Patent ID: 7627178

Claim:
An image recognition apparatus which compares an object image containing a plurality of objects with a model image containing a model to be detected and extracts the model from the object image, the apparatus comprising: feature point extracting means for extracting a feature point from each of the object image and the model image; feature quantity retention means for extracting and retaining, as a feature quantity, a density gradient direction histogram at least acquired from density gradient information in a neighboring region at the feature point in each of the object image and the model image, the density gradient direction histogram storing a number of points near the feature point having each of a plurality of gradient directions; feature quantity comparison means for comparing the feature quantity of each feature point of the object image with the feature quantity of each feature point of the model image and generating a candidate-associated feature point pair having similar feature quantities; and model attitude estimation means for detecting the presence or absence of the model on the object image using the candidate-associated feature point pair and estimating a position and an attitude of the model, if any, wherein the feature quantity comparison means itinerantly shifts one of the density gradient direction histograms of feature points to be compared in density gradient direction to find distances between the density gradient direction histograms by sequentially shifting all of the feature points in the one of the density gradient direction histograms one by one to generate a plurality of shifted histograms, and generates the candidate-associated feature point pair by determining a shortest distance between (1) an other of the density gradient direction histograms and (2) the one of the density gradient direction histograms and the shifted histograms.