Could it be that the formula for computing the chi² distance between histograms as pointed out [here](http://docs.opencv.org/modules/imgproc/doc/histograms.html?highlight=comparehist#comparehist) is wrong?
If one divides the squared difference of (h1 and h2) by h1 the distance is not symmetrical anymore which is not logical.
[Here](http://www.irisa.fr/vista/Papers/2008_cvpr_laptev.pdf) is a paper that defines the chi square distance between histograms as:
1/2 * sum over i of (h1_i - h2_i)^2 / (h1_i + h2_i)
which is symmetric and makes more sense as a distance measure
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