Add short support with vpImageConvert::convert() cv::Mat to vpImage<float>

[s-trinh]

Without this quick fix, the following code cannot run:

#include <iostream>
#include <visp3/core/vpConfig.h>
#include <visp3/core/vpIoTools.h>
#include <visp3/core/vpCannyEdgeDetection.h>
#include <visp3/io/vpImageIo.h>

int main(int argc, const char **argv)
{
  std::cout << "getBuildInformation()\n" << vpIoTools::getBuildInformation() << std::endl;

  int gaussianKernelSize = 3;
  float gaussianStdev = 0.5f;
  int apertureSize = 3;
  vpImageFilter::vpCannyFilteringAndGradientType filteringType = vpImageFilter::CANNY_GBLUR_SOBEL_FILTERING;
  // Canny parameters
  float lowerThresh = -1.;
  float upperThresh = -1.;
  float lowerThreshRatio = 0.6f;
  float upperThreshRatio = 1.5f;
  vpImageFilter::vpCannyBackendType backend = vpImageFilter::vpCannyBackendType::CANNY_OPENCV_BACKEND;
  // vpImageFilter::vpCannyBackendType backend = vpImageFilter::vpCannyBackendType::CANNY_VISP_BACKEND;

  vpCannyEdgeDetection cannyDetector(gaussianKernelSize, gaussianStdev, apertureSize,
                                    lowerThresh, upperThresh, lowerThreshRatio, upperThreshRatio,
                                    filteringType);

  vpImage<unsigned char> I_gray, I_canny_visp;
  vpImageIo::read(I_gray, "/tmp/Klimt.png");
  std::cout << "I_gray=" << I_gray.getWidth() << "x" << I_gray.getHeight() << std::endl;

  vpImageFilter::canny(I_gray, I_canny_visp, gaussianKernelSize, lowerThresh, upperThresh, apertureSize,
        gaussianStdev, lowerThreshRatio, upperThreshRatio, false,
        backend,
        vpImageFilter::CANNY_GBLUR_SOBEL_FILTERING);

  vpImage<float> dIx, dIy;
  std::cout << "vpImageFilter::computePartialDerivatives" << std::endl;
  vpImageFilter::computePartialDerivatives(I_gray, dIx, dIy, true, true, true, gaussianKernelSize, gaussianStdev,
      apertureSize, filteringType, backend);

  // Set the gradients of the vpCannyEdgeDetection
  std::cout << "cannyDetector.setGradients(dIx, dIy)" << std::endl;
  cannyDetector.setGradients(dIx, dIy);
  std::cout << "cannyDetector.detect(I_gray)" << std::endl;
  I_canny_visp = cannyDetector.detect(I_gray);

  vpImageIo::write(I_canny_visp, "/tmp/I_res.png");

  return EXIT_SUCCESS;
}

---

This is because

visp/modules/core/src/image/vpImageFilter.cpp

Line 599 in a65eebc

cv::Sobel(img_blur, cv_dIx, CV_16S, 1, 0, apertureGradient, scale, 0., cv::BORDER_REPLICATE);

returns a CV_16S mat but there is no conversion from CV_16S to vpImage<float> needed here

visp/modules/core/include/visp3/core/vpImageFilter.h

Line 169 in a65eebc

vpImageConvert::convert(cv_dIx, dIx);

Computing Sobel with CV_32F datatype would produce an issue here

visp/modules/core/src/image/vpImageFilter_canny.cpp

Line 461 in a65eebc

cv::Canny(cv_dx, cv_dy, edges_cvmat, lowerCannyThresh, upperCannyThresh, false);

since cv::Canny expects CV_16S type.

---

Maybe extend void vpImageConvert::convert(const cv::Mat &src, vpImage<float> &dest, bool flip) to not only float type but also CV_8U, CV_8S, etc?

Another possibility should be to compute the image gradient with CV_32F precision and add this conversion before calling cv::Canny():

    cv::Mat cv_dx_2 = cv_dx, cv_dy_2 = cv_dy;
    if (cv_dx.type() == CV_32F) {
      double min_val = 0, max_val = 0;
      cv::minMaxLoc(cv_dx, &min_val, &max_val);
      double alpha = 65535 / (max_val - min_val);
      double beta = -alpha * min_val;
      cv_dx.convertTo(cv_dx_2, CV_16S, alpha, beta);
    }
    if (cv_dy.type() == CV_32F) {
      double min_val = 0, max_val = 0;
      cv::minMaxLoc(cv_dy, &min_val, &max_val);
      double alpha = 65535 / (max_val - min_val);
      double beta = -alpha * min_val;
      cv_dx.convertTo(cv_dy_2, CV_16S, alpha, beta);
    }

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.

Project coverage is 53.87%. Comparing base (520efed) to head (29b54e8).
Report is 16 commits behind head on master.

Files with missing lines	Patch %	Lines
modules/core/src/image/vpImageConvert_opencv.cpp	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1488      +/-   ##
==========================================
- Coverage   53.88%   53.87%   -0.01%     
==========================================
  Files         442      442              
  Lines       53778    53784       +6     
==========================================
  Hits        28978    28978              
- Misses      24800    24806       +6     

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