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TROUBLESHOOTING APPENDIX A
The next illustration shows the effects of incorrectly interlacing a frame of video. In this case, F2 from frame
one is combined with F1 from frame two. Remember that there is nothing inherently right or wrong with a
field order of F2/F1; it just happens to be wrong in this case. At a minimum, this can create slightly blurry or
hazy video. In most situations, the video is jumpy or jittery and is unwatchable. Interlacing problems can be
especially noticeable when two adjacent frames are significantly different; for example, at a cut or in video
with fast moving action. It can also manifest itself in certain computer-generated special effects; for example,
in slow-motion sequences.
The basic problem is that there is no standard correct field order. Some capture cards use F1/F2 and some use
F2/F1. If this were the extent of our troubles, we could check out our hardware manual, look up the correct
field order and that would be that. Unfortunately (if this information is even available) the terminology used
can be equally baffling. F1 may be called the odd, upper, or A field, or (more rarely) it may be called the
even, lower, or B field. Add into the mix the fact that the first scan line might be numbered 0 or 1 (which
changes whether the field is considered odd or even), and that cropping may change which line is ultimately
scanned first, and you can see that this is not a very clear-cut problem. The remainder of this section deals
with how to sort this out in Vegas software. Fortunately, you only have to determine the correct settings
once for any particular hardware setup.
Identifying problems
Vegas software refers to the two fields as upper field first and lower field first. These are probably the most
common terms used to distinguish the two fields, and you may find a page in your hardware's manual that
says something like “Use a field order of lower first.” In many cases (but not all or even most),
Upper=Odd=A and Lower=Even=B.
F1 F2 F1 F2
frame 1 frame 1 frame 2 frame 2
F2 F1
frame on television
frame 1 frame 2