What is the error in the function fun defined in the code below to find std deviation?

% % Usage: [normim, mask, maskind] = ridgesegment(im, blksze, thresh) % % Arguments: im - Fingerprint image to be segmented. % blksze - Block size over which the the standard % deviation is determined (try a value of 16). % thresh - Threshold of standard deviation to decide if a % block is a ridge region (Try a value 0.1 - 0.2) % % Returns: normim - Image where the ridge regions are renormalised to % have zero mean, unit standard deviation. % mask - Mask indicating ridge-like regions of the image, % 0 for non ridge regions, 1 for ridge regions. % maskind - Vector of indices of locations within the mask. % % Suggested values for a 500dpi fingerprint image: % % [normim, mask, maskind] = ridgesegment(im, 16, 0.1) % % See also: RIDGEORIENT, RIDGEFREQ, RIDGEFILTER

function [normim, mask, maskind] = ridgesegment(im, blksze, thresh)

    im = normalise(im,0,1);  % normalise to have zero mean, unit std dev

    fun = inline('std(x(:))*ones(size(x))');

    stddevim = blkproc(im, [blksze blksze], fun);

    mask = stddevim > thresh;
    maskind = find(mask);

    % Renormalise image so that the *ridge regions* have zero mean, unit
    % standard deviation.
    im = im - mean(im(maskind));
    normim = im/std(im(maskind));

Error in ==>blockproc at 219 Invalid output class. The user function, FUN, returned an invalid result. The class of the result was char.

Error in ==> ridgesegment at 62 stddevim = blockproc(im, [blksze blksze],fun);