KR20020023326A - A method and apparatus for improving the quality of digital X-ray image by applying filter selectively - Google Patents

Abstract

PURPOSE: A method and an apparatus for improving a digital X-ray image through selective application of a filter are provided to correct noise and boundary of an image simultaneously. CONSTITUTION: A captured image is received(S801). A pixel value of an estimated original image corresponding to the capture image is calculated(S807). A pixel value of an estimated background image corresponding to the captured image is calculated(S809). It is judged if the absolute value of the difference between the pixel values of the original image and the pixel value of the background image is larger than a predetermined boundary value(S811). When the absolute value is larger than the boundary value, unsharp masking is performed using a predetermined constant(S815). When the absolute value is not larger than the boundary value, unsharp masking is carried out using a predetermined constant smaller than the constant(S813). The final image is generated(S821).

Description

A method and apparatus for improving the quality of digital X-ray image by applying filter selectively}

The present invention relates to an image enhancement method and apparatus for low dose digital X-rays (X-rays) that can emphasize boundaries without reducing granularity.

Most commercially available printed circuit board (PCB) mounting inspection X-ray equipment is an image acquisition device employing an image multiplier CCD camera with excellent sensitivity even at low doses by amplifying the input signal. A disadvantage of this is that a lot of quantum noise, screen noise, etc. cause a loss of granularity of the acquired image. In addition, the image multiplier uses a fluorescent material twice at the input terminal and the output terminal, and thus has a limitation in terms of resolution.

To compensate for this, flat-panel digital X-ray cameras using CMOS, a-Si and a-Se have been developed. However, these cameras have improved considerably in terms of resolution, but in the manufacturing process, random noise mixed with uneven X-ray sensitivity between the pixels of the camera, malfunctioning pixels, and fixed pattern noise due to the dark current inside the sensor. ).

To correct this noise, a method commonly known as flat field correction is used. However, even after flat plate correction, the noise is not completely removed and image quality is still degraded by quantum noise and irregular noise caused by X-ray scattering. In addition, the larger the focal point of the X-ray generator, the larger the geometric magnification, the blurred the boundary of the acquired image.

Low-dose digital X-ray images can summarize their features with blurry borders and noise in the overall image. In general, in order to improve an image having such a feature, a method of reducing noise or emphasizing a boundary line is used. However, these common methods have little effect on low dose digital X-ray images. This is because reducing the influence of noise makes the boundary even more blurry, and conversely, emphasizing the boundary further emphasizes the noise present in the low pass region and degrades granularity.

That is, the conventional image correction method has a problem in that the sharpness is blurred when the granularity is improved to remove the noise, and when the sharpness is improved, there is no effect of improving the granularity.

In addition, the conventional image correction techniques are methods that focus on either noise or a boundary line, and thus, there is a problem in that an image enhancement through simultaneous correction of noise and a boundary line cannot be provided.

Accordingly, it is an object of the present invention to provide an image enhancement method and apparatus for low dose digital X-rays through selective filter application to simultaneously correct noise and boundary lines of an image.

Another object of the present invention is to provide an image enhancement method and apparatus for low-dose digital X-rays through the application of selective filters to improve the granularity and sharpness of the image.

It is still another object of the present invention to provide a method and apparatus for improving an image of a low dose digital X-ray to which a selective filter is applied by determining whether a boundary line and a background of a pixel correction region are applied.

1 is an illustration of a low dose digital X-ray image in accordance with a preferred embodiment of the present invention.

2 is an exemplary view of an estimated original image according to a preferred embodiment of the present invention.

3 is a view showing nine 3 × 3 area distributions according to a preferred embodiment of the present invention.

4 is an exemplary diagram of an estimated background image according to an exemplary embodiment of the present invention.

5 is an exemplary diagram of a condition image calculated by an estimated original image and an estimated background image according to an exemplary embodiment of the present invention.

6 is a flowchart illustrating a process of obtaining an estimated original image according to an exemplary embodiment of the present invention.

7 is a flowchart illustrating a process of obtaining an estimated background image according to an exemplary embodiment of the present invention.

8 is a flowchart illustrating a process of applying a selective UnsharpMasking algorithm according to an embodiment of the present invention.

<Explanation of symbols for main parts of the drawings>

101: low dose digital X-ray image 201: estimated original image

401: Estimated background image 501: Conditional image

According to an aspect of the present invention to achieve the above object, to receive an image for selective filter application, calculate the pixel value of the estimated original image corresponding to the image, the pixel of the estimated background image corresponding to the image Calculates a value, and determines whether an absolute value of the difference between the pixel value of the estimated original image and the pixel value of the estimated background image is greater than a predetermined boundary value, and if the absolute value of the difference is greater than the boundary value as a result of the determination Unsharp mask processing using a predetermined constant value β, and if the absolute value of the difference is not greater than the boundary value as a result of the determination, unsharp mask processing using a predetermined constant value α smaller than β, Method for improving digital x-ray image by applying selective filter to produce final image with unsharp mask process Corresponding apparatuses and recording media can be provided.

The receiving of the captured image for applying the selective filter may include flat field correction of the captured image.

In the method of improving a digital x-ray image by applying the selective filter, the start coordinate of the image is set to x-coordinate 0 and y-coordinate 0, and the x-coordinate value is equal to the column size of the image and the y-coordinate value is the row size of the image. The selective unsharp mask process may be repeated for each coordinate until it equals to.

The area of the coordinates may be an area divided by 9 pixels of 3 × 3 having the coordinates as the center.

The estimated background image may be repeatedly generated in n × n area units with respect to the image.

The step of calculating the pixel value of the estimated original image corresponding to the image may include calculating a median value at a center value in a 3 × 3 region with respect to coordinates, and constructing the 9 × pixels constituting the 3 × 3 region. Computing a median value of a region centered on each of them, comparing the median value with a median value of each of the nine pixels, determining a region type of the 3x3 region, and determining the region. Calculating a median value of each pixel portion corresponding to the type.

The area type may be at least one of a smooth area, a horizontal line, a diagonal line in the upper left lower right direction, a vertical line, and a diagonal line in the upper left lower right direction.

In the method of improving a digital x-ray image by applying the selective filter, the start coordinate of the image is set to x-coordinate 0 and y-coordinate 0, and the x-coordinate value is equal to the column size of the image and the y-coordinate value is the row size of the image. The process of calculating the pixel value of the estimated original image corresponding to the image may be repeated for each coordinate until.

The calculating of the pixel value of the estimated background image corresponding to the image may include selecting an area corresponding to a predetermined area size and calculating a median value in the selected area.

In the method of improving a digital x-ray image by applying the selective filter, the start coordinate of the image is set to x-coordinate 0 and y-coordinate 0, and the x-coordinate value is equal to the column size of the image and the y-coordinate value is the row size of the image. The process of calculating the pixel value of the estimated background image corresponding to the image may be repeated for each coordinate until.

Next, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is an illustration of a low dose digital X-ray image in accordance with a preferred embodiment of the present invention.

2 is an exemplary view of an estimated original image according to a preferred embodiment of the present invention.

3 is a diagram illustrating nine 3 × 3 area distributions according to an exemplary embodiment of the present invention.

4 is an exemplary diagram of an estimated background image according to an exemplary embodiment of the present invention.

5 is an exemplary diagram of a condition image calculated by an estimated original image and an estimated background image according to an exemplary embodiment of the present invention.

Unsharp masking is the most frequently used technique for image enhancement in X-ray imaging, including medical imaging. This is represented by the formula (3-1).

Unsharp Masking = (A) (Original)-Lowpass

= (A-1) (Original) + Original-Lowpass (3-1)

= (A-1) (Original) + Highpass

Unsharp masking has the effect of emphasizing the boundaries by adding the components of the highpass region to the original image. However, if this technique is applied to low-dose X-ray images where the distribution of noise is irregular and the value change range is larger than the change in the boundary, the value of the noise in the low frequency region is more emphasized, improving sharpness and contrast. Granularity becomes worse. Therefore, an algorithm for selectively applying Unsharp Masking to the high pass region and the low pass region as one method for solving the disadvantage will be described with reference to FIGS. 1 to 5.

1 to 5, in the low dose digital X-ray image 101, in which the noise in the low pass region and the boundary in the high pass region are difficult to distinguish, a new method for distinguishing the two regions is required. Therefore, an estimated original image 201 and an estimated background image 401 which are less influenced by noise are generated to distinguish the regions.

As shown in FIG. 1, the low-dose digital X-ray image 101 has a large deviation in actual pixel values of the same region that should be composed of similar value distributions without a clear boundary due to noise, compared to a normal image. Therefore, in order to estimate the original image with a clearer boundary and to have a constant pixel value in the same region, nine 3 × 3 region distributions of FIG. 3 are proposed.

Referring to FIG. 3, the X-ray camera generally has a resolution of 5 [line-pair / mm] (five pairs of black and white lines in the range of 1 [mm]) or less. This means that at least one black or white line occupies two or more pixels. Therefore, the shape of the region in which the pixel is included can be expressed as a 3x3 region around the pixel. Therefore, the shape that can be represented by the 3x3 area can be divided into five types. In FIG. 3, the type 301 represents a part of the smooth area, the types 303 and 305 represent a horizontal line, and the types 307 and 309 represent a part of a diagonal area from the upper left to the lower right. The shapes of 311 and 313 represent vertical lines, and the forms of 315 and 317 represent a portion of a diagonal line from the upper right to the lower left. The pixel values E (x, y) of the estimated original image using nine proposed region distributions are shown in Equation (3-2).

, only (3-2)

Here, Med () represents an intermediate value. Omega (Ω) represents one of the forms in FIG. 3. The process to find Ω is as follows.

① Find the median value in the 3x3 area centered on (x, y).

② Repeat step ① for each of the nine pixels belonging to the 3x3 area in ①.

(3) The pixels whose difference between the intermediate value of each pixel obtained in ② and the pixel value obtained in ① are equal to or less than the boundary value Delta are determined.

(4) Find the most similar to the shape of the pixels obtained in (3) from the shape in FIG.

Im (i, j) is the value of each pixel belonging to Ω. When the original image is estimated using Equation (3-2), the estimated original image 201 of FIG. 2 is obtained. Compared to the image 101 of FIG. 1, it can be seen that the values at the boundary and the inside of the line are more uniform. A process of obtaining the estimated original image will be described in detail with reference to FIG. 6 below.

The proposed algorithm is shown in Equation (3-3).

(3-3)

The new pixel value U (x, y) is optionally replaced with Unsharp Masking according to the difference value T (x, y) between the estimated original image and the background image. Here, D (x, y) is shown in Formula (3-4).

(3-4)

D (x, y) is the pixel value O (x, y) of the original image minus the average value M (x, y) in the local region centered on each pixel. Equation (3-4) is a kind of high pass filter. The threshold serves as a criterion for distinguishing the low pass region from the high pass region, which is determined by the characteristics of the image. The conditional image 501 of FIG. 5 represents an image obtained by substituting 255 when the absolute value of the estimated original image 201 of FIG. 2 is less than the threshold value and substituting by 0 if the absolute value of the estimated background image 401 of FIG. .

If the value of T (x, y) is smaller than the boundary value, it is regarded as the low frequency region, and the gain (α) for maintaining granularity is selected as a small value. β) is chosen as a large value. The process of the optional Unsharp Masking algorithm will be described in detail with reference to FIG. 8 below.

6 is a flowchart illustrating a process of obtaining an estimated original image according to an exemplary embodiment of the present invention.

Referring to FIG. 6, after capturing a digital x-ray image to which the selective filter is applied (S601), the captured image is flat plate corrected (S603). When the correction is completed, the median value at the center pixel K in the 3x3 region is calculated (S605) starting from x-coordinate 0 and y-coordinate 0 of the image (S607). And nine pixels constituting the 3 × 3 region. Median values for 3 × 3 areas centered on each are calculated (S609).

Median Value for Center Pixel K and 9 Pixels Compare the median value of (Median Value) (S611) with the median value of K By determining whether the difference with each value is within a predetermined range (Delta), it is determined whether the 3x3 area belongs to the type of the nine areas of FIG. 3 (S613). When the type of the 3x3 region is determined, a median value in a portion corresponding to the region type is calculated (S615).

It is determined whether the x coordinate is equal to the column size of the captured image and the y coordinate is equal to the row size of the image (S617). If the determination result is the same as the column size and the row size, an estimated original image is generated (S621). If it is determined that the column size is not equal to the column size or the row size, the x coordinate value or the y coordinate value is increased (S619), and then the process returns to step S607.

7 is a flowchart illustrating a process of obtaining an estimated background image according to an exemplary embodiment of the present invention.

Referring to FIG. 7, after capturing a digital x-ray image to which the selective filter is applied (S701), the captured image is flat-field corrected (S703).

When the correction is completed, an area corresponding to a predetermined area size (15 × 15, 35 × 35, ..., etc.) is selected (S705) starting from x-coordinate 0 and y-coordinate 0 of the image (S707). After calculating a median value for the selected region (S709), it is determined whether the x coordinate is equal to the column size of the captured image and the y coordinate is equal to the row size of the image (S711).

If the determination result is the same as the column size and the row size, an estimated background image is generated (S615). If it is determined that the column size is not equal to the column size or the row size, the x coordinate value or the y coordinate value is increased (S713), and then the process returns to step S707.

8 is a flowchart illustrating a process of applying a selective Unsharp Masking algorithm according to an embodiment of the present invention.

Referring to FIG. 8, after capturing a digital x-ray image to which the selective filter is applied (S801), the captured image is flat plate corrected (S803). When the correction is completed, the pixel value O (x, y) of the estimated original image is calculated (S807) starting from x-coordinate 0 and y-coordinate 0 of the image. The pixel value B (x, y) of the estimated background image is calculated (S809).

When the values of O (x, y) and B (x, y) are calculated, it is determined whether the absolute value of the difference between O (x, y) and B (x, y) is greater than the threshold (S811). do.

If the absolute value of the difference is greater than the threshold as a result of the determination, the unsharp mask is processed on the image using β (S815). If the absolute value of the difference is not greater than the threshold as a result of the determination, the unsharp mask is processed on the image using α (S813). Here, β is a large value and α is a small value, and the above formula (3-3) is used for selective unsharp mask processing.

When the selective unsharp mask processing is completed, it is determined whether the x coordinate is equal to the column size of the captured image and the y coordinate is equal to the row size of the image (S817). If the determination result is the same as the column size and the row size, a final image is generated (S821). If it is determined that the column size is not equal to the column size or the row size, the x coordinate value or the y coordinate value is increased (S819), and then the process returns to step S607.

The present invention is not limited to the above embodiments, and many variations are possible by those skilled in the art within the spirit of the present invention.

As described above, according to the present invention, a general average filter method and an unsharp masking method used for X-ray image enhancement may minimize the disadvantage of causing granularity deterioration and improve sharpness and contrast in low-dose digital X-ray images. It is possible to provide an image enhancement method and apparatus for low dose digital X-rays by applying an optional Unsharp Masking algorithm.

In addition, according to the present invention, it is possible to provide an image enhancement method and apparatus for low-dose digital X-rays by applying a selective filter that provides a more improved image by simultaneously correcting noise and boundary lines.

In addition, according to the present invention, it is possible to provide a method and apparatus for improving an image of a low dose digital X-ray to which a selective filter is applied by determining whether a boundary line and a background are applied to a pixel correction region.

Claims (12)

Receiving a captured image for applying a selective filter; Calculating pixel values of an estimated original image corresponding to the image; Calculating pixel values of an estimated background image corresponding to the image; Determining whether an absolute value of a difference between a pixel value of the estimated original image and a pixel value of the estimated background image is greater than a predetermined boundary value; If the absolute value of the difference is greater than the boundary value as a result of the determination, performing an unsharp mask process using a predetermined constant value β; If the absolute value of the difference is not greater than the boundary value as a result of the determination, performing an unsharp mask process using a predetermined constant value α smaller than the β; And Generating final image with selective unsharp masking Method of improving a digital x-ray image by applying a selective filter comprising a. The method of claim 1, Receiving the captured image for applying the selective filter is Flat Field Correction of the Captured Image Comprising Method for improving digital x-ray image by applying selective filter, characterized in that. The method of claim 1, The method of improving the digital x-ray image by applying the selective filter The optional unsharp mask for each coordinate until the starting coordinate of the image is set to x-coordinate 0 and y-coordinate 0, and x-coordinate is equal to the column size of the image and y-coordinate is equal to the row size of the image. Repeating the process Method for improving digital x-ray image by applying selective filter, characterized in that. The method of claim 3, The area for the coordinates Being an area separated by 9 pixels of 3x3 having the coordinates as starting coordinates Method for improving digital x-ray image by applying selective filter, characterized in that. The method of claim 1, The estimated background image is To be repeatedly generated in units of n × n area with respect to the image Method for improving digital x-ray image by applying selective filter, characterized in that. The method of claim 1, Computing a pixel value of the estimated original image corresponding to the image Calculating a median value at a center value in a 3x3 region with respect to the coordinates; Calculating a median value of an area centered on each of nine pixels constituting the 3 × 3 area; Comparing the median value of the center value with the median value of each of the nine pixels; Determining a region type of the 3x3 region; And Calculating a median value of each pixel portion corresponding to the region type Method of improving a digital x-ray image by applying a selective filter comprising a. The method of claim 6, The area type is At least one of a smooth area, a horizontal line, a diagonal line from the upper left to a lower right, a vertical line, a diagonal line from the upper right to a lower left Method for improving digital x-ray image by applying selective filter, characterized in that. The method of claim 6, The method of improving the digital x-ray image by applying the selective filter Set the starting coordinate of the image to x coordinate 0, y coordinate 0, and correspond to the image for each coordinate until the x coordinate value is equal to the column size of the image and the y coordinate value is equal to the row size of the image. Iterating the process of calculating the pixel value of the estimated original image Method for improving digital x-ray image by applying selective filter, characterized in that. The method of claim 1, Computing a pixel value of the estimated background image corresponding to the image Selecting an area corresponding to a predetermined area size; And Calculating a median value in the selected region Comprising Method for improving digital x-ray image by applying selective filter, characterized in that. The method of claim 9, The method of improving the digital x-ray image by applying the selective filter Set the starting coordinate of the image to x coordinate 0, y coordinate 0, and correspond to the image for each coordinate until the x coordinate value is equal to the column size of the image and the y coordinate value is equal to the row size of the image. Repeating the process of calculating pixel values of the estimated background image Method for improving digital x-ray image by applying selective filter, characterized in that. Means for receiving a captured image for applying a selective filter; Means for calculating a pixel value of an estimated original image corresponding to the image; Means for calculating a pixel value of an estimated background image corresponding to the image; Means for determining whether an absolute value of a difference between a pixel value of the estimated original image and a pixel value of the estimated background image is larger than a predetermined boundary value; Means for performing an unsharp mask process using a predetermined constant β if the absolute value of the difference is greater than the boundary value as a result of the determination; Means for performing an unsharp mask process using a predetermined constant α, which is smaller than β, if the absolute value of the difference is not greater than the threshold as a result of the determination; And Means for generating final image with selective unsharp masking Apparatus for enhancing digital x-ray images by applying a selective filter provided with a. In the recording medium tangibly embodied and readable by the digital processing apparatus, a program of instructions that can be executed by the digital processing apparatus is implemented to perform a method for improving a digital x-ray image by applying a selective filter. The method of improving a digital x-ray image by applying the selective filter, Receiving a captured image for applying a selective filter; Calculating pixel values of an estimated original image corresponding to the image; Calculating pixel values of an estimated background image corresponding to the image; Determining whether an absolute value of a difference between a pixel value of the estimated original image and a pixel value of the estimated background image is greater than a predetermined boundary value; If the absolute value of the difference is greater than the boundary value as a result of the determination, performing an unsharp mask process using a predetermined constant value β; If the absolute value of the difference is not greater than the boundary value as a result of the determination, performing an unsharp mask process using a predetermined constant value α smaller than the β; And Generating final image with selective unsharp masking Recording medium comprising a.