let processImage f (path:string) =
    let bitmap_in = new Bitmap(path)
    let bitmap_out = new Bitmap(bitmap_in.Width, bitmap_in.Height)
    let filename = Path.GetFileName(path)
    for i in 0..(bitmap_in.Height-1) do
        for j in 0..(bitmap_in.Width-1) do
            bitmap_out.SetPixel(j,i, mirrorTrans bitmap_in i j)

    bitmap_out.Save(Path.Combine(Path.GetDirectoryName(path), filename.Insert(filename.Length - 4, "-1")),
            ImageFormat.Jpeg)
    bitmap_in.Dispose()
    bitmap_out.Dispose()

let mirrorTrans (image: Bitmap) i j =
     let pix = min (image.Width - 1) (max 0 (j + int (sin(float i / 20.0) * 30.0)))
     // printfn "pix = %A i = %A j = %A" pix i j
     image.GetPixel(pix,i)