GB2428502A

GB2428502A - Data encoding pattern

Info

Publication number: GB2428502A
Application number: GB0514586A
Authority: GB
Inventors: Emiliano Bartolome; Andreu Gonzalez
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2005-07-18
Filing date: 2005-07-18
Publication date: 2007-01-31
Also published as: GB0514586D0

Abstract

A document has a data encoding pattern thereon having a higher resolution in the transverse direction x than in the longitudinal direction y. The pattern may be formed by dots 508 and dashes 510. The scale of the pattern may be determined from the grid spacings, the position of a pen being determined from the detected pattern and the scale.

Description

DATA ENCODING PATTERN

FIELD OF THE INVENTION

The present invention relates to the generation and processing of data encoding patterns, and has particular application in position identification patterns for application to a document or other product. Such patterns are made up of markings on the product, which can be detected by a suitable detection system, for example on a pen, and used to identify positions on the product, for example to detect pen strokes on a document. The product may be a form or other printable document such as a label or note pad.

BACKGROUND TO THE INVENTION

It is known to use documents having such position identification markings in combination with a pen having an imaging system, such as a CMOS camera, within it, which is arranged to image a small area of the page close to the pen nib, which is illuminated by an infra red LED. The IR wavelength is chosen as it is reflected by carbon based black ink. The pen includes a processor having image processing capabilities and a memory and is triggered by a force sensor in the nib to record images from the camera as the pen is moved across the document. From these images the pen can determine the position of any marks made on the document by the pen. The pen markings can be stored directly as graphic images, which can then be stored and displayed in combination with other markings on the document. In some applications the simple recognition that a mark has been made by the pen on a prede fined area of the document can be recorded, and this information used in any suitable way. This allows, for example, forms with check boxes on to be provided and the marking of the check boxes with the pen detected. In further applications the pen markings are analysed using character recognition tools and stored digitally as text. Systems using this technology are available from Anoto AB.

If the pattern is applied to the document using a high resolution method, such as offset printing, then there is considerable freedom as to the construction of the pattern. However, if the pattern is to be printed on lower resolution printers, such as laser jet or ink jet printers, then the pattern needs to be carefully designed so that it can be printed accurately enough to function.

WO 02/082366 discloses a system in which the scale of the pattern is selected to suit the printer on which it is to be printed.

SUMMARY OF THE INVENTION

The present invention provides a method of producing a document having a data encoding pattern thereon comprising: generating a data encoding pattern having a first direction and a second direction, the pattern having a higher resolution in the first direction than in the second direction; identifying a document to which the pattern is to be allocated; identifying first and second directions of the document such that the document is to be printed with a higher accuracy in the first direction than in the second direction; and printing the pattern on the document so that the first direction of the pattern is aligned with the first direction of the document.

In some embodiments the dimensions of the pattern in the second direction are substantially regular and the dimensions of the pattern in the first direction vary so as to encode data. In some embodiments the elements are arranged in rows which extend in the first direction and define gaps between the rows. In some embodiments the elements are of different widths in the first direction and the widths of the elements code positional information. In some embodiments the positions of the elements in the first direction code positional information. In some embodiments widths of the elements in the second direction are substantially equal. In some embodiments the gaps between the rows are substantially equal. In some embodiments the pattern codes data defining grid coordinates and data defining a grid scale.

In some embodiments the method further comprises: identifying a scale at which the printer will print the pattern, wherein the pattern is generated so as to encode an indication of said scale.

The present invention further provides a method of determining a position on a document, the method comprising: forming an image of a plurality of pattern elements making up a position identifying pattern on the document, determining grid coordinates of the position from the image; determining a scale of the pattern from the image, and determining the position from the grid coordinates and the scale.

In some embodiments the scale of the pattern on the document is determined from the scale ofan image of the pattern within an image of an area of the document. In some embodiments the size of the grid is determined from data encoded within the pattern. In some embodiments the method includes determining the scale of the pattern in each of two dimensions. In some embodiments the scale of the pattern is estimated directly from the image and then determined by matching the estimated scale to one of a plurality of predetermined scales.

The present invention further provides a product having a position encoding pattern printed on it, wherein: the pattern comprises pattern elements that are spaced apart in a longitudinal direction and a transverse direction; the elements are arranged in rows that extend in the transverse direction with longitudinal gaps between the rows; the longitudinal dimensions of the elements and longitudinal gaps are regular; the elements in each row define gaps therebetween in the transverse direction such that the elements and gaps have lateral dimensions; and the lateral dimensions code positional information.

The present invention further provides a system for generating a data encoding pattern to be printed onto a document, the pattern having a first dimension and a second dimension, and having a higher resolution in the first dimension than in the second dimension, the system being arranged to: identify a document to which the pattern is to be allocated; identify first and second directions of the document such that the document will be printed with a higher accuracy in the first direction than in the second direction; and associate the first dimension of the pattern with the first direction of the document.

The present invention further provides a system for producing a document having a data encoding pattern on it, the system being arranged to generate a pattern according to the method of the invention and print the pattern onto the product using a printer.

The present further provides a method of generating a position encoding pattern, the method comprising the steps of: identifying a printer that will be used to print the pattern on a document; identifying a scale at which the printer will print the pattern; and generating the code so that it encodes data identifying the scale.

Data carriers for carrying data arranged to control a computer system to carry out the methods of the invention and operate as the systems of the invention are also provided. The data carrier can comprise, for example, a floppy disk, a CDROM, a DVD ROM/RAM (including +RW, -RW), a hard drive, a non-volatile memory, any form of magneto optical disk, a wire, a transmitted signal (which may comprise an internet download, an ftp transfer, or the like), or any other form of computer readable medium.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a document according to an embodiment of the invention; Figure 2 is a schematic view of a computer system according to an embodiment of the invention arranged to produce, and to process information from, the document of Figure 1; Figure 2a is a diagrammatic representation of functional units of the system of Figure 2; Figure 3 is a schematic view of a pen according to an embodiment of the invention for use with the document of Figure 1; Figure 4 is a schematic representation of a printer of the system of Figure 2; Figure 5 shows in detail position encoding pattern on part of the document of Figure 1; Figure 6 shows in detail position encoding pattern on part of the document according to a further embodiment of the invention; Figure 7 shows allocation of areas of pattern space to a document according to a further embodiment of the invention; Figure 8 is an enlarged view of an imaged area of pattern in a system according to a further embodiment of the invention; Figure 9 is an enlarged view of an imaged area of pattern in a system according to a further embodiment of the invention; and Figure 10 is an enlarged view of an imaged area of pattern in a system according to a still further embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Figure 1 a document 100 for use in a digital pen and paper system comprises a carrier 102 in the form of a single sheet of paper 104 with position identifying markings 106 printed over substantially the whole of its surface to form a position identifying pattern 108. Also printed on the paper 104 are further markings 109 which are clearly visible to a human user of the document, and which make up the content of the document 100.

The content 109 will obviously depend entirely on the intended use of the document. In this case an example of a very simple two page questionnaire form is shown, and the content includes a number of boxes 110, 112 which can be pre-printed with user specific information such as the user's name 114 and a document identification number 116. The content further comprises a number of check boxes 118 any one of which is to be marked by the user, and two larger boxes 120, 121 in which the user can write comments. The form content also includes a send box 122, to be checked by the user when he has completed the questionnaire to initiate a document completion process by which pen stroke data is forwarded for processing, and typographical information on the form such as the headings or labels 124 for the various boxes 110, 112, 118, 120. The parts of the form which the user is expected to write on or mark, that is within the check boxes 11 8, the comments boxes 120, 121 and the send box 122, are defined as active areas of the form, and the pattern 108 that is printed within those areas needs to be identified to allow pen strokes made within those areas of the form to be identified as described below.

Referring to Figure 2, a very simple system for producing printed documents having the position identifying pattern on them comprises a personal computer (PC) 200 and a printer 202. The PC 200 has a screen 204, a keyboard 206 and a mouse 208 connected to it to provide a user interface 209 as shown generally in Figure 2a. As also shown in Figure 2a, the PC 200 comprises a processor 210 and a pattern allocation module 212 which is a software module stored in memory. The pattern allocation module 212 includes a definition of a total area of pattern space and a record of which parts of that total area have been allocated to specific documents, for example by means of coordinate references. The PC 200 further comprises a printer driver 214, which is a further software module, and a memory 216 having electronic documents 218 stored in it. The user interface 209 allows a user to interact with the PC 200.

In practice the various components of the system can be spread out over a local network or the internet. For example the pattern allocation module 212 can be provided on a separate internet connected server so that it can be accessed by a number of users.

Referring to Figure 3, a pen 300 for use with the document 100 comprises a writing nib 310, and a camera 312 made up of an infra red (IR) LED 314 and an IR sensitive sensor 316. The camera 312 is arranged to image a circular area adjacent to the tip of the pen nib 310. A processor 318 processes images from the camera 312 taken at a predetermined rapid sample rate. A pressure sensor 320 detects when the nib 310 is in contact with the document 100 and triggers operation of the camera 312. Whenever the pen is being used on a patterned area of the document 100, the processor 318 can therefore determine from the pattern 108 the position of the nib of the pen whenever it is in contact with the document 100. From this it can determine the position and shape of any marks made on the patterned areas of the document 100. This information is stored in a memory 322 in the pen 300 as it is being used.

Referring to Figure 4 the printer 202 is a laser jet printer, which includes a drum 400 which can be electro-statically charged in small discrete areas by directing a laser beam 402 at it. The laser beam 402 is scanned in a transverse direction along the drum 400 in a sequence of scanning paths as the drum rotates, and is turned on and off as it scans so as to select which areas of the drum are charged and which are not. An ink transfer roller 404 picks up ink from a reservoir 406 and brings it into contact with the drum 400. The ink is retained on the drum in the required areas which have been suitable charged, and not on other areas. Paper 408 is collected from a paper tray 410 and carried along a paper path 412 by a number of rollers.

At one point in this path, the paper is brought into contact with the drum 400. The paper moves with the surface of the drum as the drum rotates and the paper moves in the longitudinal direction along its path. Ink is transferred from the drum onto the paper to produce the required image, in this case the content and pattern on the document.

The timing of the pulsed laser beam 402 can be controlled very accurately so that the location of the pattern in the transverse direction on the drum can be very accurately controlled. As the paper can also be located accurately in the transverse direction, and tends not to move laterally as it passes through the printer, the lateral location of the pattern on the document can be accurately controlled. However, the positioning of the paper in the longitudinal direction, along its path through the printer, in particular relative to the rotational position of the drum 400, can generally not be controlled so accurately. This results in the printer having different accuracies in the longitudinal and transverse directions. In some cases the nominal resolution of the printer is the same in both directions, even though the accuracy is different in the two directions. However, in some cases the printer is arranged to have a lower resolution in the direction in which it has lower accuracy. In this example the resolution is 1200 dpi (dots per inch) in the lateral direction and 600 dpi in the longitudinal direction. Other typical examples are 2400 and 1200 dpi, 4800 and 1200 dpi, and 5760 and 1440 dpi.

The pattern 108 that is applied to the document 100 is therefore arranged to have different resolutions in the longitudinal and transverse directions. The resolution of the pattern in this case is not necessarily the same as the printer resolution, but refers to the minimum distance that needs to be distinguishable in the printed pattern. The smaller this distance is, the higher is the resolution of the pattern. Clearly the pattern can only be produced on a printer having sufficient resolution and accuracy in each direction. Referring to Figure 5 the pattern is built up around a square grid 500 of imaginary longitudinal and transverse grid lines 502, 504. These lines are not printed on the document and are not a visible part of the pattern, but are used to define the coordinate positions within the pattern.

The pattern is made up of pattern elements 506 which in this case comprise dots 508 and dashes 510. The dots 508 are approximately of the same size in both the longitudinal direction y and the transverse direction x. The dashes 510 are the same length or size as the dots 508 in the longitudinal direction y, but are wider, in this case about twice as wide, in the transverse direction x.

The pattern elements 508, 510 are arranged in rows 514 that extend across the document in the transverse direction x. In this case each row is located adjacent to a respective one of the transverse grid lines 504. At each intersection 512 between two lines 502, 504, there is either a dot 508, or a dash 510 or no pattern element. Where there is a dot it is to one side of the longitudinal grid line 502, and where there is a dash, it extends to either side of the longitudinal grid line 502. Therefore, the dimensions of the dots and dashes are substantially the same in the longitudinal direction y, and the gaps in the longitudinal direction y between the rows 514 of pattern elements are all nominally of the same width, although it will be appreciated that they will vary somewhat in width due to the low accuracy of the printer in the longitudinal direction. The longitudinal dimensions of the pattern therefore do not code any data. The transverse dimensions of the pattern elements and the gaps between them in the transverse direction x vary in a predetermined sequence which codes data, in this case positional data defining the coordinates of the pattern area in pattern space.

In this example because the resolution in the transverse direction x is l200dpi, this provides a printer dot spacing of approximately 21.161.tm. A grid spacing of 14 times that produces a grid spacing of about 296.33im.

The dots 508 are formed from groups of four printer dots, arranged approximately in a square, and the dashes are made up of eight printer dots in a 2x4 group. It will be appreciated that the pattern is not shown to scale in Figure 5. The resolution of the pattern in the transverse direction x, i.e. the minimum distance over which the printer needs to be able to consistently and recognizably produce a mark or leave a gap, is about 42J1m. This is the difference in size between the dots and dashes, which the camera in the pen must be able to distinguish to read the pattern. In the longitudinal direction y, the resolution of the pattern is equal to the grid spacing, as the pen only needs to be able to distinguish one row of pattern elements 506 from the next to be able to read the pattern successfully.

It will be appreciated that the resolutions of the pattern in the longitudinal and transverse direction y, x also determine the accuracy with which the pen will be able to determine its position on the document in those directions. This is because the resolution of the pattern corresponds to the resolution of the printer in each dimension. Therefore, even if the camera on the pen has a high resolution, and could determine its position to much higher accuracy, the processor on the pen can only assume that the positioning of the pattern elements is accurate to within a distance corresponding to the resolution of the pattern in each dimension. Therefore the pen will be able to determine its position in the transverse direction more accurately than in the longitudinal direction.

In order to produce the printed document 100 the processor 210 retrieves an electronic document 218 from the memory 216 and sends it to the printer driver. The electronic document 21 8 contains a definition of the content 109, and the areas of the document 100 which are to have the pattern 108 printed on them. The printer driver 214 first determines the orientation in which the document will be passed through the printer as it is printed. This determines which will be the longitudinal axis and which the transverse axis of the document as it is printed. Typically if the document is to be printed on A4 paper the paper will pass through the printer in a longitudinal orientation, that is with the narrower top or bottom edge leading. This means that the longitudinal axis is aligned with the longer sides of the document. In this case the rectangular area of pattern to be allocated to the document needs to be defined so that its longer sides extend in the longitudinal direction y of the pattern, as indicated in Figure 5, and its shorter sides extend in the transverse direction x. However, it may be that the printer is set up to pass the paper through the printer in a transverse orientation, i.e. with one of its longer sides leading. In this case the orientation of the required area of pattern will need to be arranged so that its longer sides extend in the transverse direction x of the pattern and its shorter sides extend in the longitudinal direction y.

Once the size of the required pattern area is determined, the printer driver requests the required amount of pattern from the pattern allocation module 212 which allocates by means of coordinate references an area of the pattern space to the document. The pattern allocation module then generates the pattern 108 for that area using a pattern generation algorithm, and communicates the details of the pattern including the positions of all the required dots and dashes, back to the printer driver 214. The printer driver 214 then combines the content 109 and the pattern 108 into a single file which contains an image including the pattern and the content, converts the content 109 and the pattern 108 to a format suitable for the printer 202, and sends it to the printer which prints the content 109 and the pattern 108 simultaneously as a single image.

Although the coordinates of the pattern space are allocated initially, the generation of the pattern that encodes the coordinates is carried out as a separate step. In this embodiment, the orientation of the pattern on the document can be selected after the allocation of an area of pattern space to the document, and after it has been determined which direction on the document will be printed with higher and which with lower accuracy.

When the pen 300 is used to write on the document the image from the camera 312 is sampled at a regular rate of around 50Hz. Each sampled image is analysed by the processor 318 on the pen to determine the coordinates within pattern space of the pattern in the image. These coordinates are then used to identify the document that is being marked by the pen, and the position on that document.

In order to determine the coordinates of the imaged pattern area, the processor 318 analyses the image to identify the dots 508 and dashes 510, their positions within the image, and the orientation of the dashes. From this the processor 318 identifies the positions of the grid lines 502, 504 and intersections 512, and the longitudinal and transverse directions y, x of the pattern. It then identifies, at each intersection 512 whether there is a dot 508, a dash 510, or neither, and from this data it can identify the coordinates of the area of pattern space. In order to identify the position of each dot 508 and each dash 510, the processor 318 only needs to be able distinguish, in the longitudinal direction y, which row 514 of dots and dashes each dot 508 and dash 510 is in. It therefore only needs to be able to locate each of the pattern elements to the nearest transverse grid line 504.

In the transverse direction x, the processor 318 needs to be able to identify the dimensions of the pattern elements, and consequently also of the transverse gaps between them, to the nearest dot width. This enables it to distinguish between dots 508, dashes 510, and spaces.

The number of grid intersections 512 that need to be imaged to uniquely identify the position depends on the total size of the defined pattern space.

In this case the camera can image an area about 3mm in diameter, and an area of six by six intersections is sufficient to uniquely identify the position.

Referring to Figure 6, in a second embodiment of the invention, the pattern is the same as in Figure 5 with longitudinal and transverse grid lines 602, 604. The only difference is that, in this embodiment, each intersection has a dot 608 associated with it, but the dots can be in any of three positions, those positions being spaced apart in the transverse direction. Specifically, the dot can be adjacent, and below, the longitudinal grid line 602 of the intersection, half way between the grid line and the next, or adjacent and above the next grid line. This pattern is used in exactly the same way as that of Figure 5, except that the camera of the pen reading the pattern needs to identify the positions of the dots rather than to distinguish between dots and dashes. It will be appreciated that this pattern can also code the same amount of data per unit area as that of Figure 5, since in both cases each intersection can have one of three possible values' or pattern element options associated with it.

In the embodiments described above, it is assumed that the scale of the pattern is constant. This means that, once the pattern space coordinates have been identified, the exact location on the document can be determined.

For example if the coordinates of the top left corner of the document are known, then the horizontal and vertical distances from that point can be determined directly from the coordinates in pattern space of any point on the document. In a third embodiment of the invention, the scale of the pattern as printed on the document is allowed to vary depending on the resolution of the printer that is used to print it. This means that the size, in pattern space, of the area of pattern printed on a document will depend on the printer.

Referring to Figure 7, when a document 700 is to be printed the printer driver determines the size, in real space, of the area 702 of pattern that is required, i.e. the area of the document 700 that is to have pattern printed on it. This information is included in the electronic file defining the document 700. It then determines the resolution of the printer that has been selected to print the pattern on the document. This information can be stored in a table of available printers and their associated resolutions. From this the printer driver determines the scale at which the pattern is to be printed, which will typically be the highest resolution that the printer can print. For example, in this case the printers are selected from two types, one of which has a resolution of 1200 by 600 dpi, and the other of which has a resolution of 2400 by 1200 dpi. For printers of 1200 by 600 the pattern is printed with a grid spacing of 296.33tm in each dimension as described above. This will require an area 704 of pattern space. For the printers of resolution of 2400 by 1200 dpi it is printed with a grid spacing of half that, i.e. about 148.l6Iim, and requires a larger area of pattern space 706, which is four times as large. Therefore the pattern allocation unit 212 allocates a suitably sized area of pattern to the document and records this allocation, together with an indication of the scale at which the pattern will be printed.

Referring to Figure 8, a pen, which is similar to that of Figure 3 but programmed with different software to carry out the analysis of the captured images, is used on the document. In order to determine its position on the document the pen needs to be able to identify the position in pattern space of each imaged area of pattern, but also the scale at which the pattern has been printed. In order to do this the pen analyses each image 800 of the pattern to determine the scale of the pattern as it appears in the image. In order to do this it identifies the positions of the dots 802 and dashes 804 in the image, and determines from them the notional positions of the grid lines 806, 808 in the image. Since it can be assumed that the camera is approximately a fixed distance from the surface of the document, the grid spacing in the image should match to one of a number of possible spacings corresponding to the different possible printer resolutions, and hence different grid spacings in real space on the document. The pen therefore has stored in memory a table of possible grid spacings that can be produced from a known set of available printers. The processor on the pen selects the possible grid spacing that most closely matches that in the image, and from that determines the scale at which the pattern has been printed. From this information, together with one reference position that identifies a specific point on the documentwith a specific point in pattern space, such as the coordinates of the top left hand corner of the document, the pen can determine the position of any point on the document from the pattern that is printed on it.

During use of the pen the pen generates pen-stroke data that comprises a sequence of coordinates each with a time stamp. This sequence enables the strokes of the pen on the document to be reconstructed by the computer analysing the data. in this embodiment, the pen uses the scale of the pattern that it has determined to convert the pattern into positional coordinates in real space on the document. However, in a modification, the pen can transmit the pen-stroke data as a sequence of pattern-space coordinates together with an indication of the scale of the pattern. The application processing the pen stroke data can then convert the pattern space coordinates into real positions on the document for processing.

Clearly the number of different pattern scales or resolutions that can be distinguished will depend on the resolution of the camera in the pen. If the camera has sufficient resolution it is possible for the pen to distinguish between, for example, grid spacings of, for example, 14 times the resolution of a 600dpi printer and 14 times the resolution of a S76dpi printer.

In a further embodiment, the scale of the printed pattern is again allowed to vary depending on the printer with which it is printed, but in this case data encoded in the pattern is used to identify the scale with which it is printed.

Referring back to Figure 5, in the example described above, it is assumed that any area of six by six grid intersections and the pattern elements 506 associated with them is unique within the total area of pattern space that is defined. However, if the camera in the pen can image a larger area of pattern, such as a square of seven by seven, or eight by eight grid intersections, then this allows the pattern to encode other data apart from positional data. In this case that additional data includes an indication of the scale at which the pattern is printed. In order to achieve this, when the pattern allocation unit generates the pattern to be allocated to the document, it identifies the coordinates of pattern space that are to be allocated and also the scale at which it is to be printed. It then selects an identifier that identifies the scale at which the pattern will be printed on the identified printer. The pattern allocation unit then generates the pattern so as to encode both the coordinates and the scale identifier. When the pen analyses the pattern from the camera images, it extracts from the pattern the positional data, i.e. the coordinates in pattern space of the imaged pattern, and also the scale identifier that identifies the scale at which the pattern has been printed. From this information, and at least one reference point on the document having known pattern coordinates, it can determine the position on the document of each imaged area of pattern.

In a further embodiment of the invention, referring back again to Figure 5, the scale of the pattern in the longitudinal direction is fixed, but the scale in the transverse direction is variable depending on the printer used to print the pattern. In this case the printer can be selected from one having a resolution of 2400 by 1200 dpi, and one having a resolution of 4800 by 1200 dpi. If the 2400 by 1200 dpi printer is used, then the pattern is the same as that shown in Figure 5, except that the scale is reduced by half in both dimensions, so the grid spacing is of the order of 150tm. If the 4800 by 1200 dpi printer is used, then the longitudinal grid spacing is the same, i.e. about 150j.tm, but the transverse grid spacing is smaller, in this case only 75im. Therefore the dimensions of the pattern in the longitudinal direction are the same in both cases, but the transverse dimensions of the pattern, i.e. the size of the pattern elements and the gaps between them in the transverse dimension, are half as big for the higher resolution printers as they are for the lower resolution printers.

In this case when the processor in the pen analyses the captured images of the pattern, it can determine the scale at which it has been printed by the relationship between the grid spacing in the longitudinal and transverse directions. In this case if the transverse grid spacing is equal to the longitudinal grid spacing, then this is taken as an indication that the pattern has been printed with a transverse grid spacing of about l50tm and the dimensions of the pattern elements in the transverse direction can be interpreted accordingly to extract the positional and other data from the pattern. If the grid spacing in the transverse direction is half of that in the longitudinal direction, then this indicates that the transverse grid spacing is about 75.tm and the dimensions of the pattern elements in the transverse direction can be interpreted accordingly.

Referring to Figure 9, in a further embodiment of the invention, a position identifying pattern is again built up around a grid of imaginary longitudinal and transverse grid lines 902, 904, with a pattern element in the form of a dot 906 at each intersection 908 between the grid lines. In this case each dot can be in one of six different positions. They can be on either side of the transverse grid line 904, and they can be on either side of, or centrally located on, the longitudinal grid line 902. Therefore resolution of the pattern in the transverse direction x is half the width of the dot 906, since its position must be accurate to the nearest half dot width. In the longitudinal direction y the resolution of the pattern is twice that in the transverse direction, and equal to the width of the dots 906.

In this arrangement, the position of each dot in the longitudinal direction can code one bit of information, as it can have one of two positions in the longitudinal direction. In the transverse direction each dot can code one and a half bits of information, as it can be in any of three positions in the transverse direction. Therefore transverse dimensions of the pattern code more data than the longitudinal dimensions of the pattern. As with the previous embodiments, the pattern is printed so that the longitudinal direction y of the pattern is aligned with the longitudinal direction of the document on which it is printed, i.e. the direction in which that document passes through the printer. Therefore the higher resolution direction x of the pattern is aligned with the higher resolution direction of the printer, and the lower resolution direction y of the pattern aligned with the lower resolution direction of the printer.

Referring to Figure 10, in a still further embodiment of the invention, the pattern is similar to a combination of the patterns of Figures 5 and 6. At each grid intersection 1000 there is either a pattern element 1002, which can be a dot 1004 or a dash 1006 or a space with neither a dot nor a dash. If the element is a dot 1004, it can be in either of two positions spaced apart in the transverse direction x, on either side of the longitudinal grid line 1007. The pattern elements 1002 are arranged in transverse rows, with all of the elements in each row being aligned in the longitudinal direction. The elements are also the same size in the longitudinal direction apart from a number of timing elements 1008. These timing elements 1008 are spaced apart through the pattern at regular intervals, and each one comprises a dash that extends in the longitudinal direction y rather than the transverse direction x. Each of the dots 1004 is substantially the same size in both the transverse and longitudinal directions. The dashes 1006 are twice as long in the transverse direction as they are in the longitudinal direction. However, the timing elements 1008 are four times as long in the longitudinal direction as the dots 1004. The purpose of the timing elements is to enable the pen to identify specific grid lines in the pattern, which helps to ensure that the pattern is read accurately.

The resolution of this pattern in the longitudinal direction is again lower than that in the transverse direction, since in the longitudinal direction only the difference between one row of elements and the next, and the difference between the timing elements and the other elements needs to be distinguished. The resolution is therefore four times the dot width. In the transverse direction the resolution is equal to the dot width.

Although the embodiments described above include a laser jet printer, it will be appreciated that other types of printer also have different resolutions in the longitudinal and transverse directions. For example in an inkjet printer, where the print head is moved in the transverse direction across the document, the position of the print head can be controlled more accurately than the position of the paper in the longitudinal direction. The embodiments described above are therefore equally applicable to inkjet printers.

Tn some cases, it can be the case that the printer has a higher accuracy in the longitudinal direction, i.e. the direction in which the media passes through the printer, than in the transverse direction. In this case the pattern will need to be arranged such that the higher resolution direction of the pattern is aligned with the longitudinal direction of the printer during printing.

Claims

DATA ENCODING PATTERN CLAIMS

1. A method of producing a document having a data encoding pattern thereon comprising: generating a data encoding pattern having a first direction and a second direction, the pattern having a higher resolution in the first direction than in the second direction; identifying a document to which the pattern is to be allocated; identifying first and second directions of the document such that the document is to be printed with a higher accuracy in the first direction than in the second direction; and printing the pattern on the document so that the first direction of the pattern is aligned with the first direction of the document.

2. A method according to claim 1 wherein the dimensions of the pattern in the second direction are substantially regular and the dimensions of the pattern in the first direction vary so as to encode data.

3. A method according to claim I wherein the elements are arranged in rows which extend in the first direction and define gaps between the rows.

4. A method according to claim 1 wherein the elements are of different widths in the first direction and the widths of the elements code positional information.

5. A method according to claim 1 wherein the positions of the elements in the first direction code positional information.

6. A method according to claim I wherein widths of the elements in the second direction are substantially equal.

7. A method according to claim 3 wherein the gaps between the rows are substantially equal.

8. A method according to claim 1 wherein the pattern codes data defining grid coordinates and data defining a grid scale.

9. A method according to claim I further comprising: identifying a scale at which the printer will print the pattern, wherein the pattern is generated so as to encode an indication of said scale.

10. A method of determining a position on a document, the method comprising: forming an image of a plurality of pattern elements making up a position identifying pattern on the document, determining grid coordinates of the position from the image; determining a scale of the pattern from the image, and determining the position from the grid coordinates and the scale.

11. A method according to claim 10 wherein the scale of the pattern on the document is determined from the scale of an image of the pattern within an image of an area of the document.

12. A method according to claim 10 wherein the size of the grid is determined from data encoded within the pattern.

13. A method according to claim 10 including determining the scale of the pattern in each of two dimensions.

14. A method according to claim 10 wherein the scale of the pattern is estimated directly from the image and then determined by matching the estimated scale to one of a plurality of predetermined scales.

15. A product having a position encoding pattern printed on it, wherein: the pattern comprises pattern elements that are spaced apart in a longitudinal direction and a transverse direction; the elements are arranged in rows that extend in the transverse direction with longitudinal gaps between the rows; the longitudinal dimensions of the elements and longitudinal gaps are regular; the elements in each row define gaps therebetween in the transverse direction such that the elements and gaps have lateral dimensions; and the lateral dimensions code positional information.

16. A system for generating a data encoding pattern to be printed onto a document, the pattern having a first dimension and a second dimension, and having a higher resolution in the first dimension than in the second dimension, the system being arranged to: identify a document to which the pattern is to be allocated; identify first and second directions of the document such that the document will be printed with a higher accuracy in the first direction than in the second direction; and associate the first dimension of the pattern with the first direction of the document.

17. A system for producing a document having a data encoding pattern on it, the system being arranged to generate a pattern according to the method of claim 15 and print the pattern onto the product using a printer.

1 8. A method of generating a position encoding pattern, the method comprising the steps of: identifying a printer that will be used to print the pattern on a document; identifying a scale at which the printer will print the pattern; and generating the code so that it encodes data identifying the scale.

19. A data carrier carrying data arranged to cause a system to perform the method of claim 1.

20. A data carrier carrying data arranged to cause a system to perform the method of claim 10.

21. A product having a data encoding pattern thereon substantially as hereinbefore described with reference to any one or more of the accompanying drawings.

22. A method of generating a pattern for application to a document substantially as hereinbefore described with reference to any one or more of the accompanying drawings.

23. A system for generating a pattern for application to a document substantially as hereinbefore described with reference to any one or more of the accompanying drawings.