module Granulometry

open System
open System.Drawing

open Emgu.CV
open Emgu.CV.Structure

open Utils

// 'range': a minimum and maximum radius.
// 'scale': <= 1.0, to speed up the process.
let findRadius (img: Image<Gray, 'TDepth>) (range: int * int) (scale: float) : int =
    use scaledImg = if scale = 1.0 then img else img.Resize(scale, CvEnum.Inter.Area)

    let r1, r2 = range
    let r1', r2' = roundInt (float r1 * scale), roundInt (float r2 * scale)

    let patternSpectrum = Array.zeroCreate (r2' - r1')
    let intensityImg = scaledImg.GetSum().Intensity

    let mutable previous_n = Double.NaN
    for r in r1' .. r2' do
        let se = CvInvoke.GetStructuringElement(CvEnum.ElementShape.Ellipse, Size(2 * r, 2 * r), Point(-1, -1))
        use closed = scaledImg.MorphologyEx(CvEnum.MorphOp.Close, se, Point(-1, -1), 1, CvEnum.BorderType.Replicate, MCvScalar(0.0))

        let n = closed.GetSum().Intensity

        if not (Double.IsNaN previous_n)
        then
            patternSpectrum.[r - r1' - 1] <- abs (n - previous_n)
        previous_n <- n

    let max, _ = patternSpectrum |> Array.indexed |> Array.fold (fun (iMax, sMax) (i, s) -> if s > sMax then (i, s) else (iMax, sMax)) (0, Double.MinValue)

    float (max + r1') / scale |> roundInt