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Old 5th September 2003, 10:47   #41  |  Link
ronnylov
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All this talk of horisontal lines of resolution and pixels and oversampling is a little bit confusing. But I found this link:
http://members.aol.com/ajaynejr/vidres.htm

They talk about the circular rule. Quote from this link:
"When measuring "lines of resolution" for TV sets or monitors, a reference distance needs to be specified. Traditionally, video resolution is measured across the largest circle (not an ellipse) that fits in the space we are talking about. All the technical books on video say this, although using different words. On a standard TV screen such a circle would span 3/4 of the screen width. For U.S. HDTV (16:9 aspect ratio) the circle would span a little over half the screen width. Since the circle exactly fits the screen height (assuming no overscan), the phrase "picture height" stands for a distance equal to the diameter of the circle and is also used when talking about horizontal resolution. The circle rule also applies to film.

Under this rule, if a standard (4:3) TV set can reproduce 800 dots alternating black and white across the screen width using an input signal representing same, it is said to have 600 lines of horizontal resolution. However if the source material had just 330 lines of resolution you will see just 330 lines of resolution. A 16:9 aspect ratio TV that can reproduce just 800 dots across its screen would have 450 lines of horizontal resolution."
End of quote.

Should I interpret this as if VHS has 240 lines of reolution this would correspond to 240*4/3= 320 dots of alternating black and white across the screen on a traditional 4:3 TV? So even if I capture at a higher resolution the real resolution is not higher. But some sources can have "over 500 lines of resolution" (like DVD-players). This would correspond to over 667 dots of alternating black and white. This sound correct because if you count the overscan area this may leave around 670 "visible pixels of horisontal resolution".

I also found this link:
http://www.maxim-ic.com/appnotes.cfm/appnote_number/750

The table is a good reference. There also some formulas and stuff.

Then we had the original question of the capturing via S-VIDEO cable. If somebody could tell the bandwidth of this cable connection we could calculate what resolution it corresponds to. If it's higher than the bandwidth of the video source then the source is the limiting factor.

Since the table show that NTSC maximum limit is 338 lines of vertical resolution and 451 horisontal active pixels it seems that half D1 destination resolution is not enough to get all the details from the broadcast. SVCD resolution seems to be enough. But if your destination is DVD then you can't choose anything between 704 and 352 so 704 pixels horisontal resolution seems to be the right choice. But all sources are not of maximum quality. VHS source is fine also with half D1 resolution on the final destination format because maximum VHS resolution is 240 lines, which would correspond to 320 "pixels of visible horisontal resolution".

PAL maximum limit gives 403 lines of hor. res. and 538 "total horisontal active pixels". So you need to capture with higher resolution than 538x576. 704x576 seems to be a good choise as both capture and destination format.

I'm not sure how the overscan area should be taken into account. Maybe 480x480 is what you need for full NTSC and 576x576 for full PAL broadcast quality? Anyway the conclusion is the same - 704 pixels of horisontal capture resolution should be enough but half D1 may not show all the details of the original broadcast.

But if VHS-like resolution is good enough for your liking, then by all means choose the half-D1 DVD format as destination.

EDIT: I have read the original post again and he claims that S-VIDEO connection in theory removes 1/5 of the NTSC bandwidth. If that is true then you may end up with 384x480 just like he said. Then analogue video capture in NTSC is not much better than VHS recordings? I normally capture PAL video so that may be the reason I find that half-D1 is worse than full D1 from my analogue captures?
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Old 5th September 2003, 16:05   #42  |  Link
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ronnylov:

This approach with not involving whole hor. screen is by me very wrong.
And it's usual to consider whole width when talk about of res.

Also, as I see, you confused vertical and horizontal lines too:
"PAL maximum limit gives 403 lines of hor. res. and 538 "total horisontal active pixels". " - what this should mean???

It's not NTSC which limits bandwith or res. It's not connection which limits them. Limiter is max bandwith (freq.) by current system.
VHS has lowest (it's 25 or more year old).
Perhaps some good NTSC DVD player or digital SAT recevier has much bigger bandwith than TV programm.
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Old 5th September 2003, 16:47   #43  |  Link
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Quote:
Originally posted by ppera2
ronnylov:

This approach with not involving whole hor. screen is by me very wrong.
And it's usual to consider whole width when talk about of res.

Also, as I see, you confused vertical and horizontal lines too:
"PAL maximum limit gives 403 lines of hor. res. and 538 "total horisontal active pixels". " - what this should mean???

It's not NTSC which limits bandwith or res. It's not connection which limits them. Limiter is max bandwith (freq.) by current system.
VHS has lowest (it's 25 or more year old).
Perhaps some good NTSC DVD player or digital SAT recevier has much bigger bandwith than TV programm.
Read the links in my original post. The circle rule indicates that translation from "lines of resolution" on a display to computer pixels of the whole width is made by multiplicate with the 4:3 aspect ratio. I'm not confusing horisontal and vertical resolution. But if the circle is a circle and not an ellipse then the complete width of the display will not be included because the TV does not have 1:1 picture size. The lines are traditionally measured on a width equal the hight of the picture. And each line is either white or black (this is how the lines of resolution traditionally are measured). So if the lines of resolution is 403, then you can se maximum 403 white and black dots on the the same width of sreen as the height of the screan (normally measured in the middle of the picture). OK, this dots may be translated into horisontal pixels of a digital image. But the screen is wider than it is tall. So you need to multiplicate with 4/3 to get the horisontal number of pixels of the complete visible width that you can see on the 4:3 screen. 403*4/3. But you can't see all the pixels, some are hidden in the overscan and you cannot measure hidden pixels on a TV-screen. Thats why I add 7 %. Maybe I'm totally wrong?

403 horisontal lines within the circle on a 4:3 PAL TV:
403*4/3=537.3333
I guess there is some rounding when the table say 538 pixels.

OK, now the method was measuring on the visible picture on the TV. So let's say there is 7 % hidden invisible overscan area we need to compensate - 538*1.07=576. OK this indicate that 576x576 is the maximum analogue broadcast quality by the current analogue PAL broadcast system. I don't know if this corresponds to the maximum bandwidth in the system. Maybe 538x576 is max including the overscan area. I'm not sure if the lines are measured on a real TV or on the source signal.

But that does not meen that my receiver and capturing card and everything is capable of capturing all the details of the complete signal. I was thinking of what is the maximum quality that can be broadcasted on current analogue system and what resolution is needed to create a comparable digital video, and anything higher than that would be overkill when you digitize it. But then the DVD specification has only a few valid resolutions that is best to stick with if the destination is a DVD.

I have a DVB-C card also. Some channels send mpeg2 stream with full D1 resolution. But then I just record it digitally and does not involve any DA/AD conversions. So analogue capture is only interesting when capturing from an analogue source, otherwise try to record it digitally directly if possible. Also if you want to copy a DVD then do it digitally, don't capture it analogue.
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Old 5th September 2003, 17:22   #44  |  Link
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I still say that this aproach where looking circle res. is good just for adding more confusion in all this thing, what is obviously hard to understand for many people.

I'm start to be bored of all this thing. Resolution is just one aspect of capturing. My biggest problem by capturing TV programs is noise, and some artefacts appearing when use diverse compressors like Mpeg2, Mjpeg by compressing so noisy video. Dealing with resolution is simple in compare with noise problem.
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Old 5th September 2003, 19:56   #45  |  Link
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Quote:
Originally posted by ppera2

I'm start to be bored of all this thing. Resolution is just one aspect of capturing. My biggest problem by capturing TV programs is noise, and some artefacts appearing when use diverse compressors like Mpeg2, Mjpeg by compressing so noisy video. Dealing with resolution is simple in compare with noise problem. [/B]
Perhaps this is best moved to a different thread, though I'd be interested to see what you're using in your scripts to handle denoising. Even with as much researching as I've done, I've yet to use anything but Convolution3d(preset="movieHQ") on a consistent basis. The exception may be GuavaComb (in conjunction with C3D) which I've only started to use but I'm very impressed with it so far.
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Old 5th September 2003, 22:29   #46  |  Link
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Btw, I just found this very great thread: http://forum.doom9.org/showthread.php?s=&threadid=34122
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Old 6th September 2003, 01:22   #47  |  Link
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Yes, it's a great thread.
Didn't know that Ookami linked to Karls and my older explanations. And the Thread itself makes things clear, i think. But there is still a problem:

VHS and it's VERTICAL resolution. In theorie, VHS can save all the Scan Lines of PAL or NTSC. In Practise it's limited by the Mechanic of the VCR (maybe someone can translate "Kopfspalt" to english, it's a problem with crosstalking while reading the signals from the tape)...
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Old 6th September 2003, 04:02   #48  |  Link
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@Wilbert, head over to neuron2's forum to see this argued ad nauseum.
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Old 6th September 2003, 15:32   #49  |  Link
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Quote:
Originally posted by Piper
Perhaps this is best moved to a different thread, though I'd be interested to see what you're using in your scripts to handle denoising. Even with as much researching as I've done, I've yet to use anything but Convolution3d(preset="movieHQ") on a consistent basis. The exception may be GuavaComb (in conjunction with C3D) which I've only started to use but I'm very impressed with it so far.
We have big space to experiment with many postprocessing filters, but I think that is most important to avoid errors on first step - capturing. My experiences are that if cource is clean, most of 'capture' codec will do job well. If there is too much noise, compressors will start to make artefacts, especially by motion.
For such situations huffyuv is perhaps only solution (except uncompressed). So, big and fast HD is what we need in first place.
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Old 6th September 2003, 16:28   #50  |  Link
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I, like alot of people, have kept up with this thread to see how it's been progressing for a while now!

I think we all have to admit that when it comes capturing analogue video from a TV type source it's no as straight forward as it could be.

We should also, all be aware, that NTSC and PAL capturing don't follow the same rules and therefore the chipsets respond to the input signal in different ways.

I live in a PAL area. And my prefered method of capturing (for home use anyway) is either DV cam pass thru' or very high bitrate (9000+kbps) Mpeg2 capturing using the ADS USB 2.0 device (my thanks to Fred for this tip).

However, at the end of the day the ADS is the easiest device to setup and use and 'way' cheaper than buying an DV camcorder. Sure editing is more difficult to do with Mpeg2 but you get used to it!

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Old 6th September 2003, 20:49   #51  |  Link
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NTSC at 720 or 704 ???

Hello

I have an AverTV Stereo capture card.
Should I capture NTSC at 720 or 704 ?
There was some talk in this thread that with some capture cards it might be better to capture at 704 instead but I don't know if that applies to the card I have or not?

Thank you!

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Old 6th September 2003, 22:33   #52  |  Link
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Typically, capture at 720x480, crop off the ragged edges, process, resize if desired, compress.

When you capture at 720x480 you will typically see only 704 pixels are used for the actual content.
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Old 6th September 2003, 22:39   #53  |  Link
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hmm...

Surely this must be w/ respect to capturing VHS sources
and using Analog Capture cards as your device for obtaining the video
source.

I'm wondering what a CAM (using pass-through) has anything to add in
this myth as well as other DV devices ie, ADVC-100 etc
.
.
Never the less.. all is interesting

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Old 6th September 2003, 22:46   #54  |  Link
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Quote:
Originally posted by SeeMoreDigital
We should also, all be aware, that NTSC and PAL capturing don't follow the same rules and therefore the chipsets respond to the input signal in different ways.
Yes, absolutely. Perhaps not specificying the format leads to a lot of confusion.
Quote:
I live in a PAL area. And my prefered method of capturing (for home use anyway) is either DV cam pass thru' or very high bitrate (9000+kbps) Mpeg2 capturing using the ADS USB 2.0 device (my thanks to Fred for this tip).

However, at the end of the day the ADS is the easiest device to setup and use and 'way' cheaper than buying an DV camcorder. Sure editing is more difficult to do with Mpeg2 but you get used to it!
Good to hear you like the ADS. It's also nice because it will handle PAL, NTSC, SECAM and variants. Pretty cool for <$200 USD.
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Old 6th September 2003, 22:47   #55  |  Link
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Quote:
Originally posted by FredThompson
Typically, capture at 720x480, crop off the ragged edges, process, resize if desired, compress.

When you capture at 720x480 you will typically see only 704 pixels are used for the actual content.
It's also worth noting that even if you decide to keep the frame size at 720 (with a bordered 704 image). On most TV's you won't notice the side borders. It all depends on how well or badly your TV has been set up!

In much the same way you don't notice the side borders on many 1.85:1 DVD's. Well PAL DVD's anyway!

Cheers
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Old 6th September 2003, 23:03   #56  |  Link
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Quote:
Originally posted by vhelp
Surely this must be w/ respect to capturing VHS sources
and using Analog Capture cards as your device for obtaining the video
source.
No, all NTSC. I started with a capture card and how do DV passthru or hardware MPEG2.
Quote:
I'm wondering what a CAM (using pass-through) has anything to add in
this myth as well as other DV devices ie, ADVC-100 etc
Not myth, spec, research it and be careful of sources whose author(s) get confused by the difference between square and rectangular pixels.

Passthru doesn't give you anything special. NTSC DV does have 4:1:1 colorspace which is horrible for anything with sharp edges so conversion to 4:2:2 with 411Helper for VirtualDub or Reinterpolate411 for AviSynth is wise.

DV camcorders typically will shoot a full 720x480 image. Given an NTSC analog feed, ~704 with 16 letterbox to yield 720.
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Old 7th September 2003, 00:05   #57  |  Link
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.
.
Interesting about your DV comments..

I've ben wrestling w/ the "saw tooth" along horizontals when shooting
in 16x9 mode. When at 4:3 mode, all edges age clear and perfect, but
as soon as I switch to 16x9, all is saw tooth.

what's with this 4:2:2 and 411 helper (not to vear too far from orig.
topic) ?? ..and, if that might help w/ my 16x9 "saw tooth" situation.

See new topic start on this here:

* Shooting DV footage w/ "saw tooth" output issues

-vhelp
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Old 7th September 2003, 00:38   #58  |  Link
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Quote:
Originally posted by vhelp
.
.
Interesting about your DV comments..

I've ben wrestling w/ the "saw tooth" along horizontals when shooting
in 16x9 mode. When at 4:3 mode, all edges age clear and perfect, but
as soon as I switch to 16x9, all is saw tooth.

what's with this 4:2:2 and 411 helper (not to vear too far from orig.
topic) ?? ..and, if that might help w/ my 16x9 "saw tooth" situation.

See new topic start on this here:

* Shooting DV footage w/ "saw tooth" output issues

-vhelp
I don't know anything about the 411 helper stuff but I've heard that you can buy a special lenz attachment that will allow you to shoot in full frame 4:3 but at 16x9 due to the stretching of the image by the lenz attachment. Perhaps this might help with the "saw tooth" problem?

- John "FulciLives" Coleman
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Old 7th September 2003, 03:06   #59  |  Link
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Sigh...over the past couple of weeks I've explained the 4:1:1 issue a number of times. Perhaps I should colude with the powers-that-be to create a sticky in the DV forum which will summarize and link to the original threads.

Real quick...NTSC DV is 4:1:1 which means one chroma (color) value for 4 horizontal pixels. DV MPEG2 is 4:2:0, one chroma value for a "square" of pixels. OK, so that's a mismatch, right? That's not all. 4:1:1 is horrible for sharp edges.

I noticed this with DV passthru of video bugs (station logos) and video of houses (look at window pane dividers.) It all started to make sense when IanD asked for help with the Star Wars laserdisc captured through the Canopus ADVC-100. Xesdeeni's site and mine (http://www.geocities.com/fredthompson6) show the problem.

I suspect, but have not fully tested, these "corrections" would also help with some diagonal lines. NTSC DV hates diagonals of about 15 degrees. A lot of my camcorder source is of machinery. Lots of chromed moving surfaces and shallow angles. Probably the best example of DV's shortcomings I've ever seen.

Give me some time to get a proper writeup done and posted. I'll ask bb to make it sticky and get the same info to Wilbert.

Last edited by FredThompson; 7th September 2003 at 03:13.
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Old 29th September 2003, 07:19   #60  |  Link
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I just read through this thread and it seems to me that a lot of people never learned traditional TV engineering.

Back when TVs were actually made from 100% analog parts (you know, transistors, tubes - that sort of thing) you didn't have dots or pixels, you had frequencies and bandwidth. The way they measured the resolution of a display was to actually draw a picture and display it on the TV. The picture was just a set of alternating vertical black and white lines. You made the lines thinner and closer together until you could no longer distinguish the lines on the TV. You then counted the number of lines drawn on the picture. It was found that you could discern about 80 lines per 1 MHz of signal.

Now a black line followed by a white line can be represented as a square wave - that is how it would look on an o-scope if you had lots of bandwidth. We are still talking ANALOG signals here. The fourier of a squarewave is a sine at the fundamental frequency plus a lower amplitude sine at the third harmonic plus an even lower amplitude sine at the fifth harmonic, etc. To see EXACTLY a black line followed by a white line would require the TV to handle a signal at a set frequency plus several odd harmonics. Since the TV has a limit or bandwidth, many of the odd harmonics are lost and the signal becomes less like a squarewave and more like a sinewave. At the limit of the TV to produce a discernable line, you have only the fundamental frequency and no harmonics. That is why if a TV has a bandwidth of 3 MHz, you can discern 240 lines which actually appear as a sinewave that goes from shades of black through shades of white.

Since a TV has a set number of scanlines, you would think that the vertical resolution would be exactly the same as the number of visible scanlines. However, the scanlines on a CRT are scanned (hence the name) and combined in the brain through persistence of vision. This reduces the number of horizontal lines that can be discerned to less than the number of scanlines drawn. Even more, TV displays are interlaced which affects the number of discernable lines even more. The general rule found with long persistence phosphores was that the number of horizontal lines discernable to be about 85% the number of visible interlaced scanlines. So a TV with 440 visible interlaced scanlines gives a vertical resolution of about 374 lines.

I would hope that clears that issue up a bit, but I imagine it has some folks even more confused than ever.
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