WO2014010817A1 - Adaptive noise reduction system for digital images, and method for removing noise - Google Patents

Abstract

The adaptive noise reduction system for digital images according to one preferred embodiment of the present invention comprises: a temporal noise reduction unit for reducing temporal noise in image information; a spatial noise reduction unit for reducing spatial noise in the image information; and an image combining unit for combining a first output image from the temporal noise reduction unit and a second output image from the spatial noise reduction unit. According to the adaptive noise reduction system for digital images and to the method for removing noise according to one preferred embodiment of the present invention, both temporal and spatial noise can be simultaneously reduced so as to output a clear image.

Description

Adaptive Noise Reduction System and its Noise Reduction Method for Digital Image

The present invention relates to an adaptive image noise reduction system for a digital image and a method of removing the noise thereof, and more particularly, by adaptively reducing noise by temporal and spatial noise reduction methods of image information including noise. The present invention relates to an adaptive image noise reduction system for a digital image capable of obtaining clear image quality, and a method of removing the noise.

In general, in order to suppress noise of an image, there is a spatial method using spatial data such as a temporal method using data on a time axis.

The temporal image noise suppression method is an image processing method for pixels at the same position on a plurality of images. In the temporal image noise suppression method, important information is the degree of similarity between the pixel of the previous screen and the pixel of the current screen. Similarity information of the pixel is also called motion information. In general, according to this degree of motion, the temporal image noise suppression method has an adaptive property by suppressing noise.

The spatial image noise suppression method is an image processing method using information on each pixel and surrounding pixels on a screen. In the spatial image noise suppression method, important information is on-screen noise level and edge information. In particular, edge information plays an important role in performance evaluation of spatial image noise suppression filters. In general, using edge information, edges are preserved and have adaptive properties by adjusting the suppression strength according to the noise level.

However, as mentioned above, studies on combining the temporal image noise suppression method and the spatial image noise suppression method have been limited.

SUMMARY OF THE INVENTION The present invention has an object of solving the above technical problem, and is an adaptive noise reduction system for a digital image capable of outputting a clear image by simultaneously reducing not only temporal but also spatial noise. Its purpose is to provide a noise reduction method.

Adaptive noise reduction system for a digital image according to an embodiment of the present invention, the temporal noise reduction unit for reducing the temporal noise of the image information; A spatial noise reduction unit for reducing spatial noise of the image information; An image combiner which combines a first output image from the temporal noise reduction unit and a second output image from the spatial noise reduction unit; And a motion degree calculator configured to calculate a motion degree of image information input according to time.

The motion degree calculated from the motion degree calculator may include: a motion accumulation information value up to the video information of the current step; And a motion intensity information value for measuring the intensity of the motion by comparing the image information of the current step with the image information before the first step of the current step.

In addition, the adaptive noise reduction system for a digital image of the present invention includes: a pixel noise degree calculator for calculating noise for a pixel; And using the pixel noise calculated from the pixel noise degree calculating unit, calculating a ratio of pixels without noise among the pixels subtracted from the pixel determined as an edge from all the image information forming one frame, and then calculating the image information in the next step. If is input, the image noise calculation unit for calculating the intensity control coefficient of the noise reduction of the temporal noise reduction unit; preferably further includes.

In detail, the pixel noise degree calculator includes: a first noise calculator configured to calculate a standard deviation between a center pixel and neighboring pixels; A second noise calculator for calculating an average value of the peripheral pixels, calculating an absolute value of a difference between the center pixel and each of the peripheral pixels and the average value, and calculating a median value of the absolute values; And a third noise calculator configured to calculate an absolute value of the difference between the center pixel and the peripheral pixels, obtain a log value, and then calculate an average value of the log value. The pixel noise degree calculator may be configured to generate the pixel noise degree calculator based on a predetermined compensation pattern according to a standard of an image information signal so that the noise values calculated from the first and second noise calculators have the same value for a signal of image information of a different standard. It is preferable to compensate and output the noise values calculated from the first and second noise calculators.

In addition, the movement degree calculation unit of the present invention, the first low-pass filter for low-pass passing the video information of the current step; A second low pass filter configured to low pass image information before the first step of the current step; And a third low pass filter configured to low pass the image information obtained by mixing the image information of the current step and the image information before the first step. In addition, in the masks used in the first, second and third low pass filters, when the Bayer pattern video information is input, the weight ratio of the R: G: B pixels is 1: 2: 1. Do. In detail, the movement degree calculator may include an image obtained by mixing the output from the first, second and third low pass filters, the image information of the current stage, the image information of the current stage, and the image information before the first stage. And a motion intensity calculator for calculating the intensity of the motion of the image information of the current step from the image information before the first step by using the information and the image information before the first step.

In addition, in the adaptive noise reduction system for the digital image of the present invention, when the input image information is a Bayer pattern signal, it is determined whether the center pixel is an index among R, G, and B, and the pixel having a color different from that of the center pixel. And an image interface unit for reconstructing the image information by surrounding pixels of the same color as the center pixel. In addition, the input of the adaptive noise reduction system for the digital image of the present invention is characterized in that it comprises the image information of the current step, the motion accumulation information value up to the image information of the current step, and the image information before the first step. do.

In addition, the image combiner may select respective weights for combining the first output image and the second output image using values calculated from the motion degree calculator.

The motion degree calculating unit may further include a motion accumulation information value up to the current stage image information; And a motion intensity information value for measuring the intensity of the motion by comparing the image information of the current step with the image information before the first step, wherein the image combiner is configured to compare the first output image with the motion accumulation information value. Combining a second output image to form a first combined image, and combining the first output image and the second output image by using the motion intensity information value to create a second combined image, and the first combined image and the first And combining the two combined images to output the final combined image.

According to the adaptive noise reduction system for the digital image and the noise reduction method according to the preferred embodiment of the present invention, a clear image can be output by simultaneously reducing not only temporal but also spatial noise.

1 is a block diagram of an adaptive noise reduction system for a digital image according to an embodiment of the present invention.

2A to 2C are illustrations of processing for input signals of a video interface unit of the present invention.

3 is a block diagram of a movement degree calculation unit according to an embodiment of the present invention.

4 is an illustration of a mask used in the first, second and third low pass filters in accordance with a preferred embodiment of the present invention.

5 is a block diagram of a pixel noise degree calculator according to an exemplary embodiment of the present invention.

6 is a flowchart of an adaptive noise reduction method for a digital image according to an exemplary embodiment of the present invention.

Hereinafter, an adaptive noise reduction system for a digital image and a noise canceling method thereof will be described in detail with reference to the accompanying drawings.

The following examples of the present invention are intended to embody the present invention, but not to limit or limit the scope of the present invention. From the detailed description and examples of the present invention, those skilled in the art to which the present invention pertains can easily be interpreted as belonging to the scope of the present invention.

First, Figure 1 is a block diagram of an adaptive noise reduction system 100 for a digital image according to an embodiment of the present invention. As can be seen from FIG. 1, the adaptive noise reduction system 100 for a digital image according to an exemplary embodiment of the present invention includes an image interface unit 10, a movement degree calculator 20, and a pixel noise degree calculator 30. ), A temporal noise reducer 40, an image noise calculator 50, a spatial noise reducer 60, an image combiner 70, and a storage 80.

Hereinafter, each component of the adaptive noise reduction system 100 for the digital image of the present invention will be described in detail.

When the image information input from the image input apparatus such as the image sensor of the front stage is a Bayer pattern signal, the image interface unit 10 determines which index among the R, G, and B center pixels, It skips pixels of different colors and reconstructs image information by surrounding pixels of the same color as the center pixel. In other words, the input from the image input device may be a Y / C signal or a Bayer pattern signal, which allows the two types of input signals to be processed in the same way at the rear of the image interface unit 10. Play a role. The video signal from the video input device such as the image sensor of the front stage input to the video interface unit 10 includes the motion cumulative information value (Mh _k-1 (p)) up to the video information one step before in time, the current video. Information I _k (p), and image information I _k-1 (p) of the previous step.

2A to 2C show exemplary diagrams of processing of an input signal of the video interface unit 10 of the present invention. 2A illustrates a case in which a Y / C signal is input, the image interface unit 10 according to the present invention uses the upper 5x9 as the Y data and the lower 5x9 as the C data, assuming a 10x9 data space. At this time, 35 pixel data of the Y data is transferred to the rear end, and 25 pixel data of the C data is transferred to the rear end.

FIG. 2B illustrates an embodiment of processing when a Bayer pattern signal having a center pixel of G is input to the image interface unit 10. Assuming a 10x9 data space, only 9x9 data space is used to input the Bayer pattern signal, and 37 pixels are delivered to the rear end when the center pixel is a G pixel. At this time, the C data is deactivated.

FIG. 2C illustrates an embodiment of processing when a Bayer pattern signal having a center pixel of B or R is input to the image interface unit 10. Assuming a 10x9 data space, only 9x9 data space is used to input the Bayer pattern signal, and 25 pixels are delivered to the rear end when the center pixel is a B or R pixel. At this time, the C data is deactivated.

As can be seen from Figure 1 in the motion degree calculation unit 20 according to an embodiment of the present invention, the motion cumulative information value (Mh _k ) from the video interface unit 10 to the video information before the first step _-1 (p)), the current image information (I _k (p)) and the previous stage image information (I _k-1 (p)), the degree of movement of the image information input over time is calculated .

Motion degree calculating section (20) of the present invention, the motion cumulative values to the video information (I _k (p)) of the current step (Mh _k (p)) and the image information of the current step (I _k (p)) The motion intensity information value M _ok (p) for measuring the intensity of the motion is calculated by comparing the image information I _k-1 (p) before step 1 with the image information. In addition, the motion accumulation information value (Mh _k-1 (p)) up to the image information I _k-1 (p) before step ₁ is transmitted to the image combiner 70. In detail, the motion cumulative information value (Mh _k (p)) is a cumulative value for how many frames the motion is not detected in comparison with the image of the previous stage up to the image information of the current stage. For example, no motion was detected between the image information I _k (p) of the current stage and the image information I _k-1 (p) before the first stage, and the image information (I _k−) before the one stage. _If no motion is detected between the image information before ₁ (p)) and step 2, and before the motion is detected, the motion accumulation information value Mh _k (p) may be set to '2'. In addition, when the motion cumulative information value (Mh _k (p)) reaches a certain value, the value is maintained until a motion is detected, and a predetermined value is subtracted when the motion is detected. In addition, the motion intensity values (M _ok (p)) is that from the video information _{(I k-1 (p)} ) from the previous step, Step 1 there was how many motion picture information (I _k (p)) of the current step That is, the intensity of the movement may be expressed by a predetermined value as a value for indicating the intensity of the movement.

3 shows a block diagram of the movement degree calculation unit 20 according to an embodiment of the present invention.

As can be seen from FIG. 3, the motion degree calculator 20 of the present invention includes a fixed temporal image mixer 21, a first low pass filter 22, a second low pass filter 23, and a third low pass. A filter 24 and a motion intensity calculator 25.

First, the fixed temporal image mixer 21 mixes the current image information I _k (p) and the image information I _k-1 (p) of the previous step and outputs the output I _mk (p). An example of a blending technique is Alpha Blending.

In addition, the moving degree calculating section 20 of the present invention includes three low pass filters 22, 23, 24. That is, the first low pass filter 22 which low pass the image information I _k (p) of the current stage, and the second low pass which low pass the image information I _k-1 (p) of the previous stage The low pass of the pass filter 23 and the image information I _mk (p), which is a mixture of the image information I _k (p) of the current stage and the image information I _k-1 (p) of the previous stage. And a third low pass filter 24 to pass through.

The masks used for the first, second and third low pass filters 22, 23 and 24 have a 1: 2: 1 weight ratio of R: G: B pixels when the Bayer pattern video information is input. It is characterized by that. When viewing the Bayer pattern image information in the frequency domain, the center portion is mainly composed of the Y component, and when analyzing the ratio of the center portion, the ratio of R: G: B is about 1: 2: 1. Therefore, by using a filter in which the ratio of R: G: B is 1: 2: 1 to the Bayer pattern image information, a low pass Y component for each pixel can be obtained.

4 is an exemplary diagram of a mask used in the first, second and third low pass filters 22, 23, 24 according to a preferred embodiment of the present invention. If it is assumed that the Bayer pattern image information is viewed as a 5x5 region, it can be seen that all masks of FIG. 4 have a weight ratio of R: G: B pixels of 1: 2: 1.

In addition, the movement degree calculation unit 20 according to the present invention outputs the output I _gk (p) of the first low pass filter 22 and the output I _gk-1 (p) of the second low pass filter 23. And the output from the third low pass filter 24 (I _gmk (p)), the current stage image information I _k (p), the current stage image information I _k (p) and the previous stage Image information (I _mk (p)) obtained by mixing the video information (I _k-1 (p)) and the image information (I _k-1 (p)) of the previous step 1, From the image information I _k-1 (p), there is a motion intensity calculator 25 which calculates how many movements there are in the image information I _k (p) at the present stage, that is, the intensity of the movement. The motion intensity calculated by the motion intensity calculator 25 may be calculated through a normalization method with a threshold value.

Next, the pixel noise degree calculator 30 according to an exemplary embodiment of the present invention uses the image information _I'k (p) of the current stage reconstructed by the image interface unit 10 to apply to the pixel. To calculate the noise

5 is a block diagram of a pixel noise degree calculator 30 according to an exemplary embodiment of the present invention. As can be seen from FIG. 5, the pixel noise degree calculator 30 according to an exemplary embodiment of the present invention includes a first noise calculator 31, a second noise calculator 32, and a third noise calculator. (33), a first noise figure compensator 34, a second noise figure compensator 35, and a third noise figure compensator 36.

The first noise calculator 31 calculates the standard deviation (N_1 _'k (p)) between the center pixel and the surrounding pixels. In addition, the second noise estimator 32 calculates the average value of the surrounding pixels and the center pixel and the surrounding pixels calculated by the absolute value of the difference of each of the average value, and finally the absolute value of the median value (N_2 _'k (p Calculate)). Finally, the third noise calculator 33 calculates the absolute value of the difference value between the center pixel and the surrounding pixels, calculates the log value, and then calculates the average value N_3 ' _k (p) of the log value. do. That is, the first noise calculator 31 numerically displays the relationship between the center pixel and the peripheral pixels, and the second noise calculator 32 numerically displays the relationship between the peripheral pixels except the center pixel. The third noise calculator 33 displays an impulse noise pixel numerically.

Further, the first noise figure compensator 34 and the second noise figure compensator 35 have the same noise values calculated from the first and second noise calculators 31 and 32 for the signals of the image information of different standards. Compensates for the noise values calculated from the first and second noise calculators 31 and 32 by a certain compensation pattern according to the standard of the image information signal. That is, when the video signal inputted to the video interface unit 10 is a Y / C signal or a Bayer pattern signal, the same value is outputted. The third noise figure compensator 36 compensates for not outputting an incorrect impulse noise pixel from the third noise calculator 33, for example, an edge portion of an image, etc., as being recognized as noise. Do it.

The image noise calculator 50 of the present invention uses pixel noise calculated by the pixel noise degree calculator 30 to subtract pixels determined as edges from all the image information forming one frame. When the image information is input in the next step by calculating the ratio of pixels without noise, it serves to calculate the intensity control coefficient k of the noise reduction of the temporal noise reduction unit 40. In other words, it is possible to determine how much the noise of the temporal noise reduction unit 40 is to be reduced by the intensity adjustment coefficient k of the noise reduction.

Next, the temporal noise reduction unit 40 of the present invention serves to reduce noise on time axis data of the image, that is, to reduce temporal noise of the image information. Specifically, the temporal noise reduction unit 40 uses the current stage image information I _k (p) and the previous stage stage image information I _k-1 (p) to reduce the noise in the current stage. Image information OT _k (p) is output.

The spatial noise reduction unit 60 of the present invention serves to reduce the noise of the spatial axis data of the image, that is, reduce the spatial noise of the image information. Specifically, the spatial noise reduction unit 60 uses the image information I ' _k (p) of the current stage reconstructed by the image interface unit 10 and the output from the pixel noise degree calculation unit 30. The reduced video information OS ' _k (p) is output.

The image combiner 70 of the present invention combines the first output image from the temporal noise reduction unit 40 and the second output image from the spatial noise reduction unit 60.

In detail, the image combiner 70 combines the first output image and the second output image by using the motion accumulation information value M _{h k} (p) to make the first combined image, and the motion intensity information value M _ok. Using (p)), the first output image and the second output image are combined to form a second combined image. That is, the first combined image and the first combined image are generated by using the motion accumulation information value (Mh _k (p)) and the motion intensity information value (M _ok (p)) as weights for combining the first output image and the second output image. 2 Create a combined image. In addition, the final combined image O _mix'k (p) is output by combining the first combined image and the second combined image. When combining the first combined image and the second combined image, the two images are combined using an appropriate weight. As an image combining method in the image combiner 70, an alpha blending technique may be used.

In addition, the storage unit 80 of the present invention stores the signal output from the image combiner 70 and transmits it to the image output device, or feeds back to the image interface unit 10 adaptive noise for the digital image of the present invention The abatement system 100 can adaptively reduce noise. That is, Mh _k (p) and O _feedback'k (p) shown in FIG. 1 are the input signals Mh _k-1 (p) and I _k-1 (the input signals of the image interface unit 10 during the image processing of the next step). p).

Of course, it is also possible to transmit the image combiner 70 directly to the image output device without passing through the storage 80.

For reference, when the signal input to the image interface unit 10 is a Y / C signal, the temporal noise reduction unit 40, the sympathetic noise reduction unit 50, and the image combiner 70 may convert the Y signal and the C signal. I use it. On the other hand, the motion degree calculator 20, the pixel noise degree calculator 30, and the image noise calculator 50 use only the Y signal.

In addition, when the signal input to the image interface unit 10 is a Bayer pattern signal, the input image information I _{k -1} before the first stage other than the reconstructed image information I ' _k (p) of the current stage. (p)) motion cumulative information value (Mh _k-1 (p)), current image information (I _k (p)) and previous stage image information (I _k-1 (p)) signals Use a signal that is not reconstructed by (10).

6 is a flowchart of an adaptive noise reduction method for a digital image according to an exemplary embodiment of the present invention. As can be seen from Figure 6, the adaptive noise reduction method for a digital image according to an embodiment of the present invention, when the input image information is a Bayer pattern signal, the index of the center pixel is R, G, B Image interface step (S10) of skipping pixels of a different color from the center pixel and reconstructing the image information by neighboring pixels of the same color as the central pixel, and calculating a degree of movement of the image information input over time. A motion degree calculating step (S20), a temporal noise reduction step (S30) for reducing temporal noise of image information, a pixel noise degree calculating step (S40) for calculating noise for a pixel, and a spatial noise for reducing spatial noise of the image information A noise reduction step S50 is included.

In addition, the adaptive noise reduction method for the digital image of the present invention uses the pixel noise calculated in the pixel noise degree calculation step S40 to subtract the pixel determined as an edge from all the image information forming one frame. Among the image noise calculation steps (S60) and the temporal noise reduction step (S30), when the ratio of pixels without noise is calculated and the following image information is input, the intensity adjustment coefficient of the noise reduction in the temporal noise reduction step is calculated. The method may further include an image combining step S70 of combining the first output image and the second output image from the spatial noise reduction step S40.

As described above, according to the adaptive noise reduction system 100 and the noise removing method for the digital image according to the preferred embodiment of the present invention, clear image information is output by effectively reducing temporal and spatial noise of the digital image. It can be seen that.

An adaptive noise reduction system and a noise reduction method for a digital image according to an exemplary embodiment of the present invention can be applied to various image processing fields.

Claims (19)

A temporal noise reduction unit for reducing temporal noise of image information; A spatial noise reduction unit for reducing spatial noise of the image information; And And an image combiner configured to combine the first output image from the temporal noise reducer and the second output image from the spatial noise reducer. 2. The method of claim 1, The adaptive noise reduction system, Adaptive noise reduction system for a digital image, characterized in that it further comprises; a motion degree calculation unit for calculating the motion degree of the image information input over time. The method of claim 2, The movement degree calculated from the movement degree calculation unit is A motion accumulation information value up to the image information of the current step; And And a motion intensity information value for comparing the image information of the current step and the image information before the first step of the current step to measure the intensity of the motion. The method of claim 1, The adaptive noise reduction system, Adaptive noise reduction system for a digital image, characterized in that it further comprises; pixel noise degree calculation unit for calculating the noise for the pixel. The method of claim 4, wherein The adaptive noise reduction system, Using the pixel noise calculated by the pixel noise degree calculator, the ratio of pixels without noise is calculated from the pixels subtracted as edges from the entire image information forming one frame, and the image information is calculated in the next step. And an image noise calculator for calculating an intensity control coefficient of the noise reduction unit when the input is input. The method of claim 4, wherein The pixel noise degree calculating unit, A first noise calculator for calculating a standard deviation between the center pixel and the surrounding pixels; A second noise calculator for calculating an average value of the peripheral pixels, calculating an absolute value of a difference between the center pixel and each of the peripheral pixels and the average value, and calculating a median value of the absolute values; And And a third noise calculator configured to calculate an absolute value of the difference between the center pixel and the neighboring pixels, obtain a log value, and then calculate an average value of the log value. Adaptive Noise Reduction System. The method of claim 6, The pixel noise degree calculating unit, The noise values calculated by the first and second noise calculators may be equal to the signals of the image information of different standards from the first and second noise calculators by a constant compensation pattern according to the specifications of the image information signals. Adaptive noise reduction system for a digital image, characterized in that for outputting by compensating the calculated noise values. The method of claim 2, The movement degree calculation unit, A first low pass filter for low passing image information of the current stage; A second low pass filter configured to low pass image information before the first step of the current step; And And a third low pass filter for low-passing the image information obtained by mixing the image information of the current stage and the image information before the first stage. The method of claim 8, The movement degree calculation unit, Output from the first, second and third low pass filters, image information of the current stage, image information of the current stage image information, and image information before the first stage, and image information before the first stage. And a motion intensity calculator for calculating the intensity of the motion of the image information of the current step from the image information before the first step. 2. The method of claim 1, The adaptive noise reduction system, If the input image information is a Bayer pattern signal, the center pixel determines which index among R, G, and B, skips pixels of a different color from the center pixel, and uses the surrounding pixels of the same color as the center pixel. And an image interface unit for reconstructing the information. The method of claim 2, The image combiner, And a respective weight for combining the first output image and the second output image using the value calculated from the motion degree calculator. The method of claim 11, The movement degree calculation unit, A motion accumulation information value up to the image information of the current step; And Calculating a motion intensity information value for measuring the intensity of the motion by comparing the image information of the current step with the image information before the first step of the current step; The image combiner, The first output image is combined with the second output image using the motion accumulation information value, and the first output image is combined with the first output image and the second output image using the motion intensity information value. 2 create a combined video, Adaptive noise reduction system for a digital image, characterized in that for combining the first combined image and the second combined image to output a final combined image. A temporal noise reduction step of reducing temporal noise of the image information; A spatial noise reduction step of reducing spatial noise of the image information; And And an image combining step of combining the first output image from the temporal noise reduction step and the second output image from the spatial noise reduction step. The method of claim 13, The adaptive noise reduction method, And a motion degree calculating step of calculating a motion degree of the image information input according to time. The method of claim 13, The adaptive noise reduction method, Adaptive noise reduction method for a digital image, characterized in that it further comprises; calculating the pixel noise degree for calculating the noise for the pixel. The method of claim 15, The adaptive noise reduction method, By using the pixel noise calculated from the pixel noise degree calculating step, the next image information is input by calculating a ratio of pixels without noise among pixels except a pixel determined as an edge from all image information forming one frame. And an image noise calculating step of calculating an intensity control coefficient of the noise reduction step of the temporal noise reduction step. The method of claim 14, The image combining step, And selecting respective weights for combining the first output image and the second output image using the value calculated from the motion degree calculating step. The method of claim 17, The movement degree calculation step, A motion accumulation information value up to the image information of the current step; And And a motion intensity information value for measuring the intensity of motion by comparing the image information of the current step with the image information before the first step of the current step. The method of claim 18, The image combining step, The first output image is combined with the second output image using the motion accumulation information value, and the first output image is combined with the first output image and the second output image using the motion intensity information value. 2 create a combined video, Adaptive noise reduction method for a digital image, characterized in that for combining the first combined image and the second combined image to output a final combined image.

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