Captures are streatched if you use 720 ...

[trevlac]

If you capture at 720, you are probably streatching the picture.

I've been talking about this for a few days, and doing a poor job.

Today, someone posted some test results on doom9 here.

The big thing I got WRONG was that it is dependant upon your drivers. The card probably does not matter.

Here is a summary of the streatch (from the tests):

For PAL:

102.3% - BTWincap v5.3.6.1 (BT8x8)
103.4% - Hauppauge WDM v3.35 b 21125 (BT8x8)
103.4% - Iulabs universal WDM v3.1.28.36 (BT8x8)
103.4% - Hauppauge WDM v2.75.21070 (CX23881)
100.0% - Terratec Cameo Grabster 200 USB v3.05 (SAA7113)
102.3% - Terratec Cinergy TV 400 WDM v1.2.0.5 (SAA7134)

For NTSC:

101.1% - BTWincap v5.3.6.1 (BT8x8) I use this
104.7% - Hauppauge WDM v3.35 b 21125 (BT8x8)
104.7% - Iulabs universal WDM v3.1.28.36 (BT8x8)
104.7% - Hauppauge WDM v2.75.21070 (CX23881)
100.0% - Terratec Cameo Grabster 200 USB v3.05 (SAA7113)
102.3% - Terratec Cinergy TV 400 WDM v1.2.0.5 (SAA7134)

[erratic]

For DVD authoring this stretching can be avoided if you use the following capture resolutions:

BTWinCap NTSC - 712x480
Don't resize afterwards! Add black bars to make it 720x480 or crop to 704x480 (both are DVD compliant resolutions).
BTWinCap PAL - 704x576
Once again don't resize to 720x576. Keep the 704x576 resolution (it's DVD compliant) and make a 704x576 MPEG-2 file for DVD authoring.

Hauppauge/Iulabs NTSC - 688x480
Hauppauge/Iulabs PAL - 696x576
Don't resize! Add black bars to make it 704x480/576 or 720x480/576.

Terratec Cinergy NTSC/PAL - 704x480/576
Don't resize. Keep the DVD compliant 704 resolution and make a 704x480/576 MPEG-2 file for DVD authoring.

One thing I want to add: 704 can be resized correctly to 352 for DVD or CVD/VCD authoring - 720 can be resized correctly to 480 for SVCD authoring.

Also read this Doom9 thread.

[lordsmurf]

I wouldn't suggest non-experts on reading that doom9 thread. A bunch of people in it have no idea what they are taking above in relation to AR, making it a confusing jumble of random info. Luckily, I and others like me can weed throught the garbage, but it's likely to confuse the casual person.

[erratic]

Yes, that Doom9 thread is confusing for non-experts. That's why I summed up the correct information, based on the tests performed in this Doom9 thread. But the information in that thread is rather complicated for non-experst as well. The fact is that nearly all capture drivers have a fixed capture area and they scale it to whaterver resolution you pick.

For example: the Hauppauge WDM driver captures 688x480 NTSC. If you capture 720x480 NTSC you get 688 stretched to 720. That's not a good idea for DVD authoring because the aspect ratio will be wrong on your TV.

[trevlac]

I wouldn't suggest non-experts on reading that doom9 thread. A bunch of people in it have no idea what they are taking above in relation to AR, making it a confusing jumble of random info. Luckily, I and others like me can weed throught the garbage, but it's likely to confuse the casual person.

Can you summarize the valid/good information?

I'm a 'non-expert'. I only recently learned about this problem. 5% skew seems to be a bit much to let pass. Too bad there isn't a rule of thumb like cap at 704 not 720.


Edit:

@erratic

I didn't mean to ignore your summary. It's good for people who understand this behavior, and know their driver. But what about all of those ATI cards out there? I'd guess they cap close to 704 (based upon comments I've read).

Also, I'm surprized at how few views / comments there are on this topic. Not even senior members have anything to say. Either:

- Few care if the AR is off
- Few understand the problem

Maybe I should do a poll...
What width do you cap at ?
- 768
- 720
- 712
- 704
- 688
- 640
- 480
- 352
- Other

[erratic]

I agree with you, trevlac:
- Few care if the AR is off
- Few understand the problem

ATI AIW cards have a PAL capture area of 704x576. I've tested that with a test pattern on my TV. I can't guarantee that 704x576 is 100% correct, but it's near perfect. 720x576 is stretched a little.

I can't be sure about NTSC without testing it, but if you capture 720x480 NTSC and there are no small black bars left and right, then 720x480 is not perfect. The analog NTSC signal has a maximum of 711 active pixels per scan line, so 720 active pixels can never be correct. Recent versions of ATI MMC don't support 720x480 for AVI capturing anymore. Older versions support it, but ATI have changed it to 704x480, so I assume 704x480 is correct for NTSC with an AIW Radeon card.

MPEG-2 captures with ATI MMC are still 720x480/576. For PAL that's definitely wrong, but it can be fixed in the registry as I explained in another forum.

My capture resolutions are 704x576 or 352x576 depending on the quality I want.

I've also tested SVCD with my AIW card. 480x576 is just as stretched on my TV as 720x576, but 468x576 with black bars (6 pixels left and right) added afterwards is near perfect.

But I repeat:
- Few care if the AR is off
- Few understand the problem

[lordsmurf]

I never saw anything wrong with the AR, and I have seen black bars on 720 NTSC caps, but I'll research this when I find more time.

Again, most people should use 352x480 anyhow coming off most analog sources.

[trevlac]

Again, most people should use 352x480 anyhow coming off most analog sources.

I know there tends to be a debate about this, but I think this is bad generic advice.

Anyone worth their salt would say it depends. It depends upon (all) the equipment and it depends upon the source.

For example, by reading the technical docs, and thru a little testing / logic, it is clear that most capture cards always sample a "full" picture. They then resize to what you ask. This resize is by definiton, a loss of information and an increase in error from the sample.

Will you notice? Well that depends upon the source. VHS is one of a few sources with less horizontal luma resolution than 1/2 D1. Even NTSC broadcast has a greater TVL than 1/2 D1.

Will you notice? Well that depends upon the original resolution, the broadcast bandwidth, and finally, your TV.

Unfortunately, there is no easy answer for someone who does not have this understanding. They really should make their own decision based upon some simple testing of source and system.

[b]Please[/] don't take this the wrong way. Your intent may be to give people the easy answer they want. After all, 352 is half as big, which makes other things easier.

------------------

As far as testing what the card is generally doing, forget the borders thing. Source can have borders, which may confuse things. Instead, cap the same 'static' scene at 720 and 704. If the 704 fits nicely on top of the 720 and is just missing the sides, it is not a 'shrunk' version of the 720. (The 720 is more likely a streatched version of the 704).

To know the exact size, you'd have to use a test pattern. The AVIA disc has a pixel cliping pattern I used for this. I also used my DVCam to cap the same pattern to make sure I understood what my dvd player was doing. The player can only out 711 NTSC. My cam however does capture the entire 720.

[lordsmurf]

Well, within our scope of discussing ATI cards, which handle 352x480 capture quite well, and from most analog sources, as most top off at 544x480 at the highest point ("digital" satellite and cable), with VHS running about 240x480 and broadcast/cable being about 335x480.

Many other cards sort of need 720x480 or nearby to grab all the data, as many cards are not good at digital acquisition of the signal and poorly handle the resolutions.

Yeah, I have a number of methods to test... all I need is time.

[trevlac]

@Lordsmurf

I added this in a new post so it would not get lost in my previous ramble.


I read your site and advice on resolution. I got 3/4 thru and thought it was very good advice. Not at all the same as "generally do analog at 352".

However, I think you have a mistake. With regard to broadcast, you compare pixel resolution to TVL resolution. NTSC is ~330 TVL horizontal. The equivalent for 1/2 D1 would be ~260, not 352. TVL is measured based upon a square screen. Because 4:3 screen is not square, one must adjust the 4:3 numbers. 352 / 4 * 3 = 264. DV which is 720 is generally quoted as 540 TVL. 720 / 4 * 3 = 540.


Broadcast is the only place where this makes a difference. VHS/Beta/8mm are all still below the 260 threshold. The others are either above, or you are using pixel size to compare.

Overall, I'd say, your advice is very solid and clear. Statements like "depends on hardware and software" really hit the nail.

[trevlac]

Many other cards sort of need 720x480 or nearby to grab all the data, as many cards are not good at digital acquisition of the signal and poorly handle the resolutions.

I tell ya, all of these cards always sample (digital acquisition) the same amount of data. (For a given card/driver combo. I don't mean all cards are the same, but they are close).

They then resize to what you ask. My BT878/BTwincap combo does a poor job with the resize to anything less than 368. I don't know if it is the driver or the chip. I know how to find out, but I haven't had time.

There is a reasonable work around. Caping at 368 and triming to 352 with the BTwincap will give a very clear cap, with about a 3% AR error.

[lordsmurf]

336x480 is the nearest "perfect" digital resolution equivalent of a broadcast signal. To get your other number, reverse your algebra equation.

I think I know what you are referring to as "TVL" but don't want to make the wrong assumption. What is the definition of TVL?

I spent long, long headache-filled digusted hours figuring out resolution information and comparing to oscilliscope data and other information from numerous reliable video sources, so I'm pretty confident in the output I have.

[trevlac]

336x480 is the nearest "perfect" digital resolution equivalent of a broadcast signal. To get your other number, reverse your algebra equation.

I really don't wish to argue, and I can appreciate your position. Why believe anything said over the internet?

Here is the most accurate reputable source I can find. Unfortunately, it is not that clear. Bandwidth is also mixed into the discussion.

http://www.maxim-ic.com/appnotes.cfm/appnote_number/750/ln/en

They give 451x483 as the NTSC "digital resolution" in their chart at the bottom. Unfortunately, they don't show DV/DVD at 4:3. The first DTV is the DVB you mentioned above (640x480). Then next is DVD but at 16:9 AR. Don't be fooled by the "Total Horizontal Pixels" row. This is the total scan line including signal sync. The active part is what matters.

I'd be happy to discuss this. However, feel free to just ignore me. I really do think the help you give to people here is great. This point hardly matters for most crappy TVs. Mine included.


Edit: I just thought of a good clear source !
Go here http://www.dvddemystified.com/glossary.html
look for "lines of horizontal resolution ". VHS, NTSC, and DVD are compared side by side. 352 is about half of 720 or ~ 260 in the comparison.

[lordsmurf]

I'll add it to the list of things to double-check. Again, when I can actually find time.

Either way, 336 or 260, the optimal capture resolution to retain all data is 352x480, given that the hardware and software can adequately function at this size.

And I think our disagreement lies in the difference between playback and source, whereas the 4:3 info you quote only comes into affect when viewed, which would be separate altogether from the data that is being sent to it. I think I've had this discussion (not argument ) before, but with difference words.

The played-back 720 may be 540 or the played back 335 may be 260, but we're dealing with source, the step before playback, hence the "TVL" becomes a moot point during the source phase (only important in terms of playback).

[trevlac]

@lordsmurf

I'm glad you view this as a discussion. I don't want to prove anything. I however do really love this hobby. This includes discussing such things and learning.

My position can be summed up as: there are 2 measurements TVL & Pixels. In comparing (horizontal luma) resolution of a source one must compare TVL to TVL or Pixel to Pixel. For digital, pixels are often used. For analog, TVL is used. The chart below is a simple compare/translation of the max resolutions:

Format        TVL        Pixel
------------------------------
DVD D1        540        720
PAL           400        533
NTSC          330        440
DVD HHR       264        352
VHS           240        320

My conclusion would be that 352 is not enough to capture the max for NTSC. The max may be limited by anything in the 'filming' broadcast and playback of the video. This includes CATV bandwidth, cables/connectors/switchs used in your home, and your TV. In the case that the system bandwidth was limited to less than the max before resizing to 352 (or on the playback of 704 source), the difference may not be noticable.


Edit: BTW, chroma resolution is a different chart. For B&W (luma), ignoring vertical is ok because all formats above are the same (w/in NTSC and PAL). 480 or 576. For NTSC chroma, DVD has almost 4 times the horizontal resolution of (analog) broadcast, but it actually only has 1/2 the vertical resolution of NTSC broadcast.

[lordsmurf]

I'm guessing "TVL" mean "tv lines". I choose to not use the words 'horizonal' and 'vertical' anymore because of the confusion that follows them.

Format        TVL        Pixel 
------------------------------ 
DVD D1        540        720 
NTSC          252        336 
DVD HHR       264        352 
VHS           165-180    220-240

DVD D1 is often quoted as 500 and 525 also.
VHS range from 200-240 according to VCR makers.
S-VHS is from 400-450 according to VCR makers.
I quit paying attention to company product specs, they have no idea what they're talking about. And there's no universal measurement system.

The Half-D1 and NTSC broadcast, on oscilliscopes, represents nearest neighbors. And VHS is a far cry from the other resolutions. And again, the source (pixel) and playback (TVL) info is separate from one another, no relationships.

I also believe your PAL numbers reflect PAL S-VHS, not PAL broadcast. They're way too high.

And most tv's can only pickup 300-500 pixels. That'd be lower numbers by TVL.

The biggest catch between low res on digital vs analog is analog low res gets blurry, where digital low res gets macro-blocky. Some of these differences can be seen by the naked eye on a good large clear tv set.

[EwanG]

At the risk of confusing the issue (as opposed to already confused myself), what should I be using when I capture DV with my Canopus ADVC-100 using DVApp? I'd been capturing at 720x480, but am now wondering if that's really the best option?

Thanks,
Ewan

[trevlac]

(NTSC 336)
VHS range from 200-240 according to VCR makers.
S-VHS is from 400-450 according to VCR makers.
...
And again, the source (pixel) and playback (TVL) info is separate from one another, no relationships.

These are our main disagreements. Analog sources are given as TV Lines of Horizontal Luma Resolution. You should work digital pixel backwards to this. Since you don't give a source I will:

lines of horizontal resolution
Sometimes abbreviated as TVL (TV lines) or LoHR. A common but subjective measurement of the visually resolvable horizontal detail of an analog video system, measured in half-cycles per picture height. Each cycle is a pair of vertical lines, one black and one white. The measurement is usually made by viewing a test pattern to determine where the black and white lines blur into gray. The resolution of VHS video is commonly gauged at 240 lines of horizontal resolution, broadcast video at 330, laserdisc at 425, and DVD at 500 to 540. Because the measurement is relative to picture height, the aspect ratio must be taken into account when determining the number of vertical units (roughly equivalent to pixels) that can be displayed across the width of the display. For example, an aspect ratio of 1.33 multiplied by 540 gives 720 pixels.

This matches back to my numbers.
VHS = 240 TVL
NTSC = 330 TVL
SVHS = 425 TVL
DVD D1 = 500-540 TVL

It also gives you the calculation to get half D1 TVL (From pixels). 352/1.33 = 264.


As far as source and playback having no relationship to each other, I can't see how you can even think that is logical. The basic relationship is TVL = Horizontal Pixels / AR.

What would it take to convice you? More sources? If you could provide me with 1 (reaonable) source that backs your numbers, I would be happy to go back to the drawing board. However, I can't base my learning on some numbers thrown around.

This is my hobby, not my profession. I may be way off base, but I doubt it.


Here is another quote for your pleasure. It is from a clear explination of the subject by a professional director of photography. There is more info than my quote. It is well worth the read.

"Lines of resolution" may ultimately be replaced by a true pixel count when referring to resolution in the future (especially in all-digital systems). In the future, as digital technology becomes much more uniform across manufacturers, the main difference in overall resolution of future video system will be more or less directly related to true pixel count. So this provides a simpler, more definite point of comparison, and therefore might make more sense that using the older "lines of resolution" method. However, "lines of resolution" will remain a technically more accurate measurement, as it takes the whole system into account.

For example, since the current DVD format has 720 horizontal pixels (on both NTSC and PAL discs), the true horizontal resolution can be calculated by dividing 720 by 1.33 (for a 4:3 aspect ratio) to get 540 lines. (On a 1.78 [16:9] display, you get 405 lines) In practice, most DVD players provide about 500 lines instead of 540 because of filtering and low-quality digital-to-analog converters.

[erratic]

At the risk of confusing the issue (as opposed to already confused myself), what should I be using when I capture DV with my Canopus ADVC-100 using DVApp? I'd been capturing at 720x480, but am now wondering if that's really the best option?

DV is always 720x480 (NTSC) or 720x576 (PAL). DV converters like the Canopus ADVC-100 capture 720x480 and 720x576 correctly AFAIK.

[trevlac]

At the risk of confusing the issue (as opposed to already confused myself), what should I be using when I capture DV with my Canopus ADVC-100 using DVApp? I'd been capturing at 720x480, but am now wondering if that's really the best option?

I've not used DVApp. But is there an option? As far as I know, DV is 720x480 for NTSC. If it was any other size, it would not be DV.

BTW: It is worth learning about chroma resolution of NTSC DV. It is actually lower than an analog cap which lets you choose a different codec than DV.

Edit: erratic was too fast for me. I sound like an echo.