Super-resolution Reconstruction Method Of Air-coupled Ultrasonic Image Of Wooden Veneer

With the development of air-coupled ultrasonic(ACU)non-destructive testing technology,the application scenarios of the technology are enriched and the application rate is also increasing.The technology has the characteristics of no liquid coupling medium,non intrusive,non-contact and complete lossless,and can realize non-contact nondestructive testing.But at the same time,the technology is limited by scanning manipulator,the detection speed is very slow,and the detection efficiency is low.Therefore,it is urgent to find a method that can not only shorten the time of ACU scanning imaging,but also keep the imaging image at a high resolution.In this paper,a method of super-resolution reconstruction of ACU images is proposed,and the method is studied.The main achievements are as follows:1.Through theoretical analysis,the feasibility of the proposed method is analyzed.Firstly,the working principle of ACU nondestructive testing system for wood is discussed,and the principle of image super-resolution reconstruction based on interpolation algorithm is studied,then the computer image interpolation algorithm is introduced into ACU non-destructive testing,which can shorten the time of ACU scanning detection through the combination of the two.The interpolation algorithms introduced in this paper are: nearest neighbor interpolation,cubic interpolation,bilinear interpolation and bicubic interpolation.2.The feasibility of the proposed method is verified by a series of reconstruction experiments.Taking the wood sample in the laboratory as the research object,the ACU wood imager was used to complete the full sampling ultrasonic scanning imaging of the wood samples,and the original high resolution imaging map was obtained.Secondly,the above imager is set to different scanning intervals,and downsampled images are obtained by different proportion down-sampling scanning images of the wood samples,and then different image interpolation algorithms are used to interpolate the magnified images with different magnifications.Through the reconstruction experiments,it is found that no matter what kind of down-sampling ratio,the reconstruction algorithm can be reconstructed by interpolation algorithm to obtain high-resolution reconstruction images.3.The influencing factors of the quality of super-resolution reconstruction of ACU images are proposed and verified by experiments.In the specific experiments,the quality of super-resolution reconstruction is evaluated by comparing the visual effect of reconstructed images and the peak signal to noise ratio(PSNR).Experimental results show that the reconstruction quality is affected by many factors.First of all,the magnification is an important parameter for the ACU image reconstruction.The smaller the magnification is,the better reconstruction quality can be achieved.Another issue is related to the type of the image interpolation algorithm used.Different interpolation algorithm will result in different reconstruction quality.The last but not the least factor is the texture characteristics of the wood samples.