Mask Image by Brightness node and "Vuo black"

In an image, I’m trying to select the “Vuo black” (like the black that results from empty space with Render Layers to Image) by using Mask Image by Brightness.

The settings give me pause. How to set the Preserved Brightness? 0.01 to 1? 0.001 to 1? 0.0001 to 1? What is the good setting to catch only the “Vuo black”?

And then, the Brightness Type, again, in conjunction with the Preserved Brightness, what is the good setting to catch only the “Vuo black”?

Well, I obtained the type of mask I was looking for by passing the source image into Adjust Image Colors, setting Saturation at -1 and playing around with the Gamma.

I’m glad you figured it out. For future reference, empty space in the output of Render Layers to Image is transparent. To composite on top of another image, you can just use Blend Images.

It’s actually related to Make Random Image: I’m blending noise to an image, but I want the noise to be masked/invisible when the noise is over a black part of the background image. It’s working quite well by using a grayscale version of the background image and using it as a mask over the noise image before blending.

This is similar to audio dither plug-ins that have an auto-black (no dither on digital silence/black) option.


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