Improving the contrast of computed tomography medical images is an essential issue since most of these images suffer from the low contrast phenomenon. This study confirms that adjusting the contrast of degraded CT images before beginning the restoration process is highly desired. A comparison between seven famous techniques was conducted likewise to choose the best method among the different popular contrast enhancement methods. Then, experiments were performed to prove that adjusting the contrast before restoring CT images would lead to better restoration results. Finally, a discussion and a conclusion are provided to highlight the important issues of this paper.