Bitmap Primitives Helpers

(*
 * Bitmap Primitives Helpers
 * Partly inspired by http://fssnip.net/si.
*)
open System.Drawing

// deserialize a bitmap file
let fromFile (name : string) = new Bitmap(name)

// serialize a bitmap as png
let toFile (name : string) (bmp: Bitmap) =
    bmp.Save(name, Imaging.ImageFormat.Png) |> ignore
    bmp

// load a bitmap in array of tuples (x,y,Color)
let toRgbArray (bmp : Bitmap) =
    [| for y in 0..bmp.Height-1 do
       for x in 0..bmp.Width-1 -> x,y,bmp.GetPixel(x,y) |]   

// builds a bitmap instance from an array of tuples
let toBitmap a =
    let height = (a |> Array.Parallel.map (fun (x,_,_) -> x) |> Array.max) + 1
    let width = (a |> Array.Parallel.map (fun (_,y,_) -> y) |> Array.max) + 1
    let bmp = new Bitmap(width, height)
    a |> Array.Parallel.iter (fun (x,y,c) -> bmp.SetPixel(x,y,c))
    bmp

// converts an image to gray scale
let toGrayScale a =
    a |> Array.Parallel.map (
        fun (x,y,c : System.Drawing.Color) -> 
            let gscale = int((float c.R * 0.3) + (float c.G * 0.59) + (float c.B * 0.11))
            in  x,y,Color.FromArgb(int c.A, gscale, gscale, gscale))

(*
 * Usage example:
*)
let convertImage =
    use newBitmap =
        fromFile @"C:/Temp/with-color.jpg"
        |> toRgbArray
        |> toGrayScale // or custom in memory manipulation function
        |> toBitmap
    use savedBitmap =
        toFile @"C:/Temp/gray-scale.png" newBitmap
    ()