Patent Application
20230294325
The present invention relates to an image identification method and system for printing on rigid substrates.
In particular, the present invention relates to an image identification method and system for printing on rigid substrates, in particular ceramic or vitreous ones, and more in particular ceramic tiles or slabs.
More particularly, the present invention relates to an image identification method and system for printing on rigid substrates, the latter being adapted to receive a print executed on the basis of a digital graphic design.
In the ceramic production process, the raw materials normally used for forming tiles are ceramic powders or granules, normally called atomised materials. The production process normally entails spreading the atomised material on a belt or filling a mould with the atomised material, which first undergoes compacting by means of a press and is subsequently fired in a high-temperature kiln in order to sinter the tile and turn it into a genuine ceramic product. Over the years, the technology of ceramic tile production processes has undergone a major evolution whereby the dimensions of the classic ceramic tile have become increasingly larger, also due to market demands.
The increase in the size of ceramic tiles has led the product resulting from the new production processes to be identified with the term ceramic slab, precisely in view of the larger dimensions produced, which can reach 1800 mm in width and up to 4800 mm in length, with thicknesses of up to 30 mm. The term ceramic slab is to be understood as equivalent to ceramic tile or ceramic substrate.
The production of ceramic tiles or slabs of such considerable size has enabled the development of new printing technologies which extend beyond the surface to the inside, through the whole thickness of the slab, in order to better reproduce the characteristic veining of natural stones such as marble or granite. One example of these printing devices is described in publication WO2020026136 A1 of the same applicant.
This decoration system allows a mass decoration to be obtained before the pressing step, using coloured raw or atomised materials.
In practical terms, in addition to being able to obtain a surface decoration of the slab through wet digital printing technologies, such as inkjet, normally applied after the pressing step, today it is possible to create mass decorations before the pressing step using coloured ceramic powders or granules.
One problem that has been encountered using the two digital decoration or printing technologies, wet inkjet printing applied after pressing and dry mass decoration applied before pressing, is the non-correspondence or non-perfect superimposition of the decorations produced by each printing process before and after pressing.
The defect encountered is, for example, a non-continuity between the veins of the surface image printed by the digital printer and the veins produced within the mass.
In practical terms, the ceramic tile or slab produced does not correspond to the desired digital graphic design or rather, starting from a digital graphic file representative of the ceramic slab to be reproduced, there is not correspondence with the real image of the slab obtained at the end of the production process, i.e. after firing of the ceramic substrate.
It has been observed that during the pressing step a deformation of the mass decoration occurs, which causes the aforesaid non-correspondence between the digital graphic design and the real image.
Also in printing on raw structured substrates (rigid substrates), the pressing step generates deformations in the substrates such that the structure output by the pressing step, i.e. the structure of the compacted layer, no longer coincides with that determined by the die in the pressing step, where structure means the two-/three-dimensional shape of the compacted layer.
In this case as well, the digital image to be printed by means of an inkjet printer on the rigid substrate after the pressing step will no longer coincide with the structure of the compacted layer.
As the structure has slightly changed, there arises the problem of making the image/structure after pressing coincide with that of the initial digital graphic design, in order to obtain a correct subsequent printing phase.
The object of the present invention is to identify a correct image for printing after the pressing step on the basis of the initial graphic design, that is, to identify a print image that takes into account the deformation occurring in the pressing step.
In a first aspect, the present invention describes an image identification method for printing on rigid substrates comprising the steps of:
The identification method preferably comprises a step of processing said digital graphic design and said real image so as to render them comparable, wherein said processing step precedes said step of comparing said keypoints of the real image.
Said processing step preferably comprises a step of identifying, from said acquired real image in said acquisition step, one or more between:
Said structure of said compacted layer is preferably a structure with graphics or without graphics.
Said step of spreading a soft layer of granular or powder ceramic material on a support surface preferably provides for a decoration throughout the whole thickness of the soft layer.
Preferably, said processing step comprises a step of:
Said filtering step preferably comprises applying convolution filters and/or gradients, and/or blurring and/or colour adjustments and/or graphic adjustments.
Said detecting step preferably comprises detecting keypoints of said synthetic image of the real image.
Preferably, it is also envisaged to detect keypoints of said synthetic image of the graphic design.
Said comparing step preferably comprises comparing every keypoint of said synthetic image of the real image with all of said keypoints of said synthetic image of the graphic design.
Said comparing step preferably comprises comparing descriptors of every keypoint of the two synthetic images, wherein said descriptors comprise spatial information and neighbourhood information, thereby defining matching keypoints.
Preferably, there is provided a step of defining a transformation function between said real image and said digital graphic design as a function of the relation between said matching points.
Preferably, there is provided a step of applying said transformation function to any portion of the acquired real image, thereby obtaining said portion of said digital graphic design.
Said portion of said digital graphic design preferably represents at least one portion of said rigid substrate
Said step of acquiring a real image of the compacted layer after the pressing step is preferably carried out at the end of said pressing step.
Said step of acquiring a real image of the compacted layer after the pressing step is preferably carried out at the end of a cutting step.
In a second aspect, the present invention describes an image identification system for printing on rigid substrates comprising:
In a third aspect the invention describes a method of printing on rigid substrates comprising the steps of:
Preferably, in said printing step, said processed image portions to be printed are coordinated and aligned with one or more between
In a fourth aspect, the invention describes a system for printing on rigid substrates comprising:
Preferably, said processed portions to be printed are coordinated and aligned with one or more between
The invention achieves the following further technical effects:
The aforesaid technical effects/advantages and other technical effects/advantages of the invention will emerge in greater detail from the description, set forth here below, of an example embodiment given by way of illustration and not by way of limitation with reference to the appended drawings.
The invention describes an image identification method for printing on rigid substrates.
On the basis of a digital graphic design representative of a rigid substrate to be produced, the invention comprises producing a mass decoration that is pressed to obtain a compacted layer and of which a real image is subsequently acquired; a comparison between keypoints of the real image and of the image of the digital graphic design enables the identification of a portion of the digital graphic design corresponding to a portion of the acquired image.
With reference to the figures and in particular to
In the course of the description, rigid substrates will mean in particular ceramic or vitreous substrates, more particularly ceramic tiles or slabs.
The production process comprises an initial step of preparing the rigid substrate.
Specifically, with particular reference to
With particular reference to
The soft layer SL can have one or more areas of different colour. The spreading of the soft layer determines the graphics of the rigid substrate.
The rigid substrate, as understood in the course of the description that follows, comprises the compacted layer CL obtained as a result of a pressing step.
The graphics of the rigid substrate is the previously mentioned mass decoration.
In one embodiment of the invention, the spreading of the soft layer SL of granular or powder ceramic material on the deposition surface P provides for a decoration throughout the whole thickness of the soft layer SL.
With particular reference to
The soft layer SL is intended for a subsequent pressing step b) for obtaining a compacted layer CL, which is subjected to further cutting, decoration and firing steps.
The invention comprises a step b) of pressing the soft layer SL to obtain a compacted layer CL, comprised in the rigid substrate.
In a possible embodiment, the deposition surface P is a mobile surface which, in addition to allowing spreading, is also adapted to convey the soft layer SL to a pressing device 80.
Therefore, a pressing device 80 is adapted to carry out said pressing step b).
For example, the pressing device 80 is in the form of a belt press, known in the art for pressing large-sized slabs.
With particular reference to
At least one of the two dies is movable towards and away from the other in order to carry out pressing of the soft layer SL.
The press further comprises a mobile surface 83, in the form of a flexible belt, which has an active portion 84 disposed at least partially between the upper die 82 and the lower die 81.
The press also comprises a second mobile surface 85, in the form of a flexible belt, which has an active portion 86 disposed between the active portion 84 of the first mobile belt 83 and the upper die 82.
In a preferred but not exclusive embodiment, the soft layer SL is transferred from the deposition surface P to the mobile surface 83 of the press according to the solution described in publication WO2017051275 of the same applicant.
According to that solution, the deposition surface P, in the portion on which the soft layer SL is deposited, is substantially aligned and contiguous, at a greater height, with the active or outgoing portion 84 of the mobile surface 83, along a longitudinal forward travel direction Y, with a front end 51 of the deposition surface P at least partially above a rear end 83a of the mobile surface 83.
In an alternative solution, the deposition surface P extends between the dies 81,82, i.e. the mobile surface 83 is not present and pressing of the soft layer SL takes place directly on the deposition surface P.
Preferably, with particular reference to
The machine for mass decoration 1 is adapted to precisely control the pattern of the mass decoration V, which is created during spreading of the soft layer SL.
During pressing, the pressing device 80 can determine surface hollows and reliefs. If present, this result will be called surface structure ST, as shown in
Preferably, the rigid substrate, which comprises the compacted layer CL, can have a mass decoration and/or a surface structure ST.
Preferably, other processes can be applied to the rigid substrate, such as the application of coloured powders, coloured liquids, chiseling, engraving, 3D printing or other processes.
The digital graphic design P_G_DGT contains or is representative of all the characteristics of the rigid substrate before pressing, i.e. related to the mass decoration V, after pressing, i.e. related to the compacted layer CL with or without the surface structure ST, and after the decoration step, in particular the digital printing.
In practical terms, the digital graphic design P_G_DGT is representative of one or more of these characteristics: mass decoration V and/or surface structure ST, and digital printing.
If present, these processes will generate other product characteristics.
According to the invention, the mass decoration, the structure and the other characteristics mentioned are defined by the digital graphic design P_G_DGT, which makes them deterministic and repeatable.
Consequently, one or both of steps a) and b) are carried out on the basis of the predefined digital graphic design P_G_DGT.
As already noted, during the spreading step a) and the pressing step b), the rigid substrate undergoes mechanical deformations, not predictable beforehand, which determine a deformation of the compacted layer CL and determine a non-exact correspondence with the starting digital graphic design P_G_DGT.
In other words, the real image output from the pressing step, hereinafter indicated as IREAL, is an image that is deformed compared to the image of the starting design.
According to the invention, the deformation is calculated by comparing the real image of the rigid substrate in transit with an image representative of the starting digital graphic design.
The deformation is calculated on the basis of a perspective transformation matrix that transforms the space of the real image of the rigid substrate in transit into the space of the image of the starting digital graphic design P_G_DGT.
It will likewise be possible, by applying the inverse transformation matrix to an image of the digital graphic design, to derive a deformed image that corresponds to the rigid substrate in transit, that is, to the real image IREAL.
With reference to
The result of the aforesaid step c), in a particular example embodiment, is shown in
An acquisition system 130 is adapted to acquire the real image IREAL of the compacted layer CL after the pressing step.
The acquisition system 130 preferably comprises one or more optical detectors of a type known in the art, in particular a camera.
Preferably, one or more optical detectors 130 are positioned downstream of the pressing device 80 and upstream of a decorator device 90, in particular an inkjet printer (
Each optical detector 130 is connected to a first processing unit 40, described below, in order to transmit the acquired real image IREAL to the latter.
According to the invention, in general, the acquisition can be carried out in an interval of time falling between after the pressing step b) and before the decoration step, in particular a digital printing step.
In one embodiment, the acquisition takes place at the end of the pressing step b).
The technical effect achieved is the detection of the deformation occurring in the rigid substrate in transit, compared to the predefined digital graphic design.
In another embodiment, the acquisition takes place at the end of a cutting step, i.e. in a trimming step after the pressing step b) and before the digital printing step.
The technical effect achieved is the detection of the deformation occurring in the rigid substrate in transit, compared to the predefined digital graphic design.
In a further embodiment, the acquisition takes place both at the end of the pressing step b) and after the cutting step.
The technical effect achieved by the latter embodiment is an even greater efficiency of the entire digital printing process.
With the aim of comparing the real image output from the pressing step with the image of the starting digital graphic design, the invention comprises image processing and comparison steps.
A first processing unit 40 is provided for this purpose with reference to
In the course of the present description and in the subsequent claims, the first electronic processing unit 40 is logically divided into distinct functional modules (memory modules or operating modules) that perform the functions described.
The first electronic processing unit 40 can consist of a single electronic device, suitably programmed to perform the described functions, and the different modules can correspond to hardware entities and/or routine software that form part of the programmed device.
Alternatively, or in addition, said functions can be performed by a plurality of electronic devices over which the aforesaid functional modules can be distributed.
Moreover, the first electronic processing unit 40 can rely on one or more processors to execute the instructions contained in the memory modules; the aforesaid functional modules can also be distributed over different local or remote computers based on the architecture of the network they reside in.
According to the invention, there is provided a step e0) of processing the digital graphic design P_G_DGT and the real image IREAL in such a way as to render them comparable, that is, compatible for a comparison.
With particular reference to
In particular, step e0 comprises a sub-step of identifying, from the real image IREAL acquired in the acquisition step c), one or more between:
The first processing unit 40 is configured to carry out the described identification sub-step; in particular, the first processing unit 40 comprises a first processing module 401 configured to carry out the described identification sub-step.
Step e0, according to the invention, further comprises a sub-step g) of filtering one or more between:
According to the invention, the filtering is performed in such a way as to render the predefined digital graphic design P_G_DGT and the acquired real image IREAL comparable.
Preferably, the filtering sub-step g) comprises applying convolution filters and/or gradients, and/or blurring and/or colour adjustments and/or graphic adjustments.
The first processing unit 40 is configured to carry out the described filtering sub-step; in particular, the first processing unit 40 comprises a filter module 402 configured to carry out the described filtering sub-step.
According to the invention, there is provided a further step d) of detecting keypoints KPi_REAL of the real image IREAL.
In particular, according to the invention, step d) comprises detecting keypoints KPi_REAL of the synthetic image SINT_I of the real image.
In particular, according to the invention, step d) comprises detecting keypoints KPi_pred of the synthetic image SINT_P of the graphic design.
The first processing unit 40 is configured to carry out the described detecting step d); in particular, the first processing unit 40 comprises a detection module 403 configured to carry out the described detecting step d).
The invention comprises a step e) of comparing the keypoints KPi_REAL of the real image IREAL with keypoints KPi_pred of an image I_G_DGT obtained/derived from the predefined digital graphic design P_G_DGT.
A reference to “keypoints” in the literature can be found in the expired U.S. Pat. No. 6,711,293, entitled “Method and apparatus for identifying scale invariant features in an image and use of same for locating an object in an image”.
It is understood that the keypoints are independent of visual characteristics of the image and are rather dependent on the position of an “object” in that image.
In other words, with particular reference to ceramic substrates, the keypoints are not extracted from predefined graphic characteristics visible on the ceramic substrate, such as specific streaks and/or variegations and/or veins, but rather represent characteristic points detectable within the whole image, and thus not only in specific predefined areas. In other words, as will be described below, every keypoint is endowed with a descriptor Car_Kp that comprises spatial information I_Spa and neighbourhood information I_int.
The spatial information I_Spa comprises a position coordinate of the keypoint, whereas its value, i.e. the neighbourhood information I_int, is derived through an analysis of tone and/or brightness and/or colour present in the neighbourhood I_int thereof.
The digital graphic design P_G_DGT and the image I_G_DGT, in a particular example embodiment of the present invention, are shown respectively in
A comparison between the keypoints KPi_REAL of the real image IREAL and the keypoints KPi_pred of an image I_G_DGT in the particular example embodiment is shown in
The first processing unit 40 is configured to carry out the described comparison step e); in particular, the first processing unit 40 comprises a comparison module 404 configured to carry out the described comparison step e).
According to the invention, step e) envisages comparing every keypoint KPi_REAL of the synthetic image SINT_I of the real image with all the keypoints KPi_pred of the synthetic image SINT_P of the graphic design.
Every keypoint is endowed with a descriptor Car_Kp that comprises spatial information I_Spa and neighbourhood information I_int.
The spatial information I_Spa comprises a position coordinate of the keypoint, whereas the neighbourhood information I_int comprises a value representative of tone and/or brightness and/or colour of the keypoint.
The comparison step e) provides for a comparison between the descriptors Car_Kp of every keypoint of the synthetic image SINT_I of the real image and all the descriptors Car_Kp of the synthetic image SINT_P of the graphic design
The technical effect is a definition of matching keypoints KP_O between the synthetic images, i.e. keypoints between the synthetic images in a homographic relationship.
In general, homography, in the logics-mathematical literature, is a relationship between points of two spaces, in this specific case the two aforesaid synthetic images, so that every point of one space corresponds to one and only one point of the second space.
In particular, a homographic transformation (or transformation function) applied to the points of the synthetic image SINT_I makes it possible to obtain the transformed synthetic image SINT_P and vice-versa.
After the matching keypoints KP_O have been defined, the invention comprises a step h (
The first processing unit 40 is configured to carry out the described step h); in particular, the first processing unit 40 comprises a definition module 405 configured to carry out the described step h).
The invention comprises, at this point, a step f) of calculating a portion I_P_G_DGT of the digital graphic design P_G_DGT corresponding to a portion P_I_REAL of the acquired real image IREAL.
In particular,
In particular,
In order to obtain the portion I_P_G_DGT of the digital graphic design P_G_DGT, i.e. to calculate a portion I_P_G_DGT of the digital graphic design P_G_DGT corresponding to a portion P_IREAL of the acquired real image (IREAL) (step f), the invention envisages applying the transformation function F to any portion P_IREAL of the acquired real image IREAL.
In one embodiment, the portion P_IREAL can be the tile perimeter, thus the portion is a complete tile.
In an alternative embodiment, the portion P_IREAL is a subset, for example defined by 3 non-aligned keypoints (as in the example in
The first processing unit 40 is configured to carry out the described calculation step f); in particular, the first processing unit 40 comprises a calculation module 406 configured to carry out the described calculation step f.
The portion I_P_G_DGT of the digital graphic design P_G_DGT represents at least one portion of the rigid substrate.
In other words, the portion defines the whole rigid substrate or a subset thereof.
In another aspect, the invention comprises a method of printing on rigid substrates, with particular reference to the block diagram in
The printing method is implemented by a printing system, as schematically shown in
In the course of the present description and in the subsequent claims, the second electronic processing unit 60 is logically divided into distinct functional modules (memory modules or operating modules) that perform the functions described.
The second electronic processing unit 60 can consist of a single electronic device, suitably programmed to perform the described functions, and the different modules can correspond to hardware entities and/or routine software that form part of the programmed device.
Alternatively, or in addition, said functions can be performed by a plurality of electronic devices over which the aforesaid functional modules can be distributed.
Moreover, the second electronic processing unit 60 can rely on one or more processors to execute the instructions contained in the memory modules; the aforesaid functional modules can also be distributed over different local or remote computers based on the architecture of the network they reside in.
The method, according to the invention, comprises (i) receiving a file of an image to be printed I_PRINT corresponding at least to a subset of a digital graphic design P_G_DGT.
The received image to be printed I_PRINT, in a particular example embodiment of the present invention, is shown in
Subset means, for example, a particular channel (or layer) of one of the channels (or layers) making up the digital graphic design P_G_DGT.
With particular reference to
In particular, the processing unit 60 comprises a receiving module 601 (
The invention further comprises a step of receiving (ii) a rigid substrate, comprising the compacted layer CL, to be printed on.
The step of receiving (ii) by the decorator device 90, in particular a printing unit, is carried out by suitable conveyance means 70, for example a mobile surface.
The invention further comprises a step (iii) of detecting on the rigid substrate a portion I_P_G_DGT of the digital graphic design P_G_DGT corresponding to a portion P_IREAL of a real image IREAL.
This detecting step (iii) is carried out according to what was previously described in steps c-f of the first aspect of the invention.
Steps c-f, in a particular example embodiment of the present invention, are shown in
The first processing unit 40 (
According to the invention, the image contained in the portion I_P_G_DGT represents a portion of an image to be printed I_P_PRINT from the file of the image to be printed I_PRINT.
The image contained in the portion I_P_G_DGT in a particular example embodiment of the present invention is shown in
The invention further comprises a step (iv) of detecting a corresponding position POS P_IREAL of the portion P_IREAL of the real image IREAL to be printed with respect to the rigid substrate.
A detection system 180 is adapted to carry out step (iv).
In particular, the system is described in the published patent application WO2017/149508 of the same applicant.
The result of this step, in a particular example embodiment of the present invention, is shown in
The invention further comprises a step of processing (v) the image portion to be printed I_P_PRINT so as to be adapted to the portion P_IREAL of the real image IREAL, as a function at least of the detected position POS P_IREAL, thereby determining a corresponding processed image portion to be printed I_P_PRINT_ELAB.
In a particular example embodiment of the present invention, shown in
With particular reference to
In particular, the processing unit 60 comprises a processing module 602 (
Essentially, the second processing unit 60 modifies the image portion to be printed I_P_print on the basis of the deformation occurring in the mass decoration V during the pressing step, defined by the transformation function F, and of the detected position POS P_IREAL.
The invention envisages repeating steps (iii), (iv) and (v) for all the portions P_IREAL forming the real image IREAL.
In other words, the first processing unit 40 is configured to repeat step (iii), the detection system 180 is configured to repeat step (iv) and the second processing unit 60 is configured to repeat step (v) for all the portions P_IREAL forming the real image IREAL.
The invention comprises, as the final step, printing (vi) on the rigid substrate comprising the compacted layer (CL) all the processed image portions to be printed I_P_PRINT_ELAB.
A decorator device 90, in particular an inkjet printer, is adapted to print on the rigid substrate all the processed image portions I_P_PRINT_ELAB.
According to the invention, the processed image portions to be printed I_P_PRINT_ELAB are coordinated and aligned with a structure ST of the compacted layer CL generated in the pressing step b), as previously described.
Alternatively, or in addition, the processed image portions to be printed I_P_PRINT_ELAB are coordinated and aligned with a mass decoration V generated in step a) of spreading the soft layer SL, as previously described.
In a particular case, the term coordinated means superimposable or not offset.
In another particular case, the term coordinated means correlated.
An invention that comprises an identification of images for printing on rigid substrates and a corresponding printing method/system has been described.
The invention achieves the following additional technical effects:
| Number | Date | Country | Kind |
|---|---|---|---|
| 102020000018793 | Jul 2020 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2021/056898 | 7/29/2021 | WO |
