I have found S-spline version 2 to be a very good image resizing tool for printing my digital CCD camera shots of astronomical objects. S-spline gives you the option to review the results of the S-spline algorithm vs. bilinear, bicubic, and nearest neighbor algorithms commonly found in programs like Photoshop. My only complaint with S-spline version 2 was that the stars were sharpened excessively and had very sharply defined edges. This looked unnatural to my eye. S-spline Pro now provides the user with multiple controls that can lead to a more pleasing result. Star edges may be softened to a more natural look by altering the Intensity and Radius sliders. I have found that this only enhances the image and does not compromise the programs ability to upsize a small digital file image. S-spline Pro gives the user a few other resize methods in addition to the bilinear, bicubic, and nearest neighbor. There is now B-Spline and Lanczos. Each image I resize, I always prefer the S-spline results vs. the other algorithms. The interface is quite simple and the preview pane refreshes quickly allowing the user to tweak the settings until the desired result is obtained.
The above image is the workspace for the S-spline Pro. I have needed to convert grayscale images to RGB in order for S-spline Pro to work properly. I am not sure if the program does not handle grayscale profiles from Photoshop or if there is something I am missing in the instructions. The online support database is a little on the thin side. If you run into any trouble with the program, you may have to find your own work-around. The two images below are both enlarged S-spline images. One is from version 2 and the other is from the Pro version. Which one is the Pro version? The answer is below the images if you want to test the results for yourself.
