One of the prerequisites for many of the applications mentioned below is a method of selecting part(s) of an image, thus applying a change selectively without affecting the entire picture. Most graphics programs have several means of accomplishing this, such as: # a marquee tool for selecting rectangular or other regular polygon-shaped regions, # a lasso tool for freehand selection of a region, # a magic wand tool that selects objects or regions in the image defined by proximity of color or luminance, # vector-based pen tools, as well as more advanced facilities such as edge detection, masking, alpha compositing, and color and channel-based extraction. The border of a selected area in an image is often animated with the marching ants effect to help the user to distinguish the selection border from the image background.