Topics

Any advantage to UHD acquisition fo HD final - specifically to de-noising?

MARK FOERSTER
 

Using the Sony A7sii in Yellowknife for high iso shots of the Aurora Borealis. 
Thank god for the full-ish moon (for the researchers faces)  and I'm only pushing 32,000-40,000iso. 
Still seeing some granularity that might be difficult to remove as the northern lights themselves might look like noise to the software. 
Production says it has (heard) anecdotal evidence that a UHD to HD conversion will help with a noise reduction pass in finishing. 
Can anyone concur? 
I'm assuming the denoising is done in uhd THEN conforming to HD 
Might also help with sharpness as I'm at F1.4 all night but it's all voodoo and hearsay right now 
My final output is HD
Any input appreciated
thanks

Mark Foerster csc
Toronto  (InYellowknife) 
905 922 5555 

Gavin Greenwalt
 

Downsampling is a form of noise reduction.    Signal Averaging says your Signal to Noise ratio increases by the square root of (N) where N is the number of samples.  So if you have a 70:1 SnR UHD image and you downsample to HD you’re doing a 4x downsample for each sample (pixel) and your new Signal to Noise Ratio is now 70:1 SnR * sqrt(4 samples) = 140:1 SnR.

https://en.wikipedia.org/wiki/Signal_averaging

Long story short you should see a 1 stop reduction in noise by down sampling UHD to HD.

Gavin Greenwalt
VFX Supervisor
Seattle, WA

Justin Lovell
 

Hey Mark,

I shot up in the Yukon capturing something very similar. Yes, UHD capture and downsampling will give you a better fighting chance of reducing the noise.

We use this approach when doing scans at Frame Discreet (our film scanning studio) to reduce noise and improve overall sharpness.  

We set our Lasergraphics Scanstation scanner to 5k mode and downsample it to 2k or HD.  It's amazing what this can do to slicken up super 8 and 16mm scans especially.

As for the Aurora Borealis, longer exposures with a slow shutter can't hurt either as the colors in the sky will be dancing so much that you shouldn't feel the motion blur.  But do some tests as some camera systems introduce higher levels of sensor noise.  (The Alexa when pushed with long exposures/ slow shutter can reveal some hot pixels that don't move).

For night interviews, we also utilized bounces with low levels of light and neg fill.  This aided the snow bounce to have a very natural looking exposure on faces while maintaining detail in the sky.

Best of luck out there and stay warm,

Justin Lovell 
Cinematographer || Storyteller

Associate Member, Canadian Society of Cinematographers 

Talk: M. 416.803.1101 / O. 416.901.5332 
Reel: www.justinlovell.com
Social: @justin_lovell

°sent with tpyos from my moible

Daniel Lynn
 

I’ve always found with the a7S, that by over-exposing by 2 stops (while making sure not to clip) and bringing the image back down in post, I got rid of most of the noise. 

Hope that helps. 


On Thu, Mar 1, 2018 at 12:06 AM Justin Lovell <just.love.film@...> wrote:
Hey Mark,

I shot up in the Yukon capturing something very similar. Yes, UHD capture and downsampling will give you a better fighting chance of reducing the noise.

We use this approach when doing scans at Frame Discreet (our film scanning studio) to reduce noise and improve overall sharpness.  

We set our Lasergraphics Scanstation scanner to 5k mode and downsample it to 2k or HD.  It's amazing what this can do to slicken up super 8 and 16mm scans especially.

As for the Aurora Borealis, longer exposures with a slow shutter can't hurt either as the colors in the sky will be dancing so much that you shouldn't feel the motion blur.  But do some tests as some camera systems introduce higher levels of sensor noise.  (The Alexa when pushed with long exposures/ slow shutter can reveal some hot pixels that don't move).

For night interviews, we also utilized bounces with low levels of light and neg fill.  This aided the snow bounce to have a very natural looking exposure on faces while maintaining detail in the sky.

Best of luck out there and stay warm,

Justin Lovell 
Cinematographer || Storyteller

Associate Member, Canadian Society of Cinematographers 

Talk: M. 416.803.1101 / O. 416.901.5332 
Reel: www.justinlovell.com
Social: @justin_lovell

°sent with tpyos from my moible

--
Daniel Lynn, Cinematographer
323.821.6712
www.danielvlynn.com

Daniel Henríquez-Ilic
 

"Average" process also helps to reduce noise, and works well with time lapse. This process is available on Snell Advanced Media Quantel Rio (QUtility/Average) or within Flame software.

Daniel Henríquez Ilic
Post-Producer
Santiago de Chile