Patent application serial number 877598 is assigned to Canon Kabushiki Kaisha.
The following quote was obtained by the news editors from the background information supplied by the inventors: "Among automatic focus detection/adjustment methods for image capturing apparatuses, common methods that use a luminous flux passing through a taking lens include a contrast detection method (also called a blur-based method) and phase difference detection method (also called a shift detection method).
"The contrast detection method is often used in video movie cameras for movie shooting and electronic still cameras and uses an image sensor as a focus detection sensor. The method pays attention to an output signal of the image sensor, especially to information (contrast information) contained in a high-frequency component and regards the position of the taking lens which maximizes an evaluation value of the output signal as an in-focus point. However, the method is considered to be unsuitable for high-speed focus adjusting operation because the method, which is also known as a hill-climbing method, is required to find an evaluation value by finely moving the taking lens and continue moving the taking lens until the evaluation value turns out to be a maximum value.
"The other method, that is, the phase difference detection method, is frequently used for single-lens reflex cameras which utilize silver-halide film and is a technique which has made the greatest contribution to the commercialization of Auto Focus (AF) single-lens reflex cameras. With the phase difference detection method, first a luminous flux passing through an exit pupil of the taking lens is split into two streams, which are then received by a pair of focus detection sensors. Then, by detecting amounts of deviation between signals outputted according to amounts of light received by the focus detection sensors, that is, amounts of relative displacement in a splitting direction of the luminous flux, the phase difference detection method directly determines an amount of deviation of the taking lens in a focusing direction. Thus, once the focus detection sensors accumulate data, an amount and direction of defocus are obtained, enabling high-speed focus adjusting operation. However, in order to split the luminous flux passing through the exit pupil of the taking lens into two streams and obtain signals corresponding to the resulting two luminous fluxes, it is common practice to install light splitting unit such as a quick return mirror or half mirror on an image sensing optical path and install focus detection optics and an AF sensor behind the light splitting means. This has the disadvantage of increasing the size and cost of the apparatus.
"To overcome the above disadvantage, a technique has been disclosed which gives a phase difference detection function to an image sensor, eliminating the need for a dedicated AF sensor, and implements a high-speed phase difference AF.
"For example, Japanese Patent Laid-Open No. 2000-292686 discloses a technique for giving a pupil division function to an image sensor by splitting light-receiving units of some pixels of the image sensor into two parts. The technique carries out phase difference focus detection by arranging these pixels as focus detection pixels at predetermined intervals in image sensing pixels. Since image sensing pixels are missing in locations where the focus detection pixels are arranged, the technique creates image information by interpolation using information obtained from surrounding image sensing pixels.
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