Patent Application
20200278203
The present invention relates, in a first aspect, to a method for measuring a distance to a target, based on the operation of a thermo-optical lens without the need of emitting a probing light on the target or the need of using any sensor specific for performing the distance measuring.
The present invention also relates, in a second aspect, to a system for measuring a distance to a target, adapted to implement the method of the first aspect of the invention. In a third aspect, the present invention relates to a computer program including code instructions that when executed on at least one processor implement the steps of the method of the first aspect of the present invention.
There are different proposals in the state of the art intended to perform distance measurements to a target. Some of said proposals are disclosed in the patent documents listed below.
U.S. Pat. No. 5,764,786A discloses a moving object measurement device employing a three-dimensional analysis to obtain characteristics of the moving object, including a distance calculation based on the use of two cameras or stereoscopy. Using two cameras for distance analysis requires to have two separated full optical systems working at the same time, and both cameras must focus on the same object to get information about distance, so distance information from various objects at the same time cannot be obtained.
U.S. Pat. No. 4,827,303A discloses a distance measuring device for automatically detecting an object distance on the basis of triangulation by unidirectional optical scanning, generally by changing the angle of a camera. When using only one camera and different angles for distance measuring two main inconveniences appear: a mechanical system is needed to change position making it unsuitable for any portable device, real time calculation is unavailable and images need to be post processed.
U.S. Pat. No. 6,426,775B1 and U.S. Pat. No. 6,792,203B1 disclose calculating distance to an object by analysing the variation of the object's luminance. Using light to measure distance to an object requires to calculate the relative brightness between the object and the apparatus, a pre-lightning is needed before every calculation in order to calibrate the scene, camera focus has to point into a main object, and distances to the rest of objects are calculated by their relative brightness. This method only works under low ambient light conditions. U.S. Pat. No. 3,652,161A discloses an apparatus and method for measuring distance in which a coarse measurement of the distance is made by detecting the time of travel of a pulse, such as a laser pulse.
U.S. Pat. No. 3,901,597A discloses measuring distance to an object by using a focusing lens to direct laser optical energy into a focal saddle, where the distance measurement is determined by the position of the focusing lens where an object is present inside said focal saddle.
U.S. Pat. No. 6,697,147B2 also discloses a distance measurement method using a laser source, but in this case the distance measurement is performed by calculating a position relative to a target analysing an acquired image including three or more points formed on a target by respective laser beams.
All of said proposals based on laser beams require of complex, expensive and specific mechanisms for distance measuring, including one or more laser sources, optics, and sensors able to gather information from one or more collimated beams that scatters light on the surface of an object and/or is reflected thereon. Moreover, the information or data gathered by the sensors is presented as a number and does not provide any image of what is being measured.
U.S. Pat. No. 4,983,033A discloses an automatic range finder for a camera for setting the focus position of the camera to correspond to the closest object to the camera within a specified field of view, where the distance to the object is determined by source light triangulation. Triangulation starts from the same principle as stereoscopy, and therefore shares the same drawbacks with it. In this case an optical system and a light source is included in the system. The optical system will perform an auto focus to the first object that reflects light from the light source. Through triangle equations, a distance is calculated from the first object.
It is, therefore, necessary to provide an alternative to the state of the art which covers the gaps found therein, by providing a method and a system for measuring a distance to a target which does not have the above mentioned drawbacks of the proposals of the prior art, and which particularly constitutes a simplified approach for distance measuring and improves the results obtained therewith.
To that end, the present invention relates, in a first aspect, to a method for measuring a distance to a target, comprising:
a) supplying an excitation signal to a heating element in thermal contact with a thermo-optical material of a thermo-optical lens to change the focal length of said thermo-optical lens to focus on a target; and
The method of the present invention constitutes a passive measuring method as no probing light is emitted on the target, and also does not need of the inclusion of any sensor/detector or mechanism specific for directly or indirectly performing the distance measuring, as only the analysis of the excitation signal supplied to focus the thermo-optical lens is needed, which drastically simplifies the proposals of the state of the art.
In the present document, the terms probing light have to be understood as meaning light which properties or intrinsic or associated information is used for the distance measuring process, as it happens with the conventional time of travel distance measuring methods. In the present invention, no probing light is used at all, but only, in some cases, an illumination light to sufficiently illuminate the target in case ambient light is not enough for that purpose.
For an embodiment, the method of the first aspect of the present invention comprises supplying, as said excitation signal, an electric excitation signal to the heating element which is an electric-heating element in thermal contact with a thermo-optical material of the thermo-optical lens. Regarding this embodiment, EP3149526A1, which contents are incorporated herein by reference, discloses a thermally modulated optical lens which is focused on one or more targets by transferring heat from an electric-heating element (called therein electrically resistive element) in thermal contact with a thermo-optical material of the thermo-optical lens. No distance measuring is taught nor even suggested in EP3149526A1.
For an alternative embodiment, the method of the first aspect of the present invention comprises supplying, as said excitation signal, a light excitation signal to the heating element which is a photo-heating element in thermal contact with a thermo-optical material of the thermo-optical lens.
According to an implementation of said alternative embodiment, the method of the first aspect of the present invention comprises supplying said control signal to a controllable light source to obtain said light excitation signal, wherein, for a variant of said implementation, the control signal is an electric control signal and the controllable light source is an electrically controlled light source.
According to an embodiment, the above mentioned photo-heating element comprises one or more photo absorbing particles in thermal contact with a thermo-optical material of the thermo-optical lens, and the method of the first aspect of the present invention comprises controlling the controllable light source, by means of said control signal, for illuminating the one or more photo absorbing particles with at least one spectral component which can be absorbed by the one or more photo-absorbing particles, so that heat is generated thereby and transferred to the thermo-optical material. Regarding this embodiment, EP3120186A1, which contents are incorporated herein by reference, discloses an adaptive photo thermal lens which is focused on one or more targets by illuminating photo absorbing particles to generate and transfer heat to a thermo-optical material in thermal contact with the photo absorbing particles. No distance measuring is taught nor even suggested in EP3120186A1.
According to an embodiment, the method of the first aspect of the present invention comprises measuring a plurality of distances to a corresponding plurality of targets, preferably simultaneously, wherein:
said step a) comprises supplying a plurality of (preferably independent) excitation signals respectively to a plurality of (preferably independent) heating elements in thermal contact with thermo-optical materials of a corresponding plurality of (preferably independent) thermo-optical lenses to change the focal length of each of the plurality of thermo-optical lenses to focus on each of said targets of the plurality of targets; and said step b) comprises analysing said supplied excitation signals or control signals originating the same, to determine, based at least on the magnitude of said analysed signals, said plurality of distances between:
For another embodiment, the method of the first aspect of the present invention comprises measuring a plurality of distances to a corresponding plurality of targets, wherein:
said step a) comprises supplying a plurality of excitation signals respectively to a plurality of heating elements in thermal contact with thermo-optical materials of a corresponding plurality of thermo-optical lenses to change the focal length of each of the plurality of thermo-optical lenses to focus on each of said targets of the plurality of targets;
and said step b) comprises analysing said supplied excitation signals or control signals originating the same, to determine, based at least on the magnitude of said analysed signals, said plurality of distances between each of the focused targets and the thermo-optical lens, of said plurality of thermo-optical lenses, which focal length has been changed to focus thereon.
According to an implementation of said embodiment, the above mentioned corresponding plurality of thermo-optical lenses are arranged forming a 2D lens array.
Said 2D lens array can be formed on surfaces with any shape, whether flat or curved, and with any thickness, depending on the embodiment. For example, for an embodiment, the 2D array is arranged on a spherical surface so that light is received from space locations surrounding the spherical surface. This embodiment could be useful as part of a navigation system for a robot, such as a drone, particularly to detect obstacles all around it and measure their distances thereto.
For a preferred embodiment, the method of the first aspect of the present invention further comprises acquiring images of the focused target or targets by means of an image sensor arranged and configured to receive light coming from the target or targets once said light has passed through the thermo-optical lens or lenses or has been reflected thereon, and to sense images of said target or targets from the collected light, wherein at step a) the above mentioned change of the focal length of the thermo-optical lens(es) to focus on a target or targets refers to focus said target or targets on said image sensor.
For an implementation of said preferred embodiment, the above mentioned optical element, particularly an objective, is placed between the target(s) and the thermo-optical lens(es), wherein the distance(s) determined at step b) is/are between the focused target(s) and said objective, the distance between the objective and the thermo-optical lens(es) and image sensor being a known-in-advance distance, which is a generally fixed distance (although the use of movable objectives is also covered by the present invention).
Other types of optical elements, in addition or instead to said objective, can be included in the above mentioned optical path, for some embodiments, such as diaphragms, filters, other types of lenses, etc., the method of the present invention also comprising, for some embodiments, measuring the distance from the target to each of said other types of optical elements.
For said implementation of said preferred embodiment, when capturing an image of a scene with the above mentioned 2D lens array overlapping a corresponding 2D array of effective pixels of said image sensor, different image portions of said scene are sensed in each selected effective pixel of the image sensor, so that the whole image of the scene is composed by the array of image portions.
For an alternative implementation of said preferred embodiment, no objective is placed between the target(s) and the thermo-optical lens, wherein the distance(s) determined at step b) is/are between the target(s) and the thermo-optical lens. In this case, when capturing an image of a scene with the above mentioned 2D lens array arranged in correspondence to a corresponding 2D array of effective pixels of said image sensor, the same image (including the whole scene) is sensed in each selected effective pixel of the image sensor, but with different depth planes of the scene focused on the respective selected effective pixels.
For said alternative implementation, the 2D lens array is not necessarily overlapping the image sensor or in close distance thereto. In fact, for some cases, there may be optics between the two to ensure that the image coming from each individual lens of the 2D array is sent over the entire surface of the array of sensor pixels. According to an embodiment, when the corresponding plurality of thermo-optical lenses are arranged forming a 2D lens array in front of a corresponding 2D array of effective pixels of the image sensor, the method of the first aspect of the present invention comprises performing a three-dimensional reconstruction from the images acquired with the image sensor and from the determined distances determined at step b).
For the above mentioned implementation of the preferred embodiment for which an objective is placed between the target(s) and the thermo-optical lens, the above mentioned three-dimensional reconstruction also comprises the use of information regarding the positions of the different acquired image portions in the 2D array of effective pixels of the image sensor.
The method of the first aspect of the present invention further comprises, for an embodiment, performing previously to steps a) and b), a calibration process for each of the thermo-optical lenses, wherein said calibration process comprises separately supplying a plurality of excitation signals to the thermo-optical lens(es).
For an implementation of said embodiment, for which the method of the first aspect of the present invention is applied to only one thermo-optical lens, said calibration process comprises separately supplying said plurality of excitation signals to one heating element or to a plurality of corresponding heating elements to change the focal length of the thermo-optical lens to focus on different targets at different distances, and build a calibration relationship data structure univocally relating, for the thermo-optical lens, each supplied excitation signal, or control signal originating the same, with the distance between the corresponding focused target and one of the respective thermo-optical lens and optical element arranged in the corresponding optical path, and wherein the determination of the distance of step b) is performed by looking up in said calibration relationship data structure the value of the magnitude of the analysed signal to find a univocally related distance value therein.
For an implementation of the above mentioned embodiment, for which the method of the first aspect of the present invention is applied to a plurality of thermo-optical lenses, said calibration process comprises separately supplying said plurality of excitation signals to a plurality of corresponding heating elements (preferably to each of them) to change the focal lengths of the thermo-optical lenses to focus on different targets, and build a calibration relationship data structure univocally relating, for each thermo-optical lens, each supplied excitation signal, or control signal originating the same, with the distance between the corresponding focused target and one of the respective thermo-optical lens and optical element arranged in the corresponding optical path, and wherein said determination of said distance of step b) is performed by looking up in said calibration relationship data structure the value of the magnitude of the analysed signal to find a univocally related distance value.
Alternatively or complementarily to the above described calibration process performed previously to steps a) and b), for an embodiment of the method of the first aspect of the present invention, a non-prior calibration process is performed in the form of an auto-learning process that obtains data from the excitation signals supplied in each step a) of a plurality of steps a) carried out, and/or from the control signals originating the excitation signals, and builds a calibration relationship data structure similar to the one described above or collaborates in the building of the above described calibration relationship data structure.
For an implementation of said embodiment, parameters characterising the thermo-optical lens(es) are used in said non-prior calibration process together with the above mentioned obtained data to calculate, by using appropriate algorithm(s), the data to build and/or to be input into the calibration relationship data structure.
For another embodiment, no calibration process is performed. Instead, at step b) the distance value(s) is/are obtained by calculating the same after the corresponding step a), by using appropriate algorithms, preferably implementing auto-learning techniques, using as inputs the above mentioned data obtained from the supplied excitation signal(s) and, optionally, also the above mentioned parameters characterising the thermo-optical lens(es).
Preferably, the method of the first aspect of the present invention comprises building the calibration relationship data structure including only those pairs of values, distance versus supplied excitation signal or control signal originating the same, which follow any kind of fitting interpolation, such as one following a linear evolution, as long as it is repetitive and quantitative, so that a high accuracy in determining the distance to the target is achieved.
Optionally, for example by interpolating those pairs of values following a linear evolution, additional intermediate pairs of values can be obtained (not obtained during the above described calibration process), so that when a thermo-optical lens is focused on a target by supplying, to the associated heating element, the value of the magnitude of an excitation signal which is not one of the plurality of excitation signals supplied during the calibration process, or of a control signal originating the same, can be found in one of those intermediate pairs of values, and hence the corresponding distance value is obtained.
Therefore, for an embodiment, the method of the first aspect of the present invention further comprises obtaining additional intermediate pairs of values not obtained during said calibration process, by interpolating those pairs of values, distance versus excitation signal or control signal originating the same, of said built calibration relationship data structure, which follow a linear evolution, and, for an implementation of said embodiment, the method further comprises:
For a variant of said embodiment, the method comprises obtaining part or all of said additional intermediate pairs of values previously to said step a) at which said excitation signal which is not one of the plurality of excitation signals supplied during the calibration process has been supplied to the associated heating element.
Alternatively or complementarily to said variant, for another variant of the above mentioned embodiment, the method of the first aspect of the invention comprises obtaining one or more of said additional intermediate pairs of values after said step a) at which said excitation signal which is not one of the plurality of excitation signals supplied during the calibration process has been supplied to the associated heating element.
For an embodiment, the method of the first aspect of the invention comprises including said additional intermediate pairs of values into any of the above described calibration relationship data structures, i.e. collaborate in the building thereof by updating their contents.
As, for an embodiment, the present invention working under a “pixelated” lens (the above mentioned 2D lens array) various measurements can be taken at once, not only the distance between the object and the camera/lens can be calculated but also between objects in the scene, both in a lateral dimension (orthogonal to the optical axis of the lens) and also on an imaginary straight line joining two objects, by a triangulation process performed whether from relative inclination angles between lenses of the 2D lens array which are tilted with different inclinations or, in case the lenses of the 2D lens array are not inclined but occupying the same plane, from relative angles of different light rays impinging on the lenses (determined, for example, from their corresponding vanishing points).
Various measurements can take place during the focusing process, and an individual calibration is needed for every lens of the 2D lens array.
According to an embodiment, the method of the first aspect of the present invention comprises performing an autofocus process during or previously to step a) up to find an optimal focal length for the thermo-optical lens to focus on the target, and using the excitation signal corresponding to said optimal focal length in steps a) and b).
Alternatively, or complementarily, a manual focus adjustment can be performed to find said optimal focal length.
Generally, said optimal focal length is determined with the aid of the above mentioned image sensor, particularly based on detecting the highest image quality on a corresponding display, detected through object sharpness.
The present invention also relates, in a second aspect, to a system for measuring a distance to a target, adapted to implement the method of the first aspect of the invention, and which comprises at least:
For an embodiment, the system of the second aspect of the present invention comprises:
Said analysing unit generally comprises one or more processors which process data representing the magnitude of the excitation signals and determines the distance to the focused target or targets by calculating the same, preferably in real time or near-real time, from said data processing, said calculation generally including the above mentioned looking up in the calibration data structure which is stored in a memory accessible by the processor(s).
According to an embodiment, the system of the second aspect of the invention further comprises an image sensor arranged and configured to receive light coming from the target or targets once said light has passed through the thermo-optical lens or lenses or has been reflected thereon, and to sense images of the target or targets from the collected light.
For different embodiments, the system of the second aspect of the invention comprises some or all of the elements referred in the above description of corresponding embodiments of the method of the first aspect of the present invention, such as the image sensor, the camera objective, and the 2D array of thermo-optical lenses.
For an embodiment, the system of the second aspect of the invention comprises a plurality of thermo-optical lenses and further comprises a user input device for allowing a user to make selection of the thermo-optical lens or lenses which focus(es) is/are to be adjusted.
For an embodiment, the system of the second aspect of the invention further comprises a screen for displaying images of one or more objects placed at the focused targets.
According to an embodiment, the system of the second aspect of the invention comprises a touchscreen which includes both said screen and said user input device. For an embodiment, said touchscreen displays the acquired image in a grid each of user-actionable areas, and optionally also displays the values of the measured distances to each target.
For different embodiments, the system of the second aspect of the present invention further comprises at least one of the following optics: microscope optics, macroscope/telescope optics and standard photographic optics (including a normal lens and/or a wide angle lens), placed between the thermo-optical lens or lenses and the image sensor.
Microscope optics are used for the study of microscopic objects, leading to micrometric shifts of the focal plane in order to focus said objects. Telescope optics capable of addressing kilometric distances lead to focal plane shifts of the order of kilometres or hundreds of meters. Standard photographic optics in front of the thermo-optical lens produces displacements in focal plane in the range of the tens or hundreds of centimetres.
For an embodiment, the system comprises a camera comprising the above mentioned image sensor, and the rest of elements of the system of the second aspect of the invention.
For a variant of said implementation, said camera is a digital camera including one or more processors for processing the acquired image information and also to control the operation of the camera, wherein said one or more processors are those above mentioned which are included in the analysing unit of the system of the second aspect of the invention. In other words, no additional processors, and in fact no additional hardware or mechanical element, are added to the camera to perform the distance measuring, but only software which makes the processor(s) able to perform further functions to implement the above described data processing and calculation for performing distance measuring according to the method of the first aspect of the invention.
According to an embodiment, the system comprises a portable computing device comprising the above mentioned screen, user input device, and camera, the latter being a built-in camera of the portable computing device.
Depending on the embodiment, said portable computing device is one of a smartphone, a tablet and a laptop.
For an embodiment, said camera is adapted to acquire video sequences of images.
Image sensors operating under any light wavelength can be used according to the present invention, including the combination of more than one wavelength at a time (by including pixels sensitive to different wavelengths), for both visible and invisible (infrared, ultraviolet) light. In some cases, distances to inner surfaces of an object can be measured, for example by using an image sensor operating in the infrared wavelength for an object having an inner infrared source, such as in case of humans or animals.
In a third aspect, the present invention relates to a computer program including code instructions that when executed on at least one processor implement the steps of the method of the first aspect of the present invention according to any of the above described embodiments, including the control of the operation of an excitation signal generating unit to supply excitation signals, to implement step a) and, optionally, also to implement part of the above described calibration process, and the analysis of data representing at least the magnitude of the supplied excitation signals or of control signals originating the same to implement step b) and, optionally, also to implement the rest of the above described calibration process, including the building of and looking up in the calibration data structure.
For an embodiment, the computer program of the third aspect of the present invention also comprises code instructions for implementing the above described three-dimensional reconstruction.
Algorithms implementing several pieces of the computer program of the third aspect of the present invention are provided by the present invention, to be processed by the processor(s) of the system of the second aspect of the invention and installed in memory(s) operatively connected thereto.
With the present invention, distances to objects from a real time image can be measured simultaneously, and even to calculate curved surfaces (precision dependent on lens resolution, i.e. on the number of elements of the lens array), from measured distances to different points of the curved surface.
The present invention has many applications, such as those listed below:
In the following some preferred embodiments of the invention will be described with reference to the enclosed Figures. They are provided only for illustration purposes without however limiting the scope of the invention.
The images shown in
Particularly, those pillars boxed in boxes 1, 2 and 3 in the top image of
The three pillars 1, 2, 3, which have different heights, are therefore focused simultaneously and their heights are directly measured by analysing the excitation signals as described in a previous section, without the need of including any measuring sensor of additional mechanism to the microscope. In this case, more than the distances from the top of the pillars 1, 2, 3 to the lens (or to an optical element arranged in between), the distances of interest to be measured are those related to the whole height of each pillar, including the thickness of the plate from which the pillars extend.
In
Particularly,
The image shown in
As described in a previous section, it is possible to calibrate the distance by recording the electrical sourcing (or light sourcing) required to focus the relevant thermo-optical lens on the sign post in its area of influence. In this way, the distance to an object between the posts could be calculated from the electrical current required to focus on it and comparing it with the calibration, so that a univocally related distance value is obtained (generated, for example, by means of the interpolation process described in a previous section of the present document).
A prototype of the system of the second aspect of the present invention has been built by the present inventors, with the following constructional features, constraints and requirements.
Focal length variation is determined by the temperature gradient applied to a thermo-optical material. This material will vary its focus depending on the variables dn/dT and the thermal conductivity. In this case limiting variables for the material are: solid state, transparent to visible light (90% or more), high dn/dT and thermal conductivity, electrically insulating and able to adjust to textured surfaces.
In the built prototype, individual focuses are controlled by the heat transferred to the thermo-optical materials from a complex array of resistors using digital potentiometers, and/or switches and/or and multiplexers (not shown). Control can be individual, total or by groupings. Actual control is made by a python server that keeps track of live image and values of the electrical currents passed through the resistors.
The connection network formed by the different connection tracks W+ and W−, can be a reconfigurable connection network, like a FPGA, which can provide different alternate connection arrangements.
For the built prototype all the technology is built by 2D lithography, so that the space required is minimal and can be embedded on any surface. Current substrate is a silica (although other potential materials could be used) of about 1 cm2, on top of it a network of resistive material, such as transparent ITO or metal such as gold, with a thickness of 50 nm is arranged. Size of the individual resistors may vary from few μm up to hundreds of μm depending on the applications.
Transparency of the system is enough to be placed inside of the optical path, avoiding any extra tool and highly reducing its size.
Performance of the built prototype: Response times of the focus may vary from few μs to hundreds of ms depending on resistor size, having an active heating system and passive cooling.
Sharpness of the image is detected through object sharpness, it can either be done manually or automatically. In manual tests targets such as words or numbers are used to identify when focus has been properly adjusted. For an automatic focus different areas of the image are individually studied, sharpness transition between objects under a grey scale image defines whether it is properly focused.
The focus of the system of the second aspect of the invention can actively be adjusted to identify further images, and passively go back to the initial lens focus position. The range of distances depends on the needs of the user and is mainly limited by the collecting optics associated with the system.
The interface could also include a virtual grid (not shown) which could include further controllable elements to control further options for each box, such as OFF/ON (i.e. activating or deactivating the corresponding box of the grid), flip 90° rotation, and intensity of the voltage supplied to the corresponding thermo-optical lens.
As already stated above, the system of the second aspect of the present invention is able to scale, making it available to work in different formats. Two main paths have been explored: microscopy and photography.
With working prototypes, in microscopy, a maximum focus shift of around 1 mm has been achieved with working prototypes (that is more than the depth of field of the microscope), while in photography a maximum focus shift of 175 cm has been achieved so far (also more than the depth of field of the photographic system).
A compact implementation, without the need of reimaging system, is possible when the thermo-optical lens size matches the imaging sensor size. In this case, the thermo-optical lens can be placed very close to the image sensor.
Quality control is highly related to the appearance or the dimensional stability of products. The system of the second aspect of the present invention is able to provide both controls to those parameters in one. It is also versatile in terms of size and adaptability to different platforms.
As an example the surface of a kayak hull has been studied, and different virtual images from the obtained image and distance information were generated, for an embodiment applied to quality control, in this case applied to a manufactured boat.
Particularly, an image was taken from the top view of the boat, in this case a kayak hull. Image is then autofocused until reaching maximum border sharpness. A heat map with the different values applied to the electrodes is generated. With a CAD software a 3D surface is generating using the heat map. 2D image is placed on top of the 3D surfaces allowing the user to analyze whether the geometry has been properly fabricated.
Following the quality control field, another example where both image and geometry are combined is wood cutting or carving. Controlling wood shape plus the wood grain drawing can lead to better products.
Another field that would take advantage of the present invention is that related to topographic cameras, which could real time generate fields in a 3D environment. Limitations on this field would depend on the distances that the thermo-optical lens would be able to adjust with its focal length.
In order to broaden the capabilities of the present invention in terrain analysis, and due to its compactness, a camera implementing the system of the invention can be mounted on a drone. Real time data analysis could improve flight quality and also provide information about the environment.
Compactness is also linked to mobile technologies. An advanced version of the system of the invention will be directly deposited on the imaging sensor. Removing parts such as the glass substrate reduces thickness of the system in a great way, still there is a long way to explore the integration of circuitry over imaging chips.
The distance measuring proposed by the present invention is based on the analysis of the power being fed into heating elements of the lens to change its focal length, until the target is optimally focused, which is checked, for example, by analysing the sharpness of the images obtained, so that when a highest sharpness is obtained the target is determined to be optimally focused.
In order to calibrate the system, a study of image sharpness vs. object distances needs to be done as for every different optical configuration values will change.
To calibrate it, an 8 bits object such as a black and white grid will serve as an easy and fast tool to analyse subject.
An 8 bits histogram of the image will serve as a quantification of the sharpness of the image, the standard deviation between pixels gives the information needed to know whether colour transitions are sharp enough. First, the image is changed to grey scale meaning the colour value of the pixel is 0 to 255. Then the histogram of the zone to be analysed is made, if there is a great difference between pixels it means the colour changes are sharp and a high standard deviation will be obtained, and consequently that zone will be in focus.
For the calibration process two parameters are being changed, object distance and resistor voltage.
For every distance the object is positioned, a series of images ranging the minimum voltage admissible for the resistor to the maximum are being taken.
These images are afterwards analysed and for every voltage a sharpness value is given.
Peak sharpness apply to a certain voltage, this peaks refer to the maximum image quality that can be achieved using the thermo-optical effect of the thermo-optical lens of the system of the invention, for a working prototype.
Once the calibration table is set there is only needed to take images of random objects at distances inside the linear evolution of the graph to check if the system works properly.
For the grid, the best-focused image is obtained for a voltage of 8.6 V applied to the corresponding thermo-optical lens and for the pencil and the “100” sign a value of 6.6 V. Using the calibration curve we deduce that 8.6 V corresponds to a distance of 396 mm for the gird and 6.6 V corresponds to a distance of 346 mm for the two other objects. The positions of these 3 objects have been previously measured with a ruler: 390 mm for the grid and 350 mm for the two other objects giving an error/uncertainty of 4 mm for the grid and 6 mm for the two other objects.
As we are working under a pixelated lens various measurements can be taken at once, not only we can calculate the distance between the object and the camera but also the relative distance between objects in the scene.
Finally,
Specifically, for the arrangement shown in
For the arrangement of
An alternative arrangement is shown in
For the arrangement of
Depending on the application, the first or second arrangement shown in
However, when a more accurate selection of the target to be focused, in order to measure its distance, is required (particularly when the targets are in the same focal plane), the arrangement of
A person skilled in the art could introduce changes and modifications in the embodiments described without departing from the scope of the invention as it is defined in the attached claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17382604.1 | Sep 2017 | ES | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/074589 | 9/12/2018 | WO | 00 |
