When removing dust and scratches or when I want to apply a filter at a certain place in the image, Photoshop blurs all the image (Filter -> Noise -> Dust & Scratches). Why is that?
I just need Photoshop to blur the image at the indicated spot where the unwanted dust or scratch is located.
In order to have the dust removed, I had to use the history layers, as explained in this article.
My question is: what is the reason to blur all the image instead of blurring only the desired part of the image?