Patent Publication Number: US-2010124041-A1

Title: Systems and methods for controlling flash color temperature

Description:
BACKGROUND 
     Presently, camera flashes produce a flash of light at a factory-determined color temperature. Most flashes are designed to produce a color temperature corresponding to daylight, or about 5500 Kelvin. A flash at such a color temperature can produce undesirable effects on a photograph, however. For example, a photographer shooting on a cloudy day may specifically desire the more gray-blue ambient light quality of that particular day, and a “normal daylight” flash color temperature may interfere with this desired quality. 
     Undesirable effects from flash color temperature affect conventional photography as well as digital photography. Most digital cameras make use of an automatic white balance sensor. This sensor detects a predominant color temperature, and the camera then adjusts photographs to better match the detected predominant color temperature. Thus, the use of a flash with a given color temperature will often produce a predominant color temperature for the captured photograph, which will be further propagated into the photograph by the camera&#39;s electronics. 
     Photographers wishing for different flash color temperatures presently manually place filters in the light path between the flash and the subject. This is accomplished by purchasing and storing appropriate filters, and privately configuring means to hold a selected filter in the light path. This approach is inconvenient in the purchasing, storing, and organizing of multiple filters, the time needed to devise means for holding filters in place, and the additional photographer time required to select and position desired filters during a shoot. Moreover, the photographer is limited to the color temperatures produced by his unfiltered flash plus the specific color temperatures produced by filters in his possession. 
     The industry is in need of a better approach for controlling flash color temperature. 
     SUMMARY 
     In consideration of the above-identified shortcomings of the art, the present invention provides systems and methods for controlling flash color temperature. An adjustable camera flash unit is provided which comprises a camera flash unit, and an adjustable light filter affixed in a light path of said camera flash unit. The adjustable light filter may be electronically adjustable when coupled to an appropriately configured electronic controller, and may be adjustable along a continuous range of color temperatures. By adjusting the adjustable light filter to a desired setting prior to discharging the camera flash unit, a flash of the desired color temperature is produced. An exemplary method of adjusting flash color temperature produced by a camera flash unit may thus include receiving a flash color temperature setting, and electronically adjusting a light filter affixed in a light path of said camera flash unit to produce the flash color temperature designated by said setting upon a flash of said camera flash unit. Other advantages and features of the invention are described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The systems and methods for controlling flash color temperature in accordance with the present invention are further described with reference to the accompanying drawings in which: 
         FIG. 1  illustrates a camera equipped with apparatus for controlling flash color temperature. 
         FIG. 2  illustrates an exemplary flash unit equipped with a liquid crystal adjustable light filter. 
         FIG. 3  illustrates an exemplary flash unit equipped with a moving adjustable light filter component. 
         FIG. 4  illustrates an exemplary microcomputer such as may be used as an electronic controller for an electronically adjustable light filter. 
         FIG. 5  illustrates a human interface for controlling an electronically adjustable light filter to produce a desired flash color temperature. 
         FIG. 6  illustrates component parts of a digital camera incorporating an adjustable light filter for controlling flash color temperature as provided herein. 
         FIG. 7  illustrates an exemplary method for controlling flash color temperature. 
     
    
    
     DETAILED DESCRIPTION 
     Certain specific details are set forth in the following description and figures to provide a thorough understanding of various embodiments of the invention. Certain well-known details often associated with cameras and/or computing and electronics technologies are not set forth in the following disclosure, however, to avoid unnecessarily obscuring the various embodiments of the invention. Further, those of ordinary skill in the relevant art will understand that they can practice other embodiments of the invention without one or more of the details described below. Finally, while various methods are described with reference to steps and sequences in the following disclosure, the description as such is for providing a clear implementation of embodiments of the invention, and the steps and sequences of steps should not be taken as required to practice this invention. 
       FIG. 1  illustrates a camera  150  equipped with an electronically adjustable camera flash unit for controlling flash color temperature according to one embodiment. Illustrated in  FIG. 1  is a top view of camera  150  and lens  160  in a single-lens reflex type configuration, where camera  150  is equipped with internal flash unit  100 . An adjustable light filter  110  is affixed in a light path  101  of said camera flash unit  100 . The adjustable light filter  110  is communicatively coupled to an electronic controller  120  disposed inside the camera  150 . The electronic controller  120  sets the filter color of the adjustable light filter  110  to a desired color temperature setting. This is accomplished by sending appropriate electronic signals to the adjustable light filter  110 . 
     The electronic controller  120  may be communicatively coupled to input devices such as an ambient light sensor  130  and user controls  140 . Input devices  130  and  140  provide a desired flash color temperature setting to the electronic controller  120 , which in turn adjusts the adjustable light filter  110  to the desired setting. Various default settings may also be produced by electronic controller  120  without the need for an input setting. 
     While adjustable camera flash units comprising flash unit  100  and an adjustable light filter  110  may be incorporated into a camera  150  as an internal flash, as illustrated in  FIG. 1 , it should be emphasized that embodiments in which adjustable camera flash units are constructed as external flashes that are detachable from a camera body are also contemplated and fall within the scope of the invention. Similarly, some embodiments may decouple the camera  150  and flash unit  100  from the adjustable light filter  110 , in which case the adjustable light filter  110  and optionally also the electronic controller  120 , sensor  130 , and user controls  140  can form a separate adjustable camera flash attachment. Such a separate, adjustable camera flash attachment arrangement may include an integrated electronic controller  120 , sensor  130 , and user controls  140 , or may interface with a camera  150  or freestanding flash unit which supplies these elements. 
     In an internal flash configuration, the wiring connecting an electronic controller such as  120  with an adjustable light filter such as  110  in  FIG. 1  may form a permanent, non-detachable connection, while in an external flash configuration, the wiring may be decouplable. For example, if electronic controller  120  is disposed inside a camera  150 , while the flash unit  100  is an external unit, then the wiring attaching electronic controller  120  with the adjustable light filter  100  may be decouplable according to current techniques for configuring decouplable and re-coupleable external flash electronics, or indeed according to any of the presently available or future developed electronic communications interfaces such as Universal Serial Bus (USB), Peripheral Component Interface (PCI), and so on. A full list of all possible electronic interface types is not reproduced here but will be appreciated by those of skill in the art. 
     It should furthermore be noted that in still another advantageous embodiment, the flash unit  100  and adjustable light filter  110 , as well as the electronic controller  120 , sensor  130 , and user controls  140  may all be disposed in an external flash, thereby eliminating the need for a decouplable connection between electronic controller  120  and the adjustable light filter  110 , while simultaneously achieving an external flash configuration. 
       FIGS. 2 and 3  provide alternative exemplary embodiments of an adjustable camera flash unit. In  FIGS. 2 and 3 , the exemplary filters  110 A and  110 B are affixed in a light path  101  of the flash unit  100 . In other words, filters  110 A and  110 B are affixed to either the flash unit  100  or to a structure attached to the flash unit  100 , such as a camera  150 ; in such manner that light which emanates from the flash unit  100  upon discharge can pass through the filter. 
     The exemplary filters  110 A and  110 B may be affixed by a wide variety of techniques. A transparent adhesive may be used to glue the filters  110 A and  110 B in place. If adhesive is applied only around a perimeter of the filters  110 A and  110 B, the adhesive may be non-transparent. Alternatively, the filters  110 A and  110 B may replace the glass or plastic front pane that is normally built into flash units, and may be affixed using any of the approaches presently used or subsequently developed to affix such front panes in place. The filters  110 A and  110 B may be affixed using screws, rivets, snaps, suction cups, or magnets. The term “affixed” can thus be understood as either permanently or temporarily affixed. The filters  110 A and  110 B may also be simultaneously affixed and moveable, such as where a filter  110 A is on a hinge and latch or ratcheting swivel and is thus moveable into and out of the light path  101 . 
     The flash unit  100  may be constructed according to any of a wide variety of flash unit construction approaches. In general, camera flashes have evolved from the earliest flashes, created by a quantity of magnesium flash powder that was ignited by hand, toward today&#39;s predominantly electronic flash units. Today&#39;s flashes are often electronic xenon flash lamps. An electronic flash contains a tube filled with xenon gas, where electricity of high voltage is discharged to generate an electrical arc that emits a short flash of light. As mentioned above, today&#39;s flashes generally produce a single flash color temperature, which is a product of the light produced by the flash itself plus any reflective materials used on the internal housing of the flash, plus any filtering effect of the transparent material encasing the flash and through which the flash light must travel in the light path. While electronic flashes are common today, embodiments using other types of flash technologies such as microflash, Light Emitting Diode (LED) flashes, or indeed flashcubes and the like are also possible. 
       FIGS. 2 and 3  also demonstrate how in one embodiment, the adjustable light filter can form an adjustable camera flash attachment that is separate from camera  150  and flash unit  100 . In such embodiments, the adjustable light filter  110 A or  110 B and optionally also the electronic controller  120  as well as any number of additional inventive aspects disclosed herein can form a separate, adjustable camera flash attachment. Such an attachment may be affixable to a camera or freestanding flash assembly to produce the desired color temperature control. The electronically adjustable camera flash attachment may include an internal ambient light sensor and/or human interface for controlling flash color temperature settings, or may interface to a camera and receive flash color temperature settings from the camera. 
     Referring now to  FIG. 2  alone, an embodiment is illustrated in which a liquid crystal filter  110 A is used. A liquid crystal filter  110 A can be configured, generally speaking, as a Liquid Crystal Display (LCD) in which the flash unit  100  is the light source for the display. 
     In one embodiment, a liquid crystal filter  110 A may comprise a layer of molecules  111  aligned between transparent electrodes  112  and polarizing filters  113 , the axes of transmission of which may be nonparallel, such as by being oriented perpendicular to each other. The surface of the electrodes  112  that are in contact with the liquid crystal material  112  are treated so as to align the liquid crystal molecules in a particular direction. This treatment typically comprises unidirectionally rubbing a thin polymer layer on the surfaces of the electrodes  112  in contact with the liquid crystal  112 . Electrodes  112  may be made of a transparent conductor, such as Indium Tin Oxide (ITO). 
     Before applying an electric field, the orientation of the liquid crystal molecules  111  is determined by the alignment at the surfaces. For example, the surface alignment directions at the two electrodes  112  may be perpendicular to each other, so the molecules arrange themselves in a helical structure. Light passing through one polarizing filter  113  (left side) is rotated by the liquid crystal helix as it passes through the liquid crystal layer  111 , allowing it to pass through the second polarized filter  113  (right side). Thus when no voltage is applied across electrodes  112 , the filter  110 A is reasonably transparent. 
     When a voltage is applied across the electrodes  112 , a torque acts to align the liquid crystal molecules  111  parallel to the electric field, distorting the helical structure. This reduces the rotation of the polarization of the incident light emanating from the flash unit  100 . If the applied voltage is large enough, the liquid crystal molecules  111  are almost completely untwisted and the polarization of the incident light is not rotated as it passes through the liquid crystal layer  111 . This light will then be mainly polarized perpendicular to the second filter  113  (right side), and thus be blocked. By controlling the voltage applied across the liquid crystal layer in each pixel of the filter  110 A, light can be allowed to pass through in varying amounts. 
     To produce a desired color temperature, in one embodiment, each individual pixel of the filter  110 A may be divided into three cells, or subpixels, which are colored red, green, and blue, respectively, by additional filters (e.g. pigment filters, dye filters and metal oxide filters). The voltage applied across each subpixel can be controlled independently by electronic controller  120 A to yield thousands or millions of possible colors for each pixel. Color components may furthermore be arrayed in various pixel geometries, as is understood in the art of LCD manufacture. 
     The electronic controller  120 A may employ LCD electronics to instruct the filter  110 A to, for example, display a red color on all pixels. This may be for example a specific shade of red corresponding to a desired flash color temperature. The filter  110 A is set to this color prior to discharge of the flash unit  100 . Upon discharge, the filter will then absorb light of the undesired color temperatures, and allow light of the desired color temperature to pass through. As LCDs are capable of displaying light across the entire range of the visible spectrum, the liquid crystal filter  110 A is likewise capable of filtering to any desired color temperature across the entire visible spectrum. 
       FIG. 2  illustrates the best mode presently contemplated for the adjustable light filter, however  FIG. 3  is included herein to demonstrate that alternative arrangements are feasible in any number of configurations that could be arrived at by those of skill in the art with the benefit of the teachings herein.  FIG. 3  illustrates a flexible filter material  115  such as a plastic ribbon with a variety of different filter colors along its length. Electronically activated rollers  114  can serve to advance and retract the material  115  to situate a desired filter color in the light path  101 . The movement of rollers  114  can be under the control of electronic controller  120 B. Controller  120 B may thus for example cause a red-colored filter material corresponding to a desired flash color temperature to be situated in light path  101 . 
     The electronic controller illustrated as  120  in  FIG. 1 ,  120 A in  FIG. 2 , and  120 B in  FIG. 3 , may comprise electronics of any configuration suitable to receive a desired input flash color temperature setting, and to generate appropriate electronic signals that cause an adjustable light filter to produce the input flash color temperature setting. Many if not most of today&#39;s cameras contain multifunction microcomputers; one contemplated embodiment for electronic controller  120  is that of a microcomputer equipped to perform the flash color temperature control functions described herein, along with any other functions otherwise performed by such microcomputer. 
     While computing and software technologies are constantly and rapidly evolving,  FIG. 4  illustrates an exemplary computing device  400 , e.g., a camera, equipped with a suitable processing core  401  that may be used as an electronic controller  120 . In its most basic configuration, processing core  401  typically includes a processing unit  402  and memory  403 . Depending on configuration, memory  403  may be volatile (such as RAM), non-volatile (such as ROM, flash memory, etc.) or some combination of the two. Memory  403  contains software instructions that dictate device  400  behaviors. For example, memory  403  may contain instructions for receiving a color temperature input setting (from a user via a user interface, from a sensor or other electronic device, or as a default value), and instructions for controlling an adjustable filter to produce the input color temperature setting. 
     Additionally, device  400  may also have mass storage (removable  404  and/or non-removable  405 ) such as flash memory or magnetic or optical disks. Device  400  may also have input devices  407  such as camera user interface buttons, connected computing devices, or a touch-screen input, and/or output devices  406  such as a display that presents a GUI as a graphical aid accessing the functions of the computing device  400 . Other aspects of device  400  may include communication connections  408  to other devices, computers, networks, servers, etc. using either wired or wireless media. 
       FIG. 5  illustrates a human interface as may be included for example on the back side of a camera  550 . Such an interface may alternatively be included on an external flash, or other device incorporating an adjustable flash unit. The human interface comprises controls  560  and a display  580 , allowing a human to control an electronically adjustable light filter input setting to cause the electronic controller  120  to produce a desired flash color temperature. In the exemplary embodiment of  FIG. 5 , display  580  presents a current ambient light color temperature, denoted as XXXX. For example, if camera  550  is equipped with an ambient light color sensor, the retrieved sensor value may be displayed here. 
     Exemplary display  580  furthermore presents an adjustable flash color temperature setting  581 , denoted as YYYY. This color temperature setting will be sent to the electronic controller  120  as an input setting. By for example pressing the top and/or right button of user interface controls  560 , the user can increase the setting  581 , and by pressing the bottom and/or left button of user interface controls  560 , the user can decrease the setting  581 . It will be appreciated that the setting  581  may be converted to an input to the electronic controller  120  either each time the setting  581  is changed, or upon another event such as the user pressing the center button of user interface controls  160 , or the user navigating away from the flash color temperature control screen. 
     Finally, a feature may be provided whereby the adjustable flash color temperature setting  581  can be automatically set to substantially match an ambient light color temperature retrieved from an ambient light sensor. For example, by navigating to the selectable auto set to ambient feature  582 , and depressing the center button of user interface controls  560 , the adjustable flash color temperature setting  581  can be set to equal the ambient light color temperature (XXXX). 
     Once the auto set to ambient feature  582  is selected, the adjustable flash color temperature setting  581  can subsequently be automatically reset to ambient just prior to capturing subsequent photographs, to account for changes in ambient light color temperature between photograph captures. Alternatively, the adjustable flash color temperature setting  581  can be updated periodically, such as by subsequently checking the ambient light color temperature at predetermined time intervals, resetting the setting  581  to match, and sending this input to the electronic controller  120 . In yet another embodiment, setting to ambient  582  may be a one-time operation, requiring a user to go back to the flash color temperature control screen and re-select the auto set to ambient feature  582 . 
       FIG. 6  illustrates component parts of a digital camera  600  incorporating an adjustable light filter  664  for controlling flash color temperature as provided herein. In general, camera  600  is illustrated in a digital camera embodiment in which light collected through a lens  610  falls on an image sensor  620 , is converted to an electric signal by converter  630 , and processed by microcomputer  650 . Microcomputer  650  operates according to inputs received from elements on the right hand side of  FIG. 6 , and controls outputs to elements on the left side of  FIG. 6 . Microcomputer may also control lens  610  to some extent, such as in carrying out zoom functions and the like. 
     Microcomputer  650  may receive power from a power supply  674  such as a battery, and may store photographs in a storage  663  such as a fixed or removable flash memory, or any of the wide variety of other storage media available for digital cameras. 
     Microcomputer  650  may receive user inputs from user interface controls  671 , and may change camera settings, operate camera hardware, and support user interaction via the display  661  according to the received user inputs. User interface controls  671  may include for example the control buttons  560  illustrated in  FIG. 5 , as well as features such as zoom, focus, flash mode selections, photo navigation and viewing functions, a shutter button, and so forth. 
     One hardware component that may be controlled by the microcomputer  650  according to settings established by the user is the flash unit  662 . Flash unit  662  may discharge according to desired settings when the user depressed the camera&#39;s shutter button. Settings that may govern flash unit  662  operation are whether the flash  662  is in automatic mode in which flash triggers automatically, red-eye reduction mode which fires the flash several times just prior to exposing a photo, forced (fill-in) flash mode which keeps the flash on in situations where automatic mode would keep it off, suppressed flash mode which turns the flash off, slow sync mode which captures a dimly lit background at night by firing briefly to light the foreground subject, rear-curtain sync mode which is similar to slow sync, but the flash doesn&#39;t fire until just before the shutter closes, and flash exposure compensation mode which increases or decreases the energy output of the flash. 
     Flash energy adjuster  662 A may be a separate component or may be formed by appropriately configuring the microcomputer  650 . The role of the flash energy adjuster  662 A is to adjust flash energy to accommodate for flash energy attenuation at a flash color temperature setting. 
     Different color temperature settings at the adjustable light filter will absorb different amounts of light energy. In other words, they will result in different amounts of flash energy attenuation. For example, a light blue filter will allow more flash energy to pass through to the photographed subject than a dark blue filter. Similar effects will be experienced across the color spectrum, with different shades affecting the amount of flash energy as well as flash color temperature. This difference in flash energy affects the exposure of the resulting photograph, and if not accommodated, could lead to a photograph being over- or underexposed due to a color temperature setting at the adjustable light filter. 
     To accommodate for flash energy attenuation at a given flash color temperature setting, the flash energy adjuster  662 A can increase or decrease flash energy based at least in part on flash color temperature. In one embodiment, this can be done using a look-up table that correlates various color temperature ranges with corresponding flash energy modification needs. For example, if a particular flash color temperature setting will absorb 60% of flash energy, the look-up table might specify that the flash energy that would otherwise be used, e.g., in the absence of the adjustable flash filter, should be increased by 60%. The flash energy adjuster  662 A can thus first determine the adjustable flash filter&#39;s color temperature setting, and then look up a corresponding modification of flash energy. A final flash energy can be determined after accounting for any other flash compensation needs. The flash energy adjuster  662 A can set the energy of the flash unit to the final flash energy for example by allowing a flash capacitor to accumulate appropriate charge prior to discharging the flash unit. 
     Existing flashes use exposure compensation modes to adjust flash energy to account for a distance from the flash unit to a subject, and this may also be taken into account by the flash energy adjuster  662 A or by separate apparatus as appropriate. Techniques for adjusting flash energy based on subject distance include “Through The Lens” or TTL approaches in which subject distance is inferred from a lens focus setting, and pre-flash approaches that discharge an initial flash and measure the time for light to bounce back. Either of these techniques or other developed techniques for flash energy compensation based on subject distance may be used in conjunction with the techniques for flash energy compensation based on a color temperature setting disclosed herein. 
     The flash energy adjuster  662 A may also respond to settings entered at the user interface controls  671 , and may generate warnings or other information to be displayed on the display  661 . For example, flash energy adjuster  662 A may allow for manually setting a desired flash energy. The user may be presented with options such as “½ power,” “¼ power,” and the like, expressing flash energy as a fraction of total available energy, or with actual flash energy units such as “30 Watt-Seconds,” “60 Watt-Seconds” and the like. 
     The flash energy adjuster  662 A may send warnings to the display  661  when the flash unit does not have enough power to produce a desired target exposure level. This situation could arise for example if a subject is both far away, and a desired flash color temperature absorbs much of the flash energy. The warning may allow the user to take certain pre-set response actions, for example change the flash color temperature setting to allow target exposure, or take the photograph anyway. The user may also set defaults via the user interface controls  671  to handle the out-of-range issue. 
     Microcomputer  650  may receive inputs a variety of sensors  672  that are used to collect information about ambient conditions for display to a user or for automatic settings adjustments. An ambient light sensor  673  may detect an ambient light color temperature. This value can be supplied this as an input to microcomputer  650 , which may subsequently display the retrieved value, discard the retrieved value, use the retrieved value as a setting for the adjustable light filter  664 , or use the retrieved value as an input to a formula for determining a setting for the adjustable light filter  664 . In the case of using the retrieved value as an input to a formula, the microcomputer  650  may for example be instructed to set the adjustable light filter  664  to a color temperature that is, for example, just redder than ambient, just bluer than ambient, or the like, to produce a desired photographic effect. 
     In one embodiment, the ambient light sensor  673  may be situated inside the camera  600  such that light introduced through lens  610  falls partially upon the sensor  673 , and therefore the sensor  673  detects ambient light color temperature in a direction corresponding to a would-be subject of a photograph. Embodiments are also feasible in which existing camera  600  components such as the lens  610 , image sensor  620 , converter  630  and microcomputer  650  are configured to operate as an ambient light color temperature sensor—eliminating the need for including additional hardware such as  673  in the camera  600 . 
     Microcomputer  650  may furthermore serve as an electronic controller (e.g. element  120  from  FIG. 1 ) for an adjustable light filter  664 . In this regard, microcomputer  650  may use an appropriate setting received from the user via  671  or from the ambient light sensor  673  to adjust the adjustable light filter  664  so as to produce the color temperature of the setting upon discharge of the flash unit  662 . In general, such adjusting comprises sending appropriate electronic signals to the adjustable light filter  664  prior to any discharge of the flash unit  663 . These signals will vary depending on the type of filter used as will be appreciated. 
       FIG. 7  illustrates an exemplary method as may be carried out in accordance with various embodiments of the invention, for example by an electronic controller that adjusts flash color temperature. Such a controller may first receive a flash color temperature setting  701 . The setting may be received by virtue of being “pushed” to the electronic controller  120  or by being “pulled” such as where a sensor  673  is polled, or a computer memory is read in order to retrieve a default setting. 
     The received setting may then be used to adjust a light filter to produce the designated flash color temperature  702 . The details of performing this operation will vary with the specific electronics of individual embodiments. For example, in a liquid crystal filter embodiment, appropriate commands for LCD type electronics will generate electronic signals that produce a desired color in the liquid crystal filter. 
     Flash energy may then be adjusted  703  to account for the designated flash color temperature, as well as subject distance or other factors affecting flash energy. 
     The flash unit may then be discharged  704  in connection with taking a photograph. The flash color temperature setting may also be saved, for example as metadata with the captured photograph, for use in subsequent image processing  705 . 
     In light of the diverse embodiments that may be built according to the general framework provided herein, the disclosed systems and methods cannot be construed as limited to a particular architecture. Instead, the invention should be construed in breadth and scope in accordance with the appended claims.