JP2006311378A - Image processor and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor and image processing method for performing edge enhancement by determining an image edge region and adjusting the edge by an arithmetic operation with a correction amount of enhancement. <P>SOLUTION: An inclination detection filter 21 detects change tendency of signal strength of a center pixel by calculating a difference in luminance signal strength of the center pixel from ambient pixels. A contour component filter generation circuit 23 calculates a two-dimensional matrix obtained by making inverted inclination values calculated in the inclination detection filter 21 respective xy components. Further, the contour component filter generation circuit 23 uses a FIR (finite impulse response) filter function to calculate the total value A of the respective xy components. A luminance signal filter circuit 25 multiplies a luminance signal Y by a coefficient of a contour component filter by using the FIR filter function and generates a luminance filtering signal B by totaling multiplication resultant ones. A contour component operation circuit 28 changes a blending ratio of a normal luminance signal Y to a corrected luminance signal Y2 by the magnitude of the values of the contour components. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing apparatus and an image processing method for performing edge enhancement processing of input image information.

An enlarged image enlarged from the original image may be generated due to an increase in the size of the display. At this time, as shown in FIG. 11, there are a low luminance region α and a high luminance region β. In addition to the regions (α, β) where the luminance is flat, there may be an edge region where the luminance changes gently. Such edge regions (parts forming the contour) may become conspicuous particularly when the original image is enlarged. In such a case, a sharpening process may be performed. For example, an edge enhancement circuit using a Laplacian filter is used for the sharpening process. This filter uses the property that a portion where the shade is changed, such as an edge, is emphasized by subtracting the second derivative (Lapu Cyan) from the target image (see, for example, Non-Patent Documents 1, 2, and 3). .
Supervised by Makoto Nagao, “Digital Image Processing”, Modern Science, December 10, 1978, p. 188-193 Edited by the Institute of Television Engineers of Japan, “Television and Image Information Engineering Handbook”, Ohmsha, November 30, 1990, p. 402-403 Supervised by the Image Processing Standard Textbook Editorial Committee, “Image Processing <Image Processing Standard Text Book>”, Foundation for Image Processing Education, February 25, 1997, p. 166-168

  However, when the contour emphasis circuit using the Laplacian filter described in Non-Patent Documents 1 to 3 is applied to an image having a slowly rising edge, the output level of the Laplacian filter is reduced, and the effect as edge enhancement is achieved. Becomes thinner. If the subtraction amount of the Laplacian filter component is increased in order to increase the contour enhancement effect for this gentle edge, there is a risk that the normal edge portion will be distorted. Further, in an outline emphasis circuit using a Laplacian filter, overshoot or undershoot may occur in principle as shown in FIG. 11, and an unnatural image may be generated.

  It is known that an edge emphasis circuit using a Laplacian filter may fail if the subtraction amount is not adjusted due to the edge component of the input image. For this reason, the contour enhancement circuit using the Laplacian filter has a function of adjusting the subtraction amount from the outside.

  The present invention has been made to solve the above-described problems, and its object is to determine an edge region of an image using a simple device configuration and adjust an enhancement correction amount for the edge. An object of the present invention is to provide an image processing apparatus and an image processing method capable of performing edge enhancement processing.

In order to solve the above-described problem, the invention according to claim 1 is configured such that, for each pixel constituting a two-dimensional matrix area with respect to a specific pixel in a two-dimensional image, a difference in intensity of luminance signals of surrounding pixels of each pixel. A two-dimensional configuration using intensity trend detecting means for detecting a change tendency of the signal intensity of each pixel by calculating and a coefficient weighted to a two-dimensional matrix region with little change based on the change tendency Contour filter generating means for generating a matrix, filtering processing means for multiplying the luminance signal intensity of a specific pixel and its surrounding pixels by the two-dimensional matrix to calculate a signal intensity conversion value of the specific pixel, and the two-dimensional matrix A total value obtained by summing the constituent coefficients is calculated, and the converted luminance intensity of the specific pixel is calculated by dividing the converted signal intensity value by the total value. And summarized in that and a normalization transform means for.

  According to a second aspect of the present invention, in the image processing device according to the first aspect, a blending ratio is calculated using the total value, and the blending ratio is calculated with respect to the input luminance signal intensity and the converted luminance intensity. The present invention further includes blending processing means for calculating a composite value by applying

  According to a third aspect of the present invention, in the image processing apparatus according to the first or second aspect, the intensity tendency detecting means sets a minimum saturation value as the change tendency, and sets a value other than 0 as the minimum saturation value. The summary is given.

  According to a fourth aspect of the present invention, in the image processing apparatus according to any one of the first to third aspects, the intensity tendency detecting means determines a maximum saturation area and a minimum saturation area with respect to a change tendency of the signal intensity. The gist is that the range of these regions is set and variable.

  According to a fifth aspect of the present invention, in the image processing device according to any one of the first to fourth aspects, the contour filter generation unit acquires data related to a two-dimensional fixed matrix and generates the data based on a change tendency. The gist is to apply each element of the two-dimensional fixed matrix to each element of the two-dimensional matrix.

  According to the sixth aspect of the present invention, for each pixel constituting a two-dimensional matrix area with respect to a specific pixel in a two-dimensional image, a difference in intensity of luminance signals of surrounding pixels of each pixel is calculated. An intensity trend detection stage for detecting a change tendency of signal intensity, and a contour filter generation stage for generating a two-dimensional matrix configured by using a weighted coefficient for a two-dimensional matrix area with little change based on the change tendency; A filtering process step of multiplying the luminance signal intensity of the specific pixel and surrounding pixels by the two-dimensional matrix to calculate a signal intensity conversion value of the specific pixel, and a total value obtained by summing up the coefficients constituting the two-dimensional matrix. A normalization conversion step of calculating a conversion luminance intensity of the specific pixel by calculating and dividing the signal intensity conversion value by the total value. It is the gist of.

(Function)
According to the present invention, based on the change tendency, a two-dimensional matrix configured using a weighted coefficient for a two-dimensional matrix region having a small change is generated, and the two-dimensional matrix is converted into a specific pixel and surrounding pixels. The luminance signal intensity is multiplied to calculate a signal intensity conversion value for a specific pixel. As a result, the contour can be grasped based on the change tendency, and the contour can be emphasized according to the situation of the surrounding pixels. Further, a total value obtained by summing the coefficients constituting the two-dimensional matrix is calculated, and the converted luminance intensity of the specific pixel is calculated by dividing the signal intensity converted value by the total value, thereby changing the filtering process. Strength can be restored.

  According to the present invention, a blending ratio is calculated using the total value, and a composite value is calculated by applying the blending ratio to the input luminance signal intensity and the converted luminance intensity. For this reason, contour enhancement can be performed while utilizing the original image.

  According to the present invention, the intensity tendency detecting means sets a minimum saturation value as the change tendency and gives a value other than 0 as the minimum saturation value. For this reason, it is possible to prevent the converted luminance intensity from diverging when performing normalization conversion.

  According to the present invention, it is possible to perform image processing for determining an edge region of an image and enhancing the edge using a simple apparatus configuration.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. In this embodiment, the case where it applies to the image output apparatus which outputs an image to a large sized liquid crystal display is assumed. FIG. 1 is a principal block diagram showing an embodiment according to the present invention. In the present embodiment, description will be made using an edge emphasis processing device 20 as an image processing device provided in the image output device.

  The contour enhancement processing device 20 includes an inclination detection filter 21 as an intensity tendency detection unit, a contour component filter generation circuit 23 as a contour filter generation unit, a luminance signal filter circuit 25 as a filtering processing unit, and an amplitude as a normalization conversion unit. A normalization circuit 26 is provided. Each means executes an intensity tendency detection stage, a contour filter generation stage, a filtering process stage, and a normalization conversion stage.

  First, the RGB luminance signal Y of the original image is input to the contour enhancement processing device 20. This luminance signal Y is input to the inclination detection filter 21. Here, it is assumed that the two-dimensional image shown in FIG. 9 is input. In this two-dimensional image, the luminance signal Y of a predetermined one-dimensional axis is shown in FIG.

(Tilt detection)
The inclination detection filter 21 to which the luminance signal Y is input performs inclination detection, normalized value calculation, and saturation value calculation. Here, the change tendency of the signal intensity of each pixel (center pixel) is detected by calculating the difference in the intensity of the luminance signal of the surrounding pixels of each pixel in the (5 × 5) two-dimensional matrix region. In the present embodiment, a two-dimensional FIR filter (Finite Impulse Response Filter) is used. Here, as in the coefficient 510 shown in FIG. 2, filters of (−1, 0, 1) in the x direction and (−1, 0, 1) in the y direction are used for the center pixel. Then, using the arithmetic expression 520, the absolute values of the change values in the x direction and the y direction are totaled, and the luminance gradient around the center pixel is calculated. Here, the output result of the inclination detection filter 21 is shown in FIG. 7 for the luminance signal Y shown in FIG.

  Next, the inclination detection filter 21 performs a normalized value calculation. Specifically, the normalized normalized luminance slope value dd is calculated by dividing by the maximum change value assumed in the luminance signal.

  Further, the inclination detection filter 21 performs a saturation value calculation. Here, the normalized luminance gradient value dd is used for conversion so that the region where the luminance change is small becomes “1”. Specifically, the inversion slope value idd is calculated using the inversion characteristic 530 shown in FIG. In this case, the region below “dd = a” is a region where the intensity change of the luminance signal is small, and is the maximum saturation region of the inverted gradient value idd with respect to the normalized luminance gradient value dd. On the other hand, the region of “dd = b” or more is a region where the intensity change of the luminance signal is large, and is a minimum saturation region of the inverted gradient value idd with respect to the normalized luminance gradient value dd. In the present embodiment, the values of “a” and “b” can be changed, and the range of the maximum saturation region and the minimum saturation region can be changed.

  Then, by executing this inclination detection in the entire region of the image signal, an inclination coefficient map configured using coefficients obtained by weighting pixels with small luminance changes for each pixel is generated. In this inversion characteristic 530, a minimum saturation value is set in a minimum saturation region of “dd = b” or more, and a value other than “0” is given as the minimum saturation value.

(Contour component filter generation)
The inclination coefficient map is output to the contour component filter generation circuit 23. The contour component filter generation circuit 23 has a function as an FIR filter. Here, first, the contour component filter generation circuit 23 calculates a two-dimensional matrix having the inverted gradient value idd calculated by the gradient detection filter 21 as each xy component. In the present embodiment, for each pixel, a (5 × 5) two-dimensional matrix corresponding to the surrounding pixels is configured.

  In this two-dimensional matrix, as shown in FIG. 3, the idd of the region where the luminance change is small (flat region) is close to “1”, and the idd of the region where the luminance change is large (edge region) is close to “0”. Is set as the xy component.

  Further, the contour component filter generation circuit 23 performs correction using the two-dimensional fixed matrix 22. Then, this two-dimensional fixed matrix 22 is applied to a two-dimensional matrix configured using the inverted slope value idd. The two-dimensional fixed matrix 22 is a fixed matrix with respect to the two-dimensional matrix that changes depending on the image. For example, when a (5 × 5) matrix H is assumed, it can be expressed as follows.

ここで、ｈ（ｋ，ｌ）は、各座標の成分値を表す関数である。

Here, h (k, l) is a function representing the component value of each coordinate.

  For example, when the (5 × 5) matrix is changed to the (4 × 4) matrix, the component values around the (5 × 5) matrix are set to “0”. In addition, when weighting the center, a mountain-shaped filter having the vertex at the center is used. In this embodiment, a two-dimensional fixed matrix 22 shown in FIG. 4 is used.

Then, the contour component filter generation circuit 23 multiplies each xy component of the two-dimensional matrix generated using the inclination coefficient map by the xy component of the two-dimensional fixed matrix 22 corresponding to each coordinate. As a result, the coefficients of the two-dimensional matrix can be weighted and the adaptive range of the two-dimensional matrix can be changed. As a result, a contour component filter is generated.
Further, the contour component filter generation circuit 23 calculates the total value A of each xy component using the FIR filter function. This total value A is used for luminance correction of the entire image, which will be described later.

(Luminance signal filtering)
Next, the luminance signal of the original image is filtered using the contour component filter calculated by the contour component filter generation circuit 23. Specifically, the luminance signal filter circuit 25 multiplies the luminance signal Y by a contour component filter. The luminance signal filter circuit 25 also has a function as an FIR filter. In this case, the luminance signal Y subjected to delay compensation through the delay compensation circuit 24 is input to the luminance signal filter circuit 25 in consideration of the calculation processing time in the contour component filter generation circuit 23. The luminance signal filter circuit 25 applies a contour component filter to the luminance signal Y. In this case, as shown in FIG. 5, the luminance signal filter circuit 25 multiplies the luminance signal Y by the coefficient of the contour component filter using the FIR filter function, and sums the multiplication values to obtain the luminance filtering signal B. Generate. For example, the luminance filtering signal B at coordinates (i, j) is expressed as follows. In the case of a 5 × 5 matrix, M = 2 and N = 2 with the coordinates (i, j) as the center.

ここで、ｄｄ（ｉ＋ｋ，ｊ＋ｌ）は、輪郭成分フィルタの係数を表す。

Here, dd (i + k, j + l) represents the coefficient of the contour component filter.

  Here, since the luminance of the edge portion is close to “0”, the signal intensity is attenuated, so that the image itself becomes dark. Therefore, the amplitude normalization circuit 26 performs correction using the luminance filtering signal B calculated by the luminance signal filter circuit 25 and the total value A calculated by the contour component filter generation circuit 23. Then, the amplitude normalization circuit 26 divides the luminance filtering signal B by the total value A to calculate a corrected luminance signal Y2. This compensates for degraded luminance in the edge region. The corrected luminance signal Y2 is output to the contour component calculation circuit 28 described later.

  Here, the corrected luminance signal Y2 for the luminance signal Y shown in FIG. 6 is shown in FIG. Here, when a flat region is included in the matrix, the luminance is weighted to correct the luminance of the central pixel. The luminance of the central pixel is affected by the luminance of the flat region and acts in the direction of expanding the flat region. For this reason, as shown in FIG. 8, the edge region becomes narrower and the rise of the brightness becomes steep. On the other hand, unlike the case of the contour emphasis circuit using the Laplacian filter, since the second-order differential component for sharpening is not used, no overshoot or undershoot occurs. Furthermore, FIG. 10 shows the processing result of the amplitude normalization circuit 26 for the input two-dimensional image (FIG. 9). Comparing FIG. 9 and FIG. 10, it can be seen that the edge region is visually less blurred and a sharp image is generated.

(Blending process)
Further, the delay compensation circuit 27 compensates the luminance signal Y for the delay of the arithmetic processing time in the luminance signal filter circuit 25 and the amplitude normalization circuit 26. Then, the delay compensation circuit 27 outputs the luminance signal Y subjected to delay compensation to the contour component calculation circuit 28.

  The contour component calculation circuit 28 calculates the composite value by changing the blending ratio between the normal luminance signal Y and the corrected luminance signal Y2 with the magnitude of the value of the contour component. Here, the total value A calculated by the contour component filter generation circuit 23 is used. First, a normalized total value DD obtained by normalizing the total value A is calculated. For example, the normalized total value DD of coordinates (i, j) is expressed as follows. In the case of a 5 × 5 matrix, M = 2 and N = 2 with the coordinates (i, j) as the center.

この場合、エッジ領域においては輪郭成分フィルタの各成分は「０」に近くなるため、正規化総計値ＤＤも「０」に近くなる。一方、平坦領域においては輪郭成分フィルタの各成分は「１」に近くなるため、正規化総計値ＤＤも「１」に近くなる。

In this case, since each component of the contour component filter is close to “0” in the edge region, the normalized total value DD is also close to “0”. On the other hand, since each component of the contour component filter is close to “1” in the flat region, the normalized total value DD is also close to “1”.

Therefore, the contour component calculation circuit 28 calculates a contour emphasis signal Yk as a signal intensity conversion value using the following equation.
Yk = Y2 * (1-DD) + Y * DD
As a result, the edge emphasis signal Yk is calculated using the corrected luminance signal Y2 for the edge region and the luminance signal Y of the original image for the other region (flat region). Thereby, the image of a flat part can be maintained.

According to the image processing of the above embodiment, the following effects can be obtained.
In the above embodiment, the absolute values of the change values in the x direction and the y direction are totaled using a two-dimensional FIR filter, and the luminance gradient around the center pixel is calculated. Further, the inversion slope value idd is calculated using the inversion characteristic 530 having the maximum saturation region and the minimum saturation region. The contour component filter generation circuit 23 calculates a two-dimensional matrix having each xy component using the inverted slope value idd. As a result, the edge region and the flat region can be specified, and the signal intensity obtained by weighting the luminance of the flat region can be calculated.

  In the above embodiment, the values of “a” and “b” can be made variable to change the range of the maximum saturation region and the minimum saturation region. Thereby, the width of the edge region can be changed depending on the type of image.

  In the above embodiment, the contour component filter generation circuit 23 multiplies each xy component of the two-dimensional matrix generated using the slope coefficient map by the xy component of the two-dimensional fixed matrix 22 corresponding to each coordinate. As a result, the coefficients of the two-dimensional matrix can be weighted and the adaptive range of the two-dimensional matrix can be changed. In particular, when the pixel area of the two-dimensional matrix is large and protrudes from the edge area to the flat areas on both sides, the contour may disappear. Accordingly, the range of the (5 × 5) two-dimensional matrix can be changed using the two-dimensional fixed matrix 22.

  In the above embodiment, the contour component filter generation circuit 23 calculates the total value A of each xy component using the FIR filter function. The luminance signal filter circuit 25 multiplies the luminance signal Y by the coefficient of the contour component filter using the FIR filter function, and generates the luminance filtering signal B by summing the multiplication results. Then, the amplitude normalization circuit 26 performs correction using the luminance filtering signal B calculated by the luminance signal filter circuit 25 and the total value A calculated by the contour component filter generation circuit 23. Thereby, it is possible to correct the luminance deterioration in the edge region using the FIR filter function.

  In the above embodiment, the contour component calculation circuit 28 changes the blending ratio between the normal luminance signal Y and the corrected luminance signal Y2 based on the value of the contour component. Here, the luminance signal Y and the corrected luminance signal Y2 are synthesized using the normalized total value DD obtained by normalizing the total value A. Thereby, the edge emphasis signal Yk can be calculated using the corrected luminance signal Y2 for the edge region and the luminance signal Y of the original image for the other region (flat region).

In addition, you may change the said embodiment into the following aspects.
In the above embodiment, it is assumed that the present invention is applied to an image output device that outputs to a large liquid crystal display. However, the application field of this image processing device is not limited to this, and the image output device such as a printer is provided inside the image output device. It is also possible to do. In addition, an image processing apparatus other than the image output apparatus and the host computer can be incorporated as application software.

In the above-described embodiment, the contour component filter is generated using a (5 × 5) two-dimensional matrix, but the present invention is not limited to this as long as it can capture information on neighboring pixels.
In the above embodiment, when the matrix size is changed (for example, when the (5 × 5) matrix is changed to the (4 × 4) matrix), the contour component filter generation circuit 23 converts the two-dimensional fixed matrix 22 into the inverted gradient value. This is applied to a two-dimensional matrix constructed using idd. Alternatively, the size of the matrix may be changed at the stage of calculating a two-dimensional matrix with each xy component using the inverted slope value idd. Thereby, unnecessary arithmetic processing can be omitted, and higher-speed processing can be realized.

  In the above embodiment, the inclination is detected only in the X-axis and Y-axis directions. However, it is also possible to detect in the oblique direction by changing the filter coefficient.

Schematic of the functional block of one Embodiment of this invention. Explanatory drawing of the process in an inclination detection filter. Explanatory drawing of a contour component filter. Explanatory drawing of a two-dimensional fixed matrix. Explanatory drawing of the filtering process of a luminance signal. Explanatory drawing of an input signal. Explanatory drawing of the output result of an inclination detection filter. Explanatory drawing of the output result of an amplitude normalization circuit. Explanatory drawing of the input two-dimensional image. Explanatory drawing of the output two-dimensional image. Explanatory drawing of an edge area | region.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Contour emphasis processing apparatus as an image processing apparatus, 21 ... Inclination detection filter as intensity tendency detection means, 22 ... Contour component filter generation circuit as contour filter generation means, 25 ... Luminance signal filter circuit as filtering processing means, 26: Amplitude normalization circuit as normalization conversion means, A: Total value, Y: Luminance signal, 22: Two-dimensional fixed matrix, 510: Coefficient.

Claims (6)

Intensity for detecting the change tendency of the signal intensity of each pixel by calculating the difference in intensity of the luminance signal of the surrounding pixels of each pixel for each pixel constituting the two-dimensional matrix area with respect to the specific pixel in the two-dimensional image. A trend detection means;
A contour filter generating means for generating a two-dimensional matrix configured using a weighted coefficient for a two-dimensional matrix region with little change based on the change tendency;
Filtering processing means for multiplying the two-dimensional matrix by the luminance signal intensity of the specific pixel and surrounding pixels to calculate a signal intensity conversion value of the specific pixel;
Normalization conversion means for calculating a total luminance value obtained by summing the coefficients constituting the two-dimensional matrix and dividing the signal intensity conversion value by the total value to calculate a conversion luminance intensity of the specific pixel. An image processing apparatus. Use the total value to calculate the blending ratio,
The image processing apparatus according to claim 1, further comprising blending processing means for calculating a composite value by applying a blending ratio to the input luminance signal intensity and the converted luminance intensity.   The image processing apparatus according to claim 1, wherein the intensity tendency detection unit sets a minimum saturation value as the change tendency and assigns a value other than 0 as the minimum saturation value.   4. The intensity trend detecting means sets a maximum saturation area and a minimum saturation area with respect to a change tendency of signal intensity, and makes the range of these areas variable. An image processing apparatus according to 1.   The contour filter generation means obtains data relating to a two-dimensional fixed matrix and calculates each element of the two-dimensional fixed matrix generated based on a change tendency by applying each element of the two-dimensional fixed matrix. The image processing apparatus according to claim 1, wherein the image processing apparatus is characterized. Intensity for detecting the change tendency of the signal intensity of each pixel by calculating the difference in intensity of the luminance signal of the surrounding pixels of each pixel for each pixel constituting the two-dimensional matrix area with respect to the specific pixel in the two-dimensional image. A trend detection stage;
A contour filter generating step for generating a two-dimensional matrix configured using a coefficient weighted to a two-dimensional matrix region with little change based on the change tendency;
A filtering step of multiplying the two-dimensional matrix by the luminance signal intensity of the specific pixel and surrounding pixels to calculate a signal intensity conversion value of the specific pixel;
A normalization conversion step of calculating a total luminance value obtained by summing coefficients constituting the two-dimensional matrix and calculating a conversion luminance intensity of the specific pixel by dividing the signal intensity conversion value by the total value. An image processing method characterized by the above.

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