One of the most powerful features in any post production graphic application is curves adjustment. Curves is a non linear tool that enabled users to control the exposure of specific levels of an image without affecting others. This is accomplished by using control points (red dots) that are automatically created when a user select any point on the grid. Once created they can move these point left, right, up or down depending on how you want to adjust the image. Once the desired results are achieve the user simply selects the apply button.
Although 255 points can be created usually no more than 10 points are ever required. When the results are wrong and the user wants to start again, the "Reset" button can be selected, which deletes all the controls points. Since it is common to apply the same corrections to multiple photos, users can save their settings and reload them by selecting them from the drop down list.
In the example below we show how a slight S Curve can be achieved to increase the brightness of the highlights and reduce the brightness of the shadows by using 3 control points.