Airlight.m

%  CORRESPONDENCE INFORMATION
%  This code is written by Gaofeng MENG 
%
%  Gaofeng MENG:  
%  National Laboratory of Pattern Recognition,
%  Institute of Automation, Academy of Sciences, Beijing 100190
%  Comments and bug reports are welcome.  Email to gfmeng@nlpr.ia.ac.cn
%
%  WORK SETTING:
%  This code has been compiled and tested by using MATLAB R2009a
%
%  For more detials, please see our paper:
%  Gaofeng MENG, Ying WANG, Jiangyong DUAN, Shiming XIANG, Chunhong PAN. 
%  Efficient Image Dehazing with Boundary Constraint and Contextual Regularization, 
%  ICCV, Sydney, Australia, pp.617-624, 3-6 Dec., 2013.
%
%  Last Modified: Feb. 14, 2014, By Gaofeng MENG
%  

function A = Airlight(HazeImg, method, wsz)
% estimating the global airlight
%
if strcmp(method, 'manual')
    h = figure, imshow(HazeImg, []); 
    title('manual airlight estimation: left click to pick a most hazy pixel. ')
    [x, y] = ginput(1);
    A = HazeImg(round(y), round(x), :);
    A = double(A) -1;
    A = min(A, 255);
    close(h);
elseif strcmp(method, 'he')
    A = airlight_he(HazeImg, wsz);    
elseif strcmp(method, 'our')
    A = airlight_our(HazeImg, wsz);
else
    error('parameter error.');
end

%% 
function A = airlight_our(HazeImg, wsz)
% estimating A channel by channel separately
for k = 1 : 3
    minImg = ordfilt2(double(HazeImg(:, :, k)), 1, ones(wsz), 'symmetric');
    A(k) = max(minImg(:));
end

%%
function A = airlight_he(HazeImg, wsz)
% estimating A using He's method
hsv = rgb2hsv(HazeImg);
GrayImg = hsv(:, :, 3);
[nRows, nCols, bt] = size(HazeImg);

% computing dark channel
DarkImg = min(double(HazeImg), [], 3);
DarkImg = ordfilt2(DarkImg, 1, ones(wsz), 'symmetric');
% 
topDark = sort(DarkImg(:), 'descend');
idx = round(0.001 * length(topDark));
val = topDark(idx); 
id_set = find(DarkImg >= val);  % the top 0.1% brightest pixels in the dark channel
BrightPxls = GrayImg(id_set);
iBright = find(BrightPxls >= max(BrightPxls));
id = id_set(iBright); id = id(1);
row = mod(id, nRows);
col = floor(id / nRows) + 1;

% A is a vector
A = HazeImg(row, col, :);
A = double(A(:));