The simplest algorithm of scan conversion can do something like this
- Display the boundary of the solid object
- For each pixel on the screen, try to find out whether it lies inside the boundary or on the boundary or outside it. Suitably arrange the mask of each.
Though this method is simple and reliable, it needs enormous amounts of computations to achieve the purpose. Obviously more efficient methods for scan conversion are needed. One may note that the trade off involved is not just the time involved, but such inordinate delays avoid a proper, real time modifications and display of the picture. Hence, several algorithms have been devised so that certain inherent properties of the pictures are utilized to reduce the computations. One such broad technique is to consider figures as closed polygons and use certain properties of polygons to find out which pixels should lie inside the picture and which are not one such property is coherence.