Progressive scan is supposed to deinterlace the interlaced video on the DVD and display 25 frames per second instead of 50 fields per second. By frame, I mean every pixel
being present of the 720by567 PAL pixels as opposed to every other line being present
in the field. Progessive is where a field = a frame, although the frequency is reduced from 50 to 25. Some DVDs are recorded
progressively in which case you will not see any difference although you may
still need to activate Progessive Scan to tell the player not to interlace the
frames into fields, from 25p to 50i. AFAIK all LCD (incl PC) and Plasma displays are progressive,
CRT displays are interlaced.
Progressive video has a film look like effect while interlaced video looks like video.
Some camcorders can shoot in 24 or 25p mode, ie shoot 25 or 24 frames per second
instead of 50/60fields per second where each field only shows 50% of the spatial
information. Shooting in 50fields per second allows you to capture
more temporal information (your pictures are closer together) while shooting in
24/25p allows you to capture more spatial information (each screenful of information
is complete ie 100% of what the camera sees).
35 or 16 mm film is recorded progressively at 24 frames per second, these are complete
frames captured by an electrochemical process. Hence progressive video has a filmic
look and can also be converted to 24 fps film.
Activating my Sony's "Progressive" function does nothing for me, as my Plasma has it's own
deinterlacer, upscaler solution onboard and does its own thing.
Depending on your processor (DVD player/TV Set) you may or may not loose info
in the deinterlacing process. Some deinterlacers simply fill in the alternative fields and
throw away the second extra intelaced field. This results in detail loss.
Intelaced video great for when you want temporal information (snap more pics per second but lesser detail).
Progressive video great for spatial information (snap fewer pics per second but with greater detail).
Some cool info and examples:
http://www.100fps.com/