Parasitemia/ParasitemiaCore/ImgTools/Otsu.fs

   1 module ParasitemiaCore.Otsu
   2
   3 open Histogram
   4
   5 let otsu (hist: Histogram) : float32 * float32 * float32 =
   6     let mutable sumB = 0
   7     let mutable wB = 0
   8     let mutable maximum = 0.0
   9     let mutable level = 0
  10     let sum = hist.data |> Array.mapi (fun i v -> i * v |> float) |> Array.sum
  11
  12     for i = 0 to hist.data.Length - 1 do
  13         wB <- wB + hist.data.[i]
  14         if wB <> 0
  15         then
  16             let wF = hist.total - wB
  17             if wF <> 0
  18             then
  19                 sumB <- sumB + i * hist.data.[i]
  20                 let mB = (float sumB) / (float wB)
  21                 let mF = (sum - float sumB) / (float wF)
  22                 let between = (float wB) * (float wF) * (mB - mF) ** 2.;
  23                 if between >= maximum
  24                 then
  25                     level <- i
  26                     maximum <- between
  27
  28     let mean1 =
  29         let mutable sum = 0
  30         let mutable nb = 0
  31         for i = 0 to level - 1 do
  32             sum <- sum + i * hist.data.[i]
  33             nb <- nb + hist.data.[i]
  34         (sum + level * hist.data.[level] / 2) / (nb + hist.data.[level] / 2)
  35
  36     let mean2 =
  37         let mutable sum = 0
  38         let mutable nb = 0
  39         for i = level + 1 to hist.data.Length - 1 do
  40             sum <- sum + i * hist.data.[i]
  41             nb <- nb + hist.data.[i]
  42         (sum + level * hist.data.[level] / 2) / (nb + hist.data.[level] / 2)
  43
  44     let toFloat l =
  45         float32 l / float32 hist.data.Length * (hist.max - hist.min) + hist.min
  46
  47     toFloat level, toFloat mean1, toFloat mean2