对Lena图像进行傅立叶、离散余弦、哈达玛变换。在频域，对比他们的变换后系数矩阵的频谱情况，进一步，通过逆变换观察不同变换下的图像重建质量情况。(Fourier transform, discrete cosine transform and Hadamard transform are applied to Lena image. In the frequency domain, the spectrum of their transformed coefficient matrix is c