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Devices such as monitors, tuners, and integrated 
monitor/tuner combinations designed to handle any of 
the 18 formats officially sanctioned by the industry-led 
standard setting, Advanced Television Systems 
Committee (ATSC), for the digital transmission of video 
signals. There are three subgroups of digital televisions 
depending on their capabilities: high-definition 
(HDTV), enhanced-definition (EDTV), and standard-
definition (SDTV). 

In contrast, US analog television has been available 
for over 50 years in the single National Television 
Standards Committee (NTSC) format. This is the signal 
that has been broadcast over the air and through 
cable systems. NTSC television offers slightly more 
than 480 interlaced lines of resolution.

There are 18 standard digital TV signal formats. Each 
one provides a different picture quality. Digital TV 
formats are named using a number followed by either 
progressive (p) or interlaced (i). The letter refers to the 
way the TV uses the signals to create the picture: 

■

Progressive (p) scanning presents all the 
horizontal lines of the picture in one frame. This 
provides a sharper picture to the eye and looks 
much better than an interlaced image of the same 
resolution.

■

Interlaced (i) means that the picture appears in 
two segments: every other horizontal line of the 
picture is displayed in one frame, and the other 
half of the horizontal lines are drawn in the next 
frame of the picture. This works because it 
happens so fast that the eye is deceived into 
believing that only one picture is being shown. 

The number refers to the number of lines of resolution, 
and generally the higher the number, the better the 
picture. For example, with digital TV (DTV) there are 
two progressive formats for broadcasters to choose 
from: 480p and 720p. A 480p image is much sharper 
than a regular TV broadcast, although it is only 
considered a DTV signal and not a true high-definition 
signal. 720p has 720 horizontal scan lines and is 
considered to be true HDTV. 720p can rival a 1080i 
picture, which is 1080 horizontal scan lines displayed 
as an interlaced image. This is because of the sharper 
and more accurate (progressive) 720p picture, even 
though 1080i picture has many more scan lines and a 
much higher resolution.

The aspect ratio describes the relationship of screen 
width to screen height. Standard TV signals are based 
on the aspect ratio of 4:3 (four units wide by three 
units high). HDTV signals are based on the aspect ratio 
of 16:9, making the image 33 percent wider than a 
normal TV and allowing viewing TV and movies as if 
you were watching them in a theater. 

In addition, many DVDs look better on the widescreen 
display because most movies made in the last 50 years 
were filmed in an aspect ratio of either 1.85:1 (very 
close to 16:9, which is equal to 1.78:1) or 2.35:1 
(even wider than 16:9). 

Variable aspect ratio support enables scaling of 4:3 
and anamorphic video to fill the screen.

High-Definition Multimedia Interface (HDMI) is the first 
industry-supported, uncompressed, all-digital audio/
video interface. HDMI components can transmit both 
digital audio and video over a single cable with 
improved quality over traditional analog connections 
due to an all-digital transmission. Transferring digital 
sources to display such as DVDs and HDTV 
programming can now be done without analog 
conversions that can degrade the original signal.