ATSC - The ATSC digital television standard

ATSC

The Advanced Television Systems Committee (ATSC), founded in 1982, is the organization which is responsible for development of broadcast and cable television transmission standards in the United States. Their standards are also adopted by Canada, Mexico, South Korea and Honduras. Other countries are considering adopting ATSC standards as well.


The organization consists of representatives from a number of electronics and television and communications companies. As in other areas of electronics manufacturing, these companies have banded together to develop standards which can be used across the marketplace. Standardization serves everyone’s best interest, especially that of the consumer. Standardization of television signals is necessary to ensure that equipment manufactured is compatible with broadcasts made.


The major work of the ATSC, which they are best known for, is the development of the digital broadcast television standard, now known as HDTV (high-definition television). This took the work done by what is known as the Grand Alliance, at the bequest of the FCC, in combining the best ideas for digital television and turning them into one comprehensive specification.


There are many ATSC specifications today, dealing with both high-definition and standard definition formats. These specifications deal with the protocols that the equipment used in television broadcast and reception use, creating industry-wide commonality of methodologies.


While there is no requirement for a television equipment manufacturer or broadcaster to be e member of the ATSC, it is widely recognized that the standards developed by the ATSC are those that are considered “industry standard.” Equipment which is not manufactured or programs that are not broadcast to meet these standards will probably have trouble working with the rest of the television industry in the United States.


The ATSC digital television standard provides for a total of 18 different image sizes and formats. All of which are in a “widescreen” aspect ratio. The data is compressed using PEG-2, providing a 50 to 1 data reduction. This compression is accomplished by not retransmitting the areas of the screen which have not changed since the previous frame.


ATSC digital signals can be interlaced or progressive scan. This refers to the means of “painting” the image on the screen. An interlaced format paints all of the odd numbered lines first, and then paints all of the even numbered lines. By doing this, higher resolution is accomplished within the same bandwidth. By contrast, “progressive scan” means that the all of the lines of the image are painted on the screen sequentially. The image formats 1080i and 480i are interlaced formats, while the formats 720p and 480p are progressive scan.


 

While this may seem to be only an esoteric difference, in actuality it makes a huge difference in the image quality. However, there is no clear winner as to which method is better. That depends on the type of image being sent. The same amount of bandwidth is required to send 720p video as is required for 1080i; but the 720p will have twice as many frames per second of video information as the 1080i. Therefore, 720p is better for high action, such as sporting events, whereas 1080i is better for video where high detail is needed, such as documentaries.  

Rich Murphy