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trying to chroma key a bad blue screen job

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Heather Gulledge
trying to chroma key a bad blue screen job
on Apr 18, 2011 at 7:15:09 pm

My first time posting so I hope I word this right.

I have to edit footage that was filmed at another location against a blue screen. It is of a man playing a guitar. He has long hair that feathers across his shoulders and is wearing a white straw hat. As if the long hair and uneven lines of the footage are not bad enough I am getting a red line across the top of the hat. This remains after keying the footage.

I can use the BCS Chroma Key studio and get a nice effect overall. The hair looks good and I love the feathered effect. But my problem is that I cannot get rid of the red line/shadow/? at the top of the hat unless I matte choke it. That takes away from the hair detail and makes his long hair look plastic.

I am relatively new at Final Cut Pro and we just bought the Boris filters so I am trying to teach myself and get through this project.

So it comes down to this. Why would there be a red line during blue screening in the first place. Lighting? How do I make it go away? Or am I stuck simply using choke and losing the detail which looks so natural.

Thank you,

Heather


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Mark Suszko
Re: trying to chroma key a bad blue screen job
on Apr 18, 2011 at 8:15:54 pm

Heather, i think what you may be seeing there is not red but magenta. When you key against green, magenta is used to counter exceeeive spill. For bluem it should be yellow; you pick the color directly across the color wheel as most opposite, to use as a spill killer. Without seeing a pictuer of what this looks like, my first guess is you somehow have the magenta spill killer turned on by accident.

My second guess is that the video is too hot for levels at the place where the red is. Did you do any color correction to the footage first, to make sure it is within broadcast safe limits for white and chroma?

I'd really like to see what you're describing. In macs, there is a free tool called "Grab" that lets you take an easy snapshot of anything open on your desktop by clicking and dragging a box around it. If you can park the timeline on a still of this problem, use Grab to snap a picture, and post it here, (using that little icon on the cow web page that loks like a still camera) we can all see what you're talking abotu much more clearly than just trying to imagine what it could be. OR just export a still from the timeline and post that image, it would sure help.


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Heather Gulledge
Re: trying to chroma key a bad blue screen job
on Apr 19, 2011 at 4:09:35 pm






Have a feeling I am way out of my league here.

Posted a picture of the original blue screen footage. A light red/magenta line runs across the brim and top of the hat. Second picture is of the footage keyed with no color changes in front of the type of background he wants.

Having never worked with blue/green screen footage before most of what you said was over my head. I am a photoshop girl and although I have worked in final cut I have always worked with video shot live.
Having been given a project and the final cut manuals I am fumbling my way through this.

I have combed the web and watched many tutorials..time is running out though. I don't want to tie anyone up by having to have them baby step me through this. Is there another tutorial I should watch starting with bringing in raw blue screen footage up to keying it? Perhaps one that covers spill killers and making sure it is broadcast safe(since I again had no clue).

Thank you for ANY direction at this point,
Heather


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Mark Suszko
Re: trying to chroma key a bad blue screen job
on Apr 19, 2011 at 5:08:35 pm

Don't panic; you're most of the way there already, and it looks like you just ned to do more tweaking. While I have several tools available for chromakeying, I generally start and end using the regular chromakeyer in FCP. I will say that your keying results will always look better in a format that's better than DV25. IF you can work with this in a codec like prores or DVCpro 50 or something like that, a lot of the aliasing effects that can happen won't be as big a problem.

In the FCP chromakeyer, my first step is to prepare the footage a little bit and color-correct it. Your blue screen shot looks pretty good already. You want to reduce the blown-out white spots in highlights and get a good dynamic range overall. Being a photoshop girl, use your histogram display in the 3-Way Color Corrector and the FCP vector scope/wave form monitor to see how you treat the image for good dynamic range.

Now I'm ready to start keying. I pick green or blue as required, then go to the visual interface, where pick up the eyedropper tool to sample the color as close to the subject's face as I can. This gets things started, but you can use that picker more than once.

Next step is I grab the drag handles on the visual display and start moving the high and low limits around on the luma and chroma strips while looking at the quality of the key. I always use matets and masks for the sides so I don't worry if the edges of the shot don't key well at this stage, I am looking for a clean key along the actual body first.

The next step after that, I play with the little sliders below the main ones, which adjust the spill-killer and edge sharpess and how much the edge erodes or cuts into the key. This is kind of subjective, but the amoutn of yellow or magenta used by the spill killer becomes a bright rim of color around the subject, if you're using too much.

Finally, you don't have to get everything in one pass: you can invoke multiple instances of the keyer and composite them in ther FCP timeline so as to treat one troublesome part separate from the rest.

Last, where it is still acting up, or to remove, say, a shadow on the floor betwee the subjects' legs that won't key claen, the 4-point and 8-point masking tools are really pretty easy to use. The masks, and the chromakey settings are easy to cut and paste across multiple shots, there is a little icon in the interface for the FCP chromakey tool and the mask tool, you can drag and drop the icon over onto the next clip, and bam, all settings are identically applied.

Just those steps have let me do satisfactory keys, in plain old DV25, without a lot of pain.

You can do this, just be methodical and patient.


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Heather Gulledge
Re: trying to chroma key a bad blue screen job
on Apr 19, 2011 at 6:32:29 pm

Thank you so much. Watching tutorials is cool but I seem to grasp it better while reading it. So having a step by step that applies to what I am trying to do is great! Ok, so going to take a deep breath and follow your instructions. I think that also, not knowing how to work the filters and the adding of them, I was maybe over simplifying things.

Thank you for your time and advice. It was MUCH needed.

Heather


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Mark Suszko
Re: trying to chroma key a bad blue screen job
on Apr 19, 2011 at 6:38:32 pm

De Nada. Report back when you've aced it. I would have given you more Boris-specific tips, but I don't work in Boris for chromakeying.


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Heather Gulledge
Re: trying to chroma key a bad blue screen job
on May 2, 2011 at 6:28:08 pm

Well...aced may a bit of an stretch BUT I was able to follow your instructions step by step and achieve a pretty decent job. I was surprised at how much control I had with just the FC keying. I wound up not using the boris filters or keying at all. I did however have to do each clip depending on the background. I found a basic chroma key and color correction that worked and dragged it to each clip then was able to play with them and make it look really nice. Also,I never even knew where the vectorscope was so using those tools made it easy for me to see if I was going in the wrong direction. So, color nice, keying good, everything broadcast safe...leaves me feeling good. Thank you again for your instructions. I couldn't have done it without you.


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