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Old 28th August 2003, 15:13   #1  |  Link
dvd_maniac
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is this true? resolution myths?

got this from http://www.dvdrhelp.com/forum/userguides/98177.php
I capture with ati aiw 9700 pro from digital cable and directv sat. I use s-video and if this is true I should only cap at 352x480 if I want to author dvd with it?
Now, it is a perfect opportunity to clarify a myth here: There is no way to grabb from any analogue source (including TV broadcasts) and with the use of "S-Video in" to get a usefull resolution beyond 384 X 576/480.
The reason for this, is that in analogue technology, there are no horizontal lines like the digital world, but horizontal DOTS. 720 dots in a raw, creates what we call a line. With the analogue transmissions, if a dot is missing in the raw, there gonna be no replacement, just a null dot, a nothing. The lenght of the raw, gonna be always the same with or not some dots. For example:

A line with all the dots: ...........................................................
A line with some dots missing : ... ............. ............. ..................... ...

In theory all types of connections/cables are capable to carry a picture of CCIR-601 resolution from a source to a screen, but there gonna be loses in the dot raw line like those in the example. Those loses are more for composite, less for S-Video and even less for Component and RGB. It is not easy to expain it further in a simply post, maybe a future article
With S-Video, those loses are about 1/5 of the video in theory. In practice and mainstream cables/connectors, is more, about 2/5 or the original info.
So you end up with 384 horizontal usefull dots X 576/480 vertical lines. And becase in digital world only the usefull info counts, any grabb with the use of S-Video beyond 384 X 576/480 is a fake!
If you want source on higher resolutions, you can experiment with DV, DVB transmissions (when you grabb direct the stream with the use of special hardware), DVD - Video (ripping) and source which came from Component adaptors or RGB ones. The full Euroconnector cable (known more as SCART) includes sometimes the RGB info, but a Full SCART to SCART cable required , with high quality parts and those cables costs a lot!. Also, the difference ain't easy noticable on a TV, but is very noticable from the encoders!
Overall, don't expect higher resolutions beyond 384 X 576/480 with the use of S-Video! It is practicly impossible to have them! And because 384 X 576/480 ain't a supported resolution in any optical media, go straight for 352 X 576/480.

Last edited by dvd_maniac; 2nd September 2003 at 03:04.
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Old 28th August 2003, 15:30   #2  |  Link
Kika
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Not realy.
Try it by yourself: Capture the same Video at 704x480 and 352x480. Encode them without any resizing/filtering. Which one is the sharper one?

He is right. Max. Resolution of S-Video (NTSC) is arround 384x480. But you have to capture a higher resolution to get every horizontal Line (not Scan-Lines!). Horizontal Lines (VHS has 240, S-VHS up to 400) aren't Pixels and can't be handled like Pixels. To be correct: You have to Capture double the amount of Pixels than the Video-Type provides in (horizontal) Linies.
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Old 28th August 2003, 15:58   #3  |  Link
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tried it

I tried both, but did not encoe them. I capped directly to mpeg-2. both at 720 and 352x480.
I really couldn't tell the differnce. I have one moreestion though.
Should I be able to lower the bitrte yhalf if I cap 352 intead of 720 and expect the same quality since it is only grabbing around 352 anyways? I ask instead of trying because my eyes are not the best and want another opinion.
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Old 28th August 2003, 18:05   #4  |  Link
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I can't agree with things mentioned in that article. Even with composite connection is very visible more sharpness in higher resolutions. Aprox. over 640 I don't see difference. For me. it looks that they talk about S-VHS and not S-Video connection.
According to that, that active line time is around 52 microsec. and max freq. by broadcasting is 5-6 MHz, horizontal res. can be over 500 pixel. Better analogue (studio) eauipment has more resolution (768, declared).
However for TV is irrelevant is connection composite or S-VHS - it is multiplexed in broadcasting, and what use of that, that it's later separated?
Advantage of S-video is mostly in that, that no interference between chroma and luma. Actually it's real useful for: TV out and for capturing from S-VHS VCR.

Back to resolutions: it's always better to capture in bigger resolutions, because capture itself will be more precise (oversampling). Loss, mentioned in article will be always lower if capture in higher res. Later you can resize to desired and to source best fitting res.
Of course that for lower res. you can use lower bitrate by capture.

Last edited by ppera2; 28th August 2003 at 23:38.
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Old 31st August 2003, 20:08   #5  |  Link
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It's 704 for me..

Hi guys..

Another important fact is this...
If your goal is to make DVDs, then you want to make them w/ the highest
resolution you can go, w/out taxing your given setup, and limiting
yourself to 384x !!

I do make encodes w/ 352x480 from VHS, but am now beginning to see
an actual difference when I use 704x as my minimum.

But, don't expect to see better results if you capture at 384 and
then raise it to something like 704. That's why its better to just
bake two pies in ONE oven, and capture at highest your given system
will allow you to w/ out such issues as framedrops and others nonsense
things, ie, 704 or 720. Then, if you want, you can bring things down
a little like 352x480 for instance.

Also, note that for VHS movies that are in WideScreen format, you gotta
capture it at highest you can go.. and for me, that 720. Then, I'll
bring it down to just 704, and widescreen encode it, and it looks great
in my AD-1500 player, and in widescreen view on my cheap 13" tv.

So, for the most part, and for most people who's goal is highest
resolution for a DVD project, 704 would be minimum (for me anyways)

Have a great day all,
-vhelp
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Old 1st September 2003, 05:50   #6  |  Link
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Consider the source. DVDRHelp has a number of less-than-logical guides. If you're truly interested in knowing what is possible over analog signals, there are far better sources for information.

With ANY digital sampling, you will have far better results if you sample at a far greater frequency than the analog signal. Best is 4x or higher, 2x is still fine. To illustrate, an audio CD has 16 bits of resolution but truly professional ones are mastered at 96 and downmixed as the final operation. (OK, well, there IS a form of post-processing which can add apparent punch but that's a little different.)

If you capture at the highest rational size and depth, do your processing, then downmix for the final product, the results will be superior to those where the sample is made at the final product resolution.
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Old 1st September 2003, 06:00   #7  |  Link
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I consider vcdhelp's guides and factoids to be as honest and helpful
in many areas

But, once in a while, you find a bump on the road, and you can't help
to wonder what gives.

So, what I'm saying, is I'm a person who tipically punches through
what logic and math might say (or prove) and find myself going against
the grain hence, the dissbeleaf that you gotta capture at lower
res cause it's not "mathematicaly" or "logically" sound to capture at
higher res. I believe the opposite. You capture at the highest res
your given setup will allow, and adjust to something comfortable w/
your final goal ie, CVD or DVD etc.

So, the rule of thumb is, in this case, go against the grain
-vhelp
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Old 2nd September 2003, 02:17   #8  |  Link
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well...

my sysrem can handle 720x480 even in huffy avi capture. my problem is trying to fit as much video as possible onto dvd-r without quality loss. I record my favorite tv shows and do not want to waste too many blanks but want them too look nice.
ps does anybody here capture with ati radeon and encode with CCE?
my huffy avi's come out squashed and scrambled. And don't know how to import mpeg-2 files.
could use some help.
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Old 2nd September 2003, 02:30   #9  |  Link
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It's a huge discussion but what you describe sounds like 2 things: the noise of capture increasing your storage bandwidth, the need for proper filtering.

If filtering is done properly, it reduces the random inconsistencies of noise. Done improperly, it makes the image cartoonish. By way of comparison, satellite MPEG2 transmissions are typically less than 1G/hour of material, higher for premium source like specialty movie channels, pay-per-view, etc.

I have an All-in-Wonder Radeon but don't capture with it anymore. Maybe things have changed with the more recent models. That one did not have proper sampling. Now I use DV passthru or a hardware MPEG2 encoder at a very high bitrate.

DVD handles all kinds of resolutions and bitrates. TANSTAAFL so there comes a point where you'll have to decide which is cheaper, your time to fiddle with the captures or the media. I, personally, prefer to use a higher bitrate to keep detail under the theory that storage costs and space will continue to decline so it's better to do it "right" than to do it over, if "doing it over" is even possible.
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Old 2nd September 2003, 19:12   #10  |  Link
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There's are many 'trade off' decisions you may have to make when capturing.

Capturing 4:3 images is not so bad. But things can get a little awkward when trying to capture 16:9 images.

As you know, an NTSC 1.77:1 (16:9) image viewed on a 16:9 TV, actually starts it's life as an 1.50:1 image. So in order for the image to perfectly fit a 16:9 TV it has to be (horizonally) anamorphicly stretched, by around 20%.

PAL 1.77:1 (16:9) images start their life as just an 1.25:1 image. So in order for this image to perfectly fit a 16:9 TV it has to be (horizonally) anamorphicly stretched, by over 40%!

So as you can see the PAL image has to be stretched twice as much as the NTSC image!

Never the less, some people may find it interesting to conduct their own 'horizontal pixel' stretch tests. Just to see how far they can put up with a streched pixel before they can't take it anymore!

352 pixels is about enough for me!

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Last edited by SeeMoreDigital; 2nd September 2003 at 19:14.
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Old 3rd September 2003, 18:29   #11  |  Link
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Re: well...

Quote:
Originally posted by dvd_maniac
my sysrem can handle 720x480 even in huffy avi capture. my problem is trying to fit as much video as possible onto dvd-r without quality loss. I record my favorite tv shows and do not want to waste too many blanks but want them too look nice.
ps does anybody here capture with ati radeon and encode with CCE?
my huffy avi's come out squashed and scrambled. And don't know how to import mpeg-2 files.
could use some help.
I also cap at 720x480 (huffyuv with ATI AIW) with my destination being dvd. What I do is filter the sourc, delete commericals and resize down to 352x480 and create a second filtered source file which is also huffyuv encoded. Then using the second file, I encode to MPEG-2 Half D1 DVD (TMPGEnc) and burn it to a dvd+rw when I'm finished. Using this method, I cannot honestly tell the difference between the original source and the dvd. In fact if it's filtered correctly, it can actually look a bit better. I find 352x480 is a great resolution for TV caps.

If it's a particularly good episode, I'll encode it (second source) to DivX and dump it on a CD-R. The quality is not quite as good as on the DVD, but works well for my purposes. Of course if DVD's were as cheap as CD-Rs, there would be no question. :-)

Sorry, I can't help with CCE.
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Old 3rd September 2003, 21:16   #12  |  Link
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Quote:
I find 352x480 is a great resolution for TV caps.
Yes, it is. But you can expect better results on capturing 704x480, because Half-D1 is based on this Resolution and not on 720x480.
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Old 3rd September 2003, 21:22   #13  |  Link
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Some issues:

@ppera2,

Quote:
Back to resolutions: it's always better to capture in bigger resolutions, because capture itself will be more precise (oversampling).
I don't understand this. Sampling happens when converting the analog signal to a discrete one. The number of samples is always the same (NTSC: 910, and PAL: 1135; from page 13 data sheet Bt878). After sampling, the clip is resized to the resolution which you used when capturing (with some cards, overscan is included).

In other words: if you capture in bigger resolutions, the capture will be more precise, but not due to oversampling. It is just because you are downsizing to a less smaller resolution.

@Kika,

Quote:
Horizontal Lines (VHS has 240, S-VHS up to 400) aren't Pixels and can't be handled like Pixels. To be correct: You have to Capture double the amount of Pixels than the Video-Type provides in (horizontal) Linies.
I also don't understand this. I guess you are talking about the Nyquist frequency here. This Nyquist frequency stuff doesn't imply you have to double the amount of pixels, wrt the number of active scan lines. Like I said above the number of samples is not related to the capture resolution.

Nyquist sampling means the following: "In order to recover all Fourier components of a periodic waveform, it is necessary to sample more than twice as fast as the highest waveform frequency v." (ref: www.mathworld.com)

On the same page of the same datasheet, they talk about sampling: "UltraLock^TM operates at CLKx1 although the input waveform is sampled at CLKx2 then low pass filtered and decimated to CLKx1 sample rate".

Where CLKx2 (CLKx1) is the 8*Fsc (4*Fsc) clock signal. This is indeed Nyquist sampling.
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Old 3rd September 2003, 21:55   #14  |  Link
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Quote:
Originally posted by Wilbert
Some issues:

@ppera2,

I don't understand this. Sampling happens when converting the analog signal to a discrete one. The number of samples is always the same (NTSC: 910, and PAL: 1135; from page 13 data sheet Bt878). After sampling, the clip is resized to the resolution which you used when capturing (with some cards, overscan is included).
In other words: if you capture in bigger resolutions, the capture will be more precise, but not due to oversampling. It is just because you are downsizing to a less smaller resolution.
Interesting... So, BT chip performs some resizing during capture.
In that case it's worth to capture in final resolution. In res. what is moduo of 1135-some pixels, if I understood it well.
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Old 3rd September 2003, 21:55   #15  |  Link
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2x isn't enough, you need at least 4x to accurately sample. The theorem is correct but not accurate. 2x could conceivably sample on the 0 zero as a wave is going up and coming down, the result would be nothing.
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Old 3rd September 2003, 21:58   #16  |  Link
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@Wilbert

Quote:
I also don't understand this. I guess you are talking about the Nyquist frequency here.
No, i'm not talking about the Nyquist Theorem here. First we have to make clear what we are talking about: Horizontal Lines. They aren't Pixels. One Line is the Time for "drawing" a complete Sine-Waveform (argh, my english-problem again). It is the periodic Time of the Waveform. So a Line can start Black and end up White (or anything between them). Between the Mixima/Minima there can be any shade of greey.
240 Lines means, you can have 240 complete Waveforms per Scanline.
You have to capture 2 Pixels per Line to get the start- and endpoint of the true signal (the sine wave). If you capture only one Pixel per Line, you get the AVG of the Waveform - and that's never white or black, it is always a shade of greey.

Sorry, i can't descripe it better in english

Last edited by Kika; 3rd September 2003 at 22:03.
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Old 3rd September 2003, 21:59   #17  |  Link
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Quote:
Originally posted by ppera2
Interesting... So, BT chip performs some resizing during capture.
In that case it's worth to capture in final resolution. In res. what is moduo of 1135-some pixels, if I understood it well.
Only if you don't plan to filter and you trust the internal rescaling to be proper...
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Old 3rd September 2003, 22:01   #18  |  Link
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You mean "sine" wave. Sinus is different, the most common usage is the passage from your nostrils to your throat

Last edited by FredThompson; 3rd September 2003 at 22:17.
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Old 3rd September 2003, 22:07   #19  |  Link
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Um, i was way to slow...

@Fred

OK, corrected this sinus-sine-thing...

And yes, BT-Chips are acting like that. They are trying to eliminate this greey zone between the Max. and Min. Point of the Waveform. This results in a sharper Picture.

Oh, and the more Horizontal-Lines, the better the sharpness - in 2 ways! More Lines = more Informations AND more Lines = more sharpness of one Line, because the Lines are "smaler".
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Old 3rd September 2003, 22:37   #20  |  Link
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Quote:
Originally posted by Kika
Yes, it is. But you can expect better results on capturing 704x480, because Half-D1 is based on this Resolution and not on 720x480.
Interesting you should say that. While I haven't experimented with capturing at 704x480, I have with 640x480. If anything I've noticed fewer artifacts with a 640x480 source than a 720x480 source (albeit ever so slightly softer).

I'll give 704x480 a shot. It makes sense, horizontal being x2 Half-D1. Thanks for the suggestion.
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