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Posted by Jukka Aho on 11/15/06 05:13
wdoe999@yahoo.com wrote:
> I'm try to decipher why progressive scan video is considered better
> then interlaced.
1) Non-interlaced video is easier to deal with computers,
image-processing algorithms, and compression algorithms. (And, they're
easier to get your head around, if you're not very bright. Some computer
programmers who try to make video processing products, aren't.)
2) Modern display technologies do not "scan". Only CRTs and the ancient
electromechanical Nipkow disk televisions are based on "scanning",
natively. (It can be argued, though, that it would be possible to
_emulate_ the scanning pattern of a CRT with, for instance, a SED
display.)
3) When "progressive scan" (which is beginning to be a misnomner these
days - see point #2) is applied, it is usually assumed that at least
twice the bandwidth is used for delivering the images. Instead of
drawing, say, 240-line progressive pictures 60 times a second, or
480-line progressive pictures 30 times a second - both of which would
have the same bandwidth as an interlaced 480-line 60 Hz system, you draw
480-line progressive pictures 60 times a second. ("60" in the above is
really 60*1000/1001, and "30", respectively, 30*1000/1001.)
> Assuming that we are not dealing with old 1930's phosphors,
Do you assume those to be faster-decaying or slower-decaying than the
modern phosphors? What is the problem you assume there being with 1930s
phosphors? (This is not a trick question - there just does not seem to
be a consensus about this. Some say the early CRT-based televisions had
faster-decaying phosphors, and insist that interlaced scanning was
designed, in part, to combat this problem. Others maintain that they had
a longer afterglow. Go figure.)
> would it be fair to say that the following 2 images would be of
> the exact same quality:
>
> 480i camera --> 480i display
> 480p camera --> 480p display
Depends. Do you mean a 30 fps 480p system or a 60 fps 480p system? Still
scenes or motion?
Coincidentally, the Wikipedia article about interlace is currently under
scrutiny. You might want to read the discussion page, where lots have
been said about the relative merits of an interlaced system and the
various "related" progressive systems.
<http://en.wikipedia.org/wiki/Talk:Interlace>
See, especially, my contribution (yes, this is a shameless plug!), where
I compare an interlaced system to three related progressive systems:
<http://en.wikipedia.org/wiki/Talk:Interlace#Comparing_inter
lace_to_progressive>
(Please copy and paste the two parts of the URL together manually if
your newsreader program does not do that automatically.)
> From what I can gather, the real problem is when you try and mix the
> formats and you get jaggies?
That's a real problem whenever some sort of automatic conversion from
interlaced domain to non-interlaced domain is applied, and the source
material alternates between film-originated, "progressive scan" video,
and regular interlaced video.
> Progressive scan TVs are considered to be better, MOSTLY because DVD
> are encoded from film, which is essentially a progressive scan source.
> That is, the source and display are both progressive scan.
That's about correct. But note that NTSC (525-line 59.94
fields-per-second) countries have some additional complications due to
the 3:2 pulldown pattern which is used when transferring 24 fps film
frames to video. PAL (625-line 50 fields-per-second) countries
circumvent those problems by speeding up the film by 4 % when it is
transferred to video, so that each pair of adjacent fields comes from
the same film frame.
Also note that in the age of digital television broadcasts it is
possible to shoot real "progressive" (i.e. non-interlaced) 60 fps video
signal - such as 480p/60 or 720p/60 - and display it "as is" on a
non-interlaced display, without any tricks.
--
znark
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