And here we see the great argument begin. This is the trap people fall into with regards to 720p and 1080i.

First and foremost. TV is 30 frames per second. NTSC signals are divided into two interlaced fields: A and B. A and B make up one frame as I had explained.

Progressive scanning is the presentation of a complete picture. Our unregistered guest sort of correctly assumes that if a complete picture was presented on field A and B then math dictates 2 fields to a frame and 30 frames per second then you'd get 60 frames per second. I can see how this happens but he's wrong.

The progressive frame is repeated from field A to B so it counts as one frame since it is the same image. TV stays at 30 fps....not the 60 the guest wrongly assumed. (But let me check the standards committee at ATSC just to make sure. Also I'm speaking of NTSC TV and not film of 24fps or with the 3:2 pulldown.)


Now as to the 720 vs 1080i aspect. This again is the great debate. BUT...yes 1080i is 1080 lines of resolution but of an INTERLACED image. The image is present field A and B and each field contains only 540 lines of resolution.

NOT 1080. For that to occur it would have to be 1080p which is a format not supported. It can be argued that 720p is a progressive image therefore a complete image all at once of 720 lines of resolution vs. the 540 of the interlaced image in 1080i. It's a six of one half dozen of the other. Yes it is 1080 lines of image BUT some argue that the interlacing degrades the image and so on and so forth.

Again...as I said in the article not one or the other is better. I didn't say that 720p was higher resolution than 1080i or vice versa. I just presented what the confusion is...just like our guest...people making the incorrect assumptions.