All you must do in GIMP is use the Fill Bucket tool, holding down shift will toggle between the ‘fill similar color’ and ‘fill whole selection’ options. You can fill the current selection with either the foreground color or the background color from the Edit menu. Ctrl + , and Ctrl + . respectively on the keyboard.
What is fill tool?
The Fill Tool is used to pour large areas of paint on to the Canvas that expand until they find a border they cannot flow over. If you want to create large areas of solid color, gradients, or patterns the Fill Tool is the tool to use.
Does GIMP have content aware fill?
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GIMP has had a “Content Aware Fill” for years before Adobe tried it in Photoshop. Using Resynthesizer and the Heal Selection script to remove objects from your images, and to rebuild textures!