AfterDawn: Glossary

NTSC is a color TV standard developed in the U.S. in 1953 by the National Television System Committee. NTSC uses a Frame consisting of 486 horizontal lines in the Active Area and a Framerate of 29.97fps. The frame is interlaced, meaning it's composed of two individual fields (pictures) with a Fieldrate of 59.94fps.

The term NTSC may also be used to describe any video, including digital video, formatted for playback on a NTSC TV. This generally includes any Standard Definition (SD) video with a vertical Resolution of up to 480 Pixels and a horizontal Resolution no greater than 720, which also has a Framerate of 29.97fps. NTSC is sometimes referred to as 525/60, in reference to the total number of lines (including lines not in the Active Area) and approximate Fieldrate. Digital formats include only 480 of NTSC's 486 visible Scanlines due to the need to guarantee mod16 Resolution, meaning its divisible evenly by 16.

Geography
NTSC is used in United States, Canada, Japan, in most of the American continent countries and in various Asian countries. NTSC content can also be viewed on the majority of PAL TVs sold in recent years are also capable of displaying NTSC video, generally in a format known as PAL 60. This involves resizing the image to fill the larger number of Scanlines on a PAL TV (625 - 576 visible) and converting the color encoding to the YUV standard used by PAL TVs. The framerate remains at 29.97fps.

Framerate
NTSC's Framerate has been the source of much confusion over the years. It was chosen in order to ensure backwards compatibility with older black and white televisions already in widespread use when the NTSC standard was developed. In order to add the additional color information, the framerate had to be slowed very slightly from the then standard of 30fps. In order to avoid major changes it was slowed by a factor of 1.001, resulting in an actual framerate of 29.97002997002997002997002997003 - an infinitely repeating decimal. While it's common practice to use the (rounded) shorthand of 29.97fps, sometimes it's important to know the correct formula. For example, in order to convert film's 24fps framerate to NTSC's 29.97, the film must first be slowed down the same amount, resulting in another infinitely repeating decimal - 23.976023976023976023976023976024 (24 / 1.001), which rounds nicely to 23.976fps.

Capture Resolution
According to the ITU-R BT.601 (Rec.601) standard for capturing analog video, the correct resolution is 720x480, with the Active Area (the area containing the actual picture) represented by the center 711 horizontal Pixels. Some Capture cards will use 720 Pixels for the Active Area instead. The two lines below show the slight difference between using the full 720 Pixels versus only using the center 711.


Standard Digital NTSC Formats
Various consumer digital video formats have standards designed to work with NTSC TVs. These include VCD, SVCD, DVD, and DV. Below is a table showing the standard Resolutions for each format. In the case of DV, the Full Frame represents the Active Area of the Frame, meaning you may need to resize and add borders to the sides when converting to other formats like MPEG-2 for DVD. DVD players may also implement the digital to analog conversion improperly, resulting in the Full Frame being squeezed into the analog video's Active Area.

Format	NTSC Resolution
DVD	720x480
	704x480
	352x480
	352x240
DV	720x480
SVCD	480x480
VCD	352x240

Minimum Horizontal Capture Resolution
Since actual analog PAL video always contains 480 lines, it's best to always capture to a frame with a vertical resolution of 480. If you don't necessarily care about capturing to the Rec.601 frame size you should at least make sure you're capturing at more than twice the Bandwidth (range of frequencies) of the analog source. The table below gives the bandwidth for some common analog NTSC video sources, along with the minimum number of horizontal samples required to meet the Nyquist-Shannon sampling requirements and the lowest DVD-Video resolution that meets this requirement.

Format	Bandwidth	Min Horiz Samples	Minimum DVD Capture Size
NTSC	4.8MHz	507	704x480
VHS	3MHz	317	352x480
S-VHS	5MHz	527	704x480
Video8	3.3MHz	349	352x480
Hi 8	5.5MHz	581	704x480
Laserdisc	5.8MHz	611	704x480

Related Guides
Digital Video Fundamentals - Resolution and Aspect Ratio