I am using an R12 MATLAB evaluation version in order to evaluate its integration with Microsoft Visual C++ 6 IDE. I wish to develop a dll performing an image filtering. It is quite simple if I use fspecial calls only. But if you try to use the edge function (and other similar routines) you encounter hard problems: in such cases I was not able to make a working dll. Can someone help me? Thanks. Here is a copy of my .m file (edge detection filter): function OutMatrix = MyFuncion(InMatrix) OutMatrix = edge(InMatrix,'prewitt'); Problems I encountered: 1. When I had to modify my .m file, after I modified it I had to remove it from the project and re add it using the MATLAB Add-in for Microsoft Visual Studio, and I had to specify the kind of project I use and its characteristics (every time!). Afteward the MATLAB wizard unload the project and reload it. 2. Among files introduced in the project by the MATLAB wizard, there were some with a strange extension: .dll.m (for instance std.dll.m) and I managed this problem renaming analogous .m files in .dll.m. 3. Other files did not exist in the MATLAB working directory, so I managed this problem searching for them and copying them in the right (?) directory. 4. Some files did not exist at all (for instance bwfillc.m), so I had to remove them from the project. 5. Some compiler warnings come out. The project was compiled and linked. But when I tried to use the dll, a program abort appeared. What do I have to do? Daniele Masini Laboratori R&S Ebit S@nitS.p.A.