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21st July 2017, 07:15 | #21 | Link |
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I'm not aware of any other source of a checkboard pattern, than dot crawl.
I think you're referring to a letterboxed video. I have one theory, that the comb filtering has nothing to compare the line above it and so can't filter the top line. Does it appear on the bottom edge as well? I'll also mention a little experiment I did. You can perfectly cancel dot crawl if you have two fields of the same content. The two fields come from points in time where the colour carrier is 180 out of phase. That means if you average them, you get perfect dot crawl removal. This happens naturally in a movie with the pulldown pattern. So every (1/3? I forget these details now) frame can be perfect. Based on that, I had the idea that it could somehow be a guide to remove the dot crawl in the remaining frame, as being some kind of temporal anchor to interpolate against. Did you read the explanation of dot crawl? I think I'll summarize it here for the benefit of anyone who runs across this thread. TV was originally monochrome. They wanted to add colour in a backwards-compatible way. They did this by adding a reference short "beep" (called the colour-burst) at the left border. This beep has a frequency of 3.58MHz (NTSC) (PAL came later and used a different method). Then the line is mixed with that frequency of varying phase along the visible line. This shows up as a dotted line pattern in the line. It gets turned into colour, by comparing the "beep" reference phase with the phase along the line. Where they are in phase, it's red, and as they get out of phase, it goes through the colours of the rainbow. Further, each frame, the entire phase of this process inverts, same with each line. Therefore, if you average two frames together, assuming the image didn't change, you would exactly cancel the checkboard pattern. And if two lines are exactly the same (such as a simple-resized 2x vertically picture) you can average them to remove the dot crawl. The checkboard pattern is actually a sinewave on one line and a sinewave 180 out of phase on the next line... you could say the edges of the checkboard "squares" smoothly blur along the edges. They are most visible at the edges of strong colour boundaries because of the inability of techniques to filter out the pattern while interpreting it as colour. To finish my story in history, they added colour by adding a slight screendoor pattern to the whole picture on older TV's. Newer ones could just filter out that frequency and the picture would look perfect again (for newer monochrome TV's). Last edited by jmac698; 21st July 2017 at 07:34. |
27th July 2017, 08:09 | #23 | Link |
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I'm not. I'm referring to the extremely narrow black bars at the right and left sides of the screen in some fullscreen material, which exist due to a phenomenon called overscan (https://en.wikipedia.org/wiki/Overscan).
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27th July 2017, 12:48 | #24 | Link |
Formerly davidh*****
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It's not overscan, it's nominal analogue blanking. That they are never usually seen is because of overscan, but that's not why they exist. But then I'm blocked, so you'll never learn this.
Last edited by wonkey_monkey; 27th July 2017 at 12:53. |
27th July 2017, 19:28 | #25 | Link | |
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Quote:
The "pattern" can vaguely resemble a tiny strip of film at the edge of the picture, several pixels wide, where one "film frame" is picture and the next is black, or something along those lines, and it can appear to strobe or scroll when the video is playing. That's the best description I can manage, but I've been curious as to what causes it myself. I think I've only ever seen it when the original source was video, and therefore on 4:3 DVDs. I might try to dig out a sample later and post a screenshot. Last edited by hello_hello; 27th July 2017 at 19:40. |
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31st July 2017, 22:56 | #28 | Link |
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D3 tapes are actually digital tapes, compared to the analog Betamax or VHS tapes its still quite good quality, but still a "cheap" solution for mastering.
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1st August 2017, 00:19 | #29 | Link |
Derek Prestegard IRL
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Yep
Uncompressed digital composite. Totally crazy, but it filled a niche for awhile and was cheaper than D1 / D2. https://en.wikipedia.org/wiki/D-3_(video) It was entirely deprecated by Digital Betacam (DigiBeta) which is still in wide use today for SD tape masters. DigiBeta introduced a perceptually lossless ~2:1 DCT compression which enabled full 4:2:2 10 bit at ~90 Mbps which was totally doable with inexpensive 1/2" tape and transports. D1 needed 3/4" tape to store totally uncompressed component video (tho only in 8 bits per sample) D5 later introduced uncompressed 4:2:2 10 bit on 1/2" tape, and was eventually upgraded to support 4:1 perceptually lossless HD Last edited by Blue_MiSfit; 1st August 2017 at 00:28. |
1st August 2017, 04:39 | #30 | Link | |
Retried Guesser
Join Date: Jun 2012
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It was D-2 actually. Quality-wise, D-2 was the same as D-3: as good as PAL/NTSC ever gets, which by today's standards, is not saying much.
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Last edited by raffriff42; 1st August 2017 at 05:22. |
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