>>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.)
>
>Can you refresh my (our) memories about that
>discussion?
Here's what Trent Piepho said:
>If you have a progressive frame in 4:2:0, then
>the first chroma line is the average from lines 1
>and 2. The second chroma line is the average of
>3 and 4.
>
>If you have an interlaced frame, the first chroma
>line is the average of the first two lines of the
>first field. With the fields interleaved, they
>are lines 1 and 3. The second choroma line is
>from the first two lines of the second field,
>which are lines 2 and 4. Assuming top field
>first.
So, if I have a DV file of a 3-2 pulldown of a
24fps source, and I want to convert it back to
24fps, I first have to swap lines 2 & 3 of every 4
lines of the 4:1:1 color, in order to get the
progressive-frame color to come out right.
That's why I figure yuvkineco would have to do
this -- I imagine that swapping color lines
beforehand might conflict with its method for
detecting copied fields.
I was thinking of writing a short stupid program
that took 4:1:1 and swapped lines 2 & 3 of every 4
color lines, before the video got fed to y4mscaler
& then yuvkineco, just to see what happens.
The latest DVD of a LaserDisc I made looks
absolutely incredible, except that there's some
shimmering at the borders between the video & the
black bars at the top & bottom. (I know I should
be making a widescreen DVD...that'll be the next
thing I'll try.) It's such a fine shimmering, I
can see how it'd be due to this color issue.
>>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 :)
Eeek...I hope the author responds & gives us an idea
of how feasible this is.
Steven Boswell
ulatekh at yahoo dot com
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