What does the Operator 0 and 1 do in MorphologyEx() function of OpenCV

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Hello all,
I was writing a code with MorphologyEx() function of OpenCV, when i mistakenly gave value 0 to 'Morphology Operator' parameter of the function.

As can be seen in the function specs [^], the Operator value ranges from 2-6 for Opening, Closing, Gradient, Top, Bottom hat operations respectively.

The function should ve given some error with Operator value 0, but it worked fine, and the results i received were like a stronger Closing filter. This result is favourable for my project, but i want to know what filter it is. The function also gave some result with operator parameter set to 1.

If someone knows what the operator values 0 and 1 does, please let me know.

Posted 24-Oct-15 22:41pm

Abhishrek

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Kornfeld Eliyahu Peter · Accepted Answer · 2015-10-24T23:55:00

It is never a good idea to use direct codes where enums provided by the framework...
If you check the source code (OpenCV is on GitHub!) you will see this:

C++

switch( op )
    {
    case MORPH_ERODE:
        // ...
        break;
    case MORPH_DILATE:
        // ...
        break;
    case MORPH_OPEN:
        break;
    case CV_MOP_CLOSE:
        // ...
        break;
    case CV_MOP_GRADIENT:
        // ...
        break;
    case CV_MOP_TOPHAT:
        // ...
        break;
    case CV_MOP_BLACKHAT:
        // ...
        break;
    default:
        CV_Error( CV_StsBadArg, "unknown morphological operation" );
}

And if you search for the enum behind you will see this:

C++

enum MorphTypes{
    MORPH_ERODE    = 0, //!< see cv::erode
    MORPH_DILATE   = 1, //!< see cv::dilate
    MORPH_OPEN     = 2, //!< an opening operation
                        //!< \f[\texttt{dst} = \mathrm{open} ( \texttt{src} , \texttt{element} )= \mathrm{dilate} ( \mathrm{erode} ( \texttt{src} , \texttt{element} ))\f]
    MORPH_CLOSE    = 3, //!< a closing operation
                        //!< \f[\texttt{dst} = \mathrm{close} ( \texttt{src} , \texttt{element} )= \mathrm{erode} ( \mathrm{dilate} ( \texttt{src} , \texttt{element} ))\f]
    MORPH_GRADIENT = 4, //!< a morphological gradient
                        //!< \f[\texttt{dst} = \mathrm{morph\_grad} ( \texttt{src} , \texttt{element} )= \mathrm{dilate} ( \texttt{src} , \texttt{element} )- \mathrm{erode} ( \texttt{src} , \texttt{element} )\f]
    MORPH_TOPHAT   = 5, //!< "top hat"
                        //!< \f[\texttt{dst} = \mathrm{tophat} ( \texttt{src} , \texttt{element} )= \texttt{src} - \mathrm{open} ( \texttt{src} , \texttt{element} )\f]
    MORPH_BLACKHAT = 6  //!< "black hat"
                        //!< \f[\texttt{dst} = \mathrm{blackhat} ( \texttt{src} , \texttt{element} )= \mathrm{close} ( \texttt{src} , \texttt{element} )- \texttt{src}\f]
};