Circular target circular center positioning method

Abstract

The invention discloses a circle center locating method of a circular target, mainly relating to a great deal of target identification and target location. Firstly, rough circle center location is carried out to an image by using a simple contour centroid method, a key square region is extracted as a region of interest according to the information of a rough location circle center and a rough location radius, and pixel-level edge location is carried out to the circular target in the region of interest by a canny operator; then sub-pixel location is carried out to the circular target according to the geometric features and the gray information of the circle, therefore, a precise coordinate of sub-pixel edge points is obtained; after that, a curvature filtering method and an average filtering method are respectively used for filtering 'isolated points' and noise occurring in the sub-pixel edge points; finally, a least squares method is utilized to fit a circle to the filtered sub-pixel edge points so as to obtain the final circular center and radius. The method not only effectively improves the precision of circle center location, but also improves the robustness thereof, thus further improving the measurement precision of a measurement system and perfecting the stability of the measurement system.

Description

technical field [0001] The invention relates to a sub-pixel edge positioning method of a circular target and a sub-pixel edge point filtering method, in particular to a circle center positioning method of a circular target. Background technique [0002] In many image analysis and processing systems, quickly and accurately obtaining the center of the circle is widely used in target recognition and positioning. For example, in a 3D reconstruction system, obtaining the center of the calibration plate with high precision is of great importance to the accuracy of the entire 3D reconstruction. important influence. At present, the common algorithms for calculating the center of the circle are: centroid method, Hough transform method, Gaussian surface fitting method, and least squares curve fitting method. The centroid method requires that the gray distribution of the image is relatively uniform, otherwise there will be a large error; the Hough transform method needs to vote and re...

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Problems solved by technology

The document "Subpixel edge localization and the interpolation of still images" (Jensen K, Anastassiou, IEEE Trans on PAMI, 1995, 4(3): 285-295) is an interpolation method, which uses the pixel-level edge localization algorithm for interpolation and enlargement Image, under the premise that the actual grayscale distribution law of the actual image is consistent with the interpolation law, the edge positioning can reach sub-pixel accuracy; the literature "Detecting sub-pixel edges using tangent direction information" (Zhang Yujin, Fu Zhuo, Pattern Recognition and Artificial Intelligence, 1997 , 10(1): 69~74) mainly uses the information of tangent direction to locate the edge of the known shape of the object. This method relies too much on the information of the center and radius of the rough location, and does not make full use of the gray area of ​​the image. Degree value information; literature "A fast subpixel edge detection method using Sobel-Zemike moments operator" (Qu Ying-Dong, Cui Cheng-Song, Chen San-Ben, LiJin-Quan, Image and Vision Computing, 2005, 23: 11~17 ) using moment method to realize edge sub-pixel positioning

Moment-based methods are currently widely used, but they are not suitable for real-time processing of large bitmaps due to the use of multiple 7×7 templates; Laser, 2005, 16(8): 993~996) introduced the principle of sub-pixel edge parameter fitting, which uses Sobel operator and parameter fitting method to realize sub-pixel edge positioning, and there are two problems, the first First, the Sobel operator cannot achieve integer-pixel-level edge positioning for most images, resulting in inaccurate sub-pixel positioning; second, the method provided in this document cannot ensure the edge positioning accuracy of the quadratic curve

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