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There are two related things I want to do:

 

One thing is for a layer turn white into transparent and white-ish things into partially transparent.

Specifically, for every pixel in that layer with H, S, V, A (w, x, y, z), I want to replace it with a pixel with H, S, V, A (w, x, 0, (100-y)%*z)

 

Another thing is I want to be able to control one layer's transparency with another layer.

So basically the idea is I have a layer on top in greyscale, and a layer below it with an image at full opacity, and I want to change the image's alpha values to the color values of the layer on top.

 

Is there any plugin or layer blend mode that would let me do this?

Edited by MasN
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Try these ^ to convert brightness to transparency.

 

For the blending try this plugin

 

Check out Pin light 😊

 

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Thanks, I tried the Black and Alpha plugin, which is close to what I'm looking for.

Is there a way to do this without the color conversion? That is, I want to keep the Hue and Saturation data.

The other problem I find with this Black and Alpha plugin is that it doesn't respect the original alpha value. That is, when I tried converting a rectangle with 50% transparency and 50% brightness, I expect to get a rectangle with 0% brightness and 75% transparency, but I actually got a rectangle with 0% brightness and 50% transparency.

 

For the blending, "pin light" says "This mode causes light parts of the blend image and dark parts of the base image to show through." This is not what I want. I want something more like "This mode replaces the alpha channel of the base image with the alpha channel of the blend image." Is there a plugin for this?

 

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On 9/29/2020 at 6:52 AM, MasN said:

One thing is for a layer turn white into transparent and white-ish things into partially transparent.

Specifically, for every pixel in that layer with H, S, V, A (w, x, y, z), I want to replace it with a pixel with H, S, V, A (w, x, 0, (100-y)%*z)

 

Though it doesn't precisely fit your description, I think Color Clearer may do what you want. Set the Color to Make Transparent to white.

 

On 9/29/2020 at 6:52 AM, MasN said:

Another thing is I want to be able to control one layer's transparency with another layer.

So basically the idea is I have a layer on top in greyscale, and a layer below it with an image at full opacity, and I want to change the image's alpha values to the color values of the layer on top.

 

There's no built-in ability to do this, and no plug-in can affect multiple layers like that. However, something similar can be achieved (though perhaps not quite as conveniently) by BoltBait's Paste Alpha plugin. To use it, first copy the grayscale layer to the clipboard (with Ctrl-C), then run  Paste Alpha on the image layer. It's an effect I use all the time.

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