Getis statistic code (IDL) (This is an extract of the code, so some variables aren't properly defined etc - but it should give you an idea of what I am doing.)

gistfile1.txt

    ; Get the global mean
    GlobMean = MEAN(WholeBand, /NAN)
    
    ; Get the global variance
    GlobVariance = VARIANCE(WholeBand, /NAN)
    
    ; Get the number of values in the whole image
    GlobNumber = (NumRows * NumCols - CountOfNAN)
    
    ; Converts a distance to the length of each side of the square
    ; Eg. A distance of 1 to a length of 3
    DimOfArray = (distance * 2) + 1
    
    NumOfElements = DimOfArray * DimOfArray
    
    ; Create the kernel for the summing CONVOL operation
    Kernel = FLTARR(DimOfArray, DimOfArray)
    Kernel = Kernel + 1
    
    ; Create an image where each element is the sum of the elements within
    ; d around it
    SummedImage = CONVOL(FLOAT(WholeBand), Kernel, /CENTER, /EDGE_TRUNCATE, /NAN)
    
    ; Create an image where each element is the result of the top fraction part
    ; of the getis formula
    TopFraction = SummedImage - (FLOAT(NumOfElements) * GlobMean)
    
    ; Calculate the square root bit of the formula and then create a single variable
    ; with the bottom fraction part of the formula (this is constant for all pixels)
    SquareRootAnswer = SQRT((FLOAT(NumOfElements) * (GlobNumber - NumOfElements))/(GlobNumber - 1))
    BottomFraction = SQRT(GlobVariance) * SquareRootAnswer
    
    ; Create an image with the getis values in it
    Getis = FLOAT(TopFraction) / BottomFraction