Image from text in fsharp

TextToImage.fs

open System.Drawing

[<EntryPoint>]
let main argv =
    let text = argv.[0]
    use font = new Font("Courier New", 72.0f * 5.0f, FontStyle.Bold)
    let getTextSize str =  
        use b = new Bitmap (1, 1)
        use g = b |> Graphics.FromImage
        g.MeasureString (str, font)
    let textSize = text |> getTextSize
    use b = new Bitmap (textSize.Width |> int32, textSize.Height |> int32)
    use g = b |> Graphics.FromImage
    Color.Black |> g.Clear
    use textBrush = new SolidBrush (Color.LightGreen)
    g.DrawString (text, font, textBrush, 0.0f, 0.0f)
    g.Save |> ignore
    b.Save ("pipe.png", Imaging.ImageFormat.Png)
    0