What resolution to use for capturing Hi8 and Video8 camcorder tapes

[djenyc]

I have a few home videos on Video8 and Hi8 tapes that I want to convert to digital format before I get rid of my old analog camcorder (Sony Handycam CCD TR101). I'll be using LeadTek video capture card that can capture at either 320x240 or 640x480 resolution (60fps interlaced contents is being captured at 30fps with each frame containing both fields).

I found somewhere online that Hi8 has 420 vertical lines and Video8 has 240. So should I be capturing Video8 tapes at 240x320 30fps interlaced and Hi8 at 640x480 30fps? I'm asking, because I'm not sure if Video8 spec refers to 240 lines at 30fps or 60fps.

Thanks

[smok3]

no, always capture at full-res, that is 640x480.

[djenyc]

smok3, does your advice for capturing at 640x480 applies to Hi8 or to Video8 or for both?
I've read in a couple guides that Video8 has 240 horizontal lines, so wouldn't it makes sense to capture it at 320x240?

Thanks
Ross

[smok3]

both, if you do some searching around this forum you will quickly realize why (something to do with interlacing, and why even crappy formats need a way to store the full vertical resolution)

quote from 1st google hit http://hometheater.about.com/cs/television/a/aavideoresa.htm
The number of scan lines, or vertical resolution, of NTSC/PAL/SECAM are constant in that all analog video recording and display equipment conforms to the above standards. However, in addition to vertical scan lines, the amount of dots displayed within each line on the screen contributes to a factor known as horizontal resolution which can vary depending on both the ability of a video recording/playback device to record the dots and the ability of a video monitor to display dots on a screen.

(ok, it is not really about dots, that should be explained using frequency i believe)

so with some simplification you can assume that your video8 is like 240x480 (if you are in the NTSC land).

[djenyc]

smok3 thanks, I think I get it:
If my source (ege Video8) is half the NTSC resolution, the camera will up-converted it to NTSC resolution that is fixed at 480 interlaced vertical lines. So, when I ask my capture card to capture 240 vertical lines, the capture card will throw out second interlaced field, and I'll loose half the information and end up with progressive contents with 240 vertical line, but containing only 120 vertical lines from original source.

So what I'll need to do is capture Video8 at 640x480 interlaced and then resize to 320x240 interlaced. Is that right?

Thanks
Ross

[scharfis_brain]

no, you are completely wrong.

every analogue standard (besides some exotic formats maybe) will record FULL 480 (or 576) pixels.
But any analogue standard will introduce some minor or major bandwidth limitation, which itself will introduce a horizontal blur of the video.
this blur represents the analogue video resolution, which is misleadingly counted in lines. these lines are alternating black and white VERTICAL bars. the mor vertical bars can be retained the better the video bandwidth and thus crispness.
vhs and video8 can store up to 240 vertical lines at full vertical resolution of 480 (NTSC) or 576 (PAL) pixels.
so you should at least capture the video at 480x480 / 480x576 pixels.
but it generally is recommended to capute at full D1 resultuions like 704x480 or 704x576.
every attemt to reduce the vertical resultion from 480 or 576 to something lesser will introduce a more blurry image

[djenyc]

scharfis_brain, I got vertical and horizontal lines confused in my previous post, sorry for the confusion

So, as I understand - in analog source there are no vertical lines, but a fixed number of horizontal lines. Output of NTSC device will always be 480 horizontal lines (+ sync lines). But, from what I gather while reading guides, most tape sources have lower number of horizontal lines (e.g. 240 for Video8 and VHS, 440 for Hi8), so camera must perform up-sampling of vertical resolution (increase number of horizontal lines) to conform to NTSC spec. Is that correct?

Thanks
Ross

[scharfis_brain]

the analogue resolution is limited by the bandwidth of you media.
everything that count in analogue is phase and frequency. there are NO pixels!

This means there is NO sampling at all in analogue domain.
sampling is done in your capture card.

[JohnnyMalaria]

Each horizontal line (of which there are ALWAYS 480 or 576 - NTSC or PAL) is just an analog signal. The higher the quality of the recording technology, the higher the frequency response. VHS/Video8 are like speakers without tweeters. SVHS/Hi8 are like full range speakers. The "vertical lines" measurement is similar to the highest frequency the speakers can reproduce. In visual terms, it's how sharp the image is.

With VHS/Video you can get away with capturing at half the horizontal resolution (e.g., 320 x 480) because you are still capturing above the "vertical lines" figure. For Hi8 you need the full resolution. It's a bit like capturing audio - the high the sampling rate, the better the results. If you sample a CD at 32kHz you'll get a somewhat muddier sound compared to the original 44.1kHz. If you sample it at 96kHz, you'll get a great sound but waste a lot of space.

[djenyc]

the analogue resolution is limited by the bandwidth of you media.
everything that count in analogue is phase and frequency. there are NO pixels!

This means there is NO sampling at all in analogue domain.
sampling is done in your capture card.

scharfis, I understand that horizontal resolution of analog video is defined in terms bandwiths and sampling rate at Nyquist frequency.

For vertical resolution, I think there is as fixed number of horizontal lines being drawn on the screen (480 for NTSC) and also a fixed number of horizontal lines being recorded on tape (varies depending on source), so playback device must be doing up-conversion.

Please let me know if I didn't get it right.

[scharfis_brain]

there simply is no up-conversion and I don't know what you mean either...

[djenyc]

scharfis_brain - I'm just basing my reasoning on what I've read in video capture guide posted on this site. Don't know if I'm interpreting it correctly.

If Video8 format source tape has a fixed number of horizontal lines (240?), and video capture card is expecting a fixed number of horizontal lines (480+sync lines - NTSC spec). So camcorder during playback must be converting that 240 scan-lines source to 480 scan-lines NTSC signal.

[scharfis_brain]

all video format have a fixed amount of scanlines. 480 for NTSC and 576 for PAL. nothing will change that.

what varies from format to format is the amount of information that can be stored within ONE scanline.

[2Bdecided]

Analogue video doesn't have horizontal pixels. It just has information that, in the case of VHS and video8, is so blurry that it can be completely and accurately represented by 320 pixels.

Assuming you're going to put it on a DVD, I've never seen much point in working at less than 720x480 (or 704x480, or 720x576, or 704x576) - I know you can put half horizontal resolution formats (e.g. 360x480) onto DVD, but not all DVD authoring software supports them, and you never know what the DVD player or playback software will do with them (interpolate the samples smoothly to give the original smooth image, or just duplicate pixels to give a blocky looking image?). You might as well work at 720x480 throughout, unless you want to cram so many hours onto a DVD that 360x480 is needed to get the bitrate down.

Cheers,
David.

[JohnnyMalaria]

djenync - consider my audio analogy earlier. A video frame is like a 480-track tape recorder. There are always 480 tracks but the quality of each track may vary - less or more high frequencies. No matter how crummy the recording, there are always 480 tracks. The "240 lines" for Video8 has nothing to do with the number of tracks. It is an indication of the clarity or muddiness of each track. e.g., "240 lines" would be akin to 24kHz, "520 lines" equivalent to 52kHz etc. Whether you have a downconverted HD signal from a satellite receiver, a DV camcorder, an ancient 1980's VHS deck or a $20 black-and-white security camera from Wal-Mart, they all pump out 480 lines every frame.

Bottom line, use 640 x 480 for you case since your only other option will throw away too much detail.

[djenyc]

JohnnyMalaria, thanks for the explanation. I think I'll do capture at 640x480

Bdecided - no plans for DVD, I'll just capture and keep it in some lossless codec like Huffyuv or Lagarith till I decide to do something with it, which could be 10 years from now. The only reason I want convert it to digital now, is because I want to get rid of the camcorder.