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Tuesday, February 28, 2012

Output Sharpening

Automate the process for best results

This Article Features Photo Zoom

Image source, frequency of detail, subject, personal preference, output device, substrate or presentation device, and presentation size all play a role in sharpening. The art of sharpening gives you precise control over various image characteristics—contrast, saturation, contour (halo and line), texture and noise. It's best applied in three stages: capture, creative and output.

While there's an art to sharpening, which provides extraordinary creative freedoms, some aspects of sharpening are best automated, such as output sharpening.

2) After output sharpening

Output sharpening is used to compensate for the softening of detail that a specific device produces. Ink on paper, whether applied with an offset press or an inkjet printer, is notably susceptible to this. When drops of ink hit paper, they deform on impact and spread more or less based on the absorption characteristics of the substrate. This is called dot gain; the dots gain size. Dot gain varies with the type of printer, ink and substrate used. It also can be impacted by environmental factors such as humidity. Output sharpening typically also factors in file resolution and the scale of the final product, which is used to determine an ideal viewing distance—though the actual viewing distance is usually variable.

Output sharpening primarily benefits printed images. Projected images also can benefit somewhat. Images displayed on monitors rarely need to be sharpened for output, as they've already been sharpened based on the display device, during capture and creative sharpening.

There's always a mismatch between the quality of image detail when displayed on a monitor and when printed. Comparatively low-resolution monitors can't precisely preview what a print will look like on a high-resolution output device, much less precisely preview detail on many different output devices, with varying resolutions or on a variety of substrates with varying amounts of dot gain. So, the image on screen only can approximate, but not precisely display, the sharpness of the printed piece. (In the future, we expect algorithms to be devised to simulate this on screen.) In the end, you make the image on screen look too sharp, knowing it will soften when printed. How sharp do you make it? It depends on your printed proofs. You have to test various sharpening settings, make test prints and compare the results to determine optimum sharpening routines for a given printer and substrate combination. In addition, you should factor in the scale of the final printed piece.

Once determined, the settings used to achieve optimum results in a representative image or selection of images then can be used for all images printed with the same output conditions. You can write an Action to perform an optimum sharpening routine repeatedly. In short, after some initial testing, output sharpening can be automated.

What sharpening routine do I recommend for output sharpening? I employ a hybrid routine. I combine Unsharp Mask and High Pass sharpening methods.