How to create grayscale histogram?

Dim myHistogram As Long() = New Long(255) {}
       For i As Integer = 0 To picture.Size.Width - 1
           For j As Integer = 0 To picture.Size.Height - 1
               Dim c As System.Drawing.Color = picture.GetPixel(i, j)

               Dim Temp As Long = 0
               'Temp += c.R
               'Temp += c.G
               'Temp += c.B
             


               Temp = CInt(Temp) / 3
               myHistogram(Temp) += 1

           Next
       Next

Temp = (0.3 * c.R) + (0.3 * c.R) + (0.11 * c.B)
             
               Temp = CInt(Temp) / 3
               myHistogram(Temp) += 1

;Temp += (0.3 * c.R)
             Temp += (0.3 * c.R)
            Temp += (0.11 * c.B)

               Temp = CInt(Temp) / 3
               myHistogram(Temp) += 1