MATLAB计算图像互信息值

function mi=MI(a,b)

%Caculate MI of a and b in the region of the overlap part

%计算重叠部分

[Ma,Na] = size(a);

[Mb,Nb] = size(b);

M=min(Ma,Mb);

N=min(Na,Nb);

%初始化直方图数组

hab = zeros(256,256);

ha = zeros(1,256);

hb = zeros(1,256);

%归一化

imax = max(max(a));

imin = min(min(a));

if imax ~= imin

a = double((a-imin))/double((imax-imin));

else

a = zeros(M,N);

end

imax = max(max(b));

imin = min(min(b));

if imax ~= imin

b = double(b-imin)/double((imax-imin));

else

b = zeros(M,N);

end

a = int16(a*255)+1;

b = int16(b*255)+1;

%统计直方图

for i=1:M

for j=1:N

indexx = a(i,j);

indexy = b(i,j) ;

hab(indexx,indexy) = hab(indexx,indexy)+1;%联合直方图

ha(indexx) = ha(indexx)+1;%a图直方图

hb(indexy) = hb(indexy)+1;%b图直方图

end

end

%计算联合信息熵

hsum = sum(sum(hab));

index = find(hab~=0);

p = hab/hsum;

Hab = sum(-p(index).*log(p(index)));

%计算a图信息熵

hsum = sum(sum(ha));

index = find(ha~=0);

p = ha/hsum;

Ha = sum(-p(index).*log(p(index)));

%计算b图信息熵

hsum = sum(sum(hb));

index = find(hb~=0);

p = hb/hsum;

Hb = sum(-p(index).*log(p(index)));

%计算a和b的互信息（越大匹配结果越好）

mi = Ha+Hb-Hab;

%计算a和b的归一化互信息（越小越好）

%mi = hab/(Ha+Hb);