In recent years there has been increasing use made of printing on perforated window films. Such films, often made of PVC or vinyl, are supplied pre- perforated and are then used for printing graphical content on one side thereof. When printed, perforated films may be applied to shop windows, vehicle windows, etc. The perforations are generally arranged in a regular pattern and allow light through the printed film. Such films are generally applied such that the printed content is viewable from the outside of the window, and a plain side is viewable from the inside.

This arrangement enables a viewer to see through the inside of the window to the outside (albeit whilst reducing the amount of transmitted light), but does not allow a viewer from a reasonable viewing distance to see from the outside of the window to the inside.

Such print window films are often referred to as One-view' or One-way vision' films.

BRIEF DESCRIPTION

Examples, or embodiments, of the invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Figure 1 shows an example image to be printed;

Figure 2 illustrates a processing module according to one example;

Figure 3 is a flow diagram outlining an example method of processing an image according to one example;

Figure 4 illustrates an image mask according to one example;

Figure 5 illustrates an image mask according to one example;

Figure 6 illustrates an example modified image to be printed according to one example; Figure 7 is a flow diagram outlining an example method of processing an image according to one example;

Figure 8 is a flow diagram outlining an example method of processing an image according to one example;

Figure 9 is a drawing showing an exploded view of a printed article according to one example; and

Figure 10 is a simplified block diagram of a printing system according to one example. DETAILED DESCRIPTION

Printed one-way vision films are currently produced by printing an image on commercially available pre-perforated adhesive substrates that are backed with a non-perforated removable backing liner. One such film is Hewlett- Packard's One-view Perforated Adhesive Window Vinyl available from Hewlett-Packard Company.

However, there are numerous problems associated with producing printed one-way vision images on such perforated films. Firstly, parts of an image printed on a perforated film and that correspond with perforations in the film result in ink wastage since ink printed in such areas is printed on the removable backing liner.

Secondly, different applications may use perforated films having different perforation characteristics, such as perforation size, spacing, and shape. For example, for vehicle windows some jurisdictions dictate the minimum level of effective light transmission of such films for safety reasons, which may dictate perforation characteristics. However, in commercial applications, other perforation characteristics may be used. Accordingly, print shops may need to keep multiple rolls of perforated films in stock to be able to meet specific customer demand. Furthermore, printing throughput is reduced, and costs may be increased, when rolls of perforated film have to be changed in a printing system to meet different customer requirements. Furthermore, perforated films are somewhat expensive due to their manufacturing process, and may require careful handling to prevent deformation of their perforated structure.

Examples described herein, however, provide techniques for producing such one-way vision films in a much more flexible manner, whilst at the same time reducing ink wastage. Furthermore, such one-way vision films may be produced on non-perforated, and hence substantially cheaper, transparent adhesive films.

Referring now to Figure 1 , there is shown an example image to be printed 100 as a one-view image on a non-perforated transparent substrate. The image 100 may be described in a suitable image file format, such as JPEG image format, a bitmap image format, a portable document format (PDF), or the like.

To transform the image 100 so that it may be printed as a one-view image on a non-perforated transparent substrate a number of processing operations are performed on the image 100, as described below with reference to the flow diagram of Figure 3. By non-perforated transparent substrate is meant a transparent substrate that does not have a pattern of physical perforations formed therein.

The processing operations define a method of processing an image. The processing operations may be described in computer understandable instructions that, when executed by a suitable processing module, cause the processing module to perform the method described by the processing operations. In one example, as illustrated in Figure 2, the method may be performed by a processing module 200 that includes a processor 202 such as a microprocessor, a microcontroller, a computer processor, or the like. The processor 202 is in communication with a memory 206 via a communication bus 204. The memory 206 stores the computer understandable processing instructions 208. When executed by the processor 202, the processing instructions 206 cause the processing module 200 to perform the processing operations as described herein.

As will be described further below, in different examples the processing module 100 may be part of one of different processing entities.

For example, in one example, the method may be performed by a graphical image editing computer application for execution on a computer, laptop, server, or the like. In another example, the method may be performed by a raster image processor (RIP) application for execution on a computer, laptop, server, or the like. In a further example, the method may be performed by a printer driver for execution on a computer, laptop, server, or the like.

In a yet a further example, the method may be performed by a processor or in firmware in a printing system.

A method of processing an image, as performed by a suitable processing module, according to one example, will now be described with reference to the flow diagram of Figure 3. At block 302 the processing module obtains image data describing an image to be printed. In one example, for example where the method if performed by a printer driver or graphical editing application, the image data is arranged in a suitable image file format, such as JPEG image format, a bitmap image format, a portable document format (PDF), or the like. In one example, for example where the method if performed by a printing system, the image data may be rasterised or half-toned image data suitable for directly controlling a print engine of a printing system. At block 304 the processing module modifies the obtained image data by applying a predetermined mask thereto. A mask 400 according to one example is illustrated in Figure 4. In this example, the mask 400 is a binary mask and comprises masked portions 402, and a non-masked portion 404. In this example the mask comprises a central circular masked portion and quarter circle masked portions (of the same radius as the central circular masked portion) arranged around each corner of the mask 400. The masked portions 402 may also be referred to as 'visual holes' or 'visual apertures'. In one example, the mask 400 is a square mask having a length of about 4mm, with the circular masked portions having a radius of about 1 mm, when printed. This gives a configuration having a ratio of approximately 40% aperture to 60% substrate. In other examples other size masks and visual apertures may be used.

The arrangement of the mask 400 enables it to be tiled, in a repeated pattern, to produce a larger mask 500, an example of which is shown in Figure 5, suitable for applying to a larger image. In one example the mask 500 may be arranged to cover the whole of an image to be printed.

In another example the mask 500 may be arranged to cover only a portion of an image to be printed, for example to leave a border around the edge of the image. Advantageously this enables printed one-way vision images to be produced that are highly customisable in terms of their layout since the techniques described herein makes such images no longer dependent on the size and configuration of commercially available perforated substrates. For example, this enables a transparent non-perforated substrate to be used to produce a printed article that comprises both a one-way vision portion and a non-one-way vision portion. Producing a mix of one-way vision and non-one- way vision portions is not possible when using commercially available perforated one-way vision substrates. It will be appreciated that other mask shapes, sizes, and arrangements may be used in other examples. For example, in another example the central masked portion may be rectangular in shape with quarter rectangles arranged around each corner of the mask.

In other examples the mask 400 or mask 500 may be arranged to have an irregular pattern of masked and non-masked portions.

In other examples the mask 400 may have only a single masked portion 402 and a single non-masked portion.

The size of the mask and the size central circular masked portion within the mask 400 may also be varied to produce larger or smaller masked portions 402. This enables different kinds of perforated substrate to be simulated.

Applying the mask 500 to the obtained image modifies the obtained image such that portions of the image that correspond to masked portions 402 of the mask 500 will not be printed and thus will be effectively rendered transparent, giving the visual effect of a pattern of holes or apertures when the image is printed on a transparent substrate. The pattern of visual holes or apertures simulates an image printed on a perforated substrate. In one example this may be achieved by setting each colour of each pixel of the obtained image corresponding to a masked portion to be a pure white pixel (e.g. by setting the RGB pixels values to their maximum value, such as 255 in a 64 bit colour image). White pixels are typically not printed because most images are printed on white paper. In other examples, where the image format of the obtain image supports transparency each such pixel may be modified to be designated as transparent. Figure 6 illustrates an example modified image 600 resulting from the application of the mask 500 to the image 100. The image 600 comprises an image portion 602, and white or transparent portions 604 that correspond to the masked areas 402 of the mask 500. The modified image data representing modified image 600 may be printed by a printing system on a transparent substrate such that any image portions defined as being pure white or transparent are not printed, and thus remain transparent on the transparent substrate. The effect of this is that the image portions 604 visually simulate the perforations (or apertures) of a perforated substrate. Advantageously, no ink is wasted by printing ink on those portions simulating the holes of a perforated substrate. A further example of a method of processing an image, as performed by a suitable processing module, will now be described with reference to the flow diagram of Figure 7.

At blocks 302 and 304 the image is processed as described above.

At block 702 the processing module generates a new or additional white image layer, or white ink channel separation, corresponding to the non- masked portion 404 of the mask 500. This white image layer destined as an undercoat layer to be printed using white ink. As an undercoat layer, this is intended to be the first layer printed on the transparent substrate.

Although best results are obtainable when printing the additional white ink image layer using white ink, in other examples other suitable light colours or off-white colours may be used, although some loss of colour fidelity may arise. Accordingly, the term white ink used herein may include use of other suitable light-ink colours.

At block 704 the processing module adds the generated additional white image layer to the modified image data, such that it will be printed prior to the modified image data.

The purpose of generating an additional white image layer is to provide a white printed base layer on which the non-masked portion 602 of the modified image 600 may be printed. In this way, the colours of the printed image are accurately reproduced, since the majority of printing systems are configured to produce best colour reproduction when printing on white substrates. In another example, however, the additional white image layer may be defined to be printed on top of the modified image 600. In this way when printed the modified image 600 is viewable through the underside of the transparent substrate. One advantage of printing the additional white image layer on top is that the printed image is protected on the underside by the transparent substrate, and is protected on the top side by a layer of white ink. In this example the image to be printed may be reversed so that the image is seen as originally intended once printed.

The modified image data and additional image layer may be printed by a printing system capable of printing with white ink on a transparent substrate. Any portions of the image (apart from the white additional image layer) being pure white or transparent are not printed, and thus remain transparent on the transparent substrate. The effect of this is that the image portions 604 visually simulate the holes of a perforated substrate, but without incurring ink waste by printing ink on those portions. This also helps an observer viewing a printed substrate from the inside to see through the non-printed portions of the image.

A further example of the processing operations described in the instructions 208, as performed by a suitable processing module, will now be described with reference to the flow diagram of Figure 8.

At block 802 the processing module obtains first image data describing a first image to be printed. At block 804 the processing module modifies the obtained image data by applying a predetermined mask thereto in the manner described above. At block 806 the processing module obtains second image data describing a second image to be printed.

At block 808 the processing module modifies the obtained second image data by applying a predetermined mask thereto in the manner described above.

At block 810 the processing module generates a new or additional white image layer, or white ink channel separation, corresponding to the non- masked portion 404 of the mask 500. This additional white image layer is destined to be printed on top of first modified image, and beneath the second modified image using white ink.

At block 812 the processing module generates final image data that comprises multiple image layer that are to be printed in a specific order, such that the first modified image data is printed first, such that the white image is printed atop the first modified image data, and such that the second modified image is printed atop the white image. The generated final image data is arranged such that, when printed, the masked portions, or visual apertures, of each of the image layers are aligned with one another. In other words, when printed the image layer and white image layer are coincident.

By printing one image on one side of the white layer and the other image on the other side of the white layer, the first image is visible from one side of the substrate and the other image is visible from the other side of the substrate.

The final image data may be printed by a printing system capable of printing with white ink on a transparent substrate such that any image portions defined as being pure white or transparent are not printed, and thus remain transparent on the transparent substrate.

In one example the first image may be an image having a predetermined solid colour, such as black. In another example the first image may be an image having a predetermined graduated colour effect. In another example the first and second images may be any kind of images having any kind of content.

In a yet further example the processing module may generate an additional black image layer and an additional white image layer each corresponding to non-masked portions of the mask 500. The processing module may arrange these additional images such that the final image data comprises multiple image layer that are to be printed in a specific order, such that the first modified image data is printed first, such that a first white image is printed atop the first modified image data, such that the black image is printed atop the first white image, such that the second white image is printed atop the black image, and such that the second modified image is printed atop the second white image. The generated final image data is arranged such the masked portions of each of the image layers are aligned with one another or are coincident.

Referring now to Figure 9, there is shown an exploded view of a printed article 900 prepared in accordance with examples described herein. The printed article 900 comprises a transparent, non-perforated substrate 902 suitable for being applied to a window. In one example the underside of the substrate 902 is covered with an adhesive layer (not shown), and an additional removal backing layer (not shown) adheres to the adhesive layer. The printed article 900 further comprises a first ink layer 904 that has been printed on the top surface of the substrate 902. In one example the first ink layer is printed using white ink, or another suitable light colour, and comprises a series of non-printed portions or visual apertures arranged in a pattern. The first ink layer corresponds to the non-masked portions of the mask 500.

The printed article 900 further comprises an upper ink layer 906 that has been printed on top of the first ink layer 904. The upper ink layer comprises graphical content, such as text, photographs, images, etc. and also comprises a series of non-printed portions or visual apertures arranged in a pattern that correspond to masked portions of the mask 500. The upper ink layer is printed such that the visual apertures of the first and upper ink layers are aligned or are coincident

In a further example, the first ink layer 904 and upper ink layer 906 may be reversed, such that the upper ink layer 906 is printed first on the substrate 902, and such that the first ink layer 904 is printed on the upper ink layer 906.

In a further example the printed article 900 may comprise one or more additional ink layers intermediate the substrate 902 and the upper image layer 906, for example as described herein. In this example, all of the ink layers are printed such that their respective visual apertures are aligned or are coincident.

When the above described processing operations are performed by a printer drive, the printer driver may perform the described processing operations in response to receiving instructions to print an image from a suitable computer application. The printer driver, through an appropriate user interface, may allow a user to select an option to generate a one-way vision printed image on a non-perforated transparent substrate. In one example, the printer driver may also allow a user to select the characteristics of the one-way vision image, such as the size, shape, and spacing of the transparent image portions. When the above described processing operations are performed by a printing system, the printer system may perform the described processing operations in response to receiving a print job. The printing system, through an appropriate user interface, may allow a user to select an option to generate a one-way vision printed image on a non-perforated transparent substrate. In one example, the printing system may also allow a user to select the characteristics of the one-way vision image, such as the size, shape, and spacing of the transparent image portions or visual apertures. Such a printing system, according to one example, is shown in Figure 10. The printing system 1000 comprises a print engine 1002 for printing on a substrate, such as a transparent vinyl or PVC substrate 1004. The substrate 1004 is advanced through a print zone 1005 of the print engine 1002 by a media advance mechanism 1008 in a media advance direction 1006. In one example the media advance mechanism 1008 may include one or multiple rollers. In another example the media advance mechanism 1008 may include a transport belt or other suitable media advance device. In one example the print engine 1002 is an inkjet print engine that comprises one or multiple inkjet printheads. Each printhead comprises an array of printhead nozzles through which drops of printing fluid may be selectively ejected. The arrangement and spacing of the nozzles in the printhead defines a printing resolution of the printing system 1000. In one example the nozzles may be arranged to allow the printing system 1000 to print at resolutions of up to 600 dots per inch (DPI). In other examples the nozzles may be arranged to allow the printing system 1000 to print at other higher or lower resolutions, such as 300 DPI and 1200 DPI. The printheads are controllable by the printer controller 1010, in accordance with printhead control data representing an image to be printed, to eject drops of printing fluid, such as ink, onto a substrate pixel locations on a substrate positioned in the print zone 1005. In one example the printheads are mounted on a carriage (not shown) movable bi-directionally in an axis perpendicular to the media advance direction 1006. In another example the printheads are configured to span the entire width of the media 105 such that the printheads do not need to scan across the print zone, in a so-called page-wide array configuration. In one example the printheads are piezo inkjet printheads. In another example the printheads are thermal inkjet printheads. Where the print engine 1002 comprises multiple inkjet printheads each printhead may be configured to print with a different coloured printing fluid, such as different coloured printing inks. In one example, the print engine 1002 with may have five printheads each configured to print with one of a cyan (C), magenta (M), yellow (Y), black (K), and white ink. Ink may be supplied to each printhead by a suitable ink supply system (not shown).

The printing system 1000 provides a user interface 1012 through which a printing system operator can select to print a print job as a one-way vision image on a non-perforated transparent substrate.

Controller understandable programming instructions that, when executed or performed by the controller 1010 cause the controller 1 10 to produce a oneway vision printed image as described above, as stored in a suitable memory 1014. The memory 1014 may suitably be integrated with the controller 1010, or may accessible to the controller 1010 through a suitable communication bus (not shown).

In one example the printing fluids used by the print engine 1002 are latex- based inks, such as the Hewlett-Packard range of latex inks.

In one example the printing fluids used by the print engine 1002 are ultraviolet curable printing fluids, such as the range of Hewlett-Packard UV curable inks available from Hewlett-Packard Company, that are printed in liquid form and which are cured after printing through exposure to ultra-violet radiation from one or more UV radiation sources. In one example, one or multiple UV radiation sources are provided in proximity to the print engine to cure or pin (i.e. partially cure) printed UV curable ink. One advantage of the using the techniques described here is that because each of the different ink layers is printed by the same printing system during the same printing operation, alignment of the visual apertures is possible to a high-level of precision. Although the term transparent has been made herein, it will be appreciated that appropriate translucent substrates may be substituted for transparent substrates.

In other examples other suitable printing systems may be used for generating one-way vision films as described herein. For example, use may be made of suitable liquid electro-photographic (LEP) printing systems, such as the range of Hewlett-Packard Indigo presses. In other examples other suitable printing systems may be used.

It will be appreciated that examples and embodiments of the present invention can be realized in the form of hardware, software or a combination of hardware and software. As described above, any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are examples of machine-readable storage that are suitable for storing a program or programs that, when executed, implement examples of the present invention. Examples of the present invention may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and examples suitably encompass the same.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.