Analog to Digital TV: How to “Get” HDTV

Analog to Digital TV: How to “Get” HDTV
What are you really looking at when you gaze at a color TV screen or a newspaper photo? On a TV screen or in a newspaper or a magazine picture, or even the computer monitor screen on which you read this text, the images are formed by groups of red, green and blue dots or “pixels” (short for picture elements). In the case of a conventional television display, the groups of dots glow in varying degrees of brightness and hues, triggered by electrical pulses from the TV set's electronics. These pulses perfectly track the signals broadcast by the television station or cable system that routes the TV signals into your home.

If we sit far enough away from the TV screen, the individual clusters of colored dots blend together to form a smooth and coherent color picture that changes 30 times every second. Our eyes and brain blend the rapidly changing still images into continuous and smooth action, through a process called “persistence of vision.”

Lines and Lines The 60-year-old analog TV system all of us grew up watching is based on 525 horizontal scanning lines, although only 480 lines are actually used to scan the picture from top to bottom across the TV screen every 1/30 of a second. A single frame of TV is composed of two “fields” of 240 lines each, presented every 1/60 of a second, which are “ interlaced ” or interwoven to form a full picture every 1/30 second. This happens so quickly that our eyes blend the 60 still fields together into 30 frames (each frame is a still picture) and we see only continuous motion.

Definition: Standard and High Because the image is composed of 480 interlaced lines, the system is called 480i, and is known as standard definition in the world of digital TV. A DVD image represents standard definition. The number of scanning lines determines the amount of detail in the image (vertical detail, because the horizontal lines are stacked from the top to the bottom of the screen). Understanding this process will help you understand the differences in clarity or resolution (sharpness) between regular analog TV and digital TV, including High Definition TV (HDTV). Incidentally, just because a new TV is “digital” does NOT mean it is HDTV. Although all HDTV pictures are digital, not all digital TV is high-definition, because the North American Digital TV standard, established in 1995 by the Advanced Television Systems Committee (ATSC), enables 18 different formats and various levels of clarity— Standard Definition , Enhanced Definition (EDTV), and High Definition (HDTV).

If you get a digital TV, a DVD's 480-line image can also be progressively scanned, one line after the other in sequence, rather than interlaced. This is called 480p, and represents Enhanced Definition (EDTV). A 480p TV image has a smoother, more film-like look, especially when it's viewed on a larger screen, but a digital TV set is usually required to display progressive-scan (480p) pictures (most analog sets will not, except for a few equipped with component-video inputs that are designed to handle progressive-scan signals.) Almost all newer DVD players on the market, even inexpensive ones, will output both interlaced and progressive-scan signals, so if you are getting a new DVD player, make sure it has progressive-scan outputs as well as interlaced (you must switch your DVD player to the interlaced output to see a DVD picture on your old analog set.)