BACKGROUND

[0001] Print apparatuses, such as the print apparatuses used in induslria! printing, process large print jobs in a continuous cycle and output the printed media in a stack. The continuous nature of such print cycles combined with the stacked output means that it is often not possible to manuail check the print quality of individua! printed pieces,

BRIEF DESCRIFTSQN QF DRAWINGS

[0002J Examples wl now be described, by way of non-limiting example, with reference to the accompanying drawings, in which:

[0003] Figure 1 is a simplified schematic of an example of an apparatus for printing according to an example;

[00043 Figure 2 is a flowchart of an example of a method of determining a characteristic of a substrate;

[OOOSJ Figure 3 is a flowchart of a further example of a method of deterrnining a characteristic of a substrate;

[0006] Figure 4 is a flowchart of a further example of a method of determining a characteristic of a substrate;

[0007J Figure 5 is a fiowchart of a further example of a method of determining a characteristic of a substrate;

[0008] Figure S is a flowchart of a further example of a method of determining a characteristic of a substrate;

[OOOSJ Figure 7 is a flowchart of a further example of a method of determining a characteristic of substrate;

[0010] Figure 8 is a fiowchart of a further examp!e of a method of determining a characteristic of a substrate;

poll] Figure 9 is a flowchart of a further example of a method of determining a characteristic of a substrate; and [00121 Figure 10 Is a simplified schematic of a machine-readable medium and a processor according to an exampie.

DETAILED DESCRIPTION

[0013] According to some examples, there is a print apparatus 2 as shown schematically in Figure 1. The print apparatus 2 may comprise a laser source 4, a diffuse light source 8, an image capture device 8 and processing circuitry 10. The laser source 4 may direct iaser light onto a printable medium. The diffuse light source 0 may direct diffuse light onto the printabie medium.

[00143 ^e image capture device 8 may be operable i) to detect laser light reflected from the printabie medium and ίί) to detect diffuse Sight reflected from the printable medium. As such, the laser source 4 and diffuse light source 8 respectively direct laser and diffuse light onto the printable medium and the image capture device 8 is used to the detect Iaser and/or diffuse light that is reflected from the surface of the printable medium.

100151 The processing circuity 10 may determine, from the reflected Iaser light, a first parameter relating to the printable medium. The processing circuity 10 may determine, from the reflected diffuse Sight, a second parameter relating to the printable medium. The processing circuity 10 may determine a characteristic of the printable medium using the first and second parameters.

[001 $3 Sn this way, a characteristic of the printable medium may be determined using a parameter derived from reflected laser Sight and a parameter derived from reflected diffuse light. As a result, the apparatus in Figure 1 is able to calculate the characteristic of the printable medium more accurately than would be possible, for exampie, if the apparatus just used parameters derived from Iaser reflection, or just used parameters derived from a diffuse light source,

[00173 in some examples, the print apparatus 2 is an ink-jet printer, an electrostatic printer, a liquid electrostatic printer (LEP), a lithographic printer, a fiexographic printer, a gravure printer or an offset printer. In some examples, the print apparatus 2 i a three dimensional printer, for example, the print apparatus 2 may comprise a printer that generates three-dimensionai objects on a bed of buiid material in a layer-wise manner. These print apparatuses are merely examples, however, and the print apparatus may foe of a different type not listed here. [0018] Examples of printable media (also referred to herein as "printabie substrates" or "substrates"), Include, but are not Siroited to, paper, cardboard, transparencies and fabric (e.g. textlie-oased media).

[0019J irs some exampies, the diffuse Sight source 6 may emit tight having a specific frequency spectrum, in some exampies, the specific frequency spectrum may be predefined. The specific frequency spectrum ma be chosen arbitrarily, so long as the spectrum can be compared to a measured spectrum. The specific frequency spectrum; may be compared with a frequency spectrum of the reflected diffuse Sight as detected by the image capture device 8 to determine properties of the printable medium. The properties may inciude properties relating the colour of the printabie medium, and/or an amount of light, over a range of frequencies, absorbed and/or reflected by the printable medium, in some exampies, t e frequency spectrum is stable over the lifetime of the diffuse light source. Therefore, a reliable comparison can be made over the lifetime of the diffuse light source. In some examples, the diffuse Sight source is a CIE D50 Sight source. A CIE light source is a standard illuminant, standardised in accordance with the international Commission on Illumination. A D50 light source emits light having a correlated colour temperature of 5003 K.

[0020] In some exampies the image capture device 8 may be a camera such as an RGB camera (i.e. a camera which receives Sight as three separate components - red, green and blue). In some examples, the image capture device 8 produces image data of the reflected Iaser and/or diffuse light, in some examples, the image capture device 8 may produce a pixilated data file describing the relative detected intensities at each point (e.g. pixel) in the image. The image may be in a standardised format such as a .jpg or .png format.

[0021 J In some exampies, the processing circuitry 10 may control the iaser source 4 and the diffuse light source 6 such that, during a first period, Iaser light is directed onto the substrate by the laser source 4 and, during a second period, diffuse light is directed onto the substrate by the diffuse light source 6. The iaser source 4 and diffuse light source 8 may thus be alternated in order to obtain reflected laser light patterns and reflected diffuse light individually. The first period may be different to the second period.

£0022] in some examples, adjustments to the optics of the image captur device 8 may be made in order to optimise the detection of the reflected light (either laser or diffuse) to ensure the detected reflections are suitable for use in calculating the first and second parameters. For example, the image capture device may be focussed on different portions of the printable medium (e.g. surface, edge or printed regions of the printable medium} fo different measurements, and/or the focus of the image capture device may be adjusted depending on the resolution intended for different measurements, in some examples, different focal lengths are used io detect reflected laser light and reflected diffuse light respectively.

[0023] in some examples, the image capture device 8 may be set to a first focal length to image reflected laser !ighf and to a second focal length to image reflected diffuse Sight. The first and second focal lengths may be different, in examples where the laser source 4 and the diffuse light source 6 alternately direct laser and diffuse Sight respectively onto the printable media, the image capture device 8 may correspondingly alternate between the first and second focal lengths in order to image the reflected laser light and the reflected diffuse light.

[0024 The laser source 4 may b directed onto the printable media at an angle, For example, the laser source 4 may be shone at the printable media at an angle of about 45 degrees with respect to the surface of the printable medium, in some examples, the 0/45 geometry is used. In some examples, the image capture device 8 is positioned such that when the laser source 4 is directed onto the printable medium, the laser light that is reflected from the surface of the printable medium passes into the Sens of the image capture device 8.

[002SJ Figure 2 is a flowchart of an example of a method 20 of determining a characteristic of a substrate, in some examples, the method 20 is performed by an apparatus such as the print apparatus 2 shown in Figure 1 , and described above, in other some examples, parts of the method may be performed remotely, for example, on a remote server or a processor that is separate from the printer.

00263 In some examples, in a first block: 21, the method 20 comprises obtaining a reflection, from a substrate, of a laser light pattern. A second block 22 comprises obtaining a reflection, from the substrate, of diffuse light. A third block 23 comprises determining, using a processor, a first parameter relating to the substrate from the reflected laser light pattern. A fourth block 24 comprises determining, using a processor, a second parameter relating to the substrate from the reflected diffuse light, A fifth block 25 comprises determining, using a processor, a characteristic of the substrate from the first and second parameters. In some examples, a single processor, or processing device, may be used to perform processes of multiple blocks, in other examples, each block may fo performed by a separate processing device.

[0Q2?J As noted above, examples of substrates include, but are not limited to paper, cardboard, transparencies and fabric (e.g. textiie-based media).

[0028] Laser light is coiSimated and thus any scatter of the Iaser light from the substrate surface ma be caused by the structure of the surface from which the iaser was reflected. This can therefore be used to probe surface features of the substrate. As such, in some examples, the first parameter relates to a structural propert of the substrate. For example, the first parameter may relate to a geometric property associated with the substrate. In other words, the first parameter may be related to shape of a surface feature of the substrate. For example, the first parameter may be a surface pattern of the substrate, a thickness of the substrate, a measure of the scatter of the refiecied laser Sight, due to the profile of the surface of the substrate, a measure of the roughness of the surface of the substrate or a measure of a surface feature characteristic of the method of manufacture of the substrate. In some exampies, the thickness of the printable media is measured by directing the Sight across an edge portion (e.g. at the side or at an end) of the substrate and measuring the depth of the profile of the edge,

[00293 Reflections of diffuse Sight may, in some examples, be used to detect the colour of the substrate. As described above, if the diffuse light has a specific frequency distribution, then th specific frequency distribution can be compared to the frequency distribution of the light reflected from the substrate in order to determine the colour of the substrate (and/or the colour of a print agent applied to the surface of the substrate., as will be described in more detail below). Therefore, in some exampies, the second parameter may relate to the colour of the substrate.

[0030] Figure 3 is a flowchart of a further example of a method 30 of determining a characteristic of a substrate. The method 30 may include blocks of the method 20 of Figure 2. In some exampies, the method 30 may comprise, at block 31 , determining, using a processor, an LAB colour space vector associated with the substrate, using the reflected diffuse light. An LAB colour space vector is a vector having three dimensions, "I" representing lightness and a and b that describe green-red component and b!ue- ye!!ow components of the light, respectively, as defined in standard C!ELAB76. In some examples, the characteristic of the substrate may be determined (block 32), at !east partially, from the LAB colour space vector. [00313 ^As noted above, iaser Sight and diffuse fight probe different types of features associated with a substrate, which enable characteristics of the substrate to be determined more accurately, when compared to deriving a characteristic from either laser light or diffuse Sight alone. Determining characteristics with more accuracy in this way may facilitate improved substrate type recognition and improved automated quality control processes (e.g. detection of colour drift as described below).

[0032} in some examples, the characteristic of the substrate comprises the substrate type. For example, different substrates may have unique LAB colour space vectors, or unique combinations of colour and structural properties. In this way, the type of substrate can be accurate!y determined. This ability to determine a type of substrate may he used in quality control processes. If an incorrect substrate is fed into an industriaS printer, as noted above, the continuous nature of industrial printers can result in a large batch being printed before an opportunity for correction arises. It also facilitates automated substrate loading,

[0033| Figure 4 is a flowchart of a further example of a method 40 of determining a characteristic of a substrate. The method 40 may include blocks of the method 20 and/or 30. In some examples, the determined substrate type may be used in a qualit control process. For exampSe, the method 40 may comprise, at block 41, after determining the substrate type, performing a check to determine whether the determined substrate type matches a substrate type in a print Job profile. A print job prof lie may include specifications of the print job. in some examples, a print job profile may include, but is not limited to, information relating to the type of substrate that print agent is to be printed onto.

[00343 if ¾ ^is determined that the determined substrate does not match a substrate type in the print job profile, then appropriate action may be taken. Thus, the method 40 may comprise, at block 42, performing an action responsive to determining that the substrate type does not match the substrate type in the print job profile,

[003§| in some examples, the action to be performed (b!ock 42} may comprise alerting a user that the substrate type does not match the expected substrate type. The alert may be in the form of an error message. In some examples, the action to be performed (block 42) may comprise sending a command to a printer to instruct the printer to pause printing. The printer may be instructed to pause printing until explicitly commanded to resume printing by the user, in some exampies, the action to be performed (block 42) may comprise changing a substrate of a first type for a substrate of a second, different type {e.g. the correct substrate as detailed in the print job profile}. if it is determined at block 41 that the determined substrate does not match a substrat type in the print job profile, then the method may,, in some examples, comprise recording the determination and/or the detected substrate type in a log. Multiple actions may be performed.

[0036! Figure 5 Is a flowchart of a further example of a method 50 of determining a characteristic of a substrate. The method 50 may include blocks of the methods 20, 30 and/or 40. According to some examples, the method 50 may comprise, at block 51 , determining, using a processor, the characteristic of the substrate using a model generated from a machine Seaming process. The iaser and diffuse light setups described above provide complementary information about the substrate that can be used as input parameters to a machine learning process. Therefore, in some examples, the first and second parameters may form inputs for a machine learning process. As noted above, the output of the machine learning process may be more robust when parameters derived from both Iaser light and diffuse light are used, compared to if just Iaser Sight or just diffuse light are used alone.

10 371 in some examples, the focus of the machine learning process may be on supervised learning. In some examples, the focus of the machine learning process may be on categorisation or clustering. In some examples, operations such as k-means or support vector operations may be used. In some machine learning approaches, the machine learning process can be trained on a training data set where the training data set contains values of various parameters that are associated with a particular substrate type. This training data is used to build an initial model that can be used to predict the substrate type of an unknown substrate. The machine learning process may be further tuned in-use through user interaction. For example, a user can confirm a prediction made using a model output by the machine process as being correct, or reject a prediction as incorrect and this data can be added to the training data set to improve the model generated by the machine learning process.

[0038] Figure 6 is a flowchart of a further example of a method 60 of determining a characteristic of a substrate. The method 60 may include blocks of the methods 20, 30, 40 and/or 50. In some examples, the method 60 may comprise, at block 61 , detecting, from the reflected iaser light pattern, a skew, crease or wrinkle in the substrate. For example, the laser light may be used to detect the profile of an edge of the substrate. If the edge profile indicates that the edge of the substrate is at an angle {i.e. skewed) with respect to the direction of travel of the substrate through a printer, then this may indicate thai the paper is skewed, if an angle of t e edge profi!e changes over time (i.e. if the angle of the trailing edge changes between different pieces of print substrate) then this may indicate that the substrate is moving at an angie {i.e. a skew). Skewed substrates can lead, for example, to mis-alignment of a printed region relative to the substrate or to the substrate jamming in the printer.

[0039] in some examples, the iaser light may be scanned over at least a portion of the surface of the substrate. Reflected iaser Sight may be used to generate a surface profile of the scanned portion of the substrate surface. Surface profiles indicative of raised areas may Indicate structura! defects representative of a poor quality substrate, or of wrinkles where the substrate has been coneertinaed o bunched as it passed through the print apparatus,

[0040] in some examples, when a skew;, crease or wrinkle is detected, appropriate action may be taken. Thus, the method 60 may comprise, at biock 62, performing an action in response to detecting the skew, crease or wrinkle, in some examples, the action performed at block 62 may comprise pausing a print Job, alerting a user, delivering an error messag to a user, discarding a substrate and/or recording the detection of the skew, crease or wrinkle in a log. In some examples, the log is an error log.

[00413 Figure 7 is a flowchart of a further example of a method 70 of determining a characteristic of a substrate. The method 70 may include blocks of the methods 20, 30, 40, 50 and/or 80. In some examples, the method 70 may comprise, at block 71 , applying print agent to a portion of the surface of the substrate. The method 70 may comprise, at biock 72, determining from the reflected diffuse light, a colour of the applied print agent. At biock 73, the colour of the applied print agent may then be compared to a reference colour. In some examples, the reference colour may be part of a print job specification, as described above.

[0042] in some examples, the method 70 may comprise, at biock 74, performing an action if the colour of the applied print agent is not within a tolerance of the reference colour. The tolerance may, for example, be a difference in colour that is within the quality control bounds of the job being undertaken by the printer.

[0043] in some examples, the action performed at block 74 comprises pausing a print job, alerting a user, delivering an error message to a user, discarding a substrate and/or recording the detection of the colour difference in a log, if the colour difference metric is greater than a threshold. In some examples, the iog may foe an error log. [Q044J in some examples, a range of RGB (red, green, blue component) values may exist wthin which the colour of the applied print agent is deemed t have passed a colour-quality control test, in some examples, if the detected colour of the applied print agent is outside of the range of RGB values, this may indicate an error I the printer, for example, an error in the colour calibration, an ink error {e.g. the ong ink has been loaded into the printer) or an indication that an ink cartridge should be replaced.

[00452 Figure 8 is a flowchart of a further example of a method 80 of determining a characteristic of a substrate. The method 80 may include blocks of the methods 20, 30, 40, 50, 60 and/or 70. in some examples, the method 80 may comprise, at biock 81 , computing, using a processor, a colour difference metric. The method SO may comprise, at bock 82, pausing a print job if the colour difference metric is greater than a threshold. In some examples, alternative action may be performed if the colour difference metric is greater than a threshold, such as actions discussed above,

[0046| A colour difference metric describes the difference in RGB values between two colours {e.g. between the colour of the applied print agent and the reference colour). In some examples, the colour difference metric may be a LAB Delta E metric (calculated, for example, with CIEDE2000 metric revision),

[GQ47J Figure 9 is a flowchart of a further example of a method 90 of determining a characteristic of a substrate. The method 80 may include blocks of the methods 20, 30, 40, 50, 60, 70 and/or 80. In some examples, the method 90 may comprise, at block 91 , detecting a defective region in the applied print agent. The method 90 may comprise, at block 92, performing an action in response to determining the defective region. For example, the defective region may be due to colour drift. Colour drift (i.e. a slow change in the printed colour over time) may occur when an ink cartridge begins to run out, or due to a nozzle of a print head functioning incorrectly, in some examples, the defective region may be a sub-patch artefact. A subpaich artefact is an artefact on a scale smaller than the printing die. In some examples, the printing die contains one or more sets of nozzles (>-1000) manufactured at once from the same silicon die and fed from the same print agent channel. Ordinarily, such a set of nozzles prints a uniform patch, in terms of colour, but colour differences can occur within a die or sub-patch due to second order effects such as thermal differences within the die or aerodynamic effects on the printer.

[0048] It will be recognised thai the method and apparatus herein permit a wider range of quality controi metrics to be measured, and the detection of a wider range of print errors, than is permitted through the use of either a iaser source 4 or a diffuse Sight source 6 Individually.

[0040J Figure 10 shows, schematically, a machine-readable medium 101 and a processor 103, The machine-readable medium 101 may comprise instructions 102 which, when executed by the processor 103, cause the processor to i) obtain first image data relating to a reflection of laser light from a printabie substrate, si) obtain second image data relating to a reflection of diffuse iight from the printabie substrate iii) determine, from the first image data, a first parameter relating to the printabie substrate, iv) determine, from the second image data, a second parameter relating to the printabie substrate, and v) determine, using the first and second parameiers, a characteristic of the printable substrate.

[0050J Examples in the present disclosure can be provided as methods, systems or machine readable instructions. Such machine readable instructions may b included on a computer readable storage medium (including but is not limited to disc storage, CD- ROM, optical storage, etc.) having computer readable program codes therein or thereon, OOStJ The present disclosure is described with reference to flow charts and/or block diagrams of the method, devices and systems according to examples of the present disclosure. Although the flow diagrams described above show a specific order of execution, the order of execution may differ from that which is depicted. Blocks described in reiation to one flow chart may be combined with those of another flow chart. It shall be understood that each flow and/or block in the flow charts and/or block diagrams, as well as combinations of the fiows and/or diagrams in the flow charts and/or block diagrams can be realized by machine readable instructions.

[00523 The machine readable instructions may, for example, be executed by a general purpose computer, a speciai purpos computer, an embedded processor or processors of other programmable data processing devices to realize the functions described in the description and diagrams. In particular, a processor or processing apparatus may execute the machine readable instructions. Thus functional modules of the apparatus and devices may be implemented by a processor executing machine readable instructions stored in a memory, or a processor operating in accordance with instructions embedded in logic circuitry. The term ^" processor' is to be interpreted broadly to include a CPU, processing unit, ASIC, logic unit, or programmable gate array etc. The methods and functional modules may all be performed by a single processor or divided amongst several processors. [00S3| Such machine readable instructions may also be stored in a computer readable storage that can guide the computer or other programmable data processing devices to operate in a specific mode.

[0054J Such machine readable instructions may also be loaded onto a computer or other programmable data processing devices, so that the computer or other programmable data processing devices perform a series of operations to produce computer-implemented processing, thus the instructions executed on the computer or other programmable devices provide a process for realizing functions specified by fiow(s) in the flow charts and/or b!ock{s) in the !ock diagrams.

[OOSSJ Further, the teachings herein may be implemented In the form of computer software product, the computer software product being stored in a storage medium and comprising a plurality of instructions for making a computer device implement the methods recited in the examples of the present disciosure,

[00δ6| While th method, apparatus and related aspects have been described with reference to certain examples, various modifications, changes, omissions, and substitutions can be made without departing from the spirit of the present disciosure. It is intended, therefore, that the method, apparatus and related aspects be limited only by the scope of the following claims and their equivalents. It should be noted that the above-mentioned examples illustrate rather than limit what is described herein, and that it will be possible to design many alternative implementations without departing from the scope of the appended cl ims.

[00571 The word "comprising" does not exclude the presence of elements other than those listed in a .claim, "a" or "an" does not exclude a plurality, and a single processor o other unit may fulfil the functions of several units recited in the claims.

[ S8J The features of any dependent ciaim may be combined with the features of any of the independent claims or other dependent claims.