capturing DV for chroma key

Ted Ramasola

Ted Ramasola

Veteran
Hey guys!

I'm new in this forum, I need advice what board can capture DV that will be good for chroma key. I currently have Canopus boards that capture DV only thus producing the hair stepping effect which is so hard to key in after effects.
While canopus storm chroma key seem to up rez the image to remove hairstepping I usually work in After effects for a more flexible compositing.

I have a matrox digisuite LE that captures in m-jpeg that i can key with much better. This old board captures footage from my DVX through its S-video connectore but side by side with DV cap from canopus this has less smear and no stepping effect typical of a 4:1:1 codec. But alas this is an analog solution. Is there a better way?

Thanks
 
There is no better solution. For best quality always capture your DV footage via firewire. BUT, DV is already compressed 5:1 on the tape with the color being 4:1:1. It's not really a matter of capturing DV in any particular way. DV just doesn't key well in most cases.
 
As Constantine said, there is no better way to capture. However, if you employ a chroma smoothing filter before keying, you can usually get much better keying results. I know Vegas 5.0 has one, and FCP has one as well.
 
A chroma smoothing filter? Now you've peaked my interest. Can you explain a bit more Barry? Does Premiere Pro have one? How exactly does it work, and more importantly, how well? I've never heard of that filter before.
 
It basically executes a blur on the chroma-only channel, smoothening/softening the stairsteppy 4:1:1 edges. It really helps in keying. I don't know if Premiere Pro offers it or not. The Chroma Blur filter is one of the two essential upgrades that Vegas 5.0 offered over Vegas 4.0 (the other being Bezier masking). Graeme makes separate Chroma Blur filters for the Mac, but I don't know of any others for the PC.

It can affect the overall sharpness of the picture some, but not too terribly much. Nothing like a gaussian blur on the luma channel! The chroma blur in Vegas can be set to 4 pixels by 4 pixels, and at that point, yes, the picture does get a little blurrier. But even at 2 pixels by 2 pixels, the blur helps tremendously with smoothing stair-step edges, while having minimal impact on the picture's overall sharpness.

Of course, if you render back out to DV, you lose a lot of the benefits you gained by chroma blurring, because the image will be re-compressed at 4:1:1 again.
 
Hate to be picky, but I never blur the chroma. Blurring the chroma works, but only to an extent. What I do is actually analyse the video on pixel by pixel basis, across all three components - Y, Cb and Cr to recreate a best guess of the original chroma signal.

I've just been working on some new advancements for the next version, so I thought I'd try and post them here:

CbOriginal.jpg


CbNiceSharpen.jpg


I hope you find the results as impressive as I do!! The plugins are FCP only and will be in the next release of Film Effects, coming soon!

Graeme
 
Wow--that's really impressive and I've seen and used a lot of image processing algorithms. Do we have to tie you to a chair to convince you to port these to Vegas or will we have to resort to...more extreme methods. :evil:
 
Thanks a lot for the input guys

As of last night I removed "with nostalgic feelings" my analog digisuite le board from my PC and retained my storm 2 board. While the Le board produced superb images without the blocky edges of 4.1.1. Compositing in after effects is a breeze with LE using keylight BUT after so much testing I was able to coax DV to produce acceptable keys not only in after effects but surprisingly the Storm2 chromakeyer in PremierPro delivered AMAZINGLY!

I just dont know what kind of smmothing or interpolation technique they used coz the keys are so clean.

Perhaps Barry G or Graeme N know the magic behind this? I heard matrox RTX100
emply some sort of 4.2.2 upscaling for chroma key?
 
Barry_Green said:
It can affect the overall sharpness of the picture some, but not too terribly much. Nothing like a gaussian blur on the luma channel! The chroma blur in Vegas can be set to 4 pixels by 4 pixels, and at that point, yes, the picture does get a little blurrier. But even at 2 pixels by 2 pixels, the blur helps tremendously with smoothing stair-step edges, while having minimal impact on the picture's overall sharpness.
Click to expand...
You should always be able to pull the key from the blurred version and apply it to the original footage. But looking at Graemes results I guess with his filter it won't be necessary ...
 
If you're really serious about your chroma keying and you are using a pc nle (yuck) serious magic makes an awesome chroma key program called utrakey. With all the chroma keying I've done I've found that lighting is number one though. Make sure your backdrop is lit evenly and also throwing some backlight on your subject will take some of the green/blue spill off of them and their clothes (if they're wearing whire usually). Good luck and happy keying.
 
Yeah, Ultra is awsome! We have used it quite alot in some productions lately, and I'm impressed that you can get such good results from a DV source. Ultra also lets you do "live preview" which is very useful when setting up chroma screen sets. I use it on my laptop together with DVRack for monitoring the levels and recording directly to disk and the option to alt-tab to Ultra to see a live preview of what the final key with your desired background will look like is unbeatable.

I heard Ultra 2 is coming real soon too, which will support HD/HDV.
 
ULTRA 2 now available

ULTRA 2 now available

We released the upgrade version of ULTRA 2 on Monday this week. We are offering an introductory price of $195 to registered ULTRA 1 users (that's a 33% discount). The deal expires May 31. The full install version is off being duped and should be shipping in two weeks. Here's the link if you're interested in ULTRA 2's new and enhanced features: http://www.seriousmagic.com/products/ultra/whats_new_in_2/
 
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