public void FastHoughTransform()
{
using (var image = Image("building.jpg", ImreadModes.Grayscale))
using (var fht = new Mat())
{
CvXImgProc.FastHoughTransform(image, fht, MatType.CV_32SC1);
Cv2.MinMaxLoc(fht, out var minv, out double maxv);
Mat ucharFht = new Mat();
fht.ConvertTo(ucharFht, MatType.CV_8UC1,
255.0 / (maxv + minv), minv / (maxv + minv));
Rescale(ucharFht, ucharFht);
//Cv2.ImShow("fast hough transform", ucharFht);
//Cv2.WaitKey();
}
public void FHTSample()
{
const string imPath = @"_data\image\building.jpg";
using (var image = new Mat(imPath, ImreadModes.GrayScale))
using (var hough = new Mat())
using (var canny = new Mat())
{
Cv2.Canny(image, canny, 50, 200, 3);
CvXImgProc.FastHoughTransform(canny, hough, MatType.CV_32S /*C1*/, AngleRangeOption.ARO_315_135, HoughOP.FHT_ADD, HoughDeskewOption.DESKEW);
var lines = new List <Vec4i>();
GetLocalExtr(lines, canny, hough, 255f * 0.3f * Math.Min(canny.Rows, canny.Cols), 50);
var cannyColor = new Mat();
Cv2.CvtColor(canny, cannyColor, ColorConversionCodes.GRAY2BGR);
for (var i = 0; i < lines.Count; i++)
{
var line = lines[i];
Cv2.Line(cannyColor, new Point(line.Item0, line.Item1), new Point(line.Item2, line.Item3), Scalar.Red);
}
//cannyColor.SaveImage("cannycolor.png");
ShowImagesWhenDebugMode(image, canny, cannyColor);
}
bool GetLocalExtr(List <Vec4i> lines, Mat src, Mat fht, float minWeight, int maxCount)
{
const int MAX_LEN = 10_000;
var weightedPoints = new List <KeyValuePair <int, Point> >();
for (var y = 0; y < fht.Rows; ++y)
{
if (weightedPoints.Count > MAX_LEN)
{
break;
}
var fhtMat = new MatOfInt(fht);
var fhtIndexer = fhtMat.GetIndexer();
var pLineY = Math.Max(y - 1, 0);
var cLineY = y;
var nLineY = Math.Min(y + 1, fht.Rows - 1);
for (var x = 0; x < fht.Cols; ++x)
{
if (weightedPoints.Count > MAX_LEN)
{
break;
}
var value = fhtIndexer[cLineY, x];
if (value >= minWeight)
{
var isLocalMax = 0;
var start = Math.Max(x - 1, 0);
var end = Math.Min(x + 1, fht.Cols - 1);
for (var xx = start; xx < end; ++xx)
{
var pLine = fhtIndexer[pLineY, xx];
var cLine = fhtIndexer[cLineY, xx];
var nLine = fhtIndexer[nLineY, xx];
if (!incIfGreater(value, pLine, ref isLocalMax) ||
!incIfGreater(value, cLine, ref isLocalMax) ||
!incIfGreater(value, nLine, ref isLocalMax))
{
isLocalMax = 0;
break;
}
}
if (isLocalMax > 0)
{
weightedPoints.Add(new KeyValuePair <int, Point>(value, new Point(x, y)));
}
}
}
}
if (weightedPoints.Count == 0)
{
return(true);
}
// Sort WeightedPoints
weightedPoints = weightedPoints.OrderByDescending(x => x.Key).ToList();
weightedPoints = weightedPoints.Take(maxCount).ToList();
for (var i = 0; i < weightedPoints.Count; i++)
{
lines.Add(CvXImgProc.HoughPoint2Line(weightedPoints[i].Value, src));
}
return(true);
}
bool incIfGreater(int a, int b, ref int value)
{
if (/*value == 0 || */ a < b)
{
return(false);
}
if (a > b)
{
++(value);
}
return(true);
}
}