Photoshop - Subtracting the differences making a masked alpha photo

Question

So I have 2 images. One would be the normal image and the other has a vignette added to it. How can I subtract all the color values from the vignette version using the normal version creating an alpha png photo only from the vignette?

Normal version:

With vignette:

So I want results like this. (I did this with color range selection so it's not 100% accurate)

I tried playing with difference/subtract blend modes and Premiere Pro's difference matte. It doesn't seem to work 100% accurate. Can we even invert the colors like a keying method? I know I once saw a tutorial about this (removing a background) in Blender's video editor but I don't find it anymore. Any idea?

Answer 1

Layer modes won't work for this. Use a layer mask instead. Make a black filled ellipse on the mask, and blur it to make a vignette.

An example

Answer 2

Make the wanted single image in Photoshop (or GIMP or other comparable raster image editor)

To get the transparency to the original the vignetted version is moved to the layer mask of the original. The mask is inverted. Applying Curves to the mask is shown in the screenshot. Falling curve makes the inversion and the actual curve form is adjusted for good transparency gradient.

It would be better to have in the background some actual image which is going to get the insert. The checkerboard probably isn't enough.

I must admit I do not know what's actually wanted Maybe the versions should be swapped or something else. The version above is a guess.

The wanted version probably can at least be got by inserting a BW radial gradient to the layer mask. The process is non-destructive for the image layer, so you can well try different gradients. But have some meaningful background image during the experiments.