In the frame on the left you can see alternating brightness every two lines. This pattern starts with exactly one bright line, so the even fields are bright,dark,bright,... and the odd fields dark,bright,dark,... . The videos were from Video8 tapes recorded with (I think) Kyocera camcorders and then digitized with a Sony (Digital8) camcorder that can play analog tapes. (Insert rant about loss of chroma detail and cheap equipment here.;))
I'm trying to understand what caused this. Without access to the tapes nor an analog playback device I'm counting on your experience. My first idea was that because in PAL DV, even lines contain Cr samples and odd lines contain Cb samples, the color conversion from analog to digital messed with the luma in the sense that Cr lines get a different luma than Cb lines. I ditched that idea because while chroma samples have the same position in each field, the line pattern alternates between them. My next idea was AC interference, but at 64µs per line in PAL, neither 50Hz or 60Hz is evenly divisible. So I'm still in the blue here.
![Image]()
[Attachment 42985 - Click to enlarge]
![Image]()
[Attachment 42986 - Click to enlarge]
Next is the question how to fix this in a way that it doesn't overcompensate where one or both fields are less affected, like in the frame at the bottom. I'm using AviSynth+ 32-bit and QTGMC with additional temporal denoising and due to its stable nature, the line pattern is mistaken for static detail in skies, walls and other flat areas that sticks out even more when most other noise is removed. (It also doesn't help compression.)
I've tried DeFreq() with a vertical frequency of 100% and different window sizes on the separate fields, but it didn't single out the high frequency line pattern effectively. It does look like a straight forward mathematical solution should exist, but if not I might try to mask and blur the areas that look like the pattern in flat areas.
I'm trying to understand what caused this. Without access to the tapes nor an analog playback device I'm counting on your experience. My first idea was that because in PAL DV, even lines contain Cr samples and odd lines contain Cb samples, the color conversion from analog to digital messed with the luma in the sense that Cr lines get a different luma than Cb lines. I ditched that idea because while chroma samples have the same position in each field, the line pattern alternates between them. My next idea was AC interference, but at 64µs per line in PAL, neither 50Hz or 60Hz is evenly divisible. So I'm still in the blue here.
[Attachment 42985 - Click to enlarge]
[Attachment 42986 - Click to enlarge]
Next is the question how to fix this in a way that it doesn't overcompensate where one or both fields are less affected, like in the frame at the bottom. I'm using AviSynth+ 32-bit and QTGMC with additional temporal denoising and due to its stable nature, the line pattern is mistaken for static detail in skies, walls and other flat areas that sticks out even more when most other noise is removed. (It also doesn't help compression.)
I've tried DeFreq() with a vertical frequency of 100% and different window sizes on the separate fields, but it didn't single out the high frequency line pattern effectively. It does look like a straight forward mathematical solution should exist, but if not I might try to mask and blur the areas that look like the pattern in flat areas.