Barry - Re: "Great analysis"
Thanks - I'm glad that was appreciated.
Your questions regarding HDTV are rather broad, and I won't begin to address all the issues - they are many and complex.
However, the PC community and the HDTV/Broadcast group "initially" conflicted with the monitor display technology - the broadcasters wanted Interlaced scanning, and the PC group wanted Progressive scanning.
Interlacing, used on all current NTSC TVs in America, diplays TV images by scanning every second scan line on a TV (I think 255 out of 510 ), then after the vertical retrace (nice TV lingo), the remaining 255 scan lines (each one is between two scan lines that were previously displayed in the first pass) are displayed. Interleaving is another term to describe this.
Thus, each image that you see on TV is made up of two separately scanned frames, every 1/60'th of a second - so 2*1/60 = 1/30 of a second for a compelete image. Each scan contains half the image, and the two scans, one after the other, "paint" the complete image. The persistence of the phosphors on the display tube "hold" the first image while the second "interlaced" image is filled in.
PC monitors almost universally use progressive scanning - the display image is scanned ONCE - from top to bottom - with all scan lines displayed sequentially, one after the other. The actual number depends on the monitor and the graphics display card (640, 800, 1024, 1280, etc.)
The FCC, in order to resolve the differences between the broadcasters and the computer industry decided a few months ago that the FCC WOULD NOT DICTATE WHICH DISPLAY TECHNOLOGY WOULD BE USED FOR HDTV.
In other words, they said "Let the market decide".
So, Intel/Compaq/Microsoft are joining forces to help establish their agenda in the digital broadcast world of the future.
AS usual, costs of monitors, etc. all enter in to the economics of these decisions.
As for broadcasting "digital bits", I hate to be the bearer of bad tidings! There really is no such thing as purely digital signals. We live in an analog world, and even "digital" signals are only remotely "binary" in the usual sense.
If you ever have a chance, look at a a 100 MHz signal on a computer board, displayed by a very high bandwidth ANALOG oscilloscope - 1 GHz or greater. You will be SHOCKED - the waveforms only remotely resemble "1's" and "0's" - they all have distinct rise times, fall times, ringing, overshoot and undershoot, etc.
So, for HDTV, digital bits will be "modulated" into analog signals for broadcast and transmitted with a carrier frequency. This carrier frequency will be "tuned" by the "Digital" receiver, and the analog signal extracted, filtered, then "demodulated" to bring out the binary "digital" bits, before there are scanned on to the display.
Today, digital TV is completely possible using computers with one MAIN DRAWBACK - the high volume of digital data has no universal high speed means of transmission !
Telephone lines, the Internet, etc. all have limited bandwidth - that is, they cannot transmit all the digital data required to maintain good image quality. So, computer-types "compress" the image - reduce the number of bits that describes the image, they reduce the scan frequency, etc. in order to transmit an "ACCEPTABLE" number of bits to display video images. In all but the most exotic set ups, this "digital video" leaves a lot to be desired.
If every home and office had its own "pipe" of unlimited data transmission speed, we would all be watching Geraldo on our PC's while getting stock updates and basketball scores in a separate "window".
But, these unlimited data pipes don't exist yet (at least, not universally in homes and offices).
Patience.
Paul |
