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In video engineering, field dominance refers to the choice of which field of an interlaced video signal is chosen as the point at which video edits or switches occur.
There are two main choices for field dominance: odd or even. With odd field dominance the edit or switch occurs at the start of the odd field. With even field dominance the edit or switch occurs at the start of the even field.
Interlacing divides the frame into two fields, each containing half the number of lines. Each field is scanned in 1/60 second under the 525-line system or 1/50 of a second under the 625-line system. With interlaced systems there are an odd number of lines in each frame. This means that there is a half line offset between the fields, therefore the lines in the second field will be positionally interleaved with the lines in the first field.
The lines are numbered in the order in which they are scanned. In 525/60 systems, by convention, the first field in the frame is considered the even field. In 625/50 systems, by convention, the first field in the frame is considered the odd field.