Where does "great" quality start with horizontal resolution for vhs capture?

[aabxx]

As I've understood it, VHS has horizontally not a defined amount of lines. But how much pixels are really needed to get a "great" picture? With that I ask how many pixels represent a very good appromixation of the quality of the horizontal resolution of vhs?

Obviously 10 horizontal pixels would destroy the pictures. But where approximately is the limit where there is very little to gain by going higher? 300 pixels? 500? etc. I've seen 480 quoted before, why exactly 480?

Thanks for any answers :)

[rfmmars]

As I've understood it, VHS has horizontally not a defined amount of lines. But how much pixels are really needed to get a "great" picture? With that I ask how many pixels represent a very good appromixation of the quality of the horizontal resolution of vhs?

Obviously 10 horizontal pixels would destroy the pictures. But where approximately is the limit where there is very little to gain by going higher? 300 pixels? 500? etc. I've seen 480 quoted before, why exactly 480?

Thanks for any answers :)

Figure 80 lines for each MHZ of video bandwidth your device is able to output. So s-video could provide up to six mhz, so that would give you 480 line of resolution. Don't confuse this 480 with the fixed 480 vertical resolution.

So on an adverage of 3.2 mhz lum. (80 x 3.2)use 640x480 just to be safe for VHS or 720x480 for NTSC

Richard
photorecall.net

[Awatef]

Well, 480 is indeed sufficient for VHS sources. Why exactly 480? VHS has roughly 320 lines horizontal resolution, and there is a thumb rule, saying that you need x1.5 of the actual resolution to get all the details, that's why 480 are recommended while capturing. Of course you can then resize to 352 and still retain most details (if you plan a half-D1 DVD with up to 4 hours, which is the most suitable format for VHS sources).
As for S-VHS sources which have roughly 400 lines horizontal resolution, you guessed, at least 600 resolution is needed. Here you better go all the way up to 704 or 720 and encode to full-D1 DVD without having to resize (up to 2 hours per DVD).

[aabxx]

"VHS has roughly 320 lines horizontal resolution, and there is a thumb rule, saying that you need x1.5 of the actual resolution to get all the details, that's why 480 are recommended while capturing. Of course you can then resize to 352 and still retain most details (if you plan a half-D1 DVD with up to 4 hours, which is the most suitable format for VHS sources)."

First of all I thought there were no lines when it comes horizontal vhs resolution.

Second of all, what you said next makes little sense as capturing to 480 and then resizing to 352 is double-resizing, considering your card will already have done an internal resize when giving you 480 pixels. Capturing straight to 352 would give a very similar quality, if all the details can be retained in that resolution.

[smok3]

aabxx; card wont resize, it will just sample N pixels / line afaik.

also there are no lines not just with vhs but basically with every analog format.

[Awatef]

I don't understand you anymore, you ask a question, then criticize the answer?? :confused:
What is the point in asking if you're going to nullify my answer?!

Concerning the "lines": you called them pixel, I called them lines, 'cause VHS is an analog format, not a digital one, so there is no way I would use the word "pixel".

I want here to correct something. The number of h. lines of VHS is not 320 but 240 (roughly) [I would have accepted your critic if it was about this specific point!] Theoretically 360 would be sufficient, but one goes the next step (480) to be completely sure that everything gets into the net.

About resizing: Your capture card doesn't resize while capturing. The input is analog and gets digitized. The higher the resolution, the more details you'll get (exactly like a scanner would do with a photograph - it does not resize it!). For VHS, beyond 480x480 for NTSC or 480x576 for PAL there's nothing to gain. When you then resize to 352, the detail loss will be minimal, since a lot of details are well defined in the original capture, you're just fitting the details into a tighter frame.
If you're still not confortable with that, then go ahead and capture in full-D1 and transfer to full-D1 DVD and get happy with just 2 hours per DVD.

Hope you're satisfied with the answer now :p

[jggimi]

Two comments must be interjected here, for clarification and for control.
Clarification: Analog video ineed has "lines" -- since there is confusion on this point, please see Capture Guide Chapter 3 (http://www.doom9.org/index.html?/capture.htm).
Control: "I can turn this car around if you don't settle down back there, kids!" Keep this friendly. Re-read Rule #4 (http://forum.doom9.org/forum-rules.htm).
Thank you.

[Wilbert]

@aabxx,

First of all I thought there were no lines when it comes horizontal vhs resolution.

smok3 is correct in the sense that the lines are not "physically" present in the signal. It is just an artificial measure. More about it can be found in the analog capture guide: http://www.doom9.org/index.html?/capture/introduction.html

[setarip_old]

@aabxx

Hi!

You might find the following articles helpful:

http://www.divx-digest.com/articles/vhs_capture.html

http://www.divx-digest.com/articles/vhs_capture2.html

[Wilbert]

About the divx-digest.com links:

Capturing at a resolution of 512x384 at 29.967fps will get both fields
Yeah right.

[Chainmax]

aabxx; card wont resize, it will just sample N pixels / line afaik.
...


I've been thinking about that too, why don't, say, NTSC people capture at something like 1280x960? Since more is being sampled from the analogue signal, the capture should look more detailed, right?

[check]

it would, but the original image does not have a fidelity high enough to warrant it. You will just be capturing blur more accurately rather than capturing more detail :)

[AVIL]

Hi all,

IMHO at capture of an analog signal, greater sample rate means better fidelity of capture. I capture at max resolution of hardware (no software interpolation). In my case (PAL footage) 768 x 576. But I have never tested captures at different resolutions. In doubt, a visual test of quality can help.