Using Masks and Layers—Painting, Filling, and Color Tools - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 219

Figure 3.44
After scaling. The dashed border marks the new size and shape of the scaled layer. It was touched up
with the tonality correction.
The Scale window opens. Here you can enter the numerical values to
scale your layer. However, you want to manually transform the image by using
the mouse and a bit of visual judgment. Therefore, select Preview > Image in
the tool options. Additionally, use the Opacity slider to reduce the opacity to
about 70%. Now after you click into your image with the tool, the hazysky
layer shows a transformation frame with square handles in the middle and
on the corner points. You can drag the frame by pulling at its border while
holding down the left mouse button. Due to the reduced opacity of the layer
that is to be transformed, you can see the underlying layer shine though. Thus
you can better adapt the transformation.
Increase your working space around the image by pulling the window
borders outward. Then click the mouse on the frame's borders and drag or
move them so that they look the same as the second image.
Click the Scale button in the Scale window to produce the preset scaling.
If you are not satisfied with the result, undo the process and repeat the
steps. Save your image.
Another option is to apply the Supernova filter ( Filters > Light and Shadow
> Supernova ) to create a sun. Essentially, you can create small light reflections
on shiny surfaces or objects as well as multicolored radiating stars. Try it out!