Why Is It That The Cint() Is Only Used For Pic.GetPixel(X,Y).R) And Not For The Others

i need some help on explaining to me whats going on in the code below. Basically, the code below is used to convert a bitmap image to grayscale level (black and white).

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim pic As Bitmap
pic = picVisible.Image
Dim X As Integer

[code].....

what i dont understand is the part;

color = (CInt(pic.GetPixel(X, Y).R) + pic.GetPixel(X, Y).G + pic.GetPixel(X, Y).B) / 3

why is it that the Cint() is only used for pic.GetPixel(X,Y).R) and not for the others ? Any Image processing expert that can help explain this ?

Note: The code works well and manages to convert an image into its grayscale.