+type Histogram = { data: int[]; total: int; sum: int; min: float32; max: float32 }
+
+let histogramImg (img: Image<Gray, float32>) (nbSamples: int) : Histogram =
+ let imgData = img.Data
+
+ let min, max =
+ let min = ref [| 0.0 |]
+ let minLocation = ref <| [| Point() |]
+ let max = ref [| 0.0 |]
+ let maxLocation = ref <| [| Point() |]
+ img.MinMax(min, max, minLocation, maxLocation)
+ float32 (!min).[0], float32 (!max).[0]
+
+ let bin (x: float32) : int =
+ let p = int ((x - min) / (max - min) * float32 nbSamples)
+ if p >= nbSamples then nbSamples - 1 else p
+
+ let data = Array.zeroCreate nbSamples
+
+ for i in 0 .. img.Height - 1 do
+ for j in 0 .. img.Width - 1 do
+ let p = bin imgData.[i, j, 0]
+ data.[p] <- data.[p] + 1
+
+ { data = data; total = img.Height * img.Width; sum = Array.sum data; min = min; max = max }
+
+let histogramMat (mat: Matrix<float32>) (nbSamples: int) : Histogram =
+ let matData = mat.Data
+
+ let min, max =
+ let min = ref 0.0
+ let minLocation = ref <| Point()
+ let max = ref 0.0
+ let maxLocation = ref <| Point()
+ mat.MinMax(min, max, minLocation, maxLocation)
+ float32 !min, float32 !max
+
+ let bin (x: float32) : int =
+ let p = int ((x - min) / (max - min) * float32 nbSamples)
+ if p >= nbSamples then nbSamples - 1 else p
+
+ let data = Array.zeroCreate nbSamples
+
+ for i in 0 .. mat.Height - 1 do
+ for j in 0 .. mat.Width - 1 do
+ let p = bin matData.[i, j]
+ data.[p] <- data.[p] + 1
+
+ { data = data; total = mat.Height * mat.Width; sum = Array.sum data; min = min; max = max }
+
+let histogram (values: float32 seq) (nbSamples: int) : Histogram =
+ let mutable min = Single.MaxValue
+ let mutable max = Single.MinValue
+ let mutable n = 0
+
+ for v in values do
+ n <- n + 1
+ if v < min then min <- v
+ if v > max then max <- v
+
+ let bin (x: float32) : int =
+ let p = int ((x - min) / (max - min) * float32 nbSamples)
+ if p >= nbSamples then nbSamples - 1 else p
+
+ let data = Array.zeroCreate nbSamples
+
+ for v in values do
+ let p = bin v
+ data.[p] <- data.[p] + 1
+
+ { data = data; total = n; sum = Array.sum data; min = min; max = max }
+
+let otsu (hist: Histogram) : float32 * float32 * float32 =
+ let mutable sumB = 0
+ let mutable wB = 0
+ let mutable maximum = 0.0
+ let mutable level = 0
+ let sum = hist.data |> Array.mapi (fun i v -> i * v) |> Array.sum |> float
+
+ for i in 0 .. hist.data.Length - 1 do
+ wB <- wB + hist.data.[i]
+ if wB <> 0
+ then
+ let wF = hist.total - wB
+ if wF <> 0
+ then
+ sumB <- sumB + i * hist.data.[i]
+ let mB = (float sumB) / (float wB)
+ let mF = (sum - float sumB) / (float wF)
+ let between = (float wB) * (float wF) * (mB - mF) ** 2.;
+ if between >= maximum
+ then
+ level <- i
+ maximum <- between
+
+ let mean1 =
+ let mutable sum = 0
+ let mutable nb = 0
+ for i in 0 .. level - 1 do
+ sum <- sum + i * hist.data.[i]
+ nb <- nb + hist.data.[i]
+ (sum + level * hist.data.[level] / 2) / (nb + hist.data.[level] / 2)
+
+ let mean2 =
+ let mutable sum = 0
+ let mutable nb = 0
+ for i in level + 1 .. hist.data.Length - 1 do
+ sum <- sum + i * hist.data.[i]
+ nb <- nb + hist.data.[i]
+ (sum + level * hist.data.[level] / 2) / (nb + hist.data.[level] / 2)
+
+ let toFloat l =
+ float32 l / float32 hist.data.Length * (hist.max - hist.min) + hist.min
+
+ toFloat level, toFloat mean1, toFloat mean2
+
+