I try to find the Peaks of a Histogramm which was calculated from a Orientation Image which was created through phase(). The Code I use is from this [Anwser](http://answers.opencv.org/question/56701/find-all-peaks-for-mat-in-opencv-c/). Instead of counting every possible Angle I round them and just count every tenth step. (e.g. 11 = 1, 345 = 35 etc.)
My Problem is, that it seems, that the peaks the algorithm found are not right. (Example image at end)
First the Code:
Calculating Histogram and call Peakfinder:
Mat patch = src(Rect(px,py,15,15));
Mat Sx;
Sobel(patch, Sx, CV_32F, 1, 0, 3);
Mat Sy;
Sobel(patch, Sy, CV_32F, 0, 1, 3);
Mat ori;
phase(Sx, Sy, ori, true);
Mat hist;
int nbins = 36;
int hsize[] = {nbins};
float range[] = {0, 360};
const float *ranges[] = {range};
int chnls[] = {0};
bool uniform = true; bool accumulate = false;
calcHist(&ori, 1, chnls, Mat(), hist, 1, hsize, ranges, uniform, accumulate);
vector peaks;
findHistPeaks(hist, peaks);
Here the Peak Finder Methods:
void non_maxima_suppression(const Mat& src, Mat& mask, const bool remove_plateaus){
//find pixels that are equal to the local neighborhood not maximum (including plateaus)
dilate(src, mask, Mat());
compare(src, mask, mask, CMP_GE);
//optionally filter out pixels that are equal to the local minimum ('plateaus')
if(remove_plateaus){
Mat non_plateau_mask;
erode(src, non_plateau_mask, Mat());
compare(src, non_plateau_mask, non_plateau_mask, CMP_GT);
bitwise_and(mask, non_plateau_mask, mask);
}
}
//function that finds the peaks of a given hist image
void findHistPeaks(Mat _src, OutputArray _idx, const float scale= 0.2, const Size& ksize = Size(9,9), const bool remove_plateus = true){
Mat hist = _src.clone();
// find the min and max values of the hist image
double min_val, max_val;
minMaxLoc(hist, &min_val, &max_val);
Mat mask;
GaussianBlur(hist, hist, ksize, 0); //smooth a bit in otder to obtain better result
non_maxima_suppression(hist, mask, remove_plateus);
vector maxima; // Outputs, locations of non-zero pixels
findNonZero(mask, maxima);
for(vector::iterator it = maxima.begin(); it != maxima.end();){
Point pnt = *it;
float pVal = hist.at(/*pnt.x,*/pnt.y -1);
float val = hist.at(/*pnt.x, */ pnt.y);
float nVal = hist.at(/*pnt.x, */pnt.y+1);
// filter peaks
if((val > max_val * scale))
++it;
else
it = maxima.erase(it);
}
Mat(maxima).copyTo(_idx);
}
And drawing the histogram with circles to mark the Peaks:
double maxVal = 0;
minMaxLoc(hist,0,&maxVal,0,0);
int xscale=10;
Mat histImage;
histImage = Mat::zeros(226, 36 * xscale, CV_8UC1);
for(int s = 0; s < 37; s++){
float binVal = hist.at(s,0);
int intensity = cvRound(binVal * 36/maxVal);
rectangle(histImage, Point(s*xscale,histImage.rows), Point((s+1)*xscale-1, histImage.rows - intensity), Scalar(255, 0, 0), 1);
}
for(int i = 0; i < peaks.size(); i++){
circle(histImage, peaks[i], 25, Scalar(255,0,0), 2, LINE_8, 0);
}
imshow("histo", histImage);
When I write the values of peak vector in the console I get this result:
[0, 18]
[0, 21]
[0, 35]
and the Histogram Image looks like this:
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