Adobe® Photoshop® CS2 Studio Techniques

The Histogram Gives You Feedback

Once you have applied an adjustment to your image, you can see an updated histogram by choosing Image > Adjustments > Levels again. You should notice that after adjusting the upper-right and upper-left sliders, the histogram will stretch all the way across the area available. It's just like stretching out a Slinky…you remember, “It walks down stairs, alone or in pairs” (Figure 5.19). As you pull on the ends of the Slinky, the loops stretch out and start to create gaps. The same thing happens to a histogram—because Photoshop can't add more bars to the histogram, it can only spread out the ones that were already there. And remember, gaps in the histogram mean that certain shades of gray are missing from the image. ...