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Invert Mask with Subject and Brush Subtraction

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I'm really enjoying the new Mask features. However, I'm having an issue in trying to create an Invert Mask made up of a Subject and Brush Subtraction.

I have a picture of my grandson on a swing. When I create a Mask with Select Subject, LrC found my grandson but also associate parts of the swing. I used a subtraction brush to remove the swing parts. I was happy with the results.

I decided to try to create an inversion of this in order to make changes to the photo that was not my grandson. I duplicated the Mask. When I went to invert the copy, I found there was no invert on the Mask and when I inverted the subject and negative brush, the result was a very strange masking. Not everything except my grandson which is what I wanted.

What am I doing wrong?

Thanks

Here's the original untouched picture.
1636420117851.png

Here is the Mask (Grandson) of Subject and Subtraction ( a bit sloppy)
1636420276164.png


Here is the Mask with the subject and the subtraction inverted. Not want I wanted. I wanted the black and white to be exchanged from the above Mask
1636420473565.png
 
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See this recipe for how to invert a mask group:
https://community.adobe.com/t5/ligh...-invert-flip-mask-group/idc-p/12490945#M13146
Also, scroll to the top of that thread and click Upvote to encourage Adobe to provide a simple button that would automate these steps.
Thanks @johnrellis. That works exactly the way I wanted.
  1. Invert the bottom mask component
  2. For the mask components above the bottom convert to subtract if it has been added and convert to add if it has been subtracted.

1636465749660.png
 
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The logic of this totally escapes me but it does work. Not exactly intuitive but thanks.
The logic is actually quite simple if you think it through. Suppose you selected a subject: a model. The auto subject selection did not include the left arm however, so you add that with a brush mask. Now you want to invert the total mask, because your goal was to edit the background. When you invert the model, the left arm will become part of the background, because it wasn't part of the model initially. So if you would use a brush to correct that, you would have to subtract that brush. Keep that in mind for now.

So now let's look at the brushed correction you already made. You added a brush stroke. Your first intuition may be that inverting the brush is all you need to do, but think about what inverting does. Invert selects everything that wasn't selected, and deselects everything that was selected. So if you invert a brush stroke, then what you will get is an image that is completely selected, except for the brush stroke... That is clearly not what you want!

What you do want is to subtract a brush stroke from the mask, we already concluded that. And what you have got a is brush mask that is added. So what needs to be done is that add is changed to subtract (and vice versa).
 
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The logic of this totally escapes me but it does work.
It may be easier to visualize a simple example. Here's a linear gradient on the left (white) with a radial gradient (white) added to it:

Screen Shot 2021-11-14 at 8.49.59 AM.png


To invert the entire mask, we want the black area above -- the inverted linear gradient with the radial gradient subtracted from it:

Screen Shot 2021-11-14 at 8.50.37 AM.png


[Added borders for clarity]
 
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I released a new version of the Copy Settings plugin containing the Invert Mask command, which allows you to quickly invert an entire mask.

The plugin has a 30-day free trial, and I'm optimistic LR 11.1 (due in December) will include mask inversion built-in.
 
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