This is a quick tutorial for using the Foreground Select tool in GIMP. The tool is available from the tools menu or by selecting it from the toolbox window. This method works best on objects that have colours that are distinct from background colours of the image. After using this tool you will end up with a selection which can then be converted into a layer mask.
Options can be viewed under the tool options window. The Mode option allows you to select from Replace, Add, Subtract or Intersection selection modes. Most often you will be using the Replace mode. Antialiasing can help draw a smoother selection. Feather edges blurs the edge of the selection by the selected number of pixels. Use Contiguous for selecting a single object and uncheck it for selecting more than one object. You will use the Interactive refinements options to adjust and change how the foreground object is selected.
For this tutorial we will be selecting the dinosaur skeleton from this image. Start by drawing an outline around the object you want to end up selected. Don't worry about getting a smooth and tidy outline just try to include the whole object.
A preview of the selected area will now appear in blue. You can change the preview colour if you want. Next choose Mark foreground and adjust your brush size. Start by brushing over your foreground object. This tells the program which colours and tones are part of the object and it will try to select all matching areas from the image. When you finish a stroke the preview will be updated. Continue brushing over the foreground object covering the complete object.
Depending on your image you will notice parts of the background have also been selected by the tool. Switch to Mark background and adjust your brush size. Now brush over any areas of the background that have been selected by the tool. Repeat the process just as you did with the Foreground select option. The preview will update as you finish each stroke.
You can continue refining the selection until you are satisfied with the results. Experiment with the Colour Sensitivity settings to improve how the selection is being made. For example if your object contains blues that are close to blues in the background you may have to increase how sensitive the tool is to blues.
When you are satisfied that the foreground object has been selected press the enter key to finalize the selection. Remember that you can always edit your layer mask if areas have been missed. You will now have an area of the image selected that matches the preview area. You can now proceed with any action that can be applied to a selection.
Now you can add the selection as a Layer mask to your layer. Switch to your Layers window, select the layer, right click and choose Add layer mask. When the layer mask options window appears choose Mask from selection. Now you have a layer mask for your image. Hopefully this tutorial will help you choose which selection tool will work best for your situation.
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