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List:       mjpeg-users
Subject:    Re: [Mjpeg-users] Top-forward for DV?
From:       Hervé <herve.flores () free ! fr>
Date:       2009-06-26 8:36:11
Message-ID: 82AC6877-3245-4AE5-9341-E10AF174E3F6 () free ! fr
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Le 25 juin 09 à 12:50, Steven M. Schultz a écrit :

>> Rats...my memory of the conversation was that TOP_FORWARD was
>> necessary to correct DV of telecined video.
>
> 	And for a long time that was the prevailing method - but I ran into
> 	problems back (3 or 4 years).
>
>> (I searched the
>> mailing list archives, by asking Google for "TOP_FORWARD
>> site:mail-archive.com", but couldn't find why TOP_FORWARD was  
>> harmful.)
>
> 	I took a quick look and saw bits/pieces of the threads but not parts
> 	I was looking for.  Try searching for yuvkineco and yuvcorrect
>
> 	I've got to get out the door and don't have time to do much more than
> 	clear out the mailbox.
>
>> As an experiment, I tried running yuvkineco on video without
>> doing TOP_FORWARD, and it was visibly worse.=A0 Maybe that's
>> because yuvkineco is top-field-first only?=A0 It didn't seem to
>> complain about being given bottom-field-first video.
> 	
> 	Hmmm, I thought yuvkineco would complain about the wrong field order
>
>
>> The reverse-telecined videos I make with yuvkineco TOP_FORWARD
>> look great to me...and I thought I was nitpicky about these
>> things.=A0 :-) Have I been living a lie?=A0 What should I be doing?
>
> 	SHift the video one line up or down within the frame.  This is MUCH
> 	better (I think) than shifting the video 1/2 frame.  Here's what I
> 	wrote up about 3 years ago:
>
> #!/bin/sh
>
> N=rites
>
> # NOTE: lie and say it's a progressive stream instead of bottom  
> first.  This
> #       hushes y4mscaler and we will tag the stream as top first  
> anyhow after
> #	shifting down 1 line.
> #
> # Take the first 479 lines of a frame and place them in the last 479  
> lines
> # of the output frame.  This places 1 black line at the top and  
> converts the
> # stream from bottom to top field first:
> #  y4mscaler -v 0 -I active=704x479+8+0 -O sar=src -O size=704x480 - 
> O align=BC
> #
> # OR
> #
> # If 720x486 input we can skip one top line and take the next 480  
> lines:
> #    y4mscaler -v 0 -I active=704x480+8+1 -O sar=src -O size=704x480

my 2 cents:

if I well remember (I didn't verify with the lastest version),
TOP_FORWARD only shift luma (chroma was let in state)

Same sort of concern here with y4mscaler
if your file is 4:2:0 (or 4:1:1), the resulting chroma will be buggy  
with an odd crop
Maybe the idea will be to convert it first to 4:4:4 before any  
process... (or y4mscaler still have automatisms to handle it?)

bye



(PS (not related to this thread): thanks to Bernhard Praschinger &  
Christian Ebert for their tips to compile y4mdenoise from SVN. But I  
didn't manage. I will wait for an official release to test it)



Hervé
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