As I really enjoy underwater photography, I am wondering how does one end up with a final image like the one I share below:
Unedited on the left, desired effect on the right:
This edit seems to complex for Lightroom as it doesn't have a Channel Mixer so I presume the photographer used Photoshop or GIMP. There one can copy a blue/green channel and convert it to red.
In this case, it seems that the photographer is using two separate layers and adds the people separately, so that he can get a darker background.
Assuming that to get an image like the one shown above the photographer is not only using a pure picture and color grading, but editing multiple layers of underwater images and join them smoothly, how does one edit and join edited layers, from underwater images, in a subtle way?