Messed up chroma interlacing - how to solve?

[Lyris]

Hi Doom9,
Can anyone help out with this?

Basically I have this interview that's going to be used on a BD. The source for it is not a professional master, instead, we have to use an existing DVD.

The source is PAL (576i) video camera footage and it needs to go out to NTSC (480i). No problem.

So, my first step is to deinterlace this to 50p. Then I apply some noise reduction inside VirtualDub (Neat Video). I then take that NR'd, 50p file and perform these steps on it:

AVISource("DVD_50p_NR.avi")
antialiasing(th_luma=0)
Sharpen(0.7,0.7)
ChangeFPS(59.94)
spline64resize(720,480)
SeparateFields()
SelectEvery(4,0,3)
Weave()

The AntiAliasing line introduces this messed up chroma which I believe is the result of using YV12:

http://img856.imageshack.us/img856/2303/chroma.png

Uploaded with ImageShack.us (http://imageshack.us)

Sorry I can't post a bigger sample, but hopefully you get the idea.

Of course I've seen this before, and understand that it's the result of using progressive chroma subsampling on interlaced footage. But I don't understand why this is happening, because I'm applying the AntiAliasing filter while the footage is still in the progressive (50p) domain.

The chroma is clean with the antialiasing line removed, but the footage really needs it. I don't know how the people who edited it made it look this way, but I guess it was scaled inside the NLE with less than optimal processing quality (Final Cut Pro or something...)

Can anyone spot where things are going wrong?

[poisondeathray]

vdub treats interlaced yv12 as progressive , so chroma is upsampled incorrectly

so the workaround is to either use video=>color depth select yuy2

or convert to rgb (interlaced=true) in the script before vdub

EDIT: I think I misread what you wrote, initially I thought you're taking the screenshot in vdub, so it's converting to RGB as progressive ? What if you take the screenshot through avspmod with converttorgb(interlaced=true) ?

If you take the screenshot before re-interlacing (while it's progressive), are there chroma issues ?

[TheSkiller]

Everything is correct. It is due to the way the YV12 color is upsampled to RGB for displaying in VirtualDub. This is not done by VirtualDub itself by the way, any installed Codec that can convert YV12 to RGB does it. This pretty much always happens without taking into account that the picture is interlaced so it will look broken in VirtualDub although in fact it isn't. The way the chroma is converted is like using ConverttoRGB(interlaced=false) on an interlaced video.

For displaying purposes in VirtualDub add ConverttoRGB(interlaced=true) but be sure to remove it when encoding.