Here's a good example showing the chroma bleed/offset issue seen with some tapes. Maybe U and V are misaligned? This is from a recorded broadcast but is the same effect seen on the TV Teddy retail videos. This tape was recorded at SP speed. The tracking is poor, it's the best I could get with this Philips VCR considering it was recorded in 1992. Perhaps tracking on the original machine was misaligned during recording.
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Yeah it almost looks a bit like U and V don't quite line up. Does the chroma bleeding happen on a normal capture too? I will look a bit more at the sample later.
Well I feel silly now. That UV error was in the broadcast, specifically the WSMV bumper before the main program, which starts off in sepia tone with no color to compare against. I watched again and the other ads/segments don't exhibit this problem. Played back directly from the VCR on my LCD monitor:
Though vhs-decode does show a bit more smearing in the luma channel than the VCR's native output. But of course that's filtering and de-emphasis which is experimental, and chroma killer for the luma channel isn't implemented yet. Let me know if I can do anything else to help with anything.
Last edited by Titan_91; 10th Apr 2021 at 15:05.
I just realized a lot of the family tapes I wanted to digitize have been apparently played in a defective VCR with (probably) misaligned tape guides. This caused wrinkling of the tape over the whole length at the bottom. While digitizing them, my 2 VCRs (with classic composite capture for now) often couldn't read the sync pulses, causing one of them to blank the screen and the other one just display noise/really distorted images. The VCR that blanks the screen is a lot more sensitive to these issues, so it might just be bad "software" blanking out the screen too early, while the other one outputs what it can.
Interestingly, if I dump the same tape twice, the VCR collapses at different times, allowing some video to be recovered by merging multiple captures.
I don't have my cxadc machine set up right now, so I can't check what vhs-decode would do. Could software decoding help with the restoration of these tapes? I'm thinking of doing the merge method I described on the RF level, which should be much easier to automate.
Basic algorithm could work like this: Allow specifying multiple RF captures as input. For each frame, from all files that do have proper sync for that frame, merge the sources so that always the one with the best signal for a given point is used. This can both allow for correcting minor dropouts and also major "frame drops". It might also help with noise, due to kind of averaging out the captures.
Last edited by uff; 10th Apr 2021 at 16:24.
Partially yeah. That may be because I'm using the NTSC 2D comb filter, but there should ideally be no luma/chroma crosstalk on the tape. It may exist on the tape though, since my VCR and LCD monitor may be smoothing out this effect. The more minor difference I was pointing out though was the slightly worse luma filtering in vhs-decode, which results in a bit more smearing than the VCR's native output. Some of the PAL source material looks sharper/less smeary than this, so it may just be a matter of perfecting the NSTC filtering/de-emphasis. Here are comparison images with vhs-decode on top and native composite output on bottom:
Last edited by dellsam34; 14th Apr 2021 at 03:05.
I would think so, that's probably a clean amplified output directly from the RF backend.
I built from the latest repository again. For the news bumper segment, I applied some of the same filters in Avidemux that a modern VCR and monitor would. First I deinterlaced the sample, then added noise reduction, a contrast and brightness adjustment, and upped the color saturation. I also did an extra step and corrected the UV alignment as best as I could. On top of brightness/contrast, NR, and saturation boost I'm sure the VCR and/or LCD monitor is also doing some sharpening. Although the black lettering looks sharper on the VCR's output, there is a light halo effect around the transitions of the letters, just like you would get with a digital sharpening filter. This effect misled me into believing vhs-decode wasn't capturing all of the available luma bandwidth, when in reality it actually is. Recalling the multiburst test on my VCR, the 3MHz pattern is present in the decode (although attenuated because my equipment is inexpensive).
Post processed deinterlaced result, minus sharpening:
Applying the same filters (no UV alignment correction of course as not needed) on the Tom and Jerry retail movie decoded with today's repo, which turned out AMAZING by the way:
In short, I thought there was a regression in some of the latest code. Turns out that is not the case, and on top of what was mentioned above my broadcast source just has a lot of dot crawl in the form of crosstalk. I verified this in ld-analyse as well. My Tom and Jerry sample is attached encoded in lossless HuffyYUV. Honestly if if weren't for VHS's limited color resolution, it would have likely won the late format war against DVD.
Last edited by Titan_91; 15th Apr 2021 at 06:45.
I've now added a function that does an extra diffed demodulation pass if there is noise spikes, which should help a bit with avoiding white streaks on noisy low signal tapes.
Also, this has been possible for a while it seems, but just came up during a discussion on the discord, you can use the ld-process-vbi tool to decode NTSC closed captioning from the tbc file. After running that on the .tbc you can see subtitles in ld-analyse. It's a bit clunky though, so you have to go frame by frame for it to display properly. Another user is working on a tool to translate the subtitles from the json metadata file to something usable by other tools.
Example from titan_91's tom and jerry sample:
[Attachment 58452 - Click to enlarge]
It boosts the 3MHz region after the demod.
The flat point is between 50 and 80 and depends mostly on the VCR standard + head + amplifier combination.
It does EQ with the full numerical range precision (it is not limited to 256 greyscale levels)
I found the NTSC samples here having more high frequency video losses than the PAL samples I tested.
So maybe your captures can benefit from the video sharpness filter.
Tried the -sl 70 with the multiburst and the 3MHz burst shows better on NTSC.
(sharpness level zero, default)
(sharpness level 70 -sl 70)
Last edited by VideoMem; 17th Apr 2021 at 16:45.