i can find out the amount of greenness for the image using the below code...How can i find out the greenness using ndvi

a=0; b= 0; c=0; p=0; p1=0;

%pic=sprintf('E:\PPTFILES\img-thing.png') fnam=imread('E:\PPTFILES\images.png'); for mm = 1:size(fnam,1)

    for nn = 1:size(fnam,2)

if (fnam(mm,nn,2) -10) > fnam(mm,nn,1) & (fnam(mm,nn,2)-10) > fnam(mm,nn,3) fnam(mm,nn,1) = fnam(mm,nn,1); fnam(mm,nn,2) = fnam(mm,nn,2); fnam(mm,nn,3) = fnam(mm,nn,3);

      a=a+1;

else fnam(mm,nn,1) = 250; fnam(mm,nn,2) = 250; fnam(mm,nn,3) = 250; b=b+1;

    end
  end 
end
p = a / (a + b);
p1 = p * 100;

imshow(fnam); a = sprintf('Vegetation Pixel Count= %3d',a); b = sprintf('Non Vegetation Pixel count= %3d',b); c = sprintf('Percentage of area of veg is %3f %',p1); msgbox(a); msgbox(b); msgbox(c);