I am trying to read data from a YAML file using the tutorials available at the OpenCV website. I am using the ">>" operator as suggested.
cv::Mat R;
cv::FileStorage fs;
fs.open(filename, cv::FileStorage::READ);
R >> fs["matrix"];
It basically works but I want the matrix to be in double precision not in float precision. Typing the matrix R as a double matrix does not do the job. What would be the right way to achieve this.
To load the image as "double precision", aka of type CV_64F, the image need to be also stored as CV_64F.
If the image is saved as "single precision", aka of type CV_32F, you can however load it as CV_32F, and then convert to CV_64F with:
R.convertTo(R, CV_64F);
You can check the format of the saved matrix opening the yml file, and checking the field dt. For CV_32F formats it will have a f in it, for CV_64F formats it will have a d.
Related
Hello I am using opencv in version 3.4 and want to read an image (*.pgm) and then convert it to CV_32SC1. Therefore I use the following code (part):
img = imread(f, CV_LOAD_IMAGE_GRAYSCALE);
img.convertTo(imgConv, CV_32SC1);
The problem is the following, all pixels are converted to zero, and I don't understand why. I'm checking by (and imshow("Image", imgConv);)
cout << static_cast<int>(img.at<uchar>(200,100));
cout << static_cast<int32_t>(imgConv.at<int32_t>(200,100)) << endl;
In my example this results in
74
74
I tested several points of the image, all pixels are simply the same, but shouldn't them being converted automatically to the 32 bit range, or do I have to manage that manually?
You have to manage that manually. This is why cv::Mat::convertTo() has another parameter, a scale. For instance, if you want to convert from CV_8U to CV_32F you'd typically
img.convertTo(img2, CV_32F, 1.0/255.0);
to scale to the typical float-valued range. I'm not sure what your expected range for CV_32SC1 is, since you're going from unsigned to signed, but just add the scale factor you feel is right.
I am doing a 6-dof transformation with the RANSAC given in OpenCV and I now want to convert two matrices of cv::Mat to an Isometry3d of Eigen but I didn't find good examples about this problem.
e.g.
cv::Mat rot;
cv::Mat trsl;
// the rot is 3-by-3 and trsl is 3-by-1 vector.
Eigen::Isometry3d trsf;
trsf.rotation = rot;
trsf.translation = trsl; // I know trsf has two members but it seems not the correct way to do a concatenation.
Anyone give me a hand? Thanks.
Essentially, you need an Eigen::Map to read the opencv data and store it to parts of your trsf:
typedef Eigen::Matrix<double, 3, 3, Eigen::RowMajor> RMatrix3d;
Eigen::Isometry3d trsf;
trsf.linear() = RMatrix3d::Map(reinterpret_cast<const double*>(rot.data));
trsf.translation() = Eigen::Vector3d::Map(reinterpret_cast<const double*>(trsl.data));
You need to be sure that rot and trsl indeed hold double data (perhaps consider using cv::Mat_<double> instead).
I have two programs, one which accepts an Image as a matrix and does the processing like tracking objects using contour detection.The second program takes image as an array(IplImage) and counting no. of objects.But I want to merge these programs to count as well as track these objects.How can I merge them ?
In the following code left is CvMat, left1 is IplImage. In this way you can manually convert cvmat to IplImage.
for (int y=0;y<height1;y++)
{
uchar* leftdata=(uchar*)(left->data.ptr+y*left->step);
uchar* left1data=(uchar* )(left->imageData+y*left1step);
for (int x=0;x<width1;x++)
left1data[x]=leftdata[x];
}
or here is another link How to convert a Mat variable type in an IplImage variable type in OpenCV 2.0?
//Open the image
Mat img_rgb = imread("sudoku2.png", CV_LOAD_IMAGE_GRAYSCALE);
if (img_rgb.empty())
{
cout<<"Cannot open the image"<<endl;
return;
}
Mat img_bw = img_rgb > 128;
imwrite("image_bw.jpg", img_bw);
Now, I want to get all pixels of img_bw and save it into a matrix M (int[img_bw.rows][img_bw.cols]). How to do it in C++.
What format ?
The raw byte data in cv::Mat is available from the .ptr() function, ie img_bw.ptr().
Opencv also has an xml and json read and write functions for matrices, just by using the << operator - see opencv tutorial on xml and yaml i/o
EDIT: In c++ you can access pixels with the .at operator.
Use img_data.at<uchar>(x,y) for an unsigned char (CV_8U) pixel and img_data.at<float>(x,y) for a CV_32F image.
I am trying to make the dft of one single channeled image, and as cvDft is expecting complex values, I was adviced to merge the original image with another image with all 0's so this last one will be considered as imaginary part.
My problem comes when using cvmerge function,
Mat tmp = imread(filename,0);
if( tmp.empty() )
{cout << "Usage: dft <image_name>" << endl;
return -1;}
Mat Result(tmp.rows,tmp.cols,CV_64F,2);
Mat tmp1(tmp.rows,tmp.cols,CV_64F, 0);
Mat image(tmp.rows,tmp.cols,CV_64F,2);
cvMerge(tmp,tmp1,image);`
It gives me the next error: can not convert cvMAt to cvArr
Anyone could help me? thanks!
1) it seems like you're mixing up 2 different styles of opencv code
cv::Mat (- Mat) is a c++ class from the new version of opencv, cvMerge is a c function from the old version of opencv.
instead of using cvmerge use merge
2) you're trying to merge a matrix (tmp) of type CV_8U (probably) with a CV_64F
use convertTo to get tmp as CV_64F
3) why is your Result & image mats (the destination mat) are initializes to cv::Scalar(2)? i think you're misusing the constractor parameters. see here for more info.
4) you're image mat is a single channel mat and you wanted it as a 2 channel mat (as mentioned in the question), change the declaration to
Mat image(tmp.rows,tmp.cols,CV_64FC2);