1. A method for processing metal artifacts in a CT image, the method comprising: performing a first metal artifact processing on an original image to obtain a first processed image COR1, wherein the original image is a reconstructed CT image based on scan data obtained by CT scanning a subject, and wherein the original image contains metal artifacts, and in the process of the first metal artifact processing, the scan data involving the metal artifacts is corrected; extracting the high frequency portion of the first processed image COR1 to obtain a first high-frequency image COR1HF; performing a second metal artifact processing on the original image to obtain a second processed image COR2, wherein in the second metal artifact processing, the metal artifacts are removed without affecting the tissue information of the subject; extracting the high frequency portion of the processed image COR2 second to obtain a second high-frequency image COR2HF; extracting a metal image from the original image and obtaining a weighting function W based on the metal image; and performing a weighted combination for the first processed image COR1, the first high-frequency image COR1HF and the second high-frequency image COR2HF by using the weighting function W to obtain a result image CORImp.