You can sharpen an image in GIMP on your computer using the Sharpen tool or the Sharpen filter. Here is a full tutorial on how to do it!

Select the image you want to resize, using the Open Image file browser, and click the "Open" button to open the image in GIMP.

GIMP, a free, open source image editor, that’s available for Windows, OS X, Ubuntu, Debian, openSUSE, Fedora, Mandriva, BSD, and Solaris and one of its neat features is an automation plugin ...

The GIMP is an open source software application for editing raster graphics. It is intended to serve as a free and open alternative to high-end image editing programs for a professional audience.

Hands-on: testing the GIMP 2.8 and its new single-window interface We go hands-on with the latest update of the venerable open source image editor.