Portable electronic devices continue to get smaller and incorporate more functions, such as traditional personal digital assistant (“PDA”) functionality with cellular telephony and wireless email capabilities. In addition to functions oriented toward the business user, it is also known to incorporate music and video players as well as camera applications for consumer market devices.
Conventional film cameras use a photosensitive film to capture an image, whereas digital cameras use electronic photosensors such as charge coupled devices (CCDs) or complimentary metal oxide semiconductor (CMOS) chips. The term “photosensor” as used in this specification means any device(s) or material(s) capable of receiving and capturing radiant energy, and being at least partially capable of converting the radiant energy into electronic signals that become a virtual representation of the optical image. A CCD or CMOS “camera-on-a-chip” includes an array of very fine electronic “picture elements” or “pixels” arranged in horizontal rows and vertical columns that define an image resolution matrix.
U.S. Pat. No. 5,841,126 describes an exemplary camera chip that may be incorporated into a portable electronic device.
One problem associated with such photosensor arrays is the introduction of an image artifact referred to as “flicker” when the camera is capturing an imaged scene that is illuminated by a fluorescent light source. Flicker occurs as a result of periodic variations of light intensity in correspondence with the frequency of the alternating current (AC) power that interfere with the arrays' ability to capture all of the image information used to form an image frame.
A fluorescent lighting system that is powered by a source of 60 Hz alternating current will exhibit periodic peaks of intensity at a rate of 120 Hz, i.e., twice the frequency of the alternating current. However, in many European countries, the AC power waveform has a frequency of 50 Hz, so that the flicker frequency of concern is 100 Hz. Thus, unless the photosensor chip includes a mechanism for addressing “beats” at this frequency, an image of a gray background captured under illumination by fluorescent lighting will include readily apparent amplitude modulations of the light intensity in a particular direction (typically the vertical direction), since the light level will vary with the capture of different lines of the image.
A number of solutions have been employed to eliminate these “beats.” These include filtering systems that filter out the beat frequency, phase locking systems that attempt to lock on to the 100 Hz intensity peaks and synchronize frame capture, and a variety of other techniques.
One such other technique is set forth in U.S. Pat. No. 6,271,884 to Chung et al., which describes a digital camera with constant frame rate, but with an adjustable integration time. The integration time is defined as the amount of time that a particular sensor is permitted to capture light energy for each frame. When the camera is used in an environment having 60 Hz fluorescent lighting, the integration time is set at a multiple of 8.33 milliseconds, whereas the integration time is changed to a multiple of 10 milliseconds when the environment utilizes 50 Hz fluorescent lighting. A number of options are set forth for between the two integration times. One suggestion is that the system could detect the country in which it is operating based on system configuration data, although absolutely no details are provided on how this would be implemented.
Other approaches are known in the art for detecting flicker, such as U.S. Pat. No. 7,187,405, which detects specific repeating patterns of signal variations by processing columnar information from the device's two-dimensional sensor array.
It is also known in the art to select camera printing options for printing parameters such as printed image size and paper size in accordance with location information derived from a location subsystem, such as a GPS receiver, as described in U.S. Pat. No. 7,126,639.
It is contemplated that improvement is possible over the above-described prior art, by simplifying the manner of detecting location of a digital camera for the purpose of setting the preferred fluorescent operating mode to eliminate flicker.