Histogram Mean Calculation 
Jul 24, 2014, 14:40
Post: #1




Histogram Mean Calculation
Hello Gimpers,
Im open a image and in the histogram windows we can see mean, std dev, median, pixels, count and percentile values. Im having problem to understand how he calculate mean value. The mean standard calculation is pixels / 255 it is mean or average. I have a image with 45000 pixels, but he give me 88.3 result for mean value. I want know how GIMP calculate mean value ? I suppose it is not statistical standard mean calculation. Thanks, Sergio 

Jul 24, 2014, 17:54
(This post was last modified: Jul 24, 2014 17:56 by sergioribeiro.)
Post: #2




RE: Histogram Mean Calculation
(Jul 24, 2014 15:01)ofnuts Wrote: Hmmm. Depends on what image you are working with... If I create a 300x300 image, and fill it with a linear BlacktoWhite gradient, the Histogram display gives me a mean of 127.3 (with dithering, 127.1 without). Pretty much the expected result (in 8bit/Channel, there are roundoff errors) Thank you Ofnuts...But, how can I reproduce his calculation ? I have another image...i this link: http://tutorial.simplecv.org/en/latest/_...vlogo.png If I open her and select all image/all pixels he show me: Mean: 98.6 std dev: 78.1 Median: 59.0 Pixel: 13924 Count: 13924 If I will try to reproduce his calculation, what equation should I use ? In a histogram matrix I have (example): Histogram[0] = 5000 Histogram[1] = 0 Histogram[2] = 0 ... Histogram[255] = 350 In this case the equation "sum( Histogram ) / count( Histogram )" or "sum(Histogram) / count_nonzero( Histogram )" can't give a result of the mean equals to 98.6 I trying to discovery what equation GIMP uses. Is it a general equation founded on literacy ? Thank you. Sergio 

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