Better Sharpening for Digital Images

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Mallard Ducks Photo, RL Deconvolution Sharpening. ⇑

Digital photographers who migrate from film often complain about the lack of sharpness in digital images when compared to film. The truth is that digital sensors can produce very sharp images. However, that sharpness is compromised slightly by the use of anti-alias filters in most digital cameras. All DSLR cameras have an anti-alias filter (with the exception of medium format digital cameras and backs). This filter adds a slight blur to images, to minimize the stair-step effect seen on diagonals, and the moire effect on that sometimes appear on fine lines in digital photos. That is why all digital images need to be resharpened in camera or using software.

The typical method used to sharpen digital images is Unsharp Masking. Unsharp Masking enhances edge contrast to create the illusion of sharpness. However, there are other methods of sharpening digital images that can produce better results. I have been experimenting with another form of sharpening that is quite unlike Unsharp Mask. Rather than enhancing edge contrast (which creates a slight halo on edges in the image), RL Deconvolution is designed to undo the slight blurring that anti-alias filters add to a digital image. In effect, it reverse engineers the blurring added to images by anti-alias filters. The result is a more natural looking sharpness in digital images. Deconvolution is a sharpening technique used by by the Hubble telescope (and spy telescopes) to extract the greatest amount of detail from deep space images.

There are several programs on the market that offer Raw image deconvolution sharpening, including Photoshop CS2 (Smart Sharpen filter), DxO, and a few others as well. However, there is an excellent free raw conversion and editing program that implements RL Deconvolution sharpening; Raw Therapee. Raw Therapee offers users the choice of standard Unsharp Masking or RL Deconvolution. You may come to the same conclusion I have: In most cases, RL Deconvolution produces greater image detail and sharpness while avoiding the artifacts and halos caused by Unsharp Masking. I find that RL Deconvolution controls in Raw Therapee gives my digital images a more natural sharpness that reminds me of a good film image. It extracts details that could only be seen with extreme levels of Unsharp Masking that would leave an image looking oversharpened. For viewing images online, it produces much smaller file sizes than a similarly Unsharp Mask sharpened image (that means faster loading web pages). And, did I mention how natural the sharpened image looks?

Raw Therapee is a great tool for the finicky photographer who likes to extract every last ounce of quality from his digital images. In fact, I consider the results it produces equal to the best (and most expensive) RAW image editors on the market. The RL Deconvolution sharpening tool is a wonderful option that may work wonders on your digital images. If you are willing to master this program it can produce amazing results. You will need to read the manual to get the best from this program.

The image shown above ( Mallard Ducks) was captured with a Nikon D40 and Nikon 55-200mm VR lens at 400 ISO. The raw image was converted using Raw Therapee and sharpened using RL Deconvolution.