With black and white negs, its as easy as shooting the frame with a digital camera on a tripod, with a decent lens or its built in macro mode, open your favorite image editing software, open the file, then inverting it. However with C-41 or similar color negs, its a little more complicated. You have to deal with the color negative's color cast - that brownish hue color negs have to them. It makes it a whole lot easier if you have an unexposed frame of the same neg type. If not you need to take a sample of the negative that wasn't exposed, Invert that, then overlay that on your working file in the subtractive layer mode in photoshop. I haven't done this in a few years, but I do remember it working pretty well. Of course its 1000x better to use a negative scanner or flatbed scanner with a transparency adapter.