Use Curves for greater control when adjusting image tone. Curves are very similar to Levels in that you adjust the Shadows (Black Point), Midtones (Medium Point), and Highlights (White Point), except you do so with a curve to which you can add points to for increased accuracy. You manipulate the Curve by {Clicking}and dragging on a point. You add points to the Curve by {Clicking}and dragging on the Curve where there isn’t a point or by {Single Clicking}on the Curve where there isn’t a point. Controls for Curves include Channel, Input Values Bar and Field, Output Values Bar and Field, Black Point, Mid Point, and White Point Eyedroppers, Auto, the Curve Window and the Curve itself. The Controls common to the Levels adjustment work precisely the same in Curves.

Open the "diana.png" image again and select "Xtras/Adjust Color/Curves." The Curve is in a straight line, at 45 degrees, indicating it has not yet been manipulated. The point at the bottom left of the curve represents the current Black Point while the point at the top right represents the White Point. There is no point in the middle of the Curve by default because you can add points all along the Curve and {Click}and drag them for very accurate and precise control. However,

by {Clicking} the center of the Curve you can add a Midtone Point.

{Click} the center of the Curve to add a Midtone Point. Next {Click}, hold, and drag the Midtone Point up and down the Curve, trying to keep the Curve as straight as possible.  By doing this you are mirroring Levels controls where you {Click} and drag the Point sliders back and forth. The distance between the sliders or Points changes the tone of the image. With Curves, you have increased control because you can add multiple points between the Black, Mid, and White Points. {Click}twice at different locations on the Curve between the Midtone Point and the Black Point to add two more points. Now {Click}and drag these points back and forth and watch what happens to the Diana image. By {Clicking} and dragging the points to add curve to the Curve more drastic tonal changes occur. It takes practice to get used to using Curves but over time you’ll find them a powerful tool for tonal adjustment of your images.