Two-dimensional symbol and method for reading same

1. A two-dimensional symbol comprising:

four solid borders defining an interior region;

a plurality of first shade tick marks and a plurality of second shade tick marks arranged in an alternating pattern at the interior region of the four solid borders and adjacent to the four solid borders; and

data cells in the interior of the plurality of first shade and plurality of second shade tick marks,

wherein each of the four solid borders are made up of constituent cells; at least a first solid border is reconstructed; at least a second solid border is not reconstructed; and the at least first solid border is reconstructed based on the length of the at least second solid border.

2. The symbol of claim 1 wherein:

the four solid borders define four corners in the interior region;

and three of the corners in the interior region are forced to be a first shade and the fourth corner in the interior region is forced to be a second shade.

3. The symbol of claim 2 wherein an orientation of the two-dimensional symbol is determinable by finding the shade of at least one of the four corners in the interior region.

4. The symbol of claim 3 wherein an orientation of the two-dimensional symbol is determinable by identifying the corner in the interior region that is forced to be a second shade.

5. The symbol of claim 1 wherein the at least first solid border is reconstructed by adding cells thereto.

6. The symbol of claim 1 including:

a plurality of corners at intersections of the four solid borders;

wherein at least two of the four solid borders are projected to construct at least one of the plurality corners.

7. The symbol of claim 1 that extends a first number of cells in a first direction and extends a second number of cells in a second direction wherein the number and size of the plurality of first shade tick marks and plurality of second shade tick marks are used to determine the first number of cells and the second number of cells.

8. The symbol of claim 5 that extends a first number of cells in a first direction and extends a second number of cells in a second direction wherein the number and size of the plurality of first shade tick marks and plurality of second shade tick marks are used to determine the first number of cells and the second number of cells.

9. The symbol of claim 1 , wherein the alternating shade tick marks on the interior of the four solid borders are used to determine the number of rows and columns in the symbol.

10. A two-dimensional symbol comprising:

four solid borders defining an interior region;

a plurality of first shade tick marks and a plurality of second shade tick marks arranged in an alternating pattern at the interior region of the four solid borders and adjacent to the four solid borders;

data cells in the interior of the plurality of first shade and plurality of second shade tick marks; and

rows and columns of cells containing data;

wherein the alternating shade tick marks on the interior of the four solid borders are used to locate the rows and columns of cells containing data.

11. A two-dimensional symbol comprising:

four solid borders defining an interior region;

a plurality of first shade tick marks and a plurality of second shade tick marks arranged in an alternating pattern at the interior region of the four solid borders and adjacent to the four solid borders; and

data cells in the interior of the plurality of first shade and plurality of second shade tick marks, wherein:

each of the four solid borders has an opposite, substantially parallel solid border that is another one of the four solid borders:

at least one of the tick marks adjacent to at least a first of the four solid borders is missing; and

the tick marks adjacent to the solid border that is opposite to the first solid border are used to reconstruct the at least one missing tick mark.

12. A two-dimensional symbol comprising:

four solid borders defining an interior region;

a plurality of first shade tick marks and a plurality of second shade tick marks arranged in an alternating pattern at the interior region of the four solid borders and adjacent to the four solid borders; and

data cells in the interior of the plurality of first shade and plurality of second shade tick marks, wherein:

at least a first portion of the data cells contain encrypted information;

at least a second portion of the data cells contain compressed information;

and the data cells further contain cyclic redundancy check information, encryption key information and compression key information.

13. A method of reading an information symbol having:

four solid borders defining an interior region;

a plurality of first shade tick marks and a plurality second shade tick marks arranged in an alternating pattern at the interior region of the four solid borders and adjacent to the four solid borders; and

data cells in the interior of plurality of first shade tick marks and plurality of second shade tick marks,

the method including:

acquiring an image of the information symbol;

identifying the four borderlines in the image of the information symbol;

locating the tick marks in the image of the information symbol;

decoding data in the data cells of the image of the information symbol; and

reducing projection distortion in the image of the information symbol.

14. The method of claim 13 including binarizing the image of the information symbol.

15. The method of claim 13 including locating the centers of the data cells in the image of the information symbol.

16. The method of claim 13 including orienting the image of the information symbol.

17. The method of claim 14 including:

tiling the image of the information symbol;

generating a grayscale histogram for the data cells in each tile of the image of the information symbol;

smoothing each generated grayscale histogram to indicate two local maxima, the two local maxima having a local minimum therebetween;

determining a binarization threshold based on the location of the local minimum between the two local maxima.

18. A method of binarizing an image of an information symbol having a matrix data cells, the method including:

tiling the image of the information symbol;

generating a grayscale histogram for the data cells in each tile of the image of the information symbol;

smoothing each generated grayscale histogram to indicate two local maxima, the two local maxima having a local minimum therebetween;

determining a binarization threshold based on the location of the local minimum between the two local maxima.