Capturing with Lower Field First

[easy2Bcheesy]

I run a Matrox RT2500 with real-time TV output editing (very useful). The problem it, is doesn't have a component input. I've bought a Sweetspot capture card, which does have component and input and capture via VFW. The idea is to have the flexibility of the RT2500 for editing and the superior picture quality of the Sweetspot's component capture.

The problem is that the Matrox card captures NTSC video using (I believe) lower field first, whereas the Sweetspot captures using upper field first. This causes the usual jerkiness hilarity when the Sweetspot footage is run using the Matrox playback.

A couple of questions...

a) is there a way I can change the field order in which the footage is captured (I use Virtual Dub) or...
b) is there any way to painlessly convert the footage?

[easy2Bcheesy]

After a little research, I found this Virtual Dub filter courtesy of Donald Graft (of course!) which does the trick:

http://neuron2.net/reverse/reverse.html

But if any one can suggest a capturing utility which lets me specify which field has dominance, I would deeply appreciate it and it would save me a lot of time.

[stickboy]

Simon Walters made an AviSynth version of Reverse Field Dominance (http://www.geocities.com/siwalters_uk/reversefielddominance.html). Like Donald Graft's, it uses the scanline shifting method.

There's also my JDL_ReverseFieldDominance AviSynth function (http://www.avisynth.org/stickboy/) that reverses field dominance by using the field recombination method.

Neither will help you change the field dominance of your capture card, but the AviSynth functions hopefully should be a little easier to use with other applications.

[stickboy]

Hm, looking at my JDL_ReverseFieldDominance function again, the code I wrote to bob-deinterlace the first/last frames isn't right. Avoid using that option for now.

[Edit: I've since fixed that.]

[mustardman]

Another way of inverting the field order is to shift the image in a vertical direction by an even number.

eg: Shift the image down by 1 line.

A VDub filter for shifting is ShiftWrap. If the source is VHS, you will probably want to remove the crap at the bottom of the image. Shift the image by, say, 5 lines down, and then apply some edge compensation to smmoth the edges off (or replace them with black bars - make sure you stick to x8 for their width though!). A good filter is BorderControl (VDub).

BTW, ShiftWrap is slow, BorderControl is painfully slow - god knows what it is written in!

Like stickboy says, it is extremely unlikely you will be able to alter either of your capure devices. Either stick to one card all the time, or post-process.

MM

[avih]

hmmm, i'm at work, so i can't get vdub into capture mode, but isn't there a 'swap fields' checkbox on the capture menu??


that's on the video menu in capture mode:
doom9 capture guide (http://www.doom9.org/capture/capturing_vdub.html)

[easy2Bcheesy]

Originally posted by avih
hmmm, i'm at work, so i can't get vdub into capture mode, but isn't there a 'swap fields' checkbox on the capture menu??


that's on the video menu in capture mode:
doom9 capture guide (http://www.doom9.org/capture/capturing_vdub.html)


There is, but that puts each field in the wrong spatial location, creating a hideous scanline effect.

Thanks for the posts every one - if any one does know how to change the field order on my capture card or within any decent VFW capture utility, please let me know!

[stickboy]

Originally posted by mustardman
Another way of inverting the field order is to shift the image in a vertical direction by an even number.Hm? Did you mean to say "odd number"? :confused:
eg: Shift the image down by 1 line.That's what Donald Graft's and Simon Walters' Reverse Field Dominance filters do.

[mustardman]

Originally posted by stickboy
Hm? Did you mean to say "odd number"? :confused:
That's what Donald Graft's and Simon Walters' Reverse Field Dominance filters do.

Yeah, quite right. Very odd indeed.

I didn't know that the ReverseFeildDominance filters used this method. I'll bet they are a lot faster than ShiftWrap too!

MM