I asked for permission to share this photo. Specifically to see what people could do with it here.

Here's a try, Sallyanne (don't ask what I did; lol). Regardless, the posterization is terrible and the blowouts are unrecoverable. Short of re-texturing (and I'm a lazy filter guy so don't look to me for that), this is the best I could come up with. Posterization could be addressed, but, you loose what little details you even have if you do so. I did do some bilat filtering for some of the posterization issues.

Great try Lyle.

My try (lighter result than Lyle)

...or less light

Thank you dinasset
I have tried it twice with differing results and once the cloak was blue and once it was black

this one less coloured

Thank you Wallace.
Thought it did too.

IMO it's the best outcome, congrats Wallace !

You all got the best results from that picture.

Another attempt, still far from Wallace's one

This is fun. I used a lot of filters in G'MIC and a few in GIMP. Maybe I will post another try later.

Sallyanne, what's the original color from the cloak?

The dark parts a little darker:

@ iarga. Sorry, I don't know. Person who originally posted it didn't say but it looks to be blue - most people have got blue out of it.

Sallyanne, I shall post a totaly new try later with more blue, so you can choose.

(edit: the photo can have a blue / violet color cast, so I did a correction for that. But if the original color is unknown, you have to guess )

Another try:

My first and last combined (also the last I post, I'm out of ideas now):

Very nicely done iarga