Thorax x-ray images are used to identify tuberculous cavities. Sometimes it is difficult to detect the cavity and determine its extent in unprocessed digital image. Image processing serves to help the identification. The method used in this study is Morphological Segmentation and Unsharp Masking. The total number of images which were to be processed was 42 , yet only one of them is completely presented and discussed in this article. In all of the post processed images, it can identify tuberculosis cavity and measure its area.