This function creates a time-vs-frequency plot image for analyzing a signal s time-evolving frequency content. The signal is x, an analysis window of window_size samples is stepped through the time extent of the signal, and Fs is the sample rat

小波基为db的小波变换，可以提取输入图像的小波特征，低频高频的信息，然后得到特征后用于分类或识别-Wavelet transform is a wavelet transform, which can extract the wavelet features of the input image, low frequency and high frequency information, and then get the feature for classification or recogni

道床加速度时程曲线。功率谱密度函数 图。1/3倍频程Z振级频谱图。道床Z振级VLz（dB）。(Acceleration time history curve of ballast. Power spectral density function. Frequency spectrum of 1 / 3 octave Z vibration level. Ballast Z vibration level vlz (DB).)