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Shape description method based on fractional Fourier transform

A technique of fractional Fourier transform and shape description, applied in image data processing, instrumentation, calculation, etc.

Inactive Publication Date: 2012-10-10
三亚哈尔滨工程大学南海创新发展基地
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Problems solved by technology

However, the traditional Fourier transform uses a global basis function to determine that it can only be used to deal with certain stationary signals, and it is powerless for time-varying non-stationary signals.

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  • Shape description method based on fractional Fourier transform

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Embodiment Construction

[0010] The present invention is described in detail below in conjunction with accompanying drawing example:

[0011] The specific implementation steps of the shape description method proposed by the present invention are as follows:

[0012] Let I be the input image matrix, I contains only one target, and the target is black and the background is white.

[0013] The first step is to estimate the center of mass and the direction of the main axis of the object in the image, specifically: calculate the center of mass of the target according to (1):

[0014] o c =[M 10 / M 00 , M 01 / M 00 ] T (1)

[0015] in, The values ​​of variables k and l are 0 or 1, M kl Represents the (k+l) order moment of the image, O c is the centroid of the target in the image, W and H are the width and height of the image respectively; I(h,w) represents the element of the hth row and wth column of the input image matrix I;

[0016] combine figure 1 , estimate the main axis direction of th...

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Abstract

The invention provides a shape description method based on fractional Fourier transform. The method comprises: a first step of estimating the center of mass and the principal axis direction of a target object in an image; a second step of performing rotation and translation on the image; a third step of removing portions outside a target enclosing rectangle from the rotated and translated image to obtain a target image, and performing normalization on the size of the target image; a fourth step of calculating the fractional Fourier transforms with different orders of the normalized image; a fifth step of discarding the amplitudes of the fractional Fourier transforms, and only preserving the phases of the fractional Fourier transforms; and a sixth step of taking phase histograms of each order of fractional Fourier transform of the normalized image as shape features of the object. The shape description method provided in the invention has characteristics of rotation invariance and translation invariance, and the phase of the fractional Fourier transform is utilized. According to the method, filtration of an image in different scales is realized, and the characteristic that described features are not only related to the boundary contour of an object but also related to the internal region of the object is ensured.

Description

technical field [0001] The invention relates to a shape description method, in particular to a shape description method in digital images. Background technique [0002] The shape features of objects are widely used in object recognition, and the description of object shape is one of the important tasks of computer vision. Existing object shape description methods can be roughly divided into two categories: boundary-based shape description and region-based shape description. Among them, the boundary-based method describes the shape of the object only considering the pixels on the boundary of the object. In contrast, region-based methods extract shape features from regions of the entire target image. At present, the commonly used boundary-based object shape description techniques mainly include Fourier descriptor, wavelet descriptor, wavelet-Fourier descriptor and so on. Fourier descriptors are widely used in the field of shape description because of their simple calculatio...

Claims

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Application Information

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IPC IPC(8): G06T9/20
Inventor 郑丽颖石大明
Owner 三亚哈尔滨工程大学南海创新发展基地
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