Hallo > > > If you're in a 625line (usually "PAL") video country then VHS has > > > 576 active (vertical) lines in 2 fields just like TV and DVDs. > > > > > > VHS does lack resolution though since it effectively only has 200 > > > or so horizontal lines. > > I still have not found any reliable resource which tells about the > > limitations and real resolutions of a VCR. > That's because a real VCR is a pure analog device, so there is not > really a "resolution" concept as we think of "resolution" in the > digital world. But most people are trying to get that analog information back into something digital.
When you have only 2MHz of bandwith, you cannot have a chessboard of white/black pixles and in each row 360 white annd 360 Black pixles for PAL. The voltage level has to raise and fall. And with 2MHZ of bandwith you don't have the slew rate to acomplish that. > > The best thing I have found by now is that the video bandwith of a > > VCR is limited to 2MHz. Normal PAL has 5MHz. So calcualting back > > this would mean that VCD "samples" every 0,125us one point, which > > is close to the halfe amount of samples that PAL (every 0,067us) > > has. > Except that for a VCR, there's no sampling either. So we have only voltage levels, that sound like a VCR is able to store a unlimited number of colors. Now I would want to kown when I generate a certain color (with a pattern generator) with a very exact voltage level. How exact will the voltage be when the VCR reads the information from tape ? BTW: That does mean that if we have only one color in the Video line it really makes sense to capture at the full resolution ;) > > So that would mean that VCR should be able to recognize and play > > back 360 different points per video line. > The number you derived is a number that was sometimes quoted for > theoretical resolution on a VCR, so if it were a digital device, that > would be a close approximation. However, other factors, such as head > wear, circuit drift, tape quality, can all impact the amount of > signal that is recorded on, and read from, the tape. I know that things are always worse than the theortic calculation. Can you tell me or point to the information where the have defined these parameters ? > > The other thing is how exact they sample every point (6 or 8 Bit). > No sampling, no 6 or 8 bits. They don't work that way (well, at > least all the analog one's do not). But you will have in the analog world something like bandwith, and with a certain bandwith you can store a certain amount of information. It is a differnet question how exact you store that information. And read it again. > > And how they store every point. I have no information about that. > > And that is very important for the quality too. > It's not stored as "points", but as analog waveforms. The processing > cirucity in the vcr splits the broadcast signal into color and luma > signal components. The color components are low pass filtered (in > the digital world this would be a resolution reduction), and then > downconverted to a lower frequency carrier and recorded directly onto > the tape. The luma component is low pass filtered (another > resolution reduction), and the filtered result modulates an FM > carrier that is chosen so that when recorded with lower vestigal > sideband there's a limited amount of controlled interference between > the luma component and the color subcarrier on the tape. Then the > two signals are mixed together and recorded directly onto the tape. Do you know how much bandwith is "lost" ? That is the information I'm seeking. > > So still no final VCR reference, and guidlines. But I think > > recording at a resolution of 720x576 (PAL) is charming for a VCD, > > but not for a S-VCD. Recording at 352x576 or even 352x288 would be > > something that is really worth thinking about, unless you have too > > much free space on your HD's ;) > In any case, the simple answer becomes that if he's coming off a > consumer grade VCR, either VHS or Beta, his digital capture board > will be capable of capturing far more signal quality than his VCR is > capable of reproducing. Sadly, he will also capture all the noise > that results from the recording process, and may even have sync > issues because VCR's play fast and loose with the timing specs I would say that they are saving money for themselve, because the cheper design costs them less. And leaves more money in their own bag. > because TV's are very forgiving and playing fast and loose with the > timing allowed for a much simpler design (read as "an affordable > design"). TV design was done in the 1950. At that time a resistor was expensive ;) And you checked a transistor if it was full damaged or partially usable. None does that now, if you suspect the part to be damaged you throw it away without a second thought. The is one german saying when you measure things in the analog world that says: Wer misst, misst Mist. And it has ALWAYS been correct by now. auf hoffentlich bald, Berni the Chaos of Woodquarter Email: [EMAIL PROTECTED] www: http://www.lysator.liu.se/~gz/bernhard ------------------------------------------------------- This SF.Net email is sponsored by: YOU BE THE JUDGE. Be one of 170 Project Admins to receive an Apple iPod Mini FREE for your judgement on who ports your project to Linux PPC the best. Sponsored by IBM. Deadline: Sept. 24. Go here: http://sf.net/ppc_contest.php _______________________________________________ Mjpeg-users mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/mjpeg-users
