High Definition TV

HDTV stands for High Definition Television. HDTV images contain significantly more detail than normal television and have several differences. First let us get some terminology out of the way, before we review various HDTV related gadgets.

Pixels: The smallest element of a TV picture or a monitors display is called a pixel. Each of these pixels comprises of a red, blue and green element. Pixels in an HDTV set are usually square, smaller and placed closer together than on a regular TV screen. This results in a 4 to 6 time higher visual detail.

Line: A row of pixels is called a line.
A standard NTSC television displays 480 lines with 720 pixels on every line (resulting in 345,600 pixels being used). A HDTV display can show upto 1024 lines with 1920 pixels being used in each line resulting in 2,073,600 pixels being used.

Aspect Ratio: This is the ratio of the width of the screen v/s the height of the screen. Like widescreen cinema displays the HDTV aspect ratio is 16:9. Normal TV ratio is 4:3. The images attached show the difference between 16:9 and 4:3 displays.
16:9 Image Ratio
4:3 Image Ratio

In addition to the increase in number of lines, there is also a difference in how HDTVs display the individual lines -- this is called "scan or scanning mode".
Interlaced Scanning: In this mode, which is designated by the letter "i" ( 480i for example ) every alternate line is redrawn at a rate of once every 60th of a second, allowing a whole frame to be redrawn in a 30th of a second.
Progressive Scanning: In this mode, which is designated by the letter "p" ( 480p for example ) every line is redrawn once every 60th of a second, implying that a frame is redrawn in a 60th of a second.
By specification, HDTVs are supposed to be able to handle SDTV signals.