通过阈值去噪，最关键的就是要确定最佳阈值T 的大小.如果阈值太小，可以保留更多的小波系数，但同时噪声也被保留；相反，阈值太大，可以消除更多的噪声，但重要图像特征又将被滤掉，引起偏差.目前使用的阈值分为全局阈值和局部阈值.全局阈值对各层所有的小波系数或同一层内的小波系数都是统一的；局部阈值则是根据当前系数周围的局部情况来确定合适的阈值，具有灵活性.-Threshold denoising, the most critical is to determine the optimal threshold T s size. If the threshold is too small, you can retain more of the wavelet coefficients, but the noise was retained　the contrary, the threshold is too large, can be eliminatedmore noise, but the important image features in turn be filtered out, causing bias current threshold is divided into a global threshold and local threshold. global Threshold the wavelet coefficients of all the wavelet coefficients of the layers or on the same floorare unity　local threshold is based on the local situation of the current coefficient around to determine the appropriate threshold, with flexibility.