C++/OpenCV implementation of super long exposure ( www.flickr.com/photos/27992339@N00/9655979716/ )

super_long_exposure.cpp

// vim: filetype=cpp fileencoding=UTF-8 shiftwidth=2 tabstop=2 autoindent expandtab
//
// compile
// % g++ -o super_long_exposure super_long_exposure.cpp -fopenmp -O3 -Wall `pkg-config --libs --cflags opencv` -lm

#include <opencv2/opencv.hpp>
#include <iostream>
#include <climits>
#include <cassert>

template <class T> inline T pointer_cast(void *p)
{
  return static_cast<T>(p);
}

int main(int argc, char* argv[])
{
  assert(CHAR_BIT == 8);

  if (argc == 1) {
    std::cerr << "Usage: %s moviefile.avi output.png" << std::endl;
    return 1;
  }
  // Load parameter.
  if (argc != 3) {
    std::cerr << "Error: Specify a movie and output file." << std::endl;
    return -1;
  }
  std::string movFilepath = std::string(argv[1]);
  std::string outFilepath = std::string(argv[2]);

  std::cout << "Input movie file: " << movFilepath << std::endl;
  std::cout << "Output image file: " << outFilepath << std::endl;

  // Open the movie file.
  cv::VideoCapture capture(movFilepath);
  if (capture.isOpened() == false) {
    std::cerr << "Error: Could not load " << movFilepath << std::endl;
    return -1;
  }
  capture.set(CV_CAP_PROP_CONVERT_RGB, true);

  assert(capture.get(CV_CAP_PROP_FORMAT) == CV_8U);

  // Query the first frames to get the image width and height.
  unsigned int numOfFrames = 0;
  unsigned long *workingArray;
  cv::Mat frameMat;
  cv::Mat outputMat;

  if (capture.read(frameMat) == true) {
    assert(frameMat.type() == CV_8UC3);

    const unsigned char *const frameMatData = frameMat.data;
    const size_t dataLength = frameMat.total();

    workingArray = new unsigned long[3*dataLength];
    memset(workingArray, 0, sizeof(workingArray));
    outputMat = cv::Mat::zeros(frameMat.rows, frameMat.cols, CV_16UC3);

    #pragma omp parallel for
    for (unsigned int i = 0; i < 3*dataLength; i++) {
      workingArray[i] += frameMatData[i];
    }

    numOfFrames++;
    std::cout << "." << std::flush;
  }

  // Query frames...
  while (capture.read(frameMat) == true) {
    const unsigned char *const frameMatData = frameMat.data;
    const size_t dataLength = frameMat.total();

    #pragma omp parallel for
    for (unsigned int i = 0; i < 3*dataLength; i++) {
      workingArray[i] += frameMatData[i];
    }

    numOfFrames++;
    std::cout << "." << std::flush;
  }

  // Simple color scaling.
  {
    unsigned short *const outputMatData = pointer_cast<unsigned short*>(outputMat.data);
    const size_t dataLength = outputMat.total();

    #pragma omp parallel for
    for (unsigned int i = 0; i < 3*dataLength; i++) {
      outputMatData[i] = (unsigned short) ((unsigned long long)workingArray[i] * 257 / numOfFrames);
    }

    delete[] workingArray;
  }

  // output to file.
  if (cv::imwrite(outFilepath, outputMat) == false) {
    std::cerr << "Error: Output error." << std::endl;
    return -1;
  }

  return 0;
}