In addition to detail, images contain noisedigital captures have camera noise, film scans have film grain that may be exacerbated by scanner noise. We only want to sharpen the detail, not the noise.
We have various tricks for sharpening detail without making the noise worse. And Photoshop CS2 introduces a new Reduce Noise filter that's quite effective, particularly with noise from digital captures. However, as with all noise reduction solutions, Photoshop's Reduce Noise filter also compromises detail. When we try to improve images, we always have to walk the fine line between increasing edge detail and decreasing noise.
We generally use noise reduction in Photoshop only on very noisy imagesscans of color negatives and digital captures at ISO 800 and up are prime candidates. (We do, however, make full use of Camera Raw's noise reduction features when working with digital raw captures.) Otherwise, we prefer to concentrate on sharpening the available detail while protecting the noisy areas, partly because we don't want to soften the image unnecessarily with noise reduction, partly to avoid another step in the workflow.
When we do perform noise reductioneither Photoshop CS2's Reduce Noise filter or a third-party plug-in such as Noise Ninja, Grain Surgery, or Neat Imagewe always do so before sharpening, for the simple reason that it works better than doing so afterwards. We'll cover noise reduction further later in this chapter.