The Levels provide detailed control over the brightness level of a photo. They not only show a histogram of the brightness levels used in the photo, but also provide the ability to lighten shadows without affecting the lighter parts of the picture, to adjust contrast levels, and even to white balance the photo.
The "Brightness Levels" dialog can be opened by clicking the Brightness Levels Dialog button in the Photo Tool flyout. Start by selecting the image you want to correct and opening the Brightness Levels dialog.
Similarly to the Photo Enhance tool, the Clip tool and other tools, changes you make by adjusting the brightness levels are non-destructive and can be easily undone or corrected. All brightness level adjustments are shown as a light red histogram superimposed on top of the original dark red histogram.
The histogram is a graphical representation of the brightness of an image.
Just below the histogram are three triangles which control the black, gray and white brightness ranges. These control the histogram and the brightness levels it displays and can be moved from side to side. To adjust the brightness of the image in real time, simply click and drag the icons from side to side.
Below the histogram are three eye dropper icons for black, gray and white. These are interactive tools that can be dragged onto the image to pick out black, gray or white points of the image to optimize the brightness levels based on the selected color.
The Levels tool includes an auto-enhance button which performs a similar function to the "Enhance" button in the Photo Tool. Auto-enhance changes are reflected in the histogram.