Patent Description:
In structured light scanning methods such as fringe projection, objects may be illuminated with structured patterns of light such as sinusoidal fringe patterns. The structured patterns may be geometrically distorted or phase modulated by the objects and then recorded as images with a camera at a known angle with respect to the projections. Techniques such as Fourier transforms may be used to calculate the distortions, displacements or phase modulations by analyzing the recorded images. For example, using a suitable phase unwrapping algorithm, pattern recognition or edge detection method, depth cues in recorded images may be converted into 3D coordinates for reconstruction. For example a continuous phase distribution which is proportional to the object height variations may be obtained and the system may be calibrated to map the unwrapped phase distribution to real world 3D coordinates.

Specifically 3D information may be obtained by taking an image of the object in an observation angle that is tilted at an angle to the direction of projection of the projected pattern. The projected pattern will then be distorted according to the surface shape of the object. The features of the projected pattern may be matched to the corresponding features in the distorted image by means of image processing algorithms. A problem arises if the object being measured is translucent. Projected light penetrates into the translucent object and is diffused in its depth. Examples of such material include wax, skin or teeth. As a result, the contrast of the pattern on the object surface decreases significantly, since the diffuse, unstructured scattered light from the object's depth is superimposed on the desired light reflected by the surface of the object. A reduced contrast may result in the inability to detect the projected features since the noise may become greater than the signal amplitude. Similarly, in the case of projector-assisted stereography, no correlation between the projected and recorded images may be found. A possible improvement in this situation is to increase the amount of light on the sensor to reduce the sensor's shot noise relative to the signal. However, this is technically limited by the full-well capacities of the image sensor pixels. Furthermore, the "object noise" (disturbances caused by the object itself e.g. from a rough surface or a non-uniform coloring) cannot be reduced by increasing the amount of light. <CIT> discloses a device for three-dimensional detection of a surface structure. <CIT> discloses a method and device for the contact-free measurement of surface contours. <CIT> discloses a device for optical 3D measurement of an object. <CIT> discloses a method and apparatus for triangulation-based distance measurement. <CIT> discloses an apparatus for dental confocal imaging.

An objective of the present invention is achieved by the camera as defined in claim <NUM>. Existing limitations associated with the foregoing, as well as other limitations, may be overcome by a device, method and system for utilizing an optical array generator to generate dynamic patterns in a camera/scanner for projection onto the surface of an object, while reducing noise and increasing data density for three-dimensional (3D) measurement. Herein, projected light patterns may be used to generate optical features on the surface of the object to be measured and optical 3D measuring methods which operate according to triangulation principles may be used to measure the object. A light pattern may be projected onto an object imaged by the camera. If the surface of the object is planar without any 3D surface variation, the pattern shown in the corresponding reflected image may be the same (or similar) to that of the projected light pattern. However, if the surface of the object is non-planar, the projected structured-light pattern in the corresponding image may be distorted by the surface geometry. Information from the distortion of the projected structured-light pattern may be used to extract the 3D surface geometry of the object being measured. By using various structured illumination patterns, along with noise reduction and data density increasing setups/techniques, 3D surface profiles of objects may be measured.

In one aspect, the present description provides a 3D camera, comprising: an optical array generator for generating a plurality of dynamic patterns for projection; a first imaging optics arranged within the camera to focus the plurality of dynamic patterns onto a surface of an object to be measured; an imaging sensor arranged within the camera to record a plurality of reflected images formed from reflection of the plurality of dynamic patterns by the surface of the object to be measured; and a second imaging optics arranged within the camera to image the plurality of reflected images onto the imaging sensor, wherein the optical array generator further comprises (i) a light source including a plurality of discrete regions wherein a luminous intensity of each of the plurality of discrete regions is controlled independently, (ii) a lens array comprising a plurality of lenses constructed to image light from the light source onto an image plane to form the plurality of dynamic patterns and, (iii) a collimator constructed to direct light of the light source onto the lens array and, wherein luminous intensities of the plurality of regions of the light source are electronically controlled to generate the plurality of dynamic patterns in a time varying manner.

In another aspect, the present description may include one or more of the following features (i) a camera wherein each of the plurality of lenses is biconvex, (ii) a camera wherein the plurality of discrete regions of the light source are selected from the group consisting of LED dies, laser diodes and an end of a plurality of optical fibers that have other light sources attached to the other end, (iii) a camera further comprising multiple collimators and multiple light sources, (iv) a camera further comprising a digital signal processing unit for processing the recorded images, (v) a camera wherein the imaging sensor is constructed to perform in-pixel demodulation, (vi) a camera wherein the light source is a 2x2 LED array of LED dies, (vii) a camera wherein the wherein each of the plurality of lenses is spherical, (viii) a camera wherein the wherein each of the plurality of lenses is cylindrical, (ix) a camera wherein the thickness of the lens array is between <NUM> to <NUM>, (x) a camera wherein the lens array comprises a glass carrier, two polymer layers molded on opposite sides of the glass carrier and a structured mask applied to the glass carrier for selectively altering light of the light source, (xi) a camera wherein the mask is a structured color filter for impressing a binary or a color code on the light from the light source, (xii) a camera wherein the plurality of dynamic patterns are non-periodic, (xiii) a camera wherein the centers of the plurality of lenses of the lens array are individually offset, to produce the non-periodic dynamic patterns, (xiv) a camera wherein the plurality of dynamic patterns are periodic, (xv) a camera wherein the lens array comprises entrance and exit lens pairs, wherein the entrance lenses act as Fourier lenses and the exit lenses act as field lenses and wherein each pair creates a sub-image in the image plane, (xvi) a camera wherein the lens array comprises a first lens array having entrance lenses which act as Fourier lenses and a second lens array having exit lenses which act as field lenses and wherein the first and second micro-lens arrays have a single sided profile and are constructed to face each other, and (xvii) any combinations thereof.

In one aspect, the present description provides a method for generating a plurality of dynamic patterns for measuring an object, the method comprising: electronically controlling the luminous intensities of each of a plurality of discrete regions of a light source to generate structured light for a collimator; directing the structured light from the light source onto a lens array using the collimator; producing sub-images of the structured light using a plurality of lenses of the lens array wherein the sub-images are formed in a focal plane of the lens array to form the plurality of dynamic patterns; focusing the plurality of dynamic patterns onto a surface of an object to be measured; imaging a plurality of reflected images onto the imaging sensor; recording the plurality of reflected images with the imaging sensor, and processing the plurality of recorded images to obtain a three-dimensional image of the object using a modulation signal of the light source.

In one aspect, the present description provides a method including one or more of the following features: (i) a method further comprising reducing the average irradiance of the object by projecting and evaluating dynamic patterns in a temporal sequence to receive the same or substantially the same number of 3D data points in total as the number of 3D data points that would be received for projecting a full pattern, (ii) a method wherein the average irradiance of the object is reduced by a factor. In one aspect, the factor is a factor of <NUM>, (iii) a method further comprising: generating non-periodic patterns by individually offsetting centers of the plurality of lenses of the lens array and (iv) any combinations thereof.

In yet another aspect, the present description provides a system for generating a plurality of dynamic patterns for measuring an object, the system comprising: at least one processor operable to: electronically control the luminous intensities of each of a plurality of discrete regions of a light source to generate structured light for a collimator; directing the structured light from the light source onto a lens array using the collimator; producing sub-images of the structured light using a plurality of lenses of the lens array wherein the sub-images are formed in a focal plane of the lens array to form the plurality of dynamic patterns; imaging the plurality of dynamic patterns onto a surface of the object to be measured with illumination optics; recording a plurality of reflected images from the surface of the object with an imaging sensor, and processing the plurality of reflected images to obtain a three-dimensional image of the object using a modulation signal of the light source.

Further features and advantages, as well as the structure and operation of various embodiments herein, are described in detail below with reference to the accompanying drawings.

Example embodiments may become more fully understood from the detailed description given herein below and the accompanying drawings, wherein like elements are represented by like reference characters, which are given by way of illustration only and thus are not limitative of the example embodiments herein and wherein:.

Different ones of the Figures may have at least some reference numerals that are the same in order to identify the same components, although a detailed description of each such component may not be provided below with respect to each figure.

The embodiment in <FIG> is outside the of the scope of the invention as claimed.

In accordance with example aspects described herein, a device, method and system are provided for generating dynamic patterns in a camera for example a dental camera for projection onto the surface of an object for three-dimensional (3D) measurement.

In one aspect, an optical array generator <NUM> for generating projection patterns may be provided in a camera <NUM>, for example a dental camera. The optical array generator may comprise a collimator <NUM>, an LED array <NUM> and a lens array <NUM>. The collimator <NUM> may be constructed to direct light of the LED array <NUM> onto the lens array <NUM> which comprises sub lenses <NUM>. A computer system <NUM> may control and synchronize (i) exposure times of image sensors <NUM> and (ii) the LEDs of the LED array <NUM> to emit light in a predetermined pattern. For example, some LEDs may be turned on at the same time as other LEDs are turned off to produce a predetermined pattern of structured light. In an embodiment herein, a temporal lighting sequence of the LEDs may be repeated periodically. Each sub lens <NUM> of the lens array <NUM> may be constructed to produce an image of the controlled LED array <NUM>. As such an image/structured light produced by the LED array <NUM> may be multiplied into an array of sub-images <NUM> by the lens array <NUM>. The sub-images <NUM> of lens array <NUM> combine in the focal plane <NUM> of the lens array <NUM> to form a combined image <NUM>. Lenses <NUM> of the lens array <NUM> may be biconvex to allow for a high light efficiency due to the use of high numerical apertures in the illumination path. In an embodiment herein, a first interface of the biconvex lens may act as a Fourier lens generating an image. The second interface may act as a field lens, directing light to a pupil of an imaging optics of the camera system. In another embodiment, the camera <NUM> is provided with projection optics to project the combined image <NUM> onto a surface of the object <NUM> to be measured. In an embodiment herein, the images produced by the LED array <NUM> for conversion into sub-images may be structured and variable (non-static). In an embodiment herein, the light source may comprise LED dies <NUM>. In another embodiment, laser diodes or other light emitting elements (not shown) may be used. In yet another embodiment, the light source may be formed from one end of a plurality of optical fibers that have light sources attached to the other end. In yet another embodiment, multiple collimators <NUM> each having multiple light sources may be used.

According to another example embodiment herein, a camera system <NUM> is provided. The camera system may include an optical array generator <NUM> configured to generate projection patterns onto an object <NUM> to be measured, a sensor <NUM> for recording reflected projection patterns, and a digital signal processing unit <NUM> for processing the recorded images. In an embodiment, the sensor <NUM> may include an in pixel demodulation function wherein the sensor comprises a photodiode, preamplifier synchronous demodulator and an integrator. In another embodiment, the sensor <NUM> is a 2D-sensor for recording a continuous sequence of images for different projection patterns generated by the optical array generator. In another embodiment, the system <NUM> comprises an acquisition unit <NUM> for further processing the recorded images and displaying a three-dimensional measurement of the object <NUM>.

According to another example embodiment herein, a method for utilizing an optical array generator <NUM> to generate dynamic patterns in a camera for projection onto the surface <NUM> of an object for three-dimensional (3D) measurement is provided. According to an example embodiment herein, the method comprises generating a plurality of projection patterns from an LED array <NUM>, directing each of the plurality of projection patterns of the LED array <NUM> onto a lens array <NUM> using a collimator <NUM>, producing sub images <NUM> of each plurality of the projection patterns with sub lenses <NUM> of the lens array wherein the sub images <NUM> are formed in a focal plane <NUM> of the lens array <NUM> to form a combined image <NUM>, focusing the plurality of projection patterns onto a surface <NUM> of an object <NUM> to be measured; imaging a plurality of reflected images onto the imaging sensor <NUM>; recording the plurality of reflected images from the surface of the object <NUM> with a sensor <NUM> and processing the plurality of recorded images to obtain a three-dimensional image of the object.

In an embodiment, generating a plurality of projection patterns may include reducing the average irradiance of the object to be measured by generating time varying patterns with the LED array for projection, wherein, one or more indicia (e.g., shapes, stripes, dots and/or otherwise) of a projected pattern are omitted. In an embodiment, every nth, for example second, bright indicia (e.g., stripe, checkerboard patterns) of the projected pattern may be omitted through the control of the LED array <NUM> by the computer system <NUM>. In an embodiment in which every second bright indicia (e.g., stripe) of a projected pattern is omitted, the average irradiance of the object <NUM> may be reduced by a factor of two, which also halves the diffuse background radiation of the object <NUM> while the signal amplitude of the remaining fringes remains the same or substantially the same. In an embodiment in which every second bright indicia (e.g., stripe) of a projected pattern is omitted, the signal to noise ratio may be improved by a factor of sqrt(<NUM>). The omission of stripes decreases the number of available features for 3D reconstruction, therefore alternating patterns shifted by a factor of a period are projected in a temporal sequence such that the same or substantially the same number of 3D data points in total for 3D reconstruction are obtained, as if there had been no omissions. For example, in an embodiment, a first projection pattern and a second projection pattern, may be obtained from a standard projection pattern comprising alternating bright and dark stripes. The first projection pattern may be obtained by omitting every second bright stripe of the standard projection pattern. The second projection pattern may be obtained by shifting the first projection pattern by half a period. By projecting the first projection pattern and the second projection pattern (i.e. the first projection pattern shifted by half a period), in an alternating fashion, the same or substantially the same number of 3D data points may be obtained as if the standard projection pattern had been used for projection, thus reducing the number of bright stripes per projection that are incident on the object being measured and thus the average irradiance of the object <NUM> to be measured.

In another embodiment, the recording step may be performed with a sensor <NUM> provided with an in pixel demodulation function wherein the sensor comprises a photodiode, preamplifier, synchronous demodulator and and/or integrator. In another embodiment, the recording step may be performed with a 2D sensor for recording a continuous sequence of images for different projection patterns generated by the optical array generator. In another embodiment, the processing step comprises locating projected features in the recorded images and processing the recorded images into a three-dimensional measurement of the object <NUM>.

In yet another embodiment herein lenses <NUM> of the lens array <NUM> may be spherical or cylindrical. The device method and system may be useful for reducing the noise generated in three dimensional measurements and to increase the density of data gathered when scanning an object. The device method and system are described in more detail hereinafter.

<FIG> illustrates a block diagram of a camera system <NUM> comprising a camera <NUM> for generating dynamic patterns in a camera, and which may be constructed and operated in accordance with at least one example embodiment herein. The system may also comprises a computer system <NUM> for generating and displaying three dimensional representations of an object. The computer system <NUM> may be electrically connected to the camera <NUM>. The camera may include an optical array generator <NUM> comprising a spatially and temporally modulated light source (for example, LED array <NUM>), a collimator <NUM>, and a lens array <NUM> comprising sub lenses <NUM> for generating a combined image <NUM> of the LED array. The combined image <NUM> may comprise sub images <NUM> wherein each sub lens may generate a sub image <NUM>. An imaging optic <NUM> for illumination may project the combined image onto the object <NUM> to be measured. In an embodiment herein, the imaging optic <NUM> projects dynamic patterns comprising varying combined images onto the object <NUM> during a scanning process or exposure. The object <NUM> may be for example a tooth, skin, gums, ceramics, amalgam, gold and/or otherwise. The camera further comprises an imaging optic <NUM> for detection of the images reflected by the object <NUM> during a scanning process or exposure. The received images are propagated by, for example, a deflecting mirror <NUM> or a <NUM>° prism to a sensor <NUM> to be recorded. The sensor may be a standard 2D sensor or a sensor with in-pixel demodulation function wherein each pixel of the sensor may include a photodiode, a preamplifier, a synchronous demodulator and an integrator. The photodiode of each pixel may convert the light from the object <NUM> into photocurrent. The photocurrent may then amplified and fed into the synchronous demodulator. The demodulator may be synchronized by the modulation signal of the light sources of the optical array generator <NUM>. It may be seen that the modulation frequency may be limited only by the light sources. As such, the frequency used for modulation may be up in the MHz range if suitable LEDs or laser diodes are used. Using a high modulation frequency (such as between <NUM> - <NUM> or between <NUM> -<NUM>) may have the advantage, that the pixel integrators may not be saturated, even when very high illumination intensities are being used. The demodulator output may be summed over the exposure time by the integrator. At the end of the exposure, the integrated signal may be proportional to the amplitude of the light modulation. Constant background light is suppressed by the demodulation. For read out, the pixels of the image matrix may be addressed sequentially by a switch matrix and the voltages of the integrators may be digitized and transferred to the digital signal preprocessing unit <NUM>. When the sensor is a standard 2D-sensor, it may record a continuous sequence of images for different illumination patterns generated by the optical array generator <NUM>.

During the exposure/scan the digital signal preprocessing unit <NUM> may collect the single image frames of the sensor <NUM> and store the image in the local memory of this unit. The images may either be preprocessed on the processing unit <NUM> of the camera or transmitted to the acquisition unit <NUM> for further processing steps. Processing may include steps like image filtering to reduce noise, subtracting images generated with different light source to eliminate background light and edge detection. The acquisition unit <NUM> may comprise a display <NUM> and computer processor including a central processing unit (CPU) <NUM> and a random access memory (RAM) <NUM>.

In an embodiment herein, the preprocessed image data may be further analyzed to extract 3D point clouds representing the surface. A distortion correction applied to the points corrects for the imaging properties of the optics. When the camera is moved while recording, a series of point clouds results showing different sections of the object <NUM> from different viewpoints. These point clouds are rotated and translated individually by the CPU <NUM> to give a consistent 3D-model. This 3D-model is finally rendered on the display <NUM>.

<FIG> is a basic representation of a projector for fringe projection. Light from a source <NUM> is directed onto a mask <NUM> by the collimator <NUM>. Light from the mask <NUM> is projected onto an object <NUM> by the imaging optics <NUM> and thus becomes visible on the surface <NUM>.

In <FIG> provides a schematic representation of the optical array generator <NUM> for generating time varying dynamic patterns. <FIG> provides a top view of the LED array <NUM> of the optical array generator <NUM>. A collimator <NUM> directs the light of the LED array <NUM> onto a lens array <NUM>. Each sub-lens <NUM> of the lens array will produce a sub-image <NUM> of the LED array. The LED array is a 2X2 LED array <NUM> as shown in <FIG>.

The sub-images <NUM> combine in the focal plane <NUM> of the lens array <NUM> to form a combined image <NUM>. The combined image <NUM> in this plane may then be imaged onto the object surface by means of the imaging optics for illumination <NUM> (projection optics) of the scanner. In an example embodiment herein, as shown in <FIG>, two light sources (A, B) of the LED array <NUM> are placed in the object plane (X-Y plane) of the collimator <NUM>. Behind the collimator <NUM>, the beams originating from the light sources, form two tilted beams <NUM>. The beams may be focused by the lens array <NUM> into an image plane <NUM>. Each individual lens may generate one focus pair (A', B'). The offset between the focus points A' and B' may be determined by the choice of the incidence angle of the tilted beams <NUM> and the focal length of the lens array. In an embodiment, multiple collimators <NUM> and multiple light sources may be used. Herein, a light source is coupled with a collimator <NUM>. Individual collimators may be aligned directly under the required angle of incidence to the lens array <NUM>. However, to save space it may be advantageous to align the collimators in parallel and set the angle of incidence of light to the lens array <NUM> using deflecting elements e.g. mirrors.

<FIG> illustrates another embodiment herein. A collimator assembly <NUM> may focus the light from, for example, two LED dies <NUM> onto a cylindrical, biconvex lens array <NUM> comprising entry and exit lens pairs (<NUM>, <NUM>), wherein each pair may create a stripe in the image plane <NUM> for each LED die <NUM>. In an embodiment herein, the centers of the two LED dies may be spaced <NUM>mm apart (or for example between <NUM> - <NUM> apart) and the collimator may have an effective focal length of <NUM> mm. This may result in a tilt angle of atan ((<NUM>mm / <NUM>) / <NUM>mm) = <NUM> ° (or for example between <NUM>° - <NUM>° or between <NUM>° - <NUM>°) for the parallel light bundles exiting the collimator assembly <NUM>. Due to a refractive index of, for example, n = <NUM> of the lens array <NUM>, the angle may be reduced to <NUM> ° in the substrate of the array. From a requirement that the stripes should have a spacing of <NUM>µ, (or for example between 2µ to <NUM>), it thus results in a thickness of the lens array of (<NUM>µm / <NUM>) / tan (<NUM> °) = <NUM>mm (or for example between <NUM> to <NUM>). The distance between the centers of two adjacent micro lenses (pitch) may be twice the stripe spacing (e.g. <NUM>µm). Section <NUM> shows an enlarged, single pair of lenses of the array in cross section. The entrance lenses <NUM> may act as Fourier lenses and generate foci in the image plane <NUM>. The exit lenses <NUM> may act as field lenses ensuring that the beam cones behind the foci are perpendicular to the image plane <NUM>. As a result, the light may be imaged on the test object <NUM> by the lens <NUM> without vignetting.

<FIG> illustrates yet another embodiment herein. A lens array <NUM> may comprise a glass carrier <NUM> with two polymer layers molded thereto and a structured mask <NUM> applied to the glass carrier <NUM>. Herein, points or lines may be selectively hidden for certain light sources by the use of the mask <NUM>. In another embodiment herein, the mask may be a structured color filter, wherein a binary or a color code may be impressed on a periodic pattern produced by the LED array <NUM>.

<FIG> illustrates yet another embodiment herein a robust micro-lean array configuration may be realized wherein the configuration may be a "sandwich" configuration and may comprise a plurality of micro-lens arrays <NUM> (for example two micro-lens arrays) each having a thick, single sided profile and which may be mounted with their lenses <NUM>, <NUM> aligned and facing each other as shown in <FIG>. Herein incoming parallel rays <NUM> may be incident on entrance lenses <NUM> which may act as Fourier lenses and generate foci in the image plane <NUM>. Exit lenses <NUM> may act as field lenses ensuring that beam cones behind the foci are perpendicular to the image plane <NUM>.

Having described a system <NUM> for generating dynamic patterns in a camera for projection onto the surface of an object for three-dimensional (3D) measurement, reference will now be made to <FIG>, which shows a block diagram of a computer system <NUM> that may be employed in accordance with at least some of the example embodiments herein. Although various embodiments are described herein in terms of this exemplary computer system <NUM>, after reading this description, it will become apparent to a person skilled in the relevant art(s) how to implement the disclosure using other computer systems and/or architectures.

In one example embodiment herein, at least some components of the computer system <NUM> may form or be included in the computer system <NUM> of <FIG>. The computer system <NUM> includes at least one computer processor <NUM>. The computer processor <NUM> may include, for example, a central processing unit <NUM> as shown in <FIG>, a multiple processing unit, an application-specific integrated circuit ("ASIC"), a field programmable gate array ("FPGA"), or the like. The processor <NUM> may be connected to a communication infrastructure <NUM> (e.g., a communications bus, a cross-over bar device, or a network). In an embodiment herein, the processor <NUM> includes a CPU <NUM> that obtains image data from the preprocessing unit <NUM> of the camera <NUM> having a sensor <NUM> with an in-pixel demodulating function. The image data may be temporarily stored in memory and then analyzed. Upon moving the camera <NUM> while recording, a series of point clouds are formed. The CPU <NUM> may rotate and translate the point clouds to give a consistent 3D-model for rendering on the display interface <NUM> of the computer system <NUM>. In another embodiment, the CPU may match image features detected by the sensor <NUM> to the projected features and convert them to a 3D-point cloud by triangulation with each image resulting in a separate point cloud. Herein, the sensor may not possess in-pixel demodulating functionality. When the camera is moved a series of point clouds results. These point clouds may be rotated and translated individually by the CPU <NUM> to give a consistent 3D-model. This 3D-model is finally rendered on the display <NUM>. In an embodiment herein, direct detection of edges or features in the image data may be carried out. In yet another embodiment herein, the digital signal preprocessing unit <NUM> of the camera <NUM> may be incorporated into the computer system <NUM>.

The display interface (or other output interface) <NUM> forwards video graphics, text, and other data from the communication infrastructure <NUM> (or from a frame buffer (not shown)) for display on a display unit <NUM> (which, in one example embodiment, may form or be included in the display unit <NUM> of <FIG>). For example, the display interface <NUM> may include a video card with a graphics processing unit.

The computer system <NUM> also includes an input unit <NUM> that may be used by a user of the computer system <NUM> to send information to the computer processor <NUM>. In one example embodiment herein, the input unit <NUM> may form or be included in the input unit <NUM> of <FIG>. The input unit <NUM> may include a trackball or other input device. In one example, the display unit <NUM>, the input unit <NUM>, and the computer processor <NUM> may collectively form a user interface.

One or more steps of generating the dynamic patterns may be stored on a non-transitory storage device in the form of computer-readable program instructions. To execute a procedure, the processor <NUM> loads the appropriate instructions, as stored on storage device, into memory and then executes the loaded instructions.

The computer system <NUM> of <FIG> may comprise a main memory <NUM>, which may be a random access memory ("RAM") <NUM> as shown in <FIG>, and also may include a secondary memory <NUM>. The secondary memory <NUM> may include, for example, a hard disk drive <NUM> and/or a removable-storage drive <NUM> (e.g., a floppy disk drive, a magnetic tape drive, an optical disk drive, a flash memory drive, and the like). The removable-storage drive <NUM> reads from and/or writes to a removable storage unit <NUM> in a well-known manner. The removable storage unit <NUM> may be, for example, a floppy disk, a magnetic tape, an optical disk, a flash memory device, and the like, which is written to and read from by the removable-storage drive <NUM>. The removable storage unit <NUM> may include a non-transitory computer-readable storage medium storing computer-executable software instructions and/or data.

In further alternative embodiments, the secondary memory <NUM> may include other computer-readable media storing computer-executable programs or other instructions to be loaded into the computer system <NUM>. Such devices may include a removable storage unit <NUM> and an interface <NUM> (e.g., a program cartridge and a cartridge interface); a removable memory chip (e.g., an erasable programmable read-only memory ("EPROM") or a programmable read-only memory ("PROM")) and an associated memory socket; and other removable storage units <NUM> and interfaces <NUM> that allow software and data to be transferred from the removable storage unit <NUM> to other parts of the computer system <NUM>.

The computer system <NUM> also may include a communications interface <NUM> that enables software and data to be transferred between the computer system <NUM> and external devices. Such an interface may include a modem, a network interface (e.g., an Ethernet card, Bluetooth, or an IEEE <NUM> wireless LAN interface), a communications port (e.g., a Universal Serial Bus ("USB") port or a FireWire® port), a Personal Computer Memory Card International Association ("PCMCIA") interface, and the like. Software and data transferred via the communications interface <NUM> may be in the form of signals, which may be electronic, electromagnetic, optical or another type of signal that is capable of being transmitted and/or received by the communications interface <NUM>. Signals are provided to the communications interface <NUM> via a communications path <NUM> (e.g., a channel). The communications path <NUM> carries signals and may be implemented using wire or cable, fiber optics, a telephone line, a cellular link, a radiofrequency ("RF") link, or the like. The communications interface <NUM> may be used to transfer software or data or other information between the computer system <NUM> and a remote server or cloud-based storage (not shown).

One or more computer programs or computer control logic may be stored in the main memory <NUM> and/or the secondary memory <NUM>. The computer programs may also be received via the communications interface <NUM>. The computer programs include computer-executable instructions which, when executed by the computer processor <NUM>, cause the computer system <NUM> to perform the methods as described hereinafter. Accordingly, the computer programs may control the computer system <NUM> and other components of the camera system <NUM>.

In another embodiment, the software may be stored in a non-transitory computer-readable storage medium and loaded into the main memory <NUM> and/or the secondary memory <NUM> of the computer system <NUM> using the removable-storage drive <NUM>, the hard disk drive <NUM>, and/or the communications interface <NUM>. Control logic (software), when executed by the processor <NUM>, causes the computer system <NUM>, and more generally the camera system in some embodiments, to perform the some of the methods described hereinafter.

Lastly, in another example embodiment hardware components such as ASICs, FPGAs, and the like, may be used to carry out the functionality described herein. Implementation of such a hardware arrangement so as to perform the functions described herein will be apparent to persons skilled in the relevant art(s) in view of this description.

Having described the computer system <NUM> of <FIG>, the camera system <NUM> will now be further described in conjunction with <FIG> which show methods of generating projection patterns using different lens types.

According to an example embodiment herein, time varying patterns may be generated for projection by omitting some stripes of a projected pattern, for example, every second bright stripe of the projected pattern. This may reduce the average irradiance of the object by a factor of two, which also halves the diffuse background radiation of the object. The signal amplitude of the remaining fringes however remains the same. This will therefore improve the signal to noise ratio by a factor of sqrt(<NUM>). This is because pixel-noise is dominated by the shot noise on modern image sensors. Shot noise arises because pixels may be regarded as counters for randomly arriving photons. For a constant light intensity, the statistics of counted photons may be approximated by a normal distribution, having a standard deviation of sqrt(n), where n is the average number of counted photons. Thus the signal to noise ratio(S/N) is S/N=n/sqrt(n)=sqrt(n). The read out of a single pixel may give a signal proportional to the sum of the counted background light photons nb and the desired signal photons ns. Because in translucent materials the background light might dominate the signal (nb>>ns), the signal to noise ratio may be determined by the intensity of the background light S/N = sqrt(n) -sqrt(nb). Thus in an example embodiment herein where the diffuse scattered background light nb is halved by omitting every second bright stripe, and wherein the signal ns is kept constant because the intensity of the remaining stripes is kept unchanged, the signal to noise ratio is improved by a factor of sqrt(<NUM>).

In an example embodiment herein, the reduction of the bright stripes incident on the object <NUM> being measured, reduces the number of available features for the 3D-reconstruction. Projecting and evaluating several different patterns in a temporal sequence to receive the same number of 3D data points in total, as if there had been no omissions allows for 3D reconstruction with the same spatial resolution. For example, as shown in <FIG>, a first projection pattern <NUM> and a second projection pattern <NUM>, may be obtained from a standard projection pattern <NUM> comprising alternating bright stripes <NUM> and dark stripes <NUM>. The first projection pattern <NUM> may be obtained by omitting every second bright stripe 74b of the standard projection pattern <NUM>. The second projection pattern <NUM> may be obtained by shifting the first projection pattern <NUM> by half a period (<NUM>*P1). By projecting the first projection pattern <NUM> and the second projection pattern <NUM> (i.e. the first projection pattern <NUM> shifted by half a period), in an alternating fashion, the same number of 3D data points may be obtained as if the standard projection pattern <NUM> had been projected, thus reducing the number of bright stripes <NUM> per projection that are incident on the object being measured and thus reducing the average irradiance of the object to be measured while obtaining the same number of data points for reconstruction. By superposing the first projection pattern <NUM> and the second projection pattern <NUM> the standard projection pattern <NUM> may be obtained. In an example embodiment herein, the dark stripes <NUM> may correspond to an LED of the LED array <NUM> that is turned off and the bright stripes <NUM> may correspond to an LED of the LED array <NUM> that is turned on. It may be seen by a person of ordinary skill in the art (POSA) that the technique may be adapted for varying projection patterns. For example, every second and third bright strip of another standard projection pattern (not shown) may be omitted to obtain another first projection pattern (not shown) wherein the another first projection pattern is shifted by one-third of a period to obtain another second projection pattern(not shown) and the another second projection pattern is shifted by one-third of a period to obtain a third projection pattern(not shown), and wherein superposition of the another first, another second and third projection patterns will produce the another standard projection pattern.

To obtain the projection patterns, the intensity of each LED/die in the LED array may be controlled individually.

Turning now to <FIG>, wherein only one LED (A) of the four LEDs (A,B,C,D) is activated, a dot pattern <NUM> may be generated in the image plane of the lens array with the pattern having only a quarter (¼) of the features to be transmitted in an exposure and a quarter (¼) of the mean light intensity. Accordingly, a lower amount of scattered light results compared to the amount of scattered light that would result when all <NUM> LEDs are turned on at the same time. It may be seen that the four LED-dies (A, B, C, D), are imaged by the setup to an array of downsized images. When only one LED is turned on, a thinned dot pattern is created. If another LED is turned on, and the first LED turned off, a shifted thinned dot pattern is created. The full information in the LED array <NUM> to be transmitted to object <NUM> is therefore obtained by turning the <NUM> LEDs on successively and recording corresponding reflected images for each LED that is turned on.

It may be seen that whereas arrays of spherical lenses may be used to generate dot patterns as shown in <FIG>, a linear array of cylindrical lenses may be used to generate fringe-patterns as shown in <FIG>. Single sided lenses may also be used. Herein, the light sources (LEDs) may be arranged in a row perpendicular to the image plane <NUM>. Each lens may generate a stripe-shaped image of each light source as shown in <FIG>. By sequentially activating the respective light sources, laterally shifted fringe patterns may be generated for projection and recording.

In a further embodiment according to the invention, stereoscopic imaging and reconstruction may be used. Stereoscopic object reconstruction reconstructs a 3D object by deducing the spatial shape and position of the object through parallax between corresponding pixels from different images of the object as observed from multiple viewpoints. The principle of stereo vision techniques is triangulation, in which the unique contours of the object may be determined with the photos taken from two unparalleled cameras. Stereo vision approaches may rely on the correspondence between photo elements from two cameras which sometimes may be difficult to determine. In order to avoid ambiguity in stereoscopic object reconstruction projection patterns that are non-periodic may be used. These non-periodic patterns may also be generated by the methods described above if the centers of the lenses in a lens array <NUM> are individually offset. The offset of the lenses from the nominal grid positions may be random, and may not exceed half the lens diameter. Likewise, aperiodic tiling may serve as a basis for the lens arrangement.

Another way to avoid the periodicity of the pattern of a regular lens array may be to place a patterned mask <NUM> near the focal plane of the lens array. Herein individual stripes or spots generated by the combination of certain lenses and light sources may be suppressed. For example, in stereo imaging, one light source may be used to create a complete stripe or dot pattern for a high density of 3D-points and another source may be used to generate a thinned, random dot pattern to provide additional information for unambiguous matching of stereo images, as shown in <FIG>. A structured color filter may also be used in the focal plane of the lens array <NUM> to add an additional color code on a periodic pattern generated by the lens array <NUM>, said code being individually changeable for each light source.

A time sequential projection may require multiple image acquisitions for a fulldensity 3D reconstruction. With moving objects or moving cameras/scanners, this may lead to unwanted artifacts in the object reconstruction. It may therefore be desirable to acquire the complete 3D-infomation at one time. An alternative to the time sequential acquisition is the spectral coding of the individual image frames. For this purpose a plurality of narrowband light sources with small spectral overlap may be used. If all light sources are active at the same time, multiple colored patterns may be superposed simultaneously on the object. A color camera (not shown) with corresponding spectral channels may then be able to record the individual images simultaneously. In the simplest case, a standard RGB color sensors may be used for this purpose. If more than three colors are used, a hyperspectral sensor may be used.

In yet another embodiment, complementary patterns ay be generated. If the patterns have the same fill factor, diffuse background noise may be eliminated by subtracting the two complementary object images (for example, two patterns wherein a bright region in one pattern corresponds to a dark region in the other), since the diffuse background is identical in both images. Examples of complementary patterns may include checkerboard patterns, stripe patterns, or dot patterns each offset by half a period or otherwise.

Advantages of the embodiments described herein include robustness, as there are no moving parts. Moreover since the optical setup may not include slides or grid structures, light from the collimator <NUM> passes through the lens array <NUM> to the imaging optics for illumination <NUM> with little to no absorption. Moreover, in comparison with other devices such as cameras that use digital micro mirror devices (DMDs) or liquid crystal devices (LCDs), space may be saved due to compact size.

In view of the foregoing description, it may be appreciated that the example embodiments described herein provide a device, method and system for generating dynamic projection patterns in a camera.

Although methods and materials similar to or equivalent to those described herein may be used in the practice or testing of the disclosure, suitable methods and materials are described above.

Claim 1:
A camera (<NUM>), comprising:
an optical array generator (<NUM>) for generating a plurality of dynamic patterns (<NUM>,<NUM>,<NUM>,<NUM>) for projection;
a first imaging optics (<NUM>) arranged within the camera (<NUM>) to focus the plurality of dynamic patterns from the optical array generator onto a surface (<NUM>) of an object (<NUM>) to be measured;
an imaging sensor (<NUM>) arranged within the camera (<NUM>) to record a plurality of reflected images formed from reflection of the plurality of dynamic patterns by the surface of the object to be measured; and
a second imaging optics (<NUM>) arranged within the camera to image the plurality of reflected images onto the imaging sensor,
wherein the optical array generator further includes (i) a temporally and spatially modulated light source (<NUM>,<NUM>) including a plurality of discrete regions (A,B;C,D) wherein a luminous intensity of each of the plurality of discrete regions is controlled independently, and wherein the plurality of discrete regions of the light source are LED dies, laser diodes (ii) a lens array (<NUM>,<NUM>) comprising a plurality of sub lenses (<NUM>) and, (iii) a collimator (<NUM>) constructed to direct light of the light source onto the lens array,
wherein each sub lens (<NUM>) of the lens array (<NUM>) is constructed to produce an image of the controlled LED array of the light source (<NUM>) such that an image/structured light produced by the LED array of the light source (<NUM>) is multiplied into an array of sub-images (<NUM>) by the lens array (<NUM>), and the sub-images (<NUM>) of the lens array (<NUM>) combine in the focal plane (<NUM>) of the lens array (<NUM>) to form a combined image (<NUM>), and,
wherein luminous intensities of the plurality of regions (A,B;C;D) of the light source (<NUM>,<NUM>) are electronically controlled to generate the plurality of dynamic patterns in a time varying manner,
wherein the light source is a 2x2 LED array of LED dies, wherein the full information in the LED array (<NUM>) to be transmitted to the object (<NUM>) is obtained by turning the four LEDs on successively and recording corresponding reflected images for each LED that is turned on.