Video Capture Question

Hi, I have a question for a real video/tv format guru.

I’ve been recording some greenscreen footage for a video project. I’m using a Canon GL1. The video is captured in interlaced, not progressive, format. Once I get the footage on my computer, I deinterlace it with Virtual Dub. Then, I import it into Blender and use a pluginto get my key. I’m not at all satisfied with my results. The rendered video shows the boundary between keyed and non-keyed elements vibrating erratically back and forth.

I suppose my problem could be any one of a number of things, like my camera resolution being too low, my plugin not being high enough quality, or my greenscreen not being properly lit, but I suspect that a large part of my problem is my interlaced footage.

Is there a reliable, high-quality way to get a decent key out of interlaced footage? If not, how much could I be expected to pay for a camera that shoots progressive?

Also, if anyone knows a link to a high-quality (preferably simple-to-use) keyer that they have used with good results in the past, please let me know.

De-Interlacing in virtualdub i believe can be done by either blending the alternate frames or removing the odd or even fields… You’ll probably get better green-screen quality from not using the blending method, as it will create a lot of off-green halos around people. With the vibrating you mention this is the most likely culprit i can think of. Try using the “only odd fields” option for de-interlace, or whatever it’s called in VD. I didn’t de-interlace with it, i used Tmpeg for that… anyway, it’s pretty standard method of de-interlacing, but you’ll lose some vertical resolution in the video that way.

If it’s the compression, you could try in Virtual Dub also applying a noise-reducing filter to see if you can’t smooth out some of the problem areas.

I’ve played with the greenscreen plugin a bit … and I usually get pretty good results… :rolleyes:

From my experience you are best off just using the interlaced footage in blender. In fact, anything you do to your video (re-encoding, deinterlacing, etc…) between the camera and keying will make it harder to get a good key. If your camera outputs a format that blender will recognize, just use the origional footage.

Another thing that can cause the vibrating edges is grainy footage caused by shooting in low light conditions…

More details would be helpfull and a small clip of the video would help the most. If you don’t want to post a clip for the general pubic, you can just email a clip to me at and I will see what I can do to give you a good key.

Thanks, paprmn,

I sent you a PM with a link to a short clip.

heh… does your version of blender work with this clip? It segfaults my linux 2.45 blender…

I can’t even view it in anything but totem ( and totem doesn’t like it much…). I did manage to take a couple of screen shots and check them out with greenscreen (RGBscreen too), and you are right, interlacing is a problem with fast moves like that. the best thing to do here is leave the dv filter off and then just use edge blur.

The biggest problem is that your actor is dressed in black and you have a very dark greenscreen… you need to try and light up the screen more from the sides and more diffuse light from above to ease up those shadows. (check out this post for some lighting tips). You also need to try to stretch out the fabric on the floor, those wrinkles end up being so dark that they are impossible to key out without loosing important edges of your actor.

I will see what I can do to convert this to something that my blender won’t choke on and check it out more

Off-topic isn’t really the place for this…maybe if we ask real nice, a mod will move this to Composition, Visual Effects & Rendering…

Sounds good to me.

Also, I’ll get you a more friendly copy of that video clip. When I captured the footage off of my camera, I tried to capture it in a high-res format, but the format I picked isn’t compatible with many programs.

checkers88, i know we just barely met, but ive always loved you man. weve been through the hard times toghether. and i remeber the good times too.

i hope you get that thing to work, im pullin for ya man!

hiya checkers88,

I’ve looked at your footage a bit more now and I really don’t think that interlacing is your biggest problem…it really is the lighting. The shadows and dark areas of the floor are just too similar to the colors in edges of your actor…You might get away with it if you do some pretty fancy garbage matting but if you reshoot with better lighting and a better floor you will save yourself a lot of work and frustration in post.

I could post a couple of screenshots to show you what I mean but I won’t make your shots public unless you give the ok to do so…:wink:

BTW: you said you used vdub to convert to avi…how big was that file?

The errors you see on your key might be the results of this issue:

I made a group node in Blender that fixes this, and you can have it if you want it.

Just set the switch on the back of the GL1 that says “Normal / Frame” to “Frame.” to get progressive footage with the camera you have.

Or, you have Blender process interlaced footage by turning on “Fields” in the render options. Just bring the raw clips into Blender, don’t complicate things by screwing with it.

Wow, is it really that easy? Thanks, man.

paprhm: I fear you are right about my lighting. That’s what I get for using a cloth backdrop :). I’m afraid I’m too far into the project to reshoot. Oh well, that’ll be handy to know if I ever do anything like this again. About my file size: my seven minutes of Virtual-Dub-processed footage took up 991 Mb.

Hey, thanks for keeping my stuff under wraps. I think I’m only a few weeks away from being done with post, so I’d rather not let too much get out now.

By the way, I finally figured out that I’ve been talking this whole time to the author of the greenscreen plugin I’ve been using. I owe you a big thank you, man. Without your plugin, I probably would have retired before I finished this project.

:slight_smile: great minds lurk.

heh heh heh… I thought you knew it was me when you were willing to send me the clip…it still surprises me when I hear that people are actually using greenscreen instead of the node setups that are so popular.

Anyway, yeah, next time it would be best to take a few test shots and try keying them right away so you can add/adjust your lighting for a good key… an hour spent here will save you days in post. The dark cloth should be ok but if you need add light to the scene you are shooting…especially the screen. The key to a good key ( sorry ) is having as much contrast as possible between your screen and the actors

I am actually pretty disappointed with the key I got on the clip you sent me ( :o it points to a bug or two that I need to address as well as a few other things that could be improved…) so it is an even more pleasant surprise that you are still happy with it in spite of it’s shortcomings…

I got a slightly better key in some ways with my new experimental plugin but it’s got a few bugs that need to be resolved…besides, my little test thread didn’t generate enough interest for someone to even bother compiling a dll for you to try. I’m still working on it though and I will be using your footage to help me test it. Maybe I’ll have something better for you to use on your next project…

PapaSmurf: Great minds do great things… :spin: crackpots like me just lurk :wink: