J
Jamie
- Jan 1, 1970
- 0
i did, and it's correct.Michael said:It must be set for the wrong tinme zone. Look at your posting
times. People reply to your messages BEFORE you post them.
currently my clock is saying 10:25 PM
i did, and it's correct.Michael said:It must be set for the wrong tinme zone. Look at your posting
times. People reply to your messages BEFORE you post them.
That description may lead one astray, since in interlaced video, the
fields are not only displayed but also acquired at different instants in
time. A "video frame" is not a frame in the same sense as a film frame
is.
Only by virtue of the fact that a video frame is delivered half at a time.
A film frame is exactly where they got the name for a video frame.
They're at slightly different rates, typically film is 24 FPS, and US
TV is 30 FPS, but other than that and the interlace, the defninition of
what a "frame" _is_ is practically identical.
You might be interested to know that 24FPS movie projectors actually
project each frame twice, so you get an effective flicker rate of 48
FPS.
Cheers!
Rich
Only by virtue of the fact that a video frame is delivered half at a
time.
They're at slightly different rates, typically film is 24 FPS, and US
TV is 30 FPS,
but other than that and the interlace, the defninition
of what a "frame" _is_ is practically identical.
You might be interested to know that 24FPS movie projectors actually
project each frame twice, so you get an effective flicker rate of 48
FPS.
Radium said:Hi:
PAL video system uses 50 fields per second and 25 frames per second.
Whats the difference between "field" and "frame"?
Gene E. Bloch said:Well, to be exact, the two fields of video are not quite the same as
the three frames (not two, as I recall it - but it probably varies from
projector to projector) of a film.
The two or three frames (or call it fields - why not?) of the film are
identical to each other, since they are just the identical piece of
film projected again. If there is any motion in the subject, the two
fields of the video are different from each other, since they are taken
at different times.
I'm just repeating Jukka Aho's point here for emphasis.
What does it matter to you ?
You'll just misunderstand it because you're so damn stupid.
Michael A. Terrell said:As usual, the greaseball is wrong. A TV projector in a film chain has
a special shutter that runs the 24 FPS film to match the 30 FPS video
rate by showing every 4th frame twice:
This was done on the RCA TP-66 film chain projectors used by TV
stations for decades.
Bob Myers said:Michael A. Terrell said:As usual, the greaseball is wrong. A TV projector in a film chain has
a special shutter that runs the 24 FPS film to match the 30 FPS video
rate by showing every 4th frame twice:
[example deleted]
This was done on the RCA TP-66 film chain projectors used by TV
stations for decades.
Hate to have to disagree with you, Michael, but that's no longer the
way it's done, the TP-66 method notwithstanding.
A TV projector in a film chain [...]
Jukka Aho said:The OP's question was "PAL video system uses 50 fields per second and 25
frames per second. Whats the difference between 'field' and 'frame'?"
(Followups set to "rec.video.desktop" once again.)
Bob said:Michael A. Terrell said:As usual, the greaseball is wrong. A TV projector in a film chain has
a special shutter that runs the 24 FPS film to match the 30 FPS video
rate by showing every 4th frame twice:
[example deleted]
This was done on the RCA TP-66 film chain projectors used by TV
stations for decades.
Hate to have to disagree with you, Michael, but that's no longer the
way it's done, the TP-66 method notwithstanding.
In modern practice, 24 FPS film is actually run at ~23.97 FPS
(to enable a match to the 59.94+ Hz "NTSC" field rate), and then
converted to video using a method generally known as "3:2 pulldown,"
in which frame films are alternately captured as either 3 or 2 video
fields (i.e., one frame of film winds up as 1.5 frames of video, while
the next winds up as 1.0 frames). An example: if we have four
successive film frames, A, B, C, and D, the resulting pattern of
video FIELDS (not frames) would then contain the following:
A A A B B C C C D D ...
and so forth. While this still introduces errors (motion artifacts)
into the resulting video stream, the errors are in general more
acceptable than those which resulted from the earlier frame-
doubling process.
The original point in all this, though, I believe has been missed.
TV "frames" are in almost all cases almost a fiction from the standpoint
of image content; we speak of them only because, with the 2:1 interlaced
scanning format, it's the only way to justify talking about the effective
vertical resolution of the system (at least for still images). The two
fields, however, DO represent different sample points in time, and
therefore cannot in reality be assembled to produce a complete
frame of the resolution (or line count) that one would expect, if there
is any motion in the scene. (Moving objects, of course, will appear
in slightly different positions between the two fields.) This is one of
the factors that reduces the effective as-delivered resolution of an
interlaced system.
Bob M.
Richard said:Bob Myers said:Michael A. Terrell said:As usual, the greaseball is wrong. A TV projector in a film chain has
a special shutter that runs the 24 FPS film to match the 30 FPS video
rate by showing every 4th frame twice:
[example deleted]
This was done on the RCA TP-66 film chain projectors used by TV
stations for decades.
Hate to have to disagree with you, Michael, but that's no longer the
way it's done, the TP-66 method notwithstanding.
Perhaps that is why Mr Terrell used the past-tense "was"?
OTOH, his "greaseball" remark raises his "plonkability"
score on my end.
And I'm thinking at this point that we still haven't answered that
particular question very well, so I'm going to take a stab at it.
In the most general sense I can think of, the word "frame" refers
to the smallest unit in a motion image stream (a clumsy phrase,
perhaps, but I'm trying to cover both film and video usage
here) which includes ALL of the information for a single,
complete image (i.e., it contains all the color, luminance, etc.,
information for one image at the full resolution of the system).
Ideally, it represents one temporal sample - i.e., it is an image
which is captured at one particular point in time, in a series of
such images which together are used to give the illusion of
motion when displayed. This last point is where the notion of
a "frame" in video starts to break down, since clearly in a
raster-scanned system the entire image is not captured at the
same time. But we still use the term nonetheless.
Hope you don't mind my adding sci.electronics.basics back
in, as many of us (myself included) are following the thread
there.
I am tired of all his rants and preaching alchol and nicotine
addiction and pushing a religious cult. I have 18 different
screen names of his kill filtered, and still have to add new
ones a couple times a year.
The "greaseball" remark was (seemingly) posted in reference to me in your
post <Given the context in which that
was remark was uttered, it's quite hard to interpret it in any other way.
Bob Myers said:Michael A. Terrell said:As usual, the greaseball is wrong. A TV projector in a film chain has
a special shutter that runs the 24 FPS film to match the 30 FPS video
rate by showing every 4th frame twice:
[example deleted]
This was done on the RCA TP-66 film chain projectors used by TV
stations for decades.
Hate to have to disagree with you, Michael, but that's no longer the
way it's done, the TP-66 method notwithstanding.
Perhaps that is why Mr Terrell used the past-tense "was"?
OTOH, his "greaseball" remark raises his "plonkability"
score on my end.
However, the "greaseball" remark was in a direct reply to my post in
this part of the thread, so I assumed he meant me. Maybe he meant you,
maybe he meant Radium, I don't know. Also consider that the post to
which I replied was from someone name Rich Grise; maybe Terrell thinks
his name is pronounced like 'grease'.
If he meant me, it is in truth the most complimentary remark I've
received today; also the *only* remark I've received today
Jukka said:The "greaseball" remark was (seemingly) posted in reference to me in
your post <Given the context in
which that was remark was uttered, it's quite hard to interpret it in
any other way.