Why, oh why, the sizzling sky?

[Stewart McLain]

I've been watching some older films recently with my nephew who is staying with us for Christmas and I'm seeing an artifact in the movies that has bothered me for some time:  the sky looks like it is alive and sizzling with ameoba-like creatures.  It's always from movies that were originally shot on film. It irritates me because I'm sure that young people seeing these movies for the first time just think that film must just have looked like that. Anyway,  I'm just curious; where in the digitzalization chain does this weird degradation occur?  

[David Mullen ASC]

It’s noise from a telecine transfer or scan off of a film negative, where the darkest (densist) areas are the brightest areas in the scene, like the sky. So those areas are underexposing the sensor, causing signal noise. Not all telecines or scanners create noise in bright areas though.

[Piotr Wołoszyk]

I think the compression algorithms adds up to emphasize effects like that.

[Dan Quigley]

I was surprised to see the same thing on skin tones in my BluRay copy of Home Alone 2. Agree with David and Piotr, I think both statements are true and compound eachother.

[Frank Wylie]

Problem is, no one know exactly what "enhancements" are being applied by the BluRay player or the Monitor to the compressed signal. 

Too bad it can't all be bypassed as an option...

[Stewart McLain]

Well, thank you all for the insight.  Sounds like it can get piled on at any point in the process.  I was just reading an interview with Sydney Pollack last night where he said he would actually check projection lenses and personally clean screens at theaters that were going to show his films.  There's just so little control over how your film will ultimately be viewed.