module ParasitemiaCore.Edges
open System
open System.Drawing
open System.Collections.Generic
open Emgu.CV
open Emgu.CV.Structure
open Const
open Histogram
open Otsu
///
/// Find edges of an image by using the Canny approach.
/// The thresholds are automatically defined with otsu on gradient magnitudes.
///
///
let find (img: Image) : Matrix * Matrix * Matrix =
let w = img.Width
let h = img.Height
use sobelKernel =
new Matrix(array2D [[ 1.0f; 0.0f; -1.0f ]
[ 2.0f; 0.0f; -2.0f ]
[ 1.0f; 0.0f; -1.0f ]])
let xGradient = new Matrix(img.Size)
let yGradient = new Matrix(img.Size)
CvInvoke.Filter2D(img, xGradient, sobelKernel, Point(1, 1))
CvInvoke.Filter2D(img, yGradient, sobelKernel.Transpose(), Point(1, 1))
use magnitudes = new Matrix(xGradient.Size)
use angles = new Matrix(xGradient.Size)
CvInvoke.CartToPolar(xGradient, yGradient, magnitudes, angles) // Compute the magnitudes and angles.
let thresholdHigh, thresholdLow =
let sensibilityHigh = 0.1f
let sensibilityLow = 0.0f
let threshold, _, _ = otsu (histogramMat magnitudes 300)
threshold + (sensibilityHigh * threshold), threshold - (sensibilityLow * threshold)
// Non-maximum suppression.
use nms = new Matrix(xGradient.Size)
let nmsData = nms.Data
let anglesData = angles.Data
let magnitudesData = magnitudes.Data
let xGradientData = xGradient.Data
let yGradientData = yGradient.Data
for i in 0 .. h - 1 do
nmsData.[i, 0] <- 0uy
nmsData.[i, w - 1] <- 0uy
for j in 0 .. w - 1 do
nmsData.[0, j] <- 0uy
nmsData.[h - 1, j] <- 0uy
for i in 1 .. h - 2 do
for j in 1 .. w - 2 do
let vx = xGradientData.[i, j]
let vy = yGradientData.[i, j]
if vx <> 0.f || vy <> 0.f
then
let angle = anglesData.[i, j]
let vx', vy' = abs vx, abs vy
let ratio2 = if vx' > vy' then vy' / vx' else vx' / vy'
let ratio1 = 1.f - ratio2
let mNeigbors (sign: int) : float32 =
if angle < PI / 4.f
then ratio1 * magnitudesData.[i, j + sign] + ratio2 * magnitudesData.[i + sign, j + sign]
elif angle < PI / 2.f
then ratio2 * magnitudesData.[i + sign, j + sign] + ratio1 * magnitudesData.[i + sign, j]
elif angle < 3.f * PI / 4.f
then ratio1 * magnitudesData.[i + sign, j] + ratio2 * magnitudesData.[i + sign, j - sign]
elif angle < PI
then ratio2 * magnitudesData.[i + sign, j - sign] + ratio1 * magnitudesData.[i, j - sign]
elif angle < 5.f * PI / 4.f
then ratio1 * magnitudesData.[i, j - sign] + ratio2 * magnitudesData.[i - sign, j - sign]
elif angle < 3.f * PI / 2.f
then ratio2 * magnitudesData.[i - sign, j - sign] + ratio1 * magnitudesData.[i - sign, j]
elif angle < 7.f * PI / 4.f
then ratio1 * magnitudesData.[i - sign, j] + ratio2 * magnitudesData.[i - sign, j + sign]
else ratio2 * magnitudesData.[i - sign, j + sign] + ratio1 * magnitudesData.[i, j + sign]
let m = magnitudesData.[i, j]
if m >= thresholdLow && m > mNeigbors 1 && m > mNeigbors -1
then
nmsData.[i, j] <- 1uy
// suppressMConnections nms // It's not helpful for the rest of the process (ellipse detection).
let edges = new Matrix(xGradient.Size)
let edgesData = edges.Data
// Hysteresis thresholding.
let toVisit = Stack()
for i in 0 .. h - 1 do
for j in 0 .. w - 1 do
if nmsData.[i, j] = 1uy && magnitudesData.[i, j] >= thresholdHigh
then
nmsData.[i, j] <- 0uy
toVisit.Push(Point(j, i))
while toVisit.Count > 0 do
let p = toVisit.Pop()
edgesData.[p.Y, p.X] <- 1uy
for i' in -1 .. 1 do
for j' in -1 .. 1 do
if i' <> 0 || j' <> 0
then
let ni = p.Y + i'
let nj = p.X + j'
if ni >= 0 && ni < h && nj >= 0 && nj < w && nmsData.[ni, nj] = 1uy
then
nmsData.[ni, nj] <- 0uy
toVisit.Push(Point(nj, ni))
edges, xGradient, yGradient