[opendtv] Re: Native interlaced on progressive displays
- From: "John Shutt" <shuttj@xxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sat, 18 Oct 2008 11:20:08 -0400
Olivier,
Instead of inserting black, why didn't you simply hold the odd and even
lines for 1/30th of a second, alternately refreshing each set of lines every
1/60th of a second? In essence, with phosphor persistence that's what a CRT
does, and it would solve your brightness problem. If you wanted to get
picky, you could display the line at full brightness for the first 1/60th of
a second, then reduced it's brightness for the second 1/60th, (or 1/50th as
the case may be,) further emulating CRT phosphor brightness decay.
However, the majority of your display issues arise from trying to encode an
interlaced source with a frame based compression scheme. That leads to
temporal errors in the frame from the even and odd fields, and results in
more bit stress on the encoder.
Best to kill the interlace before it hits the first lossy encoder, I think.
At least from our experimentation on-air, we find that 1080i cross converted
to 720p then MPEG-2 compressing at 12 Mbps (average, stat muxed) looks
better in the home than the same bitrate allocated to 1080i. Then your
display has to rescale 720p to 1080p by multiplying the horizontal and
vertical by 1.5.
John
----- Original Message -----
From: "Olivier Houot" <olho_avatar_i@xxxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Saturday, October 18, 2008 9:24 AM
Subject: [opendtv] Native interlaced on progressive displays
I have long been wondering whether it was possible to show interlaced HD in
its native format on modern displays. Now that many of them are capable of
1080@60p, i have given it a try.
The idea is simply to replace the missing lines in a field by black lines
, in order to produce a full resolution progressive frame in which one
line out of two is black. You finally get a stream of 1080p frames where
the odd or even lines are black alternatively This will emulate the
interlaced scanning of CRTs.
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