Thermally-tuned depth camera light source

Various embodiments are disclosed for setting a depth camera light source operating temperature in a thermal tuning mode executed during a depth camera manufacturing process. One embodiment of a method includes illuminating a target with light from a light source at a plurality of light source temperatures; for each light source temperature, sensing an intensity of reflected light received at a light sensor through a light filter positioned intermediate the target and the light sensor; approximating a frequency response relationship between a light filter cutoff frequency and a light source emission wavelength based on a comparison of the sensed intensities and stored reference data; generating a temperature set point so that the light source emission wavelength does not overlap the light filter cutoff frequency by more than a predetermined overlap threshold; and programming a temperature controller to control the light source to the temperature set point during depth camera operation.

BACKGROUND

Depth cameras used to create three-dimensional images of objects typically include imaging filters for filtering ambient light from imaging light projected from a depth camera imaging light source. For efficient operation, most of the imaging light received at the imaging filter should be transmitted to a depth camera imaging sensor while most of the ambient light should be filtered. However, unless the imaging filter is matched to the imaging light wavelength, it becomes more difficult to filter ambient light without reducing the transmission of imaging light.

Some approaches to improving ambient light filtering without reducing the transmission of imaging light include using tunable imaging filters. However, tunable imaging filters may be expensive and may require complicated feedback circuitry to operate. Some other approaches include testing multiple imaging filters and imaging light sources so that couples may be identified and paired. However, such approaches may require expensive testing and maintenance of large inventories.

SUMMARY

Various embodiments are disclosed for setting a depth camera light source operating temperature in a thermal tuning mode executed during a depth camera manufacturing process. One embodiment of a method includes illuminating a target with light from a light source at a plurality of light source temperatures; for each light source temperature, sensing an intensity of reflected light received at a light sensor through a light filter positioned intermediate the target and the light sensor; approximating a frequency response relationship between a light filter cutoff frequency and a light source emission wavelength based on a comparison of the sensed intensities and stored reference data; generating a temperature set point so that the light source emission wavelength does not overlap the light filter cutoff frequency by more than a predetermined overlap threshold; and programming a temperature controller to control the light source to the temperature set point during depth camera operation.

DETAILED DESCRIPTION

Depth cameras may be used to create a three-dimensional image of an object from distance information captured along with image information at various depth camera pixels. For example, a depth camera may be used to build a three-dimensional model of a person being imaged by the depth camera, which can be displayed or, in some scenarios, used as input for game software of a gaming system. Thus, in this example, the three-dimensional model of the person may be used to present a graphical representation of the person in a video game display, for example by including the model in a game cut scene, or may be used to receive user input from the modeled person, such that other interactive elements of the game software, such as non-player characters, artifacts, etc., respond to movements of the modeled person.

Depth cameras typically include an illumination system to illuminate an object to be imaged with illumination light and an imaging system for generating an object image based on illumination light reflected from the object. In some examples, the illumination light may be structured light used to provide an interference pattern analyzed by the imaging system to determine three-dimensional information. In some other examples, the illumination light may be pulsed light used to provide a basis for time-of-flight measurements performed by the imaging system to determine three-dimensional information. Regardless of the method by which the depth information is captured, the imaging system is typically configured to sense reflected illumination light at a light sensor, which in some embodiments may be a charge coupled device.

Because ambient light may interfere with the analysis performed by the imaging system, in some embodiments, a light filter, such as a band pass filter, may be included in the imaging system for filtering a portion of ambient light from reflected illumination light prior to the light sensor. For example, a light filter used with an infrared light source may be configured to reject visible light and transmit infrared light. Thus, in some embodiments, the illumination light source and the light filter may be configured so that an emission wavelength of the illumination light overlaps with a pass band of the light filter. However, because of natural variation in light source and light filter manufacturing operations, some light sources may have an emission wavelength that overlaps a cutoff wavelength of some light filters. Put another way, because the illumination light frequency falls outside of the pass band of the light filter, the light filter may not pass some or all of the reflected illumination light to the light sensor. Accordingly, in some embodiments, the emission wavelength of the light source may be thermally tuned to overlap the pass band of the light filter.

While some of the example embodiments described below make reference to game consoles and gaming systems, it will be appreciated that these examples are provided only for descriptive purposes, and that the depth cameras described may be used in any suitable context and/or operating environment within the scope of the present disclosure. Other non-limiting example operating environments include mobile wireless devices, client computing devices, and server computing devices.

FIG. 1shows an embodiment of a depth camera assembly system100for assembling, configuring, and packaging depth cameras for shipment to customers. As shown inFIG. 1, depth camera assembly system100includes a depth camera assembly station102for assembling a depth camera150. For example, an illumination system and an imaging system may be installed into depth camera150at depth camera assembly station102.

At thermal tuning station104, a thermal tuning module executed by thermal tuning station104may, in a thermal tuning mode of the manufacturing process (the details of which are described in more detail below) thermally tune the emission wavelength of the depth camera light source so that it overlaps at least a portion of the pass band of the light filter. Additionally or alternatively, in some embodiments, the light source emission wavelength may be thermally tuned so that the emission wavelength of the light source does not overlap a cutoff frequency of the light filter by more than a predetermined permissible overlap threshold.

It will be appreciated that the wavelength of light emitted by a light source of the depth camera150may vary slightly based on material and manufacturing conditions, particularly since tightly controlling the tolerance on the wavelength frequency of the light source will undesirably increase the manufacturing costs, and thus light sources of lower tolerances may be selected for use in manufacture. Thermal tuning of the light source emission wavelength in this manner described herein may allow light filters and light sources to be assembled into a depth camera without first verifying that the light filter will pass the emission wavelength to the light sensor. In turn, this may allow the depth camera manufacturer to avoid using high cost light sources with tightly controlled tolerances, and to avoid time-consuming light source and light filter pairing tests and/or maintaining a large inventory of light sources and light filters that perform to slightly different wavelengths.

In some embodiments, the light source emission wavelength may be tuned at thermal tuning station104by first approximating a frequency response relationship between a cutoff frequency of the light filter and the emission wavelength of the light source. This approximation may be based on a comparison of light intensities sensed at the light sensor of the imaging system and stored intensity reference data. Subsequently, a static operating temperature set point for the light source may be generated based on the approximation. Once the static operating temperature set point is generated, a light source temperature controller may be programmed with the set point so that the set point temperature is maintained during a depth camera operation mode, as described below in detail in reference toFIG. 3.

In the example shown inFIG. 1, once the light source temperature controller is programmed with the static operating temperature set point, depth camera150is passed to depth camera packaging station106, where depth camera150is packaged for shipment to consumers, at the conclusion of the manufacturing process. A first use of depth camera150by a consumer marks the start of the depth camera operating mode. In the example shown inFIG. 1, the thermal tuning mode is only performed during manufacturing of depth camera150. However, it will be appreciated that, in some embodiments, the thermal tuning mode may be performed at any suitable time when the depth camera is not in an operating mode. Example instances where thermal tuning mode may be performed include, but are not limited to, instances in response to an initial boot-up and/or power-on of the depth camera, in response to a command received from a central server (such as during a firmware and/or software upgrade event for the depth camera), and/or in response to a user command to perform the thermal tuning mode received by the depth camera.

FIG. 3shows an embodiment of a thermal tuning station104A, including a thermal tuning device350in electrical communication with a depth camera150A. In this embodiment, depth camera150A is a computing device component that includes a processor314and memory318. Depth camera150A also includes an illumination system320and an imaging system326. In some embodiments, depth camera150A may be included in a game console310, which may include its own processor314A, memory318A, and associated mass storage device316A. Likewise, thermal tuning device350is a computing device that includes a processor354, mass storage352, and memory356, and includes program logic stored thereon to execute the functionality described herein. It will be appreciated that the embodiment of thermal tuning station104A shown inFIG. 3is merely illustrative, and that other suitable embodiments such as the embodiment illustrated inFIG. 5discussed below may be employed within the scope of the present disclosure.

The thermal tuning mode referenced above is described in more detail with reference toFIG. 2, which shows a flow chart for an embodiment of a thermal tuning method200. Thermal tuning method200may be performed by any suitable hardware and/or software, including the hardware and software modules illustrated inFIG. 3, discussed above, andFIG. 5, discussed below.

Method200comprises, at202, during a thermal tuning mode for a light source of a depth camera executed during a manufacturing process for the depth camera, setting a light source tuning temperature at the illumination system. For some light sources, such as light emitting diode lasers, varying light source temperature may vary the emission wavelength of the light source. For example,FIG. 4shows an example correlation400between light source emission wavelength and light source temperature. In the example shown inFIG. 4, setting a light source temperature to 42 degrees C. leads to light emission at 828 nm. Increasing the light source temperature leads to a corresponding increase in emission wavelength. For reference, a theoretical adjustment of the light source temperature by 30 degrees C. may result in a 10 nm wavelength shift for a standard edge emitting Fabret-Perot laser, although such a dramatic adjustment may not be typical during tuning in a manufacturing setting.

A suitable approach for setting the light source tuning temperature may be employed as follows. In the embodiment shown inFIG. 3, illumination system320includes a light source temperature controller324in thermal communication with light source322. In some embodiments, light source temperature controller324may include a thermoelectric device for heating and/or cooling light source322in response to a programmed temperature set point, though it will be appreciated other devices for varying light source temperature (e.g., fans and/or heat exchangers) may be included in light source temperature controller324. Further, it will be appreciated that, in some embodiments, light source temperature controller324may include suitable programs stored in controller memory for controlling a temperature of light source322.

Continuing withFIG. 2, at204, method200includes illuminating a reflective target with illumination light from a light source of the depth camera at the light source tuning temperature. Any suitable light source may be employed for generating the illumination light. A non-limiting example of a light source may include one or more light emitting diode lasers configured to emit infrared light at one or more emission wavelengths. In the embodiment shown inFIG. 3, light source322is included in illumination system320of depth camera150A. However, it will be appreciated that, in some embodiments, the light source may be a standalone light source, or may be included in a depth camera peripheral device.

It will be appreciated that any suitable reflective target may be employed within the scope of the present disclosure. In the example shown inFIG. 3, reflective target304is shown being illuminated by light source322. In some embodiments, the reflective target may include a reflective field having a white color, though it will be appreciated that other colors may be included and/or substituted in some embodiments. Further, in some embodiments, the reflective target may include various patterns, textures, and/or shapes. The reflective target may be positioned any suitable distance from the depth camera. In some non-limiting examples, the reflective target may be positioned approximately 1.2 meters from the depth camera.

In some embodiments, optics included in illumination system320may include one or more diffraction gratings for tuning the projected illumination light. These diffraction gratings may introduce optical artifacts in the reflected illumination light which may, when detected by the light sensor, manifest as shadows and/or hot spots. Because hot spots may saturate some light sensors and cause loss and/or distortion of sensed intensity data, in some embodiments the reflected illumination light may pass through an optical diffuser positioned intermediate the reflective target and the light filter prior to being received by the light sensor. This may smooth discrete optical artifacts and avoid saturation at the light sensor. For example, in the embodiment shown inFIG. 3, reflected illumination light is depicted passing through optical diffuser304prior to being received at imaging system326.

Continuing withFIG. 2, in some embodiments, method200includes, at206, adjusting a light source current at each light source tuning temperature so that the light source produces a uniform power at every light source tuning temperature. Using this approach, a relative light source power (compared to a reference light source power) may be determined based on a light intensity measurement at the light sensor. The relative light source power may then form a basis for approximating a frequency response relationship between a cutoff frequency of the light filter and an emission wavelength of the light source and for setting a static operating temperature set point based thereon. WhileFIG. 2refers to a current adjustment for maintain a uniform light source power, it will be appreciated that any suitable approach to maintaining a uniform light source power may be employed within the scope of the present disclosure. Table 1 provides example current adjustment parameters for a light source to maintain a uniform power of approximately 180 mW across an example range of light source tuning temperatures.

At208, method200includes receiving reflected illumination light from the reflective target at the light sensor, the reflected illumination light passing through the light filter prior to being received at the light sensor. In the embodiment shown inFIG. 3, illumination light reflected by reflective target302is received at light filter328. Light filter328passes a portion of the reflected illumination light to light sensor330. While the embodiment of light filter328inFIG. 3is described as a band pass filter, it will be appreciated that any suitable light filter having a cutoff frequency may be employed within the scope of the present embodiment.

Light sensor330is a device for sensing light intensity. For example, in one scenario, light sensor330may include one or more charge coupled devices for generating light intensity signals from incident photons. Additionally, in some embodiments, light sensor330may be configured to include a plurality of sensor pixels distributed in an array, each sensor pixel generating a light intensity signal. Such a light sensor may average (for example, by a geometric average) multiple light intensity signals, each light intensity signal corresponding to a photogeneration rate at a different light sensor pixel. In one scenario, the light sensor may average light intensity signals from the entire light sensor; in another scenario, the light sensor may average light intensity signals from selected portions of the light sensor, such as a central portion.

Continuing withFIG. 2, at210, method200includes sensing an intensity of reflected illumination light received at the light sensor of the depth camera through a light filter positioned intermediate the reflective target and the light sensor. In the example shown inFIG. 3, reflected illumination light passes through light filter328and is received at light sensor330.

In some embodiments, sensing intensity at the light sensor includes, at212, determining a relative light power based on a sensed intensity. For example, in a scenario where the light source current is adjusted to produce illumination light with a known, uniform power setting, sensed light intensity may be proportional to the amount of light passed through the light filter. Thus, a comparison of sensed intensity for the known power setting to sensed intensity at one of the light source tuning temperatures may provide an estimate of an amount of frequency overlap between the light filter and the light sensor. For example, in a scenario where the emission wavelength does not overlap the cutoff frequency range of the light filter, the sensed intensity should be approximately the same as the sensed intensity at the reference power. In another scenario, where the emission wavelength does overlap the cutoff frequency range, the sensed intensity will be attenuated relative to the sensed intensity at the reference power. It will be appreciated that any suitable reference power setting may be used to establish a power reference intensity. For example, in some embodiments, a sensed light intensity corresponding to a maximum light source power may be the power reference intensity.

At214, method200determines whether an intensity measurement at another light source tuning temperature is indicated. If additional light source tuning temperatures are indicated, method200returns to202, and the next light source tuning temperature is set. If no additional light source tuning temperatures are indicated, method200continues to216.

Sensed intensities, and in some embodiments, determinations of relative light power, from different light source tuning temperatures may be accumulated to reveal a relationship between the light filter cutoff frequency and the emission wavelength of the light source as established by the light source temperature. Thus, at216, method200includes approximating a frequency response relationship between a cutoff frequency of the light filter and an emission wavelength of the light source based on a comparison of the sensed intensities and stored intensity reference data. One example approach for approximating the frequency response relationship according to an embodiment of the present disclosure is described below. However, it will be appreciated that any suitable approach to approximate a relationship between light filter pass band and the emission wavelength of the light source may be employed within the scope of the present disclosure.

Thus, turning to the embodiment shown inFIG. 3, a light intensity signal from light sensor330is passed to thermal tuning module358. In this embodiment, the sensed intensity is classified by comparing the sensed intensity to stored intensity reference data. Specifically, in this example the sensed intensity is compared to a maximum power reference intensity. An example classification of three sensed intensities corresponding to three respective light source tuning temperatures will be explained with reference toFIGS. 3 and 4below.

In addition to depicting an example correlation400between light source emission wavelength and light source temperature,FIG. 4shows an example correlation406between reflected illumination light intensity, as detected by the light sensor, and light source temperature linked via a plurality of tie lines404. Correlation406may generally be divided into a pass band406A and cutoff frequency ranges406B. Thus, at a first light source tuning temperature of 37 degrees C., represented by tie line404A, emission wavelength408A overlaps pass band406A. As depicted inFIG. 4, emission wavelength408A produces a sensed intensity of more than 90% of a maximum power reference intensity for the light sensor. Thus, with reference now toFIG. 3, a light classification condition is set to a value of 1 at thermal tuning module358.

At a second light source tuning temperature of 42 degrees C., represented by tie line404B ofFIG. 4, emission wavelength408B overlaps more of cutoff frequency range406B in comparison to emission wavelength408A. Thus, the sensed intensity of emission wavelength408B is less than the sensed intensity of emission wavelength408A. As depicted inFIG. 4, the sensed intensity of emission wavelength408B is less than 90% of the maximum power reference intensity, but more than 80% of the maximum power reference intensity. Thus, with reference now toFIG. 3, a light classification condition is set to a value of 2 at thermal tuning module358.

At a third light source tuning temperature, represented by tie line404C ofFIG. 4, emission wavelength408C lies within cutoff frequency range406B. As depicted inFIG. 4, the sensed intensity of emission wavelength408C is less than 80% of the maximum power reference intensity. Thus, with reference now toFIG. 3, a light classification condition is set to a value of 3 at thermal tuning module358.

Taken together, these light classification conditions and the corresponding light source tuning temperatures provide a basis for approximating a frequency response relationship between the cutoff frequency of the light filter and the emission wavelength of the light source. Specifically, it will be appreciated that increasing the temperature of the light source causes the emission wavelength of the light source to be shifted from the pass band of the light filter to the cutoff frequency range.

It will be appreciated that, once approximated, a frequency response relationship may provide a basis for generating the static operating temperature set point. Thus, continuing withFIG. 2, at218, method200includes generating a static operating temperature set point for the light source so that the emission wavelength of the light source does not overlap the cutoff frequency of the light filter by more than a predetermined permissible overlap threshold. For example, in some embodiments, the frequency response relationship may be compared to a lookup table included in the stored reference intensity data. The lookup table may include a plurality of static operating temperature set point decisions for a plurality of light classification conditions at various light source tuning temperatures. For example, the embodiment shown inFIG. 3includes stored intensity reference table360, which provides stored intensity reference data to thermal tuning module358. Table 2 provides an example lookup table for three light source tuning temperatures, where a light classification condition of 1 corresponds to a sensed power of greater than 90% of a maximum power reference; a light classification condition of 2 corresponds to a sensed power of less than 90% but more than 80% of the maximum power reference; and a light classification condition of 3 corresponds to a sensed power of less than 80% of the maximum power reference. For example, in the example described above, the sensed intensity data corresponding to the set of light source tuning temperatures (37° C., 42° C., 47° C.) was classified as (1, 2, 3). With reference to Table 2, the generated static operating temperature set point would be 37 degrees C.

Because the emission wavelength of the light source may comprise an emission band of the light source, the predetermined permissible overlap threshold is configured to define an acceptable amount of overlap of the cutoff frequency with the emission wavelength. This may provide an approach to defining a manufacturing tolerance for the illumination system. For example, the predetermined permissible overlap threshold may include a manufacturer-supplied tolerance corresponding to a statistical process control limit for the depth camera manufacturing process. Thus, continuing withFIG. 2, in some embodiments, generating a static operating temperature set point may include, at220, selecting the predetermined permissible overlap threshold so that at least 90% of a maximum power of the illumination light is passed to the light sensor by the light filter during depth camera operation. While the example predetermined permissible overlap threshold depicted inFIG. 2is defined relative to the maximum power of the illumination light, it will be appreciated that any suitable approach to defining the predetermined permissible overlap threshold may be employed. Example approaches include, but are not limited to, defining the predetermined permissible overlap threshold relative to a full-width, half-maximum of the filtered illumination light and/or relative to a variance of the light filter and/or the light source. In some embodiments, the predetermined permissible overlap threshold may be included with the stored intensity reference data, though it will be appreciated that in some embodiments, the predetermined permissible overlap threshold may be stored in any suitable location, including memory of the depth camera and/or the thermal tuning device. Alternatively, in some other embodiments, generating a static operating temperature set point may include, at222, selecting the predetermined permissible overlap threshold so that there is no overlap of the cutoff frequency of the light filter by the emission wavelength of the light source.

Optionally, method200may include, at224, indicating a depth camera fault based on a comparison of the sensed intensities and stored intensity reference data. This may provide an approach to diagnosing predefined faults through the observation of physically unrealistic operating conditions. In some embodiments, the stored reference intensity data may include depth camera fault information for setting a fault condition based on sensed intensities. Table 3 includes example predefined fault conditions stored in lookup table form, using the same light classification conditions as Table 2.

At226, method200concludes with programming a light source temperature controller to control a light source operating temperature to the static operating temperature during depth camera operation. For example, with reference to the example described above and toFIG. 3, the static operating temperature set point would be programmed into light source temperature controller324, so that, light source temperature controller324will control the temperature of light source322to 37 degrees C. once depth camera150A enters an operating mode.

While the above example method has been described with reference toFIG. 3, it will be appreciated that, in some embodiments, a portion or all of the elements described in thermal tuning device350may be included in the depth camera. This may provide on-board capability for thermally tuning the light source. For example,FIG. 5schematically shows another embodiment of a thermal tuning station104B having a depth camera150B, including an illumination system520and an imaging system530. Illumination system520includes a light source522and a light source temperature controller524. Imaging system530includes a band pass filter532and a light sensor534. Depth camera150B also includes thermal tuning module518and stored intensity reference data516stored in memory514for execution by processor512. It will be appreciated that in other embodiments the depth camera may output raw images for processing by a processor and memory of a game console506.