Document and/or Image Retrieval Method, Program Therefor, Document and/or Image Storage Apparatus, and Retrieval Apparatus

A document and/or image retrieval method for retrieving a document and/or image corresponding to a captured digital image from a database by comparing features calculated based on feature points of the captured digital image with features calculated based on feature points of each of documents and/or images stored in the database, the method comprising:

• extracting the feature points from the captured digital image;
• defining a local set of feature points for each of the extracted feature points;
• selecting subsets of feature points from the defined local set;
• determining invariant values as values characterizing each selected subset for combinations of the feature points in the subset, the invariant values being invariant to a geometric transformation;
• calculating a feature by combining the determined invariant values;
• and
• performing a voting process on the documents and/or images in the database based on the preliminarily calculated features of the documents and/or images;
• so that the document and/or image corresponding to the captured digital image is retrieved from the database.

A document and/or image storage method, which causes a computer to execute the steps of:

• inputting a document and/or image;
• assigning an ID to the input document and/or image;
• extracting feature points defining an image arrangement from the input document and/or image;
• and
• performing a predetermined process on each of the extracted feature points;
• the predetermined process comprising the steps of:
• (1) selecting n feature points which are nearest to a feature point p of interest;
• and
• (2) performing a predetermined process on each of all possible sets of m feature points (m<n) selected from the selected n feature points;
• the predetermined process in the step (2) comprising the steps of:
• (a) determining features for all possible sets of d points (wherein d is a number not greater than a predetermined number m) selected from an m-point set of interest;
• (b) determining an index of a hash table based on the determined features through a predetermined computation;
• and
• (c) storing the features in relation to a point ID and a document ID in the hash table, the features being determined in the step (a) using the determined hash index, the point ID being assigned to the feature point p and the document ID being assigned to the document and/or image from which the feature point p is extracted.

A document and/or image storage program, which causes a computer to execute the steps of:

• inputting a document and/or image;
• assigning an ID to the input document and/or image;
• extracting feature points defining an image arrangement from the input document and/or image;
• and
• performing a predetermined process on each of the extracted feature points;
• the predetermined process including the steps of:
• (1) selecting n feature points which are nearest to a feature point p of interest;
• and
• (2) performing a predetermined process on each of all possible sets of m feature points (m<n) selected from the selected n feature points;
• the predetermined process in the step (2) including the steps of:
• (a) determining features for all possible sets of d points (wherein d is a number not greater than a predetermined number m) selected from an m-point set of interest;
• (b) determining an index of a hash table based on the determined features through a predetermined computation;
• and
• (c) storing the features in relation to a point ID and a document ID in the hash table, the features being determined in the step (a) using the determined hash index, the point ID being assigned to the feature point p and the document ID being assigned to the document and/or image from which the feature point p is extracted.

A document and/or image storage apparatus comprising:

• an input section which inputs a document and/or image;
• a feature point extracting section which extracts feature points defining an image arrangement from the input document and/or image;
• a feature point selecting section which selects n feature points nearest to an extracted feature point p of interest;
• and
• a feature storing section which performs a predetermined process on each of all possible sets of m feature points (m<n) selected from the selected n feature points;
• the predetermined process including the steps of:
• (a) determining features for all possible sets of d points (wherein d is a number not greater than a predetermined number m) selected from an m-point set of interest;
• (b) determining an index of a hash table based on the determined features through a predetermined computation;
• and
• (c) storing the features in relation to a point ID and a document ID in the hash table, the features being determined in the step (a) using the determined hash index, the point ID being assigned to the feature point p and the document ID being assigned to the document and/or image from which the feature point p is extracted.