When using noises to create atmosphere, I find that the edges created by 
masking can be unsatisfactory. Real smog (of the heavy variety) has a more 
eventfull edge than a simple mask can readily supply. I dealt with this by 
merging the noise with a large ramp or blur and setting the blend mode to 
minus. Check out script number 3 in this linked file for an example. It is 
somewhat overly annotated as it was meant for teaching purposes. 

http://opticalenquiry.com/nuke/documents/Noise.zip



Sent from my iPad

On 28 May, 2012, at 2:46 AM, Gary Jaeger <[email protected]> wrote:

> Cool thanks I give those a try
> 
> On Sat, May 26, 2012 at 11:45 AM, Fredrik Pihl <[email protected]> wrote:
> Gary,
>  I usually over a constant color (w alpha) ranging from blue to white/gray, 
> depending on the type of weather and time of day in the plate, modulated by 
> depth. This is the scattering of light that occurs by particles (water 
> vapour, dust etc) in the air between the observer and the distant object. 
> When the particles are very tiny this scattering is highly wavelength 
> dependant - blue light is scattered far more then red light (thats why the 
> sky is blue). Bigger particles like water droplets are not and scatter all 
> wavelengths pretty much the same - hence - clouds and mist come out white.
> 
> The distant object also loses light due to the same scattering.. losing the 
> blue wavelengths first.. so I usually multiply with yellow thru red modulated 
> by the same depth. The more air and particles there is between the object and 
> the observer the more of the short wavelengths are scattered and absorbed. 
> Thats why sunsets are so beautiful :)
> 
> refer http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html
> 
> To just plainly desat and grade usually works - but this approach is more 
> accurate to nature, and just as simple.
> 
> I once comped a cg smoke element on a plate with a bright sky and sun, 
> letting the density of the smoke affect the color of the bg.. not really 
> noticeable ,except when the thick smoke passed in front of the sun disk where 
> it going redder came out beautifully realistic :)
> 
> 
> 
> /fredd
> 
> 
> On Sat, May 26, 2012 at 2:01 AM, Darren Coombes 
> <[email protected]> wrote:
> Sometimes I use the noise node, using depth pass as mask.
> 
> Helps if the noise is larger than smaller i reckon.
> 
> then just grade the noise if need be, and comp over footage.
> 
> Cheers.
> 
> Darren.
> 
> On 26/05/2012, at 9:16 AM, Gary Jaeger wrote:
> 
>> anybody have any good recipes for adding atmosphere, probably using a depth 
>> matte I'd guess? is it mostly a contrast thing?
>> 
>> -- 
>> Gary Jaeger // Core Studio
>> 249 Princeton Avenue
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>> 650 728 7060
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> 
> Darren Coombes
> Compositor
> 
> www.resolutiondesign.com.au 
> 
> 
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> 2010 Silver One Show Entertainment Award: Online Branded Entertainment 
> 2009 Gold Promax/BDA Award: Best Broadcast Design Image Spot  
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> 2009 Finalist Creative Review Hotshop Award: Broadcast Design
> 
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> -- 
> __________________________________________________
> Fredrik Pihl - visual effects supervisor - digital compositor
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> 
> -- 
> Gary Jaeger // Core Studio
> 249 Princeton Avenue
> Half Moon Bay, CA 94019
> 650 728 7060
> http://corestudio.com
> 
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