In GIMP how to scale up image without scaling layers?

I am trying to scale images without scaling layers. I tackled the problem of scaling down the images by selecting the largest visible layer and the cropping the image to that layer. This way none of the layers are scaled down, just the image is scaled.

I am unable to scale up the image independently of the layers. The standard option Image>>Scale Image, as you must have guessed, scales the layers too.

Answer

What you want to do is scale the canvas size.

1. 
   

   Choose Image > Canvas Size and enter the new size of the canvas, making it larger than the current size.

   
   


2. 
   

   Press the Center button if you want the layers centred in the new image, otherwise they'll be at the top left.

   
   

More information about the Canvas Size dialog.

(Note: this feature is exactly the same in Photoshop: Image > Canvas Size.)