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Discussion in 'Archived Threads 2001-2004' started by Tim Kline, Jan 21, 2002.
Can anyone explain it in newbie terms? Whats it do and why would I want it?
oh yeah also is it the same thing as a 3-Line Digital Comb Filter? (thats what my TV has, no idea what it is )
Short answer: 3/2 pulldown is something that happens when film is transferred to video. It results from the fact that film runs at 24 frames per second and NTSC video runs at 30 frames per second. A good explanation is here:
WHAT THE HECK IS 3:2 PULLDOWN?
A comb filter is an entirely different issue. TV signals contain information about both black and white (luminescence) and color (chroma). In most video formats, including broadcast, cable, VHS and laserdisc, these two elements are transmitted as a combined signal. The function of the comb filter is to separate the chroma from the luminescence. It's an important step in the process; the better it's done, the better the picture.
S-VHS and DVD store the chroma and luminescence separately. That's why you want to use S-video connections with these formats (or, preferably with DVD, component, which further separates the chroma into its constituents). If the chroma and luminescence don't have to get mixed and then separated again, they come through cleaner and the picture is better.
No doubt someone more technically proficient than I am (which isn't hard) could poke a lot of holes in that explanation, but you get the idea.
3-2 pulldown sensing and optimizing is only relevant in video if you are dealing with progressive scan.
Ordinary NTSC video has (approx.) 60 half pictures (30 fields of odd scan lines and 30 fields of even scan lines every second. Ordinary U.S. movies are shot at 24 frames per second. To put the movie on video, the video fields are constructed from the film frames as:
Film frame 1 odd lines
Film frame 1 even lines
Film frame 1 odd lines again
Film frame 2 even lines
Film frame 2 odd lines
Film frame 3 even lines
and so on in a 3-2 repeat pattern.
When making full frames 60 per second (progresive scan) from the original interlaced video fields (half pictures) it is desirable to have matching even and odd scan lines, not things like film frame 1 odd lines mixed with film frame 2 even lines. The DVD player de-interlacer usually does, the TV de-interlacer (if the TV is progressive scan capable) may or may not recognize the 3-2 pattern to construct the full progressive scan frames from matching fields.
If the DVD player outputs progressive scan (de-interlaces the video) the TV's de-interlacer (doubler) is skipped.
In my opinion a 3 line digital (aka 3 line adaptive or 3 line dynamic) comb filter is the minimum comb filter needed for videophile satisfying picture quality from broadcasts and composite programs. The next step up is the 3D (3D motion adaptive; 3D Y/C). Lesser grade comb filters tend to leave the picture with dot crawl, a fine zipper like effect where two color patches meet. S-video and component video inputs skip the TV comb filter. But if the S-video was composite earlier such as from an analog channel coming over Direct TV, the video had to have gone through a comb filter or a notch filter (may or may not be better than the comb filter in the TV) sometime earlier such as in the dish receiver box.
Tim, I am very surprised no one has posted this link. This is by far the best explanation I have ever seen for progressive scan technology. Included in this link is an explanation of 3:2 pulldown.
Progressive Scan DVD