On Sun, 20 Feb 2005, Steven Boswell II wrote:
> I've been experimenting with yuvkineco for a few
> weeks. The only tool that's done more than yuvkineco
> to increase my video quality is y4mdenoise! Stripping
The combination of the ADVC300 and y4mdenoise is quite the ticket
making some good looking video -that's for sure. Add in something
like FinalCutPro and the results are astoundingly good.
> Some time ago, there was a discussion on 4:1:1 chroma
> subsampling in DV files of 3-2-pulldown sources, and
> how the color needed a special line-switch in order to
> be completely accurate. (Lines 2 and 3 of every group
> of 4 lines have to be switched, IIRC.) After thinking
Can you refresh my (our) memories about that discussion? The discussion
I remember had to do with progressive frames on DVD and how you can't
simply relable a stream from top field first to bottom field first -
I think that discussion came about from one of your postings where
you mentioned using 'yuvcorrect' to flip the field order, etc.
Matt jumped in with :
"o With 4:2:0 material, you can't just re-label a stream from
"top-field-first" to "progressive" or vice-versa: that will
screw up the chroma planes.
The chroma planes are subsampled vertically, either across each
individual field (for interlaced streams) or the entire frame
(for progressive streams). When you change the tag, you also
have to resample the chroma, or it will get muddled by the next
device/program that tries touches it.
That said,
(a) Changing tags with 'yuvcorrect' is a bad idea, *unless* you
are using it to correct a tag that is truly incorrect (hence
the name of the program).
(b) I don't remember (and I don't remember if I ever looked into it)
if yuvkineco is doing to right thing or not. If it is reading
an interlaced 4:2:0 stream and producing a progressive 4:2:0
stream, then it *should* be resampling the chroma.
If not, then what it is actually producing is a stream with
progressive _temporal_ properties (both fields at same time) but
interlaced _spatial_ properties (fields subsampled separately)."
That had to do with 4:2:0 material - not 4:1:1. As long as you're
doing everything in the 4:1:1 space and only converting to 4:2:0
immediately before going into the encoder I can't remember a mention
of line-switching to deal with 3:2 pulldown material.
> that means yuvkineco first needs to be modified to
> deal with 4:1:1 chroma subsampling.
That would be a Good Thing for those of us who work with DV material!
> Is there any interest in such a modification? I know
Of course - but I got a headache the last time I looked at the
sources :)
> my own. :-) This color-interlacing problem is the
> last remaining artifact in my video, and I'm keen to squash it.
You'd be surprised (I think) to see what a difference doing a 3-way
color correction and contrast/blacklevel/saturation correction
does for the visual quality of the final MPEG-2 file. VHS tapes (or
even laserdiscs of old films that had deteriorated and not been
restored) often have an obnoxious color cast (VHS tapes are especially
prone to this as they get old). Take a look at the data sometime
with a vectorscope and you'll see what I mean :)
Cheers,
Steven Schultz
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