Digital sharpening tools offer much more precision, control, and wealth of options than the analog darkroom ever did. The inevitable downside is that with greater control comes greater responsibility, and the more options on offer, the more opportunities for mistakes, as we'll demonstrate throughout this book.
But in the switch from optical to digital reproduction (and eventually to digital capture) it quickly became clear that whenever we turn photons into pixels, and pixels into marks on paper, we need to sharpen the image, otherwise it will appear unacceptably soft. There are simply no exceptions to this rule. The questions, to which the rest of this book is devoted to providing answers, are when to sharpen, what techniques to use, and how much sharpening to apply.
However, there's one key difference between digital and analog sharpening with which we have to contend in varying degrees, and that's the handling of noise. Analog sharpening rarely increased noise, and often had the effect of reducing it, because the mask was made from a different piece of film than the original, and hence the distribution of the film grainthe main noise component in film imageswas different. This had the desirable effect of making the noise in the mask cancel out the noise in the original. With digital sharpening, we aren't so lucky.