DVL-Digest 884 - Postings: Index - (3) PD150 Mattebox Field Render Order - Adam Wilt This is where I am still lost. If we output DV (lower field first) to > tape then play it on out TV (which from I understand form the engineers > at my station) displays upper field first, why don't se see the same > jagged motion like we see in AE if we forget to set the field > dominance? A TV plays out one field, then the next, then the next, then the next. It doesn't care about field order as long as the half lines, serrations, and equalizing pulses are in the right place. The whole "upper field first" / "lower field first" faff is simply a convention of what order the two fields are packaged in when a frame is made up for editing purposes. Computer video is frame-based in storage terms, whether the NLE does field-based processing or not. So when AE or FCP or any other NLE wants to render a comp, it fetches a frame of each of the source tracks and munges 'em together. The field dominance tells the NLE which of the two fields in the frame is positioned a line above the other one in the frame buffer. With DV, for example, there are no half lines (which might give the NLE a clue); even with 486-line formats that do include the half lines, the half lines are stored as full lines, because it's easier to do the math that way. Because there are multiple "correct" choices for which line exactly a capture starts on (the nice thing about standards is that there are so many to choose from!), the NLE needs some sort of flag to take the two fields aaaaa and bbbbb aaaaa bbbbb and make them into frames either as aaaaa bbbbb bbbbb or as aaaaa aaaaa bbbbb bbbbb aaaaa Now, if all the tracks have the same field dominance, all the even fields get combined with all the even fields, and all the odds with the odds. But if some are upper field first and some are lower field first, one of two things happens: -the NLE detects this, and to avoid interlace tearing, interpolates a new even field from the clip's "real" even field and a new odd from the odd. The result is lowered vertical resolution. -the NLE doesn't detect it, and puts the odd field from one clip atop the even field from the other. In this case, it essentially gets the fields backwards; when played out as a field-based video stream, the fields come out in reverse temporal order: a field sequence a b c d e f is rendered out as b a d c f e. Note that the FRAMES are still in order: a+b, c+d, e+f, but the fields within the frames have been flipped. Cheers, Adam Wilt PD150 Mattebox - Adam Wilt I'm just about aggravated enough with overpriced matte boxes to draw up > some plans and go into the business myself. One thing I'd like to see is > a mounting point for Lowel's flex arm and small tota flags, which would > serve great as a french flag on the camera. You do it, Danny, I'll be your first customer. I too have looked at flex arms and tota flags for French flag duty and wondered why someone hasn't done it before. Cheers, Adam "the matte box from the Nizo 6080 doesn't work either" Wilt (diese posts stammen von der DV-L Mailingliste - THX to Adam Wilt and Perry Mitchell :-) [up] |
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