SmillaEnlarger is an Open Source program that enables you produce quality enlargements of your digital photos. It enables you to convert a low resolution image into a high resolution copy while maintain as much of the details as possible and minimizing image noise. You can also clip a portion of your photo and create a high quality crop with the same or higher resolution than the original. SmillaEnlarger offers several adjustment options and an instant preview to inspect the results.
The program produces very good results, however the interface and usability features (or lack thereof) require a bit of a learning curve – there is no `Save` button for example, the program saves a copy automatically; you have to select an entire folder before you can select an image… and several other oddities that can be confusing at first. A Help document comes included with the download, you`ll probably want to take a look at it before you get started.