Chapter 2. Why Do We Sharpen?

And What Must We Take Into Account When We Do So?

Whenever we turn photons into pixels, we lose some sharpness, because no matter how high the resolution of our capture devices, they sample a fixed grid of pixels, and so they turn the continuous gradations of tone and color that exist in the real world into discrete pixels. When the pixels are small enough, they provide the illusion of continuous tone, but it is an illusion, and sharpening is one of the things we simply have to do to make the illusion convincing.

The reason that sharpening is such a complex topic (and the reason for this book) is that successful sharpening has to take into account several potentially competing factors. In this chapter, I'll discuss these factors in detail, but they fall into three basic categories:

• The image source

• The image content

• The image use

For decades, the standard operating procedure has been to punt on the question, and try to handle all sharpening in one single pass just before output. With film scans, this worked after a fashion, though I suspect the results were rarely optimal. With most digital captures, the results are even less likely to be optimal simply due to the way most digital cameras work.