function [patchHist ldpIm] = LDP( im, patch_num, rankK, plotOpt)

if nargin < 1, selfdemo; return; end

if nargin < 2, patch_num = 8; end

if nargin < 3, rankK = 1; end

if nargin < 4, plotOpt = 0; end

[w h dim] = size(im);

if dim >= 3, im=rgb2gray(im); end

I2 = zeros(w+2, h+2);

I2(2:w+1,2:h+1) = im(:,:);

patchHist = zeros(1,256*patch_num*patch_num);

M_filter = zeros(3,3,8); %LDP mask

M_filter(:,:,1) = [-3 -3 5; -3 0 5; -3 -3 5];

M_filter(:,:,2) = [-3 5 5; -3 0 5; -3 -3 -3];

M_filter(:,:,3) = [5 5 5; -3 0 -3; -3 -3 -3];

M_filter(:,:,4) = [5 5 -3; 5 0 -3; -3 -3 -3];

M_filter(:,:,5) = [5 -3 -3; 5 0 -3; 5 -3 -3];

M_filter(:,:,6) = [-3 -3 -3; 5 0 -3; 5 5 -3];

M_filter(:,:,7) = [-3 -3 -3; -3 0 -3; 5 5 5];

M_filter(:,:,8) = [-3 -3 -3; -3 0 5; -3 5 5];

blk = im2col(I2, [3 3], 'sliding'); %3*3block to one col

tmp = [];

for i = 1 : 8

tmp = [tmp; abs(sum(blk.*repmat(reshape(M_filter(:,:,i),9,1), 1, w*h)))]; %col * LDP mask

[~, idx] = sort(tmp, 'descend');

eight_bit = zeros(size(tmp));

idx = idx(1:rankK,:) + repmat(0:8:size(tmp,2)*8-1, rankK, 1);

eight_bit(idx) = 1;

ldpIm = double(reshape(compactbit(eight_bit'), w, h));

ldpPatch = im2col(ldpIm, [floor(w/patch_num), floor(h/patch_num)], 'distinct');

for i = 1 : patch_num*patch_num

tmp=histc(ldpPatch(:,i),0:255);

MAX = max(tmp);

patchHist(1,(i-1)*256+1:i*256) = tmp./MAX;

if plotOpt

subplot(1,2,1); imshow(im);

xlabel('Original Img')

subplot(1,2,2); imshow(ldpIm, []);

xlabel('LDP Img')

function cb = compactbit(b)

[nSamples nbits] = size(b);

nwords = ceil(nbits/8);

cb = zeros([nSamples nwords], 'uint8');

for j = 1:nbits

w = ceil(j/8);

cb(:,w) = bitset(cb(:,w), mod(j-1,8)+1, b(:,j));

function selfdemo

mObj=mFileParse(which(mfilename));

strEval(mObj.example);