This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
In recent years digital imaging cameras have been commonly used as imaging devices for photographing subjects. A conventional digital camera (such as a digital still camera or digital video camera) generally acquires an image by using an imaging element or the like, and records the image as digital image data in an internal memory or integrated circuit card provided inside the camera. In an imaging device such as the above-described digital imaging camera, a lens is provided for the purpose of focusing a subject image onto the imaging element with the subject is being photographed. By controlling a focusing of the lens, a focusing distance can be aligned with the subject being photographed.
To address a wide spectrum of customer needs, mobile phones are rapidly converging into multi-purpose devices that incorporate multiple different products including digital imaging cameras. Digital imaging cameras nowadays are often seen as an integrated part of any mobile phone. However, the digital imaging features of these camera phones are mostly less functional and reliable than their counterparts, stand-alone digital imaging cameras. To address this gap of functionality and reliability, camera phones manufacturers strive to offer more sophisticated features and technological know-how to ensure high quality photo images with the digital imaging features of their phones.
One important feature to be included in a camera system is autofocus (AF). The AF feature is designed to allow a user of the camera system to obtain a correct focus of a subject of particular interest without manually adjusting the lens focal length.
All automatic focusing algorithms can be divided into two broad categories: active and passive. While active AF can be achieved using the external sensors (e.g. infrared), many consumer-level digital and cell phone cameras utilize passive AF. Passive AF is used to determine the correct focus of an image by using contrast or image sharpness measurements of the image. It can be understood that these measurements for AF may be performed for one or several respective areas or windows of the image.
Generally, a passive AF is performed utilizing an AF algorithm to calculate a measurement of image sharpness or focus corresponding to the image in order to determine a best in-focus setting. The in-focus setting is usually found by choosing a respective lens position where the image sharpness or focus is maximal. Then the determined in-focus setting can be used for an AF of the image.
It is noted that the operation of the AF techniques of the prior art digital cameras may deviate in their details somewhat from the description given above. However, it can be realized that prior art AF systems, such as the ones mentioned above, may be subject to certain limitations. These limitations can become apparent for certain cases, such as for cases where a resulting calculation of an image sharpness or focus does not correspond to a particular setting of the image, or where a condition of the subject or the camera interferes with the abilities of the AF system. Some of these limitations are described below in non-limiting terms.
According to the numerous surveys, a highly frequent use of cameras in mobile devices is portrait imaging. Portrait imaging may be seen as the photographing of a single person or a group of people at a shorter distance, such as 1.5-3 meters, set to a more distant background which may constitute contrasting scenery. In a portrait image the single person or group of people of the image may be smaller parts of the image in comparison to the scenery. As such, a problem can exist where an AF technique, such as the passive AF technique as described above, may not choose the best in-focus position desired for the photograph.
In addition, it is common that while a photograph is being taken the image lighting may be low which may tend, among other things, to render parts of the image less distinguishable from other parts of the image, thus effecting an AF. Further, it is a common occurrence that during an AF the camera may inadvertently move during a photograph due to a shaking of a hand holding the camera and/or a movement of the subject being photographed. These common occurrences can subsequently lead to inaccuracies in an AF process.
Exemplary embodiments of the invention address potential AF problems, such as the ones mentioned above by example.