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 compared. Furthermore, the quality of image reconstruction under different transformations is observed by inverse transformation.)