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))

// randomize or R or G or B each 1 to 3 pixels
let randomColorize a =
    let rnd = new System.Random()
    let next = fun() -> rnd.Next(255)
    let rgb = function
        | 0 -> fun(c : System.Drawing.Color) -> Color.FromArgb(int c.A, next(), (int c.G), (int c.B))
        | 1 -> fun(c) -> Color.FromArgb(int c.A, (int c.R), next(), (int c.B))
        | _ -> fun(c) -> Color.FromArgb(int c.A, (int c.R), (int c.G), next())
    a |> Array.Parallel.mapi (
        fun i (x,y,c : System.Drawing.Color) -> 
            if i % rnd.Next(1,3) = 0 then x,y, rgb(rnd.Next(2))(c)
            else x,y,c)
(*
 * 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
    ()