Simulate the Bokeh with Gimp
This effect is used to simulate the bokeh of large aperture lenses.
The bokeh is the Blur in the out of focus areas of an image. Generally this low details areas are in the background of the picture and are typical of telephotos and low aperture lenses. This effect is really easy to simulate with Gimp. If you will shoot a photo which have a focused subject and a blurred background the subject will be highlighted, this gives a nice look to many kinds of pictures, especially portraits and macros.
Below you can see an example taken with my camera. The next photo of a chessboard has less blur as long as the value of the f/ (Aperture)
becomes larger, so low aperture lenses has less depth of field and more blur on the out of focus parts.
Look to the cross of the white king to notice better the differences.
First of all, find an image suitable for this tutorial. You need a clear subject in the foreground and a relatively far background. I chose this photo, that has been taken before a quad outgoing in the Egyptian desert. I think that this image is ideal, because the background and the foreground are very confused, and a bokeh would make the subject more visible.
Open the photo with Gimp, then duplicate the background layer (Right Click - Duplicate Layer)
Open Filters - Blur - Gaussian Blur and choose a radius (I used 30, that is quite high, you can use higher or lower value)
Now you must move the Background Layer above the Background Copy layer. You just have to click and hold left mouse button on the Background layer, then move it above the Copied layer and release.
The screenshot comes from a different tutorial, so the thumbnail doesn't match
Use the Eraser Tool, the Selections or both to delete the focused background, as you can see in the next screenshot (the blue part is the one that you have to remove). If you prefer to use the Eraser tool, remember to choose the right brush and size. If you want to use selections, but you don't know how, click here for the tutorial.
This is the result you should get with Gimp. I hope you liked this tutorial for fake the bokeh.