Broadcast can be different from production.

ATSC High-Definition Broadcast Standard

In April 1998 the Federal Communications Commission announced a new digital broadcast standard for the United States. The new standard was developed by the Advanced Television Systems Committee (ATSC) and provided specifications for high-definition television and standard definition digital television (SDTV). SDTV is what you see if you have the mini-satellite dish or digital cable at home. The new system will allow a group of standards that can be received and displayed by all digital TV sets. So if you have an SDTV set, it will receive both SDTV and HDTV and show it all in SDTV. If you have an HDTV set, it will also receive and display all of the digital standards.

The new ATSC system will be a digital system that uses the same amount of bandwidth (6 MHz) as the current NTSC system. The new system supports 18 different digital standards and will have a wide-screen format similar to motion pictures. The format's aspect ratio is 16 units wide by 9 units high, compared to the NTSC's 3 units high by 4 units wide. There will be two HDTV options. One will use 1080 scanning lines of 1920 pixels each. It will have the scanning options of 60 fields/30 frames interlace scanning or 30 or 24 frames of progressive scanning per second. This standard is usually called 1080 i. (Note that a 1080, 60-frame progressive standard is being tested as this is written.) The other option has 720 scanning lines of 1280 pixels per line and has either 60, 30, or 24 frames of progressive scanning per second. This format is usually called 720 p.

We have the different scanning rates because some engineers believe that interlace scanning gives the best pictures, especially for very large screens, but progressive scanning is easier to integrate with computers. The 24 frames per second rate makes it easier to integrate with films which are shot at that rate. In the United States, we are in the process of changing over to this standard now.

Formats for high-definition digital television.