Jump to content


Photo

Arri Alexa


  • Please log in to reply
14 replies to this topic

#1 Drazen

Drazen

    Flying Pig

  • Adv Members
  • PipPipPipPipPip
  • 86 posts

Posted 24 December 2010 - 01:47 PM

hello all!

I recieved some greenscreen footage from arri alexa, but the noise amount in blue channel is really huuuuge and edges are fu...d up, every keyer and every keying tehnique, doesn't help me to get a clean alpha

anyone tryed something with that kind of footage? alexa with greenscreen?

I can upload a still .dpx file!

thanx in advance and happy holydays!

Drazen

#2 Ray Smithers

Ray Smithers

    Administrator

  • Admin
  • PipPipPipPipPip
  • 378 posts

Posted 24 December 2010 - 03:53 PM

hello all!

I recieved some greenscreen footage from arri alexa, but the noise amount in blue channel is really huuuuge and edges are fu...d up, every keyer and every keying tehnique, doesn't help me to get a clean alpha

anyone tryed something with that kind of footage? alexa with greenscreen?

I can upload a still .dpx file!

thanx in advance and happy holydays!

Drazen


Wow I find that VERY interesting since we are considering an Alexa. It is bad lighting, camera settings or do you know. I for one would love to see a snip of the footage. I have had some luck using a de-noise filter but as you now (you will soften the image).

#3 Pilalitos

Pilalitos

    Flying Pig

  • Adv Members
  • PipPipPipPipPip
  • 791 posts

Posted 24 December 2010 - 04:06 PM

If the problem is noise then NeatVideo will probably help. Like we have mentioned before in another thread it's an unbelievably impressive and economic tool.

I am not sure about the edges though... What's wrong with them?

#4 Drazen

Drazen

    Flying Pig

  • Adv Members
  • PipPipPipPipPip
  • 86 posts

Posted 24 December 2010 - 08:37 PM

you can take a look at this download link

http://jumbo.iskon.h...2rzte0zxbjuboo/

#5 Pilalitos

Pilalitos

    Flying Pig

  • Adv Members
  • PipPipPipPipPip
  • 791 posts

Posted 24 December 2010 - 09:31 PM

you can take a look at this download link

http://jumbo.iskon.h...2rzte0zxbjuboo/


Wow! I have never seen anything like that.. :-(

Was that Arri Raw or Apple prores?

I think you can use a combination of keyers to get rid of the problem but it's gonna be tricky... I might give it a try when i go back to my desktop computer.

#6 Drazen

Drazen

    Flying Pig

  • Adv Members
  • PipPipPipPipPip
  • 86 posts

Posted 25 December 2010 - 05:12 AM

that must be prores directly from camera

yeah that's really a shame, it's like looking at a beautiful girl, but you don't know that she is evil :)

#7 Ray Smithers

Ray Smithers

    Administrator

  • Admin
  • PipPipPipPipPip
  • 378 posts

Posted 25 December 2010 - 05:57 PM

IMHO we never shoot on our green-screen stage with a shallow depth of field. You just can not have a depth of field blur and end up with a clean edge. The stage lighting is outstanding and would offer a great key but the subject approaching the camera is the only one in focus (including the car in the background).

#8 Pilalitos

Pilalitos

    Flying Pig

  • Adv Members
  • PipPipPipPipPip
  • 791 posts

Posted 26 December 2010 - 01:59 PM

IMHO we never shoot on our green-screen stage with a shallow depth of field. You just can not have a depth of field blur and end up with a clean edge. The stage lighting is outstanding and would offer a great key but the subject approaching the camera is the only one in focus (including the car in the background).


Why should the shallow depth of film be a problem? By the same logic we should never shoot with long shutter so there is no motion blur... :huh:

A good key should include both the sharp and soft edges. Otherwise it looks unnatural.

The stage lighting is good but noise in the blue channel is extensive. It's easily solvable with a good noise removal tool but i think some parts of the shot need some roto-work (like the car's windshield's frame)

#9 Ray Smithers

Ray Smithers

    Administrator

  • Admin
  • PipPipPipPipPip
  • 378 posts

Posted 26 December 2010 - 04:06 PM


IMHO we never shoot on our green-screen stage with a shallow depth of field. You just can not have a depth of field blur and end up with a clean edge. The stage lighting is outstanding and would offer a great key but the subject approaching the camera is the only one in focus (including the car in the background).


Why should the shallow depth of film be a problem? By the same logic we should never shoot with long shutter so there is no motion blur... :huh:

A good key should include both the sharp and soft edges. Otherwise it looks unnatural.

The stage lighting is good but noise in the blue channel is extensive. It's easily solvable with a good noise removal tool but i think some parts of the shot need some roto-work (like the car's windshield's frame)


You are right about noise removal and that was my first suggestion. I am not on my work computer so did not break down channels. Depth is an issue since we are almost always shooting for match move and must have the markers in focus. But soft edges can be time consuming on occasion.

#10 isotron

isotron

    Flying Pig

  • Adv Members
  • PipPipPipPipPip
  • 237 posts

Posted 04 January 2011 - 04:11 AM

have had alexa footage too, with ProRes4444 . And the quality was VERY good, with Harddisk recording DPX files the quality must be unbelieveble ;) but need Terrabytes!
On your Set must be somethink wrong :/ For very good denoise i use "furnace DeNoise", maybe only on the bluechannel?!

#11 Drazen

Drazen

    Flying Pig

  • Adv Members
  • PipPipPipPipPip
  • 86 posts

Posted 04 January 2011 - 07:57 AM

yeah, the problem is they did not record it as you recieve it :) terrabytes? not really hehe :P at least not in this case

noise nightmare :D

#12 countzep

countzep
  • Members
  • 1 posts

Posted 17 January 2011 - 05:18 PM

Hello Drazen...

We are shooting a television show here in LA and have been having a very difficult time pulling keys from the Alexa footage. Would love to compare notes with you to figure out why?
We don't seem to have an issue with other footage, whether from the Phantom camera or from the F35.

We are shooting LogC extended, but have also have experimented with LogC Legal (standard) and Rec709 to no avail.
We have ruled out problems with SR deck or our post process, by recording direct to flash drive.
We also seemed to have ruled out underexposure as an issue and have done bracketing tests on the asa and screen brightness

The only way we can get a good key is to use Neat Video and at the same time apply a LUT (provided by Arri) on top of the footage, thus linearizing it in the comp. They don't have a converter to get it back to log space which makes using this LUT problematic.

Would love to see a frame of your footage, but the link doesn't seem to work.

Best Regards...

#13 bfloch

bfloch

    Flying Pig

  • Adv Members
  • PipPipPipPipPip
  • 960 posts

Posted 18 January 2011 - 03:49 AM

Anyone asked Arri directly for recommendations / experience?

#14 Gringo

Gringo

    Associate Administrator

  • Adv Members
  • PipPipPipPipPip
  • 1,455 posts

Posted 18 January 2011 - 06:50 AM

This macro may help conceal some digital edge artefacts as well as chromatic aberrations:

Attached Files



#15 Drazen

Drazen

    Flying Pig

  • Adv Members
  • PipPipPipPipPip
  • 86 posts

Posted 25 January 2011 - 06:14 AM

hey all!

I was out for some time, but here is footage one more time, hope that link works now, enjoy key tests :D

http://rapidshare.co...1221_R1SK-v.rar




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users