Differences between PAL, SECAM and HDTV
When color television was invented, various methods for displaying color were technically possible, and different countries made different choices, leading to systems that are still incompatible. In all countries a political requirement was the program transmitted in color had to be received on existing black-and-white television sets. Consequently the simplest scheme, just encoding the earliest color system was regularized in the united state by National Television Standard Committee, which sets the acronym to the standards NTSC.
The Color-television was brought up in Europe some years later on, by which time the technology had improved substantially, leading to system with greater noise immunity and better colors. These systems are called SECAM (Sequential Color with Memory) which is used in France and Eastern Europe and PAL (Phase Alternating Line) used in rest of Europe.
In the past few years, there has been a lot of interest in the HDTV, the High Definition Television. It generates sharper images by nearly doubling the number of scan lines. The USA, Europe and Japan have all developed HDTV system; all are different and mutually incompatible. The basic principles of HDTV in terms of scanning, luminance, chrominance, etc are similar to the existing system. However all three formats have common aspect ratio of 16:9 instead 4:3 to match them better to the format used for movies.