(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2011/0025879 A1
`(43) Pub. Date:
`Feb. 3, 2011
`DRADER et al.
`
`US 2011 0025879A1
`
`(54) METHOD AND APPARATUS FOR
`CONTROLLING A CAMERAMODULE TO
`COMPENSATE FOR THE LIGHT LEVEL OF
`A WHTE LED
`
`Publication Classification
`
`(51) Int. Cl.
`HO)4N 9/73
`
`(2006.01)
`
`(75) Inventors:
`
`Marc DRADER, Kitchener (CA);
`Ken WU, Burlington (CA);
`Michael PURDY, Kitchener (CA)
`Correspondence Address:
`Borden Ladner Gervais LLP
`1100-100 Queen Street
`Ottawa, ON K1P 1J9 (CA)
`(73) Assignee:
`RESEARCH IN MOTION
`LIMITED, Waterloo (CA)
`12/903,732
`Oct. 13, 2010
`Related U.S. Application Data
`(63) Continuation of application No. 1 1/626,883, filed on
`Jan. 25, 2007, now Pat. No. 7,825,958.
`
`(21) Appl. No.:
`(22) Filed:
`
`(52) U.S. Cl. .............................. 348/223.1; 348/E09.051
`
`ABSTRACT
`(57)
`A method and an apparatus enabling use of a light source
`emitting a light of changing intensity and changing spectrum
`as a flash with a camera module having a white-balance
`routine and an exposure routine, wherein an initial value
`representative of a color spectrum emitted by the light Source
`is transmitted to the camera module, the light source is turned
`on, and the camera module is signaled to scan a plurality of
`images of the scene while the light source is turned on, allow
`ing the white-balance and exposure algorithms to be
`employed with each image scanned to refine the first initial
`value to refine the degree of compensation employed in cor
`recting a color and a light level in the last one of the images of
`the plurality of images scanned.
`
`
`
`1
`
`APPLE 1009
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`Patent Application Publication
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`FIG. 1
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`PRIOR ART
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`2
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`205
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`FIG. 2
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`3
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`Patent Application Publication
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`Feb. 3, 2011 Sheet 3 of 5
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`US 2011/0025879 A1
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`200 -
`
`a
`
`processor
`210
`
`"put
`2O4
`
`input interface
`234
`
`to Output
`device
`2O5
`
`type
`2O7
`
`output interface
`235
`
`LED interface
`237
`
`control program
`222
`
`white-balance patch
`225
`
`
`
`
`
`Storage
`220
`
`&S y
`
`
`
`processor
`26O)
`
`exposure
`Control
`element
`282
`
`image
`SCanning
`element
`283
`
`camera module
`250
`
`White-balance routine
`
`parameter data
`273
`
`exposure routine
`274.
`
`storage
`270
`
`FIG. 3
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`4
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`Patent Application Publication
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`Patent Application Publication
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`Feb. 3, 2011 Sheet 5 of 5
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`US 2011/0025879 A1
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`await user indication
`to take a picture
`51O.
`
`
`
`
`
`
`
`
`
`
`
`ls
`White LED flash
`being used?
`520
`
`transmit general
`initial values to
`Camera module
`530
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`transmit White
`balance patch to
`camera device
`540
`
`
`
`transmit initial Values
`for White LED to
`Camera module
`542
`
`signal camera module
`to Scan succession of
`images
`532
`
`
`
`signal camera module
`to Scan succession of
`images
`544
`
`
`
`
`
`
`
`
`
`
`
`undo White
`balance patch
`546
`
`FIG. 5
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`6
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`US 2011/0025879 A1
`
`Feb. 3, 2011
`
`METHOD AND APPARATUS FOR
`CONTROLLING A CAMERAMODULE TO
`COMPENSATE FOR THE LIGHT LEVEL OF
`A WHTE LED
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`0001. The present application is a continuation of U.S.
`application Ser. No. 1 1/626,883 filed Jan. 25, 2007, the con
`tents of which are incorporated herein by reference in their
`entirety.
`
`BACKGROUND
`
`0002 1. Field
`0003. The disclosed and claimed concept relates generally
`to electronic devices and, more particularly, to a method for
`controlling a camera module incorporated into a portable
`electronic device to compensate for the characteristics of a
`white LED used as a flash for taking pictures.
`0004 2. Description of the Related Art
`0005. It is widely known to use a variety of different
`Sources of light for taking a picture with a digital camera
`module, including natural Sunlight, a Xenon strobe, an incan
`descent bulb or a fluorescent bulb. Despite being very differ
`ent light sources using very different processes to emit light,
`a common characteristic of all of these light sources is that the
`spectrums of light emitted by each of them, despite being
`different, provide a range of light frequencies that resemble
`the expected behavior of radiant emissions of a blackbody at
`given temperatures.
`0006. In 1931, an international committee called the Com
`mission Internationale de L'Eclairage (CIE) met in Cam
`bridge, England, and attempted to put forward a graphical
`depiction of the full range of colors of light that the human eye
`can actually perceive. This graphical depiction, namely a
`chromaticity chart, and the resulting standard incorporating
`this chromaticity chart has come to be known as “CIE 1931'
`and is widely used by Scientists and photographers, among
`many others, in working with light in the visible light spec
`trum. FIG. 1 depicts a simplified representation of a chroma
`ticity chart 100 based on the CIE 1931 standard, with all
`visible colors of light specifiable with two dimensional color
`coordinates. As can be seen, towards the center of what is
`frequently called the “horseshoe-shaped visible region 110
`of all that the human eye can perceive is a white region 120 of
`colors of light generally categorized as “white light' and
`Surrounded by other regions generally described as non-white
`light, including a red region 121, a pink region 122 and a
`purple region 123. It should be noted that the exact boundaries
`of these regions 120-123 should be taken as approximations
`and not precise designations of color, since the classification
`of colors is necessarily Subjective.
`0007. The human brain has evolved its own form of white
`balancing capability by which human beings have little
`trouble discerning what color an object should be, even
`though it may be illuminated with light that is only marginally
`white. Such as the reddish hue of the Sun at Sunset, the orange
`glow of campfire, or the bluish tint of a mercury vapor stree
`tlight. It is due to this flexibility of the human brain that a
`number of light sources emitting a variety of different spectra
`of light, and thereby having a variety of differing color coor
`dinates that occupy different points on a chromaticity chart,
`can be classified as “white light sources with the result that
`
`the white region 120 in FIG. 1 occupies a considerable pro
`portion of the visible region 110.
`0008 Passing through the white region 120 is a portion of
`a blackbody curve 130 depicting the set of color coordinates
`of white light Sources that emit a spectrum of light frequen
`cies that substantially follow the spectrum of light frequen
`cies that would be expected to be emitted from theoretically
`ideal blackbody light sources heated to different tempera
`tures. Most commonly used sources of white light have color
`coordinates specifying a point that falls along or Substantially
`close to this blackbody curve 130, including sunlight and
`Xenon flash Strobes, as well as incandescent, fluorescent,
`high-pressure sodium and mercury vapor lamps. As a result of
`so many of the commonly used sources of light used in taking
`pictures having color coordinates representing points that fall
`on or relatively close to the blackbody curve 130, algorithms,
`constants and limit values employed in digital cameras to
`perform automatic exposure control and automatic white
`balancing are commonly chosen and designed with a pre
`sumption that all light sources that will be encountered will be
`ones with Such color coordinates. Indeed, this presumption
`has become so ingrained that it has become commonplace for
`manufacturers of camera modules incorporated into other
`electronic devices to have such choices of algorithms, con
`stants and limit values built into or preprogrammed directly
`into the camera modules, themselves.
`0009. As those skilled in the art of white-balancing algo
`rithms will recognize, a step taken by many known white
`balancing algorithms is attempting to derive a reference white
`color in a given image as an input parameter for determining
`the degree to which the colors in that image are to be adjusted
`to compensate for the lighting in the original Scene so that the
`objects in the resulting picture are presented with their correct
`colors. To do this, white-balancing algorithms typically
`require either that there bean object in the image that actually
`is white (known as the “white world' algorithm) or that the
`average of all the colors of all the pixels in the image be a gray
`(known as the “gray world' algorithm), and either of these
`approaches can provide a basis from which a reference white
`color for that image may be derived. However, it is possible to
`have images that do not provide a white object or that are
`filled with objects of colors that provide a very skewed result
`when averaging to derive a gray. An example of such an image
`is one filled with the tree leaves of a forest of trees such that
`the image is filled with different shades of green and little
`else, thereby providing no white objects and providing an
`average that will necessarily be a green color and not a gray.
`If white-balancing algorithms are allowed to process such an
`image without constraints, the result can be whited-out or
`blackened-out objects in the resulting picture, and So it is
`deemed desirable to specify boundaries for what a reference
`white color may be so as to constrain the degree to which a
`white-balancing algorithm is permitted to adjust colors.
`0010 Given the aforementioned presumption that the
`light Sources to be encountered by a digital camera are likely
`to have color coordinates specifying points falling along or
`quite close to the blackbody curve 130, the format in which
`the boundaries for what a reference white color may be are
`communicated to typical camera modules in a manner that
`comports with this assumption. In this commonly used for
`mat, a pair of color coordinates that define the endpoints of a
`straight segment in a chromaticity chart, Such as a segment
`140 depicted in FIG.1, are communicated to a camera module
`along with an error term (or “locus’) specified in terms of a
`
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`US 2011/0025879 A1
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`Feb. 3, 2011
`
`maximum perpendicular distance away from the segment
`140. These two endpoints and the error term, together, specify
`a rectangular-shaped reference white region 141 within the
`white region 110 that defines these boundaries, thereby defin
`ing a set of acceptable color coordinates within which the
`white-balancing algorithm is permitted to choose a color to be
`a reference white for a given image. This is to allow a short
`segment that should resemble a small portion of the black
`body curve 130 to be specified, such as segment 140, and this
`short segment should be positioned to either largely overlie a
`portion of the blackbody curve 130 or to be relatively close to
`and relatively parallel with a portion of the blackbody curve
`130. No allowance is made in this format for specifying the
`boundaries of a possible reference white with a reference
`white region having any other shape than a rectangular
`region, Such as the reference white region 141 shown.
`0011. Also, given the same aforementioned presumption
`that the light sources to be encountered by a digital camera are
`likely to have color coordinates specifying points falling
`along or quite close to the blackbody curve 130, it is com
`monplace to in some way build minimum and/or maximum
`limits on values used to define the reference white region 141
`such that values defining a reference white region 141 that
`does not substantially overlie the blackbody curve 130, or that
`is not at least substantially close to the blackbody curve 130
`are rejected. The effective result is to create a limit region,
`such as limit region 145 depicted in FIG. 1, into which at least
`a portion of the white region 141 must fall.
`0012. Of those light sources having color coordinates rep
`resenting points falling along or close to the blackbody curve
`130, xenon strobes have become commonplace for use as
`flashes in portable electronic devices used in photography. A
`Xenon strobe is very Small in size while producing an
`extremely bright light that very quickly illuminates a setting
`of which a picture is to be taken. The amount of illumination
`needed from a flash to Sufficiently light a scene for scanning
`its image is a measurable quantity and can be roughly calcu
`lated as the brightness of the flash multiplied by the amount of
`time it must be turned on. The brighter the light source used as
`a flash, the less time it needs to be turned on to sufficiently
`light a scene. Furthermore, the amount of time that a given
`flash needs to be turned on is not necessarily related to the
`amount of time needed for an image scanning element (Such
`as a CCD semiconductor device or a CMOS imaging device)
`to actually scan an image as part of the process of capturing
`that image. In other words, where a bright flash is used, it is
`not unheard of to actually turn off the flash before the image
`scanning element has completed Scanning the image, because
`a sufficient amount of illumination has been Supplied and
`leaving the flash on any longer would result in too high an
`amount of illumination and portions of the image being
`whited out. However, where a dimmer light source is used as
`a flash, the flash must be turned on for a longer period of time
`to achieve the same amount of illumination as a brighter light
`Source, and it is often necessary to delay the start of scanning
`an image until a high enough amount of illumination has been
`achieved.
`0013 Recently, a new artificial source of white light, the
`so-called white LED, has been introduced, providing the
`opportunity to create a flash for use in digital photography
`that requires less power than other light sources. Unfortu
`nately, the white LEDs have a range of color coordinates
`specifying a range of points that fall Substantially distant from
`the blackbody curve 130, and furthermore, at least partly fall
`
`outside the white region 120 and into the pink region 122.
`This deviation of white LEDs from the blackbody curve 130
`is largely due to the manner in which white LEDs produce
`light. White LEDs are in truth, blue LEDs that are partially
`covered with a yellowish phosphor that converts part of the
`blue light into yellow light. The result is a blending of blue
`and yellow light frequencies that approximates white light
`well enough for the human eye and the human brain to accept
`it as a source of white light. In essence, two different non
`white light emissions, each having its own spectrum of light
`frequencies, are being blended to approximate white light and
`Sucha mixing of two non-white spectra is not characteristic of
`blackbody sources of radiant energy.
`0014. Also, white LEDs, though brighter than incandes
`cent lamps of comparable size, are far dimmer than Xenon
`strobes of comparable size. As a result, to achieve a desirable
`amount of illumination of a scene when used as a flash, a
`white LED must be kept on far longer than a xenon strobe
`used as a flash, and a white LED must also be supplied with a
`very high amount of electric power that would actually dam
`age internal components of the white LED if that amount of
`power were maintained for more than a very brief period of
`time. In using a white LED as a flash, the amount of time
`during which the white LED is actually turned on can be kept
`short enough to prevent this damage. Unfortunately, even
`during the brief period in which the white LED is turned on,
`the light emitting semiconductor components of the white
`LED respond to the very high amount of power by converting
`an ever increasing proportion of that power into heat as time
`passes from the moment at which that power is first Supplied
`to the moment when that power is removed. Correspondingly,
`as time passes the proportion of that power converted to
`visible light decreases such that the white LED is initially
`very bright when that power is first applied, but that bright
`ness level almost immediately begins fading more and more
`as time passes. With this quickly fading brightness, the color
`spectrum output by a white LED also changes quickly as time
`passes from the moment that it is turned on. This changing
`light level and this changing color spectrum must be taken
`into account in both calculating the amount of time a white
`LED is to be turned on to provide a sufficient total amount of
`illumination to serve as an effective flash and in compensating
`for its changing spectrum of light output in performing white
`balancing.
`(0015. Another feature of white LEDs not exhibited by
`artificial light sources long used in photography, including
`xenon strobes and incandescent bulbs, is the high variability
`in the color spectra of each of the blue and yellow elements of
`the light emitted by white LEDs. White LEDs and the tech
`nology to manufacture them are still Sufficiently new that only
`slow progress has been made in exerting tighter control over
`the manufacture of white LEDs to achieve sufficient consis
`tency to avoid having two white LEDs from the very same
`production run emit light that is of perceptibly different hues.
`For this reason, unlike other artificial light sources that have
`far higher consistency in the spectra of their emitted light, the
`size of the region that the “white light emitted by LEDs may
`fall within is considerably larger than for other light sources.
`As a result of these various issues, current practices in con
`trolling a camera module's built-in white-balancing algo
`rithm are insufficient to accommodate the very unique char
`acteristics of white LEDs.
`BRIEF DESCRIPTION OF THE DRAWINGS
`0016 A full understanding of the disclosed and claimed
`concept can be gained from the following Description when
`read in conjunction with the accompanying drawings in
`which:
`
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`US 2011/0025879 A1
`
`Feb. 3, 2011
`
`0017 FIG. 1 is a simplified depiction of a CIE 1931 chro
`maticity chart depicting the black body curve and a PRIOR
`ART approach to specifying a reference white region within
`which a reference white color is constrained;
`0018 FIG. 2 is a depiction of an improved handheld elec
`tronic device in accordance with the disclosed and claimed
`concept;
`0019 FIG. 3 is a schematic depiction of the improved
`handheld electronic device of FIG. 2;
`0020 FIG. 4 is another simplified depiction of a CIE 1931
`chromaticity chart depicting the black body curve and an
`approach to specifying a reference white region within which
`a reference white color is constrained in accordance with the
`disclosed and claimed concept; and
`0021
`FIG. 5 is a flowchart depicting an embodiment of an
`improved method in accordance with the disclosed and
`claimed concept.
`
`DESCRIPTION
`0022. The accompanying figures and the description that
`follows set forth the disclosed and claimed concept in its
`preferred embodiments. It is, however, contemplated that per
`sons generally familiar with handheld electronic devices will
`be able to apply the novel characteristics of the structures and
`methods illustrated and described herein in other contexts by
`modification of certain details. Accordingly, the figures and
`description are not to be taken as restrictive on the scope of the
`disclosed and claimed concept, but are to be understood as
`broad and general teachings.
`0023 For purposes of the description hereinafter, the
`terms “upper”, “lower”, “right”, “left”, “vertical”, “horizon
`tal', “top”, “bottom', and derivatives thereof shall relate to
`the disclosed and claimed concept as it is oriented in the
`figures.
`0024. An improved electronic device 200 is depicted gen
`erally in FIG. 2 and is depicted schematically in FIG. 3. The
`electronic device 200 may be a handheld or other portable
`electronic device (e.g. and without limitation, a digital cam
`era, a PDA, a cell phone, a digital watch, or a laptop com
`puter). The electronic device 200 incorporates a housing 202
`on which are disposed a white LED 207 serving as a flash for
`taking pictures and a camera module 250. The housing 202
`may additionally have disposed thereon an input device 204
`and/or an output device 205. The electronic device 200 also
`incorporates a processor 210 connected to a storage 220, and
`a LED interface 237 controlling the LED 207. The processor
`210 may additionally be connected to one or more of an input
`interface 234 receiving input from the input device 204, an
`output interface providing output to the output device 205,
`and a media storage device 240 capable of interacting with a
`storage medium 241 (which may or may not be of removable
`form). The camera module 250 incorporates a processor 260
`connected to a storage 270, an exposure control element 282
`and an image scanning element 283. Although described and
`depicted as being disposed on the housing 202 of the elec
`tronic device 200, the white LED 207 and/or the camera
`module 250 may alternatively be physically separate from the
`housing 202, but linked to other components of the electronic
`device 200 through a suitable electrical, optical, radio fre
`quency or other linkage.
`0025. The processors 210 and 260 may be of any of a wide
`variety of processing devices, including and without limita
`tion, microcontrollers, microprocessors, sequencers, digital
`signal processors or state machines implemented in hardware
`
`logic. In some embodiments, one or both of the processors
`210 and 260 may be one of a number of commercially avail
`able processors executing at least a portion of the widely
`known and used "X86’ instruction set and/or another instruc
`tion set.
`(0026. The media device 240 and the storages 220 and 270
`may be of any of a wide variety of types of storage devices,
`including and without limitation, disk drives (e.g. and without
`limitation, hard drives, floppy drives, magneto-optical drives,
`magnetic tape drives or CD-ROM drives), solid state memory
`(e.g. and without limitation, static RAM, dynamic RAM,
`ROM, EEPROM or FLASH) and memory card readers. How
`ever, in preferred practice, the storages 220 and 270 are gen
`erally more capable of Supporting speedy random accesses
`than the media device 240, and the media device 240 is
`capable of Supporting removable media while the storages
`220 and 270 are not meant to be removable. In preferred
`practice, it is generally intended that the removable media
`device 240 support the exchange of data and/or software
`between the electronic device 200 and another electronic
`device (not shown) through the storage medium 241.
`(0027. The white LED 207 may be any of a variety of
`semiconductor-based light emitting diodes capable of emit
`ting light that Substantially approximates white light. The
`white LED 207 may be fabricated by applying a coating to a
`blue LED that converts at least some of the emitted blue light
`into a yellow light such that a combination of blue and yellow
`light is produced that approximates white light to the percep
`tion of the human eye. Alternatively, the white LED 207 may
`be fabricated in other ways as those skilled in the art will
`readily recognize, including, but not limited to, adding or
`applying red and green phosphors to a blue LED. The LED
`interface 237 allows the processor 210 to control when the
`white LED 207 is turned on and may allow the processor 210
`to control the intensity of the light emitted by the white LED
`207.
`0028. The camera module 250 may be any of a variety of
`commercially available camera modules fabricated by a vari
`ety of manufacturers for the purpose of being incorporated
`into other devices, such as the electronic device 200. The
`image scanning element 283 may be one of a variety of
`available charge-coupled devices (CCD) or CMOS imaging
`devices, or may be another suitable form of device capable of
`scanning an image of objects in its view. The exposure control
`element 282 provides an aperture of controllable dimensions
`through which the light from the objects in the view of the
`image scanning element 283 passes to reach the image scan
`ning element 283. Alternatively, the exposure control element
`282 may control the amount of light reaching the image
`scanning element 283 in other ways known to those skilled in
`the art.
`0029. The input device 204 may be of any of a variety of
`input devices capable of accepting input from a user of the
`electronic device 200, including without limitation switches,
`a keypad, a joystick, a rollerball, or a touchpad. In embodi
`ments that incorporate the input device 204, the input inter
`face 234 couples the processor 210 to the input device 204 to
`receive input therefrom. The output device 205 may be of any
`of a variety of output devices capable of providing informa
`tion to a user of the electronic device 200, including without
`limitation lights, a display device, an audible indicator, or a
`tactile device Such as a vibrator mechanism causing the elec
`tronic device 200 to vibrate such that a user of the electronic
`device 200 is able to feel the vibration. In embodiments that
`
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`
`incorporate the output device 205, the output interface 235
`couples the processor 210 to the input device 205 to provide
`output thereto.
`0030. When the electronic device 200 is used to take a
`picture, the processor 210 accesses the storage 220 to retrieve
`and execute a sequence of instructions of a control program
`222, thereby causing the processor 210 to transmit sequences
`of instructions and/or data to the camera module 250 and to
`operate the camera module to Scan one or more images as will
`shortly be explained. In turn, the processor 260 accesses the
`storage 270 to retrieve and execute sequences of instructions
`from a white-balance routine 272, an exposure routine 274
`and/or another sequence of instructions provided by the pro
`cessor 210, thereby causing the processor 260 to operate the
`exposure control element 282 and the image scanning ele
`ment 283 to carry out the Scanning of one or more images. The
`processors 210 and 260 are caused to interact to transfer the
`data representing the resulting picture from the camera mod
`ule 250 to be stored in the storage 220, or perhaps the media
`storage device 240 if present. Where the taking of a picture
`entails the use of the white LED 207 as a flash, the processors
`210 and 260 may be caused to further interact in controlling
`the timing and intensity of the lighting Supplied by the white
`LED 207 through the LED interface 237.
`0031. In embodiments of the electronic device 200 having
`the input device 204 and/or the output device 205, the pro
`cessor 210 is further caused by the control program 222 to
`operate the input interface 234 and/or the output interface 235
`to interact with the user of the electronic device 200 through
`one or both of the input device 204 and the output device 205.
`Where the input device 204 includes a relatively small num
`ber of switches providing the user with the ability to control
`various aspects of the process of taking a picture (e.g. without
`limitation, the focus, the landscape or portrait mode, and
`whether or not to use a flash), the processor 210 receives such
`input from the user and carries out the taking of a picture,
`accordingly. Where the input device 204 includes a keypad or
`other device providing greater flexibility of input, the user
`may be provided with the ability to enter data concerning the
`picture to be taken, such as a time, place or name of the Subject
`of the picture. Where the output device 205 includes a graphi
`cal display, the processor 210 may be caused by the control
`program 222 to present the user with a view of what the image
`scanning element 283 sees before the picture is taken and/or
`a view of the resulting picture on the output device 205.
`0032. In embodiments of the electronic device 200 having
`the media storage device 240, the processor 210 may be
`further caused to store pictures taken by the user on the
`storage medium 241 for the user to transfer to another elec
`tronic device (not shown) for display, archiving and/or print
`ing. Where such embodiments also incorporate a form of both
`the input device 204 and the output device 205 of sufficient
`ability, the processor 210 may be further caused to provide the
`user of the electronic device 200 with the ability to use the
`input device 204 and the output device 205 to view and select
`pictures to be stored on the storage medium 241, as well as to
`select pictures to be deleted. Alternatively, or in addition to
`the media storage device 240, the electronic device 200 may
`further incorporate a communications interface (not shown)
`allowing the electronic device 200 to be directly connected to
`another electronic device for the transferring of pictures,
`other data and/or Software (e.g. without limitation, a digital
`serial interface such as IEEE 1394).
`
`0033. As previously described, the camera module 250
`may be any one of a variety of commercially available camera
`modules from a variety of manufacturers for incorporation
`into various electronic devices, including the electronic
`device 200. The white-balance routine 272 may be based on
`any of a variety of widely known white-balancing algorithms
`(including the earlier-described gray world and white world
`algorithms) to derive a reference white color for a given
`image that is used to determine the degree to which the
`white-balance routine 272 is to be used to modify that image
`to compensate for the lighting used. However, as was also
`previously described, it is common practice to impose con
`straints on white-balancing algorithms to prevent overcom
`pensation for lighting that can result where the colors in an
`image do not provide white-balancing algorithms with the
`reference colors needed to function, correctly.
`0034. Unfortunately, the commonplace manner of
`describing the reference white region of color coordinates to
`which the point representing a reference white color is to be
`constrained as a rectangular region that is Substantially adja
`cent to or that substantially overlies a portion of a blackbody
`curve on a chromaticity chart is based on the assumption that
`whatever source of light is used to illuminate an image will
`exhibit characteristics largely conforming to what would be
`expected of a corresponding blackbody source of radiation.
`This same assumption has also resulted in the commonplace
`practice of incorporating into parameter data 273 within the
`storage 270 a set of minimum and maximum value limits that
`will be accepted for specifying the color coordinates defining
`the segment that partly defines that rectangular region. In
`effect, these minimum and maximum value limits describe a
`limit region into which at least a portion of the white reference
`region must fall. Unfortunately, to describe a rectangular
`region within which the color coordinates of the white LED
`207 are likely to fall requires specifying color coordinates that
`are outside such minimum and maximum value limits.
`0035. As part of the earlier-described process of taking a
`picture where the white LED 207 is employed as a flash, the
`processor 210 is caused by the control program 222 to provide
`the camera module 250 with a pair of color coordinates (i.e.,
`the pair of points defining a segment) and an error term (or
`“locus') that define a rectangularly-shaped reference white
`region to which the point defined by the color coordinates of
`the reference white color derived by the white-balance rou
`tine 272 are to be constrained. However, to overcome the
`commonplace limitations imposed by the minimum and
`maximum value limits stored within the parameter data 273,
`the processor 210 is first caused by the control program 222 to
`transmit to the camera module 250 a white-balance patch 225
`retrieved by the processor 210 from the storage 220. In some
`embodiments, the white-balance patch 225 provides at least
`one alternate minimum and/or maximum value that the pro
`cessor 260 uses in place of at least one minimum and/or
`maximum value of the parameter data 273 when executing a
`sequence of instructions of the white-balance routine 272. In
`other embodiments, the white-balance patch 225 provides an
`alternate sequence of instructions to be executed by the pro
`cessor 260 in place of at least a portion of a sequence of
`instructions of the white-balance routine 272. In still other