Note: Descriptions are shown in the official language in which they were submitted.
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DISPLAY BRIGHTNESS ADJUSTMENT
TECHNICAL FIELD
[00011 The present disclosure relates generally to portable electronic
devices, electronic
communications, and more particularly to systems and methods for controlling
the brightness
of a portable electronic device having a display.
BACKGROUND
[00021 Many portable electronic devices include a display that presents to a
user images
in various forms, such as video, still photographs, text, icons and graphics.
Some displays,
such as some liquid crystal displays (LCDs), include a backlight that
illuminates the image and
generates most of the light emitted from the display. Other displays are self-
emissive or self-
illuminating, such that the pixels of the emit light, often without the need a
backlight. Many
displays have a controllable brightness level. Brightness may be controlled by
controlling the
emission of light from the backlight or from the pixels, or both. US Patent
7,701,434 and US
Patent Application 12/612,725, for example, discuss adjusting the brightness
level of the
display in response to ambient light conditions.
SUMMARY
[00031 The concepts described herein pertain to controlling a display
brightness level as a
function of the ambient light, and controlling a display brightness level to
accommodate
human light or dark adaptation. In one aspect, the concepts are directed to a
method
comprising controlling a brightness of a display of a portable electronic
device to a first
brightness level as a function of a first level of ambient light, controlling
the brightness of the
display to a second brightness level as a function of a second level of
ambient light, and
subsequently controlling the brightness of the display to a third brightness
level without a
substantial change in the ambient light level. The second level of ambient
light is substantially
changed from the first level of ambient light, and may be lower than the first
level of ambient
light. The method may comprise controlling the brightness of the display to
the third
brightness level after an adaptation interval elapses, the adaptation interval
beginning when the
brightness of the display is controlled to the second brightness level. In
another aspect, the
concepts may be directed to a portable electronic device that can carry out
the method. In
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some embodiments, the device can measure a length of time that an ambient
light level has
been without substantial change and can control the brightness of the display
as a function of a
level of ambient light and as a function of the length of time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The accompanying figures, where like reference numerals refer to
identical or
functionally similar elements throughout the separate views, and which
together with the
detailed description below are incorporated in and form part of the
specification, serve to
further illustrate various embodiments and to explain various principles and
advantages all in
accordance with the present disclosure, in which:
[0005] FIG. 1 depicts a portable electronic device according to one example;
[0006] FIG. 2 depicts a block diagram of the portable electronic device of
FIG. 1, and
associated components in which the apparatus and methods disclosed herein may
be
implemented, in the context of an illustrative communication system, according
to one
example;
[0007] FIG. 3 graphically depicts illustrative brightness control of a display
in relation to
an illustrative model of dark adaptation, according to one example;
[0008] FIG. 4 graphically depicts a different illustrative brightness control
of a display in
relation to an illustrative model of dark adaptation, according to one
example;
[0009] FIG. 5 is a flow chart illustrating a method, in which display
brightness is changed
to accommodate adaptation, according to one example;
[0010] FIG. 6 is a flow chart illustrating example techniques by which a
substantial
change in ambient lighting may be determined, according to one example; and
[0011] FIG. 7 is a flow chart illustrating another method, in which display
brightness is
changed to accommodate adaptation, according to one example.
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DETAILED DESCRIPTION
[0012] The concepts described below generally pertain to brightness
adjustment, that is,
controlling the brightness of a display of a portable electronic device. Many
portable
electronic devices are transported in ordinary use to different light
environments. Light
environments may typically range from a brightly sunlit environment to a pitch-
black room.
Some portable electronic devices are handheld, that is, sized to be held or
carried in a human
hand. Examples of portable electronic devices that may have displays include
cell phones,
personal digital assistants (PDAs), smart phones, tablet-style computers,
portable DVD
players, global positioning system (GPS) units, laptop computers and remote
controls.
[0013] Portable electronic devices often include a light sensor that senses
the ambient
light levels. The portable electronic devices may adjust the brightness of the
display as a
function of the ambient light, to make the displayed images easier for a human
being to see.
In a typical example, when a portable electronic device is brought from
sunlight into a dark
room (e.g., less than 1 lux, lux generally being a measurement unit of the
ambient light
intensity as perceived by the human eye), the light sensor detects the low
ambient light level
and the device may automatically set the brightness to a level appropriate for
a dark
environment. The brightness of the display in a "dark" environment may be
dimmer than for a
sunlit environment.
[0014] It has been discovered by experimentation and experience that a display
brightness
setting or adjustment that is initially satisfactory may become less so. For
example, when the
brightness of the display is dimmed to correspond to the low level of light,
the amount of
brightness may be initially acceptable. As the user's eyes adjust to the
darkness, however, this
level of brightness of the display can be less satisfactory, perhaps even
straining,
overpowering and uncomfortable to view.
[0015] In some cases, the user's eyes may be adapted to a darkness level, and
when a
darkened display is illuminated, the brightness may be perceived as
uncomfortably high. An
example of a situation such as this is when a user is in bed in a pitch black
room, and then the
display becomes illuminated (e.g., to display an incoming telephone call).
[0016] The process by which human eyes become accustomed to a lighting
environment
is called adaptation. The process whereby eyes adapt from a darker environment
to a lighter
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environment is light adaptation, and the process whereby eyes adapt from a
lighter
environment to a darker environment is dark adaptation. Adaptation results
from a
biochemical process. The exact biochemical processes and mechanisms behind
adaptation are
not essential to the concepts discussed herein, but the following is provided
for general
information. In general, human eye sensitivity to light is a function of
(i.e., depends upon) the
amount of photopigments present in the rod and cone cells in the retina. There
are four
different kinds of photopigments. One kind of photopigment is present in the
rod cells, which
are sensitive to black-and-white, and three other kinds are in the cone cells,
which are sensitive
to colour. The different photopigments in the cone cells make them sensitive
to different
colours.
[0017] Photopigments undergo chemical alterations when exposed to light,
breaking
down (dissociating into different biochemical components) in the presence of
light. As
photopigments in the rod or cone cells breaks down, the cells become less
sensitive to light. If
the light is removed, a broken down photopigment is reset automatically with
the aid of
enzymes. In the dark, black-and-white vision (using the rod cells) becomes
predominant, and
dark adaptation principally involves the rod cells becoming more sensitive as
the
photopigments reset in the absence of light. Light and dark adaptation are
essentially
involuntary physiological processes.
[0018] Further, adaptation takes time. As many people are aware from their own
experience, it takes some minutes for the human eye to adapt to a markedly new
bright or dark
environment. According to some estimates, full adaptation from bright sunlight
to total
darkness can take from twenty to thirty minutes (although functional
adaptation may take
about half as long or less). Adaptation need not be constant; some sources
recognize that there
may be fast and slow phases of adaptation, and that cone cells and rod cells
take different
times to adapt. Moreover, adaptation in many people can affect the sensitivity
of the eyes
dramatically. According to one estimate, human eyes in their most sensitive
state are a million
times more sensitive than when they are in their least sensitive state.
[0019] The concepts described herein pertain to controlling a display
brightness level as a
function of the ambient light, and controlling a display brightness level to
accommodate
human light or dark adaptation. FIG. 1 depicts an example of a portable
electronic device 100
that may illustrate the concepts. As will be discussed, the portable
electronic device 100 and
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various components thereof may be configured or adapted to carry out the
operations of the
concept. (In general, if a component is "configured to" or "adapted to"
perform a function,
that component is capable of carrying out that function.) The portable
electronic device 100 is
based on a computing platform having functionality of a personal digital
assistant with cell
phone and e-mail features. Portable electronic device 100 includes a display
102. The display
102 may be any kind of a display, including a backlit display or a self-
emissive display or any
combination thereof. As depicted in FIG. 1, the display 102 may be a touch
screen display,
which presents images and also serves as an input device through which a user
may give
commands to or otherwise interact with portable electronic device 100. A
characteristic of the
display 102 is its brightness. The brightness of a display 102 may be a
function of the
brightness of (for example) individual pixels, the brightness regions of the
display 102, the
brightness of a backlight (if any), or any combination thereof. The brightness
of the display
102 is controllable, as described in more detail below.
[00201 Additional components of portable electronic device 100 may include a
speaker
104, an indicator (such as an LED indicator) 106, one or more buttons or keys
108 that may
serve as input devices, and a microphone 110 (which has a structure not
visible in FIG. 1).
Additional features may include a touchpad, trackball, one or more dedicated
function keys,
and the like. A housing 110 generally provides a supporting frame for display
102 and for
various external and internal components of the portable electronic device
100.
An alternative embodiment of the portable electronic device 100, not shown in
FIG. 1, may
incorporate a set of external keys, such as a keyboard. The keyboard, or keys
108, may be
illuminated and the brightness of the illumination may be controllable.
Further, controlling of
the brightness of the keys may be similar in many respects to controlling the
brightness of the
display 102. For purposes of simplicity, however, the discussion below will
focus upon the
controllability of the brightness of the display 102.
100211 The portable electronic device 100 may conduct wireless communication
(which
may be two-way or one-way) via one or more wireless systems, including
wireless telephone
systems, infrared systems, Bluetooth (trade-mark) and the many forms of IEEE
802.11
wireless broadband systems, over-the-air television or radio broadcasting
systems, satellite
transmission systems, and the like.
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[0022] The indicator 106 may illuminate (or may flash on and off) to indicate
an event to
a user, such as the receipt of a new email message. In some embodiments,
indicator 106 may
serve a dual function, acting as a sensor of ambient light. An example of such
an indicator is a
light emitting diode (LED), which can emit light as an output in response to a
voltage input,
and which can also receive ambient light as an input and generate a voltage as
a function of
the intensity of the ambient light. In other embodiments, a dedicated light
sensor may
generate a signal as a function of the ambient light. An indicator and a light
sensor may be,
but need not be, in close proximity to one another.
[0023] FIG. 2 is a block diagram depicting the portable electronic device 100
in one
example of a communications system 200. The communications system 200 may
include a
wireless network 202, such as a cellular telephone network. The portable
electronic device
100 comprises a processor 204 coupled to the display 102. The processor 204
may include
any electronic component that can control the brightness of the display 102.
The processor
204 may further include a component that can measure time. In the example of
FIG. 2, the
processor 204 may be a multi-purpose microprocessor that controls many other
functions or
operations of the portable electronic device 100. The processor 204 may be
embodied as a
unitary component or as a collection of components.
[0024] The brightness of the display 102 may be controlled by any of several
techniques,
depending on the kind of display being controlled. For some displays, the
brightness may be
controlled by controlling the power supplied to the display or the power
supplied to
components of the display. In some self-emissive displays, the light emitted
by a pixel or
group of pixels may be controlled. For a display with a backlight, more or
fewer illuminating
elements may be turned on, or the time intervals for illuminating the
illuminating elements
may be lengthened or shortened (e.g., via pulse-width modulation). The
concepts described
herein are not restricted to any particular technique or techniques for
controlling the brightness
of a particular display.
[0025] The portable electronic device 100 further comprises a light sensor
206. As
indicated above, the light sensor 206 may be embodied as an LED. The light
sensor 206
receives ambient light as an input and generates an ambient light signal-that
is, an electrical
signal that is generated to have one or more properties (such as a voltage, a
current, a duty
cycle of a periodic signal, a frequency, etc.) as a function of the ambient
light-and supplies
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that ambient light signal to the processor 204. The processor 204 controls the
brightness of the
display 102 as a function of (based at least in part on) the ambient light
signal. In a typical
implementation, the light sensor 206 is not continuously active. Instead, the
light sensor 206
samples the ambient light periodically. The frequency of sampling need not be
any particular
frequency, but sampling in the range of 0.5 Hz to 3 Hz may be typical in
active usage. When
the portable electronic device 100 is "asleep" (discussed below), the
frequency of sampling of
ambient light levels might be substantially lower. The sampling frequency is
under the control
of the processor 204.
[0026] The processor 204 may control the brightness of the display 102 as a
function of
other factors as well. In some cases, processor 204 may control the brightness
of the display
102 by turning the display off. If the display 102 is illuminated for a period
of time, for
example, and the portable electronic device 100 experiences no user input
during that period
of time, the processor 204 may turn off the display 102 to conserve power. In
some
embodiments, sampling of the ambient light levels via the light sensor 206 may
be suspended
when the display 102 is turned off, or the sampling may take place at a
reduced frequency.
The processor 204 may turn on the display 102 again in response to an event
such as a user
touching a key 108. Although not depicted in FIG. 2, the portable electronic
device 100 may
include one or more devices by which the processor 204 may determine that the
light sensor
206 may be blocked. For example, some portable electronic devices include
sensors that can
detect whether the device is housed in a holster or a closed container, and in
cases such as
these, the functionality of the light sensor 206 may be suspended because
ambient light signals
generated by the light sensor 206 might not necessarily be good indicators of
ambient light.
[0027] FIG. 2 also depicts a wireless transceiver 208, a memory 210, and an
input device
212. The wireless transceiver 208 supports wireless communication between the
portable
electronic device 100 and a remote element, such as a server 214. Memory 210
may comprise
volatile memory, such as RAM, or non-volatile memory, such as flash RAM or a
hard drive.
The input device 212 may comprise any element by which a user may give
commands to or
otherwise interact with the portable electronic device 100, such as keys 108,
or a touchpad or a
trackball. In some embodiments, a touch screen may be an embodiment of the
input device
212.
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[0028] The processor 204 may execute instructions that may be stored in memory
210,
including instructions pertaining to carrying out the concepts described
herein. The processor
204 or memory 210 may obtain the instructions from one or more computer
readable media.
In general, machine-readable data, instructions (or program code), messages,
message packets,
and other computer-readable information may be stored on a computer readable
medium. A
computer readable medium may include computer readable storage medium
embodying non-
volatile memory, such as read-only memory (ROM), flash memory, disk drive
memory, CD-
ROM, and other permanent storage. Additionally, a computer readable medium may
include
volatile storage such as RAM, buffers, cache memory, and network circuits.
Furthermore, the
computer readable medium may comprise computer readable information in a
transitory state
medium such as a network link and/or a network interface, including a wired
network or a
wireless network, that allow a machine, such as the processor 204, to read and
make use of
such computer readable information. In some embodiments, the instructions may
be
embodied as a tangible and non-transitory computer program product comprising
a computer
readable medium embodying program code executable by a processor (such as
processor 204)
that cause the processor to execute any of the methods or variants described
herein.
[0029] A power pack 216 supplies power to the various electronic components in
the
portable electronic device 100. The power pack 216 may be any form of power
supply, such
as a conventional rechargeable battery, a fuel cell system, a solar cell, or
the like, or any
combination thereof. Although the portable electronic device 100 in some
implementations
may be electrically connectable to a fixed power supply such as a wall outlet,
it is generally
desirable that the power supply 216 support the portability of the portable
electronic device
100.
100301 FIG. 3 includes two graphs illustrating an embodiment of the concept,
in the
context of dark adaptation. The top graph depicts an illustrative range of
dark adaptation
curves 400. The dark adaptation curves 400 indicate a typical range of dark
adaptation in
human beings. The vertical axis (which may be in log scale) represents the
intensity that
produces a visual sensation in a human eye. In general, the less sensitive the
eye is, the greater
the intensity of light to produce a sensation. The horizontal axis represents
time. Prior to time
tl, the eye is adapted to a bright environment. The curves in the top graph
may be
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mathematically represented as a typical dark adaptation curve, or a typical
range of dark
adaptation curves, that model dark adaptation of human eyes.
[00311 At time tl, the eye moves abruptly from a bright environment to a dark
environment (e.g., less than 1 lux). Very quickly dark adaptation begins. Cone
cells adapt
more quickly than rod cells. After a while (typically five to ten minutes), a
marked bend 402
appears in the adaptation curves. This bend is called the rod-cone break 402,
at which the rod
cells become more sensitive than the cone cells. In general, the sensitivity
of the eye
increases over time as the photopigments in the eye reset.
[00321 The bottom graph illustrates one implementation of the brightness
control of the
display 102. In this illustration, the processor 204 can set the brightness of
the display 102 to
any of five substantially discrete brightness levels: "high," "normal," "dim,"
"dark" and "off."
At time tl, the intensity of the ambient light drops, and the light sensor 206
generates an
ambient light signal as a function of the lower intensity of ambient light. In
response, the
processor 204 controls the brightness of display 102 to set the brightness to
"dim." (Although
depicted in FIG. 3 as a rapid transition, the processor 204 may control the
brightness of
display 102 through a less abrupt and more aesthetically pleasing transition
from one
brightness level to another.) At a later time t2, the intensity of the ambient
light may remain
substantially the same, but the processor 204 controls the brightness of
display 102 to set the
brightness to "dark," which is less bright than "dim." The change of
brightness is not a
function of a change in ambient light (because ambient light is substantially
unchanged), but
rather is a function of the time. In general, the time is a function of how
long it takes for a
human eye to adjust to the darker environment. By time t2, the eye has
regained enough
sensitivity that the brightness need not be set to "dim" to be seen clearly.
The eye may be
sufficiently sensitive that the "dim" setting may seem unpleasantly bright,
and the "dark"
setting is more pleasant to view. The time between tl and t2, which may be
referred to as an
adaptation interval, may be of any duration. Typically, however, the
adaptation interval may
be about ten minutes (e.g., about ten minutes from the time that the
substantial change in
ambient light is detected, or about ten minutes from the time that the
processor 204 controls
the brightness of display 102 to set the brightness to "dim," which typically
occurs shortly
thereafter), although typical adaptation intervals may be between five minutes
and half an
hour. Although depicted in FIGs. 3 and 4 as occurring after the rod-cone break
402, t2 may be
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selected to occur before a typical rod-cone break point would occur.
Importantly, a
mathematical model for human eye adaptation need not be exact or all-
encompassing, nor
does it need to be calibrated for any particular user. The portable electronic
device 100 may
store a mathematical adaptation model in memory 210 and may control the
brightness of the
display 102 as a function of an adaptation model, but this degree of control
(while within the
scope of the concept) is not necessary to the concept. By controlling a
display brightness level
after an adaptation interval has elapsed without a substantial change in
ambient light-that is,
even though there has not been a substantial change in the ambient light level-
the portable
electronic device 100 may control the brightness of the display 102 to
accommodate
adaptation.
[0033] FIG. 4 includes two graphs illustrating an alternate embodiment of the
concept.
As in FIG. 3, the top graph depicts illustrative dark adaptation curves 400,
and the bottom
graph illustrates one implementation of the brightness control of the display
102. In this
illustration, the processor 204 controls the brightness of display 102 to set
the brightness to
"dim" at or shortly after tl. As in FIG. 3, the eye moved abruptly from a
bright environment to
a dark environment, and in response, the processor 204 controls the brightness
of display 102
to set the brightness to "dim" fairly quickly. As in FIG. 3, the intensity of
the ambient light
may remain without substantial change over time.
[0034] In FIG. 4, unlike FIG. 3, the processor 204 controls the brightness of
display 102
to set the brightness to "dark," but does so gradually. As the eye becomes
gradually more
sensitive, the brightness of the display 102 gradually dims. That is, the
initial brightness of the
display is set to "dim" when the portable electronic device 100 is first
brought into a dark
room, but then the brightness is gradually reduced as the user's eyes adjust
to the darkness. In
one implementation, the processor 204 may execute a slow fade routine using
fuzzy logic
states to reduce the level of brightness from the "dim" state through a
sequence of intermediate
states to the "dark" state.
[0035] Effects similar to those depicted in FIGS. 3 and 4 can be applied to
light
adaptation. For example, if the intensity of the ambient were suddenly to rise
from dark to
very light, the light sensor 206 would generate an ambient light signal as a
function of the
higher intensity of ambient light. In response, the processor 204 may control
the brightness of
display 102 to set the brightness to "normal." At a later time, even though
the intensity of the
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ambient light may remain substantially the same, the processor 204 may control
the brightness
of display 102 to set the brightness to "bright."
[00361 In the scenarios depicted in FIGS. 3 and 4, if the ambient light were
abruptly to
change to a brighter ambient light before time t2, the processor 204 may
interrupt the dimming
of the display 102 to "dark," and may instead control the brightness to select
a level as a
function of the new level of ambient light.
[00371 FIG. 5 is a flowchart illustrating a method that may be carried out
automatically by
a portable electronic device 100, typically by the processor 204. In this
method, it may be
assumed for simplicity that the display 102 is on and displaying an image. (A
variant of this
method may also be applied where the user interaction with the portable
electronic device 100
is intermittent, and the portable electronic device 100 temporarily shuts off
the display 102
during the periods of inactivity.) It may further be assumed that the
processor 204 is
controlling the brightness level of the display at a first brightness level as
a function of the
ambient light. The processor 204 receives an ambient light signal from the
light sensor 206
(500). This ambient light signal is a function of the level of current ambient
light, as sensed
by the light sensor 206. The ambient light signal may itself be a value (such
as an estimated
lux value) or another quantity (such as a voltage, a current, a duty cycle of
a periodic signal, a
frequency, etc.) that is a function of the measured current level of ambient
light. The processor
204 may determine the level of ambient light as a function of the ambient
light signal. The
processor 204 may, for example, recognize the ambient light signal itself as
the quantity
representing the current ambient light level, or the processor 204 may convert
or derive
another quantity for the ambient light level as a function of the ambient
light signal (e.g., the
processor 204 may convert a voltage signal in units of volts to an estimated
ambient light level
in units of lux). The processor 204 may store in memory 210 the ambient light
level by
storing the quantity.
[00381 The processor 204 may have stored in a buffer in memory 210 quantities
representing one or more previous ambient light levels, based upon previous
ambient light
signals. For example, the processor 204 may store in the buffer ambient light
levels
representing the five most recent ambient light level samples. As new ambient
light signals
are received, the older ambient light data in the buffer may be discarded or
overwritten. As
will be discussed below, the processor 204 may process the ambient light
levels in the buffer
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by (for example) taking the arithmetic mean or computing the median. By
comparing the
level of current ambient light (by itself or along with other levels of
ambient light) to one or
more previous levels of ambient light, the processor 204 can determine whether
there has been
a substantial change in ambient light (502).
[00391 Whether a change in ambient light is substantial or not may depend upon
several
considerations. It is not a substantial change if there is no change at all in
the level of ambient
light; there may also be measurable changes in the ambient light level that
are nevertheless
deemed not substantial. One technique by which a change in ambient light may
be deemed
substantial is to determine whether the current ambient light level is in the
same range as one
or more previous ambient light levels. If the current ambient light level is
not in the same
range as one or more previous ambient light levels, then (according to this
technique) there has
been a substantial change in ambient light. For example, the processor 204 may
deem ambient
light levels above 3,000 lux to be a "bright" light environment. In such a
scheme, a change of
ambient light level from 5,000 lux to 25,000 lux would be without a
substantial change in
ambient light level, because even though the luminance changes many-fold, the
ambient light
level remains "bright." In one illustrative implementation, ambient light
levels above 3,000
lux are considered "bright," ambient light levels from 16 lux to 4,400 lux are
considered
"normal" (or "office"-level) and ambient light levels below 70 lux are
considered "dim."
Notably in this illustrative implementation, the ranges overlap. Overlapping
ranges support a
hysteresis effect, in which the significance of a current ambient light level
depends upon
previous ambient light levels. The hysteresis may be illustrated by an
example. If an ambient
light level rises from 1,000 lux to 3,500 lux, the processor 204 may determine
that there has
not been a substantial change in ambient light, because both ambient light
levels are "normal,"
even though the current ambient light level, if considered on its own, could
be deemed either
"normal" or "bright." If the ambient light level rises again 3,500 lux to
5,000 lux, the
processor 204 may determine that there has been a substantial change in
ambient light,
because the ambient light is no longer in the "normal" range, but is "bright."
If the ambient
light level thereafter falls back from 5,000 lux to 3,500 lux, the processor
204 may determine
that there has not been a substantial change in ambient light, because the
ambient light level is
still in the "bright" range (even though the current ambient light level, if
considered on its
own, could also be deemed to be "normal"). As a practical matter, hysteresis
can reduce the
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number of adjustments to the brightness of a display where the ambient light
is substantially
around the border of two ranges. The portable electronic device 100 may
recognize any
number of ranges of ambient light, and the above lux ranges are for purposes
of illustration.
Further discussion about a method for determining a substantial change in
ambient light will
be discussed below in connection with FIG. 6.
[0040] Returning to FIG. 5: If there has been no substantial change in ambient
light, then
the brightness of the display 102 need not be controlled to a new brightness
level. The
brightness level of the display may remain at the first brightness level. The
light sensor 206
may continue to generate ambient light signals at the sampling frequency under
the control of
the processor 204.
[0041] In the event that the processor 204 determines that there has been a
substantial
change in the ambient light level (i.e., a second level of ambient light is
substantially changed
from the first level of ambient light), the processor 204 may control the
brightness of the
display 102 as a function of the new ambient light level (504). The brightness
of the display
102 may be controlled to a second brightness level that is different from the
first brightness
level. In the illustrative case of the portable electronic device 100 moving
from a bright
environment into a dark environment, the processor 204 may control the
brightness of the
display 102 by setting the display brightness to a "dim" setting. The
processor 204 continues
to receive ambient light signals (506) and continues to determine whether
there has been a
substantial change in ambient light (508). If there is no substantial change,
the processor 204
may control the brightness of the display 102 to a third brightness level to
accommodate
adaptation (510). In this example involving dark adaptation, the first display
brightness level
is the brightest, the second brightness level is less bright, and the third
brightness level is the
least bright. The accommodation may take place after several samples of
ambient light are
made and compared (506, 508), and after an adaptation interval has elapsed, as
illustrated in
FIG. 3; or the accommodation may begin more promptly and may continue as long
as there is
no substantial change in the level of ambient light, as illustrated in FIG.4.
The concepts are
not limited to the accommodating adaptations as shown in FIGS. 3 and 4,
however. For
example, the brightness of the display 102 may be maintained until half of the
adaptation
interval has elapsed, and thereafter the brightness of the display 102 may be
reduced
gradually. If further samples of ambient light indicate a further substantial
change in ambient
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light levels (e.g., from a dark environment to an environment having normal
lighting), the
processor 204 may control the brightness of the display to a fourth brightness
level as a
function of the new ambient light level. Without a further substantial change
in the level of
ambient light, the processor 204 may control the brightness of the display to
a fifth brightness
level to accommodate adaptation (although in this example, the accommodation
would be for
light adaptation rather than dark adaptation).
[0042] FIG. 6 is a flow chart illustrating a technique for determining whether
there has
been a change in ambient light. At the outset of the method (600), it assumed
that a number of
ambient light signals have already been received by the processor 204, and the
ambient light
levels indicated by those ambient light signals have been stored in a buffer
in memory 210.
For purposes of illustration, it is assumed that the number of ambient light
levels stored in the
buffer is five, although the number may be more or fewer than five.
[0043] The processor 204 may compute a first average ambient light level as a
function of
the five ambient light levels stored in the buffer (602). As used herein,
"average" refers to a
value representative of the group of ambient light levels. The average may be
(but need not
be) the arithmetic mean, or it may be the median, or it may be an estimated
average, or it may
be a weighted average, or it may be some other representative value computed
in any fashion.
When a current ambient light signal is received (604), a second average
ambient light level
may be computed (606) that takes into account the current ambient light level
(as indicated by
the current ambient light signal). The second average may be computed in the
same way as
the first, or a different representative value may be chosen. The first and
second averages may
be compared to the average ambient light level (606). A substantial change may
be indicated
(608) when the first average light level is substantially different from the
second average light
level. As described above, a change may be deemed substantial when (for
example) the first
average is not in the same ambient light level range as the second average.
[0044] A potential benefit of using average values that take into account past
ambient
light levels is that a single odd sampling or a fluctuation in ambient light
level will not
necessarily trigger the processor 204 to change the brightness of the display
102. Using
average values can reduce the effect of single ambient light samples while
still supporting
reasonably rapid adjustments to the brightness of the display 102 when there
has been a
substantial change in the lighting environment.
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[00451 FIG. 7 is a flow chart illustrating another method that may be carried
out
automatically by a portable electronic device 100, typically by the processor
204. In this
method, it may be assumed for simplicity that the display 102 is turned off
(e.g., to conserve
power during times of inactivity) (700). For purposes of illustration, it will
be assumed that
the portable electronic device 100 is in a dark room, and has been so for a
considerable time.
When the portable electronic device 100 is inactive, the ambient light may be
sampled less
frequently (702) than when the portable electronic device 100 is active. The
ambient light
levels may be stored in a buffer (704), that is, saved in memory 210
temporarily, as described
previously. Although not depicted in FIG. 7, the ambient light levels may be
averaged, as
described in connection with FIG. 6. Apart from occasional functions, the
inactive portable
electronic device 100 is "asleep," consuming power at level that is low in
comparison to when
the device is active and user interaction is more frequent. The portable
electronic device 100
may experience a "wake up" event (706), but in the event there is no such
"wake up" event,
the processor 204 may measure or keep track of the length of time that the
ambient light level
has been without substantial change (708). Keeping track of time may be
accomplished by,
for example, monitoring the time with a clock or timer. Another illustrative
way to keep track
of time is to count or measure the number of the number of samples of ambient
light that have
been taken, and estimating the time based upon the sampling frequency and the
number of
samples.
[00461 As mentioned previously, there may be some circumstances, such as when
the
portable electronic device 100 is in a holster, that ambient light might not
be sampled. In
those circumstances, the portable electronic device 100 may omit the method of
FIG. 7. In a
variation, the processor 204 in a holstered portable electronic device may
keep track of how
long it has been holstered, and may treat that as the length of time that the
ambient light level
has been without substantial change.
[00471 In the event the processor 204 experiences a "wake up" event (706), the
portable
electronic device 100 may exit its "asleep" state. A "wake up" event is any
event that triggers
an exit from the "asleep" state, typically an event that causes the portable
electronic device to
be ready for more activity and that may entail increased power consumption. An
example of a
wake-up event may be an incoming telephone call. The "wake up" event may
prompt the
portable electronic device 100 to sound a ringtone and present images on the
display 102. In
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the case of an incoming telephone call, for example, the display 102 may
present the
identification of the caller. A wake up event may also be a detected sound or
a touch or some
other external stimulus. The wake-up event need not be generated in response
to external
signals or stimuli; for example, the portable electronic device may experience
a "wake up"
event at a particular time of day, and may sound an alarm loud enough to wake
a sleeping user
at a particular time selected by the user.
[0048] Optionally, the "wake up" may prompt the portable electronic device 100
to
receive a new or current ambient light signal (710), and may further
optionally prompt the
processor 204 to change the ambient light sampling frequency to a higher
sampling frequency.
In the event there has been a substantial change in ambient light (712), the
processor 204 may
control the brightness of display 102 as a function of the new ambient light
level (714). In the
event there has not been a substantial change in the level of ambient light,
the processor 204
may control the brightness of display 102 to set the brightness of the display
as a function of
the ambient light level and as a function of the time that the ambient light
level has been
without substantial change (716). In this way, the processor 204 may control
the brightness of
display 102 to accommodate the expected adaptation of the eyes of the user.
(0049] In a conventional control of display brightness, the processor 204 may
control the
brightness of display 102 as a function of the current ambient light level. In
the method of
FIG. 7, by contrast, the processor 204 may control the brightness of display
102 as a function
of the current ambient light level and how long that ambient light level has
been present. If
the ambient light level is without substantial change for the length of an
adaptation interval (or
longer), for example, the processor 204 may control the brightness of display
102 to
accommodate the expected adaptation of the eyes of the user (716). In a
variation, the
processor 204 may, using fuzzy logic for example, control the brightness of
display 102 to one
of many intermediate states (e.g., between the "dim" state and the "dark"
state, as illustrated in
FIG. 4) as a function of the length of time that the ambient light level is
without substantial
change.
[0050] The method depicted in FIG. 7 may be illustrated by an example. When
repeated
ambient light samples over several minutes are consistent with a dark or dim
environment, and
if there is no interaction between the user and the portable electronic device
100, the situation
may be that the portable electronic device is in a dark room. If the user is
in the dark room as
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well, then the user may be sleeping or trying to sleep. If the ambient light
levels have been
without substantial change for (for example) eight minutes, the user's eyes
may have
undergone substantial adaptation to the environment, regardless of what the
user is doing.
Accordingly, when the "wake up" event occurs (such as an incoming phone call),
the
processor 204 may control the brightness of the display 102 as a function of
the current
ambient light level (thereby avoiding setting the brightness of the display
102 to a level for a
bright or normal environment), and may further control the brightness of the
display 102 as a
function of the time that the ambient light level has been without substantial
change. The
processor 204 may control the brightness of the display 102 for a "dark"
setting rather than a
"dim" setting (or in a variant described above, may control the brightness to
a setting between
"dark" and "dim"). The "dark" (or darker) setting may be more pleasant than
the "dim"
setting for a user whose eyes have adapted (completely or in part) to the dark
environment. In
the event the user turns on lights before attending to the phone call, the
processor 204 may
determine that there has been a substantial change in the ambient light level
(712) and control
the brightness of the display 102 as a function of the new (e.g., normal)
ambient light level
(714).
[0051] Methods such as those shown in FIGS. 5 and 7 may be used individually
or in
concert. For example, a portable electronic device 100 may wake up and the
processor 204
may control the brightness of display 102 as a function of the new ambient
light level (714),
and thereafter, the brightness of the display may change (510) without
substantial change in
the ambient light level. Further, methods such as those depicted in FIGS. 5
and 7 may be used
in concert with many other illumination schemes, such as schemes that
illuminate as a function
of the content of the displayed image (e.g., illuminating a moving picture
more than a page of
text), schemes that take into account the inherent brightness of the image
(whether the image
is predominantly white or predominantly black, for example) or schemes that
control
illumination of the display 102 and other components (such as keys 108) in
substantially the
same fashion.
[0052] The concepts may be adapted to a variety of display illuminating
schemes. For
example, the concepts may be adapted to portable electronic devices that have
more or fewer
ambient light ranges, or that control the displays to more or fewer discrete
brightness levels, or
to no discrete brightness levels at all. The concepts may be applied to a
variety of systems that
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may sample ambient light at different frequencies or in different ways. The
concepts may be
applied to portable electronic devices that use fuzzy logic and those that do
not. It is not
essential to the concepts herein that light and dark adaptation be
accommodated in
substantially the same way. In some embodiments, the concepts may be applied
to
accommodate for dark adaptation, but to provide no accommodation for light
adaptation, or
vice versa.
[00531 Various implementations of one or more of the embodiments of the
concept may
realize one or more advantages. Some of these possible advantages have been
mentioned
already, such as the potential to have a display that is illuminated in a more
pleasant and
aesthetically pleasing manner. Some embodiments may be deemed courtesies to
others
proximate to the user. For example, patrons in a movie theatre may be less
distracted by a
display that takes into account adaptation. As previously suggested, the
concepts may be
advantageous in that they may be flexibly applied to a variety of portable
electronic devices, a
variety of display types, and a variety of illuminating schemes. Further, the
concepts may be
readily implemented without significant additions of size, space or weight in
a portable
electronic device. Considerations of size, space and weight may be of added
importance when
the portable electronic device is a handheld device. Further, controlling the
brightness of a
display to dimmer levels, as may be done to accommodate dark adaptation, may
conserve
power.
[0054] The above embodiments are for illustration, and although one or more
particular
embodiments of the device and method have been described herein, changes and
modifications
may be made thereto without departing from the disclosure in its broadest
aspects and as set
forth in the following claims.
