How to do median filter on an indexed image using MATLAB?

ring= fspecial('gaussian',21,1)
ring = ring>eps & ring<1e-9

order=sum(ring(:))/2;
B = ordfilt2(A,order,ring);

B = nlfilter(A, [m n], fun);

out = nlfilter(im, size(mask), @(x) median(x(mask)));

N = size(mask,1); %// Size of mask - Assume that # of rows = # of columns
im_pad = padarray(im, [floor(N/2) floor(N/2)]);
im_col = im2col(im_pad, [N N], 'sliding');

%// Get locations in mask that don't count towards getting median
invalid_rows = ~(mask(:));

%// Remove from column neighbourhood matrix
im_col(invalid_rows,:) = [];

%// Determine new median index
val = floor((N*N - sum(invalid_rows))/2) + 1;

%// apply algorithm as normal
sorted_cols = sort(im_col, 1, 'ascend');
med_vector = sorted_cols(val, :);
out = col2im(med_vector, [N N], size(im_pad), 'sliding');

function [outimg] = medianfilt(img,sz)
    [rows,cols] = size(img);    % get size of grayscale image
    pad = sz-1; % padding to be added
    nimg = zeros(rows+pad,cols+pad); % padded image
    nimg(pad/2+1:rows+pad/2, pad/2+1:cols+pad/2) = img;
    outimg = zeros(rows,cols);  % output / median filtered image
    for x = pad/2 + 1 : cols + pad/2  % loop over columns
        for y = pad/2 + 1 : rows + pad/2   % loop over rows 
            win = nimg(y-pad/2:y+pad/2, x-pad/2:x+pad/2);  % get mxm window
            outimg(y-pad/2,x-pad/2) = median(win(:));      % find median
        end
    end
end

if nimg(y,x) == 0 || nimg(y,x) == 255
    win = nimg(y-pad/2:y+pad/2, x-pad/2:x+pad/2);  % get mxm window
    outimg(y-pad/2,x-pad/2) = median(win(:));      % find median
else
    outimg(y-pad/2,x-pad/2) = nimg(y,x);
end