woodman

There's so much confusion and misunderstanding about this subject, that I decided to put it all down here to see if I could clear the air a bit.

To start with, those who've grown up with computers and think that they have the subject down pat, have to learn something new. That "resolution" in a video display is not the same thing as it is when applied to computers. They are quite different because - in a computer monitor, as resolution is increased, objects on the screen get smaller. In a video display, this is not the case at all. This fact changes everything - especially the notion that the number of scanning lines is directly related to the "resolution" of the image.

Let's start with some definitions of terms:

Scanning lines
... the 'lines' that are "painted" by the electron beam(s) as they sweep across the screen, making up the image.

Scanning format
... the number of scan lines that makes up one "frame" of video, plus whether it's scanned "progressively" (p) or if it's "interlaced" (i).

Interlaced scanning
... the scanning of a video image in which there are two "fields" scanned to produce each video "frame". First all of the odd-numbered lines are scanned (1,3,5,7,9,11, etc.) - creating the first field, then all of the even-numbered lines (2,4,6,8,10,12, etc)are scanned to create the second field. This method was employed when TV began in order to increase the apparent number of images per second from 30 to 60 to eliminate "flicker".

Progressive scanning
... the scanning of a video image in which all of the scan lines are scanned in succession - 1,2,3,4,5,6,7,8,9, etc. When this scanning method is employed, the scanning rate (the # of scan lines per second) must be doubled. NTSC television scanned at a 15,750Hz rate. In order to employ any device that produces 480p scanning format video, the TV set must be capable of scanning at 31,500Hz (approximate).

Resolution
... as it applies to a video display, it describes the capability of the electron beam(s) to turn on and off very rapidly as they sweep across the screen - which results in the ability of the display to show fine detail. In order to measure this capability, a test pattern is employed that consists of vertical white stripes (with blank spaces in between them) all across the screen. The number of white stripes that can be differentiated constitutes the "resolution" of the display.

The scanning formats that will be encountered are:
480i - TV broadcasts, VHS and S-VHS videotape, DVD, DBS satellite
480p - Progressive scan DVD players, EDTV broadcasts (FOX)
540p - Upconverted (in a TV set) from 480p
720p - an HDTV broadcast (ABC network)
1080i - HDTV broadcasts (everybody else) - OTA and via satellite
1080p - a HiDef format that may or may not eventually appear

These describe the number of scan lines that make a video frame, and whether it's interlaced (i) or progressive (p) scanned.

The resolution is a quality that's inherent in the medium and in the display itself. But the display, no matter what it's resolution capabilities are, cannot display any more detail in the image than what's available from the program source.

The "resolution" capabilities of the various mediums are:
VHS videotape - 240 "lines of resolution" - 480i scan format
NTSC (analog) television - 330 "lines of resolution" - 480i scan format
S-VHS videotape - 400 "lines of resolution" - 480i scan format
DBS satellite (SDTV signals) - 400 "lines of resolution" - 480i scan format
DBS satellite (HDTV signals) - 960 "lines of resolution" - 1080i scan format
DVD player - 540 "lines of resolution" - 480i or 480p scan formats
FOX network EDTV - 960 "lines of resolution" - 480p scan format
HDTV television - 960 "lines of resolution" - 720p or 1080i scan formats

It has to be borne in mind that no matter what a given format or display is capable of, does not necessarily guarantee that you will get that much "resolution" from it. Often (usually, really) it's considerably less than the maximum "rez" available.

Hope this clears up some confusion and misunderstanding ...

Any questions?

__________________
woodman

I plan to live forever ..... so far, so good!
Steven Wright