When you add two waves that are equal except one has its polarity

>>312312
...image arithmetics?

>One cool practical use of this is getting the acapella of a song by using the original song and its polarity-reversed instrumental version.
Except it never works because of mastering nuances.

>>312312
I suppose if you had the file used to make a watermark, you could invert it then use opacity or layer styles to remove it

>>312312
it would work on pictures( if the watermark is white), but not on text. if the watermark is black, you'end up with grey text

>>312312
You can remove people from pictures automatically using >>312885

>>312312
there are ways to do that, equally as easy as audio signal inversion for getting an acapella too.

but you're faced with the same issues as your are in the audio realm... It turns out like shit if your source is a low resolution.

And if the maker of the source material has any kind of brain, they wouldn't provide a high resolution file with a watermark because it's so easy to remove.

>>312312
The silence (S) consists of one arbitrary wave (W) and this same wave (-W) but polarity inverted.
This consists of 1 variable (w and -w).
The watermarked picture (W) consists of a picture (X) mixed with another picture (Y). (+some function which controls the mixing)
Now you've got 2 variables (picture X + totally diferent picture Y).
Probably impossible to seperate X and Y unless you've got the original picture or the bare watermark.

Now you could always buy the original picture to unmix the watermarked picture and get the original watermark (sort of like decrypting)
With this watermark you can unmix other pictures.

But there's multiple things that come to my mind:
* what if the watermark is not a constant but variable
* jpeg/lossy artifacts

Anyway I've probably spent to much time on this... Have a good night!

It works with images too, on theory, but it's not likely you can use the trick in a real production environment because if it's even a tad lossy, the compression artifacts and/or color loss will fuck you up.
You're better off removing watermarks with levels/median/blur tricks