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Rendering Error with Chroma Keyer

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Chris Young
Rendering Error with Chroma Keyer
on May 17, 2011 at 2:04:40 am

Hi, everyone. 50% of problems I can eventually figure out on my own; for the remaining 49% I can find answers in the forums. But now I've stumbled across one that's got me stumped and - gasp - I can't find it here. This might be my first unique problem.

Or else I'm exhausted and doing something obvious and stupid.

I'm putting together a brief video with kids on funny backgrounds. We're looking for "will make seventh-graders laugh," not "Hollywood quality." So, I've been doing some quick-and-dirty chroma keying with FCP's built in-filters (specifically, Chroma Keyer and Spill Suppressor).

All is well, all is good.

Then, along comes a clip that's not-so-good. I should have lit the scene differently, used a better backdrop, a hundred different things. But, with liberal use of filters, I get a pretty decent key out of the deal - better than I expected. I know I'll need to tinker with the footage for a while, and I don't want to re-render the stack of filters, so I prop it up against a blue matte and export.

For whatever reason, even when exporting in ProRes 444, the transparency was coming through black, so I figured solid blue would be a good substitute for transparency. I'll just add another (single) chroma keyer to get rid of the blue, and I can happily render a single filter - it's a big step above the multiple keys and garbage mattes I had to use to get here in the first place.

And it's not working.

Here's what the newly-imported clip looks like, with no filters.



Then I slap on a Chroma Keyer and eyedropper in the color blue, making minor adjustments to the others just to make it's all 'caught.'



Everything looks good (or, good enough for a middle-school audience that wants to see this before the end of the school year)... and then I render.



This is where I seem to enter a dimension not of sight or sound, but of mind. The background comes back in its entirety - except for a thick outline of transparency around the subject. The only thing that's changed is that I've rendered. If I remove the render (by moving the clip or whatever), it goes back to picture 2. Then the next render sends it back to picture 3.

I've poked at it for nearly an hour now, and I give up. I suspect there's something obvious going on, but I'm missing it. Any help would be appreciated.

Sequence is ProRes 422
Clip is ProRes 422
Final Cut Pro is 7.0.3
OS is 10.6.7, Intel Chip

Any other information I will gladly provide on request. I'm not sure what else would be pertinent.

edit: I tried exchanging Color Key for Chroma Keyer. It gave very similar results - a clear halo and ignored key.

---
Novamation Studios
http://www.NovamationStudios.com


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Jerry Hofmann
Re: Rendering Error with Chroma Keyer
on May 17, 2011 at 2:46:40 am

I think it's really tough to pull a key with FCP... Motion's Primatte keyer is a lot better... Or AE for sure...

Jerry

Apple Certified Trainer, Producer, Writer, Director Editor, Gun for Hire and other things. I ski. My Blog: http://blogs.creativecow.net/Jerry-Hofmann

Current DVD:
http://store.creativecow.net/p/81/jerry_hofmanns_final_cut_system_setup

8-Core 3.0 Intel Mac Pro, Dual 2 gig G5, AJA Kona SD, AJA Kona 2, Huge Systems Array UL3D, AJA Io HD, 17" MBP, Matrox MXO2 with MAX - Cinema Displays I have a 22" that I paid 4k for still working. G4 with Kona SD card, and SCSI card.


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Dave LaRonde
Re: Rendering Error with Chroma Keyer
on May 17, 2011 at 3:27:03 pm

There are also the issues of 1) the quality of the lighting and 2) the type of camera you used,
both of which greatly affect the quality of the key.

You can't put somebody two feet away from a chroma key background with no specialized lighting and expect miracles. There's an art and science to it and if you didn't use it, that's strike one. To learn about it, you can google "lighting for chroma key", "lighting for blue screen", etc.

You may also have used an HDV camera or an XD Camera to shoot the chroma key, both of which have lousy color sampling (aka color resolution). The following video explains the concept in a non-technical way:






Watch the ENTIRE THING, and take special note of the DV video example near the end. DV also has the same kind of stinky color resolution, so even if it's SD and not HD, it still applies.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Jerry Hofmann
Re: Rendering Error with Chroma Keyer
on May 17, 2011 at 4:14:29 pm

Agreed for sure...

Also add DSLR footage doesn't work well either... same reason: Color Space is weak. It' much like HDV.

Jerry

Apple Certified Trainer, Producer, Writer, Director Editor, Gun for Hire and other things. I ski. My Blog: http://blogs.creativecow.net/Jerry-Hofmann

Current DVD:
http://store.creativecow.net/p/81/jerry_hofmanns_final_cut_system_setup

8-Core 3.0 Intel Mac Pro, Dual 2 gig G5, AJA Kona SD, AJA Kona 2, Huge Systems Array UL3D, AJA Io HD, 17" MBP, Matrox MXO2 with MAX - Cinema Displays I have a 22" that I paid 4k for still working. G4 with Kona SD card, and SCSI card.


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Chris Young
Re: Rendering Error with Chroma Keyer
on May 18, 2011 at 3:46:21 am

I have to admit, guys, I'm frustrated with your responses. And I'd like to articulate that frustration without seeming entitled to your time or simply vicious. The Internet is a place where "tone" barely exists, and it will be easy to come off as just another angry Internet jerk hiding behind anonymity. I'm not anonymous - my name is Chris - I'm not trying to lecture or attack anyone, and I don't do sarcasm. What I say, I mean.

It's amazing that anyone wrote to respond to me at all. I haven't done anything to "deserve" your time or expertise, and I appreciate that you spent your personal time to help a stranger at no direct benefit to yourself.

That said, my impression is that you read as far as "green screen," and sent off the stock "keying" response. I worry that this will make my question appear answered, and drive off further interest from the forum-users.

I probably shouldn't have even mentioned keying in my post. My problem is that the pre- and post-rendered footage is radically different, in odd ways, for reasons I can't explain. It happens to be a "Chroma Keyer" filter that's rendering, but I'd be just as concerned and confused had it been a color correcter, blur, or literally anything else.

Dave, your post on getting a quality key was great for what it was. I'm saving the link to the video, and if I run into someone who is struggling getting their 4:1:1 camera to get a good key, I'll happily recommend it. Unfortunately, my keying is already finished, and I'm happy with it. As I said originally, I've done all the original keying, exported the clip, and am now having problems with that new, self-contained clip.

Likewise, Jerry, as luck would have it, I DID use a terrible camera for keying - and in HDV format - and I knew it would be terrible beforehand. This was about getting what footage I could in a limited time with the tools that were at hand in the school. Even so, I got a key I was happy with, as I said in my post. That part is done.

All I had left was to render; and it was a render that was dramatically different than the pre-render preview. I don't care that it was a keying filter; I care that the render itself is changing footage in way I have never seen before, instead of behaving in its usual minor-detail-oriented way.

This is partially my fault. I probably provided too much background information in my post, and didn't phrase the question clearly enough. I don't know many editors, and like to share editing stories when I can. Your time is valuable, and I chatted away before getting to my question. That was my bad.

But it was still disappointing to not only have my question go unanswered, but to be told that I "can google 'lighting for chroma key'" to learn about lighting for chroma key -- a redundantly obvious answer to an issue I never asked about and didn't even have a problem with. As I mentioned in the very beginning, the Internet has almost no "tone," and it's tremendously difficult to tell the manner in which someone is speaking. I don't want to make assumptions; and if I do, I should assume the very best of someone who's gone out of his way to offer advice. But still, if I had to guess what tone would be associated with advice like that, I'd pick "addressing a troublesome pup."

And while we're on the subject of tone, I've looked over my writings so far, and after a few revisions I'm afraid they're still coming across as slightly hostile. I truly do not mean them to. The worst of it, really, is that I still have a rendering issue; and I suppose my ego is a little bruised. I don't actually post often, but I still feel like the Cow is my community, too - and a canned lesson on a different topic feels like a careless brush-off from those who are more experienced than I.

...who still took time out of their day to deliver that lesson to me with, I'm sure, the very best of intentions.


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Scott Stolzar
Re: Rendering Error with Chroma Keyer
on May 18, 2011 at 3:53:52 pm

Hi

I unfortunately have no actual solution/advice for this besides maybe trying it in motion just to get the key done, but I've had a very similar rendering problem using the limiter with both the 2-way and 3-way Color Corrector (I ended up having to use Color). Here is a link to my post:

http://forums.creativecow.net/thread/8/1131178

The only thing I got was that it might have been a coding issue, but nothing on how to fix it.

Anyway, I wanted to get in on this thread in case there is a solution since it sounds like the same problem only with a different filter.

Thanks
Scott


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Clint Collins
Re: Rendering Error with Chroma Keyer
on Jul 12, 2011 at 6:07:40 pm

Hey Chris,
I am having the EXACT same issue as you are! I have chroma keyed a title slide that is a quicktime .mov file on top of a scene I shot with my AGHMC150. When I chroma the title slide out and get all the settings to look just like I want, it's fine. However, when I render the clip out, BOOM! the green background re-appears with the title slide and I no longer can see my background track. This totally sucks and I have tried EVERYTHING!!! Even un-installing some FX Factory plug-ins and cleaning up disk, restarting, etc... Nothing is working and I have chroma keyed numerous things before with no issue??? I have no idea what to do at this point??? If anyone can help us, it would be GREAT!


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Chris Young
Re: Rendering Error with Chroma Keyer
on Jul 12, 2011 at 6:43:33 pm

Hi, Clint.

I'm afraid I never figured it out. I ended up doing something altogether different after that. About a week afterwards, Final Cut stopped saving my preferences - which may mean it's symptomatic of something deeper. I've tried trashing and cleanup and the like; I think next is reinstalling and hoping neither problem ever appears again.

---
Novamation Studios
http://www.NovamationStudios.com


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Clint Collins
Re: Rendering Error with Chroma Keyer
on Jul 12, 2011 at 7:51:40 pm

Man! That stinks, bro! Here is what I have found so far...

Background footage was shot on an AGHMC150 at 1280X720, 24fps, transferred using Apple Pro Res 422. The Keyed footage was done in after effects and exported at 1280X720, 24fps .mov format. The Sequence is 1280X720, 24fps Apple Pro Res 422. I have not exported anything yet. I am just trying to get the key to work with the footage first. Everytime I render the Chroma filter though, all the keying goes away??? I end up with a title that looks like the footage without a chroma filter on it at all, green background behind title. What's weird is, I brought the key footage into motion, used the green/blue screen filter in there which turned the green into black background behind the title. Then exported it, brought it into Final Cut again, then Chroma keyed the black out and rendered. Voila! That worked!!! So basically if I try and key a green background out and then render it, it doesn't work, but with a black background it does??? This is so frustrating. I can use the black keyed title slide, but it is MUCH less clean looking than when I do it with a green background. Also, I have chroma keyed images MANY times with other projects and never had this issue, so I brought an older project file into this project just to see what happens. This one works fine even with the green background. The only difference is the Key footage I am using from the older project file is a JPG image instead of a .mov file. I am really confused at this point???


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Dave LaRonde
Re: Rendering Error with Chroma Keyer
on Jul 12, 2011 at 8:57:05 pm

[Clint Collins] "I brought the key footage into motion, used the green/blue screen filter in there which turned the green into black background behind the title. Then exported it, brought it into Final Cut again, then Chroma keyed the black out and rendered. Voila! That worked!!! "

Why the heck did you do THAT? Why didn't you bring both the chroma key shot and the background into Motion, pull the key, and simply render out a completed shot?

You jumped through a bunch of unnecessary hoops just to retain the ability to have foreground and background on separate layers in FCP, which is totally unnecessary.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Clint Collins
Re: Rendering Error with Chroma Keyer
on Jul 12, 2011 at 9:19:58 pm

Well, to be honest, i'm not much of a "motion" guy! I don't really know the program all that well and at the moment I was just trying to figure out any kind of way to make this work. The title was an after thought to a promo film that was already edited and the background footage was already cut and in the sequence, so I wasn't sure on how to get just that small portion out, into motion, keyed, and back into Final Cut properly without messing up my timeline or degrading quality on the background track. I am mostly a Final Cut editor and don't do alot of motion stuff, so i am slowly learning some motion attributes. the title was actually done by my AE designer in AE!


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Clint Collins
Re: Rendering Error with Chroma Keyer
on Jul 12, 2011 at 6:09:17 pm

Hey Chris,
I am having the EXACT same issue as you are! I have chroma keyed a title slide that is a quicktime .mov file on top of a scene I shot with my AGHMC150. When I chroma the title slide out and get all the settings to look just like I want, it's fine. However, when I render the clip out, BOOM! the green background re-appears with the title slide and I no longer can see my background track. This totally sucks and I have tried EVERYTHING!!! Even un-installing some FX Factory plug-ins and cleaning up disk, restarting, etc... Nothing is working and I have chroma keyed numerous things before with no issue??? I have no idea what to do at this point??? If anyone can help us, it would be GREAT!


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Jacob Cross
Re: Rendering Error with Chroma Keyer
on Sep 6, 2011 at 6:34:52 pm

Hi Chris,

Sorry I couldn't have helped sooner but I saw your post when trying to solve the exact same problem. I'll post my solution now, for posterity.

In the Sequence Settings, under Video Processing, choose Always Render in RGB. It seems that rendering ProRes video in YUV can be problematic. I haven't read up on this yet, though. Changing to RGB solved this issue for me.

Note that you must make this change on every effected sequence.

Best,
Jake


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Chris Young
Re: Rendering Error with Chroma Keyer
on Sep 6, 2011 at 9:51:33 pm

Excellent, Jacob! Thank you!

I've changed my Easy Setups and hopefully won't ever have this problem in the future. I'm generally very happy with the ProRes family, but I suppose they're allowed their quirks, too.

Chris

---
Novamation Studios
http://www.NovamationStudios.com


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Bryan Kane
Re: Rendering Error with Chroma Keyer
on Oct 31, 2014 at 9:41:28 pm

THANK YOU, THANK YOU & THANK YOU!

This simple change to Sequence Setting RGB solved my exact same green screen render issue. I would have NEVER known to look at that.

Cheers!!!!


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