VHS tests show lines in video?

[guyburns]

This thread follows on from my previous thread about testing. Before presenting the final results, I will probably have several questions to help me analyse the results. So as to prevent bias, I have not indicated how these captures were obtained, as suggested by aramkolt in my previous thread:

Quote:

Originally Posted by aramkolt

The true test I think would be to post unlabeled samples of different popular and some less popular chains all using the same starting VCR/tape and have people determine for themselves what is visually the best to them so that any bias on equipment choice is removed.

Attached are six images: three images taken from two different captures...
Video 9a
Video 9b
Video 9c
Video 11a
Video 11b
Video 11c

Ques 1
Why are there horizontal black lines through the letters of Video 9a, but not Video 11a? What could be the cause?
The "b" & "c" captures do not show such lines.

[lordsmurf]

That's not lines, that's interlace.
It's expected, desired, proper. It's not an error, nor a problem.

[guyburns]

More questions, then, about that interlacing. I want to understand all the imperfections in these captures as well as I can.

Ques 2
Because Video 11a does not show the interlacing, I assume that means it is an inferior capture. Correct?

Ques 3
What explains the fact that the letters in 9a are two fields higher than 11a? The letters are actually taller. Is this another indication that Video 11a is inferior, that the extra height has been blurred away?

Ques 4
The specs I saw on one VCR player, stated that the vertical resolution was 200 lines. A better player, I think, stated 250 lines. If that's the case, how can any capture from a VCR display 576 lines*?

Is it like that 1975 song from Pilot: "Ho ho ho it's magic"?

* I measured the fields in Video 9a using a ruler in Photoshop – at 500% magnification, each capital letter was 34 fields high. Then I zoomed out, measured again, and extrapolated. There are approximately 560 fields in Video 9a, so we can say 576.

[lordsmurf]

2. Interlaced is state of being. Interlacing lines do not always appear unless motion reveals it.

3. All you attached were images. So no idea. Multiple potential reasons, everything from timing differences in capture, to jitter, to other reasons. Not many details to go on here.

4. "lines" is an analog term, nothing to do with digital. VHS lines are set at 240, which is essentially ~352x in digital terms. (As in 352x480. In the old days, people confused "240 lines" with the wrong axis of x240, as in 352x240 VCDs.) Those are NTSC numbers, PAL is slightly different.

[aramkolt]

Hmm. For the actual quality test - You might consider capturing test patterns (which I believe some contain motion) from something like the "Video essentials" DVD which is widely available online for $5 shipped: https://www.ebay.com/itm/275960861497

Using a DVD will give you a very stable signal to capture and that will tell you what the quality will look like from an "ideal" source. You'd later want to see what happens when you have a VHS source instead, so record those DVD test patterns to a VHS tape and then try capturing the VHS tape with the same setup. There will absolutely be some quality loss when recording and playing back, but you can compare to see which card gives the most stable and best quality image from the same VHS.

Reason I like the Video Essentials DVD is that it is cheap, widely available, and will likely show you some artifacts and color issues that you might not see with most regular tape footage. That, and since it is widely available, other users can capture the same thing and post to show if they got better results capturing from DVD than you did with the capture chains that you are testing.

Ideally you'd want to post short video clips if it's just a few seconds, that way we can determine if you are getting clipped while levels or if there are interlacing capturing issues. Screenshots are also fine to show how detail is, but video files will always give more information.

I'll post some captures from my Video Essentials DVD once I see some of yours if you want to compare.

I believe the pattern with motion that can show a lot of defects at once is this one from snell and Wilcox and I'm pretty sure it is on the Video Essentials DVD as well:
https://www.youtube.com/watch?v=ObtBIBuqiWU

[Gary34]

You should go read the entire guide on this site. It you are having questions like what interlacing is then you well learn a lot from reading the guide.

[guyburns]

Thanks for the responses. Two were two problems:

1. I had confused the stated horizontal resolution (250 for my PAL player) with the number of horizontal lines. So, thinking that my tapes only had 250 horizontal lines, I couldn't explain how it could resolve 576 fields, the interlacing.
2. Another problem was that Premiere stated the file was P, progressive. Yet it was showing interlacing in the timeline. That confused me even more.

Anyway, all that's now sorted out. My player has a resolution of 250 x 576 and I can't trust Premiere to tell me whether a file is Progressive or Interlaced.

This thread can now come to an end.

[traal]

250 lines of luma resolution (lines per picture height) is about 333 pixels across (250x4/3). So that makes it 333 x 576. But you should capture at at least double the horizontal analog resolution to get all the detail from the source, so 666+ x 576. Therefore, 720 x 576 is good.

[dpalomaki]

Consider MEDIAINFO software to report video file details.

NTSC VHS was generally considered to provide about 240 lines of horizontal (B&W) resolution, and on a good day perhaps 50 lines of color resolution. S-VHS increased the B&W to about 400 lines and left the color the same. MiniDV bumped the B&W to ~500 lines, and color to about 120 lines with 8-bit color depth but added compression artifacts. NTSC broadcast was perhaps 330 lines of B&W and maybe 80 lines of color.