[opendtv] Re: Interlace Artifacts
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Thu, 13 Jan 2005 10:27:34 -0500
At 9:36 PM -0500 1/12/05, Tom Barry wrote:
>Possibly they should embrace and extend themselves to include a 4:2:2
>option.
>
>I wonder if 4:1:1 for interlace choice may have resulted from the
>assumption that much of the interlaced material was coming from DV cams?
Not likely. Remember, that NTSC is 4:1:1.
We like to think that SDTV is 4:2:2, but when it hits the NTSC
encoder, it becomes 4:1:1; when it hits an MPEG-2 encoder it
typically becomes 4:2:0, which is a significant improvement that DVD
takes full advantage of.
>
>But if much of the interlaced material is coming from ripped DVD video
>or captured 1080i HD then converting from interlaced 4:2:0 to 4:1:1
>probably leaves an effective chroma resolutions of about 1/8. That is,
>1/4 of the horizontal rez but less than 1/2 of the vertical. That would
>seem to be getting a bit thin.
The vertical started out at 1/2, so so big loss there. There will
definitely be a loss in horizontal color resolution. There will be a
loss in vertical color resolution too, but this is primarily due to
the poor handling of the color components of interlaced sources in
MPEG-2. A more realistic application would be taking "601" source
(4:2:2) then encoding it as 4:1:1, which is the trick used for 25
Mbps DV.
Regards
Craig
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