Edge staircasing in green screen shots?

grjohnson

grjohnson

Active member
I did some green screen shots with my DVX100 and on some surfaces around the key edge I can't get rid of what appears to be a "staircasing" effect on near vertical and curved edges. I know this has something to do with the fact that the camera is using something called 4:1:1 pixel sampling [?] as compared to a 4:4:4 high-end camera?

My question: Is there a setting(s) in the DVX100 using progressive scan mode that can mitigate or lessen this "staircasing" effect to pull a sharper key in post?
Thank you
 
You hit the nail on the head with the 4:1:1 sampling of DV being the culprit. I normally use the "Color Smoother 4:1:1" filter in FCP and play around with the edge controls, especially softness, to get rid of it. Takes a lot of tweaking to get a good key. Also you can play around with your lighting while filming. I'm by no means an expert on chroma keying, so hopefully someone else can help provide some more insight.

You don't need 4:4:4 to get a decent key. HD cams with 4:2:2 and 4:2:0 sampling produce much better edges. To over simplify it, it is how often the camera records color information relative to luminance and how that color information is based on neighboring pixels.
 
Ric O'Shea said:
You hit the nail on the head with the 4:1:1 sampling of DV being the culprit. I normally use the "Color Smoother 4:1:1" filter in FCP and play around with the edge controls, especially softness, to get rid of it. Takes a lot of tweaking to get a good key. Also you can play around with your lighting while filming. I'm by no means an expert on chroma keying, so hopefully someone else can help provide some more insight.

You don't need 4:4:4 to get a decent key. HD cams with 4:2:2 and 4:2:0 sampling produce much better edges. To over simplify it, it is how often the camera records color information relative to luminance and how that color information is based on neighboring pixels.
Click to expand...

Thanks for the confirmation. Unfortunately, I use Sony Vegas Pro for editing (not FCP) so I apparently don't have that post option. Are there no settings in the DVX100 that can minimize the effect during the shoot?
 
Shooting progressive (I use 30P for green/blue screen if possible) will help with apparent edge smoothness. Also, turning the camera on it's side, so that you can take advantage of a bit more actual vertical resolution will help with the stair stepping (not applicable to all subjects unfortunately). The keyer in Boris RED , is superior to the simple chroma keyer in Vegas...it has a lot more control over the matte and gives good results if you have taken reasonable care shooting the original footage.
Hope this helps,
Ken
the Screen Skins guy
 
Vegas has a "chroma blur" filter which can help; blur the chroma by 2 pixels on the horizontal, but none on the vertical.

Ken's right, turning the camera on its side can help when greenscreening individual people, giving you more effective resolution for the same usable amount of subject.

For more on color sampling and how it affects you, check out this article.
 
There is also Magic Bullet Deartifact, which may be available for Vegas.

Remember, when you go back to DV or to DVD, you go back to the limited color space, but at least you get a good key in the mean time.
 
kplo said:
Shooting progressive (I use 30P for green/blue screen if possible) will help with apparent edge smoothness. Also, turning the camera on it's side, so that you can take advantage of a bit more actual vertical resolution will help with the stair stepping (not applicable to all subjects unfortunately). The keyer in Boris RED , is superior to the simple chroma keyer in Vegas...it has a lot more control over the matte and gives good results if you have taken reasonable care shooting the original footage.
Hope this helps,
Ken
the Screen Skins guy
Click to expand...
Funny you should mention Boris RED. I am just starting to evaluate it as a plugin to Sony Vegas 8. We'll see what it can do.
 
blackdogs377 said:
so how do they make dvd's look so good when you play it back on your tv?
Click to expand...

Mostly they are shot on film and encoded for DVD, so the color space is only reduced once, and compression is only applied once.

If you are shooting DV, you are going to 4:1:1 color space and 5:1 compression, and then when you encode to DVD you reduce again to 4:2:0 color space and another 3:1 worth of compression, so it can be brutal.

Some good deartifacting can smooth the color and reduce some compression artifacts, so your DVD's look a little better.
 
You must log in or register to reply here.
Back
Top