WO2018100150A1

WO2018100150A1 - Method and mask for manufacturing a watermarked paper, method for manufacturing the obtained watermarked paper mask and method for authenticating the watermarked paper

Info

Publication number: WO2018100150A1
Application number: PCT/EP2017/081175
Authority: WO
Inventors: Yvan Thierry; Stéphane Mallol
Original assignee: Oberthur Fiduciaire Sas
Priority date: 2016-12-02
Filing date: 2017-12-01
Publication date: 2018-06-07
Also published as: FR3059682A1; RU2019115980A3; CN110050098B; EP3548663A1; KR102556073B1; RU2748464C2; RU2019115980A; BR112019010857A2; CN110050098A; KR20190089898A; FR3059682B1; BR112019010857B1

Abstract

Method for manufacturing a security paper, including the step consisting in: - producing a watermark using a mask (10) attached to a wire of a paper machine, the mask including a network of elements for forming light areas (18) on the watermark connected by linking elements (15), said light areas being arranged like the pixels of a raster image, said linking elements being fined enough that at least some of said elements for forming light areas (18) result in the formation of pixels of the raster image appearing to the naked eye in transmitted light as isolated pixels.

Description

METHOD AND MASK FOR MANUFACTURING FILIGRANE PAPER, METHOD FOR MANUFACTURING THE MASK

FILIGRANE PAPER OBTAINED AND METHOD OF AUTHENTICATING THE FILIGRANE PAPER

The present invention relates to methods of making security papers and papers and papers thus obtained.

Watermarks have been used for a very long time in the field of secure documents and are formed during the manufacture of a paperboard substrate by a variation in the thickness thereof, by acting on the fiber deposition process and / or draining.

Many improvements have been made to the achievement of

10 watermarks.

The invention is more particularly concerned with watermarks reproducing a halftone image.

EPI patents 122360 B1 and EPI 252389 B1 of the applicant describe methods of manufacturing such watermarks, offered under the trademark Pixel Watermark by the

Applicant. The masks used in the production of such watermarks are conventionally obtained by machining or etching a metal plate. Such a method makes it difficult to produce parts of great accuracy, because the spatial resolution of the detail is generally at least 0.8 times the thickness. Thus, for a workpiece thickness of 0.5 mm, the openings achievable in it must be at least 0.4

20 mm.

Other publications also deal with the manufacture of watermarks of this type, namely WO2010 / 036104 A1, WO2011 / 117828 A1 or WO2011 / 081561 A1.

The application WO2013 / 140126 A1 discloses a filigree forming mask formed of a grid on which elements designed to form the grid are attached.

The watermark motif. The areas formed by the elements in the watermark appear

disconnected from each other, which is presented as an advantage to reproduce Arabic characters. There is no question of reproduction of a halftone image in this publication.

There is a need to further improve watermarks reproducing at

At least partially a raster image and the corresponding manufacturing processes, and

in particular increase the security provided by watermarks. The invention achieves this objective through a method of manufacturing a security paper, comprising the step of:

- Making a watermark using a mask fixed on a canvas of a paper machine, the mask comprising a network of elements forming clear areas on the watermark connected by connecting elements, said light areas being arranged as the pixels of a raster image, said connecting elements being sufficiently fine so that at least some of said light-zone forming elements lead to the formation of pixels of the raster image appearing to the naked eye in transmitted light as isolated pixels.

The expression "with the naked eye" means an observation by the human eye not paired and of normal acuity, at 25 cm distance, in daylight.

The invention makes it possible to produce visually attractive watermarks, and makes it possible to reinforce the security against counterfeiting, being difficult to imitate because of their definition which can be high.

Another advantage is to allow better dewatering of the paper during its formation.

While in the prior art, bridges or a frame, together hold the various elements placed and welded on the forming fabric with a relative positioning corresponding to the pattern to be reproduced, and remain visible when the watermark is observed at the same time. naked eye, in the invention at least some elements of the drawing of the watermark appear to the naked eye disconnected from each other, which allows the obtaining of new visual effects, perceptible to the man in the street, and extends the range of achievable patterns.

In particular, the aesthetic appearance can be improved by the visual impression of fluidity conferred by the constituent elements of the pattern. The watermark can be more easily recognized by the man in the street. It is thus possible to obtain watermarks of a new kind, made at least partly in the form of frames of dots or lines of lines connected to each other, as is currently the case with pixel-type watermarks, but in the form of clouds of points or clouds of lines whose junctions are no longer visible, or are not very visible.

The subject of the invention is also a watermark formation mask for implementing the method according to the invention, comprising a set of elements of formation of light areas connected by connecting elements, these light-zone forming elements being arranged like the pixels of a raster image, for example in the form of lines such as, by analogy, the lines called "intaglio" in the field of the ticket bank, the connecting elements being thin enough not to visually appear on the watermark, said bright area forming elements appearing to the naked eye in transmitted light as isolated pixels in the image.

Halftone image

By "raster image", it is necessary to understand an image formed by pixels arranged in a frame with a spacing and / or variable size to reproduce a halftone image. Several "gray levels" can be reproduced according to the density of the pixels, their size, their height and / or their amplitude, or even according to the local opacity of the paper at each pixel. In this case, said plurality of gray levels preferably produce a three-dimensional effect, for example a relief effect.

The halftone image preferably represents a monument, a landscape, an animal, a plant or a portrait. In particular, the halftone image can represent only a part of a monument, a landscape, an animal, a plant or a portrait.

In a variant, the screened image may represent any geometrical shape, forming in particular the bottom or part of the bottom of another image, for example of a monument, a landscape, an animal, a plant or a portrait. According to this variant, the raster image makes it possible to highlight the other image.

The pixels of the raster image are in particular indistinguishable from each other when the raster image is observed with the naked eye in transmitted light. They are especially distinguishable from each other when the raster image is observed with transmitted light magnification, for example with a magnification of at least 10 times, preferably at least 20 times. This is a second level security.

According to one variant, the pixels of the raster image are distinguishable from each other when observed with the naked eye in transmitted light, which constitutes first-level security.

pixels

By "pixel" is meant an individual element on the watermark pattern, by analogy with the pixels of a digital image. The pixels may have any shape, preferably being in the form of dots, in particular of points having a circular, oval or polygonal shape, or being in the form of lines, or being in the form of letters, alphanumeric characters, ideograms or symbols. The halftone image may include different pixel shapes.

The pixels constitute the raster elements of the raster image.

The halftone image may comprise pixels arranged at a frame angle, that is to say arranged in lines forming an angle with the horizontal.

The thickness of the raster elements may be between 200 and 1500 μιη.

In the case of pixels in the form of lines, the width of the frame elements, that is to say the lines, may be greater than 50 μιη, especially 70 μιη and preferably 100 μιη.

In the case of pixels in the form of dots, letters, alphanumeric characters or ideograms, the largest dimension, thickness not included, of the frame elements, that is to say pixels, may be greater than 50 μιη , in particular at 70 μιη and preferably at 100 μιη.

The frame may be amplitude modulated, i.e., the pixel size varies while the pixels are evenly distributed, or frequency modulated, or both. In particular, from a certain pixel size, the frame may be amplitude modulation and below frequency modulation.

The frame may be stochastic, for example with a fixed pixel size whose statistical frequency is varied to reproduce the different gray levels. The pixels can have the same geometry depending on the amplitude or, alternatively, the geometry of the pixels can change with the amplitude.

The arrangement of the pixels on the image is preferably generated by software, automatically.

Mask

The mask may be made of any suitable material, in particular metal and / or plastic.

The mask has thin linking elements.

These connecting elements leave no or very little, because of their fineness, visible traces on the watermark, and ensure the assembly and holding of the elements to form the visual pattern of the watermark. The connecting elements preferably have a thickness between 20 and 200 μιη, more preferably between 30 and 100 μιη. The thickness of the connecting elements is preferably constant.

The connecting elements preferably have a width of between 20 and 200 μιη, more preferably between 30 and 100 μιη. The width of the connecting elements is preferably constant.

The connecting elements preferably have a width and a thickness of between 20 and 200 μιη, more preferably between 30 and 100 μιη. The thickness and width of the connecting elements are preferably constant.

The connecting elements are preferably elongated elements. The connecting elements are preferably arranged in a grid. In this case the smallest dimension / meshes of the grid may be greater than 300 μιη, especially between 300 μιη and 5 mm, preferably between 500 μιη and 3 mm.

The connecting elements may in particular be arranged between the base and the top of the formation elements of clear areas that they connect. They are preferably arranged between the bases or between the vertices of the clear-zone forming elements that they connect.

The height of the bright area forming elements can be constant on the mask. In a variant, the height of the light-zone formation elements is variable on the mask, in order to influence the formation of the watermark and to obtain more or less dark pixels in transmitted light.

The clear zone forming elements are preferably made of the same material as the connecting elements. In particular, the light-zone forming elements and the connecting elements preferably constitute a monolithic piece, which gives the mask greater strength.

The mask may comprise, in at least one region, clear-zone forming elements arranged like the pixels of a halftone image, and at least one forming region of another type of watermark, in particular a region without formation of bright areas arranged like the pixels of a raster image. It is thus possible to obtain a somewhat hybrid watermark resulting from the superposition and / or the juxtaposition of at least one completely screened watermark and at least one conventional watermark such as a multiton watermark obtained by means of a relief, for example from a embossing, or an "electrotype" watermark. Such a "hybrid" watermark is particularly visually attractive. The halftone image of the watermark according to the invention can thus represent only a part of a pattern, the other part, in particular the complementary part, being represented by another type of watermark, notably a multiton watermark obtained by embossing. This is particularly advantageous when the watermark represents an image, preferably a monument, a landscape, an animal, a plant or a portrait, because according to a first variant the watermark according to the invention can represent only part of said image while the another part, in particular the complementary part, is represented by another type of watermark, in particular a multiton watermark obtained by embossing, and according to a second variant a multitone watermark, in particular obtained by embossing, can represent said image while the other part , in particular the bottom or part of the bottom of said image, is represented by the watermark according to the invention. The portion represented by the watermark according to the invention is then highlighted, or if not, it is used to highlight and highlight a portion or all of the other part of the watermark.

The mask may comprise a plurality of light-zone formation elements each appearing as a pixel isolated on the image, preferably with, in at least one region of the mask, a density of elements of between 30 and 80 elements per cm ² , giving for example as many isolated pixels on the resulting image.

The mask may comprise, in one region, clear-zone forming elements arranged like the pixels of a halftone image, and in another region, the formation openings of zones appearing darker than the light zones, these openings being also arranged as the pixels of a raster image. For example, the two regions respectively correspond to dark and light regions of the image. In between, the watermark may have areas where the pixels corresponding to the light areas meet and are no longer isolated in the image. The darker areas may have the same opacity as the vellum area, and may still be referred to as vellum minizones.

At least one of the clear-zone forming elements may have a larger dimension less than or equal to 0.3 mm, in particular between 0.1 and 0.3 mm.

Such a level of detail is particularly interesting to make it difficult to imitate the watermark thus obtained. If the light-zone-forming elements are of smaller size outside the thickness, for example of width, greater than 1 mm, it is possible to make holes of very small diameter, for example less than or equal to 0.3 mm, to ensure drainage at their level during paper making.

The bright area forming members may have a section undergoing amplitude modulation along a frame line of the image, thereby reproducing differently sized dots or lines of weft, and / or a height. undergoing amplitude modulation along a raster line of the image, thereby making dots or raster lines with varying opacity. In the latter case, it is thus possible to play not only on the distribution of the pixels but also on the local opacity, thus on the brightness of the pixels in transmitted light, which offers new possibilities in terms of final appearance of the watermark .

The spatial frequency of said light-area forming elements may be constant along at least one frame of the image. The spatial frequency of said light-area forming elements may further be variable along at least one frame of the image. It is possible to combine amplitude modulation of the section of the clear-zone forming elements, amplitude modulation of their height and / or modulation of their spatial frequency, in order to obtain the best rendition on the image.

Canvas

The web is the part of the paper machine that serves to form the fibrous mat by dripping a suspension of paper fibers.

It may be the fabric of a round or flat-table machine. Preferably, it is a round machine.

It is advantageous that the fabric has a housing facing outwardly of the fibrous mat in suspension, and that the mask is disposed in this housing. This makes it possible to protect the mask, to facilitate the positioning of the mask and to optimize the opacity variations (dark / light distribution) of the watermark. The latter may have been formed by an embossing of the canvas. Alternatively, the mask is disposed on the surface of the fabric without being in a hollow thereof, or even placed on a "positive" relief of the fabric.

The mask may be fixed by any means adapted to the fabric, being for example welded, in particular brazed, on the fabric, or else glued, crimped or mechanically fixed otherwise. The fabric and the mask can be made in such a way that the watermark comprises at least one screen area and one non-screen area. This is for example the juxtaposition and / or superposition of different types of watermarks, for example an embossing in the fabric and a mask according to the invention as described above.

The watermark may be used in conjunction with other security means such as security thread, security fibers or boards, introduced into the paper at the time of manufacture, or later. More generally, the watermarked paper according to the invention may comprise, in addition to the watermark, any additional security means. Among the additional security features, some are detectable to the naked eye, in daylight or artificial light, without the use of a particular device. These security elements comprise for example colored fibers or boards. These security elements are called first level.

Other types of additional security features are detectable only with a relatively simple device, such as an ultraviolet (UV) or infrared (IR) lamp, or a magnifying glass. These security elements comprise, for example, fibers, boards, particles or microtexts. These security elements may be visible to the naked eye or not, being for example luminescent under a lighting of a Wood lamp emitting in a wavelength of 365 nm. These security elements are said to be second level.

Other types of additional security elements require for their detection a more sophisticated detection device. These security elements are for example capable of generating a specific signal when they are subjected, simultaneously or not, to one or more external excitation sources. The automatic detection of the signal makes it possible to authenticate, if necessary, the document. These security elements comprise, for example, tracers in the form of active materials, particles or fibers capable of generating a specific signal when these tracers are subjected to optronic, electrical, magnetic or electromagnetic excitation. These security elements are said to be third level.

The additional security element (s) present in the paper according to the invention or the secure document according to the invention may have first, second and / or third level security features. The subject of the invention is also a process for manufacturing a mask according to the invention, in which the clear-zone forming elements and possibly the connecting elements are produced by an additive method. This provides a higher resolution than machining or chemical etching.

By "additive process" is meant a process by adding material, as opposed to a material removal process such as machining or etching.

Preferably, said light-zone forming elements and, where appropriate, the connecting elements are made by electroforming, which can offer a higher resolution than the chemical etching.

The connecting elements are preferably made by the same additive method as the clear-zone forming elements, and are thus monolithic with them.

Electro-forming makes it possible to easily achieve, if desired, variations in height amplitude of the light-zone forming elements, variations that can be done in a continuous or discrete manner, in order to give shades of gray in the watermark. »Additional.

The technique of electroforming allows a great precision in the realization of the elements of the mask. We can have details of the order of an isolated pixel of size 0.1 mm, and play on the spacing between the pixels to create a gradient. A detail value of 0.2 mm is particularly well suited to the resolution allowed by a paperboard substrate. The largest elements preferably have a size less than or equal to 0.8 mm. Beyond this value, the elements are preferably made with very fine drip holes, for example with a diameter of between 0.2 and 1 mm.

The finer details can be formed by bright areas, in transmitted light, on the watermark.

The subject of the invention is also a watermarked paper, obtained in particular by implementing the method as defined above, comprising a watermark having light areas arranged like the pixels of a halftone image, of which at least one clear zone appears. in transmitted light, to the naked eye, as a pixel isolated on the image. The watermark may include a plurality of such light areas.

The watermark may comprise at least one region where the pixels corresponding to the light areas are no longer isolated but meet. The watermark can still have at least one region with isolated pixels darker than the light areas, these darker pixels being arranged as the pixels of the raster image.

The watermark is preferably exclusively formed of bright areas arranged as pixels of a raster image.

The watermark may comprise a region having a density of light areas each appearing in transmitted light as an isolated pixel of between 30 and 80 per cm ² , this region preferably occupying more than 20 mm ² on the watermark.

Another subject of the invention is a method for authenticating a paper of the invention, comprising examining the watermark in transmitted light in order to detect the presence of a halftone image whose pixels appear as clear areas with at least one pixel isolated in the image, more preferably several pixels isolated in the image, especially along a frame line of the image.

The invention is suitable for the manufacture of all secure documents such as banknotes, passports, and other documents of value or identity.

The invention will be better understood on reading the following detailed description, non-limiting examples of implementation of the invention, and on examining the appended drawing, in which:

FIGS. 1A to 1E show details of watermark forming masks according to the invention,

FIGS. 2a to 2c are sections of examples of masks according to the invention,

FIG. 3 represents an example of a mask according to the invention,

FIG. 4 represents the resulting image, when the watermark is observed in transmitted light,

FIG. 5 represents a detail of FIG.

FIGS. 5a and 5b respectively represent another example of mask according to the invention and the resulting image, when the watermark is observed in transmitted light, and

- Figure 6 illustrates the establishment of a mask according to the invention in a housing of the fabric.

FIG. 3 shows an example of mask 10 according to the invention.

It comprises connecting elements 15 arranged in a grid, for example with meshes of constant section, each of square or rectangular shape in the illustrated example. In a variant, the connecting elements 15 are not arranged in a grid.

FIG. 1A shows an example of a mask.

The connecting elements 15 connect isolated light-zone forming elements 18 arranged as pixels of the raster image. These clear zone forming elements 18 are of larger size w.

The elements 18 may be placed on the intersections of the grid drawn by the connecting elements 15 and elsewhere.

FIGS. 1B to 1E illustrate the possibility of using non-circular contour elements for the pixels of the image.

They may be polygonal elements, for example rectangular, as illustrated in FIG. 1B, linear, as illustrated in FIG. 1C, or L-shaped as illustrated in FIG. 1D. We can have on the same support grid elements 18 of different geometry, as shown in Figure 1E.

The smallest dimension / meshes is for example greater than 300 μιη, in particular between 300 μιη and 5 mm, preferably between 500 μιη and 3 mm.

Referring to Figs 2a to 2c, it is seen that the thickness e _g the connecting elements 15 is lower than e _e bright areas forming elements 18. The connecting elements 15 can form strands that intersect orthogonally. Part of the strands may be oriented parallel to the frames of the image and the spacing between these strands may correspond to the spacing between the frames in the image.

The height e _e of the light-zone forming elements 18 may vary on the mask 10 as shown in FIGS. 2b and 2c. This can allow for more or less clear pixels, which increases the parameters on which it is possible to play to reproduce the image. Variation in the height of the clear-zone forming elements 18 may lead to a watermark that is more difficult to reproduce.

In the example considered in FIGS. 2a to 2c, the light-zone formation elements 18 have a variable section view in view from above, as a function of the size of the raster points to be reproduced on the image. The connecting elements 15 connect the bases of the light-zone forming elements 18 as shown in FIGS. 2a to 2c. In a variant, the connecting elements 15 connect the vertices of the light-zone forming elements 18.

The present invention is not limited to connecting elements 15 connecting the bases or the vertices of the clear-zone forming elements 18. Indeed, the connecting elements 15 can connect the clear-zone formation elements 18 at points other than their base or top. Alternatively, it may be a combination of the different cases of figures, the connecting elements 15 connecting the formation elements of clear areas 18 at their base and / or their top and / or other points.

It can be seen that certain light-zone forming elements 18 of the mask are isolated, and give on the watermark 30 obtained light areas appearing as isolated pixels 20, as illustrated for example in FIGS. 4 and 5. This is the case for example on the back of the helmet.

The zone 21 surrounding the pixels 20 may have the same thickness as the vellum zone 31. FIG. 6 illustrates the possibility for the fabric T receiving a mask 10 to have a housing 100.

The mask 10 is disposed in the housing 100, the connecting elements 15 bearing in the flat bottom of the housing 100 (Figure 6) or at least a portion of the light-zone forming elements 18 bearing in the flat bottom of the housing 100.

According to one variant, all the light-zone forming elements 18 and / or all the connecting elements 15 bear against the flat bottom of the housing 100. In particular, when the light-zone forming elements 18 are of variable height, such a configuration is for example possible thanks to a housing 100 whose bottom is not planar and / or through connecting elements which follow the relief of the formation elements clear areas.

The invention is not limited to the examples that have been given.

In particular, the watermark or watermarks according to the invention can be arranged on the paper so as to cooperate with other security elements such as son or foil.

The paper may be based on natural and / or synthetic fibers. Preferably, the paper comprises natural fibers such as flax and / or cotton fibers, especially cotton linters. The paper can be monojet or multijet. In the latter case, the jets can be colored differently.

Claims

A method of making a security paper, comprising the step of:

a watermark is produced by means of a mask (10) fixed to a web of a paper machine, the mask comprising an array of light-zone forming elements (18) on the watermark connected by elements of link (15), said light areas being arranged as the pixels of a halftone image, said connecting elements being sufficiently fine so that at least some of said light-zone forming elements (18) lead to the formation of pixels of the image. a raster image appearing to the naked eye in transmitted light as isolated pixels.

2. Method according to claim 1, the pixels being in the form of points, in particular points having a circular, oval or polygonal shape.

3. Method according to claim 1, the pixels being in the form of lines or being in the form of letters, alphanumeric characters, ideograms or symbols.

4. Method according to any one of claims 1 to 3, the fabric being that of a round shape.

5. Method according to any one of the preceding claims, the fabric (T) having a housing (100), and the mask (10) being disposed in this housing.

6. The method of claim 5, the housing having been formed by an embossing of the fabric.

7. Method according to any one of the preceding claims, the mask being welded or brazed on the fabric.

8. Method according to any one of claims 1 to 7, the fabric and the mask being made such that the watermark comprises at least one screen area and a non-screened area.

9. A method according to any one of the preceding claims, the height (e _e ) of the light-zone forming elements (18) being constant on the mask.

10. Method according to any one of claims 1 to 8, the height (e _e ) of the light-zone forming elements (18) being variable on the mask.

A watermark forming mask for carrying out the method according to any one of claims 1 to 10, comprising a set of light-zone forming elements (18) connected by connecting elements, these elements of forming light areas (18) being arranged as pixels of a raster image, the connecting elements (15) being sufficiently fine not to visually appear on the watermark, said light-area forming elements leading to the formation of pixels of the raster image appearing to the naked eye in transmitted light as isolated pixels in the image.

12. Mask according to the preceding claim, the height of the light-zone forming elements (18) being constant on the mask.

13. Mask according to one of claims 1 1 and 12, the height of the light-zone forming elements (18) being variable on the mask.

14. A mask according to any one of claims 1 1 to 13, comprising in at least one region of the clear-zone forming elements (18) arranged as the pixels of a raster image and at least one other region without training elements. bright areas arranged like the pixels of a raster image.

15. Mask according to one of claims 1 1 to 14, comprising a plurality of clear-zone forming elements (18) each appearing as a pixel isolated on the image, preferably with in at least one region of the mask a density of clear zone forming elements (18) of between 30 and 60 elements per cm ² .

16. Mask according to any one of claims 1 1 to 15, at least one of the formation elements of clear areas (18) having a larger dimension (w) less than or equal to 0.3 mm, in particular between 0.1 and 0.3 mm.

A mask as claimed in any one of claims 1-16, said light-area forming members (18) having a section undergoing amplitude modulation along a frame line of the image.

A mask according to any one of claims 1-17, said light-area forming elements (18) having a height ( _ee ) undergoing amplitude modulation along a frame line of the image. .

A mask according to any one of claims 11 to 18, wherein the spatial frequency of said light-area forming elements (18) is constant along at least one frame of the image.

20. A mask according to any one of claims 11 to 18, the spatial frequency of said light-zone forming elements (18) being variable along at least one frame of the image.

21. Mask according to any one of claims 1 1 to 20, the connecting elements (15) having a thickness (¾) between 30 and 200 μιη.

22. A method of manufacturing a mask according to any one of claims 11 to 21, wherein the light-zone forming elements (18) leading to the formation of pixels of the raster image appearing to the naked eye in transmitted light as pixels isolated in the image are made by an additive process.

23. Filigree paper, especially obtained by implementing the method according to any one of claims 1 to 10, comprising a watermark (30) having light areas arranged as pixels of a halftone image, including at least one zone light appearing in transmitted light as an isolated pixel (20) on the image.

24. Paper according to claim 23, the watermark being exclusively formed of light areas arranged as the pixels of a raster image.

25. Paper according to claim 23 or 24, the watermark having several light areas each appearing as an isolated pixel (20) on the image, in particular comprising a region having a density of light areas each appearing in transmitted light as an isolated pixel included between 30 and 80 per cm ² , this region preferably occupying more than 20 mm ² on the watermark.

A method of authenticating a watermark paper according to any one of claims 23 to 25, comprising examining the watermark in transmitted light to detect the presence of a halftone image whose pixels (20) appear as clear areas with at least one pixel isolated on the image, better multiple pixels isolated on the image, especially along a frame line of the image.