Here’s an Adobe Photoshop plugin. This plugin allows you to enlarge images with less image quality loss. DOA released this one, and I got another Adobe plugin coming up for you.
Blow Up® 2 is a Photoshop® plug-in that produces enlargements dramatically sharper than any other software, especially Photoshop! Blow Up uses an innovative algorithm that temporarily converts pixels to a vector representation which results in perfectly smooth, crisp edges. Simulated texture and film grain keep photos looking natural even in extreme enlargements. Blow Up can even clean up JPEG compression artifacts when a client insists on using a low quality source image from the Web.