[photo] extracting a drop shadow as transparency

[tcurdt]

I feel a litte frustrated with the transparency support - or I am holding it wrong.

I have an object with a drop shadow.
I now remove the object with shadow through inpainting on a duplicate layer.

Now I have:
1. one image with the object and shadow on the background
2. and one being just the background.

Now I want the difference between the two images (or rather their luminosity) as transparency - as that should give me the drop shadow as transparency.

I don't see how I could do this.
Or is there another way?

It seems like working on transparency isn't quite as straight forward.
Any pointers?
 

[Callum]

Hi Tcurdt,

Unfortunately I'm not sure if I fully understand what you are trying to achieve please could you provide an example of what you are looking for and a copy of the file you are working with?

Thanks
C

[tcurdt]

Let's say this is the original imageI now remove the object to get the plain background
I have cut out the objectbut I also want the shadow. Now the shadow should just be in the alpha channel so I can move the object with shadow as I like.

One would think this should be easy as the shadow is defined by the difference of the plain background and the original file.

Does that make things clearer?

shadow.afphoto

[lepr]

Here's one of many solutions: shadow edted.afphoto

 

[tcurdt]

10 minutes ago, lepr said:

Here's one of many solutions: shadow edted.afphoto

 

Thanks @lepr!
Exactly what I am after.

It would be great if you could explain how you did it.
Even looking at the file I don't quite understand how you ended up there.

[lepr]

16 minutes ago, tcurdt said:

It would be great if you could explain how you did it.

Divide the original image by your background-only image, and then use a Channel Mixer Adjustment to map the greyscale intensity levels of the result to alpha levels of black pixels.

[tcurdt]

23 minutes ago, lepr said:

Divide the original image by your background-only image, and then use a Channel Mixer Adjustment to map the greyscale intensity levels of the result to alpha levels of black pixels.

Actually, when I re-add the background it seems like the shadow is quite gray rather than having the tone of the background.
It does not look quite like the original shadow.

Any suggestions on how to improve that?

[lepr]

16 minutes ago, tcurdt said:

Actually, when I re-add the background it seems like the shadow is quite gray rather than having the tone of the background.
It does not look quite like the original shadow.

Any suggestions on how to improve that?

You can use the 'Shadow' Group as a mask for a dark coloured object over a lighter background, or use it as a mask for an Adjustment such as Curves. To use an object as a mask, drag and drop its thumbnail on the thumbnail (not the name) of the thing that is to be masked.