CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/EP2018/058456, filed on Apr. 3, 2018, and published in German as WO 2018/185083 A2 on Oct. 11, 2018. This application claims the priority to German Patent Application No. 10 2017 205 742.4, filed on Apr. 4, 2017. The entire disclosures of the above applications are incorporated herein by reference.

FIELD

The disclosure relates to a time-of-flight camera and a method for detecting a point spread function for correcting the detected signals of a time-of-flight sensor.

BACKGROUND

This section provides background information related to the present disclosure which is not necessarily prior art.

The time-of-flight camera or time-of-flight camera systems in particular relate to all time-of-flight or 3D TOF camera systems that derive time-of-flight information from the phase shift of emitted and received radiation. As time-of-flight or 3D TOF cameras in particular PMD cameras including photo mix detectors (PMD) are suited as described for example in DE 197 04 496 C2 and available from the company ‘ifm electronic GmbH’ or ‘pmdtechnologies ag’ as Frame Grabber 03D or as CamCube. The PMD camera allows in particular a flexible arrangement of the light source and the detector which can be arranged both in a housing and separately.

SUMMARY

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

It is the object of the disclosure to further improve the compensation of phase errors.

This object is achieved in an advantageous manner by the time-of-flight camera system according to the disclosure as specified in the independent claims.

Particularly advantageous is a time-of-flight camera for a time-of-flight camera system provided with a time-of-flight sensor comprising a plurality of time-of-flight pixels for determining a phase shift of emitted and received light, wherein based on the detected phase shifts distance values are determined, wherein the time-of-flight camera comprises a memory in which at least the parameters of a point spread function are stored, wherein the point spread function takes into account a scattered light behavior and signal crosstalk of the time-of-flight camera and the time-of-flight sensor, comprising an evaluation unit, which is designed such that on the basis of the stored point spread function a detected image (I(x)) is deconvoluted and a corrected image (I0(x)) is determined, and wherein the determination of the phase shifts or distance values is implemented on the basis of the corrected image (I0(x)).

It is also useful when the deconvolution of the detected image and the stored point spread function is done in the Fourier space.

Preferably, the point spread function is complex-valued.

It is also useful when the deconvolution of the detected image and the stored point spread function is done in the Fourier space.

In a further embodiment it is provided that the detected image is reduced in resolution and a correction is determined with this reduced resolution, and thereafter the correction is scaled up to the original resolution of the detected image and the detected image is corrected with the scaled-up correction.

As a result, the computational effort for the corrections can be significantly reduced.

It is further contemplated to perform the reduction in resolution by averaging amplitudes of adjacent pixels and upscaling by duplicating the amplitudes.

Preferably, the point spread function is stored in the memory as a matrix or a lookup table and/or a Fourier transform.

It is particularly useful if the point spread function stored in the memory is determined according to one of the following methods.

Preferably, a method for determining a point spread function is provided in which a point light source and a time-of-flight camera are arranged such that a time-of-flight sensor of the time-of-flight camera detects the point light source, wherein a distance between the point light source and the time-of-flight camera and/or a beam profile of the point light source are selected such that less than 5 time-of-flight pixels in a pixel row or column or a maximum of 16×16 pixels are illuminated, wherein the point spread function is determined at least on the basis of a subset of the time-of-flight pixels of the time-of-flight sensor.

This procedure has the advantage that for the determination of a point spread function the light source can be constructed in a simple manner within certain limits.

In one embodiment, it is provided to operate the point light source unmodulated.

In this case, the modulation gates of the time-of-flight pixels of the time-of-flight sensor are driven in such a way that charge carriers in the time-of-flight pixel are primarily accumulated only at one integration node. This procedure ensures that the generated photoelectrons are preferably collected at one integration node.

According to a further embodiment, it is provided to drive the point light source and the time-of-flight sensor in phase with a modulation signal and to determine sensor difference signals with respect to at least three different phase positions.

It is particularly useful that at least two image frames with different integration times of the time-of-flight sensor and/or different light intensities of the point light source are provided for determining the point spread function.

In a further embodiment, a method for determining a point spread function for a time-of-flight camera of a time-of-flight camera system is provided in which a first 3D image I1(x) of a reference scene and a second 3D image I2(x) with an object in the foreground of the reference scene are detected by means of the time-of-flight camera, wherein the second 3D image I2(x) or at least a partial area of the second 3D image I2(x) is corrected by means of a point spread function, and based on a difference between the first and the corrected second 3D image I′2(x) parameters of the point spread function are changed until the difference between the two images I1(x), I′2(x)) at least in the selected partial areas is minimal and/or falls below a threshold, wherein the resulting point spread function can be reused as a correction point spread function.

Likewise, a method for determining a point spread function for a time-of-flight camera of a time-of-flight camera system can be provided in which by means of the time-of-flight camera a single image I(x) of a reference scene with an object in the foreground is detected under the assumption that the reference scene is formed as a flat surface, wherein the single image I(x) is corrected by means of a first point spread function, wherein for determining a correction point spread function parameters of the first point spread function are changed until a difference between the corrected image I′(x) and an expected image I0(x) is minimal and/or falls below a threshold.

In another embodiment, a method for determining a point spread function for a time-of-flight camera of a time-of-flight camera system is provided, in which a 3D image IT(x) of a step of a reference object is detected by means of the time-of-flight camera, wherein the reference object has a step of defined height and the surfaces of the step are planar and arranged plane-parallel to one another, and the reference object is disposed in relation to the time-of-flight camera so that at the edge of the step a distance jump to the more distant step level is present, wherein the detected 3D image IT(x) is first corrected by use of a first model point spread function, wherein, when the distance values d of the thus corrected 3D image IT(x) are outside a maximum allowable distance error, parameters of the model point spread function are changed until the distance values d of the corrected 3D image IT(x) are minimal and/or are below an allowable distance error, wherein the resulting point spread function can be reused as a correction point spread function.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

