Method for determining a magnification for analysing at least one geological sample, associated method and apparatus

Abstract

The present invention relates to a method for determining a magnification for analysing at least one geological sample (24), which comprises the following steps: - placing a calibration card (17) comprising at least one two-dimensional marker (26) onto a sample holder (16); - placing a photographic apparatus (30) above the sample holder (16); - activating the photographic apparatus (30) in order to take an image of the sample holder (16) including the calibration card (17); - activating a calibration system (38) in order to carry out the following sub-steps: * reading the image taken by the photographic apparatus (30); * identifying the at least one two-dimensional marker (26) present in the image; * determining at least one characteristic dimension of the at least one two-dimensional marker (26) in the image; * calculating a magnification using a characteristic dimension determined from the image and a corresponding physical dimension of the two-dimensional marker (26).

Description

[0001] TITLE: Method for determining magnification for analyzing at least one geological sample, associated method and apparatus

[0002] The present invention relates to a method for determining a magnification for analyzing at least one geological sample, characterized in that it comprises the following steps;

[0003] - to place on a substantially flat upper face of a sample holder, intended to receive at least one geological sample, a substantially flat calibration card comprising at least one two-dimensional marker of predefined structure,

[0004] - place a camera on a support element located above the sample holder, the camera having a lens defining an optical axis, the lens being positioned opposite the upper face of the sample holder so that the optical axis is substantially perpendicular to the upper face of the sample holder,

[0005] - activate the camera to take a digital image of the sample holder including the calibration card located on the sample holder,

[0006] - activate a calibration system to perform the following sub-steps, o reading the digital image taken by the camera; o identification of at least one two-dimensional marker present on the digital image; o determination of at least one characteristic dimension of at least one two-dimensional marker on the digital image; o calculation of a magnification using at least one characteristic dimension determined on the digital image and at least one corresponding predefined physical dimension of at least one two-dimensional marker.

[0007] Determining the geological composition of soils is necessary in several sectors of activity, such as the oil or mining industry.

[0008] This determination can be made by analyzing geological samples taken successively during a borehole through the ground. The analysis is based in particular on the appearance of the samples, including their geometry and color.

[0009] For this purpose, it is known to use images of the samples actually collected to determine the nature of the rocks present through image analysis by a geologist. Sometimes, algorithms are used to aid in sample identification after the sample or its image has been digitized. To use these images, it is necessary to know the correspondence between the actual colors and those in the image, as well as the magnification, that is, the ratio between an actual dimension of the sample and that same dimension as it appears in the image.

[0010] The color is classically calibrated using targets, containing patches of known color, directly integrated into the shooting process.

[0011] Methods for calibrating magnification are known, notably using visual markers that allow their recognition in order to use their dimensions to calculate magnification.

[0012] With the acquisition of digital images at increased resolutions and the addition of macrophotography settings, it is now possible to capture smaller elements in digital images for quantitative analysis. This represents a significant change, as it allows for the automation of complex processes.

[0013] Automation requires precise calibration of colors and magnification so that color-based recognition algorithms (and other types of algorithms) can operate reliably and consistently.

[0014] However, this calibration and the resulting measurements are very sensitive to slight changes in the power and spectrum of light, or to the sensitivity curves of the camera sensor, which can also exhibit slight variations over time.

[0015] Scale-based calculations, such as determining the surface area of ​​an object in an image, can in some cases be too imprecise, especially when macrophotographic parameters are used to analyze smaller structures.

[0016] One aim of the invention is to provide a robust and suitable method for determining magnification for the analysis of geological samples that is reliable and accurate, even in the case of macrophotographic image analysis, while remaining simple to implement.

[0017] To this end, the invention relates to a method for determining a magnification for analyzing at least one geological sample, characterized in that it comprises the following steps;

[0018] - to place on a substantially flat upper face of a sample holder, intended to receive at least one geological sample, a substantially flat calibration card comprising at least one two-dimensional marker of predefined structure,

[0019] - place a camera on a support element located above the sample holder, the camera having a lens defining an optical axis, the lens being positioned opposite the upper face of the sample holder so that the optical axis is substantially perpendicular to the upper face of the sample holder,

[0020] - activate the camera to take a digital image of the sample holder including the calibration card located on the sample holder,

[0021] - activate a calibration system to perform the following sub-steps, o reading the digital image taken by the camera; o identification of at least one two-dimensional marker present on the digital image; o determination of at least one characteristic dimension of at least one two-dimensional marker on the digital image; o calculation of a magnification using at least one characteristic dimension determined on the digital image and at least one corresponding predefined physical dimension of at least one two-dimensional marker.

[0022] According to other advantageous aspects of the invention, the method for determining magnification comprises one or more of the following features, taken individually or in any technically possible combination: in the absence of identification of at least one two-dimensional marker on the digital image, the calibration system generates a camera positioning alert; the calibration system determines a positioning criterion on the calibration card on the upper face and issues a positioning alert on the calibration card in case of inadequate positioning; the calibration card has several predefined two-dimensional markers spaced at a predetermined distance, the determination of a characteristic dimension using the predetermined distance; the two-dimensional markers are aligned along at least one row and / or along at least one column;The magnification calculation includes determining several characteristic dimensions of at least one two-dimensional marker and / or a plurality of two-dimensional markers, with a magnification then being determined statistically, notably from the individual magnifications, to obtain at least one average magnification; at least one two-dimensional marker is in the form of a pixel matrix, for example of the Arllco type; a magnification verification step is carried out using a known dimension measurement tool present on the digital image, the verification including a known dimension measurement of the measurement tool on the digital image; the calibration map includes at least one coloured calibration area, with the two-dimensional marker being placed in or adjacent to the coloured area.

[0023] The invention also relates to a method for analyzing geological samples, comprising the following step;

[0024] - implementation of the magnification determination method according to any one of the preceding claims, to calculate a specified magnification, the method comprising the following steps, implemented before, during or after the determination of the magnification;

[0025] - Deposition of at least one geological sample on the upper surface of the sample holder,

[0026] - activation of the camera to take a digital image of the geological sample, determination of at least one physical dimension on the geological sample using a corresponding dimension on the digital image and the determined magnification.

[0027] According to another advantageous aspect of the invention, the method of analyzing geological samples includes loading the geological sample and the calibration card onto the same sample holder, taking a digital image containing the geological sample, taking a digital image containing the calibration card, with a step of moving the sample holder being implemented between the digital image acquisitions.

[0028] The invention also relates to a device for analyzing geological samples, characterized in that it comprises:

[0029] - a sample holder having a substantially flat upper face intended to receive at least one geological sample and a substantially flat calibration card comprising at least one two-dimensional marker of predefined structure, disposed on the sample holder,

[0030] - a supporting element,

[0031] - a camera having a lens defining an optical axis, the camera being carried by the support element, the lens being positioned opposite the sample holder so that the optical axis is substantially perpendicular to the upper face of the sample holder; to allow the taking of a digital image of the sample holder including the calibration card located on the sample holder;

[0032] - a calibration system configured to: o read the digital image taken by the camera; o identify at least one two-dimensional marker located on the digital image; o determine a characteristic dimension of at least one two-dimensional marker on the digital image; o calculate a magnification using at least one characteristic dimension determined on the digital image and at least one corresponding predefined physical dimension of the two-dimensional marker.

[0033] According to other advantageous aspects of the invention, the geological sample analysis apparatus comprises one or more of the following features, taken individually or in any technically possible combination:

[0034] - the support element of the camera is movable along an elevation axis perpendicular to the plane defined by the face of the sample holder;

[0035] - the sample holder containing the calibration card contains at least one housing accommodating at least one geological sample to be measured, an external face of at least one geological sample being located substantially in the same plane as the calibration card;

[0036] - the sample holder is movable relative to the support element along at least one axis located in the plane of the face of the sample holder, preferably along two axes located in the plane of the face of the sample holder.

[0037] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the attached drawings, in which:

[0038] [Fig. 1] Figure 1 is a perspective view of a geological sample analysis apparatus according to the invention allowing the implementation of an analysis method using a magnification determined by a magnification determination method according to the invention.

[0039] [Fig. 2] Figure 2 is a partial top view of part of the device shown in Figure 1.

[0040] [Fig. 3] Figure 3 is an example of a calibration card that can be used for determining magnification, [Fig. 4] Figure 4 is a flowchart, describing the steps of an example of a method for determining magnification according to the invention,

[0041] [Fig. 5] Figure 5 is a flowchart describing the method for analyzing geological samples according to the invention,

[0042] An example of a geological sample analysis device 10 is shown in Figure 1.

[0043] The geological sample analysis device 10 is intended to be used to analyze geological samples 24 by taking digital images of the geological samples 24, including with high magnification.

[0044] By "high magnification" we mean that the magnification is similar to that of a digital camera equipped with a macrophotography lens placed less than 50 cm from the point of the geological sample 24 allowing focusing.

[0045] In one particular embodiment, the geological sample analysis device 10 is used on an oil site, on which a subsurface exploitation facility, not shown, is installed.

[0046] To optimize drilling, it is important to know the soil conditions in which the installation is located and the type of rock it is penetrating. For this purpose, geological samples, such as debris from the subsoil, are collected and analyzed by an operator to determine, among other things, the chemical composition of the samples.

[0047] It is understood that the geological sample analysis device 10 can be used for the purpose of analyzing geological samples from any type of facility, petroleum, mining or otherwise, and is not reserved exclusively for geological samples from the subsoil.

[0048] The geological sample analysis apparatus 10 in this example comprises a lower housing 12, intended to receive, support and possibly move at least one geological sample 24, advantageously a plurality of geological samples 24, an upper housing 14 intended for taking digital images of the or each geological sample 24 received in the lower housing 12 and a control unit 15 comprising a calibration system 38 of the digital images of the geological samples 24, to determine in particular a magnification enabling to quantitatively analyze the or each geological sample 24 from the digital image which has been taken of the geological sample 24.

[0049] The geological sample analysis device 10 further advantageously includes a fixing system (not shown) located on the upper housing 14 and / or on the lower housing 12 in order to make them joined together, this fixing system preferably being removable.

[0050] The lower housing 12 shown in Figure 1 contains a movable sample holder 16, a calibration card 17 carried by the sample holder 16 and at least one actuator 18 for moving the sample holder 16 in the lower housing 12, here two actuators for moving 18 along two perpendicular axes A-A' and B-B'.

[0051] With reference to figure 2, the sample holder 16 has a movable tray which has an upper face 20.

[0052] The upper face 20 extends along a plane which is generally kept horizontal when taking digital images of the geological sample or samples 24.

[0053] The upper face 20 defines at least one housing 22 intended to accommodate a geological sample 24, preferably a plurality of housings 22 to each receive a distinct geological sample 24.

[0054] The geological sample or samples 24 inserted into a housing 22 are then substantially in the same common plane defined by the upper face 20 of the sample holder 16.

[0055] The upper face 20 of the sample holder 16 also delimits an area to accommodate the calibration card 17.

[0056] In the example shown in Figure 2, the dwellings 22 are generally arranged along at least one line extending along a first horizontal axis A-A' and / or along at least one column extending along a second horizontal axis B-B' perpendicular to the first axis A-A'.

[0057] The area hosting the calibration card 17 is also located in the plane defined by the upper face 20. Thus, the calibration card 17 extends substantially to the same height, taken along a vertical axis C-C', as the geological samples 24 intended to be photographed.

[0058] The area housing the calibration card 17 is for example located on a row or column, adjacent to at least one housing 22, for example interposed between two housing 22.

[0059] In the example shown in Figure 2, the area hosting the calibration card 17 is located in a line adjacent to a longitudinal edge of the upper face 20, advantageously parallel to the first axis A-A'.

[0060] Each actuator 18 is intended to move the sample holder 16 and its upper face 20 in translation along one of the axes A-A', B-B', in order to successively position each housing 22 containing a geological sample 24 and the calibration card 17 opposite a vertical axis C-C' defined by the upper housing 14. Each actuator 18 has a fixed part and a movable part attached to the sample holder 16 in order to move the sample holder 16 along the respective axis A-A'; B-B'.

[0061] Each actuator 18 is electrically connected to the control unit 15 to control the movement of the moving part in accordance with the desired position of the sample holder 16 along the respective axis A-A'; B-B'.

[0062] The calibration card 17 is placed on the area of ​​the sample holder 16. Here it is flat and extends in the common plane defined by the upper face 20 of the sample holder 16.

[0063] In the example shown in Figure 3, the calibration card 17 has a lower face intended to be placed on the upper face 20 and an opposite upper face having at least one two-dimensional marker 26 whose structure is predefined.

[0064] The upper face 20 advantageously defines at least one calibration relief to align the calibration card 17 in a defined orientation.

[0065] By "predefined structure" we mean that the two-dimensional marker 26 is characterized by a predefined outline and / or by a predefined fill.

[0066] The predefined contour is notably polygonal, in particular rectangular, advantageously square. The sides of the polygonal contour thus each have a known physical dimension tabulated in a database of two-dimensional markers 26, the physical dimension being measured in the metric or imperial system.

[0067] Similarly, the two-dimensional marker or markers 26 advantageously have a center whose position relative to the sides of the contour is known and tabulated in a database of markers 26, measured in the metric or imperial system.

[0068] The filling here is formed of a matrix of light areas, notably white, and dark areas, notably black, defining a known and tabulated pattern in a database of two-dimensional markers 26. The pattern is specific to each two-dimensional marker 26 and is different from one two-dimensional marker 26 to another two-dimensional marker 26 on the calibration map 17.

[0069] In cases where the calibration chart 17 has a plurality of two-dimensional markers 26, these are advantageously arranged according to a predefined organization. Thus, the distance separating the centers, corners, or sides of the two-dimensional markers 26 is known and tabulated in a marker database 26, and measured in the metric or imperial system.

[0070] In the example shown in Figure 3, the 26 two-dimensional markers are arranged in a matrix, along a plurality of rows and columns. Each 26 two-dimensional marker is, for example, in the form of a pixel matrix, specifically of the "Arllco" type, as defined on the Wikipedia page at the following address: https: / / en.wikipedia.org / wiki / ARTag. Alternatively, the marker is of type ARToolkit / ARToolkit Plus, ARTag, AprilTag, QRCode, Framedge, Intersense, Matrix, BinARylD, CyberCode, VisualCode, IGD, SCR, HOM, or ReacTIVision.

[0071] Preferably, the calibration card 17 also has at least one coloured area of ​​at least one calibrated colour to perform a calibration of the colour present on the image.

[0072] The upper housing 14, shown in Figure 1, contains a support element 28 that accommodates a digital camera 30, equipped with a lens 32 that defines an optical axis. The upper housing 14 also contains an actuator 33 for moving the support element 28 along the vertical axis C-C' and a guide element 36 for moving the support element 28.

[0073] The camera 30 is configured to take at least one digital image, preferably a plurality of digital images, on an electronic photographic sensor, encoding it in a digital format.

[0074] Preferably, the 30 camera is configured for use with a macrophotography setting.

[0075] The camera sensor 30, for example, has more than 25 megapixels, preferably 30 megapixels or more, each pixel having a square shape with a side size of less than 5 pm, preferably between 5 pm and 2 pm, for example equal to 3.2 pm.

[0076] The 32 lens is particularly intended for use in a configuration where the distance between the upper face 20 and the sensor is advantageously greater than 25 cm, especially between 26 cm and 50 cm.

[0077] The camera 30 is mounted on the support element 28, preferably in a removable manner. When the camera 30 is supported by the support element 28, the lens 32 is positioned opposite the upper face 20 of the sample holder 16 so that the optical axis is perpendicular to the plane defined by the upper face 20.

[0078] The camera sensor 30 is then substantially parallel to the plane defined by the upper face 20. Advantageously, the sensor is aligned with the calibration card 17, the orientation of which is defined by the calibration relief present in the upper face 20.

[0079] The camera 30 has a shutter release (not shown), controlled by the control unit 15 to trigger image capture. In the embodiment shown in Figure 1, the support element 28 is movable, by means of the actuator 33, relative to the sample holder 16 along a vertical axis C-C' orthogonal to the upper face 20.

[0080] The guide element 36 extends vertically parallel to the axis C-C'. It is for example formed of a rail and / or a column.

[0081] The support element 28 is thus movable in translation along the axis C-C' by being guided by the guide element 36.

[0082] The distance between the objective 32 and the upper face 20 of the sample holder 16 is therefore adjustable by adjusting the position of the support element 28 along the axis C-C'.

[0083] The length of the guide element 36 along the C-C' axis defines the range of values ​​that the distance between the objective 32 and the upper face 20 can take.

[0084] The control unit 15 is configured to drive the actuators 18, 33, to place a given region of the top face 20 opposite the objective 30, at a predefined height relative to the objective 30. For example, this given region may include the calibration card 17 and / or a geological sample 24 inserted into a particular housing 22.

[0085] The calibration system 38 comprises a computer including a processor 43A and a memory 43B which receives software modules to be executed by the processor 43A to perform functions. Alternatively, the computer includes programmable logic components or dedicated integrated circuits, intended to perform the functions of the modules that will be described below.

[0086] The calibration system 38 includes an image reading module 44A, connected to the camera 30 to receive in particular at least one digital image of the calibration card 17, taken by the camera 30, and an identification module 44B of the two-dimensional marker(s) 26 located on the digital image.

[0087] The calibration system 38 further includes a module 44C for determining a characteristic dimension of the two-dimensional marker 26 on the digital image and a module 44D for calculating a magnification using at least one known dimension of the two-dimensional marker 26 and the corresponding characteristic dimension detected on the digital image.

[0088] A method 50 for determining the magnification implemented with the geological sample analysis apparatus 10 according to the invention will now be described, with reference to Figure 4.

[0089] In an initial step 52, the user creates or enters a calibration card 17 having at least one two-dimensional marker 26 as shown in Figure 3. The creation of the calibration card 17 is carried out for example using a computer system, in particular using the calibration system 38, from a database of two-dimensional markers 26 defining the predefined outline and / or predefined fill of each two-dimensional marker 26, as well as the predefined organization of the two-dimensional markers 26 on the calibration card 17.

[0090] The definition of each two-dimensional marker 26, including its outline and / or the patterns of its filling, as well as the characteristic dimensions in the metric or imperial measurement system of each two-dimensional marker 26 (for example, length of the sides, distance from the center to the sides) and / or the arrangement of the two-dimensional markers 26 on the calibration card 17 is then entered or transmitted to the calibration system 38 to be stored in memory 43B.

[0091] In step 54, the user places the calibration card 17 on the designated area of ​​the sample holder 16. The calibration card 17 is positioned approximately in the plane defined by the upper face 20.

[0092] The calibration card 17 remains fixed relative to the sample holder 16 during the implementation of the magnification determination process 50, particularly during the movement of the sample holder 16 and / or the support element 28.

[0093] At step 56, the calibration card 17 is centered with respect to the objective 32 of the camera 30 by horizontal displacement of the sample holder 56 with respect to the objective 32 implemented by the actuators 18. Optionally, the support element 28 is moved vertically with respect to the sample holder 16 to a defined position along the axis C-C'.

[0094] Next, in step 58, at least one digital image of the sample holder 16 containing the calibration card 17 is taken by activating the shutter release of the camera 30. This digital image is transmitted to the image reading module 44A which establishes the correspondences between the pixel positions in the digital image and the signal recorded by the camera 30.

[0095] At step 60, once the digital image has been read by the image reading module 44A, the identification module 44B identifies the presence of one or more two-dimensional markers 26 on the image by means of image analysis. This analysis includes, for example, identifying the patterns present on each area that could constitute a two-dimensional marker 26 on the image and comparing them with the predefined fill of the calibration card 17 stored in the memory of the calibration system 38.

[0096] In the optional step 62, if a two-dimensional marker 26 is not detected, the distance between the lens 32 and the calibration card 17 is increased. The support element 28 is translated along the C-C' axis orthogonal to the upper face 20 by means of the actuator 33, away from the upper face 20. This increases the field of view of the camera 30, allowing a larger portion of the calibration card 17 to be represented in the image. Steps 60 and possibly 62 are then repeated as long as the distance between the lens 32 and the upper face 20 can be increased so that at least one two-dimensional marker 26 is present in the image and can be detected.

[0097] Advantageously, an alert is sent to the user by the calibration system 38 to warn him of a failure to detect at least one two-dimensional marker 26 of the calibration card 17. This alert reflects a bad positioning of the camera 30 or a very deteriorated card.

[0098] At step 66, when at least one two-dimensional marker 26, preferably when all the two-dimensional markers 26 of the calibration card 17 are present on the digital image, or when the distance between the upper face 20 and the lens 32 can no longer be increased, at least one characteristic dimension of at least one two-dimensional marker 26 in the image is determined by the determination module 44C. Each characteristic dimension is determined in pixels.

[0099] As stated above, the characteristic dimension determined in pixels is, for example, the length of one side of a two-dimensional marker 26, the distance separating the center of a two-dimensional marker 26 from one side of the two-dimensional marker 26, the distance separating the centers or corners of two adjacent two-dimensional markers 26.

[0100] Advantageously, when the two-dimensional markers 26 all have the same characteristic physical dimensions, and / or are equidistant on the calibration card 17, characteristic distances are calculated along each row and / or each column of two-dimensional markers 26. A suitable positioning criterion for the calibration card 17 on the upper face 20 is then determined, for example, in the form of a regression coefficient R 2 .

[0101] Regression coefficients are then calculated for each row and / or each column using a fixed element of the markers, such as the centers of these markers. These R² coefficients must be close to 1 (for example, greater than 0.9) to indicate that the lines formed by these markers have been correctly detected, that is, that there has been no mixing between two different columns or two different rows.

[0102] A slope is calculated for each row and / or column relative to a direction on the calibration chart 17, for example, along the A-A' axis. The slope of each row or column is compared to the respective slopes of the other rows or columns; a significant variation in the slopes of the columns and / or rows indicates an inadequate positioning of the calibration chart 17.

[0103] In the latter case, an alert of inadequate positioning of the calibration card 17 is then issued by the calibration system 38. The calibration card 17 is repositioned on the upper face 20 and steps 58 to 66 are repeated.

[0104] At step 68, the computing module 44D calculates at least one magnification by correspondence between at least one characteristic dimension in pixels of at least one two-dimensional marker 26 determined in the digital image at step 66 and the corresponding physical characteristic dimension on the calibration card 17, as advantageously stored in the memory 43B of the calibration system 38.

[0105] Advantageously, the 44D calculation module calculates several magnifications from several characteristic dimensions determined on the same two-dimensional marker 26 or from several characteristic dimensions established from several two-dimensional markers 26, for example by determining a plurality of characteristic distances each corresponding to a given two-dimensional marker 26 or a plurality of characteristic distances between several two-dimensional markers 26 (for example, center-to-center or corner-to-corner distances between successive two-dimensional markers 26).

[0106] Optionally, in step 70, the 44D calculation module applies statistical processing to obtain a usable magnification, notably by averaging the different magnifications obtained and possibly determining an uncertainty associated with the average magnification obtained. For example, this uncertainty can be estimated using a Student's t-distribution.

[0107] In optional step 72, the identification module 44B detects a measuring tool that may be present in the image, for which at least one characteristic physical dimension is known. The determination module 44C then determines the characteristic dimension of the measuring tool in pixels in the image. The calculation module 44D then uses the magnification calculated in steps 68 and 70 to calculate a physical dimension of the measuring tool and compare it to the known actual physical dimension. Depending on the difference between the calculated physical dimension and the calculated physical dimension of the measuring tool, the magnification calculated in steps 68 and 70 is considered valid or invalid.

[0108] A method 65 for the analysis of geological samples, represented in Figure 5, will now be described.

[0109] This method 65 implements the magnification determination procedure 50 described above to determine a magnification and analyze at least one geological sample 24 by taking a digital image of the geological sample(s) 24 and analyzing the digital image using the determined magnification. This makes it possible to determine, for example, a distance or an area relative to the geological sample 24 from the digital image.

[0110] Figure 5 is a flowchart representing an example of the implementation of method 65.

[0111] In step 74, at least one geological sample 24 is prepared. This geological sample 24 is, for example, a slice of geological material intended for study, and has an inner face (not shown), intended to be positioned on the side of the sample holder 16, and an outer face 78, opposite the inner face. The outer face 78 is advantageously substantially flat.

[0112] Advantageously, several geological samples 24 are deposited in several compartments 22 of the sample holder 16, this allows a greater number of analyses to be carried out while minimizing the time required.

[0113] At step 77, each geological sample 24 is placed in a housing 22 of the sample holder 16 with its inner face in contact with the upper face 20 and its outer face 78 advantageously parallel to the upper face 20.

[0114] Moreover, the difference in height, taken along the C-C' axis, between the outer face 78 of the geological sample 24 and the upper face 20 of the calibration card 17 containing the or each two-dimensional marker 26 is substantially zero, that is to say generally less than 2 mm.

[0115] In step 80, the magnification determination process is implemented to determine a magnification as described above. Optionally, a colorimetric calibration is performed by the calibration system 38 by determining at least one visible color in the color calibration area on the digital image and comparing it to the actual color present on the calibration card 17.

[0116] The magnification obtained is then defined for the current position of the objective 32 with the distance separating the objective 32 and the calibration card 17. In order to improve the accuracy of the method, this distance is advantageously maintained during the image acquisition of the geological samples 24 which will be described below.

[0117] In step 82, the sample holder 16 is moved in the horizontal plane to center a first geological sample 24 with respect to the vertical axis C-C' passing through the lens 32 of the camera 30. This movement is performed by the control unit 15, which operates the actuators 18. The distance between the lens 32 and the sample holder 16, measured orthogonally to the face 20, remains constant during this movement. In step 84, the control unit 15 triggers the camera 30 to obtain a digital image of the outer face 78 of the first geological sample 24.

[0118] Steps 82 and 84 are repeated as necessary to obtain an image of each external face 78 of each geological sample 24 present on the sample holder 16.

[0119] Finally, in step 86, a physical dimension, for example a distance or an area, on each geological sample 24, measured in the metric or imperial system, is advantageously calculated by the calculation module 44D using the corresponding dimension measured in pixels on the digital image of the geological sample 24, advantageously by the determination module 44C, and the magnification obtained previously in step 80.

[0120] The nature of the geological sample 24 considered is then determined for example by a determination system including a computer, using the calculated physical dimension(s) and / or a colorimetric analysis of the sample after calibration, for example by implementing a recognition algorithm.

[0121] The determination method according to the invention therefore makes it possible to determine a magnification with high precision, thanks to the use directly on the upper face 20 of the sample holder 16 of a calibration card 17 having at least one two-dimensional marker 26 of predefined structure.

[0122] Positioning the calibration card 17 as close as possible to the housings 22 receiving the geological samples 24 to be measured, in conjunction with the precise determination of the dimensions of the or each two-dimensional marker 26 on the digital image ensures that the calculated magnification is accurate and corresponds to that which must be applied when measuring geological samples 24.

[0123] Thus, the gain in precision obtained makes it possible to work precisely in macrophotographic mode to characterize precise details of the geological samples 24, allowing easier and / or automatic identification of the geological samples 24 at different scales thanks to an adjustable distance between the camera 30 and the geological samples 24.

Claims

DEMANDS 1. A method for determining a magnification (50) for analyzing at least one geological sample (24), characterized in that it comprises the following steps: placing on a substantially flat upper face (20) of a sample holder (16), intended to receive at least one geological sample (24), a substantially flat calibration card (17) comprising at least one two-dimensional marker (26) of predefined structure; placing a camera (30) on a support element (28) located above the sample holder (16), the camera (30) having a lens (32) defining an optical axis, the lens (32) being arranged opposite the upper face (20) of the sample holder (16) so that the optical axis is substantially perpendicular to the upper face (20) of the sample holder (16),activate the camera (30) to take a digital image of the sample holder (16) including the calibration card (17) located on the sample holder (16), activate a calibration system (38) to perform the following substeps: reading the digital image taken by the camera (30); identifying at least one two-dimensional marker (26) present on the digital image; determining at least one characteristic dimension of at least one two-dimensional marker (26) on the digital image; calculating a magnification using at least one characteristic dimension determined on the digital image and at least one corresponding predefined physical dimension of at least one two-dimensional marker (26).

2. Method for determining the magnification (50) according to claim 1, in which, in the absence of identification of at least one marker two-dimensional (26) on the digital image, the calibration system (38) generates a camera positioning alert (30).

3. Method for determining the magnification (50) according to any one of claims 1 or 2, wherein the calibration system (38) determines a positioning criterion on the calibration card (17) on the upper face (20) and issues an alert on the positioning of the calibration card (17) in case of inadequate positioning.

4. Method for determining the magnification (50) according to claim 1 to 3, wherein the calibration card (17) has several predefined two-dimensional markers (26) spaced at a predetermined distance, the determination of a characteristic dimension using the predetermined distance.

5. Method for determining the magnification (50) according to claim 4, wherein the two-dimensional markers (26) are aligned along at least one line and / or along at least one column.

6. Method for determining magnification (50) according to any one of the preceding claims wherein the calculation of magnification includes the determination of several characteristic dimensions of at least one two-dimensional marker (26) and / or a plurality of two-dimensional markers (26), a magnification then being determined statistically in particular from the individual magnifications to obtain at least one average magnification.

7. Method for determining magnification (50) according to any one of the preceding claims, wherein at least one two-dimensional marker (26) is in the form of a pixel matrix, for example of the Arllco type. 18 8. Method for determining magnification (50) according to any one of the preceding claims, wherein a magnification verification step is carried out using a measuring tool of known dimensions present on the digital image, the verification comprising a measurement of known dimensions of the measuring tool on the digital image.

9. Method for determining magnification (50) according to any one of the preceding claims, wherein the calibration card (17) comprises at least one coloured color calibration area, the two-dimensional marker (26) being placed in or adjacent to the coloured area.

10. Method for analyzing geological samples (65) comprising the following step; implementation of the magnification determination method (50) according to any one of the preceding claims, to calculate a determined magnification, the method comprising the following steps, implemented before, during or after the determination of the magnification; depositing at least one geological sample (24) on the upper face (20) of the sample holder (16), activating the camera (30) to take a digital image of the geological sample (24), determining at least one physical dimension on the geological sample (24) using a corresponding dimension on the digital image and the determined magnification.

11. Method for analyzing geological samples (65) according to claim 10, comprising loading the geological sample (24) and the calibration card (17) onto the same sample holder (16), taking a digital image containing the geological sample (24), taking a digital image containing the calibration card (17), a step of moving the 19 sample holder (16) being implemented between digital image captures.

12. Apparatus (10) for analyzing geological samples, characterized in that it comprises: a sample holder (16) having a substantially flat upper face (20) for receiving at least one geological sample (24) and a substantially flat calibration card (17) comprising at least one two-dimensional marker (26) of predefined structure, disposed on the sample holder (16); a support element (28); a camera (30) having a lens (32) defining an optical axis, the camera (30) being carried by the support element (28), the lens (32) being disposed opposite the sample holder (16) such that the optical axis is substantially perpendicular to the upper face (20) of the sample holder (16); to allow the acquisition of a digital image of the sample holder (16) including the calibration card (17) located on the sample holder (16); a calibration system (38) configured to;o read the digital image taken by the camera (30); o identify at least one two-dimensional marker (26) located on the digital image; o determine a characteristic dimension of at least one two-dimensional marker (26) on the digital image; o calculate a magnification using at least one characteristic dimension determined on the digital image and at least one corresponding predefined physical dimension of the two-dimensional marker (26).

13. Geological sample analysis apparatus (10) according to claim 12, wherein the support element (28) of the photographic apparatus (30) is movable along an elevation axis perpendicular to the plane defined by the face (20) of the sample holder (16).

14. Geological sample analysis apparatus (10) according to claim 12 or 13, wherein the sample holder (16) containing the calibration card (17) contains at least one housing (22) accommodating at least one geological sample (24) to be measured, an external face of at least one geological sample (24) being located substantially in the same plane as the calibration card (17).

15. Geological sample analysis apparatus (10) according to any one of claims 12 to 14, wherein the sample holder (16) is movable relative to the support element (28) along at least one axis (A-A'; B-B') located in the plane of the face (20) of the sample holder (16), preferably along two axes (A-A'; B-B') located in the plane of the face (20) of the sample holder (16).

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