The weight value may be further used.

The calculating of the difference between the maximum value and the minimum value of the color difference signal of the input image data may include converting the RGB color coordinates of the input image data into YCbCr color coordinates and converting the color difference signals Cb and Cr of the converted YCbCr color coordinates. It can be performed using.

According to another aspect of the present invention, there is provided a recording medium recording a program for implementing the color noise removing method.

According to a preferred embodiment of the present invention, a program of instructions executable by a digital processing apparatus is tangibly embodied in a recording medium on which a program that can be read by the digital processing apparatus is recorded so that the color noise removing method is implemented. (A) calculating a difference value between a maximum value and a minimum value of the color difference signal of the input image data; (B) classifying the input color difference signal using the calculated difference value and a preset threshold value; And (c) performing filtering on each of the classified chrominance signals. The recording medium is provided with a program for implementing a method of removing color noise.

The calculating of the difference between the maximum value and the minimum value of the color difference signal of the input image data may further calculate a median value and a center average value of the color difference signal of the input image data. The classifying the input color difference signal using a value may be performed by further using a median value and a center average value of the calculated color difference signal.

Computing a difference value between the maximum value and the minimum value of the color difference signal of the input image data and classifying the input color difference signal using the calculated difference value and a preset threshold value may adjust a preset filtering intensity. The weight value may be further used.

The calculating of the difference between the maximum value and the minimum value of the color difference signal of the input image data may include converting the RGB color coordinates of the input image data into YCbCr color coordinates and converting the color difference signals Cb and Cr of the converted YCbCr color coordinates. It can be performed using.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

In describing the drawings, similar reference numerals are used for similar elements. In the following description of the present invention, if it is determined that the detailed description of the related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component.

The term and / or includes a combination of a plurality of related items or any item of a plurality of related items.

When a component is said to be "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but other components may be present in the middle. It should be understood.

On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention.

Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art.

Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art, and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, and the same or corresponding components will be denoted by the same reference numerals regardless of the reference numerals and redundant description thereof will be omitted.

First, a color noise removing apparatus according to an exemplary embodiment of the present invention will be described with reference to FIG. 2.

2 is a diagram illustrating a configuration of a color noise removing apparatus according to an exemplary embodiment of the present invention.

As shown in FIG. 2, the apparatus for removing color noise according to an exemplary embodiment of the present invention may include a color coordinate converter 200 and a color noise remover 210.

First, the color coordinate converter 200 converts the color coordinates of the image data from RGB to YCbYr.

RGB color coordinates consist of three primary colors of light, Red, Green, and Blue, and colors other than RGB, which are the basic three colors, have the characteristics of additive mixing that is generated by adding a basic amount by a certain amount.

On the other hand, YCbCr color coordinates are color coordinates used in standards such as Joint Photographic Coding Experts Group (JPEG) and Moving Picture Experts Group (MPEG).

In the YCbCr color coordinate, Y is a luminance component and can be calculated as a weighted average of RGB, and Cb and Cr are blue and red color difference signals, respectively.

On the other hand, such color coordinate conversion from RGB to YCbYr can be performed by [Equation 1].

[식 1]

[Equation 1]

The image data value converted into the YCbYr color coordinate is transmitted to the color noise remover 210.

The color difference signals Cr and Cb among the values converted by the color coordinate converter 200 are input to the color noise remover 210.

Meanwhile, although the color difference signal input from the color coordinate converter 200 to the color noise remover 210 is illustrated through three buses, the color coordinate converter 200 is transmitted from the color coordinate converter 200 to the color noise remover 210. It is apparent that the number of buses to which the color coordinate converter 200 and the color noise remover are connected may vary according to the arrangement of the color difference signals.

For example, in FIG. 2, when the color difference signal is arranged in three rows, the color difference signal is transmitted from the color coordinate conversion unit to the color noise removing unit through three buses, but the color difference signal is arranged and transmitted in four rows. The four buses can transmit the color difference signal to the color noise canceller.

On the other hand, since the color noise remover 210 processes the color difference signals transmitted through the respective buses sequentially, the color difference signals transmitted through the other buses except for one bus are stored through the line memory and then the color noise remover Processing may be performed sequentially at 210.

In FIG. 2, the process of processing the luminance component Y is not separately indicated, but the luminance component is different from the color difference signal output from the color noise removing unit 210 according to the present invention without undergoing a separate process or a separate process. Can be combined and output as image data.

The configuration of the color noise remover 210 in which color noise is removed for the color difference signal will be described in more detail with reference to FIG. 3.

3 is a diagram illustrating a configuration of the color noise removing unit 210 according to an exemplary embodiment of the present invention.

As shown in FIG. 3, the color noise remover 210 may include a preprocessor 300 and a filter 310.

As described above, the pre-processing unit 300 receives the color difference signals Cb and Cr among the image data converted by the color coordinate conversion unit 200.

Since the chrominance signal input to the preprocessor 300 alternately enters Cb and Cr, the chrominance signal input is composed of only one component of both Cb and Cr. Therefore, the preprocessor 300 alternately processes the Cb and the Cr the other.

Meanwhile, the preprocessor 300 calculates and transmits the median value C_median, the center average value C_center_ave, and the difference value Abs_diff_C between the maximum value and the minimum value of the color difference signal to the filter unit 310.

The preprocessor 300 looks at an example of a color difference signal for calculating a median value C_median, a center average value C_center_ave, and a difference value Abs_diff_C between the maximum value and the minimum value of the color difference signal among the input color difference signals with reference to FIG. 4. see.

4 is a diagram illustrating a configuration of a color difference signal processed by the preprocessor 300 that may be included in the color noise remover 210 according to an exemplary embodiment of the present invention.

4 illustrates a case in which the color difference signals are arranged in three rows and transmitted as shown in FIG. 2. In FIG. 4, the color difference signals C1_1 to C3-15 are sequentially transmitted to the color noise remover 210.

The data that has been processed by the preprocessing unit 300 to separate the color difference signal is transmitted to the filter unit 310.

The filter unit 310 may adjust the median value C_median, the center average value C_center_ave, the difference between the maximum and minimum values of the color difference signal Abs_diff_C, and the user among the color difference signals calculated by the preprocessor 300. Filtering is performed on the chrominance signal using a parameter.

The filter unit 310 alternately filters Cb and Cr, and outputs the color difference signal from which the filtering is performed.

The process of performing the filtering by the filter unit 310 may use Equation 2.

[Equation 2]

If Abs_diff_C <area_threshold1

C_out = (area_weight1 x C_median + (256-area_weight1) x C_center_ave) / 256

elseif (Abs_diff_C> = area_threshold1) and (Abs_diff_C <area_threshold2)

C_out = (area_weight2 x C_median + (256-area_weight2) x C_center_ave) / 256

else

C_out = (area_weight3 x C_median + (256-area_weight3) x C_center_ave) / 256

end

[Equation 2] illustrates an example in which image data is configured with 256 pixels based on the color difference signal illustrated in FIG. 3, and C_min = min (C_total_input) represents a minimum value among all input color difference signals, and C_median = median ( C_total_input) represents a median value among all input color difference signals.

And, C_center_ave = mean (C_center_input) = (C2_8 + C3_8) / 2 is the average value of the values located in the center of the color difference signal, C_max = max (C_total_input) is the maximum value of the input color difference signal, Abs_diff_C = C_max-C_min is The difference between the maximum value and the minimum value of the color difference signal is shown.

area_threshold1 is a threshold for distinguishing the region 1 and the region 2, and area_threshold2 is a threshold for distinguishing the region 2 and the region 3.

area_weight1 is a weight for adjusting the filtering strength in area 1, area_weight2 is a weight for adjusting the filtering strength in area 2, and area_weight3 is a weight for adjusting the filtering strength in area 3. .

This threshold is a value for classifying the input color difference signals, and performs filtering on the classified color difference signals.

The weight is a value for adjusting the degree of filtering for the classified chrominance signals, and color noise is removed by adjusting the degree of filtering for each of the divided areas.

These thresholds and weights for adjusting the filtering intensity are parameters that are preset by the user and can be adjusted to values that can be arbitrarily determined by the user.

Such a parameter may be set by a user because the degree of color noise visually recognized by each person may vary.

A schematic filtering process displayed in Equation 2 may be illustrated in FIG. 5.

5 is a diagram schematically illustrating a configuration of the filter unit 310 that may be included in the color noise remover 210 according to an exemplary embodiment of the present invention.

As shown in FIG. 5, the value for the area 1 is determined for the area 1 by using a weight for adjusting the filtering intensity in the area 1 based on a threshold for distinguishing the area 1 and the area 2.

For region 2, a value for region 2 is determined using a weight for adjusting the filtering intensity in region 2 based on a threshold for distinguishing region 2 and region 3.

For region 3, a value for region 3 is determined using weights for adjusting the filtering intensity in region 3.

Finally, the color difference signal from which the filtering is performed for each region is finally output.

Meanwhile, as described above, the parameter used in the process of filtering is a parameter that can be arbitrarily adjusted by the user according to the type of color difference signal and image data.

Accordingly, color noise may be reduced without damaging edges and boundaries, which are high frequency components, by calculating difference values of the chrominance signals and performing different filtering degrees according to the calculated difference values of the chrominance signals.

With reference to the configuration of the color noise removing apparatus according to an embodiment of the present invention will be described the order in which the color noise removal method according to an embodiment of the present invention is performed.

6 is a flowchart illustrating a sequence in which the method for removing color noise is performed according to an exemplary embodiment of the present invention.

As shown in FIG. 6, the method for removing color noise according to an exemplary embodiment of the present invention first converts RGB data into YCbCr data based on a luminance component (S600).

The conversion of the color coordinates can be converted by the above-described formula (Equation 1), which will be apparent to those skilled in the art and will not be described in detail below.

The difference value between the maximum value and the minimum value of the color difference signal is calculated for the color difference signal components Cb and Cr among the components of the image data converted into the YCbCr color coordinates (S602).

In addition, as described above, the median value and the center mean value of the input color difference signal can be calculated.

The color difference signal is filtered using the calculated difference between the maximum value and the minimum value of the color difference signal (S604).

As described above, the filtering is divided into regions using a predetermined threshold value for the received color difference signal and a difference between the maximum value and the minimum value between the color difference signals, and the filtering intensity is adjusted according to the weight for each region. It is.

FIG. 7 is a diagram illustrating an image processed by a conventional image processing process and an image processed by a color noise removing device according to an exemplary embodiment of the present invention.

In FIG. 7, part (a) is an image processed by a conventional image processing process, and part (b) is an image processed by a color noise removing apparatus according to an exemplary embodiment of the present invention.

As shown in FIG. 7, compared to an image processed by a conventional image processing process, color noise in which pixels appear lumpy in the entire image than in an image processed by a color noise removing device according to an exemplary embodiment of the present invention ( You can see that the color noise is reduced.

Preferred embodiments of the present invention described above are disclosed for purposes of illustration, and those skilled in the art will be able to make various modifications, changes, and additions within the spirit and scope of the present invention. Additions should be considered to be within the scope of the following claims.

As described above, according to the apparatus and method for removing color noise according to the present invention, an analog gain of an image sensor may be obtained in a place where the image sensor has severe interference between signals or in a place where the amount of light is insufficient, such as in a dark indoor environment. ) Also has the advantage of removing color noise.

In addition, there is an advantage that color noise can be removed without damaging the components at the edges or boundaries where the high frequency components are many.

In addition, the entire color image appears regardless of the frequency component, and the pattern can also remove a wide variety of color noise, which has the advantage of obtaining improved image quality.

Claims (11)

A preprocessing unit calculating a difference value between a maximum value and a minimum value of the color difference signal of the input image data; And Classifying the input color difference signal using a difference value calculated by the preprocessor and a preset threshold value; And a filter unit configured to perform filtering on each of the classified color difference signals by further using a weight value for adjusting a preset filtering intensity. The method of claim 1, And the preprocessing unit further calculates at least one of a median value and a center mean value of the color difference signal of the input image data to the difference value. The method of claim 2, And the filter unit further classifies the color difference signal using the median and center average values of the color difference signals calculated by the preprocessor. delete The method of claim 1, The color noise removing apparatus further includes a color coordinate conversion unit for converting the RGB color coordinates of the input image data into YCbCr color coordinates, The preprocessing unit receives the color difference signals (Cb and Cr) from the color coordinate switching unit. Calculating a difference value between a maximum value and a minimum value of the color difference signal of the input image data; (B) classifying the input color difference signal using the calculated difference value and a preset threshold value; And (C) performing filtering on each of the classified color difference signals, And a weight value for adjusting a predetermined filtering intensity in any one of steps (b) and (c). The method of claim 6, Step (a) is, And calculating at least one of a median value and a center mean value of the color difference signal of the input image data to the difference value. The method of claim 7, wherein Step (b) is, And calculating at least one of a median value and a center mean value of the chrominance signal to at least one of the difference value and the preset threshold value. delete The method of claim 6, The step (a) is performed by converting the RGB color coordinates of the input image data into YCbCr color coordinates and using the color difference signals (Cb and Cr) of the converted YCbCr color coordinates. A recording medium in which a program of instructions that can be executed by a digital processing apparatus is tangibly implemented so that a color noise removing method is implemented, and which records a program that can be read by the digital processing apparatus, Calculating a difference value between a maximum value and a minimum value of the color difference signal of the input image data; (B) classifying the input color difference signal using the calculated difference value and a preset threshold value; And And (c) performing filtering on each of the classified chrominance signals.

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