OpenCV/opencv_contrib/modules/phase_unwrapping/tutorials/unwrap/unwrap.markdown

Unwrap two-dimensional phase maps {#tutorial_unwrap}

Goal

In this tutorial, you will learn how to use the phase unwrapping module to unwrap two-dimensional phase maps. The implementation is based on @cite histogramUnwrapping.

Code

@include phase_unwrapping/samples/unwrap.cpp

Explanation

To use this example, wrapped phase map values should be stored in a yml file as CV_32FC1 Mat, under the name "phaseValues". Path to the data and a name to save the unwrapped phase map must be set in the command line. The results are saved with floating point precision in a yml file and as an 8-bit image for visualization purpose.

Some parameters can be chosen by the user:

• histThresh is a parameter used to divide the histogram in two parts. Bins before histThresh are smaller than the ones after histThresh. (Default value is 3*pi*pi).
• nbrOfSmallBins is the number of bins between 0 and histThresh. (Default value is 10).
• nbrOfLargeBins is the number of bins between histThresh and 32*pi*pi. (Default value is 5).

@code{.cpp} phase_unwrapping::HistogramPhaseUnwrapping::Params params;

CommandLineParser parser(argc, argv, keys);
String inputPath = parser.get<String>(0);
String outputUnwrappedName = parser.get<String>(1);
String outputWrappedName = parser.get<String>(2);

if( inputPath.empty() || outputUnwrappedName.empty() )
{
    help();
    return -1;
}
FileStorage fsInput(inputPath, FileStorage::READ);
FileStorage fsOutput(outputUnwrappedName + ".yml", FileStorage::WRITE);

Mat wPhaseMap;
Mat uPhaseMap;
Mat reliabilities;
fsInput["phaseValues"] >> wPhaseMap;
fsInput.release();
params.width = wPhaseMap.cols;
params.height = wPhaseMap.rows;
Ptr<phase_unwrapping::HistogramPhaseUnwrapping> phaseUnwrapping = phase_unwrapping::HistogramPhaseUnwrapping::create(params);

@endcode The wrapped phase map is unwrapped and the result is saved in a yml file. We can also get the reliabilities map for visualization purpose. The unwrapped phase map and the reliabilities map are converted to 8-bit images in order to be saved as png files.

@code{.cpp} phaseUnwrapping->unwrapPhaseMap(wPhaseMap, uPhaseMap);

fsOutput << "phaseValues" << uPhaseMap;
fsOutput.release();

phaseUnwrapping->getInverseReliabilityMap(reliabilities);

Mat uPhaseMap8, wPhaseMap8, reliabilities8;
wPhaseMap.convertTo(wPhaseMap8, CV_8U, 255, 128);
uPhaseMap.convertTo(uPhaseMap8, CV_8U, 1, 128);
reliabilities.convertTo(reliabilities8, CV_8U, 255,128);

imshow("reliabilities", reliabilities);
imshow("wrapped phase map", wPhaseMap8);
imshow("unwrapped phase map", uPhaseMap8);

imwrite(outputUnwrappedName + ".png", uPhaseMap8);
imwrite("reliabilities.png", reliabilities8);

@endcode