[fnamefpath]?=?uigetfile（{‘*.*‘;‘*.pgm‘;‘*.jpg‘}）;
name?=?strcat（fpathfname）;
if?~isequal（fname?0）
????imin?=?imfinfo（name）;
????img?=?imread（name）;
????if?imin.BitDepth?==?24
????????img?=?rgb2gray（img）;
????end
????[row_img?col_img]=size（img）;
end
img?=?double（img）;
tic;
all_pix?=?row_img?*?col_img?;

%?get?probability?of?each?pixel.
count_pix?=?zeros（1256）?;
pro_pix?=?[]?;?
for?i?=?1?:?1?:?row_img
????for?j?=?1?:?1?:?col_img
????????count_pix（1img（ij）+1）?=?count_pix（1img（ij）+1）?+?1?;?
????end
end
pro_pix?=?count_pix?/?all_pix?;

%?choose?k?value;
max_kesi?=?-1?;?
max_k?=?0?;?
for?k?=?1?:?1?:?254
????wa?=?0?;
????ua?=?0?;?
????i?=?0?;?
????while（?i?<=?k?）
????????wa?=?wa?+?pro_pix（1i+1）?;?
????????ua?=?ua?+?i?*?pro_pix（1i+1）?;?
????????i?=?i?+?1?;?
????end

????
????if?（?wa?==?0.0?）
????????continue;
????els