The prompt progress of photomask pattern shrinking leads to the overlooking for significant defects. To improve the defect detection performance, patterns must be observed thoroughly at first. These observations are also important for a total diagnostic of the lithography process. Our developing reticle inspection machine LM5000 is very suitable for such analyses. With LM5000, users are able to point any positions on the reticle very easily, view the images, measure the lengths or widths of the patterns, and the intensity at each pixel. Users are also able to apply various image processing algorithms. To follow the growth of the semiconductor processes, inspection algorithms should be developed within very short terms. LM5000 adopts a special image processing core consisted of IMAP. It has strong processing power of a super computer class, and it is programmable even by a C-like language. Libraries for development include most of the standard image processing functions. Its flexibility helps us for reducing the development periods of the new algorithms. In this presentation, the functions of the user interface of LM5000 are displayed as a mask analyzing tool, and the effects of the IMAP processing is explained.