Method and system for characterising an optical lens

Abstract

The invention relates to a method for characterising an optical lens, the method comprising the following steps: - measuring an optical transfer function, OTF, of the optical lens, individually for at least one of the following types of radiation: green radiation, blue radiation, red radiation; and - for at least one of the types of radiation: comparing the measured OTF with at least one predetermined threshold OTF to determine whether the optical quality of the lens is satisfactory. The invention also relates to a system for characterising an optical lens implementing such a characterisation method, and to a method and system for manufacturing an optical lens implementing such a characterisation method and system.

Description

DESCRIPTION Title: Method and system for characterizing an optical objective

[0001] The present invention relates to a method for characterizing an optical lens. It also relates to a system implementing such a method. It also relates to a method and a system for manufacturing optical lenses implementing such a characterization method and system.

[0002] The field of the invention is generally the field of characterization of an optical objective, in particular an optical objective, used for imaging, and more particularly for determining the optical quality of said objective. State of the art

[0003] An optical lens, or lens in the following, consists of several optical elements, such as lenses, spacers, etc., stacked in a barrel in a stacking direction. Once manufactured, the optical lens undergoes a performance test to determine whether the imaging quality of the lens is satisfactory or not. If the quality of the lens is not satisfactory, the lens is simply discarded, which decreases manufacturing efficiency, causing a waste of time and cost.

[0004] Currently, the quality of an optical lens is tested by measuring the Modulation Transfer Function (MTF) of the optical lens using white radiation. The measured MTF is compared to a predefined threshold MTF to determine whether the lens quality is satisfied.

[0005] The measured MTF is representative of all optical aberrations of the lens, namely chromatic aberration, geometric aberration and third and higher order aberrations (called "3rd order aberrations"). ème order in the following for the sake of brevity). However, The inventors discovered that some aberrations, such as lateral chromatic aberration and geometric aberration, can be effectively corrected by calculation. Therefore, there is a need for a new way to characterize an optical lens.

[0006] An aim of the present invention is to remedy at least one of the aforementioned drawbacks.

[0007] Another aim of the invention is to propose a solution for characterizing an optical objective allowing a more relevant characterization of the optical objective.

[0008] Another aim of the invention is to propose a more efficient solution for characterizing an optical objective. Statement of the invention

[0009] The invention proposes to achieve at least one of the aforementioned aims by a method for characterizing an optical objective, said method comprising the following steps: - measuring an optical transfer function, OTF, of said optical objective, individually for at least one of the following radiations: green radiation, blue radiation, red radiation; and - for at least one of said radiations: comparison of the measured FTO with at least one predetermined threshold FTO, in order to determine whether the optical quality of said objective is satisfactory.

[0010] The inventors have noticed that optical aberrations of the displacement type due to an optical lens can be corrected very effectively by calculation, i.e. by digital processing of the acquired images, whereas aberrations of the spreading type are very difficult to correct, or sometimes even impossible to correct depending on the imaged scene. Based on this observation, the present invention proposes to measure the optical quality of an optical lens using, not an MTF measured of said optical lens with white light as is currently the case, but an FTO measured individually for at least one, and in particular for each, red, green and blue components. Indeed, the characterization of the optical lens for each color individually makes it possible to obtain a more relevant characterization of the contrast quality than in white light. Indeed, in white light, it is possible to obtain poor contrast, despite high contrast on each detected color, in particular as soon as the lateral chromatic aberration becomes of the same order as the pitch of the pattern which is used to evaluate this contrast ratio, therefore the MTF.

[0011] Thus, the invention proposes a new solution for characterizing an optical objective that is more efficient and allows said optical objective to be better characterized.

[0012] By "optical aberration" we mean the notion that the image of a point in the scene becomes a more or less large luminous spot in the place (generally plane) where the image is formed. Aberration results in different types of effects: there are aberration effects whose characteristic is to move the average position of the optical spot produced by a point in the scene, in relation to a place where we would ideally have wanted it to occur. We will call them displacement aberrations. There are other effects which are that the optical spot has a spatially spread energy distribution, instead of being punctual, in the image place. We will call them spreading aberration.

[0013] Aberrations due to an optical lens are commonly referred to as chromatic aberration, geometric aberration and 3D aberration. ème order.

[0014] By "aberrations of 3 èmeorder”, we mean the set of aberrations introduced by an optical lens in an image acquired with said optical lens, except chromatic aberration and geometric aberration. These aberrations of the 3 ème order (and higher order) include for example spherical aberration, Coma, astigmatism, field curvature, distortion (of shape and energy distribution of the optical spot), etc. These aberrations of the 3 ème order are of the spreading type.

[0015] By "chromatic aberration", which results from the decomposition of light into several color bands, we mean an optical aberration which produces different positions in space of the focal point in function of the wavelength. For a so-called "lateral" chromatic aberration, it is a displacement of the focal point in the image location, as a function of the wavelength. We then observe an image with iridescent contours, or colored fringes around objects of uniform color, for example white. For a so-called "axial" chromatic aberration, it is a focusing outside the image location because the focal points are shifted along an axis perpendicular to the image location (or the axis corresponding to the central optical ray arriving at the image point, which may be oblique to the image location). We then observe an image in which certain colors are blurred. Lateral chromatic aberration can be corrected by digital processing of the image captured by a lens as long as it is quantified, that is to say measured during the design / manufacture of the optical lens. It joins the displacement type aberrations.Axial chromatic aberration, on the other hand, joins the spreading type aberrations, because if for example the green color is focused on the sensor of the image plane, the red color can focus before, and the red optical beam become widened when it meets the sensor further than the point of focus.

[0016] Geometric aberration refers to a deviation between a paraxial ray defined in the Gaussian approximation and the corresponding real ray. Geometric aberration can also be characterized by a deviation between the paraxial wave surface and the real wave surface. For example, geometric aberrations produce a distortion of the shape of the resulting image. For example, a square can become a shape equal to the outline of a barrel (turned corners), or a dressmaker's cousin (growths on the corners). Thus, the straight and vertical edges of a building can become curved, not vertical. This aberration can be corrected by digital processing of the captured image as long as it is quantified, i.e. measured during the design / manufacture of the optical lens. Geometric aberrations are of the displacement type.

[0017] By "displacement aberration" or "displacement aberration" we mean lateral chromatic aberration and geometric aberration.

[0018] By "spreading-type aberration" or "spreading aberration" is meant axial chromatic aberration and aberrations of the 3 ème order.

[0019] In the following, by "color radiation" means a red color radiation, or a green color radiation or a blue color radiation.

[0020] According to embodiments, the optical transfer function, OTF, may be the modulation transfer function, MTF (or MTF for “Modulation Transfer Function”).

[0021] According to embodiments, the optical transfer function, OTF, may be the point spread function, PSF (or FEP for “Point Spread Function”).

[0022] Regardless of the FTO, namely MTF or PSF, the FTO is measured and the FTO threshold are of the same nature, either MTF or PSF.

[0023] According to embodiments, at least one, and in particular each, measured FTO may be represented by FTO values ​​measured at several points, for example at the center of the lens on the edge of the lens, etc. Preferably, the measured FTO may be represented by a field of values ​​comprising several measured FTO values, each for a position (x,y), and in particular at a pixel of position (x,y), of an image sensor used to carry out said measurement.

[0024] Alternatively, it is possible, from the measured values, to deduce a mathematical relationship taking as input a position (x,y) of the image sensor and giving as output a measured FTO value.

[0025] Of course, at least one measured FTO can be in other forms, such as a matrix, a vector, etc.

[0026] According to embodiments, at least one, and in particular each threshold FTO, can be represented by a set of values, also called a field of values, for several positions (x,y), or for several position pixels (x,y), of an image sensor: for example at center of the sensor, on the edge, etc. According to an exemplary embodiment, for at least one position (x,y), the field of values ​​may include a minimum FTO value to be reached. Alternatively, or in addition, for at least one position (x,y), the field of values ​​may include a pair of values ​​formed by a minimum FTO value and a maximum FTO value.

[0027] Alternatively, at least one threshold FTO can be presented in the form of at least one mathematical relationship taking as input a position (x,y) of the image sensor and giving as output: - a threshold value of FTO, and in particular a minimum value of FTO, or - a pair comprising a minimum FTO value and a maximum FTO value.

[0028] Of course, at least one threshold FTO can come in other forms, such as a matrix, a vector, etc.

[0029] At least one threshold FTO may be determined by an experimental design or test plan. Alternatively, or in addition, at least one threshold FTO may be determined during the design of the optical lens. Of course, these examples are not limiting and at least one threshold FTO may be determined in another way.

[0030] According to embodiments, the measuring step can perform the FTO measurement only for a single radiation.

[0031] In this case, the FTO measured for this single radiation is compared to the predetermined threshold FTO for said single radiation. If the measured FTO satisfies the threshold FTO then the optical objective is considered to have satisfactory optical quality.

[0032] According to embodiments, the only radiation for which the FTO is measured may be green radiation. Indeed, the inventors have discovered that the green color is more representative of lateral chromatic aberrations.

[0033] According to embodiments, the measuring step can perform the FTO measurement individually for at least two, in particular for each, of the red, green and blue radiations.

[0034] In other words, the FTO measurement step performs the measurement of one FTO individually for several of the red, green and blue radiations.

[0035] In this case, for each measured radiation, a measured FTO is obtained. For example, if a measurement is made for red radiation, a measured FTO is obtained for red radiation. For example, if a measurement is made for green radiation, a measured FTO is obtained for green radiation. For example, if a measurement is made for blue radiation, a measured FTO is obtained for blue radiation.

[0036] Preferably, the FTO measuring step performs the measurement of an FTO individually for each of the red, green and blue radiation. In this case, a measured FTO is obtained for the red radiation, a measured FTO is obtained for the green radiation, and a measured FTO is obtained for the blue radiation.

[0037] When the FTO measurement step performs the measurement of an FTO individually for several, or even each, of the red, green and blue radiations, the comparison step can perform a comparison of each measured FTO to at least one predetermined threshold FTO.

[0038] In this case, the optical quality of the optical objective can be judged satisfactory if and only if each measured FTO satisfies the threshold FTO to which it is compared.

[0039] According to embodiments, the same threshold FTO can be used for at least two, and in particular all, radiations.

[0040] According to embodiments, different threshold FTOs may be used for at least two, and in particular all, of the radiations.

[0041] In other words: - a threshold FTO is associated with the red radiation and the FTO measured for said red radiation is compared to said threshold FTO; - a threshold FTO is associated with the green radiation and the FTO measured for said green radiation is compared to said threshold FTO; and - a threshold FTO is associated with the blue radiation and the FTO measured for said blue radiation is compared to said threshold FTO.

[0042] According to embodiments, for at least one radiation, the FTO measurement can be carried out for a measurement plane corresponding to the greatest focusing, or for a plane for which a satisfied focusing is obtained.

[0043] Such a measuring plane is preferably perpendicular to the axis of the optical objective.

[0044] To do this, the method according to the invention may comprise a step of identifying said measurement plane by measuring the focus for several planes and identifying the plane for which the greatest focus, a satisfactory focus is obtained. For example, a target may be arranged in front of the objective. The relative position of the target with respect to the objective may be modified along the axis of the optical objective and the value of the focus may be monitored to identify the measurement plane.

[0045] When the measurement step performs an FTO measurement for several radiations, the same measurement plan can be used for several, in particular all, radiations.

[0046] Alternatively, it is also possible to identify the measuring plane as follows. Place the measuring plane at a specific distance from the optical lens, and adjust the focus of the camera module formed by the optical lens and the image sensor for the best sharpness at this distance.

[0047] Of course, other embodiments are possible and these non-limiting examples are given for illustration purposes only.

[0048] According to embodiments, for at least one radiation, the measuring step can carry out a measurement of a value of the FTO at several points. The FTO measured, for this radiation, is represented by, or obtained from, the values ​​measured for these several points.

[0049] As indicated above, for at least one radiation, the measured FTO may be represented by a field of several values, this field of values ​​comprising said measured values, and possibly other estimated values, for example by interpolation. Alternatively, the measured FTO may be represented by a mathematical relationship deduced from the measured values.

[0050] According to embodiments, for at least one radiation, the measuring step can be carried out with a target, comprising one or more patterns, positioned in front of the optical objective.

[0051] For at least one radiation, the test pattern may directly include patterns whose color corresponds to the color of the radiation, namely red, green or blue. Alternatively, the test pattern may include transparent patterns illuminated by red, green or blue radiation.

[0052] In the case where the FTO is the MTF, the measurement of the MTF of a point corresponds to the contrast measured for said point.

[0053] According to an exemplary embodiment, a target is placed at a certain distance, called the scene distance, chosen from the sensor and the lens. This distance can also be achieved by means of an optic inserted between the target and the lens, in order to change the apparent distance of the target from the sensor, beyond the physical distance between the target and the lens. This apparent distance can even be made infinite to obtain a scene distance called infinity. The lens is possibly moved relative to the sensor to select the best sharpness of the target for this apparent scene distance. (The best sharpness can be obtained on an area of ​​the sensor, on a color component, but not necessarily on all 3 color components at once, nor the entire sensor at once...). This target includes an alternation: - patterns, called dark, which do not let the radiation pass through, and - patterns, called light, which correspond to the color of the radiation. Dark patterns are supposed to result in radiation-free patterns on the sensor since they do not allow radiation to pass through. Light patterns are supposed to result in patterns of the same color as the radiation since they allow the radiation to pass through.

[0054] In this configuration, the MTF of a point (x,y) of the sensor is calculated in the following manner. For an area centered on the point (x,y), and comprising several alternating patterns, several contrast values ​​are calculated based on the values ​​received by the pixels of said area, each contrast value corresponding to an alternating pattern in said area. The MTF value for the point (x,y) is calculated based on said measured values, for example by an average of said values.

[0055] In the case where the FTO is the PSF, the measurement of the PSF of a corresponding point is carried out in a conventional manner.

[0056] According to an exemplary embodiment, a target is arranged in front of the sensor and the lens, for example at a plane corresponding to maximum focusing, directly or via a distance adaptation optic. This target comprises a plurality of points allowing the radiation to pass through. The rest of the target is opaque and does not allow the radiation to pass through.

[0057] Each point located at a position (x,y) is captured on the sensor in the form of a more or less large task and of a more or less different shape.

[0058] When the task is a perfect circle, then the value of the PSF of the point (x,y) corresponds to the radius of the task captured on the sensor.

[0059] When the spot has another shape, the PSF can, for example, be calculated as the mean radius of the spot. The mean radius can be calculated as follows. First, the center of the spot is extracted, for example, by determining the barycenter of the positions of the points forming the spot, weighted by the intensity detected at each position. Then, the sum of the detected amplitude multiplied by the square of the distance to the barycenter is calculated. This sum is divided by the sum of the detected amplitudes. This gives a square of the mean radius of the spot. The square root is taken. This gives an effective mean radius of the spot.

[0060] According to another aspect of the same invention, there is provided a system for characterizing an optical objective, said system comprising: - at least one device for measuring an optical transfer function; and - a computing unit; configured to implement the method according to the invention.

[0061] The characterization system according to the invention may comprise, in terms of means and / or configuration, any combination of the optional characteristics described above in relation to the characterization method according to the invention and which are not repeated here for the sake of brevity.

[0062] For at least one of the red, green and blue radiations, the system according to the invention may comprise a measuring device dedicated to measuring the FTO exclusively for said radiation.

[0063] The system according to the invention may comprise an apparatus performing the FTO measurement individually for several of the red, green and blue radiations.

[0064] At least one measuring device may include a source associated with at least one target.

[0065] The light source can emit red radiation and / or green radiation and / or blue radiation. In this case, the test chart can include transparent patterns or patterns of the same color as the radiation. With a test chart including transparent patterns, it is possible to measure the FTO individually for each color by changing the color of the radiation emitted by the source, or simultaneously for white radiation emitted by the source through transparent patterns, and by analyzing the images obtained for each color filtered by the sensor, by the red, green, blue pixels.

[0066] Alternatively, the light source may emit white radiation, and the test pattern may include patterns of the same color as the radiation for which the FTO is measured. Thus, by using several test patterns, each including patterns of one of the colors red, green and blue, it is possible to measure the FTO for each color individually.

[0067] The at least one measuring device may comprise a calculation module for determining the measured FTO for at least one radiation.

[0068] The computing unit may be configured to compare the measured FTO to at least one threshold FTO, for at least one, in particular each color radiation.

[0069] At least one measuring device may include an image sensor used to measure the FTO. In this case, the image sensor may be used for FTO measurement for multiple optical lenses.

[0070] Alternatively, at least one measuring device may not include an image sensor. In this case, the optical lens is previously associated with, and in particular assembled with, an image sensor.

[0071] According to another aspect of the present invention, there is provided a method of manufacturing optical lenses comprising the following steps for at least one optical lens: - manufacture of said optical lens, - characterization of said optical objective by the characterization method according to the invention, - conservation or not of said optical objective depending on the result of said characterization.

[0072] When the FTO is measured for a single color radiation, namely red radiation or green radiation or blue radiation, then the optical objective can be retained if, for said radiation, the measured FTO satisfies at least one predetermined FTO threshold.

[0073] When the FTO is measured for several color radiations, namely red radiation and / or green radiation and / or blue radiation, the optical objective can be retained if, for each measured radiation, the measured FTO satisfies the at least one respective predetermined threshold FTO for said radiation.

[0074] According to embodiments, each manufactured optical lens can be characterized.

[0075] Alternatively, only some manufactured optical lenses may be characterized. For example, within the same batch of optical lenses, only one, or a few, optical lenses may be characterized. The FTO(s) measured for said lens(es) of said batch may be used for all lenses of the same batch.

[0076] A batch of optical lenses may correspond to lenses with the same design. Alternatively, a batch of optical lenses may correspond to lenses with the same design and assembled according to the same assembly recipe.

[0077] According to another aspect of the present invention, there is provided an installation for manufacturing optical lenses comprising: - an optical lens manufacturing line, and - a characterization system according to the invention for characterizing at least one optical objective.

[0078] The manufacturing installation according to the invention may comprise, in terms of means and / or configuration, any combination of the optional characteristics described above in relation to the manufacturing method according to the invention and which are not repeated here for the sake of brevity.

[0079] In particular, the manufacturing facility is configured to implement the manufacturing method according to the invention.

[0080] According to another aspect of the invention, there is provided a camera module comprising: - an optical objective characterized with the characterization method according to the invention; and - an image sensor associated with said optical lens.

[0081] The image sensor can be any type of image sensor combined with an optical lens, such as a CMOS or CCD image sensor, but is not limited to these image sensors.

[0082] According to another aspect of the invention, there is provided a user apparatus comprising at least one optical objective characterized with the method according to the invention

[0083] The user device according to the invention may in particular comprise at least one camera module according to the invention.

[0084] In particular, the user device may be a user device such as a smartphone, tablet, etc.

[0085] The user device may optionally include a display screen, in particular a touch screen, etc.

[0086] In particular, the user device may be a virtual reality headset or an augmented reality headset, intended to be worn by a user.

[0087] The helmet may optionally include a display screen, in particular a touch screen, etc.

[0088] In particular, the user device may be a camera or photo device, etc.

[0089] The user device of the camera or photo type may optionally include a display screen, in particular a touch screen, etc.

[0090] In particular, the user device may be a computer-type user device.

[0091] The computer-type user device may optionally include a display screen, in particular a touch screen, etc.

[0092] The computer-type user device may optionally include a keyboard, or any other equipment integrated or associated with said device.

[0093] In particular, the user device may be a television.

[0094] The television may optionally include a display screen, in particular a touch screen, etc.

[0095] In particular, the user device may be a medical imaging device.

[0096] The medical imaging device can be, for example, an endoscope, an ultrasound machine, etc.

[0097] Of course, the apparatus according to the invention is not limited to the examples which have just been given.

[0098] According to another aspect of the present invention, there is provided a vehicle comprising at least one optical objective characterized with the characterization method according to the invention.

[0099] The vehicle according to the invention may in particular comprise at least one camera module according to the invention.

[0100] According to embodiments, the vehicle may be a land vehicle, such as a car, for example non-autonomous driving, semi-autonomous driving or autonomous driving.

[0101] According to embodiments, the vehicle may be a flying vehicle, such as a drone, an airplane, a helicopter, for example with non-autonomous driving, semi-autonomous driving or autonomous driving.

[0102] According to embodiments, the vehicle may be a marine vehicle, such as a boat or a submarine, for example non-autonomously driven, semi-autonomously driven or autonomously driven.

[0103] According to another aspect of the present invention, there is provided a method of acquiring an image of a scene, said method comprising the following steps: - acquisition of an image with an optical objective characterized by the method according to the invention, and - digital processing of said image for the correction of said image.

[0104] According to embodiments, the digital processing may comprise a step of correcting the lateral chromatic aberration introduced into the image by the optical lens.

[0105] According to embodiments, the digital processing may comprise a step of correcting the geometric aberration introduced into the image by the optical lens.

[0106] According to embodiments, the optical lens can be used for 2D or 3D imaging.

[0107] According to embodiments, the optical lens can be used for image acquisition to image a scene at a given time, or for acquiring a stream of images, or a video, of a scene. Description of figures and embodiments

[0108] Other advantages and characteristics will appear on examining the detailed description of non-limiting embodiments, and the attached drawings in which: - FIGURE 1 is a schematic representation of a non-limiting exemplary embodiment of a characterization method according to the invention; - FIGURE 2 is a schematic representation of another non-limiting exemplary embodiment of a characterization method according to the invention; - FIGURE 3 is a schematic representation of a non-limiting exemplary embodiment of a characterization system according to the invention; - FIGURE 4 is a schematic representation of a non-limiting exemplary embodiment of a method for manufacturing optical objective(s) according to the invention; - FIGURE 5 is a schematic representation of a non-limiting exemplary embodiment of an installation for manufacturing optical lens(es) according to the invention; - FIGURE 6 is a schematic representation of a non-limiting exemplary embodiment of a camera module according to the invention; - FIGURE 7 is a schematic representation of a non-limiting exemplary embodiment of a method for acquiring an image according to the invention; - FIGURES 8a-8c are schematic representations of non-limiting exemplary embodiments of an apparatus according to the invention; and - FIGURE 9 is a schematic representation of a non-limiting exemplary embodiment of a vehicle according to the invention.

[0109] It is understood that the embodiments which will be described below are in no way limiting. In particular, it is 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 to confer a technical advantage or to differentiate the invention compared to the state of the prior art. This selection includes at least one preferably functional characteristic 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 compared to the state of the prior art.

[0110] In particular, all the variants and embodiments described can be combined with each other if there is no technical obstacle to this combination. [YES] In the figures and in the rest of the description, the elements common to several figures retain the same reference.

[0112] FIGURE 1 is a schematic representation of a non-limiting exemplary embodiment of a method for characterizing an optical objective according to the present invention.

[0113] The method 100 of FIGURE 1 can be used to characterize an optical lens 00 used for imaging, i.e., for acquiring an image or video. Such a lens 00 can be associated with an image sensor to form an imaging module, or a camera module, and be integrated into different devices or vehicles.

[0114] An optical lens is usually composed of several optical elements, such as lenses, spacers, etc. The different elements of the optical lens are stacked according to a stacking direction, which also corresponds to the axis of the optical lens.

[0115] The optical lens 00 may be associated with an image sensor (not shown in FIGURE 1). In this case, this image sensor is used for the characterization of said optical lens 00.

[0116] Alternatively, the optical lens may not be associated with an image sensor. In this case, an image sensor of a measuring device is used for the characterization of said optical lens 00.

[0117] The method 100 of FIGURE 1 comprises a step 102 of identifying a measurement plane, perpendicular to the optical axis of the optical objective 00, for the measurement of an optical transfer function, OTF.

[0118] To do this, for example, a target can be arranged in front of the lens. The relative position of the target to the lens can be changed along the optical lens axis (possibly by means of an adaptive optic) and the focus value can be monitored to identify the measuring plane providing the greatest focus, or a satisfactory focus value relative to a predetermined focus threshold.

[0119] Method 100 of FIGURE 1 performs a characterization of the optical objective from an optical transfer function, OTF, measured individually for each green, red and blue color.

[0120] In the example in FIGURE 1, the FTO is the MTF. Alternatively, instead of using the MTF as the FTO, it is possible to use the PSF.

[0121] The method 100 comprises a step 104 of measuring the MTF of the optical objective 00, for green radiation.

[0122] In the non-limiting example of FIGURE 1, the green radiation may be green radiation whose wavelength is between 500 nm and 570 nm, and in particular equal to 535 nm.

[0123] The measurement of the MTF can be carried out according to the technique described above. In particular, a target is positioned in the measurement plane identified during step 102. This target, associated with a light source, emits an image according to green color patterns towards the lens. The image of these patterns passes through the optical lens and is captured by the image sensor. For a point of the sensor, the MTF can be measured as the average contrast obtained on several patterns, or several lines of the pattern located around said point.

[0124] Step 104 performs a plurality of measurements of MTF values ​​for multiple points of the image sensor and provides a measured MTF represented by a field of measured MTF values, each for an (x,y) position of the sensor.

[0125] Then, a step 106 performs a comparison of the measured MTF to at least one threshold MTF.

[0126] According to an exemplary embodiment, the measured MTF is compared to a threshold MTF giving minimum MTF values. If the measured MTF is greater than the threshold MTF then the optical objective 00 is retained. Otherwise, the optical objective is rejected.

[0127] According to an exemplary embodiment, the measured MTF is compared to a first threshold MTF giving minimum MTF values ​​and to a second threshold MTF giving maximum MTF values. If the MTF measured is between the first threshold MTF and the second threshold MTF, then the optical objective is retained. Otherwise, the optical objective is rejected.

[0128] The comparison of the measured MTF to one, in particular each, threshold MTF can be performed value by value. In other words, for a sensor position (x,y), the measured MTF value for said position (x,y) is compared to the threshold MTF value for said position. The measured MTF satisfies the threshold MTF, if and only if, for each of the measurement positions (x,y), the measured MTF value satisfies the threshold MTF value. Finally, the threshold MTF can also depend on (x,y).

[0129] When the measured MTF for green radiation is satisfactory in step 106, the method 100 comprises a step 108 of measuring the MTF for red radiation, similarly to the measurement of the MTF for green radiation in step 104.

[0130] In the non-limiting example of FIGURE 1, the red radiation may be red radiation whose wavelength is between 570 and 730 nm, and in particular equal to 650 nm.

[0131] In a step 110, the measured MTF for the red radiation is compared to at least one predetermined threshold MTF for the red radiation. If the comparison shows that the measured MTF for the red radiation does not satisfy the at least one threshold MTF, the optical objective 00 is rejected. Otherwise, the optical objective 00 is retained and the method 200 continues.

[0132] When the measured MTF for red radiation is satisfactory in step 110, the method 100 comprises a step 112 of measuring the MTF for blue radiation, similarly to the measurement of the MTF for green radiation in step 104.

[0133] In the non-limiting example of FIGURE 1, the blue radiation may be blue radiation whose wavelength is between 400 and 500 nm, and in particular equal to 450 nm.

[0134] In a step 114, the measured MTF for blue radiation is compared to at least one predetermined threshold MTF for blue radiation. If the comparison shows that the measured MTF for blue radiation does not does not satisfy at least one MTF threshold, the optical objective 00 is rejected. Otherwise, the optical objective is retained.

[0135] In the example of FIGURE 1, the measured MTF for one color is compared to at least one threshold MTF before measuring the MTF for another color. This avoids measuring the MTF for said other color when the measured MTF for the current color is not satisfactory.

[0136] According to an alternative not shown, steps 104, 108 and 112 can be carried out before carrying out comparison steps 106, 110 and 114.

[0137] FIGURE 2 is a schematic representation of another non-limiting exemplary embodiment of a method for characterizing an optical objective according to the present invention.

[0138] The method 200 of FIGURE 2 can be used to characterize an optical lens 00 used for imaging, i.e., for acquiring an image or video. Such a lens 00 can be associated with an image sensor to form an imaging module, or a camera module, and be integrated into different devices or vehicles.

[0139] The optical lens 00 may be associated with an image sensor (not shown in FIGURE 1). In this case, this image sensor is used for the characterization of said optical lens 00.

[0140] Alternatively, the optical lens may not be associated with an image sensor. In this case, an image sensor of a measuring device is used for the characterization of said optical lens 00.

[0141] Unlike method 100 of FIGURE 1 which characterizes the lens based on each green, red and blue color, method 200 of FIGURE 2 characterizes the optical lens 00, from an FTO measured individually for a single color.

[0142] In the example in FIGURE 2, the measured FTO is the MTF. Alternatively, instead of using the MTF as the FTO, it is possible to use the PSF.

[0143] In the example in FIGURE 2, the only color used to characterize the optical lens is green. Of course, alternatively, it is possible to use red or blue.

[0144] Method 200 includes steps 102-106 described with reference to method 100 of FIGURE 1, and does not include steps 110 and following of method 100.

[0145] When in step 108 the measured MTF for the green radiation is satisfactory, the optical objective 00 is retained. Otherwise, the optical objective 00 is rejected.

[0146] Then, process 200 is terminated.

[0147] According to another alternative not shown in the FIGURES, the optical objective 00 can be characterized on the basis of two colors chosen from the colors green, red and blue.

[0148] FIGURE 3 is a schematic representation of a non-limiting exemplary embodiment of a system for characterizing an optical objective according to the present invention.

[0149] The system 300 of FIGURE 3 can be used to implement a method according to the invention, and in particular any one of the methods 100 or 200.

[0150] The system 300 includes a first measuring apparatus 302 for measuring an FTO with green-colored radiation. The measuring apparatus 302 may include a green-colored radiation source illuminating a target with transparent patterns, such that the optical objective receives green-colored patterns. Alternatively, the measuring apparatus 302 may include a white-colored radiation source illuminating a target with green-colored patterns, such that the optical objective receives green-colored patterns.

[0151] The system 300 includes a second measuring apparatus 304 for measuring an FTO with red color radiation. The measuring apparatus 304 may include a source of red color radiation. illuminating a target with transparent patterns, such that the optical lens receives red color patterns. Alternatively, the measuring apparatus 304 may comprise a white color radiation source illuminating a target with red color patterns, such that the optical lens receives red color patterns.

[0152] The system 300 includes a third measuring apparatus 306 for measuring an FTO with blue-colored radiation. The measuring apparatus 306 may include a blue-colored radiation source illuminating a target with transparent patterns, such that the optical lens receives blue-colored patterns. Alternatively, the measuring apparatus 306 may include a white-colored radiation source illuminating a target with blue-colored patterns, such that the optical lens receives blue-colored patterns.

[0153] It is recalled that the FTO can be the MTF or the PSF.

[0154] The system 300 further comprises a computing unit 308.

[0155] The calculation unit 308 comprises a calculation module 310. The calculation module can be configured, or programmed, to, for a given color, perform a comparison of an FTO measured for said color to one or more predetermined threshold FTOs.

[0156] The calculation module 310 may optionally be configured, or programmed, to calculate, for a given color, a measured FTO value based on the measurements made by any one of the measuring devices 302-306. This calculation operation may alternatively be integrated into at least one, and in particular each, of the measuring devices 302-306.

[0157] The calculation unit 308 may optionally comprise a control module 312 for at least one, and in particular each, of the measuring devices 302-306 for carrying out the FTO measurements.

[0158] At least one of the modules 310-312 may be a hardware unit such as a processor, a microchip, a computer, a server, etc. Alternatively, at least one of the modules 310-312 may be a unit software, such as an application or a computer program. Alternatively, at least one of the elements 310-312 may be a combination of at least one hardware unit and at least one software unit.

[0159] At least one of the modules 310-312 may be independent of the other of the modules 308-312. Both modules 310-312 may be integrated within the same module.

[0160] According to an alternative not shown, at least two, in particular all, of the measuring devices 302-306 can be integrated within a single measuring device.

[0161] In this case, the single measuring device may comprise a light source configured to emit, for example in turn, green, red and blue colored radiation. In this case, the single measuring device may comprise, or use: - a target with transparent patterns that can be used for FTO measurement for each of the colors, or - a green pattern target, a red pattern target, and a blue pattern target, used in turn.

[0162] Alternatively, the single measuring device may include a white light source. In this case, the device may use a green pattern target, a red pattern target, and a blue pattern target, used in turn.

[0163] FIGURE 4 is a schematic representation of a non-limiting exemplary embodiment of a method of manufacturing an optical lens according to the present invention.

[0164] The method 400 of FIGURE 4 can be used to manufacture optical lenses used for imaging, i.e., for acquiring an image or video.

[0165] The method 400 comprises a step 402 of manufacturing an optical lens. The manufacturing of the optical lens is carried out in a conventional and known manner and will therefore not be described in detail here.

[0166] The method 400 comprises a step 404 of characterizing one, or each, optical objective manufactured during step 402, by the method according to the invention and in particular by the method 100 or by the method 200.

[0167] The method 400 further comprises a step of retaining or not retaining the optical lens depending on the performance of the optical lens. If the performance of the optical lens is satisfactory, then the optical lens is retained. Otherwise, the optical lens is not retained and is discarded.

[0168] In method 400, each manufactured objective can be characterized.

[0169] Alternatively, only certain manufactured lenses can be characterized.

[0170] For example, when the first lenses from the same manufacturing lot are characterized and have satisfactory optical quality, the other lenses from the same manufacturing lot may not be characterized.

[0171] As another example, when the first objectives of a pairing recipe are characterized and have satisfactory optical quality, the other objectives obtained with the same pairing recipe may not be characterized.

[0172] FIGURE 5 is a schematic representation of a non-limiting exemplary embodiment of an installation for manufacturing an optical lens according to the present invention.

[0173] The manufacturing facility 500 of FIGURE 5 may be used to manufacture optical lenses used for imaging, i.e., for acquiring an image or video.

[0174] The installation 500 comprises a line 502 for manufacturing optical lens(es). The manufacturing line 502 is in the form of a known conventional optical lens manufacturing line and will therefore not be described in detail here.

[0175] The facility 500 further includes a system 504, which may be the system 300 of FIGURE 3, for characterizing one, or each, optical lens manufactured by the manufacturing line 502. If the performance of the optical lens is satisfactory, then the optical lens is retained. Otherwise, the optical lens is not retained and discarded.

[0176] FIGURE 6 is a schematic representation of a non-limiting exemplary embodiment of a camera module according to the invention.

[0177] The camera module 600 of FIGURE 6 includes an optical lens 602 characterized in accordance with the present invention, and in particular by the method 100 of FIGURE 1 or by the method 200 of FIGURE 2. The optical lens 602 may be the optical lens 00 of FIGURES 1-5.

[0178] In the non-limiting example shown in FIGURE 6, the optical lens 602 comprises four lenses 604-610, stacked in a barrel 612 in a stacking direction 614, which also corresponds to the axis 614 of the optical lens 602.

[0179] The camera module 600 further comprises an image sensor 616 associated with the optical lens 602. The image sensor 616 may be any type of image sensor such as a CCD or CMOS sensor.

[0180] Of course, the camera module 600 may include other organs / components which are not shown in FIGURE 4, such as for example a device modifying the imaged viewing angle or a device modifying the sharpness distance of the imaged area.

[0181] The camera module 600 may optionally comprise a module 618 for digitally processing the data captured by the image sensor 616. Such a digital processing module 618 may for example be arranged to carry out a correction of the image captured by the image sensor 616, for example with a view to correcting at least part of the optical aberrations due to the optical lens 602. This module 618 may for example integrate one or more previously determined aberration correction functions.

[0182] The processing module 618 may be an independent module. Alternatively, the processing module 618 may be integrated into another module or another application, such as for example a photo application used for the acquisition of image(s).

[0183] FIGURE 7 is a schematic representation of a non-limiting exemplary embodiment of a method for acquiring an image according to the invention.

[0184] The method 700 comprises a step 702 of acquiring an image with an optical objective characterized by the present invention, or with a camera module according to the invention, and in particular the camera module 600 of FIGURE 6, or the objective 00 of FIGURES 1-5.

[0185] The method 700 further comprises a step 704 of digitally processing the acquired image. Such digital processing may perform a correction of the acquired image with a view, for example, to correcting, at least in part, the lateral chromatic aberration and / or the geometric aberration, due to the optical objective used for acquiring the image. Such an aberration correction may, for example, be performed with at least one previously determined aberration correction function.

[0186] FIGURE 8a is a schematic representation of a non-limiting exemplary embodiment of an apparatus according to the present invention.

[0187] The apparatus 810 of FIGURE 8a comprises at least one imaging module according to the present invention, and in particular the imaging module 600 of FIGURE 6.

[0188] In the example shown in FIGURE 8a, the device 810 is a smartphone, or a tablet.

[0189] Optionally, the device 810 may further comprise a display screen 812 equipped with a touch surface 814, for example capacitive.

[0190] The apparatus 810 may further comprise an imaging application 816, such as a photo and / or video application, installed in said apparatus 810 and executed by said apparatus 810. The application 816 may for example integrate the processing module 618 of the imaging module 600. Alternatively, the processing module 618 may be independent of the application 816.

[0191] FIGURE 8b is a schematic representation of another non-limiting exemplary embodiment of an apparatus according to the present invention.

[0192] The apparatus 820 of FIGURE 8b comprises at least one imaging module according to the present invention, and in particular the imaging module 600 of FIGURE 6.

[0193] In the example shown in FIGURE 8b, the apparatus 820 is a virtual reality, VR, headset or an augmented reality, VA, headset.

[0194] Optionally, the headset 820 may further comprise a display screen 822. Optionally, the headset 820 may further comprise a sensor (not shown) for detecting the position aimed by an eye, or eyes, of the user on said display screen 822.

[0195] The headset 820 may further comprise an imaging application (not shown), such as a photo and / or video application, installed on said headset 820 and executed by said headset 820. The imaging application may for example integrate the processing module 618 of the imaging module 600. Alternatively, the processing module 618 may be independent of the imaging application of the headset 820.

[0196] FIGURE 8c is a schematic representation of another non-limiting exemplary embodiment of an apparatus according to the present invention.

[0197] The apparatus 830 of FIGURE 8c comprises at least one imaging module according to the present invention, and in particular the imaging module 600 of FIGURE 6.

[0198] In the example shown in FIGURE 8c, the apparatus 830 is a medical imaging apparatus, such as an endoscope, an ultrasound apparatus, etc.

[0199] Optionally, the medical imaging apparatus 830 may further comprise a display screen 832.

[0200] Optionally, the medical imaging device 830 can further be equipped with a detection surface 834, for example capacitive.

[0201] Optionally, the medical imaging device 830 may further comprise a distal objective 836 for collecting light radiation, which may or may not be part of the imaging module 600.

[0202] The medical imaging device 830 may further comprise an imaging application (not shown), such as a photo and / or video application, installed on said device 830 and executed by said device 830. The imaging application may for example integrate the processing module 618 of the imaging module. Alternatively, the processing module 618 may be independent of the imaging application of the device 830.

[0203] FIGURE 9 is a schematic representation of a non-limiting exemplary embodiment of a vehicle according to the present invention.

[0204] The vehicle 900 of FIGURE 9 comprises at least one imaging module according to the present invention, and in particular the imaging module 600 of FIGURE 6, for example integrated into a camera 902.

[0205] In the vehicle 900, the camera 1002 may for example be arranged behind the windshield of the vehicle 900 in the upper part of said windshield, or above the front windshield. Of course, this positioning is given as a non-limiting example and the camera 902 may be arranged elsewhere.

[0206] In the example shown in FIGURE 9, the vehicle 900 is a land vehicle, in particular a car. The vehicle 900 may further comprise a display screen 904 equipped with a touch surface 906, for example capacitive, arranged in the passenger compartment of the vehicle 900.

[0207] The vehicle 900 may further comprise an imaging application 908, such as a photo and / or video application. The imaging application 908 may, for example, integrate the processing module 618 of the imaging module 600. Alternatively, the processing module 618 may be independent of the imaging application 908.

[0208] Of course, the invention is not limited to a land vehicle. A vehicle according to the invention may be a flying vehicle, such as a flying drone, an airplane, a helicopter, etc. A vehicle according to the invention may be a maritime vehicle, such as a maritime drone, a boat, a submarine, etc.

[0209] The invention is not limited to the examples of devices and vehicles given with reference to the FIGURES. It can be implemented in any type of devices and vehicles comprising a camera module.

[0210] Of course, the invention is not limited to the examples which have just been described.

Claims

CLAIMS 1. Method (100;200) for characterizing an optical objective (00), said method (100;200) comprising the following steps: - measuring (104; 108; 112) an optical transfer function, OTF, of said optical objective (00), individually for at least one of the following radiations: green radiation, blue radiation, red radiation; and - for at least one of said radiations: comparison (106; 110; 114) of the measured FTO with at least one predetermined threshold FTO, with a view to determining whether the optical quality of said objective is satisfactory.

2. Method (100; 200) according to the preceding claim, characterized in that the optical transfer function is the modulation transfer function, FMT (or MTF for “Modulation Transfer Function”).

3. Method (100;200) according to claim 1, characterized in that the optical transfer function is the point spread function, FEP (or PSF for “Point Spread Function”).

4. Method (200) according to the preceding claim, characterized in that the measuring step (104) carries out the measurement of the FTO only for a single radiation.

5. Method according to the preceding claim, characterized in that the radiation is green radiation.

6. Method (100) according to any one of claims 1 to 3, characterized in that the measuring step (104,108,112) carries out the measurement of the FTO individually for at least two, in particular for each, of the red, green and blue radiations.

7. Method (100) according to the preceding claim, characterized in that the comparison step (106; 110; 114) carries out, for each radiation for which the FTO was measured, a comparison of said measured FTO to at least one predetermined threshold FTO.

8. Method (100; 200) according to any one of the preceding claims, characterized in that, for at least one radiation, the measurement (104; 108; 112) of the FTO is carried out for a measurement plane corresponding to the greatest focusing, or for a plane for which a satisfied focusing is obtained.

9. Method (100; 200) according to any one of the preceding claims, characterized in that, for at least one radiation, the measuring step (104; 108; 112) carries out a measurement of the value of the FTO at several points.

10. Method (100; 200) according to any one of the preceding claims, characterized in that, for at least one radiation, the measuring step (104; 108; 112) is carried out with a target, comprising one or more patterns, positioned in front of the optical objective (00).

11. System (300) for characterizing an optical objective (00), said system comprising: - at least one measuring device (302-306) of an optical transfer function; and - a calculation unit (308); configured to implement the steps of the method according to any one of the preceding claims.

12. Method (400) for manufacturing optical lenses comprising the following steps for at least one optical lens: - manufacturing of said optical lens (00), - characterization of said optical objective (00) by the method according to any one of claims 1 to 10, - preservation or not of said optical objective (00) depending on the result of said characterization.

13. Optical lens manufacturing facility comprising: - an optical lens manufacturing line, and - a characterization system according to claim 12 for characterizing at least one optical objective.

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