Separating dark and light pixels by threshold

[LenC]

I have a photo with an area of dark (~black) silhouetted trees against a sky that is overexposed to white. I would like to simply select the white pixels to replace with blue. Is there a numerical threshold function that can do this, presumably on a selection where the contrast is great? Obviously highlight/shadow functions do this in a more sophisticated way.

 

Thanks.

[anon1]

There is a threshold adjustment which separates the image int B/W based on a certain threshold 

- you could then use Filter > Color > erase white paper and put a solid fill layer or a rectangle underneath

 

but I´d go for a blue rectangle covering the image and then use blend If/ blend ranges

https://forum.affinity.serif.com/index.php?/topic/17364-blend-if-blend-ranges/?p=79182

 

or you can use a gradient map to get a more refined result with more variations 

https://www.youtube.com/watch?v=ZB6xO8_jONU -german but you´ll easily get the idea

 

hope that helps 

[LenC]

Thanks. Will have to work on this.