About SD, ED and HDTV

The consumer electrnoics has done a good job spreading mass confusion about video formats. There was a time when there was just a TV, then came NTSC and PAL. Americans dont know anything about PAL but some non-americans do know about NTSC. People like me who have migrated to US from some other country, have to deal with both of the formats.If that was not confusing enough, now there is SDTV, EDTV, HDTV, 480i, 480p, 720p, 1080i and some are hearing about 1080p also.

Well, let me stick with NTSC signals here because thats what I have to use 90% of the times.

TVs basically show still images, changing so fast that they look like video (or movies). In NTSC format this is done 30 times in a second or what is called 30 frames per second (30 fps). So they had 1/30 of a second to show a frame. This picture or frame consisted of 480 horizontal lines.

Old fashioned TVs could not handle this information so fast. So they used to divide this picture of 480 lines into odd and even number lines. So to show one single frame they had to do two attempts. Dividing the time alloted to show a frame by 2. In the first half or 1/60 of a second they show the odd number lines (1, 3, …439) and in the next 1/60 of a second they should the even numbered lines (2,4, …480). This scheme is called interlacing giving the name 480 interlaced or 480i or Standard Defintion TV (SDTV).

This worked fine for a while till bigger screens like 60″ started coming in. With them the interlacing scheme showed jagged lines because if an object moved between showing odd and even numbered lines, the borders of the object were jitterred.

Then came the progressive scan or the ability to show the full frame in 1/30 of a second. No need for interlacing. New chips and processors can handle this and much more. This is whats called 480p or 480 lines, progressive scan also called EDTV or enhanced defintion TV. The resolution for these two types was 640×480. (Ratio 4:3)

Then the two wide screen formats came in 1280×720 and 1920×1080. The aspect ratio changed to 16:9. But 1080 signal is still coming as interlaced called 1080i. People thought a progressive signal is better than interlaced, even with less information so cameup with 720 lines of progressive signal called 720p. Both of these are called high defintion or HDTV signals. Both have advantages and disadvantages. 1080i has more information but interlaced, 720p has less information but is progressive.

What will be the next thing?? 1080p. A signal with 1080 horizontal lines with progressive scan.