Extending a nearly plain background

[WillH]

I just bought this stock photo with the intention of extending its top edge to create lots of black space.

I thought that the background at this edge was solid black, but in fact it's very slightly off-black and speckled like you often get with low light levels.

Since this is going to print, I'm concerned that just sticking in a solid or off-black background will look bad since there will be a sharp line where the texture ends.

What's the best way of seamlessly extending this edge of the photo?

TIA

 

[iDad]

select where you want it to be black and then feature the selection to meet up with the speckled area apply your color. (best to create another layer to be safe. play around with feature distance, it should blend nicely

 

[Quantum3]

Open the Levels dialog box and move the black point till you see just black where you see texture. Then bigger the canvas and paint with black.