GB2422467A

GB2422467A - Surface pattern for encoding location and page identification

Info

Publication number: GB2422467A
Application number: GB0501245A
Authority: GB
Inventors: Guy De Warrenne Bruce Adams; David Neil Slatter
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2005-01-21
Filing date: 2005-01-21
Publication date: 2006-07-26
Anticipated expiration: 2025-01-21
Also published as: GB2422467B; GB0501245D0

Abstract

An optically detectable encoding layout for a surface comprises a plurality of location markings 8 spaced across the surface according to a notional location lattice 10, with the markings encoding for local position on the surface, and one or more page identification markings 14 within the interstitial areas formed by the location lattice. Both types of markings may carry data either by virtue of their position, or by virtue of some other detectable characteristic such as shape. The invention may be used in digital paper applications.

Description

SURFACE PATTERN FOR ENCODING LOCATION AND PAGE

IDENTIFICATION

Technical Field

The present invention relates to a surface pattern for encoding location and page identification. Particularly, although not exclusively, the invention relates to an optically detectable encoding layout to be printed onto a sheet of conventional paper. The result, sometimes known as digital paper, is designed to be written on with a pen which incorporates a small camera directed at a local area of the paper adjacent to the writing tip. As the user writes, the printed pattern within the local area is analysed to determine both the x, y, position of the writing tip on the page, as well as a unique page identifier.

Back2ronnd Art There are a number of types of optically detectable patterns or codes which can be printed onto a surface and can be used to encode digitised data. Such optically detectable codes are sometimes known as glyphs. A glyph may be defined as an optically detectable character or mark which carries encoded data by means of a distinguishable characteristic such as shape. Data may also be encoded by means of location on the surface with respect to a predefined notional lattice or grid.

Of particular importance to digital paper applications, are patterns which encode for local position.

An example of position encoding patterns is given in US patent 6,548,768 to Anoto AB. According to 768, the encoding pattern is a combination of the position of a visible dot in relation to an invisible virtual grid vertex reference point. The layout of the virtual grid is defined by the overall arrangement of the visible dots and is deduced by imaging a number of dot locations. The actual data is decoded by determining the position of the visible dot in relation to its virtual grid vertex reference point. For four dot positions around the grid vertex, four unique values can be encoded in any one grid position.

Another approach is described in European Patent 057 8692 to Bums and Lloyd. This determines x and y position using patterns that form part of two orientable binary sequences. Other approaches are described in US Patent 5051 736 to Bennett et a!, US Patent 5661 506 to Lazzouni Ct al, and US Patent application 2004/0031852 to Boitsov at el.

A further system for encoding position information is disclosed in US Patent Application 10/695,452 In addition to location information, it may also be desirable to encode some unique identifier which specifies the actual page or sheet being used. With a large enough set of sheet identifiers available, an organisation may wish to encode uniquely every page of every data-entry form that is in use.

Alternatively, a page identifier could be used to identify uniquely the specific page number within a pre-printed pad of sheets, and also if desired the specific pad from which that sheet has been taken.

One existing publication which addresses the issue of sheet identifiers is PCT application WO 99/50787 (Xerox Corporation). This provides a pattern that is split up into small areas which are repeated across the sheet. Each individual area is split up into three separate zones, a first zone specifying the area location, a second zone containing a sheet identifier, and a third zone which has a sheet orientation marker. As the pen is moved across the paper, it records and processes not only local positional information, but also information on the sheet location and the sheet identifier.

One problem with such encoding arrangements is that the viewing area of the camera within the pen has to be relatively large, which increases the need for significant processing power to decode the patterns. This not only increases the cost and complexity of the pen, but means that battery life can be limited.

A large field of view also requires relatively complex andlor expensive optics to ensure high quality imaging. The encoding arrangement shown may also be relatively visually intrusive to the user, as a result of the horizontal stripes created by the repeating page identifier information.

Another problem relates to the time taken to generate and print such patterns.

Typically, the pattern has to be generated a new as a complete image, for each page, and then merged with any content (such as text or images) that needs to be printed at the same time. This process can take a significant period due to a combination of both the amount of processing required and the time taken to transfer the output to the printer.

Disclosure of the Invention

According to the present invention, there is provided an optically detectable encoding layout for a surface, the layout comprising: (a) a plurality of location markings spaced across the surface according to a notional location lattice, the markings encoding for local position on the surface; and (b) one or more secondary markings within the interstitial areas formed by the location lattice, the secondary markings encoding for page identification Either or both of the location markings and the secondary markings may carry data by virtue of an optically detectable characteristic such as shape, size, orientation, intensity, colour, type of ink and so on. Alternatively or in addition either or both types of marking may carry data by virtue of their position with respect to the location lattice, or in other words according to their physical location on the surface or page. In a preferred embodiment, the layout includes an additional printed fixed grid of grid markers, these being used to define the physical locations at which the locations markers and the secondary markers may be positioned. Preferably, either or both of these markers may be positioned on the crossing points of a notional secondary lattice within the interstitial areas of the fixed grid.

Typically, both the location lattice and the secondary lattice will be square, although other regular lattice topology such as rectangular, triangular or hexagonal are not excluded.

By separating the location information and the page identifier in the way described, many aspects of digital pen and paper solutions can be simplified.

At any location on the page, both the x, y position and also the page id are immediately available. This allows the pen to stop processing the page id pattern shortly after initial contact has been made, and to concentrate all available processing power on the determination of x, y location. The proposed layout requires only a small field of view for the camera thereby simultaneously reducing the amount of processing power needed for image analysis and also the complexity and cost of the physical optics.

The preferred encoding arrangement is visually non-intrusive to the user, as the pattern density is fairly uniform in both the horizontal and vertical directions.

The invention further extends to a printed or manufactured article, such as a sheet of paper, which carries on its surface an optically detectable encoding layout as previously described.

The invention further extends to a method of creating a plurality of individually-identifiable articles, comprising: (a) generating in computer memory a first representation of a plurality of location markings to be spaced across a surface according to a notional location lattice, the markings encoding for local position on the surface; (b) generating in computer memory a second representation of one or more secondary markings to be located within the interstitial areas formed by the location lattice, the secondary markings encoding for a specific article; (c) merging the first and second representations, and applying the resultant merged encoding layout to the said specific article; and (d) repeating steps (b) and (c) for subsequent articles.

By separating out in this way the location information and the page id information, generation of the overall layout speed of printing can both be improved. The markings representative of the location need to be generated only once, regardless of the number of sheets to be printed. The page identification markings of course need to be generated anew for each page, but typically only a few such markings are required which are then simply repeated across the surface of the page. To print second and subsequent sheets, it is necessary only to generate a small new page identification pattern, to replicate that, and to merge that either before or during printing with the previously prepared location markings.

Brief Description of the Drawings

The present invention may be carried into practice in a number of ways, and several specific embodiments will now be described by way of example with reference to the drawings, in which: Figure 1 illustrates a first embodiment of an encoding layout according to the present invention, in which each dot encodes data by virtue of some property such as shape; Figure 2 shows a second embodiment in which data is encoded by positioning the dots at particular locations with respect to a predefined notional grid; Figure 3 shows in enlarged form part of the Figure 2 layout, illustrating a possible positioning of one of the dots providing page identifier information with respect to a fixed printed grid.

Best Mode for Carrying out the Invention

An optically detectable encoding layout according to a first embodiment of the invention is shown schematically in Figure 1. In this embodiment, the surface to be encoded has printed onto it two different classes of glyph or marking, the first encoding for position on the page and the second for the page number.

These two classes of marking are shown in Figure 1 with conventional symbols but it will be understood that in practice the individual markings may be printed in a variety different forms according to the encoding method that is chosen. For example, the individual markings could carry data by virtue of their shape, size, orientation, intensity, colour or indeed any other optically detectable characteristic that may be used distinguish one marking from another. The simplest type of coding is a binary marking system, for example using a small dot to indicate a 0 and a large dot to indicate a 1. Where the markings are encoded by a shape, an alphabet may be used to achieve the encoding, for example as is disclosed in US Application 10/693,649, the contents of which are incorporated by reference.

The data encoding layout may be printed with a conventional ink or with some ink that can be detected in the non visible region, such as infra red. It is not essential that the pattern is visible to the naked eye, and indeed in some applications there may be advantages in printing an ink which is not clearly visible. The use of an ink which is absorbing in the infra red region allows the paper to be overprinted as desired with any visible non infra red absorbing ink, without the overprinting affecting the operation of the invention.

Turning first to Figure 1, the position markings 8 are set out in a lattice or grid arrangement, shown in the figure by the notional horizontal and vertical lines or rulers' 10. It will be understood that these lines are not actually printed, but are shown in the figure merely for clarity.

The location lattice defines within it a series of interstitial areas 12, within which are printed one or more page number markings 14. These markings encode the page number, and since that will by definition be constant across the entire sheet, the markings within a given interstitial area 12 are simply repeated both horizontally and vertically. Thus, the page number markings in each of the interstitial areas will be the same.

The size of the markings and the spacing of the location grid may be chosen according to the application in hand, but in a typical digital paper example, where the markings are printed onto paper, the typical lattice spacing may be around 0.5mm, with the typical dot or marking size being around 85 micrometres.

In operation, a user writes onto a sheet of paper carrying this encoded pattern using a pen having a built-in camera adjacent the writing tip. The camera has a field of view which, in the example shown, has enough extent to capture sufficient position markings to enable successful decoding of the data contained in at least four markings both horizontally and vertically. As the user writes with the pen, the information from the changing field of view is digitised and image processing software is used to decode the corresponding changing patterns. By reading the characteristics of the position markings, the x, y position of the pen on the page can uniquely be determined. Likewise, by reading the characteristics of the page number markings, the page or sheet identifier can be uniquely determined.

In order to minimize the field of view required, a suitable binary sequence for the position encoding may be chosen whereby the pen location may be determined even when the field of view spans two adjacent location lattice areas. Encoding methods such as Dc Bruijn sequences can provide the ability to uniquely locate a short binary sequence within a larger binary number.

Since the page number markings 14 are repeated across the surface, the unique page identifier can be determined very quickly, as soon as the pen is placed anywhere on the page, and with no movement being required. Once the software has identified the page, the page number markings 14 are then ignored during the remainder of the writing stroke, allowing the image processing software to concentrate entirely on constantly updating the x, y location information using the position markings 8. The software may be programmed to check the page number again whenever the pen is lifted from the page for a sufficiently long predefined interval. If the pen is lifted for a very short time interval, for example between the user writing the body of the letter t and writing the cross stroke, there may be no need to check the page number again as there will have been insufficient time for the user to have turned a page. Additional page- number checking at intervals may improve robustness.

A sequence of pages having encoding patterns of the type shown in Figure 1 can be both generated and printed relatively rapidly. First, it will be noted that the lattice of position markings 8 is constant from page to page, and does not therefore need to be regenerated for each page. Second, the unique page identifier for a given page is defined solely by those markings 14 within one interstitial area 12. Once those markings have been generated for a particular page, they can then be repeatedly printed across the page in much the same way as predefined characters.

What has been described so far is an embodiment in which the individual markings carry data by virtue of some characteristic such as size, shape, orientation and so on. An alternative possibility is to encode data by means of the position of the markings. That possibility will now be discussed.

Turning to Figure 2, there is shown an alternative embodiment in which both position and page number data are encoded by the position of the markings with respect to a predefined fixed lattice or grid. In this embodiment, the markings may be defined by printed dots with a diameter of typically 85 micrometres, that is 300 dpi.

In the Figure 2 embodiment, the page number information is encoded by the position within the area 12 of one or more of the page number markings 14.

The exact location of each individual page number marking 14 is defined with respect to a printed fixed grid of dots 26. Between every group of 4 dots on the fixed grid, there is a single page number marking.

The positional encoding of the page number markings is shown in more detail in Figure 3 which represents a blown-up portion of the area 12 between any four of the fixed grid dots 26. The page number marking 14 is positioned so that it falls on one of the intersections of a smaller notional grid, as shown.

With a 3x3 grid of possible locations, the page number marking 14 can encode three bits of data with one location spare.

Turning back to Figure 2, it will be noted that with such an arrangement any group of 4 fixed lattice dots that does have a centrally positioned dot must surround a crossing point of the location lattice. For example, the crossing point 18 is centrally positioned between 4 fixed grid points. The central crossing point is not used as a possible marking position to make the software pattern recognition easier to achieve.

The page identifier is determined according to the combined positions of each of the page number markings 14 within the area 12.

In the example shown, there are nine page number markings within the area 12, each capable of being located in one of the eight positions shown in Figure 3, to provide a total of 24 permutations.

In figure 2, the position markings 8 do not necessarily lie on the notional rulers 10 which define the location lattice. Instead, a given position marking 16 may be located off-lattice. The possible locations of the marking 16 are defined - as with the page number markings - by a notional lattice within the interstitial area defined by the nearest four dots of the fixed grid. Thus, the possible positions are exactly as already described above and as shown in Figure 3 in connection with the page number markings.

Typically, the measured local x, y position of the area 12 will be defined by a combination of the individual encoded location values of a whole sequence of position markings, such as for example markings 15, 16, 17 (between the crossing points 18, 19), and by the sequence of markings 21, 22, 23 (between the crossing points 18, 20). There are three position markings 15, 16, 17 or 21, 22, 23 along the rulers between the intersections, and if the position of each of these is quantized and restricted to the locations shown in Figure 3, between the fixed grid, one obtains a total of 24 possible permutations.

As the pen moves across the paper, the field of view is always large enough to pick-up at least three markings within a sequence, thereby uniquely determining the x, y position of the local area 12.

Although the printed fixed grid helps to define the possible dot locations very precisely, and hence helps to reduce the processing power needed to operate a position-encoding scheme, it is not absolutely essential. Other ways of measuring dot location with respect to the page andlor to the lattice could be used instead.

In Figure 2, the crossing points 18, 19, 20 are not data-carrying, but these could also if desired be markings carrying additional data, defined by either shape or location. One possibility would be for the markings to be asymmetric to provide orientation information thereby enabling the software to calculate the orientation of the writing with respect to a vertical axis of the page.

Alternatively, the crossing markings could be used to carry error correcting information.

It is anticipated that in some embodiments (not shown) the data carried by an individual marking may be encoded partly by shape or other optically detectable characteristic, and partly by position. In Figure 3, for example, the number of possible permutations would be doubled if each crossing point could contain either a small dot representing 0 or a large dot representing 1.

Although the invention has been described by way of example and with reference to particular embodiments, it is to be understood that modifications and/or improvements may be made without departing from the scope of the appended claims.

Where in the foregoing description reference has been made to integers or elements having known equivalents then such equivalents are incorporated herein as if individually set forth.

Claims

1. An optically-detectable encoding layout for a surface, the layout comprising: (a) a plurality of location markings spaced across the surface according to a notional location lattice, the markings encoding for local position on the surface; and (b) one or more secondary markings within the interstitial areas formed by the location lattice, the secondary markings encoding for page identification.

2. A layout as claimed in claim I in which the location markings, the secondary markings, or both, carry data by virtue of an opticallydetectable characteristic such as shape.

3. A layout as claimed in claim I in which the location markings, the secondary markings, or both, carry data by virtue of their position with respect to the location lattice.

4. A layout as claimed in claim 1 including a plurality of grid markings spaced according to a notional grid which is fixed with respect to the location lattice.

5. A layout as claimed in claim 4 in which each secondary marking carries data by virtue of its position with respect to its surrounding grid markings.

6. A layout as claimed in claim 4 in which each location marking carries data by virtue of its position with respect to its surrounding grid markings.

7. A layout as claimed in claim 5 in which each secondary marking is positioned on a point of a notional secondary lattice within a interstitial area of the fixed grid.

8. A layout as claimed in claim 5 in which each location marking is positioned on a point of a notional secondary lattice within an interstitial area of the fixed grid.

9. A layout as claimed in claim 1 in which the said one or more secondary markings are repeated across the page, at a spacing defined by the spacing of the location lattice.

10. A layout as claimed in claim 9 in which there are a plurality of secondary markings with each interstitial area, the page identification being associated with a combination of the data encoded by each said secondary marking.

11. A layout as claimed in claim 1 in which the location lattice defines a lattice spacing and in which there are a plurality of location markings within the lattice spacing.

12. A layout as claimed in claim 11 in which the local position is associated with a combination of the data encoded by each said location with a combination of the data encoded by each said location marking within the lattice spacing.

13. A layout as claimed in claim 1 in which the location lattice defines lattice crossing points, the crossing points being indicated by crossing point markers.

14. A layout as claimed in claim 13 including a plurality of grid markings spaced according to a notional grid, the crossing point markers being centrally located with respect to their respective surrounding grid markers.

15. A method of creating a plurality of individually-identifiable articles, comprising: (a) generating in computer memory a first representation of a plurality of location markings to be spaced across a surface according to a notional location lattice, the markings encoding for local position on the surface; (b) generating in computer memory a second representation of one or more secondary markings to be located within the interstitial areas formed by the location lattice, the secondary markings encoding for a specific article; (c) merging the first and second representations, and applying the resultant merged encoding layout to the said specific article; and (d) repeating steps (b) and (c) for subsequent articles.

16. A printed article carrying an optically-detectable layout on a surface thereof, the layout comprising: (a) a plurality of location markings spaced across the surface according to a notional location lattice, the markings encoding for local position on the surface; and (b) one or more secondary markings within the interstitial areas formed by the location lattice, the secondary markings encoding for page identification.