You can never enlarge and image without losing quality, but there are a few things you can do to keep it looking a bit less blurry. The How-To Geek shows us how.
The How-To Geek goes through three tips in Photoshop, but most should work in the GIMP too. Basically, you can do three things to keep enlarged photos sharp:
- Enlarge them using the "Bicubic Smoother" anti-aliasing. If you're using GIMP, use "Cubic".
- Change the color mode to "Lab Color" and use Photoshop's "Smart Sharpen" feature, or a slightly more manual sharpening method in the GIMP.
- When enlarging typography, use the "Nearest Neighbor" setting, Gaussian Blur the entire thing, then use a Threshold adjustment layer to sharpen out the edges.
Of course, this won't be perfect, and it won't actually bring back the quality of the original, downsized image. However, it can take a very blurry image and make it passable, or make a slightly resized image look okay. Hit the link for the full how-to.