open System.IO

/// Writes BMP binary data
let write (writer:BinaryWriter) (pixels:int[][]) =
   let height = pixels.Length
   let width = pixels.[0].Length
   let sizeOfBmpHeader = 14
   let sizeOfDibHeader = 108
   // BMP Header
   writer.Write("BM"B)
   writer.Write(sizeOfBmpHeader+sizeOfDibHeader+(4*width*height))  
   writer.Write([|0uy;0uy|])  
   writer.Write([|0uy;0uy|])
   writer.Write(sizeOfBmpHeader+sizeOfDibHeader)
   // DIB Header
   writer.Write(sizeOfDibHeader)
   writer.Write(width)
   writer.Write(height)
   writer.Write(1us)
   writer.Write(32us)
   writer.Write(3)
   writer.Write(width*height*4)
   writer.Write(2835)
   writer.Write(2835)
   writer.Write(0)
   writer.Write(0)
   writer.Write(0x00ff0000)
   writer.Write(0x0000ff00)
   writer.Write(0x000000ff)
   writer.Write(0xff000000)
   writer.Write("Win "B |> Array.rev)
   writer.Write(Array.create 0x24 0uy)
   writer.Write(0)
   writer.Write(0)
   writer.Write(0)
   // Pixel Array
   for i = pixels.Length-1 downto 0 do
      let row = pixels.[i]
      for pixel in row do
         writer.Write(pixel)