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Saturday, September 22, 2012

••◊ Noise reduction on HDSLR footage, part 3

I'm trying to blog about these things as I figure them out in Adobe After Effects.  I won't profess to being an expert, by far, but I'm getting better as I get familiar with the software.  This post is a follow on from part 1 done in 2011 and part 2  done in May of this year on noise reduction of HDSLR footage.  I recommend reading those two posts before digging into this one.  I'm too lazy to re-write those instructions again!

This is what we're starting with...


I circled the areas where chroma noise is most obviously prevalent.  You may need to click on the picture to actually see the noise.  This is typical of high ISO HDSLR footage.  I shot this a few years ago before I owned any lights, so I was working with whatever nature gave me that day.

The first step to cleaning up this footage is to create two layers.  The top layer will the background and the bottom layer will be our subject - David Patterson.


The noise reduction/obfuscation technique from part 1 of this tutorial is applied to both layers. This involves using the Channel Combiner and Channel Blur effects to make the noise more monochrome, like film.  Note that this doesn't actually reduce overall noise, it just makes it less objectionable since it's not random rainbow colors anymore.


For simplicity I added a Color Balance (HLS) effect to the top layer and turned up the lightness.  This allows me to see where I'm applying a mask.  Then I apply a mask to the top layer to cardboard cutout our subject.  Note that the mask feathering is set to 35 pixels and the mask expansion is set to 10 pixels.  This should get us close enough.  Then the mask has to be manually key framed to follow our subject as he moves during his speech.  Sorry about the manual nature of this.  If you know a more automated way of having the mask follow the subject please leave a comment below.  I'm not an After Effects expert...for good reason.  I'd rather be doing camera work.


Since the background is stationary I turned on the Remove Grain effect on the top layer; i.e. the one with the mask that reveals the background. Not only do you want to turn on the Noise Reduction settings, but also turn on Temporal Filtering at 100%.  This is the secret sauce in this recipe.  If you don't turn on this feature then your shadows will dance around like a swarm of army ants because the noise is still there.  It's very distracting for a viewer to see that on a plain painted wall that's supposed to be out of focus.


This is the final result in After Effects after turning off the Color Balance effect on the top layer. Note that the subject movement is obscuring the monochromatic noise on the bottom layer.


Here's a comparison of the before and after of the footage, with color grading applied.  The color grading added a little vignette with helped hide the noise on the back wall even further and NO PLASTIC-Y SKIN!..as is common with a lot of video noise reduction plug-ins.  Woohoo!  I hope this helps some of you out there.  If you find improvements to this technique please leave a comment.


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