Bob displays only one field at a time. In this mode, DirectDraw automatically shifts every other field by one half pixel vertically, and then stretches each field by a factor of two vertically.
Weave displays two successive fields at a time, where the resulting displayed image has horizontal scan lines that are alternately taken from the two fields. The fields are "woven" in a single frame. The top scan line of the displayed frame is the top scan line of the first field, the second displayed scan line is the top scan line of the second field, the third displayed scan line is the second scan line in the first field, and so forth.
The following diagram shows how fields are displayed in an interlaced source, using the bob and weave interlaced video display methods. In the diagram, top field refers to the odd, or first, field, and bottom field refers to the even, or second, field.

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