Green Screen with Z1U
by Will McMahon
on
Oct 6, 2008 at 10:19:16 pm
I recently finished a green screen shoot with a Sony Z1U. I couldn't get rid of a halo around the subjects. I shot 1080i and did the key in Final Cut. I think the green screen may have been a bit too dark, and I've heard that shooting with interlaced video is not good for keying. Has anyone had good results using the Z1U for greenscreen? Would using Sony's fake 24p function help? Thanks.
We've done a *lot* of keying with the Z1. Given all aspects of keying being "right," it's quite easy to do. I wouldn't suggest FCP as a good keying app, however.
Try re-coloring the key using secondary color correction prior to the key itself.
Use a compositing app for the key as opposed to FCP.
Interlaced video is not ideal for keying, no...but it's been used by millions of people in millions of productions over the past few decades. Every night on the news channel, for that matter...
No, using CF24 won't help your problem. CF30 with a shutter of 60 will..but that's a different story.
It's all about the light...
Douglas Spotted Eagle
VASST
Certified Sony Vegas Trainer
Aerial Camera/Instructor
Re: Green Screen with Z1U by Michael Palmer on Oct 6, 2008 at 11:20:46 pm
Would using Sony's fake 24p function help?
NO. Long story, not worth the time.
If you're using FC Studio you might try Motion together with the keying filter Primatte RT. If you don't get the results you are looking for you can transcode or recapture to an all i-frame codec that should produce the results you need.
Re: Green Screen with Z1U by Tim Kolb on Oct 7, 2008 at 1:31:33 am
Interlace can make the process challenging...
De-interlacing isn't necessarily a cure-all either...
How was your shot lit? Often a key will have an aura if some DP tries to "spill suppress" with some magenta backlighting. (or in the case of a bluescreen key, straw backlight)
Depending on what keying software you're using, you can sometimes make the spill suppression pick up a custom color...
I've done some key work with the Z1 as well...I certainly don't find it to be any more difficult than any other small camera or format.
Re: Green Screen with Z1U by Danny Hays on Oct 7, 2008 at 3:30:58 am
I can get great results by de-interlacing the video, and using Keylight or Ultra for the key. I've never been able to get a good key with FCP alone. Adobe Ultra can give you a great key even with a poorly lit green screen. Keylight is made by The Foundry and there is a Keylight pluggin for FCP. Hope this helps. Danny Hays
Re: Green Screen with Z1U by Will McMahon on Oct 7, 2008 at 3:49:05 pm
I think the main problem is that the green screen wasn't lit very well. It was also a pretty dark shade of green. I might try a "tech green" color next time. Have you heard of "tech" green? Thanks
Re: Green Screen with Z1U by Jeff Brown on Oct 7, 2008 at 6:31:36 pm
The best green I've used is "chroma key green". Duh. Usually, the uglier it looks to your eye, the better a chroma green it is. But- the lighting is quite important if you want an easy time of it. I shoot for less than 1/4 stop variation, and about 1/2 to 1 stop below the talent light level (using an incident meter).
Re: Green Screen with Z1U by Will McMahon on Oct 7, 2008 at 6:58:41 pm
light levels aren't something I have considered with green screen. So there need to be very little difference between the luminance of the screen and the talent?
Re: Green Screen with Z1U by Jeff Brown on Oct 8, 2008 at 12:37:06 pm
If anything, a bit less light on the greenscreen than talent. A common mistake is over-lighting the green, which destroys the saturation, and leaves you with very little chroma to chroma-key!
Re: Green Screen with Z1U by Tim Kolb on Oct 22, 2008 at 3:39:29 am
I'll just add an alternative viewpoint to my friend Jeff's...
You have three levers to control the difference between the foreground and background:
-Saturation, the amount of color
-Hue, the phase of the color, and
-Luminance, the brightness of the color
You should try to create as much difference in each of these three factors to pull a decent color screen matte.
That also means that a background that is brighter than the foreground may be necessary where the foreground subject is dark...it will make controlling spill on the foreground critical...but it's the difference that is important, darker or brighter.
The guys at FX Guide recently tried pulling some keys in a test scenario with...I think a Viper, but I can't recall...and the background that was the brightest...well into a brightness where the saturation was being countered...keyed best. Not because overexposed green backgrounds work on everything...but it goes to show that a lower exposure isn't always the optimal approach.
Now...if the foreground you're shooting is bright green...that wouldn't work, but for this subject, I believe a blonde woman...that worked the best.
Use all three weapons available to you...and on green, lighting with daylight will also help (vs tungsten).
Re: Green Screen with Z1U by Tore Gresdal on Oct 8, 2008 at 6:29:37 pm
Hi Will
I shot some greenscreen with pretty good results using the Z1U last year. You can see the results in my demoreel here: http://www.visualfx.no/demoreel.html
(all chromakey examples using greenscreen were shot with the Z1 (the bluescreen was shot with the elderly PD150 which is a DV camera)
In my experience, editing programs are terrible for chromakeying, and I use After Effects and the excellent keylight plugin which comes bundled with it.
I did the following:
1. Do not apply any effects to the footage in your editing program
2. Export the footage to an uncompressed format such as Quicktime Animation and bring it into After Effects
3. Use a professional deinterlacer such as Fieldskit Pro or Magic Bullet (or let AE do the fields interpretation with lesser but still ok results)
4. Do garbage mattes (See Aharon Rabinowitz's excellent tutorial on supertight junkmattes in After Effects here on the COW)
5. Set the keying plugin to shrink the matte a few pixels if you have bothersome halo effects
6. Adjust the foreground and the background images to have a somewhat similar luminance and color space to sell the effect and make it blend together.
7. Render it out and put it on the videotrack on top of the raw footage in you timeline.
ps. chromakeying is an artform and really tricky to get right, I am still struggling to get it right and i often feel that it's pure luck that I get a decent result in the end.
PS! Andrew Kramer here on the COW also has some awesome tutorials on keying in After Effects.
