On Fri, 16 Jan 2009 23:24:29 +0530 magick-developers-boun...@imagemagick.org wrote:
| While using ImageMagick patched with the original kurtosis patch, I | realized I had made an error in magick/identify.c, where just like the | mean and standard deviation, kurtosis and skewness were being divided | by the values 'scale' and 'QuantumRange'. | | While this makes sense for the mean and standard deviation, it does | not in case of kurtosis and skewness. This is because the first two | are dimensional numbers. They have units associated with them. So for | the red channel the mean would be the mean amount of 'redness' as it | were, etc. | Looking at the changes as a result of this patch http://www.imagemagick.org/Usage/compare/#type_bw Channel statistics: gray: min: 0 (0) max: 127 (0.498039) mean: 9.7071 (0.0380671) standard deviation: 23.4909 (0.0921213) kurtosis: 8.75478 skewness: 3.02607 Image statistics: OverAll: min: 0 (0) max: 127 (0.498039) mean: 7.28032 (0.0285503) standard deviation: 20.7734 (0.0814645) kurtosis: 13.032 skewness: 3.60838 This is a gray scale image. Actually a Black and White image that has been 'solarized' so that the white half has been negated, so white -> black. It is really a test of how much 'gray' is present in the image. But as it is gray. how can it be that we get a different result for gray colors when compared to overall? All that would happen in this case is that overall should have the gray data repeated three times. The results in that case should be the same set of statistics. But that is obviously NOT the case! Something is definitely not right here! Anthony Thyssen ( System Programmer ) <a.thys...@griffith.edu.au> ----------------------------------------------------------------------------- Clarke's Law: Study what the most respected authorities agree can NOT be done - then do it. -- Arthur C. Clark ----------------------------------------------------------------------------- Anthony's Home is his Castle http://www.cit.gu.edu.au/~anthony/ _______________________________________________ Magick-developers mailing list Magick-developers@imagemagick.org http://studio.imagemagick.org/mailman/listinfo/magick-developers
