On Sun, 25 Mar 2001 07:37:44 +0100, Martin France wrote:
>"Evan Mann" wrote:

>>> I know this is a little off topic, but you all have Video cameras. So here
>>> goes.
>
>>> Is there much of a difference between video cameras that have interlaced images
>>> or non iterlaced. I'm thinking of getting the JVC GR DVL9800 that is ProScan
>>> non interlaced. One other camera I was looking at is the Panasonic DV800, it
>>> is interlaced. Will I notice much of a difference in the final output between the
>>> two?

>>In general, it depends on the viewing source. Most TVs are interlaced,
>>computer monitors are progressive, so you want to use interlaced on TVs, and
>>progressive on a computer monitor for the best looking results on each one.
>>There's way to convert and all that jazz too. I'm not qualified to say
>>anything about specifics, but that's just a general idea to have in mind.
>
>Yep. Broadly, the temporal resolution is halved in progressive scan.
>If you're really unlucky and have (as I do) a TRV900, it is quartered!
>
>In NTSC, you have 29.97 fps. In PAL, 25 fps.
>
>In interlaced mode each frame is split into two separate pictures, a
>lower field and an upper field using alternate scanlines.
>
>So NTSC has 59.94 pictures per second and PAL has 50 pictures per
>second.
>
>Traditionally, video provides a near-continuous picture scan; second
>line to bottom line, top line to next-to-bottom line, second line to
>bottom line, etc. More recently, this has been largely abandoned in
>favour of separate "photographs" - but still interlaced for the most
>part.
>
>Now, if you record interlaced then you have options for progressive
>display, but these will involve (one way or another) halving vertical
>resolution, and maybe halving temporal resolution too. There are three
>methods in common use.
>
>1) Ditch a field per frame and interpolate (produces stepped edges to
>diagonals, as you are removing half the scanlines).
>
>2) Merge both fields of a frame (produces temporal blur, as you see
>two pictures at a time).
>
>3) Deinterlace and create (via interpolation and motion analysis) a
>full height frame for and mainly from each field. Then, NTSC delivers
>59.94 fps and PAL 50 fps. This produces a very high sense of temporal
>resolution on computer, but can reduce the impression of vertical
>sharpness somewhat, picks up and amplifies any composite or
>compression artefacts, and can add considerable flicker to moving
>edges if you are unlucky. Also, the files will be (about) twice the
>size! In short, the best way to view interlaced material is on a TV!!
>
>For progressive scan material; this looks fine on a TV, but you'll
>notice a more jittery appearance when compared to interlaced material,
>due mainly to having only half the actual pictures (!) and (to a much
>lesser extent) also the interlaced nature of the display. Experiment
>with different "shutter" speeds..
>
>A note on NTSC: remember that a progressive scan camera *does* produce
>a full compliment of frames (TRV900, at least, excepted, I guess), so
>you don't get the motion judder associated with 3:2 pulldown of 24fps
>(23.976fps as played) progressive (mainly film-originated) material.
>But 29.97fps progressive still looks "odd" compared to most video..
>
>Marty

Thanks!
I continue to wonder why there is such a fuss over
"progressive scan", when it throws away something
of value: video's ability to show motion smoothly
and sharply... I would guess that much of what is shot
in PS-mode for computer screens or for film transfer or
for stills-capture never gets used for those purposes,
or gets reduced to half-size for computer-screen use
(thus throwing out 1/2 the scan lines anyway
["automatic deinterlaced PS-mode"...;-]).