JP2612450B2 - Contour line extraction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] The present invention calculates the magnitude and direction of a density gradient of each pixel in an input image, and determines that the gradient direction is within a predetermined angle from each of the X and Y axes. A pixel whose is equal to or larger than a predetermined threshold is extracted. Then, the extracted pixels are compared with the maximum value and the minimum value of each of the left, right, upper and lower N pixels, and pixels which are equal to the maximum value and larger than the minimum value are extracted and the contour is set. With this method, the contour can be detected accurately and quickly.

[Industrial applications]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contour line extracting device capable of accurately and quickly detecting a contour line from the magnitude and direction of a density gradient of each pixel in an input image.

[Conventional technology]

As a conventional method for extracting an outline from an input image, among pixels in which the density gradient is larger than a predetermined value set in advance, several pixels in the vicinity where the density gradient at the pixel is along a direction perpendicular to the outline are used. There is a method of selecting a pixel that is not smaller than any of the density gradients. Specifically, the third
As shown in the configuration of the main part of the conventional example, first, the magnitude and direction of the density gradient are calculated for each pixel by the density gradient magnitude calculator 1 and the density gradient direction calculator 2. Next, a pixel whose magnitude of the density gradient is larger than a predetermined value is extracted first by the density gradient maximum pixel extracting unit for each direction, and then, the magnitude of the density gradient at that pixel is calculated as the density gradient. Compared to the magnitude of the density gradient detected at several neighboring pixels along the direction, only when the magnitude of the density gradient at that pixel is the maximum (no other pixel having a larger density gradient) It is a candidate for a contour line of a pixel.

[Problems to be solved by the invention]

In the above-described contour line detection method, in a column of the magnitude of the density gradient along the direction of the density gradient, when the same value is continued for a certain number or more, the magnitude of the density gradient along the direction is maximized. Pixels that are not shown are also detected as contour line candidates, so that an inaccurate contour line is detected.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a contour line extracting device capable of accurately detecting a pixel having a maximum density gradient in the direction of the density gradient.

[Means for solving the problem]

In order to achieve the above-mentioned object, an arithmetic unit that calculates the magnitude and direction of the density gradient of each pixel in the input image, and the direction of the gradient is
An X, Y density gradient extraction unit for extracting pixels having a predetermined threshold or more within a predetermined angle from each of the X and Y axes, and the maximum of the density gradient of each of the left, right, upper and lower N pixels with respect to the extracted pixels value,
X- and Y-side means for extracting a pixel equal to the maximum value and larger than the minimum value and comparing with the minimum value to set a contour line are provided, and one of them is output.

[Action]

With the above configuration, as shown in the principle explanatory diagrams of FIGS. 1 (a) to 1 (d), the density gradient 7 which should be orthogonal to the contour line 5 of the image 4 of FIG. X, Y shown in (d)
Operation detection is performed using a spatial filter in the direction. Then, in order to detect the surrounding state with respect to the magnitude and direction of the density of the detected pixel, the magnitude of the density gradient of the X and Y axes with respect to the target pixel 6 is determined as shown in FIG. The direction is detected, and pixels whose gradient directions are equal to or larger than a predetermined threshold value within a range of ± α from the X and Y axes are extracted, and as shown in FIG.
The maximum value and the minimum value of the density gradient are detected, and if the target pixel 6 is equal to the maximum value and larger than the minimum value, it is determined that the pixel is on the contour line.

〔Example〕

FIG. 2 is an explanatory view of the configuration of the embodiment of the present invention. In the figure, an input unit 11 receives an image from a TV camera, converts the image into a 512-byte × 512-byte digital image,
Direction 12 _X and sent to the differentiating unit Y-direction 12 _Y, the differential value D _X for each pixel in the X direction, and calculates the Y-direction of the differential value D _Y. These operations are performed by scanning the spatial filters shown in FIGS. 1 (c) and 1 (d) for comparison and detection.

The differential values D _X , D from the X, Y direction differential operation units 12 _X , 12 _Y
Y is entered into the density gradient magnitude calculator 13, and the magnitude of the density gradient is calculated. Is calculated. Similar differential value D _X, with respect to the threshold or more pixels in size is preset gradient putting D _Y in the direction calculation unit 14 of the concentration gradient vector D _X, direction D _Y (0 to 360 ° ) Is calculated. Then, a code “9999” for excluding other pixels is output.

The direction information from the density gradient direction calculation unit 14 is sent to threshold processing units (1) 15 _X and (2) 15 _Y.

In the threshold processing unit (1) 15 _X, for pixels in the range direction is within alpha = ± 45 ° from the X axis gradient "1", the pixel is not the case outputs a "0".

In the threshold processing unit (2) 15 _Y, for pixels in the range direction is within alpha = ± 45 ° from the Y-axis of the gradient "1", the pixel is not the case outputs a "0".

Threshold processing unit (1) 15 _X, (2) 15 _Y corresponding respectively product unit with the output (1) 16 _X of the output density gradient magnitude extractor 13 of, (2) placed in a 16 _Y, the product Is obtained, only pixels within a range of ± 45 ° from the X axis and within ± 45 ° from the Y axis are selected.

Product unit (1) 16 directly comparing unit output value of the AND operation of the pixel within ± 45 ° from the X axis output from the _X (1) 18
_{In addition to X} , four comparators in the X direction, a left maximum value filter 17 _X1 , a left minimum value filter 17 _X2 , a right maximum value filter 17 _X3 , and a right minimum value filter 17 _X4 , a comparison operation unit (1) 18 _X Send to

These filters are for detecting the maximum value or the minimum value of the output values of the product operation unit of N pixels on the left or right side of the target pixel, for example, three pixels as shown in FIG. 1 (b).

In the comparison operation unit (1) 18 _X , the product operation unit (1) 16 _X
The output of the left maximum value filter 17 _X1 and the right maximum value filter 17 _X3
Is equal to any output of, and left minimum filter 1
If it is larger than 7 _X2 or the output of the right minimum value filter 17 _X4 , it outputs “1”; otherwise, it outputs “0”.

Similarly, the output value of the product operation unit for pixels within ± 45 ° from the Y axis output from the product operation unit (2) 16 _Y is also directly input to the comparison operation unit (2) 18 _Y, and the four filters in the Y direction are also provided. , The upper maximum value filter 17 _Y1 , the upper minimum value filter 17 _Y2 , the lower maximum value filter 17 _Y3 , and the lower minimum value filter 17 _Y4 to the comparison operation unit (2) 18 _Y. The functions of these Y-axis vertical filters are the same as those of the X-axis left and right filters.

Then, the outputs of the comparison operation units (1) 18 _X and (2) 18 _Y are passed through a logical sum calculating unit 19 to output the logical sum.

〔The invention's effect〕

As described above, according to the present invention, FIG.
As shown in FIG.
By taking into account the pixels that are equal to or larger than the threshold value within the range, only the local maximum value of the density gradient along the direction of the density gradient can be extracted, and accurate and quick detection of the contour line becomes possible. It is.

[Brief description of the drawings]

1 (a) to 1 (d) are explanatory diagrams of the principle of the present invention, FIG. 2 is an explanatory diagram of a configuration of an embodiment of the present invention, and FIG. 3 is an explanatory diagram of a conventional example. In FIG. Line, 6 is a target pixel, 7 is a density gradient vector, 8 is an extracted pixel, 9 and 10 are spatial filters, 11 is an input unit, 12 _X and 12 _Y are differential operation units, 13 is a density gradient magnitude calculation unit, 14 is a density gradient direction calculation unit, 15 _X and 15 _Y are threshold processing units, 16 _X and 16 _Y are product operation units, 17 _{X 1} , 17 _{X 2} , 17 _{X 3} , and 17 _{X 4} are left and right maximum and minimum value filters, 17 _{Y 1} , 17 _{Y 2} , 17 _{Y 3} , 17 _{Y 4} are upper and lower maximum and minimum value filters, 18 _X , 18 _Y are comparison operation units,
Reference numeral 9 denotes a logical sum calculator.

Claims (1)

(57) [Claims] An arithmetic unit (12X, 12Y, 13, 14) for calculating the magnitude and direction of a density gradient of each pixel in an input image, wherein the direction of the gradient is within a predetermined angle from each of the X and Y axes. And X, Y density gradient extraction units (15X, 15Y, 16X, 16Y, respectively) that extract pixels whose magnitude of the density gradient is equal to or greater than a predetermined threshold, a first means for detecting the magnitude maximum value and the minimum value of the concentration gradient which is output from the left or right side of the N of the operational portion (17 _X1 ~17 _X4), in relation to the Y-axis extraction second means for detecting the magnitude maximum value and the minimum value of the concentration gradient which is output from the N of the operational portion of the upper or lower pixel to pixel, which is (17 _Y1 ~17 _Y4) And the magnitude gradient density output from the calculation unit and the four outputs of the left and right maximum and minimum values from the first means. A third means (18x) for comparing and outputting a pixel whose X density gradient output is equal to any of the left and right maximum values and larger than any of the minimum values; and a magnitude of the density gradient output from the arithmetic unit. And the upper and lower maximum and minimum outputs from the second means are compared, and a pixel whose Y density gradient output is equal to any of the upper and lower maximum values and larger than any of the minimum values is output. A contour line extracting device comprising: a fourth means (18y); and a means (19) for outputting a logical sum of the third means and the fourth means.