[Gimp-user] How to optimize this workflow

[scott092707 aol com]

When I go to the drugstore to their self-print stations, I know
that their paper sizes are not the same ratio as my image sizes.
If I don't create special versions of my images, I know that they will
have their ends cut off.  This displeases me.

Before I go, I create special versions of the images, that have the same
aspect ratio as the print size.  I pad the smaller dimension with white
(the paper color), and center the image, since I am not
planning to cut off the padding after printing the image.  (If I were planning
to cut the print down to image size, I would make sure the image was all
the way to the left or right, so I would only need to make one cut).

How do I do this?

First, open the image, and change the zoom factor to make it a smaller percentage,
so there's lots of padding around the image.
Invoke Rectangle Select, click on Fixed, and enter the aspect ratio of the print size
as width <colon> height (example: for 5x7 paper, enter "7:5")  If later, you find that
you had it backwards, just click on one of the two buttons at the right of that line,
and the ratio will reverse itself, without need of re-typing.
Now, click and drag anywhere to make a rectangle, of any size. Size and position
doesn't matter (other than allowing you to see if you got the ratio in the right order).

Now, enter the smaller of the image's width/height in the right box after "Size".  
(LEFT box, if image is in portrait mode).
The dimension in the other box will change to a larger amount.
(If you enter 0 in both Position boxes, you will see the rectangle bounding box is
the same size as your image, except in one direction, where it is larger.)
You will need this new dimension in the next step, so "copy" it to the clipboard.

Now, invoke Image->Canvas Size from the main menu.
Paste the new dimension into the Width box (HEIGHT box, if image is in portrait mode),
and press <enter>.  The preview box will enlarge in one direction.
At this point, you can either click on Center to center the image in the preview box,
or you can click and drag the image all the way to one end or the other of the 
preview box.
Change Resize Layers from None to All Layers (may not be necessary).
Change Fill With to any of the options you want, and then click on "Resize".

Export the image under a different name (probably something that indicates the print ratio.)

Done!