How To Create A Postcard in GIMP

Step 2: Select Only The Castle and The Terrain

In order to make the photo more appealing we have to act differently on the land and sky sections.
You can use any selection tool available in GIMP in order to accomplish this step.
I decided to use the foreground select tool. This one may seems a little bit confusing at first if you didn't used it before, but offers good enough results. Using this tool implies several steps so be patient.

Select the tool from the toolbox:

First we have to make a free selection around the foreground. The cursor will look and behave the same as for free select tool (the lasso).
The selection should not be exactly around the foreground, but just make sure that you select everything that needs to be include. Due to this it is better to keep a safe distance from foreground edges.
Continue clicking around the foreground (click each time you have to change the paths's direction) and finally click on the starting point in order to close the curve.
See image bellow for the selection I've made (those blue roofs are excluded in purpose, otherwise we will have them white in the final result).

After closing the path as indicated above, everything that is not selected will be painted with a dark blue mask.
The cursor is automatically changed from free select to paint brush. Make sure that black is selected as foreground color and move the slider to large brush.
Paint over the non blue part, while keeping a safe distance from the edges. Just make sure that you do not paint over the sky at all.
Do this painting continuously, without releasing the mouse until finished.

After releasing the mouse the tool will reprocess the blue mask. If you have to make small adjustments, reduce the brush size as needed and paint over the areas that have to be also included. If you need to remove a section included by mistake, keep the Ctrl key pressed while painting (while Ctrl is pressed the cursor will change from brush to rudder). Each time you release the mouse, the tool will redraw the mask. Below is the result with just minor fixes.

When you are happy with the result just press Enter in order to get your selection.

In order to save our selection, we will use Select / Save to channel menu. Due to this action a new channel containing our selection is created. Double click on it and name it Land Selection. In order to continue our tutorial switch back from channels dialog to layers one, by clicking the layers tab.