Green Screen and GH2 Hack Question

R

ragnar

Active member
I'm currently shooting some Star Trek models on a green screen set up I built in my basement. I'm getting better at lighting it. I'm using all LED lights for the first time. Anyway, I'm liking the results but was wondering if doing one of those 44 or 66mb hacks to my GH2 would make a marked differnce in pulling a good key in Premiere. At the 24mb stock Creative Movie Mode 24p I'm getting pretty good results. Would upping the mbs make it much better. I know a lot of it depends on lighting it right, but I think I've got that part down, mostly. Thanks.

Harold House
 
I don't film green screen often, so I can't say it will help, but trying it surely can't hurt. The hack won't brick your camera, and you can simply revert to the stock firmware if you don't like the results.

Find a good patch over at personal-view.com, and give it a try.
 
They have a new hack for GOP1 that should be ideal for technical shooting like green screen. Let us know how it goes.
 
Chris,

I'm curious. Could you tell me the science reason why the higher bitrate hacks would be better for green screen? I use the Ultra plugin inside Premiere Pro so would it just use the extra AVCHD date from the hack to see the green color better and thus pull a better key? Thanks.

Harold House
 
The whole thing about greenscreen is edge separation. I mean, what we actually do in GS business is trying to separate an object from the background and we use a color trick. The biggest problem is not the color, as you may already know, because any color would do. The problem is the create a "good edge" around the object so that separation can be made. In this regard, the best thing we can have in our hands is to have a device with the best color definition (to separate it from any other neighboring color) and this means 4:2:2 colo space. Thus, you should go for the MJPEG 720p option with the 4:2:2 colorspace because it will give you the best material in terms of color separation. I haven't tried it myself yet because I am away from my own studio and would really like to know whether a 720p 4:2:2 format will turn out better results than a 1080p 4:2:0 standard format. I mean, with the first, we have better color separation but less resolution, with the second we have better resolution but less color space.

I hope this helps...
 
I didn't realize that using the 720p MJPEG mode on my GH2 makes it a 4:2:2 color space. I might have to try that and see if my keys are better. They're pretty good now and much better than back in my mini-dv 720x480 days. I'm also getting better at lighting the whole affair.

Harold House
 
If you go into my profile and look at my first post, there are a bunch of links about using the GH2 with the Atomos Ninja. Anyways, I believe the last link I provided states that the hdmi output has been tested and does output a 1080p24 4:2:2 stream, sorta. The stream is captured at 23.97p, put into a 59.94i package and then frames are added to get to 60i. The links also show how to fix the issue to get that original 1080p24 4:2:2.
 
atarijedi said:
If you go into my profile and look at my first post, there are a bunch of links about using the GH2 with the Atomos Ninja. Anyways, I believe the last link I provided states that the hdmi output has been tested and does output a 1080p24 4:2:2 stream, sorta. The stream is captured at 23.97p, put into a 59.94i package and then frames are added to get to 60i. The links also show how to fix the issue to get that original 1080p24 4:2:2.
Click to expand...

Link ;) http://marvelsfilm.wordpress.com/2011/04/19/panny-gh2-hdmi-recorder-bingo/
 
I tried... I shot the same scene both in MJPEG 4:2:2 720p and AVCHD 4:2:0 1080p. I was a bit skeptical about using 720p for greenscreen work. The resolution seems to be too low for a decent key. Increasing the bitrate seems to be working better for edge separation. I will try again with a live character to make sure but I guess 4:2:2 is not that great as long as it is 720p.

Edit: Correction due to missing sentence because of connection drop.
 
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From my experience in Ultra and Premiere Pro shooting actors/talent, I use GH1 hacked for high bitrate (just using the latest high bitrate stable 24p patch from Lpowell) and get better results from 1080p 24 than 720p 30 MJPEG 4:2:2. If you set things up even close to correctly (pretty evenly lit green screen, no spill on talent, few shadows, some distance between talent and green screen if possible) then the extra resolution on the edges is more important (in my experience) than the better color quality. If you're doing all that, and assuming your actor isn't wearing anything too green, you aren't having to set up a huge color range to key out. At that point it comes down to Ultra looking at the resolution and the edges and if you're using the higher bit rate the contrast on the edges is superb in AVCHD.
 
Robin B
That's a nice music video. I like the band on the wall effect. Displacement Mapping in AE? The band sounds a bit like the Foo Fighters and King's X at times.

Blazer003
What you say makes sense and as soon as Vitaily ports over to the new 1.1 firmware, I'll go to th e 66bit rate patch. I usually only shoot static model space ships against a green screen. I built a very smooth dolly track so I can do fly-bys and such; however, even with that I still need to motion track in AE to make it the ships rock solid still. With the unhacked GH1 at 108024p and using Primatte from Red Giant in AE I've been able to pull some nice looking keys so the extra bits from a patch, as you point out, can only help. I've switched all of my lights from incandescents to LED 160s and 120s. It's so much easier movng lights around without buring my fingers and arms on hot lights.

Here's two very brief clips from my current unhacked GH2 setup:

http://vimeo.com/33765934

http://vimeo.com/33765978

Harold House
 
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