Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        Dim b As Bitmap = CType(PictureBox1.Image, Bitmap)
        MakeImageGrayscale(b)
        PictureBox1.Refresh()
    End Sub
 
    Public Shared Sub MakeImageGrayscale(ByVal bmp As Bitmap)
        Dim cMatrix As New ColorMatrix(New Single()() _
            {New Single() {0.299, 0.299, 0.299, 0, 0}, _
            New Single() {0.587, 0.587, 0.587, 0, 0}, _
            New Single() {0.114, 0.114, 0.114, 0, 0}, _
            New Single() {0, 0, 0, 1, 0}, _
            New Single() {0, 0, 0, 0, 1}})
 
        Dim imageAttrib As New ImageAttributes
        imageAttrib.SetColorMatrix(cMatrix)
        Using gr As Graphics = Graphics.FromImage(bmp)
            gr.DrawImage(bmp, New Rectangle(0, 0, bmp.Width, bmp.Height), _
                0, 0, bmp.Width, bmp.Height, GraphicsUnit.Pixel, imageAttrib)
        End Using
    End Sub

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