When attempting to image complex subsurfaces with Kirchhoff methods, many difficulties may arise. In particular, amplitude behavior of the imaged reflectors can be caused by totally different physical phenomenon. A reflector that appears to fade and disappear along some distance can have several causes, including a real change in reflectivity, an error in the velocity model, or an illumination problem. All of these provide valuable information, but it is important to know which one is causing the effect. By estimating the resolution of the data it is possible to identify areas of low illumination.