Adjusts the color levels of the image by scaling the colors falling between specified white and black points to full [0, 1] range.

public procedure AdjustColorLevels(BlackPoint: Single; 
                                   WhitePoint: Single; 
                                   MidPoint: Single = 1.0);

The black point specifies the darkest color in the image, white point specifies the lightest color, and mid point is gamma aplied to image. Black and white point must be in range [0, 1].