returning the original progressive frame from two interlaced fields is what i call deinterlacing. so does wiki:

Progressive source material

Interlaced video can carry progressive scan signal, and deinterlacing process should consider this as well. Typical movie material is shot on 24 frames/s film; when converting film to interlaced video using telecine, each film frame can be presented by two progressive segmented frames (PsF). This format does not require complex deinterlacing algorithm because each field contains a part of the very same progressive frame. ...

http://en.wikipedia.org/wiki/Deinterlacing#Progressive_source_material