Method and system for characterizing an optical lens for correcting optical aberrations introduced by said optical lens into an image.

Abstract

The invention relates to a method (400) for characterizing an optical lens comprising a stack of several optical elements and intended to be associated with an image sensor for acquiring images, comprising: determining (402), by optical measurement on said stack of optical elements, at least one data set (JG), called geometric set, comprising data relating to at least one geometric parameter of at least one buried optical interface of said lens, numerical modeling (404) of said optical lens as a function of said geometric set, and determining (406), by a digital optical wave propagation simulator applied to said numerical model, at least one matrix, called aberration matrix, representative of optical aberrations introduced by said optical lens (200) in an image.It also relates to a characterization device, an image acquisition method and device, and an imaging apparatus implementing such a method. Abstract figure: Fig. 4.

Description

Title of the invention: Method and system for characterizing an optical lens for correcting optical aberrations introduced by said optical lens into an image.

[0001] The present invention relates to a method for characterizing an optical objective to determine a matrix of values making it possible to correct at least certain optical aberrations introduced by said objective in an image produced with said objective. It also relates to a characterization device, an image acquisition method and device, and an imaging apparatus implementing such a method.

[0002] The field of the invention is the field of characterization of optical objectives used for imaging, with a view to correcting optical aberrations due to said optical objective. State of the art

[0003] Optical lenses are used in various devices, such as for example cameras, cameras, smartphones, etc. to image a scene.

[0004] Generally, an optical lens consists of a stack of optical elements, such as optical lenses, separated from each other by an empty space, also called an "air gap" in English, or by a spacer, also called a "spacer" in English. They are generally assembled via a device called a barrel or barrel.

[0005] To produce an image, the optical lens cooperates with a photosensitive sensor, also called an image sensor, such as a CMOS or CCD sensor. The plane of the image sensor is called the image plane and each image sensor comprises a multitude of pixels. The assembly comprising the optical lens and the image sensor is generally called an “optical module” or “camera module”.

[0006] The trend towards miniaturization of camera modules mounted in electronic devices, such as smartphones, reduces the tolerances on the manufacturing of components and in particular on those of the optical lens and lenses that compose it. Manufacturing defects can thus appear in the form of defects in the image obtained on the image sensor. For example, optical aberrations can result in blurring of images. The brightness of a pixel of an original image is distorted and modifies the brightness of an adjacent pixel of the captured image. This phenomenon can be expressed in the form of a point spread function (PSF) indicating a degree of blurring obtained during a process in which an optical system forms an image of a scene on an image sensor. The PSF can then be used to deduce correction values, in an image, for optical aberrations due to the optical lens, for example by deconvolution.

[0007] According to a first known solution, the PSF is measured for each optical lens manufactured: this solution is time-consuming. According to a second solution, the PSF can be measured for an optical lens and reused for all optical lenses forming part of the same batch: this solution, although less time-consuming, is imprecise because it does not take into account the specifications of each optical lens.

[0008] According to a third known solution, the PSF can be estimated by calculation, for each optical objective, from the individual parameters of each optical element forming said optical objective. However, the inventors of the present invention have discovered that this solution, although less time-consuming, remains just as imprecise because it does not take into account the manufacturing parameters, and in particular those which can influence the interactions between the optical elements of an optical objective, as well as micro-defects in the production of the optical elements.

[0009] An aim of the present invention is to remedy at least one of the aforementioned drawbacks.

[0010] Another aim of the invention is to propose a solution allowing better correction of optical aberrations introduced by an optical objective while being less time-consuming. Statement of the invention

[0011] The invention proposes to achieve at least one of the aforementioned aims by a method for characterizing an optical objective comprising a stack of several optical elements and intended to be associated with an image sensor for acquiring images, said method comprising the following steps: - determination, by optical measurement on said stack of optical elements, of at least one data set, called geometric set, comprising data relating to at least one geometric parameter of at least one buried optical interface of said objective, - digital modeling of said optical objective as a function of said geometric play, and - determination, by a digital optical wave propagation simulator applied to said digital model, of at least one matrix, called an aberration matrix, representative of optical aberrations introduced by said optical objective in an image.

[0012] Thus, the invention proposes to determine an aberration matrix whose values are representative of optical aberrations introduced by the optical objective on a image taken by said optical lens, by simulation on a digital model of said optical lens and not by optical measurements carried out on said optical lens. Thus, the invention makes it possible to determine the aberration matrix in a less time-consuming manner than current solutions which carry out a measurement of these aberrations, and in particular of the PSF, on each optical lens.

[0013] Furthermore, the invention proposes to determine the aberration matrix by simulation on a digital model of the optical lens. Thus, it is possible to determine the aberration matrix individually for each optical lens, which makes it possible to obtain aberration values, and therefore correction values, individually for each optical lens, so as to obtain a more precise correction.

[0014] Above all, the invention makes it possible to determine the digital model of the optical lens as a function of the parameters of the optical interfaces of said optical lens, measured after the optical elements forming the lens have been stacked. Thus, the digital model of the optical lens takes into account the characteristics of each optical element in combination with the other optical elements of the optical lens. Such a digital model is more precise and closer to reality, makes it possible to obtain more precise values representative of the optical aberrations, and therefore to achieve better correction of the optical aberrations introduced into an image by said optical lens.

[0015] By "optical aberration" is meant in particular optical blur or optical distortion. Optical blur generally results in a spreading of a light point. Distortion generally results in a displacement of the optical point.

[0016] The optical elements composing an optical lens are stacked along a stacking direction, also called the Z axis in the following, or the axis of the optical lens. The plane perpendicular to the Z axis, that is to say the plane along which each optical element extends, is called the XY plane in the following.

[0017] By “geometric parameter of an optical interface” is meant, for example, and without loss of generality: - a position of the optical interface within the lens, in the Z axis; - a position of an APEX of the optical interface, in particular in the X- plane Y and / or - a position of an APEX of the optical interface, in particular along the Z axis, - an inclination (TIP and / or TILT) of said optical interface relative to the Z axis, - a decentering of an optical interface, or of an optical element, relative to the Z axis, in the XY plane, - a curvature or one or more terms of an equation describing an optical interface.

[0018] In the present application, by "buried optical interface" of an optical lens, we mean an interface within the optical lens which is visible, or accessible, only via at least one other optical interface of the lens. The at least one other optical interface through which the buried interface is visible may be an optical interface of the same optical element, or an optical interface of an optical element other than the buried interface.

[0019] The geometric set comprises data relating to at least one geometric parameter of at least one buried interface of said stack.

[0020] The estimated geometric game may further comprise data relating to at least one geometric parameter of at least one non-buried interface of said stack.

[0021] According to embodiments, the method according to the invention can comprise a determination of several aberration matrices for several regions, R;, of the image sensor associated with the optical objective.

[0022] Thus, it is possible to characterize more precisely the optical aberrations introduced by the optical lens in such or such region of the image sensor, these aberrations being able to change according to the regions of the image sensor. Indeed, it is for example common for the optical aberrations introduced in a central region to be different from a peripheral region. Similarly, it is likely that the optical aberrations of a peripheral region differ from the optical aberrations introduced in another peripheral region.

[0023] Each aberration matrix can be determined by simulation by the digital simulator.

[0024] To do this, in the digital simulator, for each region, a test light beam is emitted. The test beam enters the optical lens, passes through the optical lens and is received on an image sensor. The received values are compared to the input values, i.e. to the values of the test light beam. This comparison makes it possible to deduce the aberrations introduced by the optical lens by examining each pixel of the region concerned and comparing it to the emitted beam.

[0025] In particular, the aberrations can be determined by convolution of a matrix of values describing them with the intensities of the light points of a region of an observed scene, which makes it possible to obtain the intensity values received at the image sensor in the corresponding region.

[0026] By “region” is meant a region of the image sensor in its XY plane.

[0027] At least one region may comprise a single pixel.

[0028] At least one region may comprise several pixels.

[0029] At least two regions may be of the same size.

[0030] At least two regions may be of different sizes.

[0031] In this document, a region of the image sensor centered on the coordinates (Xi,Yi), in the plane (X,Y), may be denoted by R(X;,Y;), or R;.

[0032] In this document, MA denotes the aberration matrix for the entire optical lens.

[0033] MA;, or MAi(Xi,Yi) denotes the aberration matrix for the region R; of the objective. The aberration matrix MA can be obtained by concatenating or adding the aberration matrices MA;.

[0034] According to embodiments, the method according to the invention may comprise, for a region of the image sensor, a calculation of an aberration matrix by interpolation of one or more aberration matrices of one or more other regions of said optical objective.

[0035] Thus, the method according to the invention makes it possible to characterize the optical objective in less time.

[0036] In particular, the aberration matrix of a region can be calculated by interpolating aberration matrices of adjacent regions.

[0037] The interpolation can be carried out by any known technique, for example by averaging.

[0038] Alternatively, or in addition, the method according to the invention may comprise a determination of several aberration matrices for several values of a distance, called the lens-sensor distance, noted DOC hereinafter, between said optical lens and an image plane, the digital simulator taking said lens-sensor distance as input.

[0039] Thus, the method according to the invention makes it possible to quantify the optical aberrations introduced by the optical lens in an image, when the distance between the optical lens and the image plane is changing. Indeed, the inventors have noticed that, for a given lens, the optical aberrations introduced by said lens can vary as a function of the distance between said lens and the image plane.

[0040] The image plane may be the plane of an image sensor associated with the lens. The image sensor may be any type of sensor, such as a CMOS sensor or a CCD sensor, etc.

[0041] To do this, for each distance DOCj, with j>l, a test light beam is emitted opposite the objective. The test beam enters the optical objective, passes through the optical objective and is received on an image sensor. The aberration matrix is determined as a function of the received values and the input values, i.e. the values of the test light beam.

[0042] Several aberration matrices can be determined for several distances DOCj, for the entire optical objective.

[0043] Alternatively, several aberration matrices can be determined for multiple DOQ distances, for different regions of the image sensor.

[0044] Alternatively, or in addition, the method according to the invention may comprise a determination of several aberration matrices for several values of a distance, called objective-scene distance, DOS, between said optical objective and a scene, the digital simulator taking said objective-scene distance as input.

[0045] Thus, the method according to the invention makes it possible to quantify the optical aberrations introduced by the optical lens in an image, when the distance between the optical lens and the imaged scene is changing. Indeed, the inventors have noticed that, for a given lens, the optical aberrations introduced by said lens can vary depending on the distance between said lens and the scene.

[0046] To do this, for each distance DOSk, with k>l, a simulated test light beam is emitted opposite the objective. The test beam enters the optical objective, passes through the optical objective and is received on an image sensor. The aberration matrix is determined based on the received values and the input values, i.e. the values of the test light beam.

[0047] Several aberration matrices can be determined for several DOSk distances, for the entire optical objective.

[0048] Alternatively, multiple aberration matrices can be determined for multiple DOSk distances, for different regions of the image sensor.

[0049] Thus, according to embodiments, it is possible to determine a number NB=I x J x K aberration matrices for the optical objective, with: - I>1 the number of regions considered of the image sensor, - J>1 the number of DOC distances considered, and - K>1 the number of DOS distances considered.

[0050] For example, if ten (10) regions of the image sensor are characterized for 3 DOQ distances and 5 DOSk distances, then 15 aberration matrices can be determined for each region of the image sensor, and in total 150 aberration matrices for the optical lens.

[0051] In the following, for the region R; of the sensor, the distance DOQ and the distance DOSk: - MAijk the aberration matrix, and - MCijk is the correction matrix. Of course, when the DOC distance and / or the DOS distance are not variable then the MAijk and MCijk notations do not necessarily imply that these distances are variable.

[0052] According to embodiments, the method according to the invention may further comprise a step of calculating a matrix, called aberration kernel matrix, comprising coefficients making it possible to deduce at least one aberration matrix.

[0053] In this case, several aberration matrices can be determined. Then, from these matrices, a common matrix can be identified. This common matrix, called the aberration kernel matrix, can be stored in place of the multitude of aberration matrices, in relation to one or more relations, to allow the calculation of each aberration matrix. This avoids having to store a multitude of aberration matrices and therefore reduces the memory space used for storing aberration matrices.

[0054] The aberration kernel matrix can, according to a non-limiting exemplary embodiment, be determined in the following manner.

[0055] Firstly, a base of FA functions is established to describe the values of the coefficients of the aberration matrices as a function of the positions (X,Y) in the field of the image sensor, such that: MA(X,Y) = Ei aAi(X,Y) FAj(X,Y) + E(X,Y) where - 1 scans the basis of FA functions, with 1<1<L, et L> 1. - the term E(X,Y) models the differences between the combination of functions FAi and MY.

[0056] The basis FA can preferably be chosen so as to be sufficiently broad so that the term E(X,Y) retains a negligible, or even zero, effect. These functions can be orthogonal to each other in the sense of a scalar product, but not necessarily. For example, the basis of functions FAi can be the basis of functions of the Zernike polynomials. To obtain the functions aAi(X,Y), it is sufficient to use a known method from the state of the art such as a projection of MA(X,Y) onto the FAi(X,Y), in the sense of a scalar product, and to apply the appropriate matrix product to take into account their non-orthogonality, if applicable, to obtain the functions aAi(X,Y). Establishing an aberration kernel precursor (ANP) amounts to searching for a parametric model of the functions aAi(X,Y), such that for example a polynomial expression represents aAi(X,Y), for example, if 1 € {1, 2], such that aAi(X,Y) = aOi .((X-x0i)2+(Y-y0i)2) and aA2(X,Y) = a02.((X-x02)*(Y-y02)) +z02.The model representing the aAi(X,Y), here aAi(X,Y) and aA2(X,Y), is then the table of values ((aOi, xOi, yOi); (a02, x 02, y02, z02)) in this example. We can call this set of coefficients aberration kernel precursor matrix called PNA (here which can be a matrix of 1 row x 7 columns, or 2 rows by 4 columns with a zero coefficient added to the first row). As the FAi() functions are chosen so as to best model the modes of the aberrations obtained, the parametric model which represents the aAl(X,Y) functions as a function of the geometric parameters contains significantly fewer coefficients than the numerical representation of the FAi(X,Y) functions. Here for example, it contains 8 coefficients instead of for example 16 million coefficients that would have been needed to represent the aberration functions represented by 4x4 coefficients on a . X, Y field of 1000x1000 positions. There remains one last step to obtain the aberration matrix which is to represent the evolutions of the PNA coefficients as a function of the distance parameters lens sensor and lens scene DOC and DOS, which again makes a set of several parameters involved in functions modeling the PNA values as a function of DOC and DOS. It is this last set of coefficients which can, advantageously, constitute the aberration kernel matrix.

[0057] According to another exemplary embodiment, the aberration kernel matrix can be a table of matrices containing the PNA coefficients, or directly the PNA for several sets of DOC and DOS parameters. The main thing is to be able to find the aberration matrices of the objective from the geometric parameters, preferably by storing less data than these aberration matrices represent.

[0058] For example, the function basis FAi can be the function basis of the Zernike polynomials.

[0059] According to embodiments, the method according to the invention may further comprise a step of calculating, as a function of at least one aberration matrix, at least one matrix, called a correction matrix, comprising values for correcting an image captured with said optical objective.

[0060] In particular, a correction matrix can be calculated for each aberration matrix.

[0061] For at least one aberration matrix, the correction matrix can be obtained by inverting said matrix, which can be done for example by calculations in the spatial frequency domain.

[0062] According to exemplary embodiments, at least one correction matrix can be obtained by the relation: _ Tr-lf TF{Go] 1 where Go is a function representing the function form of point dispersion to be obtained after correction. It can be a function approaching a Dirac function in 2 dimensions, that is to say worth 1 at the center, and almost 0 around. Noting MTOBSijk, the matrix of the test light beam as observed, and MT its native form as it is in reality during its emission, the correction matrix MCijkde as follows: _ pp-1 f • TF{MTijk} [In a simplified form, we can assume 'jk~ [ TF {MTOBSijk} J that TF(G0) = 1, the constant function which returns 1 with zero phase at all frequencies, which is written: MCiik = TFX {.....1with: l TF{MTOBSijk} J - TF() the Fourier transform operator (in 2D) - TF '() the inverse Fonder transform operator (in 2D) - MCijk correction matrix for the region R; of the image sensor, at the lens-sensor distance DOQ and at the lens-scene distance DOSk; - MAijk the aberration matrix obtained by simulation for the region R; of the optical objective and the distances DOCj and DOSk; and - MTijk the test light beam matrix, i.e. the matrix describing the test light beam, used to measure by simulation the aberration matrix MAijk. - MTOBSijk the observed illumination matrix, obtained by simulation, in the sensor plane relative to the MTijk test matrix presented at the input of the objective.

[0063] According to embodiments, like the aberration kernel matrix calculated for the aberration matrices, the method according to the invention can further comprise a step of calculating a matrix, called correction kernel matrix, comprising coefficients making it possible to deduce at least one correction matrix.

[0064] In this case, several correction matrices can be determined. Then, from these correction matrices, a common correction matrix, denoted MC, can be identified for example by addition or concatenation of the correction matrices MCÿk. This common correction matrix can be stored in place of the multitude of correction matrices, in association with one or more relations, to allow the calculation of each correction matrix. This makes it possible to avoid having to store a multitude of correction matrices.

[0065] The determination of the correction kernel matrix can be determined in a manner similar to that described above for the aberration kernel matrix using the same basis of functions FAi, or another basis of functions which would be appropriate.

[0066] According to preferred embodiments, at least one aberration matrix may be a matrix, called a PSF matrix, of values of a point spread function (“Point Spread Function” or “PSF” in English).

[0067] Alternatively, or in addition, at least one aberration matrix may be a matrix, called an OTF matrix, of values of an optical transfer function (“Optical Transfer Function” or “OTF” in English).

[0068] Alternatively, or in addition, at least one aberration matrix may be a matrix of values obtained by wavefront analysis.

[0069] When an aberration matrix is a PSF matrix, then the correction matrix calculated for said aberration matrix can be a matrix of values, called an IPSF matrix, obtained by inversion of said PSF matrix.

[0070] The digital simulator can be any type of wave propagation simulator optics through several interfaces, elements, otics.

[0071] Such digital simulators are known to those skilled in the art and are widely available commercially.

[0072] For example, the digital simulator may be the OpticStudio simulator from Zemax. Of course, the invention is not limited to this simulator and any type of digital light beam propagation simulator may be used.

[0073] According to embodiments, at least one geometric game can be obtained by optical interferometry.

[0074] Alternatively, or in addition, at least one geometric set may be obtained by confocal measurement(s).

[0075] The geometric clearance can be determined from optical measurements made only from one face, or one side, of the stack of optical elements, without having to turn said stack over.

[0076] According to embodiments, at least one geometric clearance can be determined by confocal measurements carried out on the stack of optical elements of the target optical objective, preferably from one face of said stack.

[0077] Conventionally, a confocal measurement is carried out with a device which comprises a first opening (orifice) imaged on the surface to be measured by means of a focusing lens. This opening is illuminated by a light beam coming from a light source and which is then directed towards the surface to be measured. When the beam is reflected by a surface, it is redirected towards the focusing lens then towards a second lens placed in front of a detection element and so as to be the conjugate image of the illuminated point on the measured surface. The advantage of such a configuration is the reduction of the depth of field and therefore to be able to distinguish objects (or surfaces) one below the other more easily. To carry out the detection, the confocal measurement system is moved relatively to the measured object.A maximum intensity is detected on the detection element when a surface enters the focal point defined by the focusing lens. A particular configuration of a confocal measurement system uses a chromatic lens to focus and image a beam from a polychromatic source. The different wavelengths thus define different focal points along the optical axis of the lens. Detection with a spectrometer of the reflected light makes it possible to recognize the reflected wavelength and deduce information on the height (or distance) between the lens and the measured surface. Such a configuration makes it possible to eliminate or reduce the movement of the confocal measurement system. In particular, when the confocal measurement system is moved along a plane perpendicular to the illumination axis of the surface to be measured, topography information of a surface can be obtained.

[0078] According to embodiments, at least one geometric clearance can be determined by optical interferometry measurements carried out on the stack of optical elements of the target optical objective, preferably from one face of said stack.

[0079] Conventionally, an optical interferometry measurement is carried out with an optical interferometry apparatus comprising a low-coherence emitting light source. This light source emits, in the direction of the stack of optical elements, and more particularly along the Z axis, a beam of light, called the measuring beam. The measuring beam illuminates the stack of optical elements at a measuring point that is more or less wide depending on the focusing in the XY plane, and then travels through the stack of optical elements, in particular in the stacking direction, and passes through each optical interface in turn. At each optical interface, a portion of the beam is reflected, and constitutes a reflected beam. This reflected beam is then captured by a sensor located on the same side as the emission source, and is characterized by optical interferometry with a reference beam also coming from the light source.The term "coherence zone" means the area in which interference between the measuring beam and the reference beam can occur on the sensor. The coherence zone can be moved by varying the difference in the optical path length between the two beams, for example by changing the optical length of one or both beams. The optical interferometry apparatus can selectively detect an interference signal for each interface at which the coherence zone is positioned, i.e. for each surface located in the coherence zone. Preferably, the coherence length of the light source is adjusted so as to be shorter than a minimum optical distance between two adjacent interfaces of the optical element.Thus, for each measurement, only one interface is in the coherence zone, and therefore, an acquired interference signal only includes the contribution of one interface, or comes from one interface only. Interference measurements are carried out according to a field of view determined by the measuring means of the interferometric device.

[0080] According to one embodiment, the interferometric apparatus can operate in point mode by being configured to detect a point interference signal at a point in the field of view or at a point detector. The interference signal, or the interferogram, obtained is an intensity signal depending on the displacement of the coherence zone along the Z axis. The interference signal can, for example, be seen as a succession of interference lines associated with each optical interface.

[0081] Alternatively or additionally, the interferometric apparatus may comprise an interferometric sensor, called a full-field interferometric sensor, configured to detect a full-field interference signal in a field of view and shown, for example, in the form of a 2D image (interference image) thanks to the detection element.

[0082] An interface to be measured can thus be imaged according to the field of view in a single measurement or by scanning a beam.

[0083] In a particular example of implementation, a measurement signal can be formed by a point interference signal associated with a pixel of the detection element whose intensity is detected following the displacement in Z of the coherence zone.

[0084] According to one example, the interferometric apparatus may comprise an interferometric sensor with a Michelson interferometer. According to another example, the interferometric apparatus may comprise an interferometric sensor with a Mach-Zehnder interferometer.

[0085] According to embodiments, a point mode interferometric apparatus and a full field interferometric apparatus may be combined.

[0086] According to embodiments, at least one geometric set may comprise a value of at least one geometric parameter of an optical interface of the target objective.

[0087] For example, the geometric game may comprise, for at least one, and in particular each, optical interface of the stack: - at least one position value of the optical interface; - at least one value of decentering of the optical interface relative to the axis Z, or relative to a center position of another interface, in the XY plane; or - at least one inclination value of the optical interface relative to the Z axis, or relative to the inclination of another interface. - at least one topography or shape profile value of the optical interface, for example relative to a reference plane or axis to deduce therefrom, for example, decentering or inclination values, or shape values of the interface.

[0088] The position along the Z axis of an optical interface can be determined as being the position of an interference line corresponding to said interface.

[0089] The thickness of an optical element, along the Z axis, can be determined by calculating the distance between the interference lines corresponding to each of the optical interfaces of said optical element.

[0090] The position of an optical interface relative to the Z axis can be determined by performing several optical interferometry measurements, in particular in a central region of the image sensor. By following, over the several measurements, the position, along the Z axis, of the interference line associated with said interface, it is possible to determine the position of the APEX of said optical interface. The position of the APEX of the optical interface makes it possible to determine the position of said interface relative to the Z axis, in the XY plane, and therefore its offset relative to the Z axis.

[0091] In another example, the position of an interface relative to the Z axis can be obtained, for example, by detecting an interference image of the interface in a central region of the image sensor and analyzing this image and / or analyzing associated amplitude or phase images, in particular to obtain a profile of this surface and the position of the APEX of said optical interface.

[0092] The position of an optical element relative to the Z axis can be determined based on the positions of its optical interfaces.

[0093] The inclination of an optical interface relative to the Z axis can be determined by performing several optical interferometry measurements, in particular in a peripheral region of the image sensor. By following, over the several measurements, the position in the Z axis, of the interference line associated with said optical interface, it is possible to determine the position of the interface along the axis at its edges, which makes it possible to determine the inclination of said interface relative to the Z axis.

[0094] The inclination of an optical element relative to the Z axis can be determined based on the inclinations of its optical interfaces.

[0095] It is also possible to determine each of these geometric parameters using the amplitude of an interference line, in addition to or instead of the position of the interference line.

[0096] As indicated above, the aberration matrix can be obtained around each pixel of the sensor. In this case, the lens is illuminated by a test light beam, then the illumination received at the image sensor is measured. This illumination received at the sensor includes the information of the optical aberrations introduced by the optical lens in each captured image.

[0097] The aberration matrix can be obtained by region of the image sensor, each corresponding to several pixels on the image sensor. In this case, an illumination pattern is presented in front of the lens, such as for example a checkerboard pattern alternating white patterns and black patterns, then the illumination received at the sensor is measured. This illumination received at the sensor includes the information of the optical aberrations introduced by the optical lens in each captured image.

[0098] A transformation of the captured images may be necessary in order to obtain, for example, the point spread function (PSF) which would correspond to, for example, a test beam coming from a single light point illuminating the lens, moved in several regions of the field visible by the lens to obtain the PSFs for several regions of the sensor. But if the simulation allows the lens to be illuminated from a single movable point, these transformations can generally be omitted to obtain di- directly from PSF.

[0099] According to another aspect of the present invention, there is provided a system for characterizing an optical objective comprising a stack of several optical elements and intended to be associated with an image sensor (704) for the acquisition of images, said system comprising: - an optical measuring device, on said stack of optical elements, of at least one data set, called geometric set, comprising data relating to at least one geometric parameter of at least one buried optical interface of said objective; - at least one computing unit configured to: • digitally model said optical objective based on said geometric clearance; and • determine, by digital simulation of optical wave propagation applied to said digital model, at least one matrix, called aberration matrix, representative of optical aberrations introduced by said optical lens in an image.

[0100] Generally, the system according to the invention may comprise means configured to implement any combination of at least one of the characteristics described above with reference to the characterization method according to the invention, and which are not repeated here for the sake of brevity.

[0101] The optical measuring device may be a device comprising at least one optical interferometer, and / or at least one confocal measuring device.

[0102] The computing unit can be any type of physical or virtual machine, such as at least one server, at least one computer, at least one tablet, at least one processor, at least one computer chip, at least one calculator, etc.

[0103] The computing unit may in particular be configured to execute a digital optical wave propagation simulator, such as for example OpticStudio from Zemax.

[0104] According to another aspect of the present invention, there is provided a method of acquiring an image with an apparatus comprising an optical lens and an image sensor, said method comprising the following steps: - capturing an image with said optical lens and said image sensor; and - correcting said image according to at least one correction matrix calculated from at least one aberration matrix obtained, for said optical lens, by the method according to the invention for characterizing an optical lens.

[0105] According to embodiments, at least one correction matrix can be calculated outside the apparatus performing the acquisition of the image.

[0106] In this case, said correction matrix can be calculated before the integration of the optical lens in the device, and in particular at the time of, during or after the design of the optical lens.

[0107] The at least one correction matrix can be calculated by a characterization method or system according to the invention.

[0108] In this case, the at least one previously calculated correction matrix is loaded and stored in the device.

[0109] According to embodiments, at least one correction matrix can be calculated in the apparatus carrying out the acquisition of the image.

[0110] In this case, the correction matrix can be calculated from: - at least one aberration matrix, - an aberration kernel matrix, or - a correction kernel matrix.

[0111] In these embodiments, it is then not necessary to calculate all the correction matrices prior to the integration of the optical objective in the apparatus, and the calculation of the correction matrices is done in the apparatus, in the environment of use of the optical objective. This makes it possible to take into account specificities arising from, or dependent on, the conditions of integration of the optical objective in the apparatus, which allows greater precision.

[0112] At least one correction matrix can be calculated once and then stored in the device for use multiple times.

[0113] For example, at least one correction matrix can be calculated just after the integration of the optical lens in the device, or at the time of configuration of the device or even at the time of installation / configuration of an image acquisition application, and be stored in the device to be used over time.

[0114] At least one correction matrix can be calculated, or recalculated, on the fly at each acquisition of an image, or at each start of an image acquisition application.

[0115] In this case, it is not necessary to memorize the at least one correction matrix, the latter being calculated on the fly.

[0116] This embodiment makes it possible to avoid having to store all the correction matrices and calculate at least one correction matrix when it is used.

[0117] For example, when acquiring an image, the distances DOC and DOS can be determined and the at least one correction matrix corresponding to said distances can be determined on the fly.

[0118] The method according to the invention may further comprise a step of determining a distance, DOC, between the optical objective and an image plane, the correction taking into account said distance DOC.

[0119] The DOC distance can for example be measured by a distance sensor, such as an optical sensor, a magnetic sensor, a capacitive sensor, etc.

[0120] The DOC distance can for example be calculated from information provided by a focus adjustment mechanism modifying or controlling the distance between the lens and the image sensor.

[0121] The method according to the invention may further comprise a step of determining a distance, DOS, between the optical objective and the scene, the correction taking into account said DOS distance.

[0122] The DOS distance can for example be measured by a LIDAR, a time-of-flight camera, an ultrasonic sensor, a textured image analysis, etc.

[0123] A single DOS distance may be measured for the optical lens. Alternatively, DOS distances may be measured for different regions of the image sensor.

[0124] According to another aspect of the present invention, there is provided an image acquisition device comprising: - an optical lens comprising a stack of several optical elements, - an image sensor, and - a computing unit; configured to implement the method according to the invention for image acquisition.

[0125] According to embodiments, but in no way limiting, the device according to the invention may be a camera module integrated or intended to be integrated, in a device, such as a camera, a tablet, a Smartphone, a computer, a surveillance camera, etc.

[0126] Generally speaking, the image acquisition device according to the invention may comprise means configured to implement any combination of at least one of the characteristics described above with reference to the image acquisition method according to the invention, and which are not repeated here for the sake of brevity.

[0127] The image acquisition device may optionally comprise at least one sensor for measuring at least one DOS distance for at least one region of the optical field, when acquiring an image, said at least one distance being used for image correction. Such a sensor may be an optical sensor, a LIDAR sensor, a time-of-flight camera, etc.

[0128] The image acquisition device may optionally comprise at least one means for measuring, or calculating, a DOC distance during the acquisition of an image, said distance being used for the correction of the image. The DOC distance may for example be measured by a distance sensor, such as an optical sensor, a magnetic sensor, a capacitive sensor, etc. Alternatively, the DOC distance may for example example be calculated from information provided by an optical focusing mechanism modifying the distance between the optical lens and the image sensor.

[0129] According to another aspect of the present invention, there is provided an image acquisition apparatus comprising an image acquisition device according to the invention.

[0130] According to embodiments, the device according to the invention can be a camera, a tablet or a Smartphone, a camera module intended to be integrated into another device, a computer, a surveillance camera, etc. Description of figures and embodiments

[0131] Other advantages and characteristics will appear on examining the detailed description of non-limiting embodiments, and the appended drawings in which: - [Fig.l] is a schematic representation of a non-limiting exemplary embodiment of an optical element that can be used to manufacture an optical lens; - [Fig.2] is a schematic representation of a non-limiting exemplary embodiment of an optical objective which can be characterized by the present invention; - FIGURES 3a and 3b are schematic representations of a non-limiting example of an optical interferometry measurement embodiment that can be implemented in the present invention; - [Fig.4] is a schematic representation of a non-limiting exemplary embodiment of a method according to the invention for characterizing an optical objective; - FIGURES 5a, 5b and 5c are schematic representations of non-limiting exemplary embodiments of a method according to the invention for acquiring an image; - [Fig.6] is a schematic representation of a non-limiting exemplary embodiment of a system according to the invention for characterizing an optical objective; - [Fig.7] is a schematic representation of a non-limiting exemplary embodiment of a device according to the invention for acquiring an image; and - [Fig.8] is a schematic representation of a non-limiting exemplary embodiment of a device according to the invention for acquiring an image.

[0132] It is understood that the embodiments which will be described below are in no way limiting. In particular, it will be possible to imagine variants of the invention comprising only a selection of characteristics described below isolated from the other characteristics described, if this selection of characteristics is sufficient for confer a technical advantage or to differentiate the invention from the state of the prior art. This selection includes at least one preferably functional feature without structural details, or with only part of the structural details if it is this part which is only sufficient to confer a technical advantage or to differentiate the invention from the state of the prior art.

[0133] In particular, all the variants and all the embodiments described can be combined with each other if nothing prevents this combination from a technical point of view.

[0134] In the figures and in the remainder of the description, the elements common to several figures retain the same reference.

[0135] [Fig.l] is a schematic representation of a non-limiting exemplary embodiment of an optical element that can be used to manufacture an optical lens.

[0136] The optical element 100 of [Fig. 1] may be used with at least one other optical element to manufacture an optical lens. An example of an optical lens, given by way of non-limiting example, will be described with reference to [Fig. 2].

[0137] The optical element 100 may be a lens, a blade, etc. In the following, and without loss of generality, it is considered that the optical element is a lens.

[0138] The optical lens 100 may for example be manufactured by injection molding. An injection molding process generally follows the following sequence of steps: - polymer injection and mold filling, - pressurization, - maintaining pressure, - cooling, and - demolding Injection lens manufacturing processes, although common, can fluctuate and generate errors in the characteristic parameters of the lenses, particularly with regard to their geometry.

[0139] The lens 100 has a given geometric shape. It comprises two interfaces 102i and 1022, each also having a given geometric shape. Thus, the geometric shape of the lens 100 is determined by: - a geometric shape of each of the optical interfaces 102i and 1022; - a center of curvature, noted CCI and CC2, of each of the optical interfaces 102i and 1022; - a position of an apex, denoted Al and A2, of each of the optical interfaces 102i and 1022; - at least one thickness, noted H1 and H2, of the lens 100 along its periphery; - an inner diameter, respectively DI 1 and D21, and / or an outer diameter, respectively D12 and D22, of each of the interfaces 102i and 1022; - a concentricity or eccentricity value of the interfaces 102i and 1022 - a surface roughness of each of the optical interfaces 102i and 1022; - etc.

[0140] The value of at least one of these geometric parameters may be provided by the manufacturer. Alternatively, or in addition, the value of at least one geometric parameter may be measured for example by optical or mechanical profilometry. Alternatively, or in addition, the value of at least one geometric parameter may be determined by simulation, from a digital modeling of the lens 100. Alternatively, or in addition, the value of at least one geometric parameter may be measured for example by optical interferometry.

[0141] In addition, the lens 100 has optical characteristics since it is an optical element. It is therefore characterized by at least one optical parameter such as for example: - a refractive index, noted II and 12, of each of the optical interfaces 102i and 1022; - an Abbot number, noted Ab, - etc.

[0142] [Fig.2] is a schematic representation of an exemplary embodiment not limiting of an optical objective which can be characterized by the present invention.

[0143] An optical lens has the function of focusing an image of a scene in an image plane, generally consisting of a photosensitive sensor such as a CMOS sensor (called "CMOS Imager System" which provides the acronym CIS), or a CCD sensor. Such an optical lens is generally made up of a stack of optical elements comprising any combination of optical elements such as lenses, spacer and opacification washers, etc.

[0144] During the manufacture of the optical lens, each optical element of said lens is individually selected and stacked with the other optical elements in an assembly barrel, in a given order. The stack is then secured to the barrel by known techniques, for example by gluing.

[0145] In [Fig.2], and by way of non-limiting example only, the optical lens 200 comprises four lenses 202-208 stacked, in a stacking direction 210, also called the Z axis, in a barrel 212. At least two of the lenses 202-208 may be separated from each other by an empty space, called an “air gap”, or by a spacer, or washer, also called a “spacer”.

[0146] At least one of the lenses 202-208 may for example be the lens 100 of [Fig.l].

[0147] Each of the lenses 202-208 comprises two interfaces, namely an interface, called upstream, and an interface, called downstream, in the direction of the stack 210. Thus, the lens 202 has an upstream interface 214i and a downstream interface 2142, the lens 204 has an upstream interface 2143 and a downstream interface 2144, the lens 206 has an upstream interface 2145 and a downstream interface 2146 and the lens 208 has an upstream interface 2147 and a downstream interface 2148.

[0148] Thus, for the optical objective 200 of [Fig.2], and generally for any optical objective comprising a stack of optical elements, it is possible to determine a data set, called geometric set, noted JG in the following, comprising data relating to at least one geometric parameter of at least one, and in particular of each, optical interface 214r2148 of said stack.

[0149] Such a geometric game JG may comprise data relating to, or values of, any of the following geometric parameters: - at least one position of at least one optical interface 214r2148 of the lens 200 along the Z axis; - at least one decentering value of at least one optical interface 214i -2148 relative to the Z axis, or relative to a center position of another interface, in the XY plane; or - at least one tilt value of at least one optical interface 214r2148 relative to the Z axis, or relative to the tilt of another interface; - at least one topography or shape profile value of at least one optical interface 214r2148.

[0150] Generally, the geometric set JG can comprise for each optical interface of the optical objective M geometric parameters with M>1 and preferably M>2. If the optical objective comprises N optical elements, each optical element comprising two interfaces, then the geometric set JG can comprise 2NxM parameters and can correspond to a matrix comprising 2N rows and M columns. Of course, the geometric set JG can comprise the same number of geometric parameters for at least two optical interfaces, or different numbers of geometric parameters for at least two optical interfaces.

[0151] The geometric game JG can directly comprise the values of the geometric parameters. These values can be measured by optical interferometry or by confocal measurement(s), preferably from one side or one face of the optical objective 200, so as to avoid rotating it.

[0152] [Fig.3a] is a schematic representation of a non-limiting exemplary embodiment of an optical interferometry measurement that can be implemented in the present invention.

[0153] The optical interferometry measurement is carried out by an optical interferometry device, or interferometric device, 300 shown very schematically, on [Fig.3a]. The apparatus 300 comprises a light source 302 and an interferometry sensor 304. The source 302 emits, in the direction of the stack of optical elements, a beam 306 of coherent light, called a measuring beam, at a measuring point, or according to a field of view, 308 in the XY plane, perpendicular to the direction 210. The measuring beam 306 then travels through the stack of optical elements, in particular in the Z axis 210 and passes through each optical interface 214; in turn. At each optical interface 214;, a portion 310; of the measuring beam 306 is reflected, such that: - a beam 310; is reflected by the interface 214;, - a beam 3108 is reflected by the interface 2148,

[0154] Each reflected beam 310; of the measuring beam 306 is then captured by the sensor 304 also being optically connected to the emission source 302, and will produce an interference signal when this reflected beam 310; and a reference beam 312, also coming from the light source 302, recombines on the sensor 304, the difference in the paths traveled by the two respective beams being less than the coherence length of the emission source 302. In particular, for each reflected beam 310; the sensor 304 provides an interference line, called the main line, or an interference image, depending on the illumination and detection modes implemented, at an optical distance corresponding to the position of the interface relative to the emission source 302, or any other predetermined reference.Of course, apart from the beam 310; reflected by the first interface 214; encountered by the measuring beam 306, a part of each of the other reflected beams 3102-3108 can, itself, be reflected in the other direction when passing a previous interface, which can generate optical beams with multiple reflections (not shown) captured by the sensor 304. These beams with multiple reflections generate interference lines, called secondary lines, or secondary images, generally of lower amplitude.

[0155] Optical interferometry measurements can be performed with a measurement beam from an interferometric sensor illuminated by a low-coherence light source. For this, the optical interferometry apparatus has positioning means for relatively positioning a coherence zone of the interferometric sensor 304 at the interface to be measured. The interface to be measured can be a buried interface, i.e., one of the interfaces inside the optical element. To reach such a buried interface, the measurement beam must therefore pass through other interfaces of the optical objective. The interferometric device makes it possible to selectively detect an interference signal for each interface at which the coherence zone is positioned, i.e., for each surface located in the coherence zone since the coherence length of the source light is adjusted to be shorter than a minimum optical distance between two adjacent optical interfaces of the optical objective. Thus, preferably, for each measurement, only one interface is in the coherence zone.

[0156] The interference measurements can be carried out according to a field of view determined by the measuring means of the device. The measurements can thus be carried out either in full field or by scanning the field of view.

[0157] Digital processing means can be configured to produce, from the interference signal, the value of a geometric parameter, of the interface measured according to the field of view, and in particular the values of the geometric parameters listed above with reference to [Fig.2].

[0158] Examples of interferometric devices that can be implemented within the scope of the present invention are, for example, described in document WO2020 / 245511 A1.

[0159] [Fig.3b] gives a schematic and partial representation of raw measurement data obtained for an optical interferometry measurement, such as that described with reference to [Fig.3a].

[0160] In this exemplary implementation, illumination according to a measurement point is used, and the coherence zone is moved along the optical axis Z 210 using displacement means.

[0161] Thus, as described with reference to [Fig.3a], each interference measurement provides raw data, or an interference signal, 320. The interference signal 320 comprises main lines 322, each main line corresponding to an optical interface. For example, a main line 322i is obtained for the interface 214i, a main line 3222 for the interface 2142, etc. (the interface 2148 not appearing in the example illustrated by [Fig.3b]).

[0162] The interference signal 320 also includes secondary lines corresponding to multiple reflections, and associated with the interfaces 2142-2148.

[0163] The optical position of each line is given on the abscissa and the normalized amplitude of each line is given on the ordinate.

[0164] As described above, the geometric parameters of each optical interface of the optical objective can be calculated from the interference lines. In particular: - the position along the Z axis of an optical interface can be determined as being the position of an interference line corresponding to said interface; - by carrying out several optical interferometry measurements, in particular in a central zone of the optical objective, and by following, on the several measurements, the position, along the Z axis, of the interference line associated with said interface, it is possible to determine the position of the APEX of said optical interface; - the position of the APEX of an optical interface makes it possible to determine the position of said interface relative to the Z axis, in the XY plane, and therefore its offset relative to the Z axis; - the inclination of an optical interface relative to the Z axis can be determined by carrying out several optical interferometry measurements, in particular in a peripheral zone of the optical objective. By following, on the several measurements, the position in the Z axis, of the interference line associated with said interface, it is possible to determine the position of the interface along the Z axis at its edges, which makes it possible to determine the inclination of said interface relative to the Z axis.

[0165] Thus, the geometric parameters of each optical interface of the optical objective can be determined from one or more interferometric measurements, carried out from one side of the optical objective without having to return said objective.

[0166] Of course, the invention is not limited to interferometric measurements. It can implement any type of optical measurements for determining the geometric parameters of the optical interfaces of the objective, such as for example confocal measurements.

[0167] [Fig.4] is a schematic representation of a non-limiting exemplary embodiment of a method according to the invention for characterizing an optical objective.

[0168] The method 400 of [Fig.4] can be used to characterize any type of optical objective for image acquisition, and more particularly the objective 200 of [Fig.2].

[0169] The method 400 comprises a step 402 of determining, by optical measurement, geometric parameters of the optical interfaces of the objective. In particular, the determination of the geometric parameters of each optical interface can be carried out by optical interferometry, as described with reference to FIGURES 3a and 3b. Thus, step 402 provides a geometric set JG comprising values of the geometric parameters of each interface of the optical objective, such as: - the position in the Z axis of the optical interface, - the position of the APEX of the optical interface, - the offset of the optical interface relative to the Z axis in the XY plane; - the inclination of the optical interface relative to the Z axis in the XY plane; - etc. The JG geometric set thus includes all the geometric values allowing the optical objective to be modeled in digital form.

[0170] During a step 404, the optical objective is modeled in digital form, with a modeling tool.

[0171] In a step 406, one or more aberration matrices are measured using the digital model of the optical objective in an optical wave propagation simulator.

[0172] Step 406 may determine a unique aberration matrix for the optical lens.

[0173] Alternatively, step 406 can be repeated several times in different regions, denoted R;, of the image sensor to determine at least one aberration matrix for each region of the image sensor.

[0174] Alternatively, or in addition, step 406 may be repeated several times for different lens-image sensor distances, denoted DOCj, to determine at least one aberration matrix for each distance DOCj.

[0175] Alternatively, or in addition, step 406 can be repeated several times for different objective-imaged scene distances, denoted DOSk, to determine at least one aberration matrix for each DOSk distance.

[0176] In the example described, it is considered that the step of determining an aberration matrix is carried out for each combination {R;, DOCj, DOSk}. Considering that there are I different regions, J different DOC distances and K different DOS distances, step 406 is therefore repeated I x J x K times and therefore makes it possible to determine as many aberration matrices, noted MAijk.

[0177] Each aberration matrix MAijk comprises values representative of the optical aberrations introduced, in a captured image, by this region R; of the optical lens for this distance DOCj between the optical lens and the image sensor, and for this distance DOSk between the optical lens and the scene.

[0178] Steps 404 and 406 may be performed with simulation software. Such simulation software may for example be the OpticStudio® software from Zemax®. Of course, the invention is not limited to this software and other tools may be used.

[0179] According to embodiments, all the aberration matrices are stored and the method 400 is terminated.

[0180] According to embodiments, the method 400 may comprise an optional step 408, of calculating a matrix, called aberration kernel matrix, noted MNA, comprising coefficients making it possible to deduce each aberration matrix, from said aberration kernel matrix.

[0181] Such an aberration kernel matrix can be calculated, as described above.

[0182] Thus, the aberration kernel matrix makes it possible to avoid having to memorize all the aberration matrices.

[0183] According to embodiments, the method 400 may comprise an optional step 410 of calculating a matrix, called a correction matrix, for each aberration matrix. The correction matrix may comprise the values used for

[0184]

[0185]

[0186]

[0187] correct an image. For each aberration matrix MAijk, the correction matrix, denoted MCijk, can be determined. According to exemplary embodiments, at least one correction matrix can be obtained by the relation: _ Tr-lf TF{Go] 1 where Go is a function representing the function form of point dispersion to be obtained after correction. It can be a function approaching a Dirac function in 2 dimensions, that is to say worth 1 at the center, and almost 0 around. Noting MTOBSijk, the matrix of the test light beam as observed, and MT its native form as it is in reality during its emission, the correction matrix MCijkde as follows: MC ~ TF~[In a simplified form, we can assume 'jk~ [ TF {MTOBSijk] J that TF(GO) = 1, the constant function which returns 1 with zero phase at all frequencies, which is written: MCiik = TF1 {.....1with: l TF{MTOBSijk} J - TF() the Fourier transform operator (in 2D) - TF '() the inverse Fourier transform operator (in 2D) - MCÿk correction matrix for the region R; of the image sensor, at the lens-sensor distance DOC; and at the lens-scene distance DOS; ; - MAijk the aberration matrix obtained by simulation for the region R; of the image sensor and the distances DOC; and DOS; ; and - MTijk the test light beam matrix, i.e. the matrix describing the test light beam, used to measure by simulation the aberration matrix MAijk. - MTOBSijk the observed illumination matrix, obtained by simulation, in the sensor plane relative to the MTijk test matrix presented at the input of the objective. According to embodiments, all the MCijk correction matrices can be stored for later reuse to correct an image. Alternatively, the method 400 may comprise an optional step 412 of calculating a matrix, called the correction kernel matrix, denoted MNC, comprising coefficients making it possible to deduce each correction matrix from the correction kernel matrix. Such a correction kernel matrix MNC may be calculated in the same way as the aberration kernel matrix, using the same function base FAi or another function base.

[0188] Each aberration matrix MAijk can be a matrix indicating values: - a point spread function, or “PSF” in English, and - an optical transfer function, “Optical Transfer Function” or “OTF” in English; in response a test light beam. The determination of such a matrix is well known to those skilled in the art and can be carried out by digital simulators such as Optic Studio ® from Zemax ®.

[0189] In summary, a test light beam is emitted onto a region presented in front of the optical lens. The test light beam enters the optical lens, passes through it and is received on an image sensor. The received radiation values are compared with the input values, i.e., with the values of the test light beam. This comparison makes it possible to deduce the aberrations introduced by the optical lens for each region.

[0190] [Fig.5a] is a schematic representation of a non-limiting exemplary embodiment of a method according to the invention for acquiring an image.

[0191] The method 500 of [Fig.5a] can be implemented in any type of image acquisition device using an optical lens associated with a photosensitive sensor, and in particular the lens 200 of [Fig.2]. The photosensitive sensor can be any type of sensor such as for example a CCD sensor or a CMOS sensor.

[0192] The device can be any type of device such as an imaging module, a smartphone, a tablet, a computer, a surveillance camera, etc.

[0193] The method 500 comprises a step 502 of acquiring an image by the apparatus using the optical lens and the sensor. The acquired image is in the form of a matrix of values, provided by the sensor, and denoted IMa. The IMa matrix comprises digital values for each pixel of the sensor. For example, for an RGB image, the IMa matrix comprises three values for each pixel, one for each color.

[0194] The acquired image, and therefore the IMa matrix, comprises the optical aberrations introduced by the optical lens, such as for example optical blur or displacement. It can be corrected, in part or in full, by correcting the values of the IMa matrix at least for certain pixels. The correction of the image can be carried out using at least one correction matrix deduced from at least one aberration matrix previously determined for the optical lens.

[0195] The image correction can be carried out using a single correction matrix, denoted MC, for the entire lens. Alternatively, the image correction can be carried out using several correction matrices MG, each for a region R; of the image sensor, and therefore for a part of the image. In the Subsequently, without loss of generality, we consider that several correction matrices MC; are used, each to correct the aberrations introduced by a region R; of the sensor.

[0196] In the method 500 of [Fig.5a], it is considered that the correction matrices are previously calculated, and stored in a memory area of the device carrying out the acquisition of the image. In particular, each correction matrix can be determined during a characterization of the optical objective, as described with reference to the method 400 of [Fig.4], in particular in step 410 of the method 400.

[0197] In this case, the method 500 comprises a step 504 of reading each correction matrix MC, from the memory area of the device.

[0198] Then during a step 506, the captured image is corrected using each correction matrix MC;.

[0199] For example, by denoting IMC the matrix of values representing the corrected image, the correction of the image can be obtained by convolution of the matrix IMa by each correction matrix MC; for the pixels concerned by the region R;, in turn or at the same time: BMI = conv(IMa, MCi) with i=l,.., I and I>1

[0200] [Fig.5b] is a schematic representation of another exemplary embodiment not limiting of a method according to the invention for acquiring an image.

[0201] The method 510 of [Fig.5b] comprises the steps 502 of acquiring an image and the steps 506 of correcting the image with one or more correction matrices.

[0202] Unlike method 500, in method 510, each correction matrix MC; is not previously determined and stored in a memory area of the device.

[0203] The method 510 comprises a step 512 of calculating each correction matrix: - from a correction kernel matrix, - from at least one predetermined aberration matrix, or - from an aberration kernel matrix. as described with reference to [Fig.4].

[0204] In method 510, optionally, each correction matrix may be stored in the apparatus to be reused for the correction of at least one other image. In this case, steps 502 and 506 may be repeated several times using each correction matrix calculated in step 512, without having to perform step 512 at each iteration.

[0205] Step 512 can be performed: - when integrating the optical lens into the device, - when configuring the device, - when installing a photo application in the device, - when starting the said photo application, or - when acquiring the image.

[0206] In the example of [Fig.5b], step 512 of calculating each correction matrix is performed before the image acquisition step. Of course, according to other examples not shown, step 512 of calculating each correction matrix can be performed during step 502 of acquiring the image, or after step 502 of acquiring the image, or at any time before the correction step 506.

[0207] [Fig.5c] is a schematic representation of another exemplary embodiment not limiting of a method according to the invention for acquiring an image.

[0208] The method 520 of [Fig.5c] may comprise an optional step of determining a distance, denoted DOC, between the optical lens and the photosensitive sensor. The distance DOC may for example be measured by a distance sensor, such as an optical sensor, a magnetic sensor, a capacitive sensor, etc. The distance DOC may for example be calculated from information provided by an optical focusing mechanism modifying / adjusting the distance between the optical lens and the image sensor.

[0209] Alternatively, or in addition, the method 520 of [Fig.5c] may comprise a step of determining a distance, denoted DOS, between the optical objective and the scene. The DOS distance may for example be measured by a LIDAR, a time-of-flight camera, an ultrasonic sensor, etc. The DOS distance may be measured for different regions R; of the image sensor. Alternatively, a single DOS distance may be measured for the entire objective.

[0210] Then, the method steps 500 or 510 can be performed to correct the image. The correction matrix(s) used to correct the image can be selected in step 504, or calculated in step 512, based on the DOC and / or DOS distances determined in steps 522 and / or 524.

[0211] Thus, the acquired image is corrected by taking into account the DOC distance and / or the DOS distance, at the time of image acquisition, which allows better correction of the image.

[0212] The method 520 thus allows on-the-fly correction of an image, taking into account the precise conditions in which the image was taken.

[0213] [Fig.6] is a schematic representation of an exemplary embodiment not limiting of a system according to the invention for characterizing an optical objective.

[0214] The system 600 of [Fig.6] can be used to characterize any type of optical objective used for image acquisition, and more particularly the objective 200 of [Fig.2],

[0215] The system 600 of [Fig.6] can be used to implement a method according to the invention for characterizing an optical objective, and in particular the method 400 of [Fig.4].

[0216] The system 600 comprises a device 602 for optical measurement of at least one geometric clearance, denoted JG, comprising data relating to at least one geometric parameter of at least one optical interface of an optical objective, such as for example the objective 200 of [Fig. 2]. The device 602 may be the interferometer 300 of FIGURE 3. The device 602 may alternatively be a confocal measurement device configured to measure the geometric clearance JG.

[0217] The system 600 further comprises a computing unit 604 configured to: - digitally model the optical objective based on the geometric clearance JG provided by the optical measuring device 602; and - determining, by optical wave propagation simulation applied to said digital model of the optical lens, at least one aberration matrix, representative of optical aberrations introduced by said optical lens in an image.

[0218] The calculation unit 604 can execute a modeling interface 606 taking as input the geometric game JG and a digital optical wave propagation simulator 608 to measure the at least one aberration matrix. According to embodiments, the modeling interface 606 and the digital simulator can be integrated into the same computer tool, in particular software, such as for example the OpticStudio software from Zemax.

[0219] The calculation unit 604 may optionally comprise a calculation module 610 configured to calculate: - at least one aberration kernel matrix, - at least one correction matrix, or - at least one correction kernel matrix; from the at least one aberration matrix determined by the digital simulator 608. The calculation module 610 may be a physical module such as a processor, a chip, a calculator, or a software module such as a computer program or a software application.

[0220] The computing unit 604 may be in a hardware form, such as a computer, or a server for example. Alternatively, the computing unit 604 may be in a software form, such as one or more computer programs. According to yet another alternative, the computing unit 604 may be formed by any combination of at least one hardware means and at least one software means.

[0221] [Fig.7] is a schematic representation of an exemplary embodiment not limiting of a device according to the image acquisition invention.

[0222] The device 700 of [Fig.7] can be used to implement a method according to the invention for acquiring an image, and in particular any one of the methods 500, 510 and 520 of FIGURES 5a, 5b and 5c.

[0223] The device 700 comprises an optical lens 702, which may be for example the optical lens 200 of [Fig.2].

[0224] The device 700 further comprises a photosensitive sensor 704, cooperating with the optical lens 702 to take an image of a scene. The image sensor 704 is provided to provide a matrix of values, denoted IMa, representing the acquired image of the scene.

[0225] Optionally, the device 700 may comprise a sensor 706 provided for measuring the distance DOC between the optical lens and the image sensor 704. Such a sensor 706 may be a capacitive sensor, a resistive sensor or even an image sensor. This sensor 706 provides a distance value, or a value of an electrical quantity representative of the distance DOC, such as for example a voltage, a current, etc.

[0226] Optionally, the device 700 may comprise a sensor 708 intended to measure the DOS distance between the optical objective and the imaged scene. Such a sensor 708 may be a LIDAR sensor for example. This sensor 708 provides a distance value, or a value of an electrical quantity representative of this DOS distance, such as for example a voltage, a current, etc.

[0227] The device 700 further comprises a calculation unit 710 configured to correct the image captured by the sensor 704, and in particular the matrix IMa, and provide a matrix, denoted IMC, representing the corrected image, as a function of at least one correction matrix.

[0228] The computing unit 710 may be a hardware unit such as a processor or a computer chip. Alternatively, the computing unit may be a computer program or an application.

[0229] According to one embodiment, for example described with reference to [Fig.5a], the at least one correction matrix can be read from a memory area, or a database, 712. In this case, the calculation unit 710 reads said at least one correction matrix, optionally the at least one matrix associated with the DOC and / or DOS distances measured during image capture.

[0230] According to one embodiment, for example described with reference to [Fig.5b], the calculation unit 710 can further be configured to calculate the at least one correction matrix, as a function of: - a correction kernel matrix, - at least one predetermined aberration matrix, or - an aberration kernel matrix; stored in the database 712. In this case, the calculation unit reads said at least one matrix and calculates the at least one correction matrix from said at least one matrix. least one matrix read, and optionally DOC and DOS distances.

[0231] The optical lens 702, the sensor 704, and optionally the sensors 706 and 708 form an imaging module, also called a camera module 714. The camera module 714 may include other components than those shown, such as for example a focus adjustment mechanism (not shown) modifying the distance between the image sensor 704 and the optical lens 702.

[0232] The calculation unit 710, and optionally the database 712, can be integrated into a photo application, 716, installed or executed within a device such as a Smartphone, a tablet, a computer, etc.

[0233] [Fig.8] is a schematic representation of a non-limiting exemplary embodiment of an image acquisition apparatus according to the invention.

[0234] The apparatus 800 comprises a device according to the invention for acquiring an image, and in particular the device 700 of [Fig.7].

[0235] According to embodiments, the device 800 may be a camera, a tablet or a Smartphone, a computer, a surveillance camera or a camera module intended to be integrated into another device, etc.

[0236] In the example shown, the device 800 is a Smartphone comprising a display screen on the front face and the optical module 714 opening onto its rear face, a photo application 716 integrating the calculation module and the database 712.

[0237] Of course, the invention is not limited to the examples which have just been described.

Claims

Claims

1. Method (400) for characterizing an optical objective (200) comprising a stack of several optical elements (202-208) and intended to be associated with an image sensor (704) for acquiring images, said method (400) comprising the following steps: - determination (402), by optical measurement on said stack of optical elements, of at least one data set (JG), called geometric set, comprising data relating to at least one geometric parameter of at least one optical interface (2142-2148) buried in said objective (200), - digital modeling (404) of said optical objective (200) as a function of said geometric set (JG), and - determination (406), by a digital simulator (608) of optical wave propagation applied to said digital model, of at least one matrix, called aberration matrix, representative of optical aberrations introduced by said optical objective (200) in an image.

2. Method (400) according to the preceding claim, characterized in that it comprises a determination of several aberration matrices for several regions of the image sensor (704).

3. Method (400) according to any one of the preceding claims, characterized in that it comprises a determination of several aberration matrices for several values of a distance, called objective-sensor distance, DOC, between said optical objective (200) and an image plane, the digital simulator (608) taking said objective-sensor distance as input.

4. Method (400) according to any one of the preceding claims, characterized in that it comprises a determination of several aberration matrices for several values of a distance, called objective-scene distance, DOS, between said optical objective (200) and a scene, the digital simulator taking said objective-scene distance as input.

5. Method (400) according to any one of the preceding claims, characterized in that it comprises a step (408) of calculating a matrix, called aberration kernel matrix, comprising coefficients allowing at least one aberration matrix to be deduced.

6. Method (400) according to any one of the preceding claims, characterized in that it further comprises a step (410) of calculating, as a function of at least one aberration matrix, at least one matrix, called a correction matrix, comprising values for correcting an image captured with said optical objective (200).

7. Method (400) according to any one of the preceding claims, characterized in that at least one aberration matrix is: - a matrix, called a PSF matrix, of values of a point spread function ("Point Spread Function" or "PSF" in English), and / or - a matrix, called an OTF matrix, of values of an optical transfer function ("Optical Transfer Function" or "OTF" in English).

8. Method according to any one of the preceding claims, characterized in that at least one geometric set (JG) is obtained by optical interferometry, or by confocal measurement(s).

9. System (600) for characterizing an optical objective (200) comprising a stack of several optical elements (202-208) and intended to be associated with an image sensor (704) for acquiring images, said system (600) comprising: - an optical measuring device (602; 300), on said stack of optical elements (202-208), of at least one data set (JG), called geometric set, comprising data relating to at least one geometric parameter of at least one buried optical interface (2142-2148) of said objective (200); - at least one calculation unit (604) configured to: • numerically model said optical objective (200) as a function of said geometric set (JG); and • determining, by digital simulation of optical wave propagation applied to said digital model, at least one matrix, called aberration matrix, representative of optical aberrations introduced by said optical objective (200) in an image.

10. Method (500;510;520) for acquiring an image with an apparatus (800) comprising an optical lens (200;702) and an image sensor (704), said method (500;510;520) comprising the following steps: - capturing (502) an image with said optical lens (200;702) and said image sensor (704); and - correcting (506) said image as a function of at least one correction matrix calculated from at least one aberration matrix obtained, for said optical lens (200;702), by the method (400) for characterizing an optical lens according to any one of claims 1 to 8.

11. Method (510; 520) according to the preceding claim, characterized in that it comprises a step (512) of calculating at least one correction matrix within said apparatus (800).

12. Method (520) according to any one of claims 10 or 11, characterized in that it further comprises a step (522) of determining a distance, DOC, between the optical objective (200; 702) and an image plane, the correction taking into account said distance DOC.

13. Method (520) according to any one of claims 11 to 13, characterized in that it further comprises a step (200;702) of determining a distance, DOS, between the optical objective (200;702) and a scene, the correction taking into account said distance DOS.

14. Device (700) for acquiring an image comprising: - an optical objective (200; 702) comprising a stack of several optical elements (202-208), - an image sensor (704), and - a calculation unit; configured to implement the method (500; 510; 520) according to any one of claims 10 to 13.

15. Apparatus (800) for acquiring an image, such as a camera, a tablet or a smartphone, comprising a device (700) for acquiring an image according to the preceding claim.

Images