是因為電視系統有美規(NTSC)歐規(PAL和SECAM)之分別
台灣跟著美國走，所以用的是NTSC
NTSC - National Television System Committee

The first colour TV broadcast system was implemented in the United States in 1953. This was based on the NTSC - National Television System Committee standard. NTSC is used by many countries on the American continent as well as many Asian countries including Japan.

PAL - Phase Alternating Line
The PAL - Phase Alternating Line standard was introduced in the early 1960's and implemented in most European countries except for France.
The PAL standard utilises a wider channel bandwidth than NTSC which allows for better picture quality.


SECAM - Sequential Couleur Avec Memoire
The SECAM - Sequential Couleur Avec Memoire or Sequential Colour with Memory standard was introduced in the early 1960's and implemented in France. SECAM uses the same bandwidth as PAL but transmits the colour information sequentially.