how to apply chi-square distance to find the distance between the quert image and the images present in the database?

I am doing a project on content - based image retrieval. I am trying to retrieve most similar images as query image even in the presence of noise. I am adding salt and pepper noise and trying to retrieve the images by using euclidean distance and the filter using to reduce the noise is median filter but the problem is i am not getting satisfactory results. so i want to use other distance measures to find the distance between the histograms of query image and the database images. i came to know chi-square distance is better for finding the distance between the histograms of query image and database image. so suggest me which distance measure is suited and please provide matlab source code.