Creating a vignette in Gimp
A vignette was originally produced deliberately by burning in the images at the corners under the enlarger in the darkroom. A white vignette was produced by dodging the edges of the paper by holding a hole (in a card or in the center of two hands) and exposing some or all of the exposure through this hole while moving the hole to avoid a strong edge to the image. Some lenses actually focus less light into the corners of the image than in the centre and naturally produce a vignette to some degree.
A dark vignette at the corners of an image is often used to concentrate the viewer's attention on the subject of the photograph.
Gimp is a free image editor. It has a vignette function built in, but it is not very friendly or flexible.
Here I will show how I can create a more flexible and subtle vignette.
Screen shot of gimp with a photo opened for editing.
GIMP's built in vignette has a very sharp cut off and limited choice of shapes. As far as I can determine, the vignette is merely formed by a flood fill of a selected colour rather than the more subtle adjustment of lightness/darkness.
Here we have made a selection around the area we want to stand out and are increasing the feathering to a very large value to make the vignette come in gradually and subtly. We could use a pre-designed selection shape such as an oval, but here I decided to draw the selection freehand.
Here we have inverted the selection so that it is the background that is selected.
Compare the outlines of the selection in this picture (black area at extremme right of screen shot) with the picture above.
Now we are prepaing to darken the outside of the picture using the brightness/ contrast option.
Darkening just a little gives a more natural looking vignette to the picture than Gimp's built in vignette. Using this method has the added flexibility of an unlimited range of shapes that we can use.