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Re: New Sony 24sF format



>Interlace requires that the vertical resolution be limited
>to prevent small area flicker or twitter [...] Sony uses the term
>"segmented" to mean that that isn't done, so you get the
>full progressive resolution, and you get to keep on using
>the legacy interlace equipment with this non-vertically-
>limited signal.  But if you look at it on an interlaced
>display, it will flicker like crazy.

Hi John,

There are actually two things going on here.  Old Mr. Kell taught us, 60-odd
years ago, that the vertical resolution of any raster-scanned TV display or
imaging device is limited to about 70% of the scan lines, best case, due to
the fact that some fine detail will always fall between the lines.  It
doesn't make any difference if the scans are progressive or interlaced.

However, interlaced systems suffer an additional loss of vertical resolution
in any part of the image that has some component of vertical motion, because
only half the lines are being scanned at any one time.  The so-called
"interlace factor" effectively reduces vertical resolution of most TV images
to only 50% (at best) of the scan lines.

As you point out, changing an image scanned a certain number of lines
progressively to the same number of lines interlaced requires low-pass
filtering in the vertical direction because the interlace factor is greater
than the Kell Factor, and the vertical detail that can't be portrayed
interlaced just ends up causing aliasing artifacts.

Regarding sF, one has to wonder exactly what purpose is being served.  If
the final product is going to be interlaced, there is little point in
carrying the added vertical detail information of progressive video through
a recording and distribution chain just to throw it away at the display end.
On the other hand, if you want to preserve the quality by staying
progressive, wouldn't it be preferrable to have a system made for the
purpose, rather than trying to compress it through existing equipment
designed to handle the lower bandwidth requirements of interlaced video?

Best regards,
Christopher Bacon


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