OpenCV contourArea() not working - c++

I'm pretty new to OpenCV and having a slight problem which is probably something very easy to fix.
Basically im doing some basic image processing, I'm trying to find contours which have an contourArea() of < 3000.
The problem is, I'm getting the following error when trying to draw contours and/or call contourArea() function:
The error is occuring on the cv:contourArea() line, the error message is:
OpenCV Error: Assertion failed (contour.checkVector(2) >= 0 && (contour.depth() == CV_32F || contour.depth() == CV_32S)) in cv::contourArea,
file ..\..\..\..\opencv\modules\imgproc\src\contours.cpp, line 1904
Any help is greatly appreciated. The code is below:
using namespace cv;
cv::Mat greyMat, binaryMat, newMat;
cv::Mat image = cv::imread("image.png", 1);
// First convert image to gray scale
cv::cvtColor(image, greyMat, CV_BGR2GRAY);
cv::adaptiveThreshold(greyMat, binaryMat, 255, cv::ADAPTIVE_THRESH_GAUSSIAN_C, cv::THRESH_BINARY_INV, 45, 0);
erode(binaryMat, binaryMat, getStructuringElement(MORPH_ELLIPSE, Size(2, 2)));
dilate(binaryMat, binaryMat, getStructuringElement(MORPH_ELLIPSE, Size(1, 1)));
// Remove unclosed curves (the circled hashtag)
cv::copyMakeBorder(binaryMat, newMat, 1, 1, 1, 1, cv::BORDER_CONSTANT, 0);
cv::floodFill(newMat, cv::Point(0, 0), 255);
newMat = 255 - newMat;
cv::Mat cMat;
newMat.copyTo(cMat);
std::vector<std::vector<cv::Point>> contours;
cv::findContours(cMat, contours, cv::RETR_EXTERNAL, cv::CHAIN_APPROX_NONE);
std::cout << "Found: " << contours.size() << " " << contours[0][0] << std::endl;
for (size_t i = 0; i < contours.size(); i++)
{
if (cv::contourArea(contours[i]) < 3000)
{
cv::drawContours(newMat, contours, i, 255, -1);
}
}
cv::imshow("Debug", newMat);
cv::waitKey(0);
return 0;

Not sure, but from what I read in the error message, the function expects a floating point value, and you give him vector of vector of Point.
According to the current manual, this type is an integer point, so maybe this is the problem.

Related

Basic Shape recognition (openCV C++)

I have a project that I need to make for classes and I chose task that is a bit out of my skills.
Target is to count result of dice rolls.
For now, I'am trying to make it work on a sample pic:
sample pic of dices
and my current code is added below:
#include "opencv2/core/core.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "iostream"
using namespace cv;
using namespace std;
Mat KostkaFunkcja(Mat image, Mat in, Scalar low, Scalar high);
int getMaxAreaContourId(vector <vector<cv::Point>> contours);
vector<Point> contoursConvexHull(vector<vector<Point> > contours, int index);
Mat ZnakiFunkcja(Mat image, Mat in, Scalar low, Scalar high);
int main(int argc, char** argv)
{
Mat image;
image = imread("kostki.jpg", CV_LOAD_IMAGE_COLOR);
if (!image.data)
{
cout << "Could not open or find the image" << std::endl;
return -1;
}
Mat imgHSV;
Mat workimage = image;
cvtColor(workimage, imgHSV, COLOR_BGR2HSV); //Convert the captured frame from BGR to HSV
//red dice
workimage = KostkaFunkcja(workimage, imgHSV, Scalar(146, 0, 31), Scalar(179, 255, 255));
//green dice
workimage = KostkaFunkcja(workimage, imgHSV, Scalar(25, 147, 0), Scalar(98, 255, 154));
//yellow dice
workimage = KostkaFunkcja(workimage, imgHSV, Scalar(22, 45, 161), Scalar(91, 255, 255));
//black dice
workimage = KostkaFunkcja(workimage, imgHSV, Scalar(98, 0, 0), Scalar(179, 232, 107));
//white symbols
workimage = ZnakiFunkcja(workimage, imgHSV, Scalar(58, 0, 183), Scalar(179, 145, 255));
namedWindow("Kostki_kontur", CV_WINDOW_AUTOSIZE);
imshow("Kostki_kontur", workimage);
waitKey(0);
return 0;
}
Mat KostkaFunkcja(Mat image, Mat in, Scalar low, Scalar high)
{
Mat temp;
inRange(in, low, high, temp);
erode(temp, temp, getStructuringElement(MORPH_ELLIPSE, Size(5, 5)));
dilate(temp, temp, getStructuringElement(MORPH_ELLIPSE, Size(5, 5)));
dilate(temp, temp, getStructuringElement(MORPH_ELLIPSE, Size(5, 5)));
erode(temp, temp, getStructuringElement(MORPH_ELLIPSE, Size(5, 5)));
Mat srcBlur, srcCanny;
blur(temp, srcBlur, Size(3, 3));
Canny(srcBlur, srcCanny, 0, 100, 3, true);
vector<vector<Point> > contours;
findContours(srcCanny, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);
int largest_contour_index = getMaxAreaContourId(contours);
Mat drawing = Mat::zeros(srcCanny.size(), CV_8UC3);
for (int i = 0; i< contours.size(); i++)
{
Scalar color = Scalar(255, 255, 255);
drawContours(drawing, contours, i, color, 2);
}
vector<Point> ConvexHullPoints = contoursConvexHull(contours, largest_contour_index);
polylines(image, ConvexHullPoints, true, Scalar(0, 0, 255), 2);
return image;
}
vector<Point> contoursConvexHull(vector<vector<Point> > contours, int index)
{
vector<Point> result;
vector<Point> pts;
for (size_t j = 0; j< contours[index].size(); j++)
pts.push_back(contours[index][j]);
convexHull(pts, result);
return result;
}
int getMaxAreaContourId(vector <vector<cv::Point>> contours)
{
double maxArea = 0;
int maxAreaContourId = -1;
for (int j = 0; j < contours.size(); j++) {
double newArea = cv::contourArea(contours.at(j));
if (newArea > maxArea) {
maxArea = newArea;
maxAreaContourId = j;
}
return maxAreaContourId;
}
}
Mat ZnakiFunkcja(Mat image, Mat in, Scalar low, Scalar high)
{
Mat temp;
inRange(in, low, high, temp);
erode(temp, temp, getStructuringElement(MORPH_ELLIPSE, Size(5, 5)));
dilate(temp, temp, getStructuringElement(MORPH_ELLIPSE, Size(5, 5)));
dilate(temp, temp, getStructuringElement(MORPH_ELLIPSE, Size(5, 5)));
erode(temp, temp, getStructuringElement(MORPH_ELLIPSE, Size(5, 5)));
Mat srcBlur, srcCanny;
blur(temp, srcBlur, Size(3, 3));
Canny(srcBlur, srcCanny, 0, 100, 3, true);
vector<vector<Point> > contours;
findContours(srcCanny, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);
Mat drawing = Mat::zeros(srcCanny.size(), CV_8UC3);
for (int i = 0; i< contours.size(); i++)
{
Scalar color = Scalar(255, 255, 255);
drawContours(drawing, contours, i, color, 2);
polylines(image, contours, true, Scalar(0, 0, 255), 2);
return image;
}
}
Yet I have no idea how to count different shapes (hearts, lightnings, shields, numbers).
I will be greatfull if anybody would give me a tip or solution of how to do the job.
1) sorry for bad english
2) we had no openCV in classes [only basic c++]
3) tryed to found anything usefull on internet, but even if I found anything, I could't understand what was happening in the code
Your project can be splited in three steps:
find the dices.
extract the shapes from the visible face of
the dices.
count the faces.
For the first step among all the possible approaches I think saliency map approaches can help.
Saliency map are a family of segmentation algorithm that aim to detect the parts in the image which are more likely to attract visual attention.
OpenCV have a saliency API that already implement several saliency algorithm and for each of them you can get an segmentation map.
It is highlikely considering the example image you gave the saliency will be focus on the dices.
From this you can so extract the dices as rois from the original image.
For the step 2) saliency algorithms may also fit... or not that depend a lot of the statistical criterions that are used by the algorithm.
However the previously extracted rois should only contain the face of the dice that does contain the shapes you want to count in step 3) so approaches based on contours detection may give quite good result.
Once you get the shapes among the way to count each shape you can use templateMatching (that is also already implement in OpenCV),a clustering approach based on the a shape sensitive metric (Hausdorff, Dice, ...), or many other.
Here is a code that can help you to deal with the two first step.
#ifndef _DEBUG
#define _DEBUG
#endif
#include <iostream>
#include <opencv2/core.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/saliency.hpp>
#include <opencv2/highgui.hpp>
#include <list>
CV_EXPORTS_W void get_regions_of_interest(cv::InputArray _src, cv::OutputArrayOfArrays mv, cv::OutputArrayOfArrays mv2 = cv::noArray());
int main()
{
cv::Mat tmp = cv::imread("C:\Desktop\dices.jpg");
if(!tmp.empty())
{
cv::imshow("source",tmp);
cv::waitKey(-1);
}
std::vector<cv::Mat> rois;
get_regions_of_interest(tmp,rois);
std::cout << "Hello World!" << std::endl;
return 0;
}
void get_regions_of_interest(cv::InputArray _src, cv::OutputArrayOfArrays _rois, cv::OutputArrayOfArrays _contours)
{
// Check that the first argument is an image and the second a vector of images.
CV_Assert(_src.isMat() && !_src.depth() && (_src.channels() == 1 || _src.channels() == 3) && _rois.isMatVector() && (!_contours.needed() || (_contours.needed() && _contours.isMatVector()) ) );
static cv::Ptr<cv::saliency::StaticSaliencySpectralResidual> saliency;
if(!saliency)
saliency = cv::saliency::StaticSaliencySpectralResidual::create();
cv::Mat src = _src.getMat();
cv::Mat gray;
if(src.depth() == src.type())
gray = src;
else
cv::cvtColor(src,gray,cv::COLOR_BGR2GRAY);
bool is_ctr_needed = _contours.needed();
std::list<cv::Mat> final_ctrs;
// Step 1) Process the saliency in order to segment the dices.
cv::Mat saliency_map;
cv::Mat binary_map;
saliency->computeSaliency(src,saliency_map);
saliency->computeBinaryMap(saliency_map,binary_map);
saliency_map.release();
// Step 2) From the binary map get the regions of interest.
cv::Mat1i stats;
std::vector<cv::Mat> rois;
cv::Mat labels;
cv::Mat centroids;
cv::connectedComponentsWithStats(binary_map, labels, stats, centroids);
labels.release();
centroids.release();
// prepare the memory
rois.reserve(stats.rows-1);
// Sort the stats in order to remove the background.
stats = stats.colRange(0,stats.cols-1);
// Extract the rois.
for(int i=0;i<stats.rows;i++)
{
cv::Rect roi = *reinterpret_cast<cv::Rect*>(stats.ptr<int>(i));
if(static_cast<std::size_t>(roi.area()) == gray.total())
continue;
rois.push_back(gray(roi));
#ifdef _DEBUG
cv::imshow("roi_"+std::to_string(i),gray(roi));
#endif
}
// Step 3) Refine.
// Because the final number of shape cannot be determine in advance it is better to use a linked list than a vector.
// In practice except if there is a huge number of elements to work with the performance will be almost the same.
std::list<cv::Mat> shapes;
int cnt=0;
for(const cv::Mat& roi : rois)
{
cv::Mat tmp = roi.clone();
// Slightly sharpen the regions contours
cv::morphologyEx(tmp,tmp, cv::MORPH_CLOSE, cv::noArray());
// Reduce the influence of local unhomogeneous illumination.
cv::GaussianBlur(tmp,tmp,cv::Size(31,31), 5);
cv::Mat thresh;
// Binarize the image.
cv::threshold(roi,thresh,0.,255.,cv::THRESH_BINARY | cv::THRESH_OTSU);
#ifdef _DEBUG
cv::imshow("thresh"+std::to_string(cnt++),thresh);
#endif
// Find the contours of each sub region on interest
std::vector<cv::Mat> contours;
cv::findContours(thresh, contours, cv::RETR_TREE, cv::CHAIN_APPROX_SIMPLE);
cv::Mat dc;
cv::merge(std::vector<cv::Mat>(3,thresh),dc);
// cv::drawContours(dc, contours,-1,cv::Scalar(0.,0.,255),2);
// cv::imshow("ctrs"+std::to_string(cnt),dc);
// Extract the sub-regions
if(is_ctr_needed)
{
for(const cv::Mat& ctrs: contours)
{
cv::Rect croi = cv::boundingRect(ctrs);
// If the sub region is to big or to small it is depreate
if(static_cast<std::size_t>(croi.area()) == roi.total() || croi.area()<50)
continue;
final_ctrs.push_back(ctrs);
shapes.push_back(roi(croi));
#ifdef _DEBUG
cv::rectangle(dc,croi,cv::Scalar(0.,0.,255.));
cv::imshow("sub_roi_"+std::to_string(cnt++),roi(croi));
#endif
}
}
else
{
for(const cv::Mat& ctrs: contours)
{
cv::Rect croi = cv::boundingRect(ctrs);
// If the sub region is to big or to small it is depreate
if(static_cast<std::size_t>(croi.area()) == roi.total() || croi.area()<50)
continue;
shapes.push_back(roi(croi));
#ifdef _DEBUG
cv::rectangle(dc,croi,cv::Scalar(0.,0.,255.));
cv::imshow("sub_roi_"+std::to_string(cnt++),roi(croi));
#endif
}
}
}
#ifdef _DEBUG
cv::waitKey(-1);
#endif
// Final Step: set the output
_rois.create(shapes.size(),1,CV_8U);
_rois.assign(std::vector<cv::Mat>(shapes.begin(),shapes.end()));
if(is_ctr_needed)
{
_contours.create(final_ctrs.size(),1,CV_32SC2);
_contours.assign(std::vector<cv::Mat>(final_ctrs.begin(), final_ctrs.end()));
}
}

How to count white object on Binary Image?

I'm trying to count object from image. I use logs photo, and I use some steps to get a binary image.
This is my code:
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
#include <features2d.hpp>
using namespace cv;
using namespace std;
int main(int argc, char *argv[])
{
//load image
Mat img = imread("kayu.jpg", CV_LOAD_IMAGE_COLOR);
if(img.empty())
return -1;
//namedWindow( "kayu", CV_WINDOW_AUTOSIZE );
imshow("kayu", img);
//convert to b/w
Mat bw;
cvtColor(img, bw, CV_BGR2GRAY);
imshow("bw1", bw);
threshold(bw, bw, 40, 255, CV_THRESH_BINARY);
imshow("bw", bw);
//distance transform & normalisasi
Mat dist;
distanceTransform(bw, dist, CV_DIST_L2, 3);
normalize(dist, dist, 0, 2., NORM_MINMAX);
imshow("dist", dist);
//threshold to draw line
threshold(dist, dist, .5, 1., CV_THRESH_BINARY);
imshow("dist2", dist);
//dist = bw;
//dilasi
Mat dilation, erotion, element;
int dilation_type = MORPH_ELLIPSE;
int dilation_size = 17;
element = getStructuringElement(dilation_type, Size(2*dilation_size + 1, 2*dilation_size+1), Point(dilation_size, dilation_size ));
erode(dist, erotion, element);
int erotionCount = 0;
for(int i=0; i<erotionCount; i++){
erode(erotion, erotion, element);
}
imshow("erotion", erotion);
dilate(erotion, dilation, element);
imshow("dilation", dilation);
waitKey(0);
return 0;
}
As you can see, I use Erosion and Dilation to get better circular object of log. My problem is, I'm stuck at counting the object. I tried SimpleBlobDetector but I got nothing, because when I try to convert the result of "dilation" step to CV_8U, the white object disappear. I got error too when I use findContours(). It say something about channel of image. I can't show the error here, because that's too many step and I already delete it from my code.
Btw, at the end, i got 1 channel of image.
Can i just use it to counting, or am i have to convert it and what is the best method to do it?
Two simple steps:
Find contours for the binarized image.
Get the count of the contours.
Code:
int count_trees(const cv::Mat& bin_image){
cv::Mat img;
if(bin_image.channels()>1){
cv::cvtColor(bin_image,img,cv::COLOR_BGR2GRAY);
}
else{
img=bin_image.clone();;
}
if(img.type()!=CV_8UC1){
img*=255.f; //This could be stupid, but I do not have an environment to try it
img.convertTo(img,CV_8UC1);
}
std::vector<std::vector<cv::Point>> contours
std::vector<Vec4i> hierarchy;
cv::findContours( img, contours, hierarchy, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);
return contours.size();
}
I have the same problem, here's an idea I'm about to implement.
1) Represent your image as an array of integers; 0 = black, 1 = white.
2) set N = 2;
3) Scan your image, pixel-by-pixel. Whenever you find a white pixel, activate a flood-fill algorithm, starting at the pixel just found; paint the region with the value of N++;
4) Iterate 3 until you reach the last pixel. (N-2) is the number of regions found.
This method depends on the shape of the objects; mine are more chaotic than yours (wish me luck..). I'll make use of a recursive flood-fill recipe found somewhere (maybe Rosetta Code).
This solution also makes it easy to compute the size of each region.
try to apply that on the your deleted img
// count
for (int i = 0; i< contours.size(); i = hierarchy[i][0]) // iteration sur chaque contour .
{
Rect r = boundingRect(contours[i]);
if (hierarchy[i][2]<0) {
rectangle(canny_output, Point(r.x, r.y), Point(r.x + r.width, r.y + r.height), Scalar(20, 50, 255), 3, 8, 0);
count++;
}
}
cout << "Numeber of contour = " << count << endl;
imshow("src", src);
imshow("contour", dst);
waitKey(0);

OpenCV find contours of close objects

I am writing a C++ Application using the OpenCV library to detect objects in images. These images look like this:
http://fs1.directupload.net/images/150311/my6uczfn.png
The upper part of the image, which is black, can be ignored.
I know, that every pixel, which is not part of a desired object, will be colored in white. What I am trying to do is to find out how many objects of interest are on an image and where they are.
Up until now I wrote the following code:
Mat image = imread("2.png", CV_LOAD_IMAGE_COLOR);
if(!image.data)
{
std::cout << "Could not open or find the image." << std::endl;
}
Range range_rows(0, image.size().height);
Range range_columns_left(0, image.size().width);
Range range_columns_middle(image.size().width, image.size().width * 2);
Range range_columns_right(image.size().width * 2, image.size().width * 3);
Mat display_mat(image.size().height, image.size().width * 3, CV_8UC3);
Mat left(display_mat, range_rows, range_columns_left);
image.copyTo(left);
Mat classified_image;
threshold(image, classified_image, 254, 255, THRESH_BINARY);
Mat middle(display_mat, range_rows, range_columns_middle);
classified_image.copyTo(middle);
Mat cimage = Mat::zeros(image.size(), CV_8UC3);
Mat classified_grayscale_image;
cvtColor(classified_image, classified_grayscale_image, CV_RGB2GRAY);
std::vector< std::vector<cv::Point> > contours;
findContours(classified_grayscale_image, contours, CV_RETR_LIST, CV_CHAIN_APPROX_NONE);
for(size_t counter = 0; counter < contours.size(); counter++)
{
std::cout << "Contours size: " << contours[counter].size() << std::endl;
if(contours[counter].size() < 6)
continue;
Mat pointsf;
Mat(contours[counter]).convertTo(pointsf, CV_32F);
RotatedRect box = fitEllipse(pointsf);
drawContours(cimage, contours, (int)counter, Scalar::all(255), 1, 8);
ellipse(cimage, box, Scalar(0,0,255), 1, CV_AA);
std::cout << "Ellipse Parameter:\t";
ellipse(cimage, box.center, box.size*0.5f, box.angle, 0, 360, Scalar(0,255,255), 1, CV_AA);
Point2f vtx[4];
box.points(vtx);
for( int j = 0; j < 4; j++ )
line(cimage, vtx[j], vtx[(j+1)%4], Scalar(0,255,0), 1, CV_AA);
}
Mat right(display_mat, range_rows, range_columns_right);
cimage.copyTo(right);
namedWindow("Results", CV_WINDOW_AUTOSIZE);
imshow("Results", display_mat);
waitKey(0);
return 0;
The result looks like this:
http://fs1.directupload.net/images/150311/toiy3aes.png
As you see, the classification, what is an object and what is not, is not perfect, so 2 objects are recognized as one. The classification will be improved, but something like this can happen, if those objects are very close. Even more of a problem is, when they are touching each other.
How can I do a proper object recognition in the case shown above? Any ideas?
You have got few options:
use some filtering/thresholding method on your result image to split objects from each other. Otsu binarization should be enough in this case, alternatively you can try to use dilate operation.
inverse your result image and than use distance transform and Otsu binarization (or some other kind o thresholding - most of them should work fine). It will make you objects smaller but will make counting them much easier.
if you need to mark the objects as precise as possible you need to use more complicated method. Here there is an tutorial which use techniques i've described above and connected components and watershed.

Derivatives in OpenCV

I'm writing a program using opencv that does text detection and extraction.
Im using the Sobel derivative in order to do edge detection and have gotten the following result:
But I wish to get the following result:
(I appologize for the blurry image.)
The problem I'm having is the "blank areas" inside the edges "confuse" the algorithem I'm using so when the algorithem detects the "blank part" seperating between two lines from the lines themselves it gets confused and start running into the letter themselves instead of keepeing between two lines. This error, I believe would be solves by achieving the second result.
Anyone knows what changes i need to make? in the soble derivative? maybe use a different derivative?
Code:
Mat ProfileSeamTextLineExtractor::computeDerivative(){
Mat img = _image;
Mat gradiant_mat;
int scale = 2;
int delta = 0;
int ddepth = CV_16S;
GaussianBlur(img, img, Size(3, 3), 0, 0, BORDER_DEFAULT);
Mat grad_x, grad_y;
Mat abs_grad_x, abs_grad_y;
Sobel(img, grad_x, ddepth, 1, 0, 3, scale, delta, BORDER_DEFAULT);
convertScaleAbs(grad_x, abs_grad_x);
Sobel(img, grad_y, ddepth, 0, 1, 3, scale, delta, BORDER_DEFAULT);
convertScaleAbs(grad_y, abs_grad_y);
/// Total Gradient (approximate)
addWeighted(abs_grad_x, 0.5, abs_grad_y, 0.5, 0, gradiant_mat);
return gradiant_mat;
}
Regards,
Try using the second sobel derivative, add, normalize (this may do the same as addWeighted), and then thresholding optimally. I had results similar to yours with different threshold values.
Here's an example:
cv::Mat result;
cvtColor(image, gray, CV_BGR2GRAY);
cv::medianBlur(gray, gray, 3);
cv::Mat sobel_x, sobel_y, result;
cv::Sobel(gray, sobel_x, CV_32FC1, 2, 0, 5);
cv::Sobel(gray, sobel_y, CV_32FC1, 0, 2, 5);
cv::Mat sum = sobel_x + sobel_y;
cv::normalize(sum, result, 0, 255, CV_MINMAX, CV_8UC1);
//Determine optimal threshold value using THRESH_OTSU.
// This didn't give me optimal results, but was a good starting point.
cv::Mat temp, final;
double threshold = cv::threshold(result, temp, 0, 255, CV_THRESH_BINARY+CV_THRESH_OTSU);
cv::threshold(result, final, threshold*.9, 255, CV_THRESH_BINARY);
I was able to clearly extract both light text on a dark background, and dark text on a light background.
If you need the final image to consistently be white background with black text, you can do this:
cv::Scalar avgPixelIntensity = cv::mean( final );
if(avgPixelIntensity[0] < 127.0)
cv::bitwise_not(final, final);
I tried a lot of different text extraction methods and couldn't find any that worked across the board, but this seems to. This took a lot of trial and error to figure out, so I hope this helps.
I don't really understand what your final aim is. Do you eventually want a nice filled in version of the text so you can recognise the characters? I can give that a shot if that's what you are looking for.
This is what I did while trying to remove inner holes:
For this one I didn't bother:
It fails at the edges where the text is cut off.
Obviously, I had to work with the image that had already gone through some processing. I might be able to give you more help if I had the original and produce a better output. You might not even need to use derivatives at all if the background is clean enough.
Here is the code:
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
using namespace cv;
using namespace std;
void printInnerContours (int contourPos, Mat &filled, vector<vector<Point2i > > &contours, vector<Vec4i> &hierarchy, int area);
int main() {
int areaThresh;
vector<vector<Point2i > > contours;
vector<Vec4i> hierarchy;
Mat text = imread ("../wHWHA.jpg", 0); //write greyscale
threshold (text, text, 50, 255, THRESH_BINARY);
imwrite ("../text1.jpg", text);
areaThresh = (0.01 * text.rows * text.cols) / 100;
findContours (text, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_NONE);
Mat filled = Mat::zeros(text.rows, text.cols, CV_8U);
cout << contours.size() << endl;
for (int i = 0; i < contours.size(); i++) {
int area = contourArea(contours[i]);
if (area > areaThresh) {
if ((hierarchy[i][2] != -1) && (hierarchy[i][3] == -1)) {
drawContours (filled, contours, i, 255, -1);
if (hierarchy[i][2] != -1) {
printInnerContours (hierarchy[i][2], filled, contours, hierarchy, area);
}
}
}
}
imwrite("../output.jpg", filled);
return 0;
}
void printInnerContours (int contourPos, Mat &filled, vector<vector<Point2i > > &contours, vector<Vec4i> &hierarchy, int area) {
int areaFrac = 5;
if (((contourArea (contours[contourPos]) * 100) / area) < areaFrac) {
//drawContours (filled, contours, contourPos, 0, -1);
}
if (hierarchy[contourPos][2] != -1) {
printInnerContours (hierarchy[contourPos][2], filled, contours, hierarchy, area);
}
if (hierarchy[contourPos][0] != -1) {
printInnerContours (hierarchy[contourPos][0], filled, contours, hierarchy, area);
}
}

How to find contours from a webcam frame using opencv and c++?

My goal is to find contours by capturing frame from a webcam. I was able to do it with static images but then I tried to use the same concept in a webcam frame and its giving me this error:
"OpenCV Error: Assertion failed (mtype == type0 || (CV_MAT_CN(mtype) == CV_MAT_CN
(type0) && ((1 << type0) & fixedDepthMask) != 0)) in cv::_OutputArray::create, f
ile C:\builds\2_4_PackSlave-win64-vc11-shared\opencv\modules\core\src\matrix.cpp
, line 1486"
This is the code that I used to find the contours in my program;
Rng rng(12345);
Mat captureframe,con,threshold_output;
vector<vector<Point> > contours; //
vector<Vec4i> hierarchy;
while(true)
{
capturedevice>>captureframe;
con = captureframe.clone();
cvtColor(captureframe,con,CV_BGR2GRAY);
threshold( con, threshold_output, thresh, 255, THRESH_BINARY );
findContours( threshold_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );
Mat drawing = Mat::zeros( threshold_output.size(), CV_8UC3 );
for( int i = 0; i< contours.size(); i++ )
{
Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
drawContours( drawing, contours, i, color, 1, 8, vector<Vec4i>(), 0, Point() );
}
imshow("contour drawing",drawing);
}
I think that the problem is in the following two lines:
con = captureframe.clone();
cvtColor(captureframe,con,CV_BGR2GRAY);
In the first line, you are making con as a clone of captureFrame which means that con is a 3 channel image and in the Second line you are trying to make con a grayScale image which is 1 channel therefore you are getting the fault related to the image type.
You should try to do the following (i am not sure whether your code would run after this or not but you should not get the current error after this):
con.create(captureframe.rows , captureframe.cols, CV_8UC1);
cvtColor(captureframe,con,CV_BGR2GRAY);
Guys thank you so much for your help. I finally figured out my mistake and there was a problem in my declaration. I was looking online for some references and then i stumbled upon this code for object detection. The guy actually declared "contour" like this - "std::vector < std::vector < cv::Point > >contours; " and my declaration was "vector contours". My declaration worked for static images but it gave me this error while finding contours from webcam. Can anyone explain me the difference between the above two declarations? Also, as suggested by skm i converted my frame capture to a 1 channel depth image by using the con.create(frame.rows,frame.cols,cv_8uc1) and then converting it to grayscale image. This step is really crucial. So, here is my complete working code!! Thanks
VideoCapture capturedevice;
capturedevice.open(0);
Mat frame,con;
Mat grayframe;
std::vector < std::vector < cv::Point > >contours; //this is very important decalartion
while(true)
{
capturedevice>>frame;
con.create(frame.rows,frame.cols,CV_8UC1);
cvtColor(frame,con,CV_BGR2GRAY);
cv::findContours (con, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);
cv::drawContours (frame, contours, -1, cv::Scalar (0, 0, 255), 2);
imshow("frame", frame);
waitKey(33);
}