相关系数方程不起作用

Question

我写了一个VB代码来计算原始图像和加密图像之间的相关系数。相关系数值介于 0 到 1 之间，但是，在执行下面的代码后，这些值大于 2 或 4 等值。我使用的等式如下： 请检查一下为什么我会得到这些 vales。

这是我使用的代码，请注意在 x 和 y 循环之前所有变量都设置为零：

For y = 0 To hgt-1: For x = 0 To wid-1
meanr_o = meanr_o + Red(x, y)
meang_o = meang_o + Grn(x, y)
meanb_o = meanb_o + Blu(x, y)

meanr_e = meanr_e + nred(x, y)
meang_e = meang_e + nGrn(x, y)
meanb_e = meanb_e + nBlu(x, y)

N = N + 1
Next x: Next y

meanr_o = meanr_o / N
meang_o = meang_o / N
meanb_o = meanb_o / N
meanr_e = meanr_e / N
meang_e = meang_e / N
meanb_e = meanb_e / N

 For y = 0 To hgt-1: For x = 0 To wid-1

sumr1 = sumr1 + ((Red(x, y) - meanr_o) * (nred(x, y) - meanr_e))
sumr2 = sumr2 + ((Red(x, y) - meanr_o) ^ 2)
sumr3 = sumr3 + ((nred(x, y) - meanr_e) ^ 2)
''''''''''''''''''''''''''''''''''''''''''
sumg1 = sumg1 + ((Grn(x, y) - meang_o) * (nGrn(x, y) - meang_e))
sumg2 = sumg2 + ((Grn(x, y) - meang_o) ^ 2)
sumg3 = sumg3 + ((nGrn(x, y) - meang_e) ^ 2)
''''''''''''''''''''''''''''''''''''''''''
sumb1 = sumb1 + ((Blu(x, y) - meanb_o) * (nBlu(x, y) - meanb_e))
sumb2 = sumb2 + ((Blu(x, y) - meanb_o) ^ 2)
sumb3 = sumb3 + ((nBlu(x, y) - meanb_e) ^ 2)

Next x: Next y
sumr1 = sumr1 / N
sumr2 = sumr2 / N
sumr3 = sumr3 / N

sumg1 = sumg1 / N
sumg2 = sumg2 / N
sumg3 = sumg3 / N

sumb1 = sumb1 / N
sumb2 = sumb2 / N
sumb3 = sumb3 / N

Corr_r = sumr1 / Sqr(sumr2 * sumr3)
Corr_g = sumg1 / Sqr(sumg2 * sumg3)
Corr_b = sumb1 / Sqr(sumb2 * sumb3)
Corr = (Corr_r + Corr_g + Corr_b) / 3
Label1.Caption = Corr

Answer 1

我已将您的代码 sn-p 限制为红色，并创建了两个函数，它们只为 x=0 和 y=0 返回一个像素值。此代码 sn-p 似乎正在工作并返回 -1 和 1 之间的相关系数。请注意，我已将 meanr_o、meanr_e、sumr1、sumr2、sumr3、Corr_r 声明为双精度数.我也在使用Math.Sqrt 而不是Sqr，你可以找到一个.NET fiddle here。

Public Module Module1
    Function Red(ByVal x As Integer, ByVal y As Integer) As Integer
        ' local variable declaration */
        Dim result As Integer
        If (x = 0) And (y = 0) Then
            result = 255
        Else
            result = 0
        End If
        Red = result
    End Function

    Function nred(ByVal x As Integer, ByVal y As Integer) As Integer
        ' local variable declaration */
        Dim result As Integer
        If (x = 0) And (y = 0) Then
            result = 255
        Else
            result = 0
        End If
        nred = result
    End Function

    Public Sub Main()
        Dim hgt, wid, N As Integer
        Dim meanr_o, meanr_e, sumr1, sumr2, sumr3, Corr_r As Double
        hgt = 255
        wid = 255
        For y = 0 To hgt - 1 : For x = 0 To wid - 1
                meanr_o = meanr_o + Red(x, y)
                meanr_e = meanr_e + nred(x, y)
                N = N + 1
            Next x : Next y

        meanr_o = meanr_o / N
        meanr_e = meanr_e / N

        For y = 0 To hgt - 1 : For x = 0 To wid - 1
                sumr1 = sumr1 + ((Red(x, y) - meanr_o) * (nred(x, y) - meanr_e))
                sumr2 = sumr2 + ((Red(x, y) - meanr_o) ^ 2)
                sumr3 = sumr3 + ((nred(x, y) - meanr_e) ^ 2)
            Next x : Next y
        sumr1 = sumr1 / N
        sumr2 = sumr2 / N
        sumr3 = sumr3 / N

        Corr_r = sumr1 / System.Math.Sqrt(sumr2 * sumr3)
        System.Console.WriteLine("Correlation is : {0}", Corr_r)

    End Sub
End Module