Matlab code for padding an image.

padImage.m

% Code created by Xavier Weber

function outimg = padImage(I, pad)
%padImage Pads an image with black pixels (zero-values)
%   Works with single or multi-channels

% Get input dimensions
img_size = size(I);
src_height = img_size(1);
src_width = img_size(2);
src_channels = 1;
if length(img_size) == 3
    src_channels = img_size(3);
end

% round padding up
pad = ceil(pad);

% create destination image, single or multi-channel
outimg = zeros(src_height+2*pad, src_width+2*pad, src_channels);

for channel = 1:src_channels
    for row = 1+pad:src_height+pad
        for col = 1+pad:src_width+pad
            outimg(row,col,channel) = I(row-pad,col-pad,channel);
        end
    end

outimg = uint8(outimg);
end