High-Definition television (HDTV) refers to the broadcasting of television signals with a higher resolution than traditional formats (NTSC, SECAM, PAL) allow. Except for early analog formats in Europe and Japan, HDTV is broadcast digitally, and therefore its introduction sometimes coincides with the introduction of digital television (DTV): this technology was first introduced in the USA during the 1990s, by the Digital HDTV Grand Alliance.

HDTV is defined as 1080 active interlaced lines, or 720 progressive lines. 16 : 9 aspect ratio in ITU-R BT.709. The term "high-definition" can refer to the resolution specifications themselves, or to media capable of similar sharpness such as movie film.

PAL, short for phase-alternating line, phase alternation by line or phase alternation line, is a colour encoding system used in broadcast television systems in large parts of the world. Other common analogue television systems are SECAM and NTSC. PAL was developed by Walter Bruch at Telefunken in Germany, and the format was first introduced in 1967.

The term "PAL" is often used informally to refer to a 625-line/50 Hz (principally European) television system, and to differentiate from a 525-line/60 Hz (principally North American/Central American/Japanese) "NTSC" system. There are two more variants of PAL based on the sound system. They are PAL-M(525-line/60Hz) and PAL-N(625-line/50Hz).PAL-N is more like PAL and PAL-M is like PAL's Number of lines with NTSC's Frame rate. Accordingly, DVDs are labelled as either "PAL" or "NTSC" (referring informally to the line count and frame rate) even though technically neither of them have encoded PAL or NTSC composite colour.

NTSC is the analog television system in use in Canada, Japan, South Korea, the United States, and some other places, mostly in the Americas (see map). It is named for the National Television System(s) Committee, the industry-wide standardization body that created it.

The NTSC format - or more correctly the M format - consists of 29.97 interlaced frames of video per second. Each frame consists of 484 lines out of a total of 525 (the rest are used for sync, vertical retrace, and other data such as captioning). The NTSC system interlaces its scanlines, drawing odd-numbered scanlines in odd-numbered fields and even-numbered scanlines in even-numbered fields, yielding a nearly flicker-free image at its approximately 59.94 hertz (nominally 60 Hz/1.001) refresh frequency.

Video resolution has the same parameters like image resolution (lines and columns, or number of pixel, image ratio) and extends them with temporal aspects (image frequency).

The image frequency is measured in Hertz, one has to recognize the difference between the frequency of fields (half a picture) or frames (full picture, progressive). The first generally occurs in interlaced transmissions.