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Creating shadow, midtone and highlite Luma Mattes?

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jim bachalo
Creating shadow, midtone and highlite Luma Mattes?
on Jul 17, 2011 at 2:32:15 pm

Hi
I'm trying to create shadow midtone and highlite masks for a given layer.
Purpose: primarily to be able to selectively apply effects to highlights, mid-tones, shadows etc.

I think this would be a fairly common operation in AE, and I can previsualize what my masks will look like, just having a problem getting there.

Some combination of Levels, and perhaps Blendmodes and-or Calculations or even the Luma Key effect?

Playing in Photoshop, I discovered I can create an 'inverse Luma Matte' but just for the midtones by
1-duplicating a layer
2-inverting all the colors
3-changing the blend mode to difference

A filter like this Luma Mask pro but for AE would be ideal!
http://goo.gl/U8dAN

Any ideas?

Local is the new global


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Max Weissenbacher
Re: Creating shadow, midtone and highlite Luma Mattes?
on Jul 18, 2011 at 9:00:53 am

Hi Jim,
yes, this is a very common operation indeed in compositing, often used to light- or shadow-match objects (so creating or eliminating clues where the light comes from).
So the workflow is: create a simple high-con matte for your layer (I recommend Colorama or Levels) so you only have the area that you're trying to affect left. Then create garbage masks or mattes or edge mattes to further limit and clean up your selection. Finally apply your new matte as a trackmatte (or inversed, depending on your selection) to an adjustment layer or if you want to limit a solid or whatever you wish with it.

Cheers,
Max


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jim bachalo
Re: Creating shadow, midtone and highlite Luma Mattes?
on Jul 18, 2011 at 2:50:44 pm

Thanks Max!
A little simpler and more straightforward than I thought.

Local is the new global


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Walter Soyka
Re: Creating shadow, midtone and highlite Luma Mattes?
on Jul 18, 2011 at 5:57:40 pm

Other really useful effects for creating and manipulating mattes include Curves [link], Find Edges [link], Invert [link], Channel Combiner [link], Set Matte [link], and Minimax [link].

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
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Max Weissenbacher
Re: Creating shadow, midtone and highlite Luma Mattes?
on Jul 19, 2011 at 8:20:06 am

You're very welcome! The simplest solutions are most often the best! Also thanks to Walter for adding some tools to that. What Walter also mentioned (and what I forgot to mention) is that you should look through your R, G and B channels to see which one offers the best contrast. Then use Set Channels to set the R, G, B channels all to the same (so f.e.: R=B, G=B, B=B) to achieve a grayscale representation of your chosen channel. Then creating the matte will probably be easier!!

Good luck!

Cheers,
Max


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