Microsoft Patent | Foreign substance detection in a depth sensing system

Patent: Foreign substance detection in a depth sensing system

Publication Number: 10192147

Publication Date: 2019-01-29

Applicants: Microsoft

Abstract

Disclosed are an apparatus and a method for detection of foreign substances in a depth sensing system. In one embodiment, a depth sensing device includes a light source to emit light, an image sensor and a processor. The image sensor receives through an optical component the light reflected by environment of the depth sensing device. The image sensor further generates a depth map including a plurality of pixel values corresponding to distances between the depth sensing device and the environment. The processor detects a blurred portion of the depth map due to a presence of a foreign substance on the optical component. The processor may further cause outputting a user alert of the presence of the foreign substance on the optical component.

Background

Depth sensing technology can be used to determine a person’s location in relation to nearby objects or to generate an image of a person’s immediate environment in three dimensions (3D). One application in which depth sensing technology may be used is in head-mounted display (HMD) devices and other types of near-eye display (NED) devices. Depth sensing technology can employ a time-of-flight (ToF) depth camera. With ToF based depth sensing technology, a light source emits light onto nearby objects, and a ToF camera captures the light after it reflects off surfaces of the objects. The time taken for the light to travel from the light source and to reflect back from an object to the ToF camera is converted, based on the known speed of light, into a depth measurement (i.e., the distance to the object). Such a measurement can be processed with other similar measurements to create a map of physical surfaces in the user’s environment (called a depth image or depth map) and, if desired, to render a 3D image of the user’s environment.

A ToF camera typically includes various optical components through which the received light travels. The optical components can include, for example, a camera lens and a protective visor. Through normal use of the camera, a foreign substance such as dust, debris, or a fingerprint smudge may adhere to a surface of one or more of those optical components. Any foreign substance on the optical components can decrease accuracy of the depth measurements by the ToF camera, by causing scattering of the light and therefore distortion of the depth map.

Summary

Introduced here are at least one apparatus and at least one method (collectively and individually, “the technique introduced here”) for detecting foreign substances in a depth imaging system. In some embodiments, a depth imaging device includes a light source to emit light, an image sensor and a processor. The image sensor receives through an optical component the light reflected by environment of the depth imaging device. The image sensor further generates a depth map including a plurality of pixel values corresponding to distances between the depth imaging device and the environment. The processor detects a blurred portion of the depth map due to a presence of a foreign substance on the optical component. The processor may further generate a user alert of the presence of the foreign substance on the optical component.

In certain embodiments, the processor can detect that the depth map is blurred based on a determination that a total number for the intermediate depth pixels exceeds a threshold number. More specifically, and for example, the processor can detect in the depth map a plurality of intermediate depth pixels caused by light scattering of the foreign substance on the optical component. The intermediate depth pixels have values corresponding to depths that are smaller than depths for background of the environment and are larger than depths for foreground of the environment. The processor detects that the depth map is blurred based on a determination that a total number for the intermediate depth pixels exceeds a threshold number.

In certain embodiments, the processor can detect in the depth map a plurality of gradient ramps caused by light scattering of the foreign substance on the optical component. Each gradient ramp is indicative of a transition between foreground of the environment and background of the environment. The processor detects that the depth map is blurred based on the gradient ramps and lengths of the gradient ramps.

Other aspects of the disclosed embodiments will be apparent from the accompanying figures and detailed description.

This Summary is provided to introduce a selection of concepts in a simplified form that are further explained below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

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