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Author: Michael_McAloon, Contributing Editor
| Brightening and Darkening Images
Brightening and Darkening of images is accomplished in three different ways: a general adjustment, a precise adjustment using levels, and a precise adjustment using curves. These adjustments can be made in one of these two places that you can see at the top of the window: The Layer pull down (see Figure 7) or the Tools pull down (see Figure 8). |
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| Brightness-Contrast Sliders. When you select the Brightness-Contrast tool, the dialog box shown in Figure 9 opens.
To see the effect changing the brightness and contrast will have on your image, check the Preview box as shown above. |  |
 | Color Levels. If you decide to use the Levels tool as your way of adjusting the brightness and/or contrast, you will get the dialog box shown in Figure 10. Note, that although GIMP refers this as color levels you are actually change tone, or value, levels.
There is a histogram of the image (the black wave) in the Input Levels windows. Just beneath these windows are the Light, Dark and Midtone sliders that I’ve circled in Figure 10.. As you move the sliders, the image in the histogram is automatically adjusted. The basic adjustment begins by moving the Dark slider to the left side of the histogram just where the wave starts (this is the beginning of information on the darks in your image). Next move the Light slider to the right side of the histogram just where the wave begins there (where data on the lights starts). This will establish where your lightest and darkest values are. As we all know, this is very important. Finally, adjust the Midtone slider as needed to gain midtones in your image. There are also eyedroppers that can be used when you are familiar with the original scene shown in the image and know where the lightest and darkest spots are or if you want to specify where they are. You can see three of them in the All Channels section of the window. Select the Light eyedropper on the right and use it to designate the lightest spot on the scene; repeat with the Dark eyedropper on the left for the darkest spot; then use the Midtone eyedropper in the middle to select that portion of the scene |
| Curves. If you select the Curves tool to adjust brightness and contrast, you will see the dialog box shown in Figure 11.
The Curves tool lets you adjust the different areas (light, dark and midtone) independently. Notice the bars on the side and underneath the window. They indicate that the darks are in the lower left and the lights are in the upper right. Notice the line running diagonally from one corner to the other. By grabbing the line at any point with your cursor, you can adjust the lights or darks at that point by pushing the line up to lighten and down to darken |
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