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07-16-2021, 12:04 AM
vhsnewb vhsnewb is offline
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I'm working on a project to digitize my family's collection of random tapes full of giant quantities of TV, but peppered with little bits of my siblings and I goofing around with the camcorder. Here's my setup:

JVC HR-J692U consumer VCR --> Datavideo TBC-1000 --> ATI TV Wonder 600 USB --> Win7 PC w/VirtualDub 1.9.11 & ATI drivers from this forum.

I got the TV Wonder and VirtualDub based on recommendations in this forum and they are new to me. I'm seeing some artifacts in the captured video (see the attachments). It kinds looks like interlacing to my untrained eye, but it's only showing up on every third frame. The images badframe1-720x640.png and badframe2-720x640.png have the artifact, the goodframe-720x640.png image doesn't.

Also, hanging off the TBC, I have a Canopus AVDC110 feeding into an old MacBook running an old version of iMovie. I'm not seeing these artifacts in parallel captures taken at exactly the same time with that equipment, nor I am I seeing them on the TV I have hooked up. badframe1-canopus.png and badframe2-canopus.png correspond to the two badframe images from the TV Wonder.

That makes me think this is a problem with the TV Wonder or VirtualDub. What is this kind of artifact called?
What exactly is going on? Are there any settings I can tweak to fix this?

----

Also, on a completely unrelated note, what resolution should I use to capture TV-recorded VHS? On some threads I see strong recommendations to use 720x480, but my impression that's done with an eye towards creating DVDs, because that's a valid DVD resolution. If I'm not planning on making DVDs or Blurays from any of this video, is there any reason I should not capture at 640x480 (which seems to be double the actual VHS resolution, if I'm reading Wikipedia correctly)?


Attached Images
File Type: png badframe1-720x640.png (576.1 KB, 33 downloads)
File Type: png badframe2-720x640.png (576.0 KB, 20 downloads)
File Type: png goodframe-720x640.png (577.2 KB, 22 downloads)
File Type: png badframe1-canopus.png (560.7 KB, 15 downloads)
File Type: png badframe2-canopus.png (560.6 KB, 12 downloads)
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  #2  
07-16-2021, 01:08 AM
latreche34 latreche34 is offline
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Analog video is sampled by the capture card at 720x480 that includes some overscan around the frame as safe margins, The actual video resolution is 704x480 non square pixel after removing the black pillars on the sides, You can resize 704 to 640 for square pixel but there is no need for it anymore, There is no native monitors and/or computers that are limited to this resolution, Computers and TV's can display any resolution nowadays, not only that but 640 may not be compatible with some video codecs.

If you are not capturing at 720x480 the artifact could be related to this.
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  #3  
07-16-2021, 01:37 AM
vhsnewb vhsnewb is offline
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All the captures I posted are at 720x480. That's certainly true of the TV wonder captures where I'm seeing the artifacts.

However it looks like VLC stretched the Canopus captures to 720x540 when it created the png (probably to get the aspect ratio right). Looking at the codec metadata in VLC shows that capture is natively 720x480, however. That's not super relevant since that's not the capture I'm having an issue with, just a comparison.
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  #4  
07-16-2021, 08:27 AM
traal traal is offline
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It could be 3:2 pulldown, or some kind of artifact from the digital processing at the TV station. You're capturing at 29.97 frames per second, right? (If NTSC.)

720 vs. 640 pixels across probably doesn't matter for standard VHS if you don't intend to make a DVD.

I notice some squiggles in the screencaps that would be fixed by a VCR with built in TBC.
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  #5  
07-16-2021, 10:54 AM
vhsnewb vhsnewb is offline
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Quote:
Originally Posted by traal View Post
It could be 3:2 pulldown, or some kind of artifact from the digital processing at the TV station. You're capturing at 29.97 frames per second, right? (If NTSC.)
I'm pretty sure I'm capturing at 29.97 fps (IIRC, that was listed in the bottom corner of the capture window). Also, this capture is of an information channel that was specifically generated for TV, it wasn't a film capture. It sounds like 3:2 pulldown is something about the 24 fps film -> 29.97 TV conversion. I see the artifacts in computer generated section as well in the full motion commercial section.

Could this be a "comb artifact"? Oddly enough, when researching the 704x480 capture resolution suggested by a poster here, I found this:

http://www.digitalfaq.com/guides/vid...d-sources.htm:

Quote:
What is de-interlace? ... The only use gained by de-interlacing is to remove combs on a progressive display that has no access to on-the-fly de-interlacing software or hardware. My biggest pet peeve is people that mindlessly de-interlace interlaced footage....

There are several rules to follow:
  • Always match your source when capturing. This means capture interlaced footage as interlaced. And capture progressive source as progressive.
  • Always match the output device when encoding. This means you should encode for viewing on the desired device. Encode interlaced for viewing on an interlaced viewing device (TV). Encode progressive for viewing on a progressive display (computer monitor). Most people should be capturing and encoding interlaced!
I found this page (https://www.engon.de/audio/vhs4_en.htm) that says:

Quote:
Note: Movies are usually broadcasted at 25 frames per second (25 fps) and with a bit of luck, when grabbing, exactly the two fields that came from an original film frame will be combined in one video frame. However, with a probability of 50%, the two fields of a frame could also originate from adjacent film frames. Therefore, deinterlacing is almost always required as first step.
It has an example before/after image of deinterlacing, and the before looks similar to what I'm seeing (see attached deinterlacing.jpg).

So are these "comb artifacts"? Are there any capture settings I can use to make this better, or is it just a fact of life?

Quote:
Originally Posted by traal View Post
720 vs. 640 pixels across probably doesn't matter for standard VHS if you don't intend to make a DVD.
After a bit more research, I found this about "Analog Source Resolutions":

http://www.digitalfaq.com/guides/vid...d-sources.htm:

Format:Analog Measurement:Digital Equivalent:Audio and Other Info:Suggested Capture Size:
Broadcast antenna television and analog cableUp to 4.2 MHz, drop-frame 60hz power cycle, 300-340 lines of resolution, interlaced350x480 to 400x480 interlaced29.97fps NTSC, audio approximately 44.1kHz, 4:2:2 sampling352x480
...    
VHSUp to 3.0 Mhz (very weak), 240 lines of resolution, interlaced250x480 to 300x480 interlaced29.97fps NTSC, HiFi audio about 44.1kHz, 4:2:2 sampling352x480

That table only has "suggested capture sizes" of 704x480 and 720x480 for higher quality sources than I have (regular VHS recorded on consumer grade equipment, not SVHS or digital).

So is 640x480 a weird middle resolution for VHS? It seems like I should capture at 352x480 OR 702x480? 702x480 has some appeal because it seems like its an integer multiple of the native VHS resolution on both axes, while 352x480 only doubles one.

Quote:
Originally Posted by traal View Post
I notice some squiggles in the screencaps that would be fixed by a VCR with built in TBC.
Is that the difference between the "line-based TBC" and "full frame TBC"? IIRC, the TBC-1000 is the latter and was active in this capture.


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File Type: jpg deinterlacing.jpg (60.2 KB, 3 downloads)
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  #6  
07-16-2021, 02:47 PM
traal traal is offline
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Quote:
Originally Posted by vhsnewb View Post
I see the artifacts in computer generated section as well in the full motion commercial section.
In the computer generated section, was there movement at the time of the artifacts? Was the text scrolling?

Quote:
Originally Posted by vhsnewb View Post
Are there any capture settings I can use to make this better, or is it just a fact of life?
You'll get interlacing like that during capture. Then you can decide whether to deinterlace or detelecine depending on the source (video or film) or just keep it interlaced if you only plan to view it on an analog TV.

Quote:
Originally Posted by vhsnewb View Post
So is 640x480 a weird middle resolution for VHS? It seems like I should capture at 352x480 OR 702x480? 702x480 has some appeal because it seems like its an integer multiple of the native VHS resolution on both axes, while 352x480 only doubles one.
According to Nyquist, you'll want at least 2x horizontal resolution to fully capture the information. For VHS, the table says "240 lines of resolution" which is 320 pixels horizontally, so 640x480 and 720x480 are both good.

Quote:
Originally Posted by vhsnewb View Post
Is that the difference between the "line-based TBC" and "full frame TBC"?
Yes.
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  #7  
07-16-2021, 03:43 PM
themaster1 themaster1 is offline
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@vhsnewb
Think of a perfect vertical straight white line. Without the line-tbc the line will be crooked (a lot or slightly that is tape dependant) , with a line-tbc it'll be almost straight (and i guess with $$$ tbc it can be perfect).

Full frame tbc is another beast generally for very difficult tapes
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  #8  
07-16-2021, 05:51 PM
vhsnewb vhsnewb is offline
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Quote:
Originally Posted by traal View Post
In the computer generated section, was there movement at the time of the artifacts? Was the text scrolling?
Yes, the program information was scrolling upwards.

Quote:
Originally Posted by traal View Post
You'll get interlacing like that during capture. Then you can decide whether to deinterlace or detelecine depending on the source (video or film) or just keep it interlaced if you only plan to view it on an analog TV.
I don't plan to watch this stuff on an analog TV, so I guess I'll have to consider deinterlacing. I think I read somewhere that "avisynth" is the best tool for that?

Think of a perfect vertical straight white line. Without the line-tbc the line will be crooked (a lot or slightly that is tape dependant) , with a line-tbc it'll be almost straight (and i guess with $$$ tbc it can be perfect).

Quote:
Originally Posted by themaster1 View Post
@vhsnewb
Think of a perfect vertical straight white line. Without the line-tbc the line will be crooked (a lot or slightly that is tape dependant) , with a line-tbc it'll be almost straight (and i guess with $$$ tbc it can be perfect).

Full frame tbc is another beast generally for very difficult tapes
What are some line TBCs? From what I was reading it seems like most are built into high-end VCRs and some people use DVD recorders in a pass-through configuration. My parents have two dubbing VCR/DVD combo decks, but I don't have them with me now.

Maybe I'll hunt one down later, especially if I decide to re-digitize our home movie tapes (my Mom had already done that with the Canopus years ago). My current project is almost more of an exploratory survey: I want to get the best quality out of the equipment I have, but the tapes I'm working on aren't valuable enough to reach for the absolute best quality.

Some of these tapes have also already gunked up one VCR into uselessness, and I'm hesitant to get something nice if it'll just get wrecked.
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  #9  
07-16-2021, 09:02 PM
dpalomaki dpalomaki is offline
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We use 480 lines for digital because analog NTSC has a nominal 486 scan lines of video, and the "lost" 6 rarely if ever have useful image content.

Horizontal resolution is based on the number of black and white vertical lines that can just be resolved in a distance equal to the image height, i.e., the point where they blent into uniform gray. Given that traditional SD is a 4x3 image, 240 lines resolution amounts to 320 lines in the picture width. Resolution is based on a B&W image. Judging this on a typical color TV screen/monitor can be difficult, although the concept applies to the complete system, display included. If the dot pitch is not fine enough. Color resolution of SD NTSC is much less. A rough approximation is you get about 80 lines of horizontal resolution for every 1 mHz of signal bandwidth.

Thus the 3 mHz of VHS luma bandwidth nets about 240 lines of resolution. As a point of reference broadcawst industry Betacam SP tapes have about 4 mHz of luma bandwidth and 1.5 mHz of chroma bandwidth. They they could provide ~320 B&W, and ~120 lines of color resolution measured 3 to 4 dB down. However, VHS & SVHS tape formats (and the 8mm variants) have much lower bandwidth allocated to chroma (less than 500 kHz, so color resolution is on the order of 40 lines at best.

Keep in mind that the bandwidth figures are based on frequency and amplitude response. Analog copies degrade according to the frequency response of the systems and noise contribution of each step. A signal that is 10 dB down on the original may be 20 dB down on the copy assuming similar response systems. That is why the quality of VHS & Video8 copies degrade so quickly with successive generations compared to the broadcast formats.

FWIW: The color bandwidth limitation also acts as a low-pass filter and can cause colors to shift and smear with successive copies.

320 pixels is in theory adequate for a VHS luma signal. However, it is not adequate to capture broadcast signal luma which is more like 440 lines per picture width, or SVHS/Hi8 at ~530 lines per picture width, DV at ~660 lines per picture width, or high quality live camera analog output.

Last edited by dpalomaki; 07-16-2021 at 09:15 PM.
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  #10  
07-16-2021, 09:14 PM
Hushpower Hushpower is offline
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Quote:
What are some line TBCs? From what I was reading it seems like most are built into high-end VCRs and some people use DVD recorders in a pass-through configuration. My parents have two dubbing VCR/DVD combo decks, but I don't have them with me now.
Panasonic ES-10, ES-15 are good DVD recorder line "TBCs"; they are not dedicated TBCs but do a pretty good job straightening up wobbly videos. The ES-35 (VHS>DVD combo) also has the same functionality.

If you have a wobbly tape, the straightening effect will be immediately obvious when you pass-through the video signal. Use S-video if you can.
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