DE-102024115359-B4 - Light time-of-flight camera

Abstract

Light time-of-flight camera for distance measurement with a time-of-flight sensor with at least one time-of-flight pixel, with a lighting system for emitting modulated light, the time-of-flight camera is designed for distance measurements according to a phase measurement principle and is designed in this way, that, a) for at least a part of the light travel time pixels, for determining a distance (d w ) of an object at least two measurements (A 1 , A 2 , ...) are carried out with different modulation frequencies (f 1 , f 2 , ...) and thus different uniqueness ranges (UR 1 , UR 2 , ...), wherein in each measurement (A i ) a residual distance (d i = mod(d, UR i )) is measured, b) starting from these residual distances (d i ) for each light time-of-flight pixel, a sub-area index M of a total distance curve (UR extd ) is initially assigned, c) a field of the initially assigned sub-area indices M is processed using a "nearest neighbor filter" and/or a temporal filter, to generate a corrected, final sub-area index (M_final) for the respective light-time-of-flight pixel, and only then, d) the distance (d w ) is determined by projecting the residual distances (d i ) onto that sub-area of the total distance curve which is defined by the corrected, final sub-area index (M_final).

Inventors

• Philipp Backes
• Stephan Ulrich

Assignees

• IFM ELECTRONIC GMBH
• pmdtechnologies ag

Dates

Publication Date

20260513

Application Date

20240603

Priority Date

20230630

Claims (4)

1. Time-of-flight camera for distance determination, comprising a time-of-flight sensor with at least one time-of-flight pixel, and an illumination system for emitting modulated light, wherein the time-of-flight camera for distance measurements is designed according to a phase measurement principle and is configured such that, a) for at least a portion of the time-of - flight pixels, at least two measurements ( A1 , A2 , ...) with different modulation frequencies ( f1 , f2 , ...) and thus different uniqueness ranges ( UR1 , UR2 , ...) are performed to determine the distance (d_w) of an object, wherein a residual distance (d _i = mod(d, UR_i )) is measured in each measurement (A_i ), b) starting from these residual distances (d_i), a sub-range index M of a total distance curve (UR _extd) is initially assigned to each time-of-flight pixel, c) an array of the initially assigned sub-range indices M is filtered by means of a "nearest neighbor filter". and/or processed using temporal filtering is used to generate a corrected final sub-area index (M_final) for the respective light-time-of-flight pixel, and only then, d) is the distance (d w ) determined by projecting the residual distances (d i ) onto that sub-area of the total distance curve which is defined by the corrected final sub-area index (M_final).
2. Light time-of-flight camera after Claim 1 , wherein to determine the sub-area index (M) an estimate of the sub-area index (M(x, y, t)) for the given pixel is first determined, which is then calculated with the estimates for spatially neighboring pixels and/or temporally prior measurements.
3. Time-of-flight camera according to one of the preceding claims, wherein the calculation of the initial sub-areas or the estimates of the sub-area index (M(x, y, t)) is carried out via a mean, a median, a weighted mean, or a weighted median.
4. Time-of-flight camera according to one of the preceding claims, wherein the filtering of the initial sub-area index or the estimation of the sub-area index (M) is calculated based on an initially estimated combined distance and the known uniqueness ranges UR i used in the measurement.

Description

The invention relates to a time-of-flight camera according to the preamble of claim 1. Time-of-flight cameras are intended to include, in particular, cameras that derive time-of-flight information from the phase shift of emitted and received radiation. PMD cameras with photomixing detectors (PMDs) are especially suitable as time-of-flight or 3D-TOF cameras. DE 197 04 496 A1 described. To extend the uniqueness range of such a camera, multiple modulation frequencies are preferably used. (See the literature.) DE 10 2013 214 677 B3 , DE 10 2013 207 647 A1 and DE 10 2018 104 668 A1 For example, various approaches have been mentioned. The DE 10 2020 127 332 A1 Disclosure reveals a method for operating a time-of-flight camera system on a vehicle, in which the vehicle's movement is detected. Raw distance values are determined at a first modulation frequency for each detection frame and converted into distance values. These distance values are then recalculated, taking into account the vehicle's movement in the interim, into distance values from a previous detection frame. By comparing the recalculated distance value with a raw distance value of the same pixel in the previous frame, the determined distance value is output as valid if the threshold is not met, and this process is repeated. The DE 10 2014 204 423 A1 Disclosure reveals a method for operating a time-of-flight camera system in which object distance is determined based on a phase shift and the detection range comprises at least two uniqueness ranges. In an initialization phase, objects in the detection range are detected, assigned to the respective uniqueness ranges, and at least one distance-dependent parameter is acquired for each object. In the subsequent position determination, the object's spatial position is determined, and the distance-dependent parameter is then acquired again. The determined spatial position is output as valid if a check confirms that the distance-dependent parameter is plausible for this spatial position. The purpose of the inventions is to improve the accuracy of multi-frequency methods. The problem is solved by the camera according to claim 1. Advantageously, a time-of-flight camera is provided for distance determination. with a time-of-flight sensor with at least one time-of-flight pixel, with a lighting system for emitting modulated light, the time-of-flight camera is designed for distance measurements according to a phase measurement principle and is designed in such a way that for at least a part of the light travel time pixels, at least two measurements with different modulation frequencies and thus different uniqueness ranges are carried out to determine the distance of an object, where a residual distance is measured in each measurement, where, starting from these residual distances from the at least two measurements, the residual distances are initially assigned to a sub-area or a corresponding sub-area index M of a total distance curve of a modulo diagram, where a final assignment of the sub-area indices M is made depending on a “nearest neighbor filtering” and/or a temporal filtering of the initially assigned sub-area indices M, where the distance is determined by projecting the remaining distances onto the sub-area, with the value of the finally assigned sub-area index M. This approach has the advantage that, before a potentially complex calculation of a distance, an assignment to a sub-area of a total distance curve is ensured, which simplifies the subsequent distance calculations and contributes to reducing distance noise. They show: 1 schematically the basic principle of photomixed detection, 2 a modulated integration of the generated charge carriers, 3 a distance measurement using a wavelength, 4 a distance measurement using two different wavelengths, 5 a method according to the invention, 6 Residual distances in a modulo diagram, 7 a nearest neighbor filter. In the following description of preferred embodiments, identical reference numerals denote identical or comparable components. 1 shows a measurement situation for optical distance measurement with a time-of-flight camera, as used, for example, in the DE 197 04 496 A1 is known. The time-of-flight camera system 1 comprises a transmitter unit or illumination module 10 with an illumination 12 and an associated beam shaping optics 15, as well as a receiver unit or time-of-flight camera 20 with a receiving optics 25 and a time-of-flight sensor 22. The time-of-flight sensor 22 has at least one time-of-flight pixel, preferably also a pixel array, and is in particular designed as a PMD sensor. The receiving optics 25 typically consist of several optical elements to improve the imaging properties. The beam-shaping optics 15 of the transmitting unit 10 can, for example, be designed as a reflector or lens optics. In a very simple embodiment, optical elements can optionally be omitted on both the receiving and transmitting sides. The measurement principle of this arrang