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-   -   Cameras for blue/green screen work (http://www.dvinfo.net/forum/open-dv-discussion/22698-cameras-blue-green-screen-work.html)

Thomas Smet March 10th, 2004 09:56 AM

Cameras for blue/green screen work
 
I am a compositor and I currently have a Canon XL1. I have been curious to what others think are the best cameras for keying type work. I know all the ins and outs of keying with dv. Forget about the format and just think about the raw image coming from the camera. I want to find out what camera is the best for this type of work.

Things to think about...

1. number of pixels per CCD to give lots of detail

2. pixel shift or no pixel shift

3. Whether the YC output or component is true 4:2:2 video and not already 4:1:1 compressed by the camera

4. electronic edge sharpening by the camera

5. any odd color shifting problems such as the one with the dvx100


I didn't know where to put this but I do want replies that lean more towards compositing for film and not the electronic keying look. I do most of my compositing in Combustion or Shake.

Not every camera is equal when it comes to shooting a blue/green screen and this is a topic that is very seldom talked about. I look forward to hearing from others.

Patrick MCMurray March 10th, 2004 10:29 AM

the first thing to come to mind <even before you mention odd color shifts> is the xl's reddish tint Ive heard about lots of times. I assume you shoot mostly people? the extra red might help separate them from the blue/green backdrop. just a thought...

Daniel Kohl March 10th, 2004 01:24 PM

My experience with chrome keying is that the quality of the lighting is paramount.

Or let me put it this way – not properly lit chrome keys are hell, regardless of the resolution you’re filming with. This applies to 16mm and 35mm telecined, Beta SP, DVC Pro etc.

It would be nice to see a controlled test series, with the same chrome key scene, filmed with all available resolutions, formats and cameras. I think that would be the only way to really answer your question.

When the light has been right, I have gotten very good results with my XL-1.

Thomas Smet March 10th, 2004 04:08 PM

yeah I know it would be hard to judge without doing a side by side look at all of them. I figured this was the best way to figure out what other people were using and seeing how it worked for them. I have gotten good results using my XL1 but I am always looking for better quality. I have been thinking of getting a dvx100a for my new camera and then I heard about the color phasing problem on pans. I will still get one soon because I do a lot of music videos that require a lot of compositing of many shot elements. I need a 24pa to not only get the highest quality but to also be able to resize my shot elements without having to de-interlace or worry about interlace flicker. Anyways I am getting off track.

I know the right way to shoot a blue/green screen setup and I do not need any tips. I just want to hear from other people out there what kind of results they get with different cameras.

Emmanuel Decarpentrie March 12th, 2004 04:45 AM

Adam Wilt said he would never recommend a DVX100 (or DVX100A) for blue/green screen (because of the chroma shift, among other reasons). However, he said you can get pretty good results with it, so long you rely at least a little on the Luma rather than solely on the chroma signal. In other words, the DVX100 is perfect for Luma Keying or Chroma (i.e. green screen) keying where Luma is the primary parameter.

So, I think you will get good results with the DVX100, but you must carefully experiment before, and pay maximum attention to the lighting: the green background should be much dimmer than your caracter(s).

Robert Knecht Schmidt March 12th, 2004 04:52 AM

"In other words, the DVX100 is perfect for Luma Keying or Chroma (i.e. green screen) keying where Luma is the primary parameter."

Meaning your foreground element must be dimly lit and your background color must be brightly lit and exposed to near saturation?

Jeff Patnaude March 12th, 2004 07:43 AM

I've shot chroma key with Beta SP and with DV, and DV was a beeyatch. The compression algorythm (love that word) made the edges irregular, and there was a ton of noise around the edges. I tried compositing with After Effects and FCP.

Uncompressed Beta SP is tricky enough on its own, but I have been successful getting good results with- as the other posters mentioned- proper lighting and exposure control.

I've read that you dont even want to try it with anything less than DVC pro (at 4:2:2- correct me?).

But dont let this stop you. If you get good enough results for you and your client- thats what will matter I guess.

As always- good luck!

Jeff Panaude

Thomas Smet March 12th, 2004 09:06 AM

I have been using my Canon XL1 with great success for 4 years doing numerous blue/green screen work and the results have been pretty good. I know the DV format is weak for color channels. this isn't what this post was supposed to be about.

What I want to hear from people is what cameras they are using and what kind of results do they get. Every dv camera is built different. Some have more electronic edge enhancement then others which can make keying difficult. There are a lot of factors in the camera itself the determine what kind of image you get. The 4:1:1 dv format is one thing but if the camera dumps a bad image into 4:1:1 then it will be even worse. I want to sort of get a poll of people out there as to the results they get from a certain camera. I do not care about the format just the raw image from the camera itself.

To make this easier forget about the 4:1:1 issue and pretend the images are 4:4:4. How would they look then? How many artifacts are there besides the lower color resolution? The sort of info I am looking for is the type of problem with the dvx100a with the color phasing problem. Both the dvx100a and the XL1 both record dv at 4:1:1 but clearly the color is not handled the same by both cameras. Some may say the XL1 is better because of this. Others may say that even with the color phasing problem the dvx100 is much cleaner than the xl1 due to a much more detailed image.

I haven't had a chance to check this with blue/green screen footage but with footage from other cameras over the years from different people I would do a test and check how well the color channels were recorded. I have found that all cameras are different in the way this is done. 1/2 ccd cameras for instance like the jvc 5000 or a sony dsr300/500 seem to do much better compared to the XL1.

4:1:1 is a problem but it isn't as major as many like to think it is. With chroma upsampling or chroma blurring keys can be just as good as 4:2:2 or 4:4:4 footage just a little bit softer edges. A lot of times people add edge softening to keys anyways.

Daniel Broadway March 20th, 2004 07:12 PM

Alright Thomas, I know what you're asking. I shoot my greenscreen setups on a Canon GL2. You can look at the bottom of this page to see how good my results were. I filmed this with the edge sharpening set to -2. Also, I shot it interlaced, and then de-interlaced it using a field blending trick. Then I pulled the key with Primatte.

As you can see, the guy in front of the greenscreen had long fuzzy hair. Check it out....(bottom of page)

http://www.geocities.com/night_sky_vfx/effectstests.html

Filip Kovcin March 21st, 2004 02:14 AM

to Daniel Broadway
 
Daniel,

what kind of software you used for that sw1/2 test shots?
it looks really nice.

filip

Daniel Broadway March 21st, 2004 03:38 PM

I used 3ds max. All of those space craft are CGI.

Jay Rogers May 21st, 2004 11:24 PM

So How did it Go?
 
Thomas, I am trying to decide between the XL1, the DVX100a, and the PD-170 - and I've decided that chroma fidelity for keying is my major differentiator on the purchase.

I also saw the Adam Wilt article on the Panasonic, and thought that it was a strike against the DVX100a.

So I'm interested in how you finally made your decision.

Julian Luttrell May 24th, 2004 02:37 AM

Will you be able to record straight to computer through the camera's analog output (usually svideo, but componentis better)? If so, and you have an uncompressed or very-little-compressed capture card then this route can give a very good key by bypassing the DV25 compression that is applied to the taped results.

I personally use a 20 year old analog Ikegami HC230 for this - gorgeous keys, even if the camera looks rather old!

Julian

Robin Davies-Rollinson May 24th, 2004 09:23 AM

Julian,
I thought that the image had already been compressed by the time it leaves the camera, either by firewire or as an analogue signal by a/v...

Robin

Julian Luttrell May 24th, 2004 09:32 AM

AFAIK the svideo/component output in (most?) dvcams is before the DV25 compression stage. Wherever in the chain it lies, the important thing is that the svideo/component output does not have the 4:2:0/4:1:1 chroma blocking effects apparent in DV25 tape material.

Why not try it out to see for yourself?

If anyone has any more information about this please post.

Regards,

Julian


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