中文说明： 滤波反投影法采用先修正、后反投影的做法，同样可得到原始的度函数。其基本方法是：在某一投影角下取得了投影函数（一维函数）后，对此一维投影函数作滤波处理，得到一个经过修正的投影函数；然后再将此修正后的投影函数作反投影运算，得到所需的密度函数。这一方法中要解决的主要问题是如修正投影函数才能使之在反投影后能重建原密度函数。
English Description：
In the filtered back projection method, the original degree function can also be obtained by using the method of correction before back projection. The basic method is as follows: after the projection function (one-dimensional function) is obtained at a certain projection angle, a modified projection function is obtained by filtering the one-dimensional projection function; then the modified projection function is back projected to obtain the required density function. The main problem to be solved in this method is to modify the projection function so that the original density function can be reconstructed after back projection.