Contrast / Negative effect

Hi,

I have a transparent watermark which is basically a rectangle with white borders and the letters of my website inside written in white as well. The rest is transparency. It works very well but as you can imagine, when I apply this watermark on bright images, my watermark doesn't show up, it's almost invisible.

It would be nice if we could have an option to adjust the watermark image contrast/colors depending of the background, just like `mix-blend-mode` in CSS: https://css-tricks.com/almanac/properties/m/mix-blend-mode/

To make it short: a watermark that adapts to the background.