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Photo Format shoot on ChromaKey

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Zvi Twersky
Photo Format shoot on ChromaKey
on Jan 21, 2010 at 10:17:16 pm

I know that when shooting video on green screen, we should shoot in the highest resolution we can afford. I would assume the same rule would apply to digital photography but I wanted to ask just to be sure.

Would it be correct to say that when shooting digital photography on a green screen, we should set the camera to use a lossless compression algorithm like TIFF and not a compressed format like JPEG?

Thank you.



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Todd Terry
Re: Photo Format shoot on ChromaKey
on Jan 21, 2010 at 10:23:12 pm

Correct.


T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com






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Zvi Twersky
Re: Photo Format shoot on ChromaKey
on Jan 21, 2010 at 10:52:36 pm

Thanks Ted.

I am not trying to get into any debates, but rather trying to get all my facts in order. This is why I asked this question in a few places and this is what one Walter Graff from http://bluesky-web.com answered me:

It really should not make a difference. The problems of green screen and video involve codec (ie formats) and that issue does not occur the same way in still photography. High resolution (quality SLR) cameras should have no issues with green screen. If you are shooting video on a still camera, then the issues may be present as again its about codec and video formats. Resolution alone does not make green screen better or worse.

Since it's not like you said, I am respectfully asking if you can go a little more into specifics about this. The camera we are using is a Nikon d5.

Thank you



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Emre Tufekci S.O.A.
Re: Photo Format shoot on ChromaKey
on Jan 22, 2010 at 1:34:19 pm

The biggest differences comes from dealing with one frame on Photoshop vs thousands of frames in video.

Since video is compressed in different ways, color space (4:4:4; 4:2:2, 4:2:0,3:1:1, 4:1:1..etc)

http://en.wikipedia.org/wiki/Chroma_subsampling

the bit rate varies (14-12-10-8 bit)

http://www.larryjordan.biz/articles/lj_video_bit_depth.html

resolution (1080, 720, 486, 480) and the scan methods differ progressive vs interlaced there is a lot to deal with so prolonged clean mattes are difficult to achieve.

Still images don’t have to deal with the issue of color space, bits, resolution and I vs P as same as the limitations of video.

Also the process of keying differs in still photography. In video most common is the chroma key. But in still photography you can use chroma, luminance, contrast or neat tools like magic wand to cut out images.

There are also nice plug-ins available to make the process easier: (just a sample there are much more)

http://www.adobe.com/cfusion/marketplace/index.cfm?event=marketplace.offeri...

http://www.adobe.com/cfusion/marketplace/index.cfm?event=marketplace.offeri...

So to summarize it:

Yes-shoot the highest resolution possible so when your feather or clean up your matte's edges you will see less softness.

Yes- try to use less compressed formats as there will be more information work with.

Again this does not mean with a 1000X1000 pixel, jpeg format still can't be keyed cleanly. It just makes sense to shoot large and then reduce it as you need it.


Emre Tufekci
http://www.productionpit.com



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Emre Tufekci S.O.A.
Re: Photo Format shoot on ChromaKey
on Jan 22, 2010 at 1:38:58 pm

Now having said all that, when we do photography that will be used in a video we do not use chroma key. We use contrast.

We shoot the subjects agains a white background (overexposed) and than set up a automation in photoshop to use magic wand to process the pictures.

We get super clean images an can process thousands of pictures in minutes.

Just another way of doing it.

Emre Tufekci
http://www.productionpit.com



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Mark Suszko
Re: Photo Format shoot on ChromaKey
on Jan 22, 2010 at 3:17:31 pm

If you can, why not shoot the stills in RAW format then?


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Zvi Twersky
Re: Photo Format shoot on ChromaKey
on Jan 22, 2010 at 8:33:31 pm

First, thanks for the replies. I will respond in order:

To Emre:

1. Our photos shoot 4288x2848. So are you saying that since that is plenty information to work with, keying it will be just fine in JPEG format? But still, if TIFF or RAW is higher quality yet, why not just shoot in those formats? Since to shoot it in TIFF or RAW is just the change of a setting. If there is any chance for a better key, why not?

2. I know that 35mm film shoots 4:4:4 and DV shoots 4:1:1. But that only means that on each frame, the color information updates itself on DV every 4 pixels. Pixels refer to a frame. A still image from a digital camera is a frame too. Doesn't JPEG compress itself the same way by combining similar pixels (and loosing data)? I know that video has another codec\cpmression method to further reduce size (and reducing quality) called DCT (Discrete Cosine Transform) where it shaves off higher frequencies in the data and then when converted back to a picture, we end up with a lower quality image. This I can understand does not apply to still images. (or maybe I'm wrong?)

3. Yes, I have studios shoot on white but our studio is a green screen cyc, set up for video and stills so I would need a good reason to convince my boss to buy a white backdrop instead of using the green. If it is just a of matter of it being easier to key off luminance then chroma... I don't think I can convince him of that. If you are saying that keying off luminance will give better results (not faster) that could be something to work with. So what are you saying?

4: What format do YOU shoot in your studio?

To Mark:

I am not a digital photographer but I know we use Nikon D5. It seems from googling it, it CAN shoot RAW. I will ask the photographer about it. He shoots mostly weddings so I don't think he ever shot RAW before. Would it be correct to say that you all agree that with still photography, RAW is the best way to go for keying? (or if RAW is not an option, TIFF rather then JPEG?)

Thanks again



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Emre Tufekci S.O.A.
Re: Photo Format shoot on ChromaKey
on Jan 22, 2010 at 9:03:16 pm

1-Raw or Tiff will produce better result. you just have to deal with larger files. If this is no inconvenience go for RAW.

2- You are correct, after DCT there are a lot more that goes in the camera to compress the image further. If you want to totally geek out watch these series:

http://media.panavision.com/ScreeningRoom/Screening_Room/Demystifying_Part1...

3- White background will speed up the process, other than that green background will be just fine.

4- We primarily deal with DVCPROHD and AVC-I formats. But over the years depending on project needs we have used every high-end format under the sun.


Emre Tufekci
http://www.productionpit.com



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Zvi Twersky
Re: Photo Format shoot on ChromaKey
on Jan 23, 2010 at 11:35:15 am

Thank you for all the advice. Very appreciated.

p.s. I'm a little silly for not thinking that since we will be shooting mostly brides with white wedding gowns, I don't think a white BG would work ;-) Just out of curiosity, can you shoot brides on a black background as well or is it only the blown out luminosity in white that can do that trick?





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Emre Tufekci S.O.A.
Re: Photo Format shoot on ChromaKey
on Jan 23, 2010 at 1:28:41 pm

Not really, hair and other objects would be a problem. they probably would bleed in if you are using contrast to cut them out. Same thing with white and wedding gowns.

Emre Tufekci
http://www.productionpit.com



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