Resizing in GIMP

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Step 1
Save the file with a different name.
(Important – you can then go back to the old file if things go wrong!)
Step 2
Go to ‘Scale Image’ on the tool bar and check that the chain link between width and height is connected
Step 3
For Landscape images change width to 1600 pixels

For Portrait images change height to 1200 pixels

Then hit the ‘scale’ button
Step 4
Go to Canvas Size and check the chain link between Width and Height is disconnected and ‘Centre’ option is selected
Step 5
For Landscape images change width to 1600 pixels

For Portrait images change height to 1200 pixels

Then hit the resize button
Step 6
Create a new layer with the foreground colour set to ‘black’
Step 7
Go to the layer options and select ‘Stack’ and then ‘Reverse Layer Order’
Step 8
Save the resized image