Patent ID: 6360948
Filing Date: 2002-03-26
Classification: G06K

Abstract:
A method of reading information out of a two-dimensional code made up of a matrix of cells having a given optical pattern, the two-dimensional code having at least one location symbol used to locate the two-dimensional code and at least one alignment symbol used to locate the cells, comprising the steps of:capturing an image around the two-dimensional code in a bit mapped pattern; detecting a position of the location symbol to determine a position of the two-dimensional code in the captured image; calculating a central position of the alignment symbol in the captured image mathematically using a predetermined positional relation of the alignment symbol to the location symbol; selecting a dot in the captured image lying at the calculated central position of the alignment symbol as a reference brightness check dot and dots lying in some of the cells around one of the cells of the captured image in which the reference brightness check dot exists as surrounding brightness check dots to define an alignment symbol optical pattern with a combination of the reference brightness check dot and the surrounding brightness check dots; comparing the alignment symbol optical pattern with a plurality of reference optical patterns each formed with one of possible combinations of one of the cells lying at an actual central position of the alignment symbol and as many cells arranged adjacent the one of the cells as the surrounding brightness check dots to select one of the reference optical patterns matching up with the alignment symbol optical pattern; correcting the calculated central position of the alignment symbol based on a position of one of the surrounding brightness check dots in the captured image corresponding to the one of the cells of the selected matching up reference optical pattern at the actual central position of the alignment symbol and a geometry of the alignment symbol to determine an actual central position of the alignment symbol in the captured image; determining positions of the cells of the two-dimensional code in the captured image based on at least one of the position of the location symbol and the actual central position of the alignment symbol in the captured image; and reading the cells of the two-dimensional code in the captured image optically to decode the information carried by the two-dimensional code.