FR3051278A1 - METHOD FOR CALIBRATING A SPECTRUM OBTAINED USING AN ELECTRONIC APPARATUS EQUIPPED WITH A REMOVABLE ACCESSORY - Google Patents

Abstract

The invention relates to a method implemented in a system (1000) comprising: - an electronic device (600) such as a mobile phone or a digital tablet, comprising in particular a color photosensitive multi-pixel sensor; and a removable accessory (100) having a housing (110) attached to the electronic apparatus, the housing receiving wavelength dispersing means and beam straightening means. The method according to the invention is implemented by computing means (603) of the electronic apparatus (600), and notably comprises a preliminary step of determining wavelength calibration data, with a step of adjustment comprising the following substeps: - receiving an adjustment image provided by the multi-pixel photosensitive sensor (601); searching for a region in which a difference in light intensity, measured on two neighboring pixels each associated with the detection of a different wavelength, is minimal; - from a comparison between first wavelength calibration data, and the position of said region on the adjustment image, determining second wavelength calibration data.

Description

METHOD OF CALIBRATING A SPECTRUM OBTAINED USING AN ELECTRONIC APPARATUS EQUIPPED WITH A REMOVABLE ACCESSORY

DESCRIPTION

TECHNICAL FIELD The invention relates to the field of spectrometry, that is to say the measurement of a distribution of light intensity as a function of the wavelength, the so-called light spectrum.

STATE OF THE PRIOR ART

Various spectrometry apparatuses are known in the prior art, a spectrometry apparatus generally comprising: a light source, for example an infrared, ultraviolet or visible source, for illuminating an object to be analyzed; wavelength dispersion means for spatially separating the different spectral contributions of a light beam reflected by the illuminated object; a detection strip, for the detection of these spectral contributions; and calculating means, for calculating a light spectrum from a signal detected by the detection bar.

Document US 2012/0184827 illustrates an example of such a spectrometry apparatus, dedicated more specifically to medical applications. The device is miniaturized, allowing it to come for example in the form of a simple bracelet, to perform blood glucose checks on a user.

A disadvantage of these devices, however, is their high production cost.

An object of the present invention is to provide a solution for performing light spectrum measurements at low cost.

STATEMENT OF THE INVENTION

This objective is achieved with a removable accessory for an electronic device provided with a multi-pixel photosensitive sensor, computing means and a screen, such as a mobile phone or a digital tablet, and a method associated to exploit a image acquired using the electronic device equipped with the removable accessory. The invention relates in particular to the method, involving the use of the removable accessory mentioned above.

According to the invention, the removable accessory comprises: a housing, receiving wavelength dispersion means and beam straightening means for compensating for a mean deviation provided by the wavelength dispersing means; and main fixing means, for the removable attachment to the electronic device.

An idea underlying the invention consists in proposing an accessory to be installed on an electronic device such as a mobile phone or a digital tablet, to form a spectrometry apparatus. The electronic device is not an integral part of the removable accessory according to the invention. The removable accessory makes it possible to turn into spectrometer any electronic device such as a mobile phone or a digital tablet.

For this, it exploits in particular the fact that a part of the components of a spectrometer apparatus are found in mobile phones and digital tablets, including: the multi-pixel photosensitive sensor, for the detection of different spatially separated spectral contributions; the calculation means, in particular a processor, for the exploitation of the signals detected by the multi-pixel photosensitive sensor; and the screen, in particular for displaying data relating to a light spectrum calculated by the calculation means.

These electronic devices are widely used, especially with the general public, so that the additional investment for the user is limited to the purchase of the removable accessory according to the invention. The user can thus obtain a spectrometry apparatus for a particularly reduced cost. The accessory can be limited to three basic functions that are attachment to the electronic device, wavelength dispersion, and the compensation of an average beam deflection provided by the wavelength dispersion, so It has a small footprint and weight, allowing great maneuverability and great portability.

The attachment of the accessory is removable, so that outside the precise moments of use of the electronic device as spectrometry apparatus, the electronic device can maintain a compact shape and a small footprint, and the camera function or Camera of the electronic device is not disturbed.

Preferably, the accessory is devoid of a light source, and adapted to the measurement of the light spectrum of an object in natural lighting, or the measurement of the light spectrum of an object illuminated by a light source forming an integral part of the light. 'electronic device. The removable accessory is then devoid of power supply, and forms a passive device.

The housing of the removable accessory not only receives wavelength dispersion means, but also so-called straightening means, to compensate for an average beam deflection provided by these wavelength dispersion means.

The straightening means are configured so that the mean direction of propagation of a light beam, at the output of the housing, is aligned with the direction of propagation of this beam, upstream of the wavelength dispersion means and means of straightening.

This direction directly defines a line of sight of an object for which it is desired to measure the spectrum, which facilitates the aiming of the object.

This axis of sight advantageously corresponds to the longitudinal axis of the housing.

Preferably, the wavelength dispersing means comprise at least one diffraction grating and / or at least one prism.

The main fastening means advantageously comprise: a front wall, from which the housing extends; a rear wall spaced from the front wall; an intermediate element, fixed on one side to the front wall and the other to the rear wall, to keep the front wall and the rear wall integral with each other so that they together form a configured guide to receive the electronic device; and clamping means configured to mechanically hold the electronic apparatus between the front wall and the rear wall.

The housing may be configured to slide inside a rail integral with the main fastening means, and comprise secondary fixing means configured to release or block the sliding of the housing inside the rail. The invention also relates to a system comprising: an electronic device provided with a photosensitive multi-pixel sensor, calculation means and a screen, such as a mobile phone or a digital tablet; and a removable accessory attached to the electronic apparatus, wherein the removable accessory is an accessory according to the invention, attached to the electronic device by the main fixing means, housing covering the multi-pixel photosensitive sensor of the apparatus electronics so that the multi-pixel photosensitive sensor receives a spectrally spread light beam.

The method according to the invention is implemented by the calculation means of the electronic device of said system according to the invention, and comprises the following steps: reception of an image, provided by the multi-pixel photosensitive sensor; image processing, using wavelength calibration data and intensity calibration data, to obtain a light spectrum.

The method is implemented using a system according to the invention in which the multi-pixel photosensitive sensor is a color sensor, and comprises a preliminary step of determining the wavelength calibration data, this preliminary step comprising an adjustment step which itself comprises the following substeps: receiving an adjustment image provided by the multi-pixel photosensitive sensor; searching, on the adjustment image, a region in which a difference in luminous intensity, measured on two neighboring pixels each associated with the detection of a different wavelength, is minimal; from a comparison between first wavelength calibration data, and the position of said region on the adjustment image, determining second wavelength calibration data, said region being associated at a so-called adjustment wavelength.

Advantageously, the method is then implemented using a system according to the invention in which the photosensitive multi-pixel sensor is a so-called RGB sensor, comprising a first type of pixel dedicated to the detection of red, a second type of pixels dedicated to the detection of green, and a third type of pixels dedicated to the detection of blue, and: the search on the adjustment image comprises the search for a region in which a difference in luminous intensity, measured on a pixel dedicated to the detection of red and on a pixel dedicated to the detection of green, is minimal; and the adjustment wavelength is between 570 nm and 590 nm.

Preferably, the preliminary step of determining the wavelength calibration data also comprises a step of determining said first wavelength calibration data, comprising the following sub-steps: reception of an image of wavelength calibration data wavelength calibration, provided by the multi-pixel photosensitive sensor, associated with a so-called reference light source, and comprising at least three light lines or three light spots; for each line or point, matching a predetermined wavelength and a position of the light line or light spot on the calibration image and on the multi-pixel photosensitive sensor; from the pairs associating a predetermined wavelength and a position on the multi-pixel photosensitive sensor, calculating first wavelength calibration data.

The method according to the invention may further comprise a preliminary step of determining the intensity calibration data, the determination of the intensity calibration data comprising the following substeps: receiving an intensity calibration image, provided by the multi-pixel photosensitive sensor, and associated with a light source of the black body type; comparing the intensity calibration image, and a reference spectrum formed by the light spectrum of the terrestrial solar radiation, to obtain the intensity calibration data.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood on reading the description of exemplary embodiments given purely by way of indication and in no way limiting, with reference to the appended drawings in which: FIG. 1 schematically illustrates a first embodiment of FIG. a removable accessory according to the invention; Figure 2 illustrates, in a perspective view, the removable accessory shown schematically in Figure 1; Figure 3 illustrates the accessory of Figure 2, in a side view; Figure 4 illustrates, in an exploded view, some elements of the accessory of Figure 2; Figure 5 illustrates the accessory of Figure 2, according to a front view; Figure 6 illustrates, in a side view, the accessory of Figure 2 mounted on an electronic device to form a system according to the invention; FIGS. 7A and 7B illustrate a second embodiment of a removable accessory according to the invention; Figures 8 and 9 respectively illustrate third and fourth embodiments of a removable accessory according to the invention, including a light source; Figure 10 schematically illustrates steps of the method according to the invention; and FIGS. 11 and 12 schematically illustrate displays proposed to a user, during the wavelength calibration according to the invention, of a spectrometer formed by a removable accessory according to the invention, mounted on a device electronic.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

Figure 1 illustrates, schematically, a first embodiment of a removable accessory 100 according to the invention.

To facilitate the understanding of Figure 1, the rules of the perspective are not respected, the removable accessory as a whole being shown in a side view, and some of its elements being represented in perspective. The removable accessory comprises a housing 110, shown in phantom, and main fixing means 120, represented by hatched surfaces.

The main fastening means 120 are configured to allow attachment of the accessory 100, removably, to a nomadic electronic device such as a smartphone (smartphone) or a digital tablet.

An exemplary embodiment of the main attachment means 120 is described in detail below.

The housing 110 is formed of an opaque material.

It has, for example, and without limitation, a cylinder shape of revolution. One of the ends of the cylinder is fixed to the main fastening means 120. At this end, the cylinder is open over a large section, to let light rays. The other end of the cylinder, on the opposite side to the main fixing means 120, is closed by a wall 111 provided with a slot 112.

In Figure 1, the wall 111 is shown in perspective.

The wall 111 closes the cylinder hermetically to light, except at the slot 112.

The slot 112 has a width much greater than its height. It forms an entrance slot of the light inside the housing 110, or source slot. Inside the housing 110 extend a collimating lens 113, a transmission diffraction grating 114 and a prism 115.

The collimating lens 113 is disposed on the side of the source slot 112, between the source slot 112 and the diffraction grating 114. It collimates a light beam having passed through the slot 112, so that its light rays arrive on the diffraction grating. 114 parallel to each other.

Preferably, the collimating lens extends along the entire internal section of the housing 110.

The diffraction grating 114 makes it possible to achieve a wavelength dispersion of the light beam having passed through the slot 112, then the collimation lens 113. It thus forms wavelength dispersion means for spatially separating the various components. wavelength of this light beam.

The diffraction grating 114 is etched here on one side of the prism 115, the two together forming a grism.

The network 114 is made up of slots parallel to each other, distributed regularly (not constant), which extend here parallel to the slot 112.

The prism 115 is used here for its function of deflecting a light beam. It forms beam straightening means. It makes it possible to compensate for a mean deviation induced by the diffraction grating 114, on the light beam having previously passed through the slot 112, then the collimation lens 113.

Indeed, the diffraction grating 114 deflects each spectral component of an incident light beam at an angle that depends on the wavelength of this spectral component. At the output of the diffraction grating, the different spectral components are distributed around an average direction which is inclined relative to the direction of the incident light beam. The average direction is an average position of the light rays at the output of the diffraction grating.

Thanks to the compensation provided by the prism 115, the mean direction of propagation of the spectrally spread beam at the output of the housing is aligned with the direction of propagation of this beam, at the input of the housing.

These directions together define a line of sight.

With the straightening means, the line of sight is a straight line, not a broken line. It is thus particularly easy for the user to aim at an object to measure its spectrum.

The line of sight preferably corresponds to the longitudinal axis of the housing, here the axis of symmetry of the cylinder.

When the removable accessory is mounted on an electronic device, the prism 115 allows a light beam at the output of the removable accessory to propagate in a direction approximately orthogonal to the plane of the multi-pixel photosensitive sensor of the electronic device. (for example, within +/- 3 °).

The prism 115 is disposed on the side of the housing opposite the source slot, and the diffraction grating 114 is between the prism 115 and the collimator lens 113.

In Figure 1, the prism 115 and the array 114 are shown in perspective.

FIG. 1 also schematically shows the light beam passing through the slot 112 and the collimating lens 113, and the light beam 200, spread spectrally by the wavelength dispersion means 114 and rectified by the straightening means 115. For reasons of readability of the figure, this spectrally spread beam 200 is shown in perspective.

According to a variant not shown, the network is formed on an exit face of the prism, on the opposite side to the entry slot 112. The compensation is then implemented prior to the average deviation by the diffraction grating.

Numerous other variants can be implemented without departing from the scope of the invention, in which the wavelength dispersing means comprise one or more diffraction gratings (x) in transmission, and / or one or more networks ( x) diffraction in reflection, and / or one or more dispersive prism (s).

In the same way, other straightening means can be implemented, comprising at least one prism, and / or at least one mirror.

The housing 110 may or may not accommodate optics such as one or more collimating lenses.

Figure 2 illustrates, in a perspective view, the removable accessory 100 shown schematically in Figure 1.

FIG. 2 illustrates in particular the main fixing means 120, and the housing 110 having here a tube shape fixed at one of its ends to the main fastening means 120.

On the opposite side to the main fixing means 120, the tube has a cover 116 in the center of which is the entrance slot (not visible in Figure 2).

The main fixing means 120 comprise here: a front wall 121, on which the housing 110 is fixed; a rear wall 122, spaced from the front wall, and which extends here parallel thereto; and a spacer element 123, which extends here perpendicular to the front and rear walls, fixed on one side against an edge of the front wall, and on the other side against an edge of the rear wall. The longitudinal axis of the housing is orthogonal to the front wall 121.

The front wall 121, the rear wall 122, and the spacer 123 together form a guide configured to receive the electronic apparatus.

In particular, the electronic device is inserted between the front wall 121 and the rear wall 122, preferably until it abuts against the intermediate element.

Here, the front wall 121 and the rear wall 123 are parallel to each other.

Only an end portion of the electronic apparatus is inserted between the front wall 121 and the rear wall 122, in particular a portion receiving a window covering a photosensitive multi-pixel sensor of the electronic apparatus.

Figure 3 illustrates the accessory of Figure 2, in a side view.

The distance DI between the front wall 121 and the rear wall 122 corresponds substantially to the thickness of the electronic device.

So that the main fastening means 120 can be adapted to electronic devices of different thicknesses, the distance DI is slightly greater than a maximum thickness of such a device. The distance DI is for example between 1 cm and 2 cm.

Clamping means make it possible to maintain the electronic device between the front wall 121 and the rear wall 122.

Here, the clamping means are constituted by two screws 124 and two corresponding threaded holes in the rear wall 122.

The threaded holes are through holes, so that the respective ends of the two screws 124 abut against a surface of the electronic device to press against the front wall 121, and thus maintain it in position between the front wall 121 and the rear wall 122. The invention is not limited to these main attachment means 120, and many variants can be implemented without departing from the scope of the present invention.

For example, the screws and the threaded holes may pass through the front wall, to press the electronic apparatus against the rear wall 121, the front and rear walls being fixed relative to one another.

Alternatively, the front wall and the rear wall may be movable in translation relative to each other, to adjust the space between the two depending on the thickness of the electronic device.

Alternatively, the front wall and the rear wall can be tilted relative to each other. They can in particular be articulated together using a spring, to form a clamp.

In any case, the removable accessory is configured to be fixed to the electronic device, so that a longitudinal axis of the housing is substantially orthogonal (for example within +/- 3 °) to a wall of the electronic device on which the housing is based. The assembly formed by the electronic device and the removable accessory is particularly compact.

Figures 4 and 5 illustrate an advantageous characteristic of the removable accessory according to the invention.

For this, the front wall 121 is provided with a rail 125 (see FIGS. 1 and 5), to guide a translational movement of the housing 110 relative to the main fastening means 120.

It is thus possible to position the housing 110 in front of the multi-pixel photosensitive sensor, regardless of the dimensions of the electronic device and the position of the multi-pixel photosensitive sensor on it (within the limits of the race of the housing on his rail).

Here, the rail 125 is formed by an oblong-shaped through opening in the wall 121.

The housing 110 is formed in two parts. A main part 110A, in which are housed in particular the wavelength dispersion means, and a ring 110B.

The main portion 110A and the ring 110B are shown in Figure 4, in an exploded view.

The ring 110B has a cylindrical portion 110iB, having a thread on its outer surface, and a ring IIO2B, outer diameter greater than that of the cylindrical portion 110iB.

The cylindrical portion 110B has an outside diameter slightly less than the width of the oblong opening forming the rail 125. The difference in diameter is preferably much less than 1 mm, for example less than 0.2 mm. Thus, the cylindrical portion 110B can move in translation within the rail 125, along an axis parallel to the direction of elongation of the rail (here along an axis parallel to the axis (z)).

The thread of the cylindrical portion 110B cooperates with a thread formed inside the main portion 110A of the housing, to secure the main portion 110A and the ring 110B.

The ring IIO2B has an outer diameter greater than that of the oblong opening forming the rail 125.

In practice, the cylindrical portion 110B is inserted into the oblong opening forming the rail 125, until the ring 11O2B abuts against the front wall 121. The ring 110B is then moved along the rail 125, for position at the desired height along the rail. Finally, the main portion 110 is screwed onto the ring 110B, the main portion 110A and the ring 110B then being disposed on one side and the other of the front wall.

It is thus possible to position and fix the housing 110 at the desired location along the rail 125 so that it is opposite the multi-pixel photosensitive sensor when the removable accessory is mounted on an electronic device.

The ring 110B and the thread inside the main part 110A together form secondary fastening means, making it possible to release and block the sliding of the casing in the rail 125. In FIG. 5, the removable accessory according to FIG. a front view. The double arrow symbolizes the degree of freedom of the housing 110 relative to the front wall 121, when the cylindrical portion 110B is inserted into the rail 125 and the screwing with the main portion 110A is not tight.

FIG. 6 illustrates the system 1000 constituted by the removable accessory 100, and by an electronic device 600 to which the removable accessory 100 is fixed.

The attachment is removable, the removable accessory 100 can be mounted on the electronic device when a user wants to use it, and then disassembled. The electronic device 600 is for example a smart phone, or a digital tablet. It can also be a digital camera.

This is a nomadic electronic device, or portable.

It is equipped with a photosensitive multi-pixel sensor 601, protected by a protection window. The electronic apparatus comprises in particular a photosensitive multi-pixel sensor, that is to say a photon-sensitive sensor, and comprising a plurality of pixels, for example more than 1000 pixels.

The multi-pixel photosensitive sensor 601 is preferably a matrix sensor consisting of a grid of N * M pixels, with N and M being integers strictly greater than unity.

Alternatively, the multi-pixel photosensitive sensor 601 may be a simple pixel array.

The multi-pixel photosensitive sensor 601 is here a color sensor consisting of different types of pixels, each dedicated to the detection of a predetermined wavelength range. This is for example a CMOS sensor.

The housing 110 of the removable accessory is pressed against a wall of the electronic device, so as to completely cover said protection window. The longitudinal axis of the housing 110 is substantially orthogonal to the face of the electronic device receiving this protection window (within +/- 3 °). This longitudinal axis is aligned with the line of sight as defined above.

Thus, a light beam incident on the housing along an axis parallel to the longitudinal axis of the housing is spread spectrally and forms an image on the multi-pixel photosensitive sensor 601.

The spectrally spread light beam advantageously corresponds to a series of images of the slot 112 distributed over the photosensitive multi-pixel sensor 601, preferably along the width axis of the multi-pixel photosensitive sensor.

Preferably, the housing 110 has a mark, to orient the lines of the diffraction grating 114 (see Figure 1) parallel to the axis of the height H of the electronic device 600, so that the spectrally spread light beam is extends along the axis of the width of the multi-pixel photosensitive sensor.

For example, a line 117 may be etched on the cover 116 of the housing 110, parallel to the lines of the diffraction grating 114. The user can thus, when he screws the main part 110A with the ring 110B, control the final orientation features of the diffraction grating 114.

Such a marker is particularly advantageous when the slot is hardly visible from outside the housing. The electronic device 600 also comprises a processor 602, receiving the images acquired by the multi-pixel photosensitive sensor 601, and a screen 603. The screen 603 forms a human machine interface, in particular for displaying a light spectrum. The screen may also enable a user to formulate instructions for spectrometry software implemented within the processor 602, and / or to display calculation results made using this spectrometry software .

There is illustrated here a removable accessory in which the main fixing means are adjustable, and allow to fix the housing 110 to an electronic device, regardless of the dimensions of the latter (within a predetermined range).

Alternatively, the removable accessory can be dedicated to specific dimensions of an electronic device. The main attachment means are then in the form of a shell, specific to an electronic device model in particular.

The shell is fixed to the housing 110, for example in a removable manner, thanks to a first threaded ring integral with the shell, which cooperates with a complementary thread on the housing 110.

Alternatively, the shell is fixed to the housing 110 permanently, the housing and the shell being formed integrally.

FIGS. 7A and 7B illustrate a second embodiment of a removable accessory 100 'according to the invention.

This second embodiment differs from the embodiment described above, only in that the slot is replaced by an optical fiber 118 with a small heart, whose heart acts as a source hole.

The optical fiber 118 extends from the cover 116, and covers by surrounding an opening 112 'formed in the cover. The diameter of the opening is greater than 200 μm.

The optical fiber 118 is a flexible fiber, which allows the light to be transported to the source hole, from a remote region that can be difficult to access for the electronic device.

The spectrally spread light beam then advantageously corresponds to a series of points distributed over the multi-pixel photosensitive sensor 601, preferably along the axis of the width of the multi-pixel photosensitive sensor.

The marker for correctly orienting the lines of the diffraction grating is then particularly advantageous.

According to another variant not shown, the slot is replaced by a source hole, that is to say a circular opening of small dimension formed in an opaque material. The diameter of the source hole is for example less than 30 μm.

Figure 8 illustrates a third embodiment of a removable accessory 100 '' according to the invention.

According to this embodiment, the removable accessory 100 "further comprises a light source 130.

It may be a light-emitting diode, for illuminating an object using a light beam having known characteristics, including wavelength.

The light source 130 may for example provide a monochromatic illumination at an absorption wavelength of a predetermined component, to then detect the emission or not, in response, of a fluorescence signal.

The light source 130 may also provide white light, or any other type of illumination (infrared, ultraviolet, visible, etc.).

The light source 130 can integrate its own power supply means, to be autonomous in energy.

Alternatively, the light source 130 may be connected to wired electrical connection means, for connection to the electronic device and the power supply of the light source 130 because last.

According to a variant not shown, the removable accessory 100 '' comprises a support, for removably attaching such a light source 130. It is thus possible to associate the removable accessory to different light sources, depending on a desired use.

Figure 9 illustrates a fourth embodiment of a removable accessory 100 '' 'according to the invention.

To facilitate understanding of this fourth embodiment, the removable accessory 100 '"is shown mounted on an electronic device 600.

According to this embodiment, the removable accessory 100 '"is further provided with a light guide 140, which extends from one end to the other of the housing 110, crossing if necessary the front wall 121 .

A first end 141 of the light guide is configured to face a photographic flash 604 of the electronic apparatus 600.

A second end 142 of the light guide is placed at the end of the housing 110, on the opposite side to the main attachment means.

The light guide 140 makes it possible to guide the light rays emitted by the photographic flash 604. The removable accessory 100 '' may comprise guide and fixing means for moving the first end 141 of the light guide relative to the housing 110, and thus position it exactly in the light of the 604 photographic flash.

This fourth embodiment makes it possible to use a photographic flash of the electronic apparatus as a light source for illuminating an object or a scene that it is desired to analyze spectrally. The invention is not limited to these examples. In addition, many improvements can be made to the removable accessory, for example by fixing a bowl which is placed in front of the source slot or the source hole, the bowl can in particular receive a liquid, or by attaching an optical diffuser or an optical filter that is placed in front of the source slot or the source hole.

It then illustrates a method implemented within the processor of the electronic device, when the apparatus is equipped with a removable accessory according to the invention.

Figure 10 illustrates steps of this method for calculating a light spectrum.

According to this method, the processor receives as input an image Im (O) acquired by the multi-pixel photosensitive sensor of the electronic device. The image Im (O) corresponding to a light beam coming from an object O, spread spectrally (the different contributions in wavelength of this beam are separated spatially).

Using C (X) wavelength calibration data and C (1) intensity calibration data, the processor calculates a light spectrum Ιο (λ).

In particular, it is possible to calculate an emission spectrum (for example a fluorescence spectrum, a luminescence spectrum, a black-body spectrum, etc.), an absorption spectrum, a transmission spectrum, and / or a spectrum of reflection.

The wavelength calibration data C (A) and the intensity calibration data C (1) are advantageously stored in an internal memory of the electronic device.

Alternatively, they are stored in a remote memory, accessible via the Internet through wireless communication means of the electronic device.

The wavelength calibration data C (λ) connects a position on the multi-pixel photosensitive sensor and a wavelength value for a predetermined wavelength range. In all the following, the positions designate a position along an axis corresponding to a spectral spreading direction of a light beam at the output of the removable accessory. Preferably, this axis is aligned with the width axis of the multi-pixel photosensitive sensor.

The intensity calibration data C (1) connects a measured light intensity on the multi-pixel photosensitive sensor, and a so-called intrinsic value of the light intensity, for a predetermined wavelength range. The intrinsic value of the light intensity does not depend on an optical transfer function of the removable accessory and the electronic device.

The calculation of a light spectrum therefore consists of matching illuminated regions of the image Im (O) with wavelengths, and light intensities on these regions with intrinsic intensities.

The calculated light spectrum thus provides the wavelength values of the different spectral components of a light beam, and associated intrinsic intensity values.

It can be in the form of a graph in which the abscissa axis corresponds to the wavelength, and the ordinate axis corresponds to the intrinsic intensity. The processor can control the display of this graph on the screen of the electronic device.

The processor can implement data processing to exploit the light spectrum thus calculated, for example a maximum amplitude detection and the associated wavelength.

Figures 11 and 12 each illustrate an exemplary display provided by the screen of the electronic apparatus, in a preliminary step of determining the wavelength calibration data C (A).

Preferably, the wavelength calibration data is determined in two steps: a first step, implemented at least during the first use of the removable accessory according to the invention, to determine data. say first wavelength calibration data (see Figure 11); and if necessary, an adjustment step, to correct if necessary the first wavelength calibration data and obtain data called second wavelength calibration data (see Figure 12).

The wavelength calibration data C (A) is constituted by the first wavelength calibration data, or by the second wavelength calibration data if it exists.

The first step, to determine the first wavelength calibration data, advantageously comprises the following substeps: Receipt of a so-called wavelength calibration image, provided by the photosensitive multi-pixel sensor . The wavelength calibration image is obtained using a reference light source, whose emission spectrum is known, and consists of a finite number of lines well spaced from each other.

To obtain the wavelength calibration image, the input of the removable accessory (source slot or source hole or optical fiber end) is oriented towards the reference light source, and an image is acquired by the multi-pixel photosensitive sensor.

The reference light source is for example a neon lamp, or a compact fluorescent lamp (low consumption lamp, in everyday language).

Each line is a ray of emission, that is to say, a colored line on a dark background.

The lines can be replaced by dots, when one has a source hole rather than a source slot. In addition, the shape of a line is not necessarily rectangular, but is the image of the entrance opening in the housing of the removable accessory. • For each line, matching a predetermined wavelength and a position of the line on the wavelength calibration image.

The predetermined wavelengths are the known wavelengths of the emission spectral lines of the reference source.

The lines on the wavelength calibration image are arranged in wavelength order, which makes it easy to perform this matching.

A position on the wavelength calibration image corresponds to a position on the multi-pixel photosensitive sensor of the electronic apparatus, so that ultimately each predetermined wavelength and a position on each other can be connected. the multi-pixel photosensitive sensor.

This matching can be performed by the processor alone, by automatic recognition of illuminated regions on the wavelength calibration image.

According to an advantageous variant, this mapping can involve the user. For this purpose, the screen of the electronic device proposes to the user the display of FIG. 11. This display comprises a zone 1101 for displaying the wavelength calibration image, a zone 1102 of predetermined wavelength display VI to V4, and a reference data display area 1103 for the user. In area 1102, the predetermined wavelengths are arranged in ascending order of wavelength value from left to right. The user is prompted to successively select each predetermined wavelength, and to position a cursor 1104 on the corresponding line 1105a, 1105b, 1105c or 1105d. Thus, the processor can map a selected position of the cursor 1104, and a predetermined wavelength. Area 1103 may indicate to the user a color associated with each predetermined wavelength.

For example, for a reference lamp formed by a compact fluorescent lamp, the emission spectrum comprises four main lines, respectively at VL = 436 nm, V2 = 488 nm, V3 = 546 nm and V4 = 612 nm (one line additional 405 nm can be considered, depending on the detection capabilities of the multi-pixel photosensitive sensor). The wavelength VI is therefore assigned to the leftmost line 1105a on the wavelength calibration image, the wavelength V2 to the next line 1105b to the right, the wavelength V3 to the next line 1105c to the right, and the wavelength V4 to the next line 1105d to the right. • Then, we use the pairs associating a predetermined wavelength (VI, V2, V3, V4) and a position on the multi-pixel photosensitive sensor (position of the line 1105a, 1105b, 1105c, 1105d), to calculate the first calibration data.

The first calibration data relates a position on the multi-pixel photosensitive sensor and a wavelength for a continuous wavelength interval.

The calculation preferably comprises an interpolation, in particular a linear interpolation of the points defined by the series of pairs, to determine a dispersion in nm / pixel of the multi-pixel photosensitive sensor.

We can then adjust the first calibration data, for example to verify that the removable accessory has not moved relative to the multi-pixel photosensitive sensor (especially after a certain period of use or after disassembly and reassembly of the accessory removable on the electronic device).

This adjustment step implies that the multi-pixel photosensitive sensor of the electronic device is a color sensor, in particular a so-called RGB sensor consisting of pixels for detecting red (R pixels), pixels for detecting green ( pixels G), and pixels for detection of blue (pixels B). The adjustment step advantageously comprises the following substeps: Receiving an adjustment image provided by the multi-pixel photosensitive sensor.

Preferably, the adjustment image is obtained using a direct source of white light (for example the sun or a halogen lamp), or indirect, that is to say a white surface illuminated by such direct source.

To obtain the adjustment image, the entrance of the removable accessory is directed towards the direct or indirect source of white light, and an image is acquired by the multi-pixel photosensitive sensor. • Search, on the adjustment image, of a region in which a difference in luminous intensity between a pixel R and a directly adjacent pixel G is minimal.

In other words, the processor looks for a macro-pixel detecting the same light intensity on its red component and its green component, a macro-pixel being the elementary pattern of a color matrix sensor.

The same value of the red component and the green component corresponds to a yellow light, to a so-called adjustment wavelength.

The adjustment wavelength is thus identified with an uncertainty of only about 10 nm.

The adjustment wavelength is between 570 nm and 590 nm, for example 580 nm.

The processor thus automatically locates a pair associating a position on the multi-pixel photosensitive sensor, called the position of interest, and a wavelength, the so-called adjustment wavelength. From the first wavelength calibration data and this pair, the processor calculates second wavelength calibration data.

In particular, the processor can automatically compare the position on the photosensitive multi-pixel sensor associated with the adjustment wavelength according to the first wavelength calibration data, and the position previously by comparison of red and green components. If there is an offset between these two positions, the processor calculates corrected calibration data, called second wavelength calibration data. This calculation can simply consist in calculating this offset, and in translating from this offset the position values in the first wavelength calibration data, without modifying the corresponding wavelength values.

If this offset is zero, the processor determines that the second calibration data is equal to the first calibration data.

According to an advantageous variant, this sub-step can involve the user. For this purpose, the screen of the electronic device proposes to the user the display of FIG. 12. This display comprises a zone 1201 for displaying the first calibration data, and a zone 1203 for displaying data of set for the user. The display of the first calibration data is, for example, in the form of an image simulation acquired by the multi-pixel photosensitive sensor and associated with a white light. The image simulation comprises a spectrum 1206, connecting a position on the multi-pixel photosensitive sensor and a color displayed in the area 1201 at the corresponding position.

A slider 1207 is displayed in the area 1201, to indicate the position of interest determined by comparison of red and green components. The user is prompted to move this slider to the yellow region of the 1206 spectrum. Moving the slider allows the processor to calculate the offset between the position on the multi-pixel photosensitive sensor associated with the wavelength of adjustment (and to the yellow color) according to the first calibration data, and the position of interest determined by comparison of red and green components.

FIG. 12 shows an arrow 1208 symbolizing this offset. Other variants of this adjustment can be implemented, for example when the multi-pixel photosensitive sensor is a color sensor associated with elementary components other than R, G, and B, and therefore composed of pixels other than R, G , and B.

We then define a new value of the adjustment wavelength, always associated with two elementary components of the same value.

This adjustment can be implemented from first calibration data obtained otherwise than by exploiting a known line spectrum.

Finally, a preliminary step of determining intensity calibration data Ι (λ) is described.

This step advantageously comprises the following substeps: Reception of an intensity calibration image provided by the multi-pixel photosensitive sensor, and associated with a light source of the black body type.

The light source of black body type is in particular a source of direct or indirect emission of solar radiation (the sun, or a white surface illuminated by the sun, including a sheet of paper, a bulletin board, a wall, etc. .).

In order to obtain the intensity calibration image, the entry of the removable accessory is oriented towards the black body light source, and an image is acquired by the multi-pixel photosensitive sensor. • Comparison between the intensity calibration image, and a reference spectrum, to obtain intensity calibration data.

The reference spectrum is in particular the known light spectrum of terrestrial solar radiation.

It is thus possible to connect, for each wavelength, an intensity value measured by the multi-pixel photosensitive sensor, and an intrinsic intensity value which does not depend on the detection means used (these means including in particular the accessory removable, and the image acquisition chain of the electronic device). In other words, the intensity calibration integrates the sensor response (here the removable accessory and the electronic device).

The preliminary stages of wavelength calibration, respectively in intensity, do not require the use of expensive standards or light sources.

The system according to the invention can therefore be calibrated in a particularly simple and fast manner. The invention makes it possible to exploit the on-board intelligence of the electronic apparatus, when coupled to the removable accessory according to the invention, for measuring, processing, recording and / or exploiting a spectrum of light, for applications technical or everyday.

These applications involve accurate measurement of a light spectrum or wavelength. Among these applications, there may be mentioned, for example:

Safety control of light sources (tanning lamp, toy for children, etc.);

Colorimetric measurement of dental prosthesis;

Colorimetric measurement of a decorative element, a garment or fashion accessory, a makeup, etc., to verify that the color corresponds to what is sought;

Diagnosis of light sources (measurement of the color temperature of a light);

Measurement and / or detection of a chemical compound, based on a colorimetric reagent (allergen detection in food, pollutant detection, detection of viruses or bacteria, pH measurement, detection of disease including meningitis, etc.) ; Educational demonstration;

Rapid measurement of the spectral response of an optical filter or an optical mirror;

Identification of gems, precious and semi-precious stones;

Traceability and authentication of special inks (authentication of spirits, works of art, banknotes, etc.).

These different applications can use a database embedded on the electronic device, or remote and accessible through wireless communication means which is provided with the electronic device.

The database includes, for example, a library of reference spectra for identifying, by comparison, gems, precious and semi-precious stones.

It is also possible to use wireless communication means of the electronic device for sending results and measurements, in particular via the Internet. The invention is not limited to the examples cited, and many variants can be implemented without departing from the scope of the invention, these variants relate to the structure of the removable accessory, or the method implemented for the use of this removable accessory.

Claims (6)

A method implemented in a system (1000) comprising: an electronic apparatus (600) provided with a multi-pixel photosensitive sensor (601), computing means (602) and a screen (603), such as a mobile phone or digital tablet; and a removable accessory (100; 100 '; 100 "; 100'") comprising: a housing (110) receiving wavelength dispersing means (114) and beam straightening means (115) for compensating for a mean deviation provided by the wavelength dispersing means (114); and - main fixing means (120), for removable attachment to the electronic device; the removable accessory being attached to the electronic device (600) by the main fixing means (120), and the housing (110) of the removable accessory covering the photosensitive multi-pixel sensor (601) of the electronic device so that the multi-pixel photosensitive sensor (601) receives a spectrally spread light beam, the method being implemented by the computing means (602) of the electronic apparatus (600) and comprising steps of: receiving an image (Im (O)) provided by the multi-pixel photosensitive sensor (601); image processing, using wavelength calibration data (C (\)) and intensity calibration data (C (I)), to obtain a light spectrum (Ιο (λ )); characterized in that the multi-pixel photosensitive sensor (600) is a color sensor, and in that the method comprises a preliminary step of adjusting first wavelength calibration data, comprising the following sub-steps: receiving an adjustment image provided by the multi-pixel photosensitive sensor (601); searching, on the adjustment image, a region (1207) in which a difference in light intensity, measured on two neighboring pixels each associated with the detection of a different wavelength, is minimal; from a comparison between said first wavelength calibration data, and the position of said region (1207) on the adjustment image, determining second wavelength calibration data, said region being associated with a so-called adjustment wavelength. 2. Method according to claim 1, characterized in that the multi-pixel photosensitive sensor (600) is a so-called RGB sensor, comprising a first type of pixel dedicated to the detection of red, a second type of pixel dedicated to the detection of the green, and a third type of pixels dedicated to the detection of blue, and in that: the search on the adjustment image comprises the search for a region (1207) in which a difference in light intensity, measured on a pixel dedicated to the detection of red and a pixel dedicated to the detection of green, is minimal; and the adjustment wavelength is between 570 nm and 590 nm. 3. Method according to claim 1 or 2, characterized in that the adjustment image is an image of a white light source, or an image of a surface illuminated by a white light source. 4. Method according to any one of claims 1 to 3, characterized in that the determination of the second wavelength calibration data comprises: calculating an offset between a position associated with the wavelength d adjusting, on the multi-pixel photosensitive sensor (600), based on the first wavelength calibration data, and the position of said region (1207); and translating the position values on the multi-pixel photosensitive sensor into the first calibration data and without changing the corresponding wavelength values by a value equal to the calculated offset. 5. Method according to any one of claims 1 to 4, characterized in that it further comprises a preliminary step of determining said first wavelength calibration data, comprising the following sub-steps: reception of a wavelength calibration image, provided by the multi-pixel photosensitive sensor, associated with a so-called reference light source, and comprising at least three light lines (1105a, 11105b, 1105c, 1105d) or three light spots; for each line or point, matching a predetermined wavelength (VI, V2, V3, V4) and a position of the light line or light spot on the calibration image and on the sensor multi-pixel photosensitive; from the pairs associating a predetermined wavelength and a position on the multi-pixel photosensitive sensor, calculating the first wavelength calibration data. 6. Method according to any one of claims 1 to 5, characterized in that it further comprises a preliminary step of determining the intensity calibration data (C (1)), the determination of the calibration data in intensity comprising the following sub-steps: receiving an intensity calibration image, provided by the multi-pixel photosensitive sensor (601), and associated with a black body light source; - comparison between the intensity calibration image, and a reference spectrum formed by the light spectrum of terrestrial solar radiation, to obtain intensity calibration data (C (1)).