After resolution and color, sharpening can have the most impact on perceived image quality. Most digital cameras deliver slightly soft images (unless the capture format is set to JPEG or TIFF with in-camera sharpening turned up). This results from the almost universal use of anti-aliasing filters to combat moiré patterns. Scanning camera backs and some medium-format backs — especially those able to work in multi-shot mode — may not have this feature. If we assume single-shot RAW file capture, it is entirely appropriate to request a small amount of default “capture” sharpening. Without it, digital image files may look too soft.
Stock image distributors often request “unsharpened” digital files. It might be better to request no sharpening beyond capture sharpening, since online catalog images need to look reasonably sharp. Most RAW processing software applies a certain amount of sharpening as a default, although you can usually adjust this or turn it off. Some photographers, worried there will be no output sharpening, increase this somewhat when processing RAW files. Providing education to clients about how best to sharpen images from their collection should be something that every stock distributor provides. After all, digital images will only look their best when sharpened for the type of output at the final size of that output.
Magazine publishers usually specify unsharpened files, as well. But a small amount of capture sharpening will do no harm, while neglecting to sharpen will definitely affect printed quality.
Publication designers and web designers vary in their understanding of sharpening. One possible strategy is to deliver layered .TIFF or .PSD files at or near final size, with sharpening applied to a duplicate layer, and a ReadMe file or delivery memo explaining the layer. It is a good practice, in such a case, to name the layer “sharpening.” Fuzzy pictures on the web often result from extreme down-sampling of large camera files. One strategy is to deliver smaller files to web designers, typically in the 1024- to 768-pixel range for height or width, and apply a degree of sharpening that looks right at that size. Better web designers will request no sharpening beyond capture (or RAW conversion), but will indicate they plan to sharpen appropriately as they resize.
Sharpening is a very complex topic. For a more complete discussion, see Bruce Fraser’s Real World Image Sharpening, Peachpit Press, 2006.