how to resolve ArgumentOutOfRange Exception in the following code(in the code which is underlined)

Private Sub GrayscaleToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles GrayscaleToolStripMenuItem.Click
        Dim bm As New Bitmap(PictureBox2.Image)
        Dim X As Integer
        Dim Y As Integer
        Dim clr As Integer

        For X = 0 To bm.Width - 1
            For Y = 0 To bm.Height - 1
                clr = (CInt(bm.GetPixel(X, Y).R) + _
                       bm.GetPixel(X, Y).G + _
                       bm.GetPixel(X, Y).B) \ 3
                bm.SetPixel(X, Y, Color.FromArgb(clr, clr, clr))
            Next Y
        Next X

        PictureBox2.Image = bm
    End Sub
    Private Function Average(ByVal Size As Size, ByVal imageSize As SizeF, ByVal PixelX As Integer, ByVal Pixely As Integer) As Color
        Dim pixels As New ArrayList
        Dim x As Integer, y As Integer
        Dim bmp As Bitmap = PictureBox2.Image.Clone

            For x = PixelX - CInt(Size.Width / 2) To PixelX + CInt(Size.Width / 2)
            For y = Pixely - CInt(Size.Height / 2) To Pixely + CInt(Size.Height / 2)
                If (x > 0 And x < imageSize.Width) And _
                   (y > 0 And y < imageSize.Height) Then
                    pixels.Add(bmp.GetPixel(x, y))
                End If
            Next
        Next

          Dim thisColor As Color

        Dim alpha As Integer = 0
        Dim red As Integer = 0
        Dim green As Integer = 0
        Dim blue As Integer = 0

        For Each thisColor In pixels
            alpha += thisColor.A
            red += thisColor.R
            green += thisColor.G
            blue += thisColor.B
        Next

        Return Color.FromArgb(alpha / pixels.Count, _
                                red / pixels.Count, _
                             green / pixels.Count, _
                             blue / pixels.Count)
    End Function

    Private Sub gausianBlur(ByVal alphaEdgesOnly As Boolean, ByVal blurSize As Size)
        Dim PixelY As Integer
        Dim PixelX As Integer
        Dim bmp As Bitmap = PictureBox2.Image.Clone

        For PixelY = 0 To bmp.Width - 1

            For PixelX = 0 To bmp.Height - 1
                If Not alphaEdgesOnly Then
                    bmp.SetPixel(PixelX, PixelY, Average(blurSize, bmp.PhysicalDimension, PixelX, PixelY))
                ElseIf bmp.GetPixel(PixelX, PixelY).A <> 255 Then
                    bmp.SetPixel(PixelX, PixelY, Average(blurSize, bmp.PhysicalDimension, PixelX, PixelY))
                End If

            Next
        Next

        PictureBox2.Image = bmp.Clone
        bmp.Dispose()
    End Sub