System and method for checking the chromatic uniformity of a plurality of portions of an object

Abstract

The system (10) and the method provide for the following : S1) illuminating a portion (Aj) of an object (A) under a respective illumination condition (Cλi) by means of a light beam having selectively a respective illumination wavelength (λi); S2) acquiring a respective monochromatic digital image (Iλi, Aj ) representative of the portion (Aj) under the respective illumination condition (Cλi); S3) repeating steps SI and S2 for a plurality of predetermined illumination conditions (Cλ1i, Cλi, Cλn) and for each portion (Aj) whose chromatic uniformity has to be compared; S4) for each monochromatic digital image (Iλi, Aj), computing a respective luminous intensity value (Vλi, Aj ), representative of the luminous intensity reflected by the portion (Aj) under the respective illumination condition (Cλi); S5) for each combination (CAh,Ak) comprising a first portion (Ah) and a second portion ( Ak) of the object (A), computing a respective chromatic comparison value ( TAh,Ak ) representative of the chromatic uniformity of such portions (Ah, Ak) according to a mathematical model (M) as a function of the luminous intensity values, (Vλ1,A1,...,Vλi,Aj,..., Vλn,An); and S6) outputting uniformity data (D) representative of the chromatic uniformity of the portions (A1,... Aj,..., Am) as a function of the chromatic comparison values ( TAh,Ak ).

Description

[0001] SYSTEM AND METHOD FOR CHECKING THE CHROMATIC UNIFORMITY OF A PLURALITY OF PORTIONS OF AN OBJECT

[0002] DESCRIPTION

[0003] Technical field

[0004] The present invention relates to a system and a method for checking the chromatic uniformity of a plurality of portions of an object.

[0005] Technical background

[0006] In the manufacturing industry, it is generally important that the manufactured objects intended for sale have homogeneous characteristics throughout the production process and for all customer orders. In particular, it is desirable that the aesthetic characteristics of the manufactured objects remain as uniform as possible.

[0007] Particularly, but not exclusively, in the textile industry, chromatic uniformity among a plurality of portions of an object is of the utmost importance.

[0008] Traditionally, the chromatic uniformity of an object is checked visually on a fabric sample.

[0009] Prior to executing the visual inspection, a piece of material (commonly called "cut-length", and generally having a size of 20cm x 150cm) is physically cut. Subsequently, the cut-length is prepared by bringing mutually distant fabric areas near each other to obtain the actual fabric sample to be examined. The visual check is then carried out by trained operators, who visually evaluate the chromatic uniformity of the fabric sample.

[0010] Visually checking fabric samples implies, however, several drawbacks.

[0011] One of the most important drawbacks lies in the fact that evaluations are subjective and operator-dependent, and that one operator's judgements may vary on different days or at different times of the day. Moreover, much time needs to be spent in order to prepare the fabric sample. In addition, material wastes are created when cutting the piece of fabric to be used as a sample. Much time is also spent by the operator for executing the visual inspection and for completing the decision-making process to determine if the fabric sample has the desired levels of colour uniformity.

[0012] In addition to the above-mentioned visual check, systems and methods are also known in the textile industry which can measure colours, in particular by means of a spectrophotometer .

[0013] However, such systems and methods suffer from a few drawbacks as well.

[0014] One drawback lies in the fact that, because of the technology employed, the area framed by the spectrophotometer is extremely small (typically, a diameter not exceeding 30mm). Another drawback lies in the fact that a spectrophotometer can be effectively used for solid-colour fabrics only, since the presence of any patterns would give different results depending on the framed area. Yet another drawback lies in the fact that a spectrophotometer is difficult to use for testing "hairy" fabrics (e.g. wool, cashmere, etc.), in that the principle of operation is based on the angle of incidence of light on the fabric.

[0015] One example of such systems and methods making use of a spectrophotometer can be found in patent publication DE 101 02 607 Al. In such patent publication, in order to check the colour of fabrics and similar materials, a digitized image obtained from a positive model is compared, by a data processing unit, with images acquired from the test fabric.

[0016] However, also this example has a few drawbacks that should be remedied. According to what is disclosed in patent publication DE 101 02 607 Al, one drawback lies in the fact that it is necessary to perform a white calibration (usually at the beginning of each day or period of the day) in order to always be able to refer to a standard "basic" condition.

[0017] A further drawback is that, in the system described in patent publication DE 101 02 607 Al, the observed object must lie flat (flatly) and it is necessary to make distinct analyses of the different colour areas by physically separating the areas of the image. This leads away from the principle of analogy of the human visual check (which does not distinguish between individual parts).

[0018] US 2013 / 293702 Al describes a multispectral imaging colour measurement system, comprising a dark room, a sample platform, and an imaging device for capturing an object to be measured; a controllable illumination device, a filter wheel unit, an imaging signal processing unit, and an electronic control unit. A method for processing imaging signals of the multispectral imaging colour measurement is also proposed.

[0019] US 9 838 612 B2 describes an inspecting device for inspecting a target. The inspecting device includes a mono- colour image-retrieving module, illuminating modules, and a control module. The mono-colour image-retrieving module is disposed above the inspection target with an optical axis orienting towards the inspection target. Each of the illuminating modules includes light-emitting elements of different colours. The control module controls the illuminating modules to sequentially generate illuminating lights in an order of different colours and different incident angles to further control the mono-colour image- retrieving module to sequentially retrieve mono-colour images, each in response to one illumination of the illuminating lights. The control module performs an inspection of the inspection target based on the mono-colour images.

[0020] Summary of the invention

[0021] It is one object of the present invention to provide a system and a method which can overcome some drawbacks of the prior art.

[0022] According to the present invention, this and other objects are achieved through a system and a method having the technical features set out in the appended independent claims.

[0023] In particular, compared with the above-discussed visual check, the present invention provides a system and a method ensuring repeatability when checking the chromatic uniformity of a plurality of portions of an object, even at different times and under different operating conditions. There is also a considerable reduction in the time taken by the operator to complete the check. Furthermore, in particular when checking the chromatic uniformity of a textile object, it is no longer necessary to physically cut the material to create the so-called "cut-lenght ". Lastly, more in-depth process data are obtained, which can be stored by means of information technology systems.

[0024] In addition, compared with the colorimetric uniformity inspection, in particular performed by means of a spectrophotometer, a system and a method are provided wherein the framed area to be checked can be defined as large as desired, whereas a spectrophotometer is limited to very small dimensions due to the technology employed. Moreover, the system and the method according to the present invention take colour-independent measurements based on luminous intensity, and are therefore effective also in the presence of patterns, etc. Furthermore, unlike solutions using a spectrophotometer, the system and the method of the present invention encounter no difficulty in checking the chromatic uniformity of "hairy" fabrics (e.g. wool, cashmere, etc.), since the type of illumination and image acquisition is not significantly affected by the angle of incidence of light on the object under examination.

[0025] According to an advantageous aspect of the present invention, the system and the method avoid the need for continual and frequent calibrations, since it will suffice to make a periodic verification (e.g. once every month) to ensure measurement repeatability over time (keeping an object as a reference standard).

[0026] It is understood that the appended claims are an integral part of the technical teachings provided in the following detailed description of the present invention. In particular, the appended dependent claims define some preferred embodiments of the present invention that include some optional technical features.

[0027] Further features and advantages of the present invention will become apparent in light of the following detailed description, provided herein merely as a non- limiting example and referring, in particular, to the annexed drawings as summarized below.

[0028] Brief description of the drawings

[0029] Figure 1 is a perspective view of a system for checking the chromatic uniformity of a plurality of portions of an object. The system is made in accordance with an exemplary embodiment of the present invention.

[0030] Figures 2 and 3 are front and lateral elevation views of the system shown in Figure 1. Figure 4 is a front elevation view similar to Figure 2, showing only an illuminating device of the system illustrated in the preceding figures. Unlike Figure 2, it shows the light sources that make up the illuminating device.

[0031] Figure 5 is a lateral elevation view similar to Figure 3, showing only an illuminating device of the system illustrated in the preceding figures. In particular, Figure 5 depicts a light source of the illuminating device and the optical radiation emitted by said light source.

[0032] Figure 6 is a sectional lateral elevation view, wherein the system shown in the preceding figures is illustrated in an exemplary and preferred application for the textile industry.

[0033] Figure 7 is a functional block diagram of the system shown in the preceding Figures.

[0034] Figure 8 is a schematic flow chart illustrating a series of steps of a method for checking the chromatic uniformity of a plurality of portions of an object. The method is implemented in accordance with an exemplary embodiment of the present invention, and can be used in a system shown in the preceding figures.

[0035] Figure 9 is a front perspective view of the system illustrated in Figure 6 for applications in the textile industry.

[0036] Figure 10 is a schematic view of a fabric whose chromatic uniformity is checked by means of the system shown in Figures 6 and 9.

[0037] For completeness' sake, the following is a list of alphanumerical references and names used herein to identify parts, elements and components illustrated in the above- summarized drawings.

[0038] A. Objectm. Portions of the object Predetermined positions Illumination axes

[0039] Y. Optical axis Z . Fixing axis W. Transversal axis di2. Illumination distance dis. Detection distance Illumination conditions Illumination wavelengths Monochromatic digital images Luminous intensity values cAh,Ak’ Combination of portions A Luminous intensity differences TAh,Ak- Chromatic comparison value S. Threshold value D. Uniformity data 10. System 12. Illuminating device Light sources 16. Image acquisition device 18. Support structure 20. Bracket body 22 . Frame 24 . Base plate 26. Lateral arms 28. Control unit

[0040] 100 . Casing

[0041] 102 . Window Detailed description of the invention

[0042] With reference to Figures 1 to 4, there is shown a system, designated as a whole as 10, made in accordance with an exemplary embodiment of the present invention.

[0043] System 10 is configured for checking the chromatic uniformity of a plurality of portions Ai, ..., Aj, ..., Amof an object A. As will become apparent in light of the detailed description that follows, system 10 is particularly suitable for use in the textile industry. For example, the system can be used for checking the chromatic uniformity of a fabric band. Nevertheless, the use of system 10 should not be intended to be limited to the textile industry. As will be apparent to a person skilled in the art, system 10 may find application in any manufacturing field. By way of non- limiting example, the system and the associated method are also applicable, in addition to the textile industry, to the food, clothing, printing, plastic, paper, wood, leather, packaging and cosmetic fields, and more generally to any field where colour checking is important.

[0044] In Figure 1, object A whose chromatic uniformity is to be checked, is shown in schematic form - e.g. as a structure shaped as a thin parallelepiped. Of course, the shape of object A shown in Figure 1 should not be intended to limit the objects whose chromatic uniformity can be checked using system 10 of the present invention.

[0045] With particular reference to Figures 1 to 4, system 10 comprises a multispectral illuminating device 12 configured for successively emitting, towards an object A whose chromatic uniformity needs to be checked, a light beam having a wavelength selectively chosen among a plurality of predetermined wavelengths Xi, ..., X±, ...Xn. More specifically, illuminating device 12 is configured for assuming a plurality of illumination conditions ...,C^,■■■>C^n. Under each illumination condition C^, illuminating device 12 emits, towards object A, a light beam having a respective illumination wavelength selected among the n predetermined illumination wavelengths Xi, X±, Xn, which are different from one another.

[0046] In the illustrated embodiment, illuminating device 12 comprises, in turn, a plurality of light sources 14-^, ,14,., ,14- / n. Each light source 14xfis configured for emitting an optical radiation towards object A to be checked, in order to illuminate it.

[0047] In the embodiment illustrated herein with particular reference to Figure 4, n light sources 14-^, ,14,., ,14- / nare a plurality of LEDs contained in illuminating device 12.

[0048] With particular reference to Figure 5, each light source 14x. has an illumination axis X^. that defines the main direction of propagation of the associated optical radiation towards object A. In particular, Figure 5 shows a beam emitted by an LED, which, in the illustrated embodiment, is a radiation emitted by a respective light source 14^. From Figure 5 it can be inferred that each light source 14^ has its illumination axis X^. converging towards optical axis Y. For example, illumination axes X^,...,Xi.,...,Xynof light sources may be convergent towards a common point (not shown) located along an optical axis Y of an image acquisition device 16, which will be described in more detail below.

[0049] Under each illumination condition each light source 14^ is configured to be selectively activated, unlike the other n-1 light sources so as to emit a respective optical radiation having a respective predetermined wavelength X±, different from n-1 wavelengths Xl, Xi-1, Xi+1,..., Xn of the optical radiations emitted by the other n-1 light sources •

[0050] As will be apparent to a person skilled in the art, the number n of light sources 14^, ,14^., ,14^ can be selected according to object A to be checked, and anyway can be adapted as necessary. Wavelengths can be selected within the whole luminous spectrum (even outside the visible spectrum, i.e. ultraviolet or infrared). By way of non-limiting example, n may be 8.

[0051] As mentioned above, in the illustrated embodiment light sources are LED devices.

[0052] System 10 further comprises, as aforementioned, a monochromatic image acquisition device 16 configured for acquiring a plurality of monochromatic digital images hi,Aj>■■■>hn,Am• Each monochromatic image hi.Aj is representative of a respective portion Aj of m portions Ai, ..., Aj, ..., Amof object A whose chromatic uniformity needs to be checked, when said portion Aj is illuminated by illuminating device 12 under a respective illumination condition inother words, there are m portions Ai, ..., Aj, ..., Amof object A, for which corresponding monochromatic digital images h1,A1>--->hi,Aj>■■■>hn,Amare acquired; for each portion Aj, n images are thus acquired, corresponding to respective illumination conditions .

[0053] Therefore, the total number of monochromatic digital images acquired is n x m.

[0054] In more detail, the image acquisition device 16 comprises an optical sensor - e.g. a CCD or CMOS sensor - configured to convert an optical image of each portion Aj of object A, when illuminated by illuminating device 12 under each illumination condition into a respective monochromatic digital image •

[0055] Preferably, image acquisition device 16 is a photo camera or a video camera.

[0056] Image acquisition device 16 has an optical axis Y indicating the direction in which a light beam, reflected by portion Aj of object A when illuminated by illuminating device 12, will enter the focal plane of the optical sensor included in said image acquisition device 16 substantially perpendicular thereto.

[0057] In the illustrated embodiment, each monochromatic digital image 1^-A- isabitmap image consisting of, in a per se known manner, a matrix of dots (or pixels), wherein each dot is represented according to a shade defined along a scale (or levels) or grey, variable from white to black. In particular, with each dot a value is associated which corresponds to the intensity exhibited by the shade within the grayscale. By way of non-limiting example, the acquired image may have a resolution of 2MP (1600x1200 pixels).

[0058] In the illustrated embodiment, illuminating device 12 is situated around optical axis Y defined by image acquisition device 16. In particular, the relative positioning of illuminating device 12 and of image acquisition device 16 is such that the light sources 14^^ ,14j., surround optical axis Y. More particularly, light sources are arranged circumferentially around optical axis Y, preferably angularly equidistant from one another.

[0059] With reference to Figure 6, there is shown, merely by way of non-limiting example, a preferred application of system 10 for the textile industry. In particular, in such an application system 10 is configured for checking the chromatic uniformity of a fabric that, in such a case, represents object A.

[0060] In the embodiment illustrated in Figure 6, system 10 is mounted inside a substantially box-shaped casing 100. Casing 100 has a window 102, through which the fabric, i.e. object A, faces towards system 10. Therefore, illuminating device 12 can illuminate the fabric through window 102, and image acquisition device 16 can acquire the monochromatic digital images h1,A1>---> >■■■>hn,Amthrough window 102.

[0061] In particular, when illuminating the fabric that, in Figure 6, represents object A, illumination distance di2 between illuminating device 12 and portions Ai, ..., Aj, ..., Amof object A remains substantially constant under the different illumination conditions C^,■■■>C^n. Also, when acquiring the images representative of the fabric, detection distance dis between image acquisition device 16 and portions Ai, ..., Aj, ..., Amof object A remains substantially constant during the acquisition of the different monochromatic digital images h1,A1>---> h^Aj>■■■>hn,Am•Inmore detail, in the exemplary embodiment of Figure 6 illumination distance di2 is considered along a straight line substantially perpendicular to the plane in which the LEDs lie, which preferably constitute light sources 14i, ..., 14n(in particular, said straight line being substantially parallel to the optical axis Y), while detection distance dis is considered along a straight line coinciding with optical axis Y.

[0062] In the illustrated embodiment, system 10 comprises a support structure 18 that supports the illuminating device 12 and image acquisition device 16, in particular in the above-defined relative positions.

[0063] In the illustrated embodiment, support structure 18 comprises a bracket body 20 configured to support image acquisition device 16. Furthermore, support structure 18 comprises a frame 22 connected to bracket body 20 and having illuminating device 12 situated on its surface intended to face towards object A whose chromatic uniformity has to be checked. In particular, light sources 14 are carried by bracket body 20. Frame 22 has, conveniently, an annular or circumferential shape, in particular having optical axis Y as its centre. Optionally, frame 22 is mounted to bracket body 20 at a fixing axis Z, visible in Figures 1 and 2. Fixing axis Z is substantially perpendicular to optical axis Y. In more detail, fixing axis Z is situated diametrically in relation to frame 22.

[0064] Advantageously, but not necessarily, bracket body 20 comprises a base plate 24, on which image acquisition device 16 is mounted. In addition, bracket body 20 comprises a pair of lateral arms 26 connected to frame 22, in particular on laterally or radially opposite sides of optical axis Y.

[0065] As can be noticed in Figure 6, system 10 is assembled by fixing bracket body 20 to the inner walls of casing 100.

[0066] With particular reference to Figure 7, there is shown a functional block diagram of the system illustrated in the preceding figures. In this functional block diagram, system 10 further comprises a control unit 28 coupled to illuminating device 12 and to image acquisition device 16.

[0067] In the illustrated embodiment, control unit 28 is configured to sequentially bring illuminating device 12 into each illumination condition • Thus, control unit 28 actuates illuminating device 12 to assume, in succession, all illumination conditions C^, C^n.

[0068] In the illustrated embodiment, control unit 28 is configured to selectively activate only one respective light source 14^ under each illumination condition in particular, as aforementioned, the remaining n-1 light sources 14X1,....14x.t, 14x.+i,....14Xnwill stay off. In this manner, illuminating device 12 can emit a light beam having the respective wavelength of light source 14^, selected among predetermined illumination wavelengths Xi, ..., X±, ...,

[0069] Control unit 28 is also configured to actuate image acquisition device 16 in order to acquire the plurality of monochromatic digital images representative of the m portions Ai, ..., Aj, ..., Amof object A under the n respective illumination conditions C^,...,CK'i,...,C^nassumed by illuminating device 12. As mentioned above, control unit 28 commands the acquisition of each monochromatic digital image - by image acquisition device 16, wherein said monochromatic digital image is representative of a corresponding portion Aj of object A under the respective illumination condition assumed by illuminating device 12. In other words, for each one of portions Aj of object A and under each illumination condition image acquisition device 16 is actuated to obtain a respective monochromatic digital image every time portion Aj of object A is illuminated by the light beam emitted by illuminating device 12 and having respective wavelength corresponding to illumination condition •

[0070] Control unit 28 is also configured to receive as input the plurality of monochromatic digital images <■■■<I^ Aj>■■■>hn,Amobtained by image acquisition device 16.

[0071] Furthermore, control unit 28 is configured for computing a plurality of luminous intensity values wherein each luminous intensity value VxI-'A- J is computed for a respective monochromatic digital image lx-A- and is representative of the luminous intensity reflected by portion Aj of object A towards image acquisition device 16 under respective illumination condition .

[0072] Merely by way of non-limiting example, each luminous intensity value V A- can be computed as a linear function of the numerical values associated with each one of the monochromatic pixels of the respective monochromatic digital image I^ Aj- In particular, a respective numerical value can be associated with each pixel - e.g. in the range of 0 to 255 (when an 8-bit channel is considered) - which identifies a specific shade of grey. In more detail, mathematical model M may advantageously compute each luminous intensity value Vx-A-as a weighted sum, e.g. the mean of the numerical values associated with the monochromatic pixels making up the respective monochromatic digital image h^Af In further detail, each luminous intensity value V A-may range between 0 and 255.

[0073] Subsequently, for each combinationcAh,Akcomprising a first portion Ah and a second portion AR, different from the first portion Ah, taken from the set of portions Ai, ..., Ah, ..., AR, ..., Amof object A, control unit 28 is configured for computing a chromatic comparison value TAh Akaccording to a mathematical model M, e.g. by means of a statistic regression - e.g. a linear regression.

[0074] In the exemplary embodiment described herein, according to mathematical model M, each chromatic comparison value TAh Akassociated with the respective combinationcAh,Akis determined as a function of a plurality of luminous intensity differences > ^V^ cAflAk^ cAh,Akcomprising:

[0075] In brief, for each combinationcAh,Aknluminous intensity differences arecomputed, wherein each luminous intensity difference is computed for the respective illumination condition C^, between:

[0076] - the luminous intensity value Vxi,Ahof the first portion Ah and

[0077] - the luminous intensity value Vxi,Akof the second portion Ak.

[0078] In the illustrated embodiment, control unit 28 is configured for comparing each chromatic comparison value TAh,Akobtained for each combination CAh,Akwith a respective predetermined threshold value S.

[0079] Lastly, control unit 28 is configured to output uniformity data D representative of the chromatic uniformity of object A, obtained as a function of chromatic comparison values TA Aof combinations cA A. According to a preferred example of the present invention, if for at least one of combinations cAfi Akthe respective chromatic comparison value TAh,Akis greater than predetermined threshold value S, then uniformity data D will indicate that the object should be considered as "NON-COMPLIANT" ("KO" in Figure 7). Vice versa, according to the same example, if for all combinations ^Ah,Akevery chromatic comparison value TAh,Akis lower than or equal to predetermined threshold value S, then uniformity data D will indicate that the object should be considered as "COMPLIANT" ("OK" in Figure 7).

[0080] With particular reference to Figure 8, there is shown a flow chart representing a method according to an exemplary embodiment of the present invention. The method is aimed at checking the chromatic uniformity of a plurality of portions Ai, ..., Aj, ..., Amof an object A, and, particularly but not exclusively, can be executed by the system shown in Figures 1 and 6. As will become apparent to a person skilled in the art, said method may also, in fact, be implemented by different systems.

[0081] The method comprises the following steps SI to S6.

[0082] In step SI, at least a portion Aj of object A is illuminated under a respective illumination condition by a light beam having selectively a respective illumination wavelength

[0083] In step S2, a respective monochromatic digital image I^Aj is acquired, which is representative of the respective portion Aj of object A illuminated under the respective illumination condition .

[0084] In step S3, steps SI and S2 are repeated for a plurality of predetermined illumination conditions C^nand for each portion Aj of object A whose chromatic uniformity needs to be checked. Under each illumination condition C^, the light beam illuminates object A with a respective illumination wavelength selected among a plurality of predetermined illumination wavelengths Xi, ..., X±, ..., Xn, different from one another.

[0085] In step S4, for each monochromatic digital image 1^-A-> I' J a respective luminous intensity value Vx-A-is computed, which is representative of the luminous intensity reflected by respective portion Aj of object A under the respective illumination condition .

[0086] In step S5, for each combination cAh Akcomprising a first portion Ah and a second portion AR, different from the first portion Ah, taken from the set of portions Ai, ..., Ah, ..., AR, ..., Amof object A, a chromatic comparison value TAfiiAkrepresentative of the chromatic uniformity of combinationcAh,Akis computed according to a mathematical model M as a function of at least one subset of m x n luminous intensity values • In particular, mathematical model M will compute each chromatic comparison value TAfi Akas a function of the 2 x n luminous intensity values computed for the first portion Ah and for second portion AR. Even more particularly, and as previously exemplified herein, according to mathematical model M, each chromatic comparison value TA Aassociated with the respective combination cA Ais determined as a function of a plurality of luminous intensity differences ^ ,cAfiAkr wherein each luminous intensity difference ^rAi,cAhAkis computed, for the respective illumination condition C^, between:

[0087] - the luminous intensity value Vxi,Ahof the first portion Ah and

[0088] - the luminous intensity value Vxi,Akof the second portion AR.

[0089] In step S6, uniformity data D representative of the chromatic uniformity of portions Ai, ...Aj, ..., Amof object A are outputted as a function of each one of chromatic comparison values TA A.

[0090] Preferably, in step S3 each luminous intensity value V^.A. is computed as a linear function of the numerical values associated with each one of the monochromatic pixels of the respective monochromatic digital image I±.

[0091] Preferably, in step S6 each chromatic comparison value TAh,Akis compared with a respective predetermined threshold value S.

[0092] Preferably, in step S5, uniformity data D indicate non- compliance (KO in Figure 7) of object A when, for at least one of combinations CAh,Akr the respective chromatic comparison value TAh,Akis above predetermined threshold value S.

[0093] Preferably, in step S5, uniformity data D indicate compliance (OK in Figure 7) of object A when, for all combinations cA A, each chromatic comparison value TA Ais smaller than or equal to the predetermined threshold value S.

[0094] For completeness' sake, the following will describe, with reference to Figures 6, 9 and 10, one example of a preferred application of the present invention, in particular for the textile industry.

[0095] Let us assume that the system and method are to be used on a plurality of portions Ai, ..., Aj, ..., Amof a fabric - which in this application represents the object - whose chromatic uniformity needs to be checked. As will be described in more detail below, in this example the number m of portions is 4.

[0096] In this illustrative application, a fabric is wound and tensioned around tensioning cylinders, and the system 10 faces towards a fabric band. In particular, system 10 is contained in casing 100 and faces towards the fabric band through window 102.

[0097] In this application, the number n of LEDs constituting light sources 14-^, ,14,., ,14- / nis, by way of example, assumed to be 8, as is the number n of wavelengths Xi, ..., X±, ...Xn.

[0098] System 10 further comprises a motor (not shown) configured to move illuminating device 12 and associated image acquisition device 16 (which are integrally connected, e.g. by means of support structure 18) in a direction W transversal to optical axis Y. Transversal direction W corresponds to the direction of the length of the fabric band, and the movement of devices 12, 16 corresponds to a translation thereof in said transversal direction W.

[0099] In the application example illustrated herein, there is a guiding structure 104 whereon system 10 is guidedly mounted. Guiding structure 104 is essentially a rail to which system 10 is slidably coupled in a per se known manner. In particular, the sliding coupling occurs between support structure 18 and the rail that constitutes the guiding structure 104. In the illustrated application example, guiding structure 104 is supported within casing 100; in particular, the ends of guiding structure 104 are secured to transversally opposite internal sides of casing 100.

[0100] In the illustrated application example, control unit 28 is further configured to control the motor to sequentially move the integral assembly including devices 12, 16 in transversal direction W and into a plurality of m predetermined positions PA1,...,PA.,...,PAm. In each predetermined position PA.fimage acquisition device 16 faces towards a different portion Aj of the fabric, i.e. of the object whose chromatic uniformity has to be checked.

[0101] In the illustrated application example, with particular reference to Figure 10, the number m of portions Ai, ..., Aj, ..., Amand of corresponding predetermined positions PA1,...,PA.,...,PAmis 4. In particular, the first position PA1corresponds to a left selvedge portion Ai, the second position PAzcorresponds to a left central portion A2, the third position PA3corresponds to a right central portion A3, and the fourth position PA4corresponds to a right selvedge portion A4.

[0102] In the illustrated application example, the above- described steps SI, S2 and S3 are repeated every time system 10 is moved by the motor into each predetermined position PA. as commanded by control unit 28. This results, for each predetermined position PA., in n monochromatic digital images being acquired, under illumination Qn, of fabric portion Aj that faces system 10 in each predetermined position PA..

[0103] In more detail, in the first position PA1a first plurality of monochromatic digital images h1,A1> are acquired at the left selvedge portion Ai under illumination conditions Q ,...,Q , respectively. In the second position PAz, a second plurality of monochromatic digital images 4q,A2’‘"’ are acquired at the left central portion A2 under illumination conditions respectively. In the third position PJ43, a plurality of monochromatic digital images are acquired at the right central portion A3 under illumination conditions ■■■<G.8, respectively. Lastly, in the fourth position PA4, a plurality of monochromatic digital images h4,A4>■■■>^8,A4are acquired at the right selvedge portion A4 under illumination conditions respectively.

[0104] In the illustrated application example, in step S4 32 respective luminous intensity values are computed for 32 monochromatic digital images previously acquired.

[0105] Let us now consider a combination cAfl,Akwith a first portion Ah and a second portion AR,wherein, for example, h = 2 and k = 3. For such a combination CA2IA3, which involves left central portion A2 and right central portion A3, a plurality of n = 8 luminous intensity differences are computed, wherein each one of them is determined by the formula In particular:

[0106] Subsequently, for combinationCA2,A3a respective chromatic comparison value is determined, which is computed as a function of the luminous intensity differences previously obtained with the above formulae.

[0107] The above-described steps are then repeated for all possible combinations CAh Akof portions Ai, ..., Ah, ..., AR, ..., Am, with h k, so as to obtain a plurality of corresponding chromatic comparison values TAh,Ak. In this case, for portions Ai, A2, A3, A4 there are 6 possible combinations, i-e. corresponding to 6 chromatic comparison values, i.e. TA A,TA A,TA^A^ TA2,A3’ TA2,A4> TA3IA4.

[0108] Lastly, each chromatic comparison value TAhAkthus computed is compared with a predetermined threshold value S.

[0109] If for at least one of combinations cAhAkthe respective chromatic comparison value TAh,Akis above threshold value S, then uniformity data D will be outputted which will indicate non-compliance (KO) of object A.

[0110] If, on the contrary, for all combinationscAh,Akeach chromatic comparison value TAhAkis smaller than or equal to predetermined threshold value S, then uniformity data D will indicate compliance (OK) of object A.

[0111] Of course, without prejudice to the principle of the invention, the forms of embodiment and the implementation details may be extensively varied from those described and illustrated herein merely by way of non-limiting example, without however departing from the protection scope of the invention as set out in the appended claims.

Claims

CLAIMS1. System (10) for checking the chromatic uniformity of a plurality of portions (Ai, Aj, Am) of an object (A); said system comprising:- an illuminating device (12),- an image acquisition device (16), and- a control unit (28) coupled to said image acquisition device (16) and said illuminating device (12); wherein said illuminating device (12) is a multi- spectrum one; wherein said image acquisition device (16) is a monochromatic one and is configured for acquiring a plurality of monochromatic digital images UA1,A1>--->>■■■>hn,Am')r wherein each monochromatic digital image ( / ^ A-') is representative of a respective portion (Aj) of said object (A) illuminated by said illuminating device (12); characterized in that said illuminating device (12) is configured for assuming a plurality of illumination conditions, wherein under each illumination conditionsaid illuminating device (12) emits, towards at least one of said portions (Ai, ..., Aj, ..., Am), a light beam having a respective illumination wavelength (X±) selected among a plurality of predetermined illumination wavelengths (Xi, ..., X±, ...Xn, different from one another; in that each monochromatic digital image Ux-A-') is associated with a respective illumination conditioninto which said illuminating device (12) is brought; and in that said control unit (28) is configured to execute the following steps:S4) for each monochromatic digital image UAI-'AJ-),computing a respective luminous intensity valuerepresentative ofthe luminous intensity reflected by the respective portion (Aj) of said object (A) towards said image acquisition device (16) under the respective illumination condition;55) for each combination (CA A) of a first portion (Ah) and a second portion (AR), different from said first portion (Ah), of said portions (Ai, Aj, Am) of said object (A), computing a respective chromatic comparison value CTAhAk) representative of the chromatic uniformity between said first portion (Ah) and said second portion (AR) according to a mathematical model (M) as a function of at least a part of said luminous intensity values56) outputting uniformity data (D) representative of the chromatic uniformity of said portions (Ai, ... Aj, ..., Am) of said object (A) as a function of said chromatic comparison values (TAh:Ak).

2. System according to claim 1, wherein said illuminating device (12) comprises a plurality of light sources3. System according to claim 2, wherein each light source (14x.) is an LED.

4. System according to claim 2 or 3, wherein each light source (14^) is configured to emit towards said object (A) an optical radiation having only a respective predetermined illumination wavelength (X±).

5. System according to claim 4, wherein each light source (14x.) has an illumination axis (X^J that defines the main direction of propagation of said optical radiation emitted towards said object (A).

6. System according to claim 5, wherein said optical axesof the light sources (14X1,....14x., 14Xn) are convergent towards a common point.

7. System according to any one of claims 2 to 6, wherein said light sources (14^, 14^., 14^) surround an optical axis (Y) defined by said image acquisition device (16).

8. System according to claim 7, wherein said light sources14x„) are angularly equidistant from one another.

9. System according to any one of the preceding claims, wherein said image acquisition device (16) comprises an optical sensor configured to convert an optical image of each portion (Aj) of said object (A) illuminated by said illuminating device (12) under each illumination condition (Qf) into the respective monochromatic digital image •10. System according to claim 9, wherein said image acquisition device (16) is a photo camera or a video camera.

11. System according to claim 9 or 10, wherein said image acquisition device (16) has an optical axis (Y) indicating the direction in which a light beam, reflected by each portion (Aj) of said object (A) when illuminated by the illuminating device (12), will enter the focal plane of said optical sensor substantially perpendicular thereto.

12. System according to any one of claims 9 to 11, wherein each monochromatic digital image ( / ^ A-) is a bitmap image.

13. System according to any one of the preceding claims, further comprising a support structure (18) that supports said illuminating device (12) and said image acquisition device (16).

14. System according to claim 13, wherein said support structure (18) comprises a bracket body (20) configured to support said image acquisition device (16).

15. System according to claim 14, wherein said support structure (18) comprises a frame (22) connected to saidbracket body (20) and supporting, on its surface facing towards said object (A), said illuminating device (12).

16. System according to claim 15, wherein said frame (22) has an annular or circumferential shape.

17. System according to any one of the preceding claims, wherein said control unit (28) is configured to sequentially bring said illuminating device (12) into each illumination condition (Qf).

18. System according to any one of the preceding claims, wherein said control unit (28) is configured to command the acquisition of each monochromatic digital image Ux-A-') by said image acquisition device (16) every time said illuminating device (12) assumes a respective illumination condition (G.J and illuminates a respective portion (Aj) of said object (A).

19. System according to any one of the preceding claims, further comprising a motor configured to integrally move said illuminating device (12) and said image acquisition device (16) in a transversal direction (W), guided by a guiding structure (104).

20. System according to claim 19, wherein said illuminating device (12) and said image acquisition device (16) are movable into a plurality of predetermined positions (PA1,...,PA.,...,PAm), wherein in each predetermined position (PAj) said image acquisition device (16) faces towards a respective portion (Aj) of said object (A).

21. Method for checking the chromatic uniformity of a plurality of portions (Ai, ..., Aj, ..., Am) of an object (A); wherein said method comprises the following steps:SI) illuminating at least one respective portion (Aj) of said object (A);52) acquiring a respective monochromatic digital image Utt-A-} representative of said respective portion (Aj) of said object (A); said method being characterized in that during said step SI said respective portion (Aj) of said object (A) is illuminatedby a light beam having selectively a respective illumination wavelength (X±); in that during said step S2 said respective monochromatic digital imageis representative of said respective portion (Aj) of said object (A) when illuminated under said respective illumination condition; and in that it further comprises the following steps:53) repeating steps SI and S2 for a plurality of predetermined illumination conditionsand for each portion (Aj) of said object (A) whose chromatic uniformity has to be compared, wherein under each illumination condition (G.;) the light beam illuminates at least the respective portion (Aj) of said object (A) with a respective illumination wavelength (X±) selected among a plurality of predetermined illumination wavelengths (Xi,Xi, Xn), different from one another;54) for each monochromatic digital image UA I-'AJ-), computing a respective luminous intensity value > representativeof the luminous intensity reflected by the respective portion (Aj) of said object (A) under the respective illumination condition (Qf);55) for each combination (CA^A^ comprising a first portion (Ah) and a second portion (AR), different from said first portion (Ah), of said portions (Ai, Aj, ..., Am) of said object (A), computing a respective chromatic comparisonvalue (TAh Ak) representative of the chromatic uniformity between said first portion (Ah) and said second portion (AR) according to a mathematical model (M) as a function of at least a part of said luminous intensity valuesS6) outputting uniformity data (D) representative of the chromatic uniformity of said portions (Ai, ... Aj, ..., Am) of said object (A) as a function of said chromatic comparison values (TAh Ak).

22. Method according to claim 22, wherein, in said step S3, each luminous intensity value (V^.A.) is computed as a linear function of the numerical values associated with each one of the monochromatic pixels of the respective monochromatic digital image (1^.4.).

23. Method according to claim 21 or 22, wherein, in said step S5, according to said mathematical model (M), each chromatic comparison value (TAhiAk) is determined as a function of a plurality of luminous intensity differencesWherein each luminous intensity differencecAhAk) is computed, for the respective illumination condition, between:- the luminous intensity value (V^A / J of said first portion (Ah) and- the luminous intensity valueof said second portion (AR).

24. Method according to claim 23, wherein, in said step S6, each chromatic comparison values compared with a predetermined threshold value (S).

25. Method according to claim 24, wherein, in said step S6, said uniformity data (D) indicate non-compliance (KO) ofsaid object (A) when, for at least one of said combinations (£4,4 ), the respective chromatic comparison value (TA A) is above said predetermined threshold value (S).

26. Method according to claim 24 or 25, wherein, in said step S6, said uniformity data (D) indicate compliance (OK) of said object (A) when, for all combinations (cAh Ak), each chromatic comparison value (TAh Ak) is smaller than or equal to the predetermined threshold value (S).

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