FR3090865A1 - Colorimetric and spectrometric control process on a physical support provided with a test pattern - Google Patents

Abstract

The present invention relates to a method for controlling the printing of a physical information medium, the method comprising a step of: - providing a medium information physical provided with a test pattern printed on the support, the test pattern comprising a set of dots each having a predefined color and spatially arranged according to a predefined arrangement, the physical information support being chosen in particular from the group consisting of a sheet, cardboard, plastic support and textile support, - simultaneous measurement of the reflectance of each target of the target using a single device, to obtain measured reflectances, and - extraction at least one piece of information using a comparison between the measured reflectance and the reflectance corresponding to the predefined color, the comparison being implemented for each point. Figure for abstract: None

Description

Description

Title of the invention: Method of colorimetric and spectrometric control on a physical support provided with a target

The present invention relates to a method for obtaining information. The present invention also relates to a computer program product, a readable information medium and an associated obtaining system.

In order to guarantee the quality of color printing, it is recommended to print a set of reference colors used to reconstruct a color image at the edge of the printing medium and to measure these reference colors. . The reference colors are those of the inks used in the printing machine, namely cyan, magenta, yellow and black (denoted respectively C, M, J, N) in the case of a four-color printing, possibly supplemented by specific inks, hereinafter called spot colors, defined as required.

The usual control means on a printing line include, for example, a camera or a set of trichromatic or multispectral cameras located statically on or outside the printing machine. The control means take a photo of a set of reference color patches located online on a sheet margin and compare the measured information with a photo taken on a reference standard, for example a proof print validated by a customer.

However, such a method is tedious to implement and generates unwanted errors.

There is a need for a more reliable method of controlling printing on a physical medium.

For this, the present description relates to a method of controlling the printing of a physical information medium, the method comprising a step of providing a physical information medium provided with a test pattern printed on the support, the test pattern comprising a set of dots each having a predefined color and spatially arranged according to a predefined arrangement, the physical information support being chosen in particular from the group consisting of a sheet, a cardboard, a support plastic and a textile support, a step of simultaneous measurement of the reflectance of each target of the target using a single device, to obtain measured reflectances, and a step of extraction of at least one piece of information using a comparison between the measured reflectance and the reflectance corresponding to the predefined color, the comparison being implemented for each point, the information being in particular chosen from the group consisting of at least one information is information selected from the group consisting of compliance information, information for adjusting the parameters of a printing machine, information relating to test pattern printing and a profile of printing of a printing machine.

According to particular embodiments, the determination method comprises one or more of the following characteristics, taken in isolation or in any technically possible combination:

- during the supply step, the physical information medium is also provided with a code printed on the medium, the code coding the predefined arrangement and all of the predefined colors, the code being, for example, a barcode, microchip or digital watermarking, the method further comprising a step of:

- reading the code, and

- decryption of the code to obtain the predefined arrangement and all of the predefined colors.

- the target and the code are combined.

- The method includes a step of determining the position of the target using the detection of markers printed on the physical information medium or using a feature extraction technique.

- the method includes a step of restoring at least one piece of information extracted in the form of a document to be displayed and interpretable by a human eye, in particular a document in PDF, CxF, JSON, TXT, PNG, JPG or XML format.

- the test pattern checks at least one of the following properties:

- the predefined arrangement is a checkerboard,

- the predefined arrangement is chosen so that the points form a logo,

- the predefined colors are at least 20 in number,

The predefined colors include the colors cyan, magenta, yellow and black,

- the predefined colors include several colors corresponding to the same printing color at a plurality of different inking rates, each inking rate being non-zero,

- the predefined colors include four colors corresponding to the same printing color at a respective inking rate, each inking rate being non-zero,

The predefined colors include the colors red, green and blue, and

- the predefined arrangement includes an unprinted patch.

The present description also relates to a computer program product comprising a readable information medium, on which is stored a computer program comprising program instructions, the computer program being loadable on a processing unit. and adapted to cause the implementation of at least the extraction step of a method as previously described when the computer program is implemented on the data processing unit.

The present description also relates to a readable medium of information storing a computer program comprising program instructions, the computer program being loadable on a data processing unit and suitable for driving the implementation. at least the step of extracting a method as previously described when the computer program is implemented on the data processing unit.

The present description also relates to a control system for a sup, the obtaining system comprising a single device capable of simultaneously measuring the reflectance of each point of a test pattern printed on a physical information medium, the test pattern comprising a set of points each having a predefined color and spatially arranged according to a predefined arrangement, and a computer adapted to extract at least one item of information using a comparison between the measured reflectance and the reflectance corresponding to the predefined color , the comparison being implemented for each point.

An example of a method for obtaining at least one item of information is now described.

The obtaining process aims to obtain at least one piece of information from a physical medium.

The method includes a step of providing physical support.

The physical medium is a physical medium of information.

The physical information medium is a sheet, a cardboard, a plastic support, and a textile support.

The physical support is provided with a target.

The test pattern printed on the support.

The test pattern includes a set of points each having a predefined color and spatially arranged according to a predefined arrangement.

Many targets can be envisaged.

In the following, several properties are described by way of example, knowing that when this is technically possible, these properties can be combined.

According to a first example of property, the predefined arrangement is a checkerboard.

According to a second example of property, the predefined arrangement is chosen so that the points form a logo.

According to a third example of property, the predefined colors are at least 20 in number.

According to a fourth example of property, the predefined colors include the colors cyan, magenta, yellow and black.

According to a fifth example of property, the predefined colors include several colors corresponding to the same print color at a plurality of different inking rates, each inking rate being non-zero.

According to a sixth example of property, the predefined colors include four colors corresponding to the same printing color at a respective inking rate, each inking rate being non-zero.

According to a seventh example of property, the predefined colors include the colors red, green and blue.

According to an eighth example of property, the predefined arrangement includes an unprinted patch. Otherwise formulated, the predefined layout includes an unprinted space.

The method also includes a step of simultaneously measuring the reflectance of each point of the pattern.

The step of simultaneous measurement of the reflectance is implemented using a single device.

Such a measurement step makes it possible to obtain measured reflectances.

The method also includes a step of extracting at least one item of information.

The extraction step is implemented using a comparison between the measured reflectance and the reflectance corresponding to the predefined color.

The comparison is implemented for each point.

The control method thus makes it possible to collect all the information necessary for checking the conformity of a print or for establishing the colorimetric profile of a printing machine according to a rapid, simplified approach which does not involve redefine the operation of the printing machine.

Colorimetric and spectrometric control provides two elements of response to the needs of a printer. In a first use case it allows to establish a conformity report of the print quality. In a second use case it makes it possible to define the colorimetric profile of the printing machine for a given printing medium.

Otherwise formulated, the method makes it possible to facilitate the measurement of conformity of a print both for the operator of the printing machine and for the customer.

The method also makes it possible to facilitate the transmission of a compliance report between the supplier and his customer.

The method finally makes it possible to facilitate the establishment of the colorimetric profile of a printing machine for a given batch of inks and a printing medium.

Optionally, the physical information medium is also provided with a code printed on the medium.

The code codes the predefined arrangement and all of the predefined colors,

The code is, for example, a barcode, an electronic chip or a digital tattoo,

According to one embodiment, the code and the test pattern are combined.

In such a case, the method includes reading the code and deciphering the code to obtain the predefined arrangement and all of the predefined colors.

According to one embodiment, the method comprises a step of determining the position of the target using the detection of markers printed on the physical information medium or using a technique of feature extraction.

According to another embodiment, the method comprises a step of restoring the at least one piece of information extracted in the form of a document to be displayed and interpretable by a human eye, in particular a document in PDF, CxF, JSON format , TXT, PNG, JPG or XML.

The Portable Document Format, commonly abbreviated as PDF, is a page description language presented by the company Adobe Systems in 1992 and which became an ISO standard in 2008.

CXF or Apache CXF is an open-source framework in Java language, facilitating the development of web services. It results from the crossover of two open source projects: Celtix developed by IONA Technologies (acquired by Progress Software in 2008) and XFire developed by a team hosted by Codehaus. These two projects were combined by people working together at the Apache Software Foundation. The name CXF is derived from the names of the Celtix and XFire projects.

JavaScript Object Notation (JSON) is a textual data format derived from the notation of objects in the JavaScript language. It allows to represent structured information as XML allows for example. Created by Douglas Crockford between 2002 and 2005, it is described by IETF RFC 7159. A JSON document has the function of representing information accompanied by labels allowing to interpret the various elements, without any restriction on the number of these.

The acronym TXT designates a text file.

Portable Network Graphics (PNG) is an open format of digital images, which was created to replace the GIF format, at the time. PNG is a lossless format specially suited for publishing simple images including solid colors.

JPEG (acronym for Joint Photographie Experts Group) is a standard which defines the recording format and the decoding algorithm for a compressed digital representation of a still image.

The Extensible Markup Language, generally called XMLnote 1, “extensible markup language 1” in French, is a generic markup computer metalanguage derived from SGML. The SGML or Standard Generalized Markup Language is a description language with tags, ISO standard (ISO 8879: 1986).

Given the options previously proposed, according to a more elaborate embodiment of the method described with an alternative vocabulary, the method comprises a step of printing a set of colors, denoted Ci, according to an arrangement or a diagram. spatial uniquely defined for any type of printing, subsequently called SpectralChecker (literally meaning "spectral checker").

For example, the colors Ci can be printed in a checkerboard pattern and framed by positioning markers also uniquely defined, or printed in the form of a uniquely defined logo. The diagram is defined on the margins of the document for which compliance is sought, or on the document itself if the objective is to calibrate the printing machine.

A spatial descriptor or code is also printed containing the expected colorimetric and / or spectral information Ca of the printed colors Ci. The colorimetric / spectral information Ca can either be directly contained in the descriptor locally, or contained in a database remote data to which the descriptor gives access (for example via a URL).

The acronym URL (from the English: Uniform Resource Locator, literally "uniform resource locator"), designates the uniform naming (in the universal sense: "in a naming repository") of a localized resource (c. ie "a resource identified by its location").

The method then includes the use of a camera to record the SpectralChecker lit by a lighting system.

The positioning of the SpectralChecker is determined relative to the camera, preferably automatically by methods implemented by a processing unit.

The method then comprises measuring or calculating the spectral reflectances of each of the colors printed Ci by the processing unit using information collected by the camera during lighting by the lighting system.

For the above example of application to compliance control, the method comprises a step of comparing the calculated spectral reflectances of the colors Ci with the expected data Ca by the processing unit. The expected data can for example be a spectral reflectance or colorimetric coordinates such as La * b *, XYZ, Lu’v ’or others. These data are, depending on the case, contained in the spatial descriptor or stored in a database accessible to the processing unit.

The processing unit then issues a compliance report comprising, for each of the colors printed Ci, the differences between the measured value and the expected value. The compliance report is defined specifically so that it can be easily read by a human. The compliance report is for example a PDL document, a CxL document, an XML document or a document capable of being interpreted and displayed on a screen the processing unit 3 containing the tools for interpreting it. The document can be interpreted by a human eye and describes all of the print metadata (date, batch of print, type of print medium, inks used, and any other information deemed useful for monitoring production) as well as the set of calculated reflectances and comparison measurements with the expected values.

In a particular example, the compliance report is transcribed into a file interpretable by the printing machine allowing it to adjust its printing parameters.

For the above example of application to the establishment of a color profile, for example, the processing unit issues a report containing the measured spectral reflectances Ci associated with the color data used to print the SpectralChecker (for example stored in the spatial descriptor). The report is for example a PDL document, a CxL document, an XML document or a document capable of being interpreted and displayed on a screen the processing unit containing the tools for interpreting it. The document can be interpreted by a human eye and describes all of the printing metadata (date, batch of printing, type of printing medium, inks used, and any other information deemed useful for calibrating the whole)

The method then comprises a step of transforming the report into a print profile file, for example of the ICC profile type, with a view to characterizing the printing machine for a batch of inks and a printing medium. given. The profile contains in particular the spectrometric information of the colors Ci translated into a standard colorimetric space. The profile can also contain unmeasured colors and restored from a mathematical model in order to enrich the profile.

As a variant, in the aforementioned applications, the printed colors Ci may consist of a set of 20 colors defined by standard ISO 12647-2 in the following manner: the four primary colors of the four-color printing C, M , J, N declined each with four different and non-harmful ink rates, then the secondary Red, Green, Blue as well as an unprinted patch to indicate the spectral nature of the print medium. The colorimetric / spectral values of the expected colors Ca are then permanently stored in the processing unit.

In another example, the number of colors Ci is variable and defined in the spatial descriptor.

According to yet another example, the spatial descriptor of the expected colorimetric or spectral values Ca uses a compression process. According to simplified embodiments, the spatial descriptor is a code of type “EAN”, “QR-code” (registered trademark) or a code of type “Data Matrix” (registered trademark) or a code of type “Aztec” ( trademark).

The spatial descriptor also returns a URL containing the expected data Ca in the form of a standardized file, for example a file in CxF format.

It can also be envisaged that the positioning markers around the SpectralChecker allow the operator to position the camera exactly relative to the SpectralChecker.

According to one embodiment, the position of the camera is not determined in advance and the detection of the SpectralChecker by the camera is done by the use of feature extraction algorithms and then area detection of interest: the processing unit compares the image filmed by the camera with a reference image containing expected positioning markers. The markers are printed in the vicinity of the SpectralChecker. Their detection by an algorithm then makes it possible to determine the coordinates of the points of the colors Ci using the transformation function. The transformation function transcribes pixel coordinates into spatial coordinates allowing to understand the geometry between the camera, the target and the lighting system.

According to one embodiment, the spatial descriptor contains the positioning markers required for the alignment of the camera.

According to the particular embodiments, the spatial descriptor and the SpectralChecker form the same single object: the spatial arrangement of the colors Ci alone constitutes information detectable by the camera on their nature.

According to particular embodiments, the SpectralChecker is an image, an icon or a logo.

In each of the embodiments which have just been described, the obtaining process can be implemented using a control system.

For example, a control system includes a measuring device and a calculator.

The measuring device is suitable for simultaneously measuring the reflectance of each point of the target.

The measuring device comprises at least one light source and a detector such as a camera.

The computer is an electronic computer capable of handling and / or transforming data represented as electronic or physical quantities in registers of the computer and / or memories into other similar data corresponding to physical data in memories, registers or other types of display, transmission or storage devices.

According to one example, the computer is a system in the form of a computer.

In such a case, the system includes a processor comprising a data processing unit, memories and an information carrier reader. The system 10 also includes a keyboard and a display unit.

The computer program product includes a readable information medium.

A readable information medium is a medium readable by the system, usually by the data processing unit 14. The readable information medium is a medium suitable for storing electronic instructions and capable of being coupled to a computer system bus.

By way of example, the readable information carrier is a floppy disk or flexible disk (from the English name of "floppy disk"), an optical disk, a CDROM, a magneto-optical disk, a ROM memory, a RAM memory, an EPROM memory, an EEPROM memory, a magnetic card or an optical card.

On the readable information medium is stored a computer program comprising program instructions.

The computer program is loadable on the data processing unit and is adapted to entail the implementation of a obtaining process.

In another example, to obtain a more compact system, the computer is produced in the form of an integrated circuit.

In particular, the computer is produced in the form of a programmable logic circuit, such as an FPGA (acronym referring to the English name of "field-programmable gate-array" literally meaning network of programmable doors in situ) or a PAL (acronym referring to the English name of "programmable array logic" literally meaning programmable logic network).

Alternatively, the computer is produced in the form of an ASIC (acronym referring to the English name of "Application-Specific Integrated Circuit" meaning integrated circuit specific to an application).

The invention relates to the combination of all the technically possible embodiments.

Claims (1)

Claims [Claim 1] Method for controlling the printing of a physical information medium, the method comprising a step of: supply of a physical information support provided with a test pattern printed on the support, the test pattern comprising a set of dots each having a predefined color and spatially arranged according to a predefined arrangement, the physical information support being chosen in particular from the group consisting of a sheet, a cardboard, a plastic support and a textile support, - simultaneous measurement of the reflectance of each point of the target using a single device, to obtain measured reflectances, and - extraction of at least one item of information using a comparison between the measured reflectance and the reflectance corresponding to the predefined color, the comparison being implemented for each point, the information being chosen in particular from the group made up of at least one piece of information is information chosen from the group made up of compliance information, information for adjusting the parameters of a printing machine, information relating to the printing of the test pattern and a printing profile of a printing machine. [Claim 2] Control method according to claim 1, in which, during the supplying step, the physical information medium is also provided with a code printed on the medium, the code coding the predefined arrangement and the set of colors. predefined, the code being, for example, a barcode, an electronic chip or a digital watermarking, the method further comprising a step of: - reading the code, and - decryption of the code to obtain the predefined arrangement and all of the predefined colors. [Claim 3] Control method according to claim 2, in which the test pattern and the code are combined. [Claim 4] Control method according to any one of claims 1 to 3, in which the method comprises a step of determining the position of the target using the detection of markers printed on the physical information medium or by using a feature extraction technique. [Claim 5] Control method according to any one of claims 1 to 4, in which, the method comprises a step of restoring the at least one piece of information extracted in the form of a document to be displayed and interpretable by a human eye, in particular a document in PDF, CxF, JSON, TXT, PNG, JPG or XME. [Claim 6] Control method according to any one of claims 1 to 5, in which the test pattern checks at least one of the following properties: - the predefined arrangement is a checkerboard, - the predefined layout is chosen so that the dots form a logo, - the predefined colors are at least 20 in number, - the predefined colors include the colors cyan, magenta, yellow and black, - the predefined colors include several colors corresponding to the same printing color at a plurality of different inking rates, each inking rate being non-zero, - the predefined colors include four colors corresponding to the same printing color at a respective inking rate, each inking rate being non-zero, - the predefined colors include the colors red, green and blue, and - the predefined layout includes an unprinted patch. [Claim 7] Computer program product comprising a readable information medium, on which is stored a computer program comprising program instructions, the computer program being loadable on a data processing unit and suitable for driving the implementation at least the step of extracting a method according to any one of claims 1 to 6 when the computer program is implemented on the data processing unit. [Claim 8] Readable information medium storing a computer program comprising program instructions, the computer program being loadable on a data processing unit and adapted to entail the implementation of at least the extraction step d 'A method according to any one of claims 1 to 6 when the computer program is implemented on the data processing unit. [Claim 9] Control system for printing a physical information medium, the control system comprising: - a single device suitable for simultaneously measuring the reflectance of each point of a test pattern printed on a physical information medium, the test pattern comprising a set of points each having a predefined color and spatially arranged according to a predefined layout, and - a computer adapted to extract at least one item of information using a comparison between the measured reflectance and the reflectance corresponding to the predefined color, the comparison being implemented for each point.