• Adobe After Effects

  Blurring Street lights in BG of Night Shot Without Affecting Foreground?

  Posted by Mike Healey on October 7, 2009 at 12:24 am

  I have a video that I shot of someone in the back of a car that is driving through a city at night-time. I would like to blur out and color correct the street lights in the background to try to re-create a shallow depth of field, while not affecting the person in the car in the foreground. I obviously know that it would have been better to try to do this in production as opposed to post, but this wasn’t an option due to a variety of factors (budget, very tight schedule for pre-production and production, etc).

  I was wondering if there was a way to create a mask based on the luminance of the lights in the background, or find some other way to apply effects only to the background and not the foreground? Any help would be greatly appreciated. I’m also open to trying this out in an application other than AE if that might help…

  Thanks!
  -Mike

  Mike Healey
  mi**@****on.tv
  https://www.kneeon.tv

  Marcello Mazzilli replied 16 years, 7 months ago 3 Members · 2 Replies
• 2 Replies

• 

  Jon Geddes

  October 7, 2009 at 1:38 pm

  Well, if the background has a much brighter luminance, you could duplicate the footage, desaturate and apply a levels adjustment to create the matte, precompose, and apply a lens blur to your original footage, using the precomp as the Depth Map Layer.

  Jon Geddes
  http://www.precomposed.com
• 

  Marcello Mazzilli

  October 7, 2009 at 1:50 pm

  Well the first thing is to find a way of selecting just what you want to blur. You can do this with luminance (as suggested), with chrominance (lights could be the only orange thing), but also you can combine fixed masks (like simple boxes) for darker corners etc… Viceversa you can create negative masks forcing some parts not to be cut out (i presume the lower part of the screen). If the objctive of the the mask is to work on blurs then probably it is possible to soften the mask to reduce edge imperfections. I don’t have the footage (or a foto) so it’s not easy just to guess. Once you have an alpha mask then you just have to use it as a matte for the whole frame. After FX will do fine for me.

  siRoma di Marcello Mazzilli
  Corporate video productions in Italy
  http://www.siroma.com

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