Patent Description:
A ToF module is conventionally covered by a cover glass in order to protect the ToF module from the environment. An exemplary ToF system having a ToF sensor behind an optically transparent cover glass is proposed in document <CIT>. Difference values representing a respective time period between sending pulses and received pulses are binned into a histogram. A crosstalk response is determined within a predetermined range of bins in the histogram, and the histogram is calibrated using the crosstalk response. An output signal indicative of a ToF is generated based on an evaluation of the calibrated histogram.

Document <CIT> further proposes a LiDAR sensor unit using detection light to detect information relating to the outside of a vehicle. A light adjusting mirror is disposed in such a way as to cover a detecting surface of the LiDAR sensor unit.

Various characteristics such as temperature may influence the measurements of the ToF module.

Hence, there may be a demand for characterization of a ToF sensor.

The demand may be satisfied by the subject matter of the appended claims.

An example relates to a method for characterizing a ToF sensor. The ToF sensor is covered by a cover exhibiting an adjustable transmittance. The method comprises selectively adjusting the transmittance of the cover such that the cover is opaque for light emittable by the ToF sensor. Further, the method comprises performing at least one ToF measurement with the ToF sensor while the cover is opaque for obtaining measurement data for light reflected from the cover back to the ToF sensor. The method additionally comprises determining characterization data based on the measurement data. The characterization data indicate a quantity related to the ToF sensor.

Another example relates to an apparatus comprising a ToF sensor. The apparatus further comprises a cover covering the ToF sensor and exhibiting an adjustable transmittance. Additionally, the apparatus comprises circuitry for adjusting the transmittance of the cover, wherein the circuitry is configured to selectively adjust the transmittance of the cover such that the cover is opaque for light emittable by the ToF sensor. The ToF sensor is configured to perform at least one ToF measurement while the cover is opaque for obtaining measurement data for light reflected from the cover back to the ToF sensor. In addition, the apparatus comprises a processing circuit configured to determine characterization data based on the measurement data. The characterization data indicate a quantity related to the ToF sensor.

It will be understood that when an element is referred to as being "connected" or "coupled" to another element, the elements may be directly connected or coupled via one or more intervening elements. If two elements A and B are combined using an "or", this is to be understood to disclose all possible combinations, i.e. only A, only B as well as A and B, if not explicitly or implicitly defined otherwise. An alternative wording for the same combinations is "at least one of A and B" or "A and/or B". The same applies, mutatis mutandis, for combinations of more than two Elements.

Whenever a singular form such as "a", "an" and "the" is used and using only a single element is neither explicitly nor implicitly defined as being mandatory, further examples may also use plural elements to implement the same functionality. It will be further understood that the terms "comprises", "comprising", "includes" and/or "including", when used, specify the presence of the stated features, integers, steps, operations, processes, acts, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, acts, elements, components and/or any group thereof.

<FIG> illustrates a flowchart of an example of a method <NUM> for characterizing a ToF sensor. The method <NUM> will be described in the following further with reference to <FIG> which illustrates an exemplary arrangement of a ToF sensor <NUM> and a cover <NUM> covering the ToF sensor <NUM>. The cover <NUM> protects the ToF sensor <NUM> from dust, moisture, dirt, etc..

The cover <NUM> exhibits an adjustable transmittance. In other words, the cover <NUM>'s effectiveness in transmitting radiant energy is adjustable (controllable, adaptable). In particular, the transmittance of the cover <NUM> may be adjusted such that the cover is opaque (blocking the passage of light) or (substantially) transparent for light emittable by the ToF sensor <NUM>. That is, depending on the adjusted transmittance of the cover <NUM>, light emitted by the ToF sensor <NUM> may transmit (pass) essentially completely through the cover <NUM> or be essentially completely reflected by the cover <NUM>. In other words, the reflectivity of the cover <NUM> may be adjusted.

The cover <NUM> may, e.g., be made up of glass, plastics or any other suitable material. For example, the cover <NUM> may be an electrochromic device such as an electrochromic glass. Alternatively, the cover <NUM> may be a liquid crystal device such as a liquid crystal glass or a liquid crystal display. In other examples, the cover <NUM> may be an electrophoretic device such as an electrophoretic display (also known as "e-ink"). If the cover <NUM> is one of an electrochromic device, a liquid crystal device or an electrophoretic device, the transmittance of the cover may be controlled by applying a voltage to the cover <NUM>. For example, a corresponding circuitry may be used for adjusting the transmittance of the cover <NUM>. However, it is to be noted that the cover <NUM> is not limited to the above examples. The cover <NUM> may be any element that is capable of protecting the ToF sensor <NUM> from the surrounding environment and that exhibits an adjustable transmittance for light emitted by the ToF sensor <NUM>. For example, the cover <NUM> may be a component of a mobile device (e.g. mobile phone, tablet computer, laptop computer) or an automotive ToF system.

The method <NUM> comprises selectively adjusting <NUM> the transmittance of the cover <NUM> such that the cover is opaque for light emittable by the ToF sensor <NUM>. In other words, the transmittance of the cover <NUM> is selectively adjusted such that light emitted by the ToF sensor <NUM> is essentially completely reflected by the cover <NUM>. As described above, the transmittance of the cover <NUM> may be adjusted by applying a voltage to the cover <NUM> (e.g. implemented as electrochromic device or liquid crystal device) in order adjust the transmittance of the cover <NUM> such that the cover <NUM> is opaque for light emittable by the ToF sensor <NUM>.

The method <NUM> comprises performing <NUM> at least one ToF measurement with the ToF sensor <NUM> while the cover <NUM> is opaque for obtaining measurement data for light reflected from the cover <NUM> back to the ToF sensor <NUM>. In general, any number of ToF measurements may be performed. For example, exactly one (i.e. a single) ToF measurement may be performed for obtaining the measurement data. In other examples, at least two, three, four or more ToF measurements may be performed while the cover <NUM> is opaque for obtaining the measurement data. In other words, the measurement data of the cover <NUM> comprises one or several frames. The at least one ToF measurement may comprise at least one Coded Modulation (CM) measurement, at least one Continuous Wave (CW) measurement or a combination of CM and CW measurements.

As can be seen from <FIG>, light <NUM> is emitted by an illumination element <NUM> of the ToF sensor <NUM> in each ToF measurement. The illumination element <NUM> generates the light <NUM> based on an illumination signal exhibiting an alternating series of high and low pulses. For a CM measurement, the pulses may be of varying duration (length). Accordingly, the light <NUM> for a CM measurement may be a series of light pulses with varying pulse length and varying pulse spacing. For a CW measurement, the pulses are of equal duration (length). Accordingly, the light <NUM> for a CW measurement is a series of light pulses with equal pulse length and equal pulse spacing. For example, the illumination element <NUM> may comprise one or more Light-Emitting Diodes (LEDs) or one or more laser diodes (e.g. one or more Vertical-Cavity Surface-Emitting Lasers, VCSELs) which are fired based on the illumination signal.

The light <NUM> is reflected from the cover <NUM> back to the ToF sensor <NUM> while the cover <NUM> is opaque. In particular, the light <NUM> is reflected (at least in part) from the cover <NUM> towards a light capturing element <NUM> of the ToF sensor <NUM>. The light <NUM> may be reflected at a surface of the cover <NUM> and/or inside (within) the cover <NUM> while the cover <NUM> is opaque. The reflected light is denoted by the reference sign <NUM> in <FIG>. Typically, the illumination element <NUM> and the light capturing element <NUM> are arranged in a common cavity that is (at least partly) covered by the cover <NUM> in order to protect the ToF sensor <NUM> from dust, moisture, dirt, etc..

The reflected light <NUM> arrives at the ToF sensor <NUM> without leaving the module while the cover <NUM> is opaque. The light capturing element <NUM> measures the reflected light <NUM>. The light capturing element <NUM> may comprise various components such as e.g. optics (e.g. one or more lenses) and electronic circuitry. For example, the electronic circuitry may comprise an image sensor comprising a plurality of photo-sensitive elements or pixels (e.g. each comprising a Photonic Mixer Device, PMD) and driver electronics for the image sensor. All or only selected elements/pixels of the plurality of photo-sensitive elements/pixels may be used for measuring the reflected light <NUM>. A reference signal is used for driving the electronic circuitry of the light capturing element <NUM> (e.g. the photo-sensitive elements or pixels) for measuring the reflected light <NUM>. Similarly to what is described above for the illumination signal used for driving the illumination element <NUM>, the reference signal exhibits an alternating series of high and low pulses. For a CM measurement, the pulses are of varying duration (length). For a CW measurement, the pulses are of equal duration (length). It is to be noted that the illumination signal and the reference signal used for a ToF measurement may be identical, time-shifted (phase-shifted) with respect to each and/or be different from each other. Further, if more than one ToF measurement is performed, different illumination signals and/or reference signals may be used for the individual ToF measurements.

In some examples, an illumination signal exhibiting an alternating series of high and low pulses of equal duration (length) may alternatively be used for a CM measurement together with a reference signal exhibiting an alternating series of high and low pulses of varying duration (length). Irrespective of the shape of the illumination signal and the reference signal, a correlation function of the ToF sensor <NUM> may be a periodic sinusoidal function without gaps for a CW measurement, and be a function that is substantially zero for one or more predetermined distance ranges for a CM measurement. The respective correlation function illustrates (indicates) the expected output of the ToF sensor <NUM> for the CW or the CM measurement depending on the distance between the ToF sensor <NUM> and an object reflecting the light of the ToF sensor <NUM>.

The ToF sensor <NUM> generates and outputs measurement data based on the light arriving at the light capturing element <NUM>. Since the transmittance of the cover <NUM> is adjusted such that the cover <NUM> is opaque for light emittable by the ToF sensor <NUM> during the at least one ToF measurement, the light <NUM> emitted by the ToF sensor <NUM> is substantially completely reflected by the cover <NUM> back to the ToF sensor <NUM>. Accordingly, (substantially) only light reflected from the cover <NUM> back to the ToF sensor <NUM> arrives at the light capturing element <NUM>. Therefore, measurement data for (of) light reflected from the cover <NUM> back to the ToF sensor <NUM> is obtained for the at least one ToF measurement.

The method <NUM> additionally comprises determining <NUM> characterization data based on the measurement data for the light reflected from the cover <NUM> back to the ToF sensor <NUM>. The characterization data indicate a quantity related to the ToF sensor <NUM>.

The cover <NUM> is a known object at a known, fixed distance to the ToF sensor <NUM>. Accordingly, the light path of the light <NUM> to the cover <NUM> and back to the ToF sensor <NUM> has a fixed distance. Further, the transmittance of the cover <NUM> is adjusted to a known transmittance and, hence, reflectivity. Taking into account the knowledge about the cover <NUM>, the reflected light <NUM> arriving at the light capturing element <NUM> from the cover <NUM> allows to characterize ToF sensor <NUM>. Hence, the method <NUM> may allow to characterize the ToF sensor <NUM> by means of the characterization data derived from the measurement data for light reflected from the cover <NUM> back to the ToF sensor <NUM> while the cover <NUM> is opaque.

The characterization data may be of various types and may indicate various quantities related to the ToF sensor. In the following, some exemplary types of characterization data will be described in detail. However, it is to be noted that the present disclosure is not limited to the examples described in the following.

According to some examples, the characterization data indicate a distance error correction value for correcting distance values determined based on ToF measurements performed by the ToF sensor <NUM> while the transmittance of the cover <NUM> is adjusted such that the cover <NUM> is transparent for light emittable by the ToF sensor <NUM>. ToF sensors such as the ToF sensor <NUM> conventionally suffer from a distance (depth) measurement error (offset), which may depend on various factors such as a temperature or aging. For example, the generation of the illumination signal and the driver electronics operation is temperature dependent. Accordingly, the temperature may affect the indirect light path over the cover <NUM>. The distance measurement error is to be compensated in order to obtain correct distance (depth) measurement results. As described in the following, the known path distance between the cover <NUM> and the ToF sensor <NUM> and the obtained measurement data enable to correct for this error.

To obtain the distance error correction value, determining <NUM> the characterization data comprises determining a measured distance of the cover <NUM> to the ToF sensor <NUM> based on the measurement data. In other words, the distance of the cover <NUM> to the ToF sensor <NUM> is measured via the at least one ToF measurement while the cover is opaque. Further, determining <NUM> the characterization data comprises determining the distance error correction value based on a comparison of the measured distance of the cover <NUM> to the ToF sensor <NUM> to the known distance of the cover <NUM> to the ToF sensor <NUM>. By comparing the measured distance of the cover <NUM> to the ToF sensor <NUM> to the known distance of the cover <NUM> to the ToF sensor <NUM>, a discrepancy between the measured distance of the cover <NUM> to the ToF sensor <NUM> and the actual distance of the cover <NUM> to the ToF sensor <NUM> may be determined and the distance error correction value may be derived therefrom.

Assuming that a distance value is indicating a distance of the ToF sensor <NUM> to an object in a scene (not illustrated in <FIG>) sensed by the ToF sensor <NUM> is determined based on one or more ToF measurements performed by ToF sensor <NUM> while the transmittance of the cover <NUM> is adjusted such that the cover <NUM> is transparent for light emittable by the ToF sensor <NUM>, the method <NUM> may further comprise correcting the distance value using the determined distance error correction value. For example, the distance error correction value may be a distance error correction offset which is added to or subtracted from the distance value, or the distance error correction value may be a factor which is multiplied with the distance value. Accordingly, the distance value suffering from the distance measurement error of the ToF sensor <NUM> may be corrected in order to provide an error corrected distance value.

For example, if the light capturing element <NUM> comprises a plurality of photo-sensitive elements or pixels, a respective distance error correction value may be determined for each or at least part of the plurality of photo-sensitive elements or pixels. In other words, the distance error correction value may be calculated based on a pixel-by-pixel basis.

As described above, there is a temperature-depended depth measurement error in ToF sensors/systems. It is to be noted that temperature is one major contribution to the error among others. In order to compensate for it, one may conduct a reference measurement which solely depends on this offset. A reference measurement however needs a lightpath of a known distance, which does not change with the sensed scene. For example, if a ToF camera of a mobile device is covered by an electrochromic glass, the electrochromic effect may be used as described above to reflect ToF light pulses back into the ToF sensor. Since the transmittance of the electrochromic glass can be changed by applying a voltage, the reflectivity of the electrochromic glass can be changed. If the electrochromic glass is transparent, it is possible to conduct any kind of ToF measurement. If the transmittance of the electrochromic glass is decreased, light from the illumination unit of the ToF sensor is reflected by the electrochromic glass. This light directly travels to the ToF sensor. Since the distance between the ToF sensor and the electrochromic glass is constant, the resulting images can be used for error correction of ToF data. In other words, for correcting this error, a depth image with opaque cover glass may be captured using the same processing pipeline as normal ToF sensing. For example, the measured distance may then be subtracted from the normal ToF measurement and the known distance (glass to ToF sensor) may then be added. That is, a distance error correction value is effectively added to the normal ToF measurement. The exposure time of the reference measurement can be different from the actual exposure time.

In other examples, the characterization data indicate a measured output power of the illumination element <NUM>. The output power of the illumination element <NUM> may depend on various factors such as temperature or aging. The transmittance and, hence, the reflectivity of the cover <NUM> is adjusted to a predefined value. Accordingly, the reflected light <NUM> arriving at the light capturing element <NUM> is proportional to the output power of the illumination element <NUM>. Optionally, the output power of the illumination element <NUM> may be measured using a dedicated photodiode of the ToF sensor for measuring the reflected light <NUM>.

For example, if the output power of the illumination element <NUM> is drifting due to temperature variations, the drift in output power may be measured and be used as an input of a control system (controller) of the illumination element <NUM> in order to regulate the emitted optical power. Accordingly, a constant optical power output of the illumination element <NUM> may be achieved. For example, a constant optical power output of the illumination element <NUM> for different temperatures may be achieved. In other words, the method <NUM> may comprise controlling the output power of the illumination element <NUM> based on the characterization data. For example, the illumination signal for controlling the illumination element <NUM> may be generated based on the characterization data according to the method <NUM>. By varying the illumination signal based on the characterization data, the output power of the illumination element <NUM> may be controlled. Similarly, regulation of the driving current of the illumination element <NUM>, duty cycle adaptation, pulse skipping or exposure time adaptation may be performed based on the characterization data in order to achieve a (substantially) constant average output power of the illumination element <NUM>. For example, a control algorithm for controlling light emission by the illumination element <NUM> may receive the characterization data as input. Similarly, a current supplied to the illumination element <NUM> may be adjusted based on the characterization data.

In case the illumination element <NUM> comprises more than one light source (e.g. an LED or a VCSEL), the method <NUM> may be applied for each of the light sources separately in order to measure the output power of the light sources of the illumination element <NUM> separately. Accordingly, each of the light sources of the illumination element <NUM> may be controlled individually based on the respective measured output power.

Similar to what is described above for the characterization data indicating the distance error correction value, the characterization data indicating the measured output power of the illumination element <NUM> may be used for calibrating any kind of two-dimensional images the ToF sensor <NUM> produces. Speaking more generally, the method <NUM> may comprise modifying, based on the characterization data, image data of an image determined based on ToF measurements performed by the ToF sensor <NUM> while the transmittance of the cover <NUM> is adjusted such that the cover is transparent for light emittable by the ToF sensor <NUM>.

In further examples, the characterization data indicate a status of at least one photo-sensitive element or pixel of the light capturing element <NUM>. Since the transmittance and, hence, the reflectivity of the cover <NUM> is adjusted to a predefined value, the power of the reflected light <NUM> arriving at the light capturing element <NUM> is substantially known. Accordingly, the reflected light <NUM> arriving from the opaque cover <NUM> at the light capturing element <NUM> may be used for self-testing in order to identify photo-sensitive elements or pixels which are not working correctly.

For example, determining <NUM> the characterization data may comprise comparing the measurement data to reference data. The reference data indicate an expected output of the light capturing element <NUM> or individual photo-sensitive elements or pixels of the light capturing element <NUM>. Accordingly, determining <NUM> the characterization data may further comprise determining the status of the at least one photo-sensitive element or pixel of the light capturing element <NUM> based on the comparison of the measurement data to reference data. For example, if a deviation of the measurement data to the reference data is above a threshold (i.e. the deviation is too large), it may be determined that the at least one photo-sensitive element or pixel of the light capturing element <NUM> is malfunctioning. On the other hand, if the deviation of the measurement data to the reference data is below a threshold (i.e. the deviation is small enough), it may be determined that the at least one photo-sensitive element or pixel of the light capturing element <NUM> is functioning correctly. If it is determined that a photo-sensitive element or pixel of the light capturing element <NUM> is malfunctioning, an error message may, e.g., be output or the malfunctioning photo-sensitive element or pixel of the light capturing element <NUM> may be omitted in future ToF measurements.

The status may be determined for all photo-sensitive elements or pixels of the light capturing element <NUM> according to some examples. In other examples, the status may be determined for only a sub-set of all photo-sensitive elements or pixels of the light capturing element <NUM>. For example, the status may be determined only for the photo-sensitive elements or pixels of the light capturing element <NUM> to be used for a subsequent capture of a sequence of ToF measurements for obtaining an image of a scene.

As described above for various examples, placing a ToF sensor behind a cover with adjustable transmittance (e.g. an electrochromic cover glass) and changing the transmittance of the cover may allow to conduct a reference measurement for error-calibration or self test.

In some examples, the at least one ToF measurement for obtaining the measurement data may be performed sporadically, i.e. independent from image capture by the ToF sensor <NUM>. For example, the at least one ToF measurement for obtaining the measurement data may be performed after predefined time-interval lapses (i.e. in regular intervals).

In other examples, the at least one ToF measurement for obtaining the measurement data may be performed during or before image capture with the ToF sensor <NUM>. The at least one ToF measurement for obtaining the measurement data may, e.g., be performed in a sequence of ToF measurements for obtaining an image of a scene. For example, if the determined characterization data indicate a distance error correction value as described above, a distance value determined based on the sequence of ToF measurements may be corrected using the distance error correction value in the process of obtaining the image of the scene. Similarly, if the characterization data indicate a measured output power of the illumination element <NUM>, the output power of the illumination element <NUM> during the sequence of ToF measurements may be controlled based on the measured output power in order to achieve a (substantially) constant average output power of the illumination element <NUM> during the sequence of ToF measurements. The at least one ToF measurement for obtaining the measurement data may be performed at an arbitrary position in the sequence of ToF measurements for obtaining the image of the scene. Alternatively, the at least one ToF measurement for obtaining the measurement data may be performed prior to capturing the sequence of ToF measurements for obtaining the image of the scene.

In other words, the ToF sensor may perform a reference measurement before it is used in an application, while it is used in an application or in regular intervals. The cover <NUM> (e.g. an electrochromic glass) is controlled accordingly.

An example of an apparatus <NUM> according to the proposed technique is further illustrated in <FIG>. The apparatus <NUM> comprises a ToF sensor <NUM>. The ToF sensor <NUM> comprises an illumination element <NUM> and a light capturing element <NUM> for performing ToF measurements according to the above described technique. The illumination element <NUM> and the light capturing element <NUM> are arranged in a common cavity <NUM> that is (at least in part) covered by a cover <NUM>. The cover <NUM> (e.g. an electrochromic device or a liquid crystal device) exhibits an adjustable transmittance.

The apparatus <NUM> comprises (adjustment) circuitry <NUM> for adjusting the transmittance of the cover <NUM>. In particular, the circuitry <NUM> is configured to selectively adjust the transmittance of the cover <NUM> such that the cover is opaque for light emittable by the ToF sensor <NUM>. For example, if the cover <NUM> is an electrochromic device (glass) or a liquid crystal device (glass), the circuitry <NUM> may be configured to adjust the transmittance of the cover <NUM> such that the cover <NUM> is opaque for light emittable by the ToF sensor <NUM> by applying a voltage to the electrochromic device or the liquid crystal device.

The ToF sensor <NUM> is configured to perform at least one ToF measurement while the cover <NUM> is opaque for obtaining measurement data for light reflected from the cover <NUM> back to the ToF sensor <NUM>.

Further, the apparatus <NUM> comprises a processing circuit <NUM>. For example, the processing circuit <NUM> may be a single dedicated processor, a single shared processor, or a plurality of individual processors, some of which or all of which may be shared, a digital signal processor (DSP) hardware, an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). The processing circuit <NUM> may optionally be coupled to, e.g., read only memory (ROM) for storing software, random access memory (RAM) and/or non-volatile memory. The processing circuit <NUM> is configured to perform processing according to the above described technique. In particular, the processing circuit <NUM> is configured to determine characterization data based on the measurement data. The characterization data indicate a quantity related to the ToF sensor <NUM>.

Although illustrated as separate elements in <FIG>, functionalities of the processing circuit <NUM> and the circuitry <NUM> may be implemented in a single circuitry according to alternative examples.

The apparatus <NUM> may comprise further hardware - conventional and/or custom. For example, the apparatus <NUM> may be a mobile device (e.g. mobile phone, tablet computer, laptop computer) or an automotive ToF system.

The examples as described herein may be summarized as follows:
Some examples relate to a method for characterizing a ToF sensor. The ToF sensor is covered by a cover exhibiting an adjustable transmittance. The method comprises selectively adjusting the transmittance of the cover such that the cover is opaque for light emittable by the ToF sensor. Further, the method comprises performing at least one ToF measurement with the ToF sensor while the cover is opaque for obtaining measurement data for light reflected from the cover back to the ToF sensor. The method additionally comprises determining characterization data based on the measurement data. The characterization data indicate a quantity related to the ToF sensor.

According to some examples, an illumination element of the ToF sensor for emitting the light and a light capturing element of the ToF sensor for measuring the light reflected from the cover are arranged in a common cavity that is covered by the cover.

In some examples, the method further comprises modifying, based on the characterization data, image data of an image determined based on ToF measurements performed by the ToF sensor while the transmittance of the cover is adjusted such that the cover is transparent for light emittable by the ToF sensor.

According to some examples, the characterization data indicate a distance error correction value for correcting distance values determined based on ToF measurements performed by the ToF sensor.

In some examples, determining the characterization data comprises: determining a measured distance of the cover to the ToF sensor based on the measurement data; and determining the distance error correction value based on a comparison of the measured distance of the cover to the ToF sensor to a known distance of the cover to the ToF sensor.

According to some examples, the method further comprises correcting, using the distance error correction value, a distance value indicating a distance of the ToF sensor to an object in a scene sensed by the ToF sensor, wherein the distance value is determined based on ToF measurements performed by the ToF sensor while the transmittance of the cover is adjusted such that the cover is transparent for light emittable by the ToF sensor.

In some examples, the characterization data indicate a measured output power of an illumination element of the ToF sensor for emitting the light.

According to some examples, the method further comprises controlling an output power of the illumination element based on the characterization data.

In some examples, the characterization data indicate a status of at least one photo-sensitive element of a light capturing element of the ToF sensor.

According to some examples, determining the characterization data comprises: comparing the measurement data to reference data; and determining the status of the at least one photo-sensitive element of the light capturing element based on the comparison of the measurement data to reference data.

In some examples, determining the status of the at least one photo-sensitive element of the light capturing element comprises determining that the at least one photo-sensitive element is malfunctioning if a deviation of the measurement data to the reference data is above a threshold.

According to some examples, the at least one ToF measurement for obtaining the measurement data is performed after a predefined time-interval lapses. Alternatively, the at least one ToF measurement for obtaining the measurement data is performed in a sequence of ToF measurements for obtaining an image of a scene. Further alternatively, the at least one ToF measurement for obtaining the measurement data is performed prior to capturing the sequence of ToF measurements for obtaining the image of the scene.

In some examples, the cover is an electrochromic device or a liquid crystal device, wherein adjusting the transmittance of the cover such that the cover is opaque for light emittable by the ToF sensor comprises applying a voltage to the electrochromic device or the liquid crystal device in order adjust the transmittance of the electrochromic device or the liquid crystal device such that the electrochromic device or the liquid crystal device is opaque for light emittable by the ToF sensor.

Other examples relate to an apparatus comprising a ToF sensor. The apparatus further comprises a cover covering the ToF sensor and exhibiting an adjustable transmittance. Additionally, the apparatus comprises circuitry for adjusting the transmittance of the cover, wherein the circuitry is configured to selectively adjust the transmittance of the cover such that the cover is opaque for light emittable by the ToF sensor. The ToF sensor is configured to perform at least one ToF measurement while the cover is opaque for obtaining measurement data for light reflected from the cover back to the ToF sensor. In addition, the apparatus comprises a processing circuit configured to determine characterization data based on the measurement data. The characterization data indicate a quantity related to the ToF sensor.

According to some examples, the cover is an electrochromic device or a liquid crystal device, wherein the circuitry is configured to adjust the transmittance of the cover such that the cover is opaque for light emittable by the ToF sensor by applying a voltage to the electrochromic device or the liquid crystal device.

Examples of the present disclosure may enable ToF reference measurements using an electrochromic cover glass.

Claim 1:
A method (<NUM>) for characterizing a time-of-flight sensor, wherein the time-of-flight sensor is covered by a cover exhibiting an adjustable transmittance, the method comprising:
selectively adjusting (<NUM>) the transmittance of the cover such that the cover is opaque for light emittable by the time-of-flight sensor;
performing (<NUM>) at least one time-of-flight measurement with the time-of-flight sensor while the cover is opaque for obtaining measurement data for light reflected from the cover back to the time-of-flight sensor; and
determining (<NUM>) characterization data based on the measurement data, wherein the characterization data indicate a quantity related to the time-of-flight sensor.