Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
2002-06-26
2004-05-11
Lee, Michael G. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462100, C235S462080, C235S494000
Reexamination Certificate
active
06732927
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for data decoding, and more particularly to a method which decodes data stored in a partial area of a coding pattern on a surface, based on a recorded image of the partial area, the coding pattern containing elements which each have at least two possible decoding values. The invention also relates to a device for data decoding, and more particularly to a data decoding device having a processing unit for decoding data which is stored in a partial area of a coding pattern on a surface. Moreover the invention relates to a memory medium on which is stored a computer program with instructions which, when executed by a processor, perform a method for data decoding based on an image. The invention also relates to a method of data decoding which performs decoding using probability calculations based on an image of a coding pattern.
BACKGROUND ART
In many situations it is desirable to be able to decode data stored in coded form on a product. One example of such data decoding is to determine the position on a surface provided with a coding pattern. Such position determination is useful, for instance, when using a reading pen on a writing surface.
Applicant's Patent Publication WO 01/26032, which is herewith incorporated by reference, describes a device for position determination and a product that has a surface that is provided with a coding pattern. The device is arranged to record an image of the surface, to locate a predetermined number of symbols in the image, to determine the value of each of the symbols and to determine its position on the surface based on these values.
There are many other types of coding patterns in the form of position codes, for example, those in which each position is coded by a complex symbol with a special appearance.
A problem in decoding the known types of coding patterns is that the values of the symbols cannot always be determined with full accuracy. When the coding pattern is printed on a surface, the limited resolution of printers may imply that the symbols are not printed completely exactly. The symbols can, for example, be printed somewhat deformed or somewhat displaced from their “nominal” location. If it is the shape or location of the symbol that determines its value, the deformation and the displacement, respectively, mean that it may be difficult to determine the value of the symbol unambiguously.
It sometimes also happens that a symbol is not printed at all.
Another problem may arise if the coding pattern is printed on a surface that has a structure of its own that can interfere with the location of symbols in the recorded image. Structures in the surface can then be perceived as symbols by a device for data decoding. It can also happen that there are impurities, for instance in the form of dust, on the surface on which the coding pattern is printed. These impurities may give rise to noise symbols in the recorded image. Such noise symbols may then by mistake be identified as symbols in the coding pattern. Also, sensor noise from a sensor for recording the image may cause noise symbols in the image. Noise symbols in the recorded image may also originate from a defect on one of the components in the device, for instance damaged pixels in the sensor. On account of the above reasons there is therefore a risk that data cannot be decoded from the coding pattern in a recorded image.
SUMMARY OF THE INVENTION
According to a first aspect, the present invention relates to a method for decoding of data. The method according to this aspect of the invention decodes data stored in a partial area of a coding pattern on a surface, based on a recorded image of the partial area. The coding pattern contains elements, which each have at least two possible decoding values. The method identifies in the image a plurality of such elements, calculates, for each identified element, an associated value probability for each possible decoding value that the element has this decoding value, and decodes data based on the decoding values and the corresponding value probabilities.
For the reasons discussed above, the coding pattern on a surface, and/or the imaging of the same, is usually not completely perfect. One single decoding value for an element can usually not be determined with complete certainty as there is a possibility that the element has another of the possible decoding values. According to an aspect of the invention, for each element and for each of the decoding values, a value probability is therefore calculated that the element has that decoding value. If an element is determined unambiguously, then the value probability that corresponds to the unambiguously determined decoding value of the element will be maximum, while the other value probabilities for the element are zero. The more uncertain the decoding value of an element, the less difference there is between its value probabilities. If an element is missing in one place in the coding pattern, the value probabilities for the element will therefore be equally high. The present invention thus enables a relatively robust decoding of the coding pattern.
In the recorded image, more than a predetermined number of elements that are required for decoding of data may be identified according to one exemplary implementation of the present invention. The predetermined number of elements which may contribute most information in decoding can therefore be selected. As stated above, these elements are those having a dominating value probability for one of the decoding values. Consequently the chance increases that data can be decoded based on the recorded image since an element contributing little information can be sorted out.
The method may further comprise decoding at least a first set of decoding values for the predetermined number of identified elements.
The method may further comprise calculating sequence probabilities for a sequence of elements in the recorded partial area in the image. For instance, if the predetermined number of identified elements is a matrix, the sequence of elements can be the elements in a column or row in the matrix. The sequence probabilities can be calculated based on the value probabilities for the decoding values in the first set that correspond to the elements in the sequence. A value probability can be calculated for each of a plurality of a permissible combinations of decoding values. For each element, each of the possible decoding values corresponds to a value probability. The sequence probability for a combination may be determined based on the value probabilities for the decoding values which constitute the combination. In the same way as a value probability for an element corresponds to the element having the corresponding element value, a sequence probability for a sequence of elements corresponds to the sequence consisting of the corresponding combination. Of course, there are other ways than that described above in which sequence probabilities can be calculated.
The method may comprise selecting one of the possible decoding values for each of the elements which correspond to the first set of decoding values. The selection can be made based on a condition, given by the coding pattern, for the relation between the decoding values of the elements. The condition conveniently indicates which combinations of decoding values may exist among the elements in the coding pattern in the recorded image. In other words, the condition is given by how the used coding pattern is made up. The condition for existing combinations can be given at a global level, i.e., seen over all elements in the image, or at a local level, i.e., over an ensemble of elements in the image, for instance by columns and/or rows. Probability calculations are used to combine the information in the image, corresponding to the condition, so that the decoding values of the elements can be selected based on the probability calculations, within the scope of the condition.
The condition may indicate the above-discussed permissible combinations of decoding
Olsson Andreas
Petterson Mats Petter
Anoto AB
Lee Michael G.
Nguyen Kimberly
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