If you own a 30-bit or higher scanner and your scanning software contains a histogram and has the same adjustment controls available, you can make adjustments within your scanning software. Most scanners can deliver a histogram without gaps because they can look back to the image and pick up extra shades of gray that would fill the gaps. These days, almost all scanners are 30-bit or higher. If your scanner is capable of delivering a 16-bit grayscale image to Photoshop, then the only adjustment you need to make during scanning is to make sure the highlights and shadows still have detail. If the histogram in your scanner has spikes at the ends, then lower the contrast setting and rescan until you don't get the spikes.
Anytime you adjust an image, you run the risk of introducing some artifacts that might not be all that pleasant. So let's take a look at what can happen to your image after applying Levels. But don't worry—remember, in Photoshop there is usually at least one “fix” for every artifact.
