FR3060112A1 - METHOD FOR DETERMINING THE NACRE THICKNESS ON A PEARL, IN PARTICULAR A PEARL OF CULTURE - Google Patents

Abstract

The object of the invention is a method for determining the pearl thickness of a pearl, by means of X-rays working on a zone Z, in particular a cultured pearl, comprising a spherical nucleus, mother-of-pearl and optionally at least one cavity, said bead being disposed in a cell A of a support P intended to contain it, characterized in that it comprises the succession of the following steps: - Segmenting the bead, - Detecting the Nucleus, - Detecting at least a cavity, and - Calculate the thickness of the mother-of-pearl.

Description

(57) The object of the invention is a method for determining the thickness of mother-of-pearl of a pearl, by means of X-rays working on a zone Z, in particular a cultured pearl, comprising a spherical nucleus, of the mother-of-pearl and possibly at least one cavity, said pearl being placed in a cell A of a support P intended to contain it, characterized in that it comprises the succession of the following stages:

- Segment the pearl,

- Detect the Nucleus,

- Detect at least one cavity, and

- Calculate the thickness of the mother-of-pearl.

METHOD FOR DETERMINING THE THICKNESS OF NACRE ON A PEARL, IN PARTICULAR A CULTURED PEARL

The present invention relates to the determination of the thickness of mother-of-pearl on a pearl, in particular a cultured pearl.

The invention also relates to a method of identifying the conformity of said pearl, the thickness of mother-of-pearl having been measured by the method of determining the thickness of mother-of-pearl according to the present invention.

The process is more particularly applicable to cultured pearls because the breeding is complicated, long and it is necessary to enhance the quality of the pearls obtained. Independently of the other criteria which are the color, the shape, the reflectance, it is necessary to determine the thickness of mother-of-pearl because on the one hand it guarantees a quality of the pearl and a durability of the effects of other go. In all cases, there are many quality criteria that producers, administrations and traders have decided to adopt and in this case, one of the criteria retained is the thickness e of the mother-of-pearl. Breeding has been concentrated for a large part in Polynesia since the 1980s and a lot of work has been done since the 1920s during which Japan developed the first grafts.

Cultured pearls are obtained by using Pinctada morgoritifero oysters which are mostly grown in the wild. These oysters are obtained from spat collected in a natural environment from collectors such as production oysters and intended for consumption.

Once the size of the oyster is reached, beyond 12 cm and the sexual maturity obtained, which requires approximately 3 years, the oyster is ready to undergo a grafting operation.

This grafting consists, after restricted spacing of the shells, in introducing into a cavity formed in a selected gonad of said oyster, a Nucleus, after having half-opened the two shells and by maintaining this opening by means of a dilator.

This Nucleus is itself made from the mother-of-pearl of freshwater bivalve shells. These Nuclei are machined and must be perfectly round, to hope for a final pearl also round.

Each Nucleus must also present an extremely polished surface finish, since any surface roughness will lead to an irregularity in the natural deposit of mother-of-pearl as will be understood later.

There are very many reasons for a cultured pearl to have defects, it is therefore necessary not to introduce defects on the materials used during grafting. These Nuclei have different diameters depending on the size of the oyster and its constitution, the choice of diameter depending on the expertise of the grafter.

This Nucleus is inert and it is associated with a graft to generate a production of mother-of-pearl on said Nucleus. Mother-of-pearl is made of calcium carbonate with a very small platelet structure. This mother-of-pearl is produced naturally by the oyster to generate its shell and growth as it is developed by the mantle epithelial cells.

The graft is a piece of this mantle, cut from said mantle in the form of narrow strips, a portion of the mantle strap constituting the graft being positioned by the grafter around the nucleus to be implanted. The mantle is oriented with its secretion surface towards the Nucleus so that the nacre can develop there.

This set of the two elements Nucleus and Graft is implanted in the cavity formed in the chosen gonad.

The oyster dilator is removed and the oyster closes, then it is returned to the water. The duration of these operations must be very limited, of the order of two minutes, so as not to traumatize the oyster.

Numerous stages of monitoring the persistence of the Nucleus in the oyster, cleaning, immersion at suitable depths, checks for the absence of parasites, etc. are carried out during breeding, parameters which influence the quality and production of mother-of-pearl but which does not concern the measurement method according to the invention which makes it possible to verify the thickness of mother-of-pearl resulting from these operations.

The graft during this phase produces mother-of-pearl which is fixed on the surface of the Nucleus, by accumulation of calcium carbonate platelets.

Once the growth time has passed, the oyster is collected and the Nucleus, coated with mother-of-pearl, is collected by removing the oyster.

The thickness e of the mother-of-pearl is currently estimated by experts, therefore by control using X-rays, which, although carried out by experts in very small numbers, remains subject to a certain subjectivity.

This subjectivity can even be completely unconscious. The work is extremely painful because each expert has to control a very large number of pearls. Several millions are produced and the number of experts very limited, in the order of ten.

Also, a batch sampling method is used, certain pearls of each batch being checked by an expert, which therefore leads to acceptance or rejection of the complete batch of pearls to which the controlled pearls belong.

Not only is it a statistical method with possible errors but the procedure remains very long and during this period, the producers do not sell. As this is an industry, this poses significant problems.

The time required for the inspection services, the qualities of the sampling inspection, the variations as a function of the expert's fatigue and / or saturation led the applicant for this application to develop an automatic, total process. i.e. without sampling. The advantages of such a process are numerous because the process can be implemented for very many hours, even 24/24, 7/7, it suffices to supply the materials used according to the steps of the process. Human fatigue being eliminated, the reproducibility of the control is proven. The duration should not exceed ls, normal time for an expert and better, it would be interesting to reduce this duration.

Currently, the beads are placed on a tray-type support, each comprising 300 cells. Each support is placed on an X / Y / Z table. The expert works with both hands, one maneuvering a first joystick for suitable positioning of the plate in X / Y and the other maneuvering a second joystick for moving the support comprising the balls in relation to the emitting gun X-rays which remains fixed.

In order to be able to increase the rates, it is planned to treat two cells therefore two pearls at each movement and each focusing.

The surface treated by the beam is 1000/1000 pixels or 35/35 mm, this choice being linked to the parameters of the available X-ray emitting gun.

The expert evaluates the thickness because the thickness corresponds to a given number of pixels, in this case currently for French Polynesian pearls, the minimum thickness is 0.8mm or 23 pixels in the techniques currently adopted.

It is also understood that the evaluations can prove to be complex due to certain configurations so that the expert is led to spend more time on one or more of the beads of the tray. In some cases, it is even necessary to treat said pearl in isolation, out of the support which is very time consuming.

The method according to the present invention is now described according to an embodiment, without limitation, with reference to the appended drawings, drawings in which the various figures represent:

Figure 1: a sectional view of a pearl schematically,

Figure 2: an X-ray view of the same pearl,

Figure 3: a view of the image of a pearl after segmentation,

Figures 4A to 4C: evolution of the circle and its refocusing to determine the border of the nucleus of a pearl,

Figure 4D: curve of the mean probabilities as a function of the number of iterations,

Figure 4E: a simplified illustrative view of the movement of the circle,

FIGS. 5A to 5D: view of the virtual growth stage to determine the presence of at least one cavity,

Figure 6A: schematic representation of the boundaries of the structure of a pearl, Figure 6B: representation of the measurement vectors, oriented radially from the outside to the inside,

Figure 6C: summary table of the measurements in millimeters for each of the vectors from the pixels,

Figures 7: summary table of the measurements in millimeters for each of the vectors from the pixels, with the compliance value fixed.

In Figure 1, there is shown, schematically, a section of a pearl 10 on which there is a Nucleus 12, a layer of mother-of-pearl 14 peripheral to the Nucleus and a cavity

16.

Figure 2 shows an X-ray image of a pearl with its Nucleus 12 and mother-of-pearl 14.

Nucleus 12 is perfectly spherical while the layer of mother-of-pearl 14 is irregular. There is also a visible cavity 16.

There are of course many growth configurations since mother-of-pearl is produced naturally. When there is a peripheral cavity, therefore between the Nucleus and the layer of mother-of-pearl, the thickness is easily assessable. When the cavity is peripheral but very thin, the evaluation is more complex for the expert. When the cavity is punctual and localized, the external peripheral shape is necessarily asymmetrical. When there is no cavity, the X-rays do not allow the thickness to be distinguished, but the pearl is considered to have sufficient thickness.

The criterion of rejection of conformity of a pearl as retained, is a thickness e of mother-of-pearl less than 0.8mm, over more than 20% of its periphery, this measured on a 2D image obtained by emission of X-rays.

Also, according to the present method, it is planned to use an X-ray device and automatic image acquisition at a predefined position.

The pearls are placed in a support of the tray type P of known type, comprising substantially 300 cells A.

The position predefined by the method consists in positioning the taking of images relative to the known depth of each cell of the tray and to the geometry of each cell. Each cell is also marked in X / Y relative to the plate.

Likewise, the intensity distribution in each pearl depends on the power of the X-rays emitted. It is therefore necessary to determine iteratively and by testing the average values of the emission adjustment parameters.

In the selected embodiment, the voltage is 130kv and the current is 35μΑ.

Thus, the positioning of the beam and the characteristics of the beam are determined.

The pearls concerned are pearls with Nucleus, that is to say that the so-called keshi pearls are not concerned. This can be verified, for example after grafting, by placing each oyster in a pocket so that, if the nucleus is rejected, it remains in the pocket. These oysters will therefore not be affected.

Once the characteristics of the X-ray beam have been established, once the plateau and the alveoli of the plateau have been located, the method chosen provides for the analysis of at least one pearl by at least one pearl and, in this case, the analyze plans to analyze two pearls by two pearls, within the tray so as to work under the same conditions as the manual way.

In order to determine which pearls are retained, unclassifiable or considered to be satisfactory, the method provides for considering determining the thickness of mother-of-pearl in 4 steps:

1. Segment the pearl,

2. Detect the Nucleus,

3. Detect at least one cavity, and

4. Calculate the profile of the 2D thickness of the mother-of-pearl.

The invention also aims during a step 5 to identify the beads to be rejected as non-compliant as will be detailed further in the description.

Stage 1 of segmentation consists in retaining only the useful part of each pearl.

This avoids having to analyze a surface which would include non-useful information, information which is likely to increase the analysis time.

To proceed with the segmentation, the surface treated Z by the X-ray beam is 35 × 35 mm as indicated in the preamble and to remain in the selected working model.

Variations of attenuations A1 were recorded which can be represented in gray levels on the surface of said surface Z, in the absence of pearl.

The same surface Z presents variations of different attenuations A2 during the examination of the same surface Z with a given pearl PI on this defined surface Z. These variations of attenuations A2 are then recorded.

The method provides for mathematically subtracting from the intensity variations A2 the intensity variations Al on the same surface Z.

One then obtains an image as represented in FIG. 3, namely black on all the surfaces at zero intensity and white on the surfaces of differential variable intensities which perfectly defines the image of the pearl and only of the pearl .

Step 2 of Nuclear detection is carried out by iterations. Indeed, to determine the diameter of the Nucleus and its center, a specific step is necessary because it is recalled that the diameter of the Nucleus is chosen by the grafter and its position in the mother-of-pearl envelope is completely random.

This step provides for using a heuristic circle detection algorithm. This algorithm provides for a step of detecting the intensity peak of the X-ray image and a small diameter circle is virtually initialized around this area because it must correspond to the Nucleus.

Then, a logical limit probability is established so as to distance the initialized circle corresponding to pixels linked to the nucleus, as a function of the intensities and gradients of the X-ray image.

If the circle sees its diameter increasing, it is because we are still in the pearl and the peripheral limit of the Nucleus is defined by a measurement of the gradient and the intensity of the shades of gray.

Thus, if the probability that a few pixels of the circle touching the border, the peripheral limit of the Nucleus is high, the circle is enlarged beyond the region analyzed as indicated below.

Mathematically, the movement v with an iteration t and a circle of i pixels with a normal vector η, and a probability bi, the formula can be written:

Κ = Σ ^ι ~ hth

Thus if we consider 4 pixels pl to p4 at the cardinal points of a circle, only for explanatory purposes, the probability towards the north and the east is 1 while it is 0 for the two other directions. The movement of the circle according to rp, component of the two vectors will lead to move the circle away from these pixels at the borders, which therefore allows a refocusing as illustrated in FIG. 4E.

In order to refine this calculation, as by assumption the Nucleus is a sphere, the probability at the peripheral limit of the Nucleus is the second derivative of the radial gradient of the moving circle. If is p _it is the i-th peripheral pixel of the circle, nor its normal vector pointing outwards and k a scalar which defines the neighboring rank, the logical limit probability for the iteration t and the image / is ht = Kht - ^k h) ~ Kht) ^> \ ^/ (ht + ^k h) ~ ^z (Pi, t) |

To avoid the background noise generated when the circle does not touch any pixel around the nucleus, a probability function based on intensity is used. At each iteration, the background noise level is tested and a decision based on a predefined threshold value to modify the gradient or intensity is used.

The center of said nucleus is therefore also determined.

The heuristic circle can be illustrated as in FIGS. 4A to 4C which show three selected examples of the evolution of the circle and its refocusing. It is noted that the number of vectors is considerably increased in order to have high precision.

Figure 4D shows the average of the probabilities as a function of the number of iterations and the peak corresponds to the limit of the Nucleus.

This process is fast and compatible with the expected analysis times and above all this process is independent of the size of the Nucleus and therefore adapts to all Nucleus diameters. Step 3 consists in determining the presence or not of a cavity. To this end, the method consists in starting from the periphery of the pearl towards the center and in applying a procedure known as growth by successive iterations which consists in determining the light intensity of the image with X-rays. The growth procedure is interrupted when the maximum intensity is reached or when the peripheral limit of the Nucleus is reached if this has been determined.

In this case, the growth is interrupted locally when the movement leads to an identical intensity value during the next movement or when there is a cavity. The representations of FIGS. 5A to 5D are obtained, respectively the complete pearl, the peripheral limit, the start of the growth procedure, after a certain number of iterations and when the growth procedure is complete.

Step 4 is the determination of the profile of the thickness of the mother-of-pearl, in the plane which has been chosen, knowing that it is a necessarily variable layer on the periphery of the Nucleus.

The method according to the present invention consists in reusing the parameters already obtained, namely:

the segmentation therefore the defined external shape of the external periphery of the pearl, the diameter of the nucleus and its position, the possible presence of at least one cavity.

The number of pixels comprised according to radially oriented vectors, from the outside inwards to the nucleus or to the cavities if they exist, can be determined. The number of pixels counted corresponds to a distance in millimeters due to the resolution adopted. This is the schematic representation of Figure 6A, which shows the three borders.

In FIG. 6B, the representation of the measurement vectors has been shown and in FIG. 6C the summary table for converting pixels into millimeters.

As indicated above, once the thickness has been determined, it is useful to be able to automatically determine whether a pearl conforms or not according to the established criteria and in particular of a minimum thickness e.

Step 5 consists of an automatic determination of the conformity of the pearl analyzed leading to an identification as being potentially marketable or an identification of non-conformity leading to its final rejection.

In Figure 7, there is shown the graph of Figure 6C, on which is mentioned the line of thickness e, in this case 0.8 mm. This step 5 provides for representing a graph of the thicknesses on the periphery, for identifying the value of thickness e of conformity and for calculating the areas above and below the curve and for comparing with a compliance ratio.

Thus it is possible to determine if x% of the surface is of a thickness greater than e.

In the case shown, it can be seen that 46% of the thickness on the periphery is less than the conformity thickness, ie 0.8mm in this case.

Such a pearl is rejected on the basis of the gross measurement of mother-of-pearl thickness with regard to the criteria imposed.

After the implementation of the determination of the thickness e of the mother-of-pearl, the identification method nevertheless provides for introducing a tolerance T. In fact, it is possible to consider a measurement tolerance of ± lpixel for example and we notes that pearls considered rejected would, on the contrary, be valid for possible marketing.

In this case, the tolerance is two pixels for each vector so that we must consider this tolerance by calculating a second curve with 2 more pixels and determine only on this curve if the percentage of the thickness of mother of pearl greater than 0 , 8 mm is much higher than 80%.

Tolerance is a question of definition from the adopted compliance rules but the method according to the present invention remains perfectly applicable whatever the type of pearl, the diameter and the position of the nucleus, the presence of cavities and the compliance rules, these can vary because the process is very quickly adapted.

The method thus makes it possible to automatically determine the beads of a cell tray, the cells of which are located and identified according to whether they are of a thickness which corresponds to the required criteria or not.

It then suffices to have automatic gripping devices to remove the non-conforming beads 5 from the tray.

These devices are not part of the present invention because the means for performing such a gripping automatically are very numerous, in particular a robotic arm, the end of which would be provided with a vacuum suction cup.

Such an operation can be carried out outside the steps of the method according to the present invention in order not to cause loss of time in using the ray generator.

X.

The control of each pearl with the method according to the present invention with measurement, identification of conformity, recording of data is less than one second.

The algorithms used for the different steps may vary and are not directly the subject of the present process.

Claims (9)

1. Method for determining the thickness of mother-of-pearl of a pearl, by means of X-rays working on a surface Z, in particular a cultured pearl, comprising a spherical nucleus, mother-of-pearl and possibly at least one cavity, said pearl being placed in a cell A of a support P intended to contain it, characterized in that it comprises the succession of the following stages: Segment the pearl, Detect the Nucleus, Detect at least one cavity, and Calculate the thickness of the mother-of-pearl. 2. Method for determining the thickness of mother-of-pearl of a pearl according to claim 1, characterized in that a predefined working position is chosen with respect to the depth and the geometry of the cell A and the values average x-ray power, namely voltage and amperage. 3. Method for determining the thickness of mother-of-pearl of a pearl according to claim 1 or 2, characterized in that the surface treated Z by the X-ray beam is 1000/1000 pixels or 35/35 mm, the voltage is 130kv and the current is 35μΑ. 4. Method for determining the thickness of mother-of-pearl of a pearl according to any one of the preceding claims, characterized in that the segmentation of the pearl consists in recording the variations of attenuations Al of the X-rays emitted on the surface Z , in the absence of a pearl, the variations in attenuation A2 are recorded on the same surface Z in the presence of said pearl and the variations in intensity A1 are mathematically subtracted from variations in intensity A2. 5. Method for determining the thickness of mother-of-pearl of a pearl according to any one of the preceding claims, characterized in that the detection of the Nucleus is carried out by the detection of the peak of intensity of the image by X-rays, by initialization of a virtual circle of small diameter around this zone, and by an enlargement and a refocusing of said circle by a limit probability, logical, according to intensities and gradients, until the maximum growth of said corresponding circle to the Nucleus. 6. Method for determining the thickness of mother-of-pearl of a pearl according to any one of the preceding claims, characterized in that the detection of at least one cavity consists in starting from the periphery of the pearl towards the center and at apply a procedure known as growth by successive iterations and to interrupt said growth procedure when the maximum intensity of the X-ray image is reached or when there is a cavity. 7. Method for determining the thickness of mother-of-pearl of a pearl according to any one of the preceding claims, characterized in that the thickness of mother-of-pearl is determined by the number of pixels measured according to radially oriented vectors, from the periphery of the pearl, previously determined by segmentation, inward to the Nucleus, whose position is previously determined. 8. Method for determining the pearl thickness of a pearl according to any one of the preceding claims, characterized in that a tolerance T is introduced in the measurement of the number of pixels of the radially oriented vectors. 9. Method for identifying a non-conforming pearl with respect to a given thickness e, measured by the method according to any one of the preceding claims, characterized in that it consists in representing a graph of the thicknesses e on the periphery , of 15 locate the value of thickness e of conformity and calculate the areas above and below the curve and compare with a compliance ratio. 1/3