Image Directional Power Spectrum Theory And Its Applications

In some applied fields such as target detection and product measurement and so on,the geometric parameters of many linear targets need to be measured. The measuring accuracy of traditional contact measuring method is limited to the measuring principle and processing assembly precision of the mechanical equipment, and its measuring process is complex. The high precision equipment also is expensive. Machine vision technology is a kind of non-contact measuring method which is developed in recent years and it is used in many applied fields. However, this method is often needed to extract target by threshold segmentation, and the wrong measuring results and large measuring errors will appeared while it is applied to the image with low contrast and non-uniform illumination.To withdraw the threshold segmentation and to conveniently calculate the extension direction angle of linear target, this paper proposes the image directional power spectrum theory by combining the two-dimensional Fourier transformation with polar transformation, also the numerical simulation and the precision analysis are completed.Additionally, the applied research of rectangular target width and fringe contrast measurement is completed on the basis of the theoretical research achievement. When the actual objects are measures by using the image directional power spectrum method, at first, directly calculate the extension directional angle of the original image; then calculate the gray directional projection to the original image according to the calculated angle value; finally, combing the projective curve with the data processing method to obtain the measured parameters of width and contrast.This paper has studied the image directional power spectrum and its applications in rectangular width and fringe contrast measurement from the theoretical and experimental aspects. The theoretical achievement of image directional power spectrum provides a novel research idea and solving method for the linear target detection, also it holds important scientific significance and engineered application value. At the same time, the simulation analysis verifies that the calculating precision of the image directional power spectrum is equal to ±0.1° with the frequency domain resolution of 512×512 pixels, and this precision do not affect the next result of the gray directional projection. The proposed width measuring method for rectangular target does not need to extract target by threshold segmentation technology and hence avoid the measuring errors from theintermediate image analysis. The mentioned fringe contrast calculating method may reduce effective the influence of random noise in the interference fringe by using the integral operation. In addition, the contrast can be real time calculated in the experimental process, then the ploarizer in interferometer is adjusted automatically to obtain the interference fringe with the maximum contrast, and as a result, it is very helpful to improve the precision of wave surface recovery.