Changing the size of the canvas?

[Ulodesk]

I have created a book cover for someone, for Amazon print-on-demand, which measures spine width by paper thickness x pages. I have made an estimate for final page number and sized the back/spine/front cover image accordingly. If the spine width should need to be increased, and thus the entire background layer/canvas, what's the best way to do this? 

I tried enlarging the canvas, which left a transparent sliver on one edge. I tried filling the transparent area with the background layer color but nothing happened. 

So, first, I don't know how to get the added real estate in the background layer, and second. I really would like to avoid having to move each layer over a tiny a mount to recenter.

Thank you!

[sallyanne]

Change your canvas size as per normal then add another layer that size the colour of your book cover's background. send to the bottom and merge..... 

I would always do it this way until I noticed in the canvas resize options to 'fill with'. At default it is transparent

   

[rich2005]

@Ulodesk  Is this a KTP type template ?  Could really know if your project has many layers or just a single layer.  You might have to mess around with selected layers or use layer groups.

Quote:...I really would like to avoid having to move each layer over a tiny a mount to recenter.

 
I guess that answers my question.  Put them in a layer group and move the layer group or probably better, select the appropriate layers

All sorts of ways, however for what it is worth. Something like this.

   

Stages
(1) split in two.  (2) increase canvas size   (3) move layer (4) fit canvas to layers (5) flatten image
As a 3 minute video  https://youtu.be/F7o_CO6WI_o

Edit: Since you are using Gimp 2.10 a script-fu sg-group-linked-layers.scm (will also ungroup) Attached, unzip and goes in your scripts folder.  Find it in Layers -> Stack.   Might come in useful for moving layers in step, although you can do the same just by linking layers. Pays to be tidy.

[Ulodesk]

Thank you both. This does not have to go into a KTP template. I'll work through your remedies tomorrow when I get back to the project. Much obliged.