Adobe Photoshop CS5 for Photographers - Martin Evening [294]
Print sharpening
Earlier in Chapter 4, I outlined how you can use the Detail panel sharpening sliders in Camera Raw to capture sharpen different types of images. This pre-sharpening step is something that all images require. The goal in each case is to prepare an image according to its image content so that it ends up in what can be considered an optimized sharpened state: the aim is to essentially sharpen each photograph just enough to compensate for the loss of sharpness that is a natural consequence of the capture process.
Output sharpening is a completely different matter. Any time you output a photograph and prepare it for print – either in a magazine, on a billboard, or when you send it to an inkjet printer – it will always require some additional sharpening beforehand. Some output processes may incorporate automatic output sharpening, but most don't, so it is therefore essential to always include an output sharpening step just before you make any kind of print output. The question next is how much should you sharpen? While the capture sharpening step is tailored to the individual characteristics of each image, the output sharpening approach is slightly different. It is a standard process and one that is dictated by the following factors, namely: the output process (i.e. whether it is being printed on an inkjet printer or going through a halftone printing process), the paper type used (whether is glossy or matte) and finally, the output resolution.
Judge the print, not the display
It is difficult, if not impossible to judge just how much to sharpen for print output by looking at the image on a display. Even if you reduce the viewing size to 50% or 25%, what you see on the display bears little or no resemblance to how the final print will look. The ideal print output sharpening can be calculated on the basis that at a normal viewing distance, the human eye resolves detail to around 1/100th of an inch. So if the image you are editing is going to be printed from a file that has a resolution of 300 pixels per inch, the edges in the image will need a 3 pixel Radius if they are to register as being sharp in print. When an image is viewed on a computer display at 100%, this kind of sharpening will look far too sharp, if not down right ugly (partly because you are viewing the image much closer up than it will actually be seen in print), but the actual physical print should appear nice and sharp once it has been printed from the ‘output sharpened’ version of the image. So, based on the above formula, images printed at lower resolutions require a smaller pixel radius sharpening and those printed at higher resolutions require a higher pixel radius sharpening. Now, different print processes and media types also require slight modifications to the above rule, but essentially, output sharpening can be distilled down to a set formula for each print process/ resolution/media type. This was the basis for the research that was carried out by the late Bruce Fraser and Jeff Schewe when they devised the sharpening routines used for Photokit Sharpener (see sidebar) and also elaborated upon in Real World Image Sharpening with Adobe Photoshop, Camera Raw, and Lightroom (2nd Edition), also by Bruce Fraser and Jeff Schewe (ISBN: 978-0321637550).
Photokit Sharpener
A demo version of Photokit Sharpener is available on the DVD and there is also a special discount coupon available at the back of this book which entitles you to a 10% discount. Photokit Sharpener provides Photoshop sharpening routines for capture sharpening, creative sharpening and output sharpening (inkjet, continuous tone, halftone and multimedia/Web). The Camera Raw sharpening sliders