How to Adjust Brightness in GIMP

Adjust Brightness Using "Curves" Menu

1. Open the "Curves" menu. To do this, click on "Colors" in the main tool bar, and then click on "Curves." This menu can also be accessed through the "Tools" option.

2. Familiarize yourself with the curves interface. In the "Curves" menu, you will see a 2-axis graph with a line stretching between the lower-left and upper-right corners. The horizontal axis represents the current tonal spectrum of your layer, while the vertical axis represents the adjusted tonal spectrum. By clicking and dragging the line to adjust its shape, you are telling GIMP to adjust each tone on the x-axis to its new position on the y-axis.

3. Add a control point to the curves graph. To begin editing your graph, you need to add a control point. To do this, click once at any point along the linear graph. You will see a small circular node appear. This is a control point, which you can use to adjust the shape of the graph. Additional control points can be added later to achieve more intricate shapes.

4. Adjust the shape of the graph. To make your layer brighter, for instance, click on the control point you created and drag it upwards. This will turn the linear graph into an upward curve. The mid-tones of the image are now brighter, but the darkest and lightest tones have remained unchanged, so the image will not have a washed-out appearance. To make the image darker, drag the control point downwards.

5. Save your changes. Click the "OK" button to apply the changes you've made. Make sure to save your image before exiting GIMP.