• Drop Shadows
• Unsharp Mask
• Adjusting Contrast
• Bump Mapping
• Image Watermark
• Gradients Tutorial
• Colour Enhancing
• What are Layers?
• GIMP Interface

GIMP Levels & Gamma tutorial

Apply the auto levels tool

With the value layer selected open the levels dialogue found on the image toolbar

Layer » Colours » Levels(GIMP version 2.2)
Colours » Levels(GIMP version 2.4)

Click the Auto option, which will activate Gimp's automatic correction of colour, contrast and brightness.