Distance measurement method and measuring device

Abstract

The invention relates to a method (100) for carrying out a distance measurement, comprising the following method steps: - Illuminating (110) a measurement object with multiple light pulses using a light source, - Receiving (120) light pulses reflected from the object being measured using a light-sensitive sensor unit, - Measurement (130) of the transit time of the received light pulses, - Create (140) a frequency distribution A(i) from the measured transit times, where A denotes the number of received photons in a histogram class i; - Determine (150) the histogram classes i for which the value of the frequency distribution A(i) meets a given threshold A thr exceeds; - Selection (160) of a histogram class i from the previously determined histogram classes i taking into account at least one selection criterion; - Determining (170) the distance of the object being measured based on the selected histogram class i.

Description

[0001] The present invention relates to a method for carrying out a distance measurement using a light-sensitive sensor unit as well as a corresponding measuring device and a corresponding measuring system.

[0002] Numerous methods for distance measurement using light-sensitive sensor units are known from the prior art. These methods are often based on a so-called "direct time-of-flight" measurement (also known as dTOF measurement or time-of-flight measurement). In such measurements, light pulses are emitted from a light source towards a measurement object, and the light reflected from the measurement object is detected by the light-sensitive sensor unit. This allows the propagation time of the light pulses required for propagation from the light source to the measurement object and from the measurement object to the transmitter unit to be determined. For this purpose, the difference between a first time at which a light pulse was emitted and a second time at which the reflected light pulse was detected by the sensor unit is determined.This time difference, together with knowledge of the speed of light, can be used to calculate the distance between a measuring device and a measuring object.

[0003] The so-called histogram method is often used to evaluate the measurement data determined using the method described above. In this method, a histogram with N histogram classes (also called histogram bins), which often have a fixed width, is determined from the determined travel times. The determined histogram or a frequency distribution describing the histogram is then searched for a peak (or maximum). The position (or histogram class) of the peak indicates which travel time is most likely. Consequently, the position of the peak can be used to calculate the distance between the measuring device and the measurement object. The position of the peak within the histogram is proportional to the distance between the measuring device and the measurement object.

[0004] While the method described above delivers very good measurement results in many measurement scenarios, it is quite error-prone in some situations. Particularly with single-photon avalanche diode-based lidar systems (also known as SPAD-based lidar systems) and in cases where the measurement object has a retroreflector, the method described above reaches its limits. Often (usually due to parasitic optical paths in the receiving optics) scattered light from different areas reaches the active surface of the sensor unit (i.e., different pixels of a planar sensor unit or different diodes of a diode array). In some situations, the scattered light can be dominant, so that the peak determined during the distance measurement is caused by the scattered light and not by the light pulse reflected from the measurement object and reaching the sensor unit via the direct optical path.The susceptibility to errors is particularly pronounced in measurement systems that use full-flash illumination (also known as full-flash illumination) or sequential flash illumination (also known as sequential flash or rolling shutter). In these cases, the emitted light pulses on a retroreflector can cause stray light, which is detected by a larger area of ​​the sensor unit and thus leads to widespread falsification of the measurement results across multiple pixels of the sensor unit (in the case of a sensor unit configured as a camera sensor) or across multiple diodes (in the case of a sensor unit configured as a diode array) of the sensor unit.

[0005] Based on the above-described disadvantages of the methods known from the prior art, the object of the present invention is to provide a reliable method for distance measurement that is particularly robust even in measurement scenarios in which the measurement object has a retroreflector. In particular, the object of the present invention is to provide a measurement method that enables efficient suppression of artifacts caused by stray light generated by retroreflectors.

[0006] To achieve the above-described object, the present invention proposes a method for carrying out a distance measurement, which comprises the following method steps: - Illuminating a measuring object with several light pulses using a light source; - Receiving light pulses reflected from the measuring object using a light-sensitive sensor unit; - Measurement of the transit time of the received light pulses; - Creating a frequency distribution A(i) describing a histogram from the measured travel times, where A denotes the number of received photons in a histogram class i; - Determine the histogram classes i for which the value of the frequency distribution A(i) exceeds a given threshold A thr exceeds; - selecting a histogram class i from the previously determined histogram classes i, taking into account at least one selection criterion; and - Determine the distance of the measuring object based on the selected histogram class i.

[0007] The method according to the invention allows for the simultaneous consideration of multiple peaks in a frequency distribution and the subsequent selection of the correct peak within the frequency distribution. This enables multi-echo or multi-event detection during the evaluation of the frequency distribution, as well as subsequent filtering of the detected echoes, so that echoes caused by stray light (especially when the measurement object has retroreflectors) detected according to the prior art can be efficiently suppressed.

[0008] While prior art methods only consider the strongest or most pronounced peak to determine the propagation time with the highest probability and thus the distance to a measurement object, the method according to the invention considers all peaks that exceed a predetermined threshold. This threshold can be adjusted, in particular, depending on the intensity of the extraneous light (or ambient light) in a measurement setup.

[0009] By taking into account all peaks that exceed the threshold value and subsequently selecting the correct peak taking into account at least one selection criterion, the method according to the invention allows for a reliable suppression of incorrect measurements caused by retroreflectors, thereby significantly increasing the reliability of the measuring method according to the invention.

[0010] In the method according to the invention, it can be provided, in particular, that the light source is designed as a laser beam source. The laser beam source can be configured to emit numerous laser pulses with a short pulse duration. The measurement object can, for example, be point-shaped or flat. It can be provided that the measurement object is flat and that a plurality of measurements are performed to measure the distance at several points on a surface of the measurement object and subsequently combine the measurement results to determine the overall shape of the measurement object.

[0011] The sensor unit can comprise a photodiode, a single-photon avalanche diode (SPAD), a photodiode array, a SPAD array, or an image sensor. The image sensor can be embodied, in particular, as a CMOS sensor or a CCD sensor.

[0012] To measure the travel time of the received light pulses, methods known from the prior art can be used. In particular, a first time point at which a light pulse was emitted can be determined, as well as a second time point at which the reflected light pulse was received. The travel time of a light pulse can then be calculated from the difference between the two times.

[0013] In the method according to the invention, a frequency distribution A(i) is created from the measured runtimes, which describes a histogram with a total of N histogram classes (also referred to as histogram bins).

[0014] In the subsequent determination of the histogram classes i for which the value of the frequency distribution A(i) exceeds the specified threshold value A threxceeds, all peaks (or their histogram classes i) are determined for which the value of the frequency distribution A(i) is greater than the specified threshold A thr . The threshold A thr can be selected depending on various parameters. In particular, the threshold can be selected depending on the ambient light present in a measurement scenario, the intensity of the light source, and the distance between the measuring device and the measurement object. The threshold is a value that is usually determined experimentally and serves to identify peaks that can be assigned with a certain probability to a reflected light pulse. In other words, the threshold A thr to determine the peak candidates within the histogram or frequency distribution A(i), from which the peak is then selected that can actually be assigned to a reflected light pulse.

[0015] Subsequently, a histogram class i is selected from the previously determined histogram classes i, taking into account at least one selection criterion. This results in a filtering of the histogram classes i determined in the previous method step. As explained in more detail below, different selection criteria can be defined within the scope of the present invention to ensure efficient suppression of the peaks caused by scattered light and thus provide a particularly reliable distance measurement method.

[0016] In the method according to the invention, it can be provided in particular that the selection of a histogram class i from the previously determined histogram classes i comprises the following: - if, when determining the histogram classes i for which the frequency distribution A(i) exceeds a given threshold A threxceeds, a total of two histogram classes i have been determined: Selecting the histogram class i with the higher histogram class value.

[0017] If a total of two peaks are determined for which the value of the frequency distribution A(i) exceeds the specified threshold value A threxceeds, the peak with the higher histogram class value is selected. In other words, the right-hand of the two peaks in the histogram is selected, which corresponds to a reflected laser pulse with a longer propagation time and thus a greater distance between the measuring device and the measurement object. This is based on the assumption that retroreflectors usually generate a significant amount of stray light when they are in close proximity to the measuring device. Therefore, the probability is relatively high that the right-hand of two peaks in a histogram (i.e. the peak with the higher histogram class value) can be assigned to a reflected light pulse, while the left-hand of two peaks in a histogram (i.e. the peak with the lower histogram class value) is based on a false positive detection caused by stray light generated by a retroreflector in the measurement object.This selection criterion therefore reduces the risk of false-positive detection and thereby significantly increases the reliability of the measurement method (especially if the measurement object has a retroreflector and this is located at a relatively short distance to the measuring device).

[0018] The method according to the invention can also provide that the selection of a histogram class i from the previously determined histogram classes i comprises the following: - if, when determining the histogram classes i for which the frequency distribution A(i) exceeds a given threshold A thr exceeds, exactly one histogram class i has been determined: Selecting this one histogram class i.

[0019] If only one histogram class i has been determined, the probability is relatively high that the peak assigned to this histogram class can actually be attributed to a reflected light pulse. Therefore, this peak can be reliably used to calculate the distance to the measured object.

[0020] Furthermore, the method according to the invention can provide that the selection of a histogram class i from the previously determined histogram classes i comprises the following: - if, when determining the histogram classes i for which the frequency distribution A(i) exceeds a given threshold A thr exceeds, more than two histogram classes i have been determined: Selecting the histogram class i with the higher histogram class value.

[0021] This selection criterion is based on the assumption that the peaks caused by stray light generated at a retroreflector have a significant value when the retroreflector is located in close proximity to the measuring device. Therefore, the probability that the peaks observed at lower histogram classes i of the frequency distribution A(i) are caused by stray light is greater than the probability that the peaks observed at higher histogram classes i of the frequency distribution A(i) are due to stray light. This increases the reliability of the method according to the invention even in cases where more than two peaks are detected for which the value of the frequency distribution A(i) exceeds the specified threshold.

[0022] Furthermore, the method according to the invention can provide that the selection of a histogram class i from the previously determined histogram classes i comprises the following: - if, when determining the histogram classes i for which the frequency distribution A(i) exceeds a given threshold A thr exceeds, more than two histogram classes i were determined: - Select the two histogram classes i with the highest values ​​of the frequency distribution A(i). - Selecting the histogram class i with the higher histogram class value from the two previously selected histogram classes i.

[0023] This selection criterion ensures that a preselection is made first and then the peak with the higher histogram class is selected.

[0024] According to some preferred embodiments of the method according to the invention, the method may comprise the following steps: - measuring an intensity of ambient light; and - Determination of the threshold value A thr depending on the measured intensity.

[0025] In this way, the current measurement scenario and the current ambient light intensity can be taken into account, further increasing the reliability of the method according to the invention. Various approaches known from the prior art can be used to measure the ambient light intensity. For example, the method according to the invention can provide for a light intensity to be measured over a predetermined measurement period and for an ambient light parameter P to be derived from the measured light intensity. ambwhich is proportional to the intensity of the ambient light. Then, for example, the threshold value A thr to one of the ambient light parameters P amb dependent value. For example, A thr = 0.8 × P amb , A thr = 0.9 × P amb , or A thr = 0.95 x P amb The threshold value A thr can therefore be chosen in such a way that the number of determined histogram classes i can be varied.

[0026] According to further preferred embodiments of the method according to the invention, the measurement object can be illuminated with multiple light pulses using a single light source, either by full-flash illumination (also referred to as full-flash illumination) or sequential flash illumination (also referred to as sequential flash illumination). Experimental studies have shown that the artifacts described above, as well as the distortion of the measurement results caused by scattered light, are particularly pronounced in cases of full-flash illumination and sequential flash illumination. Therefore, the reliability of the method can be significantly increased with such illumination.

[0027] Furthermore, the method according to the invention can provide for the selection of the histogram class i from the previously determined histogram classes i to take into account a histogram class selected during a previous measurement or a value calculated from several histogram classes selected during previous measurements. For example, a histogram class i=20 may have been selected during a previous measurement. If two peaks are now determined at i=10 and i=22 during the current measurement, the histogram class whose distance to the histogram class selected during the previous measurement is smaller (in this case i=22) can be selected. This is based on the assumption that the distance to a measurement object is generally relatively small when two measurements are carried out consecutively (within a short period of time).This allows additional information from past measurements to be taken into account to further increase the reliability of the distance measurement. It can also be planned to calculate an average from the past m measurements, and for the current measurement, the peak with the smallest distance to the average is selected from the candidate peaks. In this way, the information from several past measurements can be used to increase the reliability of a current measurement.

[0028] In addition, to solve the problem described above, a method for detecting light pulses by a light-sensitive sensor unit is proposed, the method comprising the following steps: - Receiving light pulses using a light-sensitive sensor unit; - Measuring a travel time for each of the received light pulses; - Creating a frequency distribution A(i) from the measured travel times, where A denotes the number of received photons in a histogram class i; - Determine the histogram classes i for which the value of the frequency distribution A(i) exceeds a given threshold A thr exceeds; - selecting a histogram class i from the previously determined histogram classes i, taking into account at least one selection criterion; and - Determine the distance of a measuring object based on the selected histogram class i.

[0029] Furthermore, to achieve the object described above, the present invention proposes a measuring device for measuring the distance of a measuring object, wherein the measuring device comprises a light-sensitive sensor unit, a memory unit, and a computing unit. In the measuring device according to the invention, it is provided that - the computing unit is designed to - to measure the travel times of received light pulses; - to create a frequency distribution A(i) from the measured travel times, where A denotes the number of received photons in a histogram class i; - to determine histogram classes i for which the value of the frequency distribution A(i) exceeds a given threshold value A thr exceeds; - to select a histogram class i from the previously determined histogram classes i, taking into account at least one selection criterion; and - to determine the distance of the measuring object based on the selected histogram class i.

[0030] In the measuring device according to the invention, it can be provided in particular that the light-sensitive sensor unit has a photodiode, a single-photon avalanche diode (SPAD), a photodiode array, a SPAD array and / or an image sensor, wherein the image sensor can be designed in particular as a CMOS sensor or as a CCD sensor.

[0031] In some embodiments of the measuring device according to the invention, it can be provided that it additionally comprises an event counter, which is connected to an output terminal of the sensor unit and is further designed to count the events detected by the sensor unit. The event counter is preferably configured to determine an ambient light parameter that quantifies the intensity of the ambient light in a measurement scenario. As a result, the event counter can be used to record the intensity of the ambient light. Knowledge of the ambient light in a specific measurement scenario can be used to determine the threshold value A thr in an appropriate manner.

[0032] Furthermore, the measuring device according to the invention can be provided with an additional calculation unit which is designed to determine the threshold value A thrdepending on the measured ambient light parameter. If the measured intensity of the ambient light is relatively high, the threshold value A thr be set to a higher value, while the threshold A thr can be set to a lower value if the measured ambient light intensity is relatively low.

[0033] Furthermore, in the measuring device according to the invention, it can be provided that the computing unit is designed to select a histogram class i from the previously determined histogram classes i depending on a histogram class i selected in a previous measurement. This makes it possible to take the previous measurement results into account and, for example, to select a peak whose distance to the peak from the previous measurement is smaller. By taking this additional information into account, the reliability of the measuring device according to the invention can be further increased. As already explained above in connection with the method according to the invention, this embodiment of the invention assumes that the distance between a measurement object and a measuring device does not usually change significantly between two successive measurements (taking place within a short time interval).

[0034] Finally, to solve the problem described above, a measuring system for measuring the distance of a measuring object is proposed, wherein the measuring system has the following: - a light source configured to emit a sequence of light pulses in the direction of a measurement object; and - a measuring device according to one of the embodiments described above.

[0035] In the measuring system according to the invention, it can preferably be provided that the light source is designed as an LED or as a laser diode.

[0036] The above-mentioned components of the measuring device according to the invention or of the measuring system according to the invention can be implemented as separate components of the measuring device or of the measuring system or alternatively can be designed as integral components of an integrated circuit (also referred to as integrated circuit or IC).

[0037] The present invention is explained in more detail below with reference to the figures. Fig. 1 a measurement object and the measurement data determined for the measurement object, Fig. 2 measurement data determined for a measurement object, where the frequency distribution for a selected pixel has one or two peaks, Fig. 3 an embodiment of the method according to the invention, Fig. 4 an embodiment of the measuring device according to the invention, and Fig. 5 measurement data obtained for a measurement object, each with and without suppression of parasitic effects.

[0038] In the Fig. Figure 1 shows a measurement object (see left) being measured using a measuring device, along with the corresponding measurement data obtained during the measurement (see right). The measuring device, which can be designed in particular as a lidar measuring device, is usually configured to emit light pulses towards the measurement object and to detect and subsequently evaluate the light points reflected by the measurement object. As shown in the Fig. As can be seen in Figure 1, the measuring object has a retroreflector in the shape of a traffic sign. The measurements were taken from two different distances. While the measurement at a relatively large distance between the measuring device and the measuring object provides quite reliable measurement results (see figure top right in the Fig. 1), the measurement provides erroneous measurement data when the distance between the measuring device and the measuring object is relatively short (see figure bottom right in the Fig. 1). The erroneous measurement data are caused in particular by the scattered light generated by the retroreflector. It can be seen that the scattered light also leads to artifacts outside the area attributable to the retroreflector (see the two rectangles in the figure below right in the Fig. 1). These artifacts occur particularly when the measurement object has a retroreflector and the distance between the measurement object and the measuring device is relatively short. Therefore, the aim of the present invention is to suppress such artifacts and thus provide a reliable measurement method.

[0039] In the Fig. 2 shows the measurement data obtained for a test object. In the figures on the left, Fig. 2 the determined distance to the measuring object is shown, while in the figures on the right in the Fig. 2 shows the frequency distributions determined for a selected pixel. In the measurement, the results of which are shown above in the Fig. 2, the frequency distribution has exactly one peak. However, the measurement, the results of which are shown below in the Fig. 2, the frequency distribution has two peaks. It is obvious that not both peaks can represent the correct distance to the measurement object at the selected pixel. With the measurement methods known from the state of the art, there is therefore a risk that the left peak (ie the earlier peak) in the bottom right of the figure is mistakenly Fig. 2 has a larger value than the right peak (i.e. the later peak) and is therefore wrongly identified as the relevant peak. This leads to erroneous measurement results, which can lead to the Fig. 1 described artifacts.

[0040] In the Fig. 3 schematically illustrates an embodiment of the method 100 according to the invention. In the method 100 according to the invention, in a first method step 110, a measurement object is illuminated with a plurality of light pulses using a light source. The light source can be designed, in particular, as a laser beam source configured to emit a plurality of laser pulses with a relatively short pulse duration. The measurement object can be point-shaped or (as shown in the examples explained above) have a surface to be measured. In the latter case, the measurement can be performed for various points on the surface of the measurement object, wherein the individual measurement values ​​are combined following the measurement to create a two-dimensional or three-dimensional image that characterizes the measurement object and reproduces the overall shape of the measurement object.In a second method step 120, the light pulses reflected from the measurement object are received using a light-sensitive sensor unit, wherein the light-sensitive sensor unit can be designed in particular as a SPAD, a SPAD array, or a CMOS sensor. In a third method step 130, the propagation time of the received light pulses is measured. For this purpose, the time difference between a first point in time at which a light pulse was emitted and a second point in time at which the reflected light pulse was received at the sensor unit is calculated. In a fourth method step 140, a frequency distribution A(i) is created from the measured propagation times, where A denotes the number of received photons in a histogram class i. The frequency distribution A(i) can be represented graphically in the form of a histogram.In a fifth method step 150, the histogram classes i are determined within the frequency distribution A(i) for which the value of the frequency distribution A(i) exceeds a predetermined threshold value A. thr In contrast to the methods known from the state of the art, not always a single peak of the histogram is taken into account, but all peaks that exceed the specified threshold A threxceed. This makes it possible to filter the determined peaks in a subsequent step. In a sixth method step 160, a histogram class i is then selected from the previously determined histogram classes i. At least one selection criterion is taken into account. In particular, the selection criterion can be defined such that if two or more than two histogram classes i are determined, the histogram class i with the higher histogram class value is selected. This can significantly reduce artifacts that can be caused in particular by a retroreflector.As already explained above, this embodiment of the method according to the invention takes into account that the scattered light generated by a retroreflector can impair the measurement result, particularly at short distances, so that the probability is relatively high that, in the case of multiple peaks in a histogram, the peak with the lower histogram class was caused by the scattered light and can therefore be discarded during the measurement. Finally, in a seventh method step 170, the distance of the measurement object is determined based on the selected histogram class i. For this purpose, the approaches known from the prior art can be used. In particular, the distance to the measurement object can be determined taking into account the determined travel time of the light pulses and the speed of light according to the equation. D=(c⋅T) / 2 where D is the distance to the measuring object, c is the speed of light and T is the determined travel time.

[0041] In the Fig. 4, an embodiment of the measuring device according to the invention is shown schematically. The measuring devices known from the prior art usually have a SPAD, a TDC (time-to-digital converter), a histogram storage unit, a data processing unit, and a reset unit. In addition to the components of the measuring devices known from the prior art, the Fig. The exemplary embodiment of the measuring device according to the invention shown in Figure 4 comprises the components shown in dashed lines in this figure. In particular, the measuring device according to the exemplary embodiment shown here has an event counter configured to determine an ambient light parameter. For example, the number of photons can be counted during a measurement period during which the light source emits no light pulses and, accordingly, no light pulses are received by the sensor unit. Depending on the determined ambient light parameter, a calculation unit can then calculate a threshold value. The threshold value can be selected such that the probability of the threshold value being exceeded by extraneous light is relatively low. In particular, the threshold value can be selected dynamically and depending on the intensity of the current ambient light.In the illustrated embodiment, the data processing unit is configured such that it searches for one or more peaks in a frequency distribution determined in a measurement or within a histogram described by the frequency distribution. The determined peaks or the histogram classes i belonging to the peaks are then transmitted to a retroreflector filter unit (also referred to as a filter unit or computing unit). In the filter unit, a histogram class i is selected from the determined histogram classes i, taking into account at least one selection criterion. In particular, it can be provided that if several peaks are determined, the histogram class i with the larger histogram class value is selected. In addition, it can be provided that in the measurements carried out, the peak determined in a measurement (orthe histogram class i) assigned to the peak is stored in a memory unit, and the histogram class i is selected depending on the peak determined during the previous measurement (or the histogram class i assigned to the peak). For example, a first measurement may have determined a peak in histogram class i=40. A second measurement may then, for example, result in two histogram classes i1 = 22 and i2 = 42. In this case, a selection criterion can be selected such that the histogram class selected for the second measurement is the one whose distance from the histogram class determined in the first measurement is smaller (in this case i2 = 42). In this way, according to preferred embodiments of the device according to the invention, the correlation of the distance values ​​between the individual measurements can be utilized to increase the reliability of the measuring device according to the invention.

[0042] Finally, in the Fig. 5 Measurement data are shown which were determined when measuring a measurement object, once without suppressing the artifacts caused by the retroreflector (see above in the Fig. 5) and once with suppression of the artifacts (see below in the Fig. 5). The above figure in the Fig. Figure 5 shows that, in the presence of a retroreflector and without the suppression mechanism according to the present invention, the measured data exhibit strong artifacts caused by the scattered light generated by a retroreflector. The suppression mechanism according to the present invention can significantly reduce these artifacts (see the lower figure in the Fig. 5), which significantly increases the reliability of the method according to the invention. LIST OF REFERENCE SYMBOLS 100 procedures 110 first procedural step 120 second process step 130 third procedural step 140 fourth procedural step 150 fifth procedural step 160 sixth procedural step 170 seventh procedural step

Claims

[1] Method (100) for carrying out a distance measurement, comprising the following method steps: - illuminating (110) a measurement object with a plurality of light pulses using a light source; - receiving (120) light pulses reflected from the measurement object using a light-sensitive sensor unit; - measuring (130) the transit time of the received light pulses; - creating (140) a frequency distribution A(i) from the measured propagation times, where A denotes the number of received photons in a histogram class i; - Determining (150) the histogram classes i for which the value of the frequency distribution A(i) exceeds a given threshold value A thr exceeds; - selecting (160) a histogram class i from the previously determined histogram classes i taking into account at least one selection criterion; and - Determining (170) the distance of the measuring object based on the selected histogram class i. [2] Method (100) according to claim 1, characterized by that the selection of a histogram class i from the previously determined histogram classes i comprises the following: - if, when determining the histogram classes i for which the frequency distribution A(i) exceeds a given threshold A thr exceeds, a total of two histogram classes i have been determined: Selecting the histogram class i with the higher histogram class value. [3] Method (100) according to claim 1 or 2, characterized by that the selection of a histogram class i from the previously determined histogram classes i comprises the following: - if, when determining the histogram classes i for which the frequency distribution A(i) exceeds a given threshold A thr exceeds, exactly one histogram class i has been determined: Selecting this one histogram class i. [4] Method (100) according to one of claims 1 to 3, characterized by that the selection of a histogram class i from the previously determined histogram classes i comprises the following: - if, when determining the histogram classes i for which the frequency distribution A(i) exceeds a given threshold A thr exceeds, more than two histogram classes i have been determined: Selecting the histogram class i with the highest histogram class value. [5] Method (100) according to one of claims 1 to 3, characterized by that the selection of a histogram class i from the previously determined histogram classes i comprises the following: - if, when determining the histogram classes i for which the frequency distribution A(i) exceeds a given threshold A thr exceeds, more than two histogram classes i were determined: - Select the two histogram classes i with the highest values ​​of the frequency distribution A(i). - Selecting the histogram class i with the higher histogram class value from the two previously selected histogram classes i. [6] Method (100) according to one of claims 1 to 5, characterized by that the method (100) comprises the following steps: - measuring an intensity of ambient light; and - Determination of the threshold value A thr depending on the measured intensity. [7] Method (100) according to one of claims 1 to 6, characterized by that the illumination of the measuring object with several light pulses using a light source is carried out by full flash illumination or sequential flash illumination. [8] Measuring device for measuring the distance of a measuring object, comprising a light-sensitive sensor unit, a storage unit and a computing unit, wherein - the computing unit is designed to - to measure the travel times of received light pulses; - to create a frequency distribution A(i) from the measured travel times, where A denotes the number of received photons in a histogram class i; - to determine histogram classes i for which the value of the frequency distribution A(i) exceeds a given threshold value A thr exceeds; - to select a histogram class i from the previously determined histogram classes i, taking into account at least one selection criterion; and - to determine the distance of the measuring object based on the selected histogram class i. [9] Measuring device according to claim 8, characterized by that the sensor unit comprises a photodiode, a single-photon avalanche diode, SPAD, a photodiode array, a SPAD array and / or an image sensor. [10] Measuring device according to claim 8 or 9, characterized byan event counter connected to an output terminal of the sensor unit and configured to count the events detected by the sensor unit, wherein the event counter is preferably configured to determine an ambient light parameter defining the intensity of the ambient light in a measurement scenario. [11] Measuring device according to claim 10, characterized by an additional calculation unit designed to determine the threshold value A thr depending on the determined ambient light parameter. [12] Measuring device according to one of claims 8 to 11, characterized by that the computing unit is designed to select a histogram class i from the previously determined histogram classes i depending on a histogram class i selected in a previous measurement. [13] Measuring system for measuring the distance of a measuring object, comprising - a light source configured to emit a sequence of light pulses in the direction of a measurement object; and - a measuring device according to one of claims 8-12.

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