BACKGROUND

Description of the Relevant Art

Both still cameras and a video cameras capture optical images of a particular scene, and these images are converted into electrical signals such as digital data. For example, the camera includes an image sensor that captures the optical image and converts this information into analog electrical signals. An analog-to-digital converter (ADC) converts the analog electrical signals into digital electrical signals. Components of the camera or external components are capable of compressing the digital data, storing the digital data, and editing the digital data. Prior to performing these operations, the components of the camera attempt to capture a high quality image for the user.

Although in some cases, a user purposely performs over- or underexposure of a scene or creates freezing or blurring of a captured image for a particular effect, typically, users prefer a captured image of a scene with highly visible details that are properly lighted. For example, the objects in the scene are easily discernible in the captured image when the digital data is rendered and presented on a display for viewing. One of the many factors that contribute to capturing a detailed and clear image is exposure. Exposure is the amount of light per unit area reaching a frame of the surface of photographic film or an electronic image sensor of a digital camera. The amount of light per unit area is adjusted based on shutter speed (or exposure time) and lens aperture (or size of the aperture of the camera lens that allows light to enter the camera). The amount of light per unit area is also adjusted based on ISO sensitivity (or the sensitivity toward light of the photographic film or digital image sensor of the camera), and luminance of the scene that contains the one or more objects being photographed. The luminance of the scene is the amount of light being reflected from the one or more objects.

The camera's exposure determines how light or dark an image will appear when the image is captured, rendered and output on a display for the user to view. When one or more objects are initially overexposed, the one or more objects appear very bright or white. In contrast, when one or more objects are initially underexposed, the one or more objects appear very dark or black. Rather than rely on the user to determine the particular exposure, many cameras provide an automatic method executed by hardware for finding the particular exposure. This automatic method is referred to as “auto exposure” or “AE.” The auto exposure methods of cameras have a trade-off between speed of brightness adjustments and smoothness. Aggressive auto exposure methods provide higher speed, but with a cost of little smoothness that provides discomforting preview images to the user. On the other hand, conservative auto exposure methods provide high smoothness that is pleasing to the user glancing at preview images, but with a cost of low speed.

In view of the above, methods and mechanisms for efficiently determining a final amount of camera exposure are desired.

