Announcement

**DarrenD** · 11 November 2003, 06:14

I have that as well. It seems to be a fault somewhere in the capture driver (I think).

I asked this question before. The answer I got was that if you're capture is going to be displayed on a TV then do not worry about it as you cannot see the full picture on a TV (the outer edges are off-screen). If you're capture is going to be displayed on a monitor then you will see it. You might want to crop the black edge (probably doing the same to the right hand side as well). Than you might want to get rid of noise at the bottom (cropping the same at the top).

If you do crop then you want to make sure your final output is not resized as this will affect quality, you simply want to have the edges deleted/made black. To check this I would create your output file and load it back into Virtual Dub and just check.

Here is my original thread (search for "Black strip down left hand side") or click here http://forums.murc.ws/showthread.php?s=&threadid=38270 (hope it works).

**Petr** · 13 November 2003, 04:40

I very thank for your answer, but I have still doubts about. . .

If you want adjust picture aspect ratio 4:3, you must at clipping bargain for it - for example in video capture at resolution 704x576 points, is for readjustment aspect ratio 4:3 suitable cut picture up and down about 30 line, left and on the right then about 8 point, whereby reach at display desktop matching what you see on TV set resolution 688x516 point. Is it right?

The 30 lines up and down it sems me lot – large piece picture will be off! By reason of present left vertical black strip I have to remove yet more!

The alternative is don't clip picture at all and leave two black stripes at the sides picture (for keepeng aspect ratio 4:3 – resize to 640x480 or 512x384, check keep aspect ratio in Virtual Dub).

Question 1: Will the black stripes at the sides visible on the TV in this second case? (At the desktop PC Monitor, of course yes.)
Question 2: Which one of presented two procedures is correct (accurate)?
Question 3: Why a lot of TV cards has just 704x576, when TV transmissions picture (PAL) in resolution 768x576? Has extent 704 point some logical signification?

Thank you to everyone behind understanding and specification!!!

**DarrenD** · 13 November 2003, 05:46

According to responses from others in my original thread...

The strip on the left and noise at the bottom should not be visible on a TV (overscan is the keyword to seach for), therefore, cropping the picture will not make a difference on a TV (if you can't see the strip/noise you will not see blank[crop]). My idea of cropping top/bottom, left/right in same proportions was just to make it look nice and centred on a PC.

The questions I asked were originally to do with MPEG-2 has a bit-rate per frame so could it compress the cropped black areas better than the strip/noise. If it could then that would allow for more bit-rate for the rest of the visible picture and so get better quality home DVDs.

part 2 on next post.....

**DarrenD** · 13 November 2003, 05:47

...from part 1 in previous post

You will want the 688x516 cropped video to be centred in a final video size of 704x576. The extra 8 left/right and 30 top/bottom will be black. By not resizing you will keep the quality and also reduce conversion to MPEG time as it does not need to resize.

For testing purposes (using TMPGENc) you can set the border colour to red. Do a few seconds encoding and satisfy yourself that your 688x516 video is in the middle with a red border all around.

This is just my understanding of the issues and there are more qualified people than me that can highlight my errors.

Please chip in guys if I am wrong as we all need educating!

**Brian Ellis** · 14 November 2003, 00:55

Sorry, guys, you should ignore this black band. This is a normal, integral part of a TV signal.

Before each line starts, there is a synchronisation pulse which tells the TV that "a new line starts now". The TV signal itself is generally 30% (black) to 100% (white) of the voltage and the synch pulse is down to 0% ('blacker than black'). Now TVs have different reaction times to this signal and it also depends on the received signal strength and signal-to-noise ratio. Just after the synch pulse, there is a threshold where the signal stays black for a very short time, to tell the TV where the black level really is. In the case of the vertical synching, there are several lines used with reverse line synching (this is partly why you have only 576 picture lines and not 625 in PAL) and the TV set detects this change and integrates the black level until it triggers the field time base. Again, the moment it does so varies.

Now, TV sets are always designed to make sure that the picture you see never includes the residues from these synch pulses or black thresholds, which may occur on either side and top or bottom. In order to do so, it simply cuts off about 5% of the picture, all round. This invisible area that is cut off is the overscan, and is somewhat unpredictable. For this reason, titling facilities in most NLE software, such as MediaStudio Pro, usually tells you where to place your titles, so that there is no risk that they are cut off by the overscan area.

Cropping the picture to "eliminate" the black areas, which show only on computer screens, is a totally useless exercise. All it does is to cause you to lose even more of your picture to the overscan area AND it therefore degrades your picture quality, as well as increasing your rendering times. Do not do it. You gain nothing, you only lose.

**Dr Mordrid** · 14 November 2003, 09:15

Brian's correct. Leave it alone as it won't show on a TV. Only be concerned with it if you're displaying on computer screen.

Dr. Mordrid

**Patrick** · 17 November 2003, 20:52

But...

Cropping this area is a waste of time, but masking it works out great. When I use TMPGEnc to encode to MPEG, I use a black mask around the perimeter of the whole screen. Gets rid of all kinds of stuff you don't want to see, especially from analog captures. As has already been stated, you don't see the stuff you want to hide (or the mask) when watching on TV, but it will show up on a computer monitor. However, the black mask looks fine while watching video on a computer monitor.

Another benefit of the black mask is that there is less area of "moving" video to be encoded when creating an MPEG file. Therefore, better picture quality. Such a bonus!

**Brian Ellis** · 18 November 2003, 02:35

Patrick

I see your point re the computer screen viewing, but if the DVD is for TV viewing, you could never guarantee whether the mask would fall in the viewable area on any given TV set, as they are all different, unless the mask is only, say, 2 or 3% all round. This is the opposite of the "forbidden area" for titling, where you want to guarantee all the titles to be visible; here, you want the mask to be invisible, which is not the same thing.

I'm curious, if you have, say, 2% mask all round, what is the file size compared with no mask, all other things being equal?

The down side of masking is that AVI rendering time will be increased as the whole project would need to be re-rendered (no smart rendering).

**DarrenD** · 18 November 2003, 06:09

Patrick,

That's what I thought, a mask/crop leaving 688x516 (in Petr's case) would have less information to compress (since the mask should be able to be highly compressed) and hence give better quality of the 688x516 for a given bit-rate.

It is the same principle as why low bit-rates of a video shot with a tripod should be "a lot" better than hand-held shots since most of the background will be stationary with a tripod whereas it will be moving with handheld. If the background is stationary it can be highly compressed giving more bit-rate for the motion parts.

That was the angle I was coming from. My issues with reduced rendering time was that Petr should not resize his 688x516 back up to 704x576. I accept Brian's comments about smart rendering.

**DarrenD** · 18 November 2003, 06:12

Brian

If the source is PICVideo quality 19 captured with AVI_IO and the final video is to be MPEG-2 how does smart render work? Surely the video is all rendered to MPEG-2? I can understand if I am simply cutting parts out and saving back to a PICVideo quality 19 based AVI file that a direct byte-by-byte copy of the raw data is all that is required (except where transitions etc. occur).

**Brian Ellis** · 19 November 2003, 01:45

Darren

Yes, you are right. Smart rendering cannot work when you are changing the project settings, such as when you are creating an MPEG file from an AVI one, but it is a valuable tool when saving work in the same format. Many finish their AVI project (DV or MJPEG) by creating a complete new AVI file after editing and before encoding to MPG. With smart rendering (assuming that there are many parts untouched or that short bits have already been re-rendered when viewing during editing, this usually takes only a very small fraction of the play time of the project. I recently did a 75 minute project of a UN mission in Viet Nam and the final DV AVI rendering took only 9.5 minutes, including all the titles, filtered bits, transitions, added sound etc. Well worth while, as I had to produce VHS tapes, as well as DVD, in both NTSC and PAL, so this file became my master.

**DarrenD** · 19 November 2003, 05:51

Brian

I have a few Hi-8 tapes captured on my PC using my Matrox G400-TV Marvel, AV_IO, PICVideo quality 19. The rest of my VHS, 8mm and Hi-8 tapes will be put onto the PC through the AV pass-through on my new Digital camcorder (finally got one - Canon MV600i). All new stuff will obviously be on DV tape.

My aim is to edit the stuff using MS Pro 7 VE (just arrived 2 days ago) and author using DVD Workshop 1.3 SE onto DVD. My disc space is one IBM GX120-80Gb and one Hitachi GX180-60Gb drives.

I am only a humble home user doing camcordering of my kids (currently 17 x 3-hour VHS tapes [already edited], 10 x 8/Hi-8mm tapes [waiting to be edited]). I want them all on DVD eventually. Whilst my camcorder is DV-in/out I don't really intend using that feature (famous last words) hence my apparent dismissal of smart render.

Thanks for sharing your knowledge.

**Petr** · 20 November 2003, 06:38

I thank all for suggestive ideas, especially Brian Ellis for understanding. . .
I have searched for some specifications any farther, related with original question.

Taken from http://www.doom9.org/index.html?/aspectratios.htm :

"In 625-line television systems (PAL) sampled to ITU-R BT.601-5, only the central 702 luminance samples (and corresponding
chrominance samples) of the digital active line are used to carry the active picture. (In your captures, the remaining samples will be black.)

704/720/768x576 (Full PAL) = High Quality
In case your capture card performs horizontal scaling the resizing process is very simple: don't crop, and resize to a 4:3 format (like 640x480). If you want to use FitCD and GKnot to determine your resize settings, it becomes more difficult. If you captured at 720x576, you have to use a generic PAR (Pixel Aspect Ratio). They are listed in the following table:

capturing: horizontal scaling generic PAR:
704x576 12/11 (accepting a small error, use PAR = 1/1)
720x576 48/45
768x576 1/1

In case your capture card is ITU compliant the resizing process becomes more difficult. Der Karl's calculations (Der Karl's Aspect Ratio for Dummies) give us a result of approx. 702 (active, horizontal) pixels for the right resolution, which gives us a PAR of 128/117 (note that 768/702 = 128/117). It's outside the scope of this guide to explain this in detail here. It follows that if you captured at 704x576 or 768x576 you can resize directly to a 4:3 format (like 640x480). If you captured at 720x576, it implies that you have to crop the overscan away (ending with 704x576) and resize to a 4:3 format (like 640x480).

If you want to use FitCD and GKnot to determine your resize settings, the PAR's are given in the following table: (see link)

There are two ways to get rid of the horizontal black borders (in case your capture contains them as is often the case). The easiest is to crop overscan and resize first, and then crop away the horizontal black borders. Note that your final clip will not be 4:3 anymore. The hardest way is to crop away the horizontal black borders first, and then resize to a correct format.
If you want to do this correct, you have to use the appropriate PAR's. Since the first method is much easier and you will not have much black borders anyway, I suggest to use the first method. . ."

Final resume (to my mind): The Vertical black strip left isn't at the expense of picture - the capture card only varies horizontal scale (see above) it is possible directly resize on Letterbox for example 640x480. . .If I want create e.g . DivX in finale.
The fact, that vertical strip "extend further to the picture", than is overscan area, it's due to "different reaction times to synch pulse signal (and the following treshold) and it also depends on the received signal strength and signal-to-noise ratio", I think, how Brian explained me - thanks once more!

If I ll want to create DVD, it will most probably necessary leave the picture how it is, i.e. 704x576 and set the Letterbox 4:3 in TMPGENC.

Have you any qualifications or correction?

Thanks so much!!!

Petr (Czech Republic)

**Petr** · 20 November 2003, 06:49

Oh sorry. My link is wrong!

Correction: http://www.doom9.org/capture/preface.html

Announcement

Matrox Rainbow Runner: Black vertical strip after capture in Virtual Dub

Matrox Rainbow Runner: Black vertical strip after capture in Virtual Dub

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment