Calibrated image-sensor-based ambient light sensor

An electronic device may be provided with an image sensor for capturing digital images. The image sensor may be used as part of image-sensor-based ambient light sensing circuitry for producing ambient light sensor readings. The image-sensor-based ambient light sensing circuitry may include a reference array. The reference array may be formed from an array of light sensor elements that are matched to elements in the image sensor but that are covered with a light blocking material. Control circuitry can measure current flow into the reference array and the image sensor array and can use current measurements from these arrays in producing a calibrated ambient light sensor reading. The control circuitry may make current measurements by measuring a decay time associated with the voltage of a discharging capacitor. A comparator, pulse generator, and switch may be used in periodically recharging the capacitor. The capacitor may be adjusted to ensure accurate readings.

BACKGROUND

This relates generally to electronic devices, and more particularly, to image-sensor-based ambient light detection circuitry for electronic devices.

Electronic devices such as portable computers and cellular telephones are often provided with ambient light sensors. Ambient light sensors can be used to measure the amount of ambient light in the immediate vicinity of an electronic device. When ambient light conditions change, an electronic device may take appropriate actions. For example, display brightness levels may be adjusted to accommodate bright or dim lighting conditions.

Ambient light sensors are typically mounted under dedicated ambient light sensor windows in electronic device housings. The need for individual ambient light sensors and mounting arrangements can add undesired cost and complexity to an electronic device. Ambient light sensor windows may also detract from the appearance of an electronic device.

It would therefore be desirable to be able to provide improved ambient light detection circuitry for electronic devices.

SUMMARY

An electronic device may be provided with an image sensor for capturing digital images. The image sensor may be used as part of image-sensor-based ambient light sensing circuitry for producing ambient light sensor readings. Ambient light data from the image-sensor-based ambient light sensing circuitry may be used to make adjustments to display brightness or other adjustments during operation of the electronic device.

The image-sensor-based ambient light sensing circuitry may include a optically-black reference array. The reference array may be formed from an array of light sensing elements that are matched to active light-sensing elements in the image sensor but that are covered with a light blocking material.

Control circuitry can open and close switches to measure current flow into the reference array and the image sensor array. The current measurements from these arrays can be used in producing a calibrated ambient light sensor reading.

The control circuitry may make current measurements by measuring a decay time associated with the voltage of a capacitor that is discharged using current flowing into the reference array or image sensor array. A comparator, pulse generator, and switch may be used in periodically recharging the capacitor. The capacitor may be adjusted by the control circuitry.

DETAILED DESCRIPTION

Electronic devices such as electronic device10ofFIG. 1may be provided with ambient light sensor circuitry. The ambient light sensor circuitry may be used to support operations such as display brightness level adjustments and other operations in an electronic device. The ambient light sensor circuitry may use data that is gathered from an image sensor array and may therefore sometimes be referred to as image-sensor-based ambient light sensor circuitry.

Image-sensor-based ambient light sensor circuitry may be used in an electronic device such as electronic device10ofFIG. 1. Electronic device10may be a portable electronic device or other suitable electronic device. For example, electronic device10may be a laptop computer, a tablet computer, a somewhat smaller device such as a wrist-watch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, a cellular telephone, or a media player. Device10may also be a television, a set-top box, a desktop computer, a computer monitor into which a computer has been integrated, or other suitable electronic equipment.

Device10may include a housing such as housing12. Housing12, which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of these materials. In some situations, parts of housing12may be formed from dielectric or other low-conductivity material. For example, glass structures, plastic structures, or other dielectric structures may be used to form exterior and interior portions of housing12. In other situations, housing12or at least some of the structures that make up housing12may be formed from metal elements.

Device10may, if desired, have a display such as display14. Display14may be a touch screen that incorporates a touch sensor array or may be insensitive to touch. A touch sensor array for display14may be formed from capacitive touch sensor electrodes or touch sensors based on other touch technologies (e.g., acoustic touch, light-based touch sensor configurations, force sensor arrangements, etc.). Display14may include image pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable image pixel structures. A display cover layer such as a clear plastic layer or transparent glass layer may cover the surface of display14. Peripheral regions of the display cover layer may be provided with an internal opaque masking layer to help hide internal components from view by a user. Buttons such as button16may pass through openings in the cover layer. The cover layer may also have other openings such as an opening for speaker port18.

One or more optically clear windows such as window20may be provided in device10. Windows such as window20may be formed from glass or plastic elements that are mounted within an opening in an opaque housing structure or may be formed by creating an opening in an opaque masking layer on the underside of a display cover layer or other transparent member. In the example ofFIG. 1, window20has been formed in a portion of the display cover layer for display14(e.g., by creating an opening in a peripheral opaque masking layer that overlaps inactive portions of display14). If desired, windows such as window20may be formed on the rear surface of device10, on sidewall surfaces of device10, or elsewhere in device10.

Optical components may be mounted within housing12in alignment with optical windows such a window20. For example, discrete ambient light sensor devices, light-based proximity sensors, status indicator lights, digital image sensors, and other optical devices may be mounted under windows such as window20. To enhance the compactness of device10and to enhance device aesthetics by reducing unnecessary additional optical windows, one or more ambient light sensors for device10may be formed using image sensor circuitry. With this type of approach, a digital image sensor may be mounted under window20. When operated in digital image sensor mode, device10may obtain digital image sensor data from the image sensor. The digital image sensor data may be processed to form digital images and video clips. When operated as an ambient light detector, the same digital image sensor may be used in collecting ambient light sensor readings. Because a single image sensor can be used for both digital imaging operations and ambient light measurements, space within device10may be conserved and device aesthetics may be enhanced. Device cost and complexity may also be reduced.

FIG. 2is a schematic diagram of device10showing how device10may have control circuitry22and input-output circuitry such as sensor circuitry24. Control circuitry22may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Control circuitry22may also include processing circuitry based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc.

The storage and processing circuitry of control circuitry22may be used to run software on device10, such as internet browsing applications, voice-over-internet-protocol (VoIP) telephone call applications, email applications, media playback applications, operating system functions, software for supporting display brightness adjustment functions and other functions associated with gathering and using data from ambient light sensor circuitry and other sensors, etc. To support interactions with external equipment, storage and processing circuitry28may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry28include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, cellular telephone protocols, etc.

Input-output circuitry24may be used to allow data to be supplied to device10and to allow data to be provided from device10to external devices. Input-output circuitry24may include input-output devices such as touch screens, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device10by supplying commands through these input-output devices and may receive status information and other output from device10using the output resources of these input-output devices. Wireless communications circuitry in circuitry24may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications).

The sensors in circuitry24may include discrete ambient light sensors, proximity sensors (e.g., light-based proximity sensors that include an infrared transmitter and an infrared receiver or other light-based proximity sensor circuitry), capacitance sensors (e.g., for touch sensor and/or proximity sensing applications), force sensors (e.g., for touch sensing devices), accelerometers (e.g., an accelerometer for measuring the force of gravity and thereby determining the orientation of device10relative to the surface of the Earth), digital image sensors (e.g., image sensor arrays) and other sensors.

The sensors in circuitry24may include one more image-sensor-based ambient light detectors. Image-sensor-based ambient light detectors may be based on digital image sensor integrated circuits. Digital image sensor circuits can be used for capturing digital images or can be used to produce ambient light measurements.

The digital image sensor for an image-sensor-based ambient light sensor may be based on an image sensor array that contains rows and columns of image sensor pixels. Each image sensor pixel may contain a light sensitive element (e.g., a semiconductor-based device such as a photodiode or phototransistor) and associated support circuitry (e.g., transistors for transferring charge from the light sensitive element to a charge storage node, transistors for forming pixel-based amplifier circuitry, readout transistors for controlling the transfer of signals from the image sensor pixels to column-based readout circuitry, etc.).

To ensure accurate operation, it may be desirable to provide image-sensor-based ambient light sensor circuitry in device10with circuitry for calibrating the response of the light sensitive elements in the image sensor pixels. The response of the semiconductor light sensitive elements may fluctuate as a function of PVT variations (i.e., variations in fabrication process parameters (P), fluctuations in power supply voltage (V), and temperature (T) changes during operation). To prevent errors related to PVT variations, the performance of the image-sensor-based ambient light sensor circuitry may be calibrated using a set of reference light sensor elements. The reference light sensor circuitry may, as an example, be formed from the same type of light sensitive elements that are used in forming the light sensor elements in the image sensor pixels of the digital image sensor array, but may be coated with a light-blocking coating. This reference circuitry, which may sometimes be referred to as dark current reference circuitry, optically-black pixels, reference pixels, reference light sensitive elements, or reference array, may be used to make reference current measurements (i.e., dark current measurements). The amount of current that flows into the reference light sensor circuitry is affected by process, voltage, and temperature conditions, but is not influenced by the amount of ambient light that is present. Accordingly, the amount of current that is measured as flowing into the reference light sensor circuitry may be subtracted from the amount of current that is measured as flowing into the image sensor to calibrate the image sensor ambient light data.

FIG. 3Ais a cross-sectional side view of a portion of an illustrative image-sensor-based ambient light sensor integrated circuit. As shown inFIG. 3A, image-sensor-based ambient light sensor circuitry26may be formed from a semiconductor substrate such as substrate28. Substrate28may be formed from silicon or other semiconductor materials. Light sensitive elements may be formed in substrate28. The light sensitive elements may be formed from phototransistors, photodiodes, or other light-sensitive devices.

Some elements such as light-sensitive element32may be uncovered by light-blocking layers. As a result, light-sensitive elements such as element32may receive and measure light36(e.g., to form a digital image when element32is operated in digital image sensor mode or to gather ambient light data when element32is operated in ambient light sensing mode). Other elements such as reference element30may be covered with an opaque layer such as light-blocking structure40. The attributes of reference elements such as reference element30(e.g., the size, shape, doping concentration, and other properties of the reference elements) are preferably matched to those of elements such as element32, so that elements30may be used in accurately calibrating elements32. Structures such as opaque structure40in each reference element30may be formed from metal or other opaque material. During operation, the amount of reference signal that flows into reference elements30will be unaffected by the strength of ambient light34, because structure40will block light34and thereby prevent light34from contributing to the response of element30.

Elements32may be organized into rows and columns to form an image sensor array (e.g., an image sensor array having, thousands or millions of pixels). Elements30may be organized into groups in the vicinity of the image sensor array. For example, elements30may be used to form one or more arrays that are smaller in size than the image sensor array (e.g., thin rectangular arrays running along the edge of the image sensor array). To ensure that the process, voltage, and temperature variations experienced by reference elements30are representative of the process, voltage, and temperature variations experienced by the image sensor array formed from elements32, reference elements30may be formed adjacent to the image sensor array on substrate28(i.e., reference elements30and image sensor elements32may be formed as part of a common integrated circuit).

As shown inFIG. 3B, reference elements30may be organized to form a set of reference sensing elements30A (sometimes referred to as dark pixels) and light sensing elements32may be organized to form an adjacent image sensor array32A. Biasing and readout circuitry42may be used to control the operation of reference elements30A and image sensor array32A. For example, when image sensor array32A is being used as an image sensor for a digital camera, circuitry42may be used to capture and read out digital image data from array32A and/or30A. When image-sensor-based circuitry26is being used to make ambient light measurements, readout and biasing circuitry42and other control circuitry (collectively control circuitry22) may be used to measure the amount of current that collectively flows into the light sensing elements of image sensor array32A and, by subtracting the amount of measured dark current flowing into reference elements30A, may calibrate the data from image sensor array32A to produce calibrated ambient light sensor readings. Some or all of light sensing elements32may be used during ambient light sensing operations using array32A (e.g., all elements in array32A, a subset of elements in array32A, elements in array32A of a particular color or colors, etc.).

FIG. 4is a diagram of illustrative image-sensor-based ambient light sensing circuitry26. As shown inFIG. 4, circuitry26may include an image sensor array such as image sensor array32A formed from rows and columns of light sensitive elements (image sensor pixels)32and a set of reference pixels30A (e.g., an array of reference elements30). Circuitry such as current controlled oscillator circuitry60may be used in measuring signals from reference pixels30A and image sensor pixels32A. Circuitry60may include switches such as switches S0, S1, and S2(e.g., transistor-based switches or other suitable switches) or other switching circuitry for controlling current flow to reference pixels30A and image sensor pixels32A during use of image-sensor-based ambient light sensor circuitry26to collect ambient light sensor data.

When switch S1is closed and switch S2is open, circuitry60may measure the magnitude of current Iarray. Current Iarray corresponds to the cumulative current drawn by a set of the image sensor pixels32in image sensor pixel array32A in parallel (e.g., all of the image sensor pixels in array32A) when image sensor array32A is being used as an ambient light sensor. When switch S2is closed and switch S1is open, circuitry60may measure current Iref. Current Iref corresponds to the reference current (dark current) drawn by reference pixels30A during operation of circuitry26as an ambient light sensor. By using circuitry22and circuitry60, device10may calibrate the current measurements associated with array32A using the reference current measurements associated with reference pixel array30A.

Power supply circuitry and voltage reference circuitry (e.g., a band gap voltage reference circuit or other voltage reference circuitry that is part of control circuitry22) may be used to supply a power supply voltage such as voltage Vaapix to power supply node44, bias voltage Vbias for transistor48, and threshold voltage Vth for comparator50.

Capacitor46may be charged to voltage Vaapix by momentarily closing switch S0to short node74to terminal4). Capacitor46may then be discharged through switch S1or switch S2. By measuring the rate at which capacitor46discharges when switch S1or S2is closed, control circuitry22can measure the amount of current flow through array32A or the amount of current flow through array30A, respectively.

The states of switches S1and S2may be controlled by control circuitry22using control signals on control paths70and78, respectively. Variable capacitor46may exhibit a capacitance that is controlled by control signals supplied to input62from control circuitry22. The capacitance Cosc of capacitor46may be given by equation 1.
Cosc=k*C0  (1)
In equation 1, capacitance C0is a fixed capacitance value and k is a variable scaling factor that is controlled by control circuitry22by application of corresponding control signals to input62of variable capacitor46. Capacitance Cosc is the corresponding capacitance for capacitor46. Control circuitry22can adjust the capacitance value exhibited by capacitor46to ensure sufficient accuracy when making current measurements (i.e., to prevent capacitor46from being too large and thereby discharging too slowly to effectively measure or from being too small and thereby discharging too quickly to effectively measure).

Comparator50may be used in monitoring the discharge of capacitor46. As shown inFIG. 4, comparator50may have inputs52and54. Input54may receive threshold voltage (reference voltage) Vth. Input52may receive the voltage Vx from capacitor46while switch S0is open. During capacitor discharge operations, comparator50may compare the voltage on input52with the voltage on input54and may produce a corresponding output voltage on output56. So long as voltage Vx is greater than voltage Vth, the signal on output56of comparator50may be deasserted (i.e., held at a logic low value). When voltage Vx falls to Vth, comparator50may assert its output (i.e., comparator50may take the signal on output line56high). In response, one-shot pulse generator72will generate an output pulse of a fixed duration. The output of pulse generator72(voltage Vcnt) may be provided to the control input of switch S0using path58. So long as output56is deasserted and no pulse is being generated by pulse generator72, the value of Vcnt will be low and switch S0will be open. In this situation, capacitor46may discharge and voltage Vx may fall towards Vth. Once voltage Vx reaches Vth, comparator50will assert the output signal on output56, pulse generator72will generate an output pulse (e.g., a pulse having a positive voltage), and switch S0will be closed (i.e., for the duration of the output pulse from pulse generator72).

When S0is momentarily closed in this way, voltage supply terminal44at voltage Vaapix will be shorted to node74, capacitor46will be charged, and capacitor voltage Vx will be raised to Vaapix. After recharging capacitor46in this way, capacitor46can be discharged through array32A using closed switch S1and open switch S2or can be discharged through array30A using closed switch S2and open switch S1, as appropriate.

When switch S2is closed and switch S1is open, the amount of current Iref that is drawn from capacitor46will be equal to cumulative dark current of all of the dark (optically black) pixels30in reference pixels30A. When switch S1is closed and switch S2is open, the amount of current Iarray that is drawn from capacitor46will be equal to the cumulative current of the pixels in array32A (or a selected subset of these pixels). The value of Iarray includes a current contribution due to the detection of ambient light and includes a dark current contribution. To calibrate image-sensor-based ambient light sensor circuitry26, control circuitry22may subtract a scaled version of the reference current measured by reference pixels30A (Iref) from the measured value of Iarray.

Control circuitry22may be used in measuring the values of currents Iref and Iarray. To make a current measurement, control circuitry22can receive a clock signal such as clock CLK. Using a counter such as counter21or other suitable circuit that is driven by clock signal CLK, control circuitry22may measure the amount of time between successive changes in the state of signal Vcnt. These measurements are indicative of the decay time associated with discharging capacitor46from Vaapix to Vth and are therefore indicative of the magnitudes of currents such as currents Iref and Iarray.

Consider, as an example, the trace of voltage Vx that is shown in the graph ofFIG. 5. In the example ofFIG. 5, curve76corresponds to the discharge of capacitor46when a current of a first magnitude is being drawn. Curve78corresponds to the voltage on discharging capacitor46when a current of a second magnitude that is smaller than the first magnitude is being drawn.

As shown inFIG. 5, the voltage Vx on capacitor46is reset to Vaapix at time t1, following application of a pulse of duration TD from pulse generator72to switch S0. Starting at time t1, current is drawn from capacitor46by pixels in array32A or by pixels in array30A, depending on whether control circuitry22has closed switch S1and opened switch S2or vice versa.

As shown by curve76, when the current of the first magnitude is drawn from capacitor46, voltage Vx will fall to voltage Vth at time t2. When comparator50senses that Vx has fallen below Vth, comparator50will take its output on line56high and pulse generator72will again generate a momentary pulse of length TD for switch S0to reset the voltage Vx on capacitor46to Vaapix. This process may repeat, so that control circuitry22may make a series of measurements (e.g., to average data or otherwise process data to enhance accuracy).

If the current being drawn from the capacitor has the second magnitude, the voltage Vx will decrease slower, as indicated by curve78. As a result, voltage Vx will not reach voltage Vth until time t3.

Control circuitry22may use a counter or other circuitry for measuring the duration of the Vaapix to Vth decay time. In the example ofFIG. 5, the current that resulted in voltage decay curve76is associated with a time period TP0, whereas the current that resulted in voltage decay curve78is associated with a time period TP1. Control circuitry22may measure decay periods such as TP0and TP1(e.g., using a counter or other timing circuitry) and can convert the measured decay time (i.e., the time between successive pulses output from pulse generator72) to measured current values. Using this type of technique, control circuitry22may measure array current Iarray and reference current Iref. The values of these measured currents may, in turn, be processed (e.g., using digital processing techniques implemented using control circuitry22), to produce calibrated ambient light data.

A flow chart of illustrative steps involved in using image-sensor-based ambient light sensor circuitry26to make an ambient light sensor reading representative of an ambient light level to which the sensor circuitry is exposed is shown inFIG. 6. At step80, control circuitry22may measure dark current Iref associated with reference pixels30in reference pixel array30A. During these measurements, control circuitry22may supply switches S2and S1with control signals to close switch S2and open switch S1.

Initially, the value of k (i.e., the value of capacitor Cosc) may be set to a default value. If the value of capacitance Cosc is too low, the decay period TP of voltage Vx will be too short to effectively measure using control circuitry22. If the value of capacitance Cosc is too high, the decay period TP of voltage Vx will be too long to effectively measure using control circuitry22. Accordingly, control circuitry22may, during the operations of step80, ascertain whether decay period TP is greater to a predetermined satisfactory lower decay time threshold TPLOWER and less than a predetermined satisfactory upper decay time threshold TPUPPER. If the measured decay time TP is not within this range, control circuitry22may adjust k to increase or decrease Cosc as appropriate. The measurement operations of step80may then be repeated with the newly selected value of k (and the corresponding newly selected value of Cosc).

Once a satisfactory k value and Cosc value have been selected, the resulting measured value of TP will fall within an acceptable range that allows control circuitry22to make accurate measurements. Accordingly, the value of TP associated with reference current Iref (and the corresponding value of k) may be retained by control circuitry22for use in calibration operations. Processing may then proceed to step84, where control circuitry22may measure the current Iarray that is associated with pixels32of image sensor array32A (e.g., using a value of k=1 or using a default value of Cosc that is appropriate for making Iarray measurements).

The value of Iarray is equal to the sum of an ambient light contribution (i.e., a current component due to the magnitude of ambient light received by pixels32) and a dark current contribution. The dark current contribution may be affected by PVT variations. For example, changes in operating temperature for image sensor array32A may have a significant impact on the magnitude of Iarray. The pixels in array30A are likewise affected by PVT variations, but because the reference pixels in array30A are optically blocked and do not receive light, the reference pixels in array30A are not affected by changes in the amount of ambient light that is present. To calibrate Iarray and thereby produce an accurate ambient light reading, control circuitry22may, at step86, compute the value of calibrated current Iambient using equation 2.
Iambient=Iarray−(N*k/M)*Iref  (2)
In equation 2, Iambient corresponds to a calibrated current value that is proportional to the amount of ambient light detected by image-sensor-based ambient light sensor26. Current Iarray is the measured current drawn by N light sensor elements (i.e., N pixels) in array32A as measured using circuitry60and circuitry22. Current Iref is the measured current drawn by M reference pixels30A in reference pixel array30A as measured using circuitry60and circuitry22. The scaling factor k corresponds to the size of capacitor46that was selected during the operations of step82, assuming that k was 1 during the operations of step84. If k has a value other than 1 during the operations of step84, k in equation 2 may be set to the ratio of Cosc during step80to Cosc during step84.

By scaling the value of Iref using equation 2, control circuitry22can compensate for the smaller size of array30A relative to array32A and the settings used for adjustable capacitor46when computing calibrated ambient light current Iambient. Calibrated current Iambient serves as an accurate ambient light reading for device10and may be used in taking any suitable action in device10. For example, device10may use the value of Iambient in determining whether to increase and/or decrease the brightness of display14. The measurement process ofFIG. 6may be performed multiple times to produce averaged ambient light data (e.g., data that is processed using a digital low-pass filter and/or other signal processing techniques).

If desired, device10may use ambient light data from one or more image-sensor-based ambient light sensors in conjunction with additional sensor data in determining how to control the operation of device10. A flow chart of illustrative operations associated with controlling device10using multiple sensor inputs of this type is shown inFIG. 6.

At step88, device10may use image-sensor-based ambient light sensor circuitry26to make ambient light sensor measurements. One or more image-sensor-based ambient light detectors may be used in gathering ambient light readings. For example, in an electronic device that has both front-facing and rear-facing digital cameras, a front-mounted sensor circuit may be used to gather front-facing ambient light data and/or a rear-mounted sensor circuit may be used to gather rear-facing ambient light data.

At step90, device10may use additional sensors to gather sensor readings such as accelerometer readings to determine whether device10is face up or face down or has another orientation relative to the surface of the Earth, proximity sensor readings to determine whether ambient light sensor data may have been corrupted by shadows due to external objects in the vicinity of the image-sensor-based ambient light detector(s), data from touch sensors indicating whether or not a user is using a touch screen on the front (or rear) of a device, and data from other sensors.

At step92, control circuitry22may take appropriate action based on one or more of the sensor readings gathered during the operations of steps88and90. If, for example, the rear ambient light sensor is darker than the front ambient light sensor reading and accelerometer data and touch sensor data indicate that device10is facing upwards and is being used by a user, the ambient light sensor data from the rear ambient light sensor can be considered to be inaccurate (because the rear camera is being shadowed by being placed on a table or in a user's hand). Control circuitry22may therefore discard the rear ambient light sensor data (in this example).

Following adjustment of display brightness or other suitable actions, processing may return to step88, as indicated by line94.