State output probability calculating method and apparatus for mixture distribution HMM

• US 7,813,925 B2
• Filed: 04/06/2006
• Issued: 10/12/2010
• Est. Priority Date: 04/11/2005
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Yamamoto, Hiroki, Yamada, Masayuki
• Primary Examiner(s): YEN, ERIC L
• Application Number:
  US11/398,620
• Publication Number:
  US 20060229871A1
• Time in Patent Office: 1,650 Days
• Field of Search: 704/231, 704/236, 704/239, 704/240, 704/256
• US Class Current: 704/240
• CPC Class Codes: G10L 15/144 Training of HMMs

Abstract

When adjacent times or the small change of an observation signal is determined, a distribution which maximizes the output probability of a mixture distribution does not change at a high possibility. By using this fact, when obtaining the output probability of the mixture distribution HMM, a distribution serving as a maximum output probability is stored. When adjacent times or the small change of the observation signal is determined, the output probability of the stored distribution serves as the output probability of the mixture distribution. This can reduce the output probability calculation of other distributions when calculating the output probability of the mixture distribution, thereby reducing the calculation amount required for output probabilities.

Claims

1. A state output probability calculating method for a mixture distribution HMM, executed by a pattern recognition apparatus which performs pattern recognition of an observation signal by using the mixture distribution HMM, wherein an event of a recognition target stored in a memory is modeled in the mixture distribution HMM, comprising:

a first output probability calculating step of calculating weighted output probabilities of all distributions belonging to a state for a first observation signal, obtaining a maximum value of the weighted output probabilities and a maximum distribution which outputs the maximum value, and defining the obtained maximum value as an output probability of a mixture distribution;

a maximum distribution storage step of storing, in the memory, information which specifies the maximum distribution obtained in the first output probability calculating step; and

a second output probability calculating step of calculating only a weighted output probability of the maximum distribution specified by the information stored in the memory in the maximum distribution storage step, for a second observation signal observed after the first observation signal, instead of calculating weighted output probabilities of all distributions, in a case that a predetermined period of time is not elapsed from the time at which the maximum distribution is obtained in the first output probability calculating step, and of defining the calculated weighted output probability calculated in the second output probability calculating step as the output probability of the mixture distribution.

3. A non-transitory computer-readable storage medium having stored thereon a plurality of instructions, the plurality of instructions when executed by a computer, cause the computer to perform an output probability calculating method defined in claim 1.

2. An output probability calculating apparatus for calculating an output probability of a mixture distribution HMM state, comprising:

first output probability calculating means for calculating weighted output probabilities of all distributions belonging to states to obtain a maximum value thereof and a maximum distribution serving as a distribution which outputs the maximum value, and for defining the obtained maximum value as an output probability of a mixture distribution;

storage means for storing information which specifies the maximum distribution obtained by said first output probability calculating means;

a second output probability calculating means for calculating only a weighted output probability of the maximum distribution specified by the information stored in said storage means, instead of calculating weighted output probabilities of all distributions, in a case that a predetermined period of time is not elapsed from the time at which the maximum distribution is obtained by the first output probability calculating means, and for defining the calculated weighted output probability calculated by the second output probability calculating means as an output probability of a mixture distribution; and

control means for switching between said first output probability calculating means and said second output probability calculating means in accordance with whether a predetermined condition is satisfied.