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TVs, VCRs, DVD players, Home Theater systems and more.

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I'm tired of all the partial information about i and p here

Posted by DavidLD on April 29, 2008 at 05:05:45:
TV began broadcasting in the US much earlier than in the rest of the world. In order to do this efficiently, they could transmit only a very limited numbers of scan lines information. Because the limited number of scan lines, only 240 visible horizontal lines across the screen the picture would be very crude, but someone decided the picture would look better if they had each picture scanned twice, offsetting the lines a second time (there are more than the 240 visible scan lines that get transmitted, I think actually 270). This became the 480i, interlaced or NTSC picture.
The rest of the world adopted different standards using more scan lines, most notably PAL or SECAM, not NTSC, and that is why European TV sets didn't work in the US etc. The US up until 2009 never wanted to make anyone's TV set obsolete, not even a B&W one built in 1948, and stuck doggedly with 480 interlaced as their analog television broadcast standard, even as the rest of the world was using more scan lines in their analog signals and getting clearer pictures. The studios in the rest of the world were broadcasting a more complicated signal too, with more scan lines.

Then, along came digital. Any cathode ray tube makes a picture by shooting a horizontal line to excite phosphors on a glass screen, and in the case of a color picture the electrons excite phospors of different colors.
The digital world works differently in that everything is a matrix of colored phosphors and in a digital world it is a simple matter of turning individual cells in the matrix (aka pixels) on or off and or varying how bright each pixel is in order to make a color picture.

In a digital world there was no longer any need for a second pass, or interlacing of scan lines, and the each picture could be assembled in one pass, or what we know as progressive scan video or in the standard DVD world s 480p. 480p is the signal that pops out the component video outputs of your standard DVD player and if you have purchased a TV in recent years, it can probably accept this input signal directly.

But meanwhile, for those dreming up HDTV, 480p (standard DVD resolution) was nor good enough. Obviously to get a clearer picture than 480i we can do either one of two things, either up the number of lines to 720 and send out a progressive signal, or we could double the scan lines of the old 480p signal and ccontinue to interlace or make two passes per picture, offsetting the scan lines with each pass. The former became 720p and the latter became 1080i. Broadcasters, of course couldnt agree. Interlacing has always had its problems as the second pass of the interlaced signal happens a milisecond after the first, and this results in blurring when something like an athlete moves rapidly across the screen. But for a still picture the 1080 scan lines has a real advantage in clarity over 720.

No one wanted to try sending out a 1080p signal from the broadcaster because that would eat up way too much bandwidth. So you ended up with the Discovery Channel that wanted max resolution of slow camera pans in nature shows choosing 1080i whereas companies like ABC who is a component of Disney who owns ESPN going the 720p route? Why? they didnt want the feet of the basketball players to blurr when they ran across the screen and couldn't care less about the resolution of the Discovery channel's nature shows.

Then along comes Blu Ray (and the short-lived HD DVD). Finally a format that outputs a true 1080p and it suddenly becomes a bit worthwhile to have a TV that can display a true 1080p signal, and the current mess we know have with respect to TV specs.

And all the TVs we now see that have all sorts of different capabilities.

My old Rear Projection Sony HDTV with a CRT dating from 2004 is fully capable of displaying anything the broiadcasters are currently sending out either as 1080i or 720p. It can in fact create an interlaced 1080i display, no problem. Interlacing is a CRT tube's middle name.

As I understand it, if a 720p LCD or Plasma set gets a 1080i signal from a broadcaster it accepts it but downscales the signal and displays it as 720p. internally. These sets are happy with an HDTV broadcast from abc or ESPN because its a "native" 720p and the scalers have nothing to do.

There are few if any new TVs that can display and interlaced 1080i signal directly as HD CRT displays either direct view or rear projection have all but disappeared from the marketplace.

As I understand it, however, a 1080p set can take a 1080i signal, deinterlace it internally and potentially display it as 1080p. Whether this actually looks any better than a 1080i signal descaled to 720p on a 720p set depends on the quality of the sets and the quality of the scalers in the sets.

Large screen 1080p sets often seem to be priced at only a very few dollars more than theiy 720p counterparts and the price gap seems to be narrowing. In screen sizes under 42 inches there seems to be little interest in resolutions higher than 720p, tho Sharp just brought out a 1080p in a 32 inch size. Two years from now it will be tough to find a 720p set in scren sizes larger than 37 inches, but 720p likely will be around for smaller screens.

D

David