Introduction

Almost every digital image (captured either by scanning or directly with a digital camera) needs some form of sharpening. There are a lot of tools out there that provide different methods of sharpening, and this article compares as many of them as I could find.

How sharp an image appears is a factor of the resolution of the image, contrast and acutance (edge contrast). Sharpening increases the contrast of adjacent areas by making the darker side even darker and the lighter side even lighter. If you sharpen too much you can end up with haloes around the edges (a one or two pixel much lighter border along the edge) or jaggies (previously anti-aliased edges are darkened two much, effectively becoming aliased). A higher resolution image can get away with a stronger sharpening effect because the one-pixel wide halo occupies less physical space on the printed page and is much less noticeable. Consequently, my favorite method is to, as the final step prior to printing, double the resolution of the image and then sharpen it.

Sharpening tools fall into two basic categories: dumb sharpening and smart sharpening. Dumb sharpening applies the sharpening method to the entire image, which means noise and artifacts get sharpened as well, increasing their visibilty. Smart sharpening attempts to limit the sharpening method to the edges, limiting the increase in visible noise. Of course you can turn a dumb tool into a smart tool by selecting the edges yourself before applying sharpening

In comparing the tools, I looked for how "smart" they were and at what point they introduced unacceptable haloes and/or jaggies. I examined them all first on screen only and then made the final comparison of the best three via prints.

I used the following three source images which were shot with no in-camera shaprening. They were initially processed with Neat Image (with no sharpening applied) to reduce overall noise - my usual workflow. Click on the thumbnail for the original images so that you can conduct your own tests if you wish.

Camera: Olympus C-3000 Quality: HQ ISO: 100 Shutter: 1/160 F-Stop: 2.8 Not a lot of obvious edges here, so this one will be tricky.	Camera: Minolta DiMage 7i Quality: fine ISO: 100 Shutter: 1/125 F-Stop: 8 Man-made structures provide nice obvious edges, so this one should sharpen easily.	Camera: Minolta DiMage 7i Quality: fine ISO: 100 Shutter: 1/125 F-Stop: 3.5 This image was a little soft due to camera shake. The challenge here is to try and rescue it.

Due to disk space constraints I can only show a 400x400 sample patch from each image. Rolling over a sample will show the original unsharpened image. The images are saved as PNGs to prevent introducing new JPEG artifacts.

I tested the following 10 products:

• Photoshop Unsharp Mask
• The Imaging Factory Unsharp Masking Pro
• ABSoft Neat Image
• nik SharpenerPro
• PowerRetouche Sharpness Editor
• JB's Smart Sharpeners (Action)
• D100 Sharpening(Action)
• Fred Miranda Intellisharpen (Action)
• Media Chance DCE AutoEnhance
• Digital Domain Inc. Qimage Pro