Exposure control method

#The present invention relates to an exposure control method for adjusting brightness of images, and more particularly to an automatic exposure control method based on object detection.

#In photography, exposure is the total amount of light allowed to fall on the photographic medium (photographic film or image sensor) during the process of taking a photograph. To avoid overexposed or underexposed, exposure should be adjusted to control the amount of light from the subject. Nowadays, most cameras can be operated in an automatic exposure mode to automatically calculate and adjust exposure settings in order to properly capture images. The exposure settings include exposure time and illumination level, controlled by shutter speed and lens aperture, respectively. Slower shutter speeds (longer exposure time) and greater lens apertures (admitting more light) result in greater exposures.

#Please refer to FIG. 1, a flowchart illustrating the conventional exposure control method. At the beginning, an image is captured (step 102). Then the system analyzes brightness of the entire image (step 104). If the analysis result is unsatisfactory or unacceptable, the system adjusts the exposure settings to be used for the next capture (step 106). For example, if the image is too bright, the system may shorten the shutter time or decrease the lens aperture or take both. Hence, the next photographing receives less light to make the next image a little dark.

#The above contents of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which:

#FIG. 1 is a flowchart illustrating the conventional exposure control method;

#FIG. 2 illustrates an exemplifying image whose exposure settings are usually erroneously adjusted by the conventional exposure control method;

#The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.

#Please refer to FIG. 3, a flowchart illustrating a preferred embodiment of an exposure control method according to the present invention. At the beginning, an image is captured (step 302). Then an object detection procedure is performed to acquire foreground object(s) and background from the image (step 304). According to the present invention, the method considers the influence degree of the foreground object(s) to determine the exposure adjustment. The judgment standard may be the area of each foreground object or overall area of the foreground object(s) (step 306). The area may be expressed as an area value or an area percentage in the image. If the foreground object is big enough to affect the brightness of the image, the foreground object should be taken into account. Hence, the brightness of the entire image is analyzed (step 308) to determine whether the brightness is proper or not. The method adjusts the exposure settings, for example exposure time or lens aperture according to the analysis result, so as to increase or decrease exposure to meet the brightness requirement (step 312). On the contrary, if the foreground object is considered to be insignificant and negligible, the brightness analysis neglects the foreground object. The method analyzes the brightness of only the background rather than the entire image (step 310). The exposure settings are adjusted according to the brightness analysis result (step 312). For example, if the background is too bright, the method shortens the shutter time or decreases the lens aperture or takes both. Hence, the next photographing receives less light to make the next image a little dark.

#In the case of multiple foreground objects, the judgment standard may be focused on each foreground object or all of the foreground objects. There are some possible applications. In an embodiment, if any foreground object has an area greater than the predetermined area, all of the foreground objects are taken into consideration in the brightness analysis. In another embodiment, only the foreground having an area greater than the predetermined area is taken into consideration in the brightness analysis. In a further embodiment, if a foreground object is not moving, the foreground object may be integrated into the background for the brightness analysis. The selection is made according to the practical applications.