Patent ID: 8363530

Claim:
An information reading method, comprising: a reading step of decoding information from a reproduction signal read from an information recording medium; and a detection step of detecting a length error and a phase error of a recording mark based on a difference between squares of Euclidean distances between a plurality of error patterns corresponding to a correct pattern obtained by the decoding and the reproduction signal; wherein: the detection step includes the step of detecting a first error pattern and a second error pattern among the plurality of error patterns; a square of a Euclidean distance between the first error pattern and the correct pattern and a square of a Euclidean distance between the second error pattern and the correct pattern are different from each other; and the detection step further includes the steps of: calculating a first pattern shift amount by normalizing a difference between the square of the Euclidean distance between the first error pattern and the reproduction signal and a square of a Euclidean distance between the correct pattern and the reproduction signal, using the square of the Euclidean distance between the correct pattern and the first error pattern, in accordance with a time relationship between the correct pattern and the first error pattern; calculating a second pattern shift amount by normalizing a difference between the square of the Euclidean distance between the second error pattern and the reproduction signal and the square of the Euclidean distance between the correct pattern and the reproduction signal, using the square of the Euclidean distance between the correct pattern and the second error pattern, in accordance with a time relationship between the correct pattern and the second error pattern; and calculating the length error and the phase error by a sum of, or a difference between, the first pattern shift amount and the second pattern shift amount.