局部边缘保持滤波(LEP)高动态范围图像HDR压缩 matlab程序（一）

本文程序根据论文"Gu B, Li W, Zhu M, et al. Local edge-preserving multiscale decomposition for high dynamic range image tone mapping[J]. Image Processing, IEEE Transactions on, 2013, 22(1): 70-79."编写，主要为论文中提出的一种LEP局部边缘保持滤波程序，高动态图像压缩的程序在下一篇博客里。

下面为LEP函数程序：

function out = LocalWls_HDR(I, alpha, beta, r)

if ~exist('alpha','var')
    alpha = 0.1;
end
if ~exist('beta','var')
    beta = 1;
end
if ~exist('r','var')
    r = 4;
end

[hei, wid] = size(I);
N = boxfilter(ones(hei, wid), r); % the size of each local patch; N=(2r+1)^2 except for boundary pixels.

mean_I = boxfilter(I, r) ./ N;
mean_II = boxfilter(I.*I, r) ./ N;

var_I = mean_II - mean_I .* mean_I;

I_x = diff(I,1,2);
I_x = padarray(I_x, [0 1 0], 'post');%进行列方向差分，求dx
I_y = diff(I,1,1);
I_y = padarray(I_y, [1 0 0], 'post');%进行行方向差分，求dy
I_gradient=abs(I_x+I_y);
I_gradient=I_gradient.^(2-beta);
I_gradient=alpha*boxfilter(I_gradient,r)./N;

a = var_I ./ (var_I + I_gradient+0.00000001); 
b = mean_I - a .* mean_I; 

mean_a = boxfilter(a, r) ./ N;
mean_b = boxfilter(b, r) ./ N;

out = mean_a .* I + mean_b; 
end

其中用到的boxfilter()函数来自引导滤波，为：

function imDst = boxfilter(imSrc, r)

%   BOXFILTER   O(1) time box filtering using cumulative sum
%
%   - Definition imDst(x, y)=sum(sum(imSrc(x-r:x+r,y-r:y+r)));
%   - Running time independent of r; 
%   - Equivalent to the function: colfilt(imSrc, [2*r+1, 2*r+1], 'sliding', @sum);
%   - But much faster.

[hei, wid] = size(imSrc);
imDst = zeros(size(imSrc));

%cumulative sum over Y axis
imCum = cumsum(imSrc, 1);
%difference over Y axis
imDst(1:r+1, :) = imCum(1+r:2*r+1, :);
imDst(r+2:hei-r, :) = imCum(2*r+2:hei, :) - imCum(1:hei-2*r-1, :);
imDst(hei-r+1:hei, :) = repmat(imCum(hei, :), [r, 1]) - imCum(hei-2*r:hei-r-1, :);

%cumulative sum over X axis
imCum = cumsum(imDst, 2);
%difference over X axis
imDst(:, 1:r+1) = imCum(:, 1+r:2*r+1);
imDst(:, r+2:wid-r) = imCum(:, 2*r+2:wid) - imCum(:, 1:wid-2*r-1);
imDst(:, wid-r+1:wid) = repmat(imCum(:, wid), [1, r]) - imCum(:, wid-2*r:wid-r-1);
end

运行程序为：

clear all
I = double(imread('..\images\stripes.png')) / 255;

alpha=0.1;
beta=1;
r=2;

out = LocalWls_HDR(I, alpha, beta, r);

figure();imshow([I, out], [0, 1]);title('input,LEP');
row=155;
figure;plot(1:size(I,2), I(row,:,1),1:size(I,2), out(row,:,1), 'LineWidth', 2);
legend('input','LEP');

效果图为：