Patent ID: 7546950

Claim:
A method of extracting a bitstream from a machine-readable symbol in an image, the symbol comprising three finder patterns adjacent respective corners of the symbol and generally defining the corners of a right-angled triangle, the method comprising: using one or more computer processing units to perform the following: identifying the finder patterns in the symbol; orienting the symbol using the finder patterns, the orienting comprising determining which of the three finder patterns is positioned at the corner of the triangle opposite its hypotenuse (“top left finder pattern” ), and labeling the remaining two finder patterns based on the relative distance between the remaining two finder patterns that would result if one of the remaining two finder patterns were rotated about the top left finder pattern less than 180 degrees, wherein the labeling comprises: initially labeling the remaining two finder patterns respectfully as top right and bottom left finder patterns; rotating a selected one of the top right and bottom left finder patterns about the top left finder pattern; and after rotation, comparing the relative distance between the top right and bottom left finder patterns before and after rotation to verify the initial labeling; on the basis of the orienting, delineating the symbol, wherein the delineating comprises: determining the top left bottom left, and top right corners of the symbol based on the top left bottom left and top right finder patterns; and using a skew and pitch sensitive technique based on the top right and bottom left finder patterns to determine the bottom right corner of the symbol; mapping a decoding grid to the delineated symbol; and extracting bit values from the mapped symbol.