Camera with automatic fluorescent lighting mode

A novel method and apparatus for controlling operation of a photosensor array in a portable electronic device to reduce flicker resulting from fluorescent light having a periodic intensity. The method comprises selecting a time zone in which the device is to be operated, correlating the time zone with a corresponding frequency of the fluorescent light, and signaling the photosensor array to operate in accordance with a mode optimized to reduce flicker based on the selected time zone.

FIELD

The present disclosure relates generally to digital cameras and more particularly to a digital camera with automatic fluorescent lighting mode, adapted for use within a portable electronic device.

BACKGROUND

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.

DETAILED DESCRIPTION OF THE EMBODIMENTS

As discussed in greater detail below, according to an aspect of this specification, the photosensor array of a camera is configured to operate in an appropriate fluorescent lighting mode, based on the time zone that the portable electronic device is configured to operate in. This approach differs, for example from prior art approaches for establishing the fluorescent lighting mode (or other camera characteristic) based on what country the device is operating in. Indeed, since the selection of fluorescent lighting mode is based on time zone there is no need to reconfigure the fluorescent lighting mode when traveling between different countries in the same time zone.

Therefore, according to an exemplary embodiment there is provided a method for controlling operation of a photosensor array in a portable electronic device to reduce flicker resulting from fluorescent light having a periodic intensity, the method comprising selecting a time zone in which said device is to be operated; correlating said time zone with a corresponding frequency of said fluorescent light; and signaling said photosensor array to operate in accordance with a mode optimized to reduce flicker based on the selected time zone.

According to a further embodiment there is provided a portable electronic device comprising at least one user input device for selecting a time zone in which said device is to be operated; a chip having a photosensor sensor array adapted to operate in one of a plurality of modes for reducing flicker resulting from fluorescent light having a periodic intensity; a display; a persistent storage device; and a processor interconnecting said user input device, said chip, said display, and said persistent storage device, and configured to correlate said time zone with a corresponding frequency of said fluorescent light and signal said chip to operate in accordance with a mode optimized to reduce flicker based on the selected time zone.

Referring now toFIG. 1, a front view of a portable electronic device in accordance with an embodiment is indicated generally at30. In a present embodiment, device30includes the functionality of a wireless telephone, a wireless email paging device and a digital camera.

As best seen inFIG. 1, device30includes a housing34that frames a plurality of input devices in the form of a keyboard38, a set of keys42(one of which may be a menu key), a trackball46and a microphone50. Housing34also frames a plurality of output devices in the form of a display54and a speaker58.

Accordingly, a user of device30can interact with the input devices and output devices to send and receive emails, conduct voice telephone calls, manage appointments and contacts, browse the Internet, and perform such other functions as can be found on a known or as-yet unconceived electronic device such as device30.

It is to be understood that device30is simplified for purposes of explanation, and that in other embodiments device30can include, additional and/or different functions and/or applications, and include input and output devices accordingly. Such other functionality can include music playing, audio recording and video playing. An example of a combined input/output device would include a Universal Serial Bus (“USB”) port, a headset jack to connect a handsfree headset to device30, or a Bluetooth™ (or equivalent technology) transceiver. Likewise, it will be understood from the teachings herein that certain functions included in device30can be omitted.

In a present embodiment, device30also includes a camera. Referring now toFIG. 2, a rear view of device30is shown. Device30thus also includes an additional input device in the form of a camera lens60and an additional output device in the form of a flash66. As discussed in greater detail below with reference toFIGS. 3 and 4, lens60focuses light on image capturing photosensor chip62, which incorporates an array of photosensitive elements, for creating an electronic signal of the image that impinges thereon via the camera lens60.

In one embodiment, the form factor of device30is constructed so that a user can grasp device30with either a left hand, or right hand, and be able to activate keys42and trackball46with the thumb. (While trackball46is configured for the thumb, it should be understood that users can use other digits on their hands as well). By the same token, lens60and photosensor chip62are disposed behind display54so that the index finger of the user, when wrapped around device30, does not obscure the lens and thereby interfere with the use of device30as a camera. The positioning of lens60behind display54also improves the usability of display54as a viewfinder when device30is acting as a camera, as the display54will present the scenery to the user that is directly behind display54.

Referring now toFIG. 3, a block diagram representing certain internal components of device30is shown. Device30thus includes a processor78which interconnects the input devices of device30(i.e. trackball46, keys42, keyboard38, photosensor chip62and microphone50) and the output devices of device30(i.e. speaker58, display54and flash66). Processor78is also connected to a persistent storage device82. (Persistent storage device82can be implemented using flash memory or the like, and/or can include other programmable read only memory (PROM) technology and/or can include read-only memory (ROM) technology and/or can include a removable “smart card” and/or can be comprised of combinations of the foregoing.) As discussed in greater detail below, processor78executes a plurality of applications stored in persistent storage device82, such as an email application, telephony application, Web-browsing application, calendar application, contacts application, camera application and other applications that will be known to a person of skill in the art.

Device30also includes a wireless radio86disposed within housing34that connects wirelessly to one of a network of base stations to provide the wireless email, telephony and Web-browsing application functionality referred to above.

Device30also includes a battery90which is typically rechargeable and provides power to the components of device30. In a present, purely exemplary embodiment, battery66is a lithium battery having an operating voltage of between about 3.0 Volts minimum to about 4.2 Volts maximum. InFIG. 3, for simplicity battery90is only shown connected to processor78, but it will be understood that battery90is connected to any component (e.g. photosensor chip62, radio88, display54and flash66) within device30that needs power to operate.

Device30also includes volatile storage94, which can be implemented as random access memory (RAM), which can be used to temporarily store applications and data as they are being used by processor78.

As discussed above, examples of known photosensor chips62include CCDs and CMOS devices, which create an electronic signal of the image that impinges thereon via the camera lens60. As will be known to a person of skill in the art, photosensor chip62incorporates an array of horizontal rows and vertical columns of photosensitive pixels that define an image resolution matrix. The maximum resolution of the camera determines the size of the pixel array. Thus, a 1.3 MP camera has a pixel array of dimensions 1280×1024, while a 2 MP (megapixel) camera has a pixel array of dimensions 1600×1200 (actually 1.9 MP). Each pixel also has an image resolution “depth”. For example, the pixel depth may be 8 bits, wherein the minimum pixel brightness value is 0 and the maximum pixel brightness (saturation) value is 255.

Upon exposure to imaging light from a subject, the lens60focuses the light onto the array of photosensor chip62which collect discrete light energies or photon charges corresponding to or mapping the photographic subject or object column-by-column, row-by-row, and pixel-by-pixel such that a photon charge representation of the subject is obtained. The photosensor chip62processes the photon charges and converts them into useful digital signals that are clocked out for storage in volatile memory94.

Also, as discussed above, it is known that when taking pictures in fluorescent lighting, the photosensor chip62must be configured to operate in one of either a 50 Hz mode or a 60 Hz mode in order to eliminate flicker. Whether the photosensor chip62should be configured to operate in the 50 Hz mode or the 60 Hz mode depends on where the device30is being operated (i.e. in what country).FIG. 4is a map of time zones circumscribing the world, and Table A correlates standard time zones (i.e. offset from GMT) with the required fluorescent operating mode for the camera application.

From Table A, it will be noted that there are a small number of exceptions where there are instances of countries within a particular time zone characterized by a difference in fluorescent operating mode frequency from other countries in that time zone. For example, Saudi Arabia operates at 60 Hz, whereas the rest of the countries in standard time zone C operate at 50 Hz. For these rare occurrences, the user can ‘force’ the correct fluorescent operating mode by configuring the device30to operate in a different time zone with the desired frequency.

Referring now toFIG. 5a method of controlling the fluorescent operating mode of the camera application for the portable electronic device30is represented in a flowchart and indicated generally at300. To assist in understanding method300, the method will be explained in terms of its performance using device30. However, it is to be understood that this discussion is not be construed in a limiting sense, and that method300can be performed on devices other than device30, and/or that method300can be varied.

Beginning at step310, the user chooses an Options icon from the main menu (not shown), for example by user rotation of trackball46for scrolling through the various device applications, until the Options icon is highlighted on display54(not shown). Once highlighted, the user can depress trackball46to activate the Options application, resulting in the menu display ofFIG. 6A. When processor78receives an input via trackball46that the user desires to activate the Options application, method300will advance from step310to step315.

Next, at step315, the user rotates the trackball46, to choose Date/Time, and then depresses trackball46, resulting in the menu display ofFIG. 6B. With the cursor position over the “Time Zone” field, the user depresses trackball46(step320), resulting in a drop down menu in display54, as shown inFIG. 6C. The user may then, at step325, select the time zone in which device30is located. For example, the user may select Eastern Time, as shown in the highlighted portion ofFIG. 6C. The user may then depress the trackball46to confirm the time zone selection, and depresses the trackball once more to Save the selection (step330).

It should be noted that the foregoing description of a method for selecting a time zone within which the device30is to operate, is purely exemplary. Many other methods may be used depending on the nature of the device30. For example, the user may instead configure the appropriate time zone by launching a “setup wizard” upon initializing the device30. Time zone information can also be received wirelessly via radio86(e.g. in communication with a basestation or a wireless network, as a result of a regular network update or network ping messages). Time zone information can also be determined by GPS location (e.g. GPS coordinates may indicate that the device30is in Toronto, with the result that the appropriate time zone is Eastern Standard Time). Likewise, time zone information may also be extracted from file information relating to pictures taken, for example, if pictures are taken and then saved in a folder including the name “NYC” or “Paris”, the device30can surmise its location and thereby automatically configure the appropriate time zone.

Once the user has configured the correct operating time zone for the device30, processor78consults a table stored in persistent storage device82(step335) containing a correlation of the configured time zone with the appropriate fluorescent lighting mode (i.e. 50 Hz or 60 Hz), as set forth in Table A, above. Upon determining the correct fluorescent lighting mode, processor78then issues a command to photosensor chip62, indicating the correct fluorescent lighting mode (step340), whereupon the chip62operates in accordance with the appropriate fluorescent lighting mode to eliminate flicker from captured images (e.g. using a technique such as set forth in U.S. Pat. No. 6,271,884 or 7,187,405).

The foregoing represents exemplary embodiments and is not intended to restrict the scope of the claims attached hereto. For example, it is contemplated that the device30may be programmed to automatically update time zone information when the user moves from one location to another. This and all other such alternatives are believed to be within the sphere and scope of the attached claims.