Though I haven't used this, I thought I'd mention Reshade
, since I recall hearing some good things about it. Here's the developer's blurb on CNET:
Reshade Image Resizer offers the most powerful photo enlargement framework available on the market. Resize images without the usual blur, jagged edges, halos, loss of sharpness or detail associated with image up-rezing. Easy to use, intuitive controls, make Reshade the best choice for beginners and experts alike. Create photo-realistic resizes at almost any zoom factor, 20x and more. Quickly adjust images for printing, high resolution publishing or other photograpic display, web design or scientific purposes. Crop and batch process your pictures easily while resizing them in various file formats like jpeg, tiff, png, bmp (supports most image modes including CMYK).
It's very pricey, but I think you can download it and try it out, which may be all you need.