You can choose how your digital camera meters a scene to determine the exposure. Your Canon EOS 7D has the following metering modes from which to pick:
Evaluative: This is the default mode for your camera. You can use this mode for most of your work, including backlit scenes. The camera divides the scene into several zones and evaluates the brightness of the scene, direct light, and backlighting, factoring these variables to create the correct exposure for your subject.
Partial: This mode meters a small area in the center of the scene. This option is useful when the background is much brighter than your subject. A perfect example of this is a beach scene at sunset when you’re pointing the camera toward the sun and your subject is in front of you.
Center-Weighted Average: This metering mode meters the entire scene, but gives more importance to the subject in the center. Use this mode when one part of your scene is significantly brighter than the rest; for example, when the sun is in the picture. If your bright light source is near the center of the scene, this mode prevents it from being overexposed.
Spot: This mode meters a small area in the center of the scene. Use this mode when your subject is in the center and is significantly brighter than the rest of your scene. You camera may have the option to spot meter where the autofocus frame is. If your camera can move the autofocus frame to your subject, you can accurately spot meter a subject that isn't in the center of the frame.