Also known as Standard Definition Television according to AbbreviationFinder, SDTV is the acronym for receiving signals from television that can not be considered high – definition signals (HDTV) signal or enhanced definition television (EDTV).
What is known historically as SDTV was born with broadcasts in PAL, SECAM or NTSC (depending on the format used in each country) and dates back to the early 1960s, when the first color broadcasts were made in these formats.
Since its inception, analog TV has not undergone any variation in resolution or performance, except for the appearance of teletext, first broadcast by the BBC in 1972. Despite the fact that the standard has remained unchanged in the last 40 years, the improvement in the quality of electronic devices, both transmitters and receivers, has allowed current televisions to show the signal with a higher quality than that of the first electronic devices. color.
As regards Spain, the first color broadcasts on RTVE were made in 1973 in PAL format and it has also maintained the standard until today.
Later, and due to similarities in image quality, other systems that are not technically SDTV have also been classified as SDTV quality. This is the case of the analog video storage formats VHS and Betta and the digital MPEG-1.
In recent years, the acronym SDTV has been widely used, especially among manufacturers of television sets and multimedia in general, to emphasize the superiority of HDTV and encourage consumers to replace their devices and thus enjoy images of more quality.
Comparison between SDTV and HDTV (Left half is PAL, 575i, while right half is HDTV 1080i)
It is the dominant video resolution from the origin of television to the advent of high definition. The system is around a resolution of 500 horizontal lines. PAL works with a resolution of 720 × 576, while NTSC provides 720 × 486. It uses a speed between 25 to 29.97 frames per second in NTSC, and 25 for PAL format.
Until the appearance of digital systems, SDTV only had one meaning, but currently it is used to refer to two systems of digital coding and sending of video signals: On the one hand, SDTV is used to call 480-line analog signals (NTSC) or 576 (PAL and SECAM) and which have been the majority standards for the last 50 years. Its aspect ratio is always 4: 3, while the scan is interlaced.
On the other hand, SDTV is also used generically to refer to television signals, analog or digital, which have a quality equivalent to analog SDTV. So of the formats like VCD, VHS, Beta or SVCD with qualities similar to analog television, they are also often said to have an SDTV quality. In this case, the scan can be progressive in low resolution systems or interlaced if it reaches 480 or 576 lines. The aspect ratio is usually 4: 3 although it can also be 16: 9.
Due to the use of the acronym SDTV to refer to all types of systems that are not HDTV, it is common to confuse the terms and classify EDTV systems such as DVD in the group of SDTV.
The resolution of the SDTV moves between the 480 horizontal lines of the NTSC system and the 576 of PAL and SECAM, leaving the aspect ratio always in 4: 3. Other formats like MPEG-1 have similar capabilities; only 288 lines, but progressive scan make it look quite similar to PAL or NTSC quality.
The temporal resolution is always 50 images (60 in NTSC) interlaced per second.
These features were initially considered adequate due to the measurements of the first television sets, since they rarely exceeded 20 inches of screen diagonal. However, the limitations of SDTV are becoming more and more evident in modern devices, often with screen diagonals of more than 30 inches and electronics of much higher quality than those of the first reproducers.
The future of SDTV
Since the appearance of DVD in 1995, SDTV has been progressively replaced by EDTV, the former being relegated only to analog broadcasts, since systems such as digital terrestrial television or satellite broadcasts already broadcast on EDTV and it is to be expected that in a few years they will start broadcasting on HDTV.
However, the number of devices that only support SDTV is still very high and the replacement by EDTV or HDTV televisions will be quite slow, so that despite the fact that since 2009 analog broadcasts have disappeared in Spain and that the rest of the systems broadcast will be EDTV or HDTV, both satellite and DTT receivers as well as BRD and HDDVD players will continue to be compatible with SDTV devices, lowering the resolution of the signal and sending it to the device in interlaced fields in order to allow it to be viewed on older devices.