對兩幅圖像進行相似度的衡量，除了用眼睛觀察的方法外，我們可以更加精確地用數據來客觀的評估歸一化，歸一化的相關系數(NC)提供了度量工具。其計算公式如下：

MATLAB代碼如下所示：

function dNC = nc(ImageA,ImageB)

if (size(ImageA,1) ~= size(ImageB,1)) | (size(ImageA,2) ~= size(ImageB,2))

error('ImageA <> ImageB');

dNC = 0;

return ;

end

ImageA=double(ImageA);

ImageB=double(ImageB);

M = size(ImageA,1);

N = size(ImageA,2);

d1=0;

d2=0;

d3=0;

for i = 1:M

for j = 1:N

d1=d1+ImageA(i,j)*ImageB(i,j) ;

d2=d2+ImageA(i,j)*ImageA(i,j) ;

d3=d3+ImageB(i,j)*ImageB(i,j) ;

end

end

dNC=d1/(sqrt(d2)*sqrt(d3));

VC代碼則根據自己所用庫進行相應的修改，下面附上我自己所用的代碼片段：

int imgA_width;

int imgA_height;

int imgB_width;

int imgB_height;

imgA_width = m_img1_file.GetWidth();

imgA_height = m_img1_file.GetHeight();

imgB_width = m_img2_file.GetWidth();

imgB_height = m_img2_file.GetHeight();

if((imgA_width != imgB_width) || (imgA_height != imgB_height))

{

AfxMessageBox(_T("輸入圖像大小不相等！"));

return;

}

double d1=0.0;

double d2=0.0;

double d3=0.0;

COLORREF colorA;

COLORREF colorB;

BYTE byteA;

BYTE byteB;

//相關系數計算

for(int i=0;i<imgA_height;i++)

{

for(int j=0;j<imgA_width;j++)

{

colorA = m_img1_file.GetPixel(j,i);

colorB = m_img2_file.GetPixel(j,i);

byteA = GetRValue(colorA);

byteB = GetRValue(colorB);

d1 = d1+byteA*byteB;

d2 = d2+byteA*byteA;

d3 = d3+byteB*byteB;

}

}

m_ctNC = d1/(sqrt(d2)*sqrt(d3));

this->UpdateData(false);