(ilwis-list) filter avg 3x3

[Joelle Dagnelies]

Dear list members,

I have a question concerning the avg3x3 filter : I used this filter on an 
image, and wanted to verify the result. For this, I choosed a pixel in the 
original image (in the central part of the image) (with DN = 2507, see 
below), made the mean with it and its 8 surrounding pixels (result : 
1765.667) and compared the result with the same pixel in the filtered image 
(result : 1800 !?). Can somebody explain me where this value is coming from 
? maybe I didn't understand the filter avg3x3 principle ?!...

pixel and its surroundings : 1050  1948  1771
                                    1204  2507  2641
                                    827   1782  2161
Thank you,

Joelle

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