1. An image processing apparatus comprising: decision means for deciding a similarity between a first pixel and a second pixel which constitute an image, by testing, the similarity between the first pixel and the second pixel being decided by use of a result of comparison between a vector value obtained by arraying scalar values which the first pixel takes in an image of an object photographed by an imaging apparatus and a vector value obtained by arraying scalar values which the second pixel takes in the image of the object; and average means for subjecting the first pixel and the second pixel to weighted averaging on a basis of a decided result by the decision means, wherein the average means multiplies a value of the second pixel value by a large weighting factor by the multiplication means when the similarity between the first pixel and the second pixel is high, and multiplies the value of the second pixel by a small weighting factor when the similarity is low, and the average means subjects weighted values of the first pixel and the second pixel to the weighted averaging.