I have an image and I want to get a first row (and then the second, and so on...)
I wrote this code, but it doesn't work as expected:
int main(int argc, char** argv)
{
Mat img = imread("a.jpg");
Mat line, ROI;
for (int i = 0; i<img.rows; i++)
{
for (int i = 0; i<img.cols; i++)
{
ROI = img.clone();
// ROI=img(cropRect);
Mat line = ROI(Rect(0, i, ROI.cols, 1)).clone();
}
}
imshow("line", line);
int k = waitKey(0);
return 0;
}
You can use row to create a matrix header for the specified matrix row. If you need a deep copy, you can then use clone.
Also, you need imshow and waitKey to be inside the loop, or you'll see only the last row.
#include <opencv2/opencv.hpp>
using namespace cv;
int main()
{
Mat img = imread("path_to_image");
Mat line;
for (int i = 0; i < img.rows; i++)
{
line = img.row(i);
// Or, for a deep copy:
//line = img.row(i).clone();
imshow("line", line);
waitKey(0);
}
return 0;
}
Related
Hello and thanks for your help.
I would like to test the use of shapes for matching in OpenCV and managed to do the matching part.
To locate the rotated shape, i tought the AffineTransformer Class would be the right choice. As I don't know how the matching would work internally, it would be nice if someone has a link where the proceedings are described.
As shawshank mentioned my following code throw an Assertion failed-error because the variable matches is empty when passed to estimateTransformation function. Does anybody know how to use this function in the right way -respectively what it really does?
#include<opencv2/opencv.hpp>
#include<algorithm>
#include<iostream>
#include<string>
#include<opencv2/highgui/highgui.hpp>
using namespace std;
using namespace cv;
bool rotateImage(Mat src, Mat &dst, double angle)
{
// get rotation matrix for rotating the image around its center
cv::Point2f center(src.cols/2.0, src.rows/2.0);
cv::Mat rot = cv::getRotationMatrix2D(center, angle, 1.0);
// determine bounding rectangle
cv::Rect bbox = cv::RotatedRect(center,src.size(), angle).boundingRect();
// adjust transformation matrix
rot.at<double>(0,2) += bbox.width/2.0 - center.x;
rot.at<double>(1,2) += bbox.height/2.0 - center.y;
cv::warpAffine(src, dst, rot, bbox.size());
return 1;
}
static vector<Point> sampleContour( const Mat& image, int n=300 )
{
vector<vector<Point>> contours;
vector<Point> all_points;
findContours(image, contours, cv::RETR_LIST, cv::CHAIN_APPROX_NONE);
for (size_t i=0; i <contours.size(); i++)
{
for (size_t j=0; j<contours[i].size(); j++)
{
all_points.push_back(contours[i][j]);
}
}
int dummy=0;
for (int add=(int)all_points.size(); add<n; add++)
{
all_points.push_back(all_points[dummy++]);
}
// shuffel
random_shuffle(all_points.begin(), all_points.end());
vector<Point> sampled;
for (int i=0; i<n; i++)
{
sampled.push_back(all_points[i]);
}
return sampled;
}
int main(void)
{
Mat img1, img2;
vector<Point> img1Points, img2Points;
float distSC, distHD;
// read images
string img1Path = "testimage.jpg";
img1 = imread(img1Path, IMREAD_GRAYSCALE);
rotateImage(img1, img2, 45);
imshow("original", img1);
imshow("transformed", img2);
waitKey();
// Contours
img1Points = sampleContour(img1);
img2Points = sampleContour(img2);
//Calculate Distances
Ptr<ShapeContextDistanceExtractor> mysc = createShapeContextDistanceExtractor();
Ptr<HausdorffDistanceExtractor> myhd = createHausdorffDistanceExtractor();
distSC = mysc->computeDistance( img1Points, img2Points );
distHD = myhd -> computeDistance( img1Points, img2Points );
cout << distSC << endl << distHD << endl;
vector<DMatch> matches;
Ptr<AffineTransformer> transformerHD = createAffineTransformer(0);
transformerHD -> estimateTransformation(img1Points, img2Points, matches);
return 0;
}
I have used AffineTransformer class on a 2D image. Below is the basic code which will give you an idea of what it does.
// My OpenCv AffineTransformer demo code
// I have tested this on a 500 x 500 resolution image
#include <iostream>
#include "opencv2/opencv.hpp"
#include <vector>
using namespace cv;
using namespace std;
int arrSize = 10;
int sourcePx[]={154,155,159,167,182,209,238,265,295,316};
int sourcePy[]={190,222,252,285,314,338,344,340,321,290};
int tgtPx[]={120,127,137,150,188,230,258,285,305,313};
int tgtPy[]={207,245,275,305,336,345,342,332,305,274};
int main()
{
// Prepare 'vector of points' from above hardcoded points
int sInd=0, eInd=arrSize;
vector<Point2f> sourceP; for(int i=sInd; i<eInd; i++) sourceP.push_back(Point2f(sourcePx[i], sourcePy[i]));
vector<Point2f> tgtP; for(int i=sInd; i<eInd; i++) tgtP.push_back(Point2f(tgtPx[i], tgtPy[i]));
// Create object of AffineTransformer
bool fullAffine = true; // change its value and see difference in result
auto aft = cv::createAffineTransformer(fullAffine);
// Prepare vector<cv::DMatch> - this is just mapping of corresponding points indices
std::vector<cv::DMatch> matches;
for(int i=0; i<sourceP.size(); ++i) matches.push_back(cv::DMatch(i, i, 0));
// Read image
Mat srcImg = imread("image1.jpg");
Mat tgtImg;
// estimate points transformation
aft->estimateTransformation(sourceP, tgtP, matches);
// apply transformation
aft->applyTransformation(sourceP, tgtP);
// warp image
aft->warpImage(srcImg, tgtImg);
// show generated output
imshow("warped output", tgtImg);
waitKey(0);
return 0;
}
I have recently used this piece of code to save frame data from a webcam
#include <opencv\cv.h>
#include <opencv\highgui.h>
#include <opencv2/opencv.hpp>
using namespace cv;
#include <fstream>
using namespace std;
int main(int argc, char** argv)
{
VideoCapture cap(0); // open the default camera
if (!cap.isOpened()) // check if we succeeded
return -1;
cap.set(CV_CAP_PROP_FPS, 15);
Mat edges;
namedWindow("image", 1);
std::vector<cv::Mat> images(100);
for (int i = 0; i < 100; ++i) {
// this is optional, preallocation so there's no allocation
// during capture
images[i].create(480, 640, CV_8UC3);
}
for (int i = 0; i < 100; ++i)
{
Mat frame;
cap >> frame; // get a new frame from camera
frame.copyTo(images[i]);
}
cap.release();
for (int i = 0; i < 100; ++i)
{
imshow("image", images[i]);
if (waitKey(30) >= 0) break;
}
After this, I want to use imread to analyse the newly splitted frames. However, I cannot think of a way to accomplish this.
I tried: Mat colorImage = imread(images[i]);
However, it leads to:
error C2664: 'cv::Mat cv::imread(const cv::String &,int)': cannot convert argument 1 from 'std::vector<cv::Mat,std::allocator<_Ty>>' to 'const cv::String &'
with
[
_Ty=cv::Mat
]
Thanks a lot in advance :)
imread function is used to open the image from disk.
You already have vector of images so you just do:
Mat colorImage = images[i];
and btw. there is no need for this:
for (int i = 0; i < 100; ++i) {
// this is optional, preallocation so there's no allocation
// during capture
images[i].create(480, 640, CV_8UC3);
}
because you are allocating new space anyway except you capture the frames directly like this:
cap >> images[i];
Why is webcam image processing is very slow while using Xcode for this OpenCV project, and only one out of three windows are working (similar spaces and HSV windows are not turning up) and are very slow? How to increase the speed of execution of the program?
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <iostream>
using namespace cv;
using namespace std;
Mat img, hsv, res;
char *win1 = "RGB";
char *win2 = "HSV";
char *win3 = "similar spaces";
uchar thresh = 5;
void setColor(uchar hval){
int i,j;
for (i = 0; i < res.rows; ++i){
for (j = 0; j < res.cols; ++j){
if( hsv.at<Vec3b>(i,j)[0] <= hval+thresh
&& hsv.at<Vec3b>(i,j)[0] >= hval-thresh)
res.at<uchar>(i,j) = 255;
else res.at<uchar>(i,j) = 0;
}
}
imshow(win3, res);
}
void MouseCallBackFunc(int event, int x, int y, int flags, void* userdata){
if(event==EVENT_LBUTTONDOWN){
cout<<"\t x,y : "<<x<<','<<y<<endl;
cout<<'\t'<<img.at<Vec3b>(y,x)<<endl;
setColor(hsv.at<Vec3b>(y,x)[0]);
}
}
int main()
{
img = imread("/usr/share/opencv/samples/cpp/stuff.jpg", CV_LOAD_IMAGE_COLOR);
hsv = Mat::zeros(img.size(), CV_8UC3);
res = Mat::zeros(img.size(), CV_8UC1);
char c;
int i,j;
namedWindow(win2, CV_WINDOW_NORMAL);
namedWindow(win3, CV_WINDOW_NORMAL);
cvtColor(img, hsv, CV_RGB2HSV);
imshow(win1, img);
imshow(win2, hsv);
imshow(win3, res);
setMouseCallback(win1, MouseCallBackFunc, NULL);
// VideoCapture stream(0); //0 is the id of video device.0 if you have only one camera.
// if (!stream.isOpened()) { //check if video device has been initialised
// cout << "cannot open camera";
// }
// while (true) {
// Mat cameraFrame;
// stream.read(cameraFrame);
// imshow("test", cameraFrame);
// c = waitKey(30);
// if(c==27)
// break;
// }
while((c=waitKey(300))!=27){}
return 0;
}
I have a code where i will copy a video to another video
When i copy it somehow the angle change
heres a link for a picture
http://i24.photobucket.com/albums/c22/Klifford_Kho/wrongpixel_zpsloshtqqy.png
Mat frame;
Mat processedImage;
void copy()
{
for (int i = 0; i<400; i++)
{
for (int j = 0; j<200; j++)
{
int b = frame.at<cv::Vec3b>(i, j)[0];
int g = frame.at<cv::Vec3b>(i, j)[1];
int r = frame.at<cv::Vec3b>(i, j)[2];
processedImage.at<cv::Vec3b>(i, j)[0] = b;
processedImage.at<cv::Vec3b>(i, j)[1] = g;
processedImage.at<cv::Vec3b>(i, j)[2] = r;
}
}
int main()
{
VideoCapture cap(0); // get first cam
while (cap.isOpened())
{
if (!cap.read(frame)) // cam might need some warmup
continue;
processedImage = cv::Mat(frame.size().height, frame.size().width, CV_8UC1);
processedImage.setTo(cv::Scalar::all(0));
copy();
imshow("Original", frame);
imshow("Processed", processedImage);
if (waitKey(10) == 27)
break;
}
return 0;
}
P.S. I didnt use frame.cols and frame.rows in the condition because it generated an error
heres a picture of the error
http://i24.photobucket.com/albums/c22/Klifford_Kho/wrongpixel_zpswze5qjrr.png
It is because you create single channel destination image.
processedImage = cv::Mat(frame.size().height, frame.size().width, CV_8UC1);
Change CV_8UC1 to CV_8UC3, it should help also with error mentioned at question end.
I am trying to obtain the first image, make some modification pixel by pixel and write the resultant to a second image.
int main(int argc, char* argv[])
{
namedWindow("Frame");
testVid("D:\\Penguins.mp4");
destroyAllWindows();
return EXIT_SUCCESS;
}
void testVid(char* videoFilename)
{
VideoCapture capture(videoFilename);
Vec3b pixel;
if (!capture.read(frame))
return;
Mat finalframe(frame.rows,frame.cols, CV_8UC3, Scalar(0, 0, 0));
for (int i = 0; i < frame.rows; i++)
for (int j = 0; j < frame.cols; j++)
{
pixel = frame.at<Vec3b>(Point(j, i));
finalframe.at<Vec3b>(Point(j, i)) = pixel;
}
imshow("Frame", finalframe);
keyboard = waitKey(30);
capture.release();
getchar();
}
However, when I display second image using imshow() , A blank grey image is shown.
Now even if I do not choose to do any modifications, I face similar problems when I tried second = first;
The only thing that seems to work is first.copyTo(second);
Any reason why the second image refuses to do anything ??