DV Mattes… Am I Incompetent?

[BenBen]

I’ve been trying very hard lately to pull a key from some DV (in this case 640*480) footage that I have, with little success. Any tips? It’s really hard…

[lwaldron]

DV can be real tough to key. the discreet Master Keyer does a very nice job and with a little cleanup it comes out fine. We key DV25 from a SDX900 quite often and in a pinch we can get a clean key from the DV25, but the DV50 keys MUCH easier and cleaner without much cleanup at all.

[shah alam]

I’ve done a fair bit of keying with DV footage for our film and have found that greenscreen will normally produce better results than blue (I think that blue gets sub-sampled more than green). If however your footage is bluescreen you could try blurring the blue channel a little, even just by 1 pixel and that should help soften the blocky edges enough to get a better matte edge. Apart from that, we found that if a little time is spent while lighting the blue/green screen so that it’s vibrant (the lights that we lit the screen with, we actually gelled them blue) will really help in post.

Here’s a link that I picked up from one of the fxguide podcasts: http://www.dvgarage.com/prod/prod.php?prod=dvmatteae I think it works by combining a chromakey with a lumakey (the luma information in DV isn’t sub-sampled) that helps produce good edges.

Good luck with it.

[Amit]

i know there is a shake macro, which convert RGB space to YUV, then blur the U and V channel a little(the ones that are sub-sampled), and go back to RGB.
Then you have just to key.
I ‘ve tried it and it works quite well, but i’ve lost it and don’t really know where you can download it… Sorry 😆

[naaz Martin]

I should probably have been more specific, but this is great feeback, despite my fairly ambiguous original post. Here’s some more info:

It is a blue screen shot that I will not have the oppurtunity to re-shoot.

This is really an ameteur project for my demo reel, so I can use whatever software I can get my hands on, but I’ve mostly been working in DF 5.01.
The software I’m second most comfortable in is Combustion, but I’ll try anything.

That being said:

Ultimind: As, I said, I’m something of an ameteur (I have a terrible feeling that I’m butchering this spelling), so I had to spend a minute on wikipedia before I knew what you were talking about. I shot with my school’s (VFS) minDV Panasonic100A, prosumerish, I am told. I’ve now graduated and at the moment don’t have any friends with high-end camcorders, so I’m sorta stuck with the footage I have. I will certainly remember you advice if I ever have the chance to be on any type of vfx shoot again (not that it was really a much of a shoot in this case – just my friend and I). I’m going to assume that the master keyer is a Flame/Inferno tool… or at least Flint. Unfortunately, I don’t have access to anything like that.

ctaylor: Awesome, your first post was for me! Like I said, I’m stuck with this footage, but I will try blurring the blue. I’ve been hungrily devouring “Digital Compositing for Film & Video” and a similar technique is recommended in it.
Is it common practice to gel blue screen lights blue? I will think about that plugin. Has anyone here tried it? I don’t have too many extra piles of $200 lying around, but I suppose it could mean the difference between a job and none (although, I don’t know how impressive using a plugin would be to an employer), in which case it’s a steal.

Vince: Do shake macros work in any other software? Maybe that’s a silly question… I’ve gotten too used to AE plugins working for everything. I have only a PC on Windows, but my friend has installed OSX on his PC in order to learn shake, so perhaps I could try it at his house. Or I could try to install red hat on my pc, which sounds hard. Anyway, that sounds like a brilliant idea. I was horrified when I first learned about YUV. How could they do that to our colours? I want to make T-shirts that say NTSC Killed My Father, but I don’t know if anyone would buy them.

[shah alam]

I’m not sure if gelling lights blue for illuminating bluescreens is common practice or not, it was just an idea that our DoP put into practice; he may have got the idea from a cinematography resource. I’ll ask him next time I speak with him; we’ve got a greenscreen shoot this coming wednesday so I’ll ask him then.

I haven’t tried the plugin myself, so can’t offer any advice on how well it works. I was about to download the trial version a few months ago but never got round to it as I got pretty good results by just blurring the blue channel

[bnw]

BenBen wrote:

ameteur (I have a terrible feeling that I’m butchering this spelling)

Amateur 😉

Quote:

Is it common practice to gel blue screen lights blue?

Sounds like quite a bad plan to me, you lose a pile of output whenever you gel so you’d need more lights, you’d have to be more careful not to spill light from the screen lights onto the foreground objects than normal, and the gels are unlikely to be the exact same colour as the screen. But if it works, I’ll just shut up 🙂

Quote:

Vince: Do shake macros work in any other software? Maybe that’s a silly question…

They don’t but you can do it in Fusion easily. Add a Color Space node set to “to colour” and YUV, then a blur, set to Gaussian, blur blue and green only, unlock x and y, blur x by 4 pixels or whatever works well, y by 0 pixels, then add another Color Space node set to “to RGB” and YUV, et voila! Worth a try anyway, should get rid of some stair-steps on your edges.

Quote:

How could they do that to our colours? I want to make T-shirts that say NTSC Killed My Father, but I don’t know if anyone would buy them.

I would so buy one of those 🙂 I’m not sure I’d wear it in public though.

[shah alam]

I spoke to our DoP about the blue/greenscreen lighting and he agreed the use of full CTB (colour temperature blue) that we used almost certainly reduced overall illumination by about a stop. For our shoot that was fine as we were only lighting a small three metre wide screen (enough to cover two guys in alien makeup and costume).

He also said that for a large stage shoot the screens may well be lit using HMI’s, that would create a blue cast which would in effect do something similar to gelling the lights (not to the same level though), although this would only work for bluescreens and not greenscreens.

[Author]

Posts