MSER: Sample class from OpenCV

class CV_EXPORTS_W MSER : public Feature2D
{
public:
    //! the full constructor
    CV_WRAP static Ptr<MSER> create( int _delta=5, int _min_area=60, int _max_area=14400,
          double _max_variation=0.25, double _min_diversity=.2,
          int _max_evolution=200, double _area_threshold=1.01,
          double _min_margin=0.003, int _edge_blur_size=5 );

    CV_WRAP virtual void detectRegions( InputArray image,
                                        CV_OUT std::vector<std::vector<Point> >& msers,
                                        std::vector<Rect>& bboxes ) = 0;

    CV_WRAP virtual void setDelta(int delta) = 0;
    CV_WRAP virtual int getDelta() const = 0;

    CV_WRAP virtual void setMinArea(int minArea) = 0;
    CV_WRAP virtual int getMinArea() const = 0;

    CV_WRAP virtual void setMaxArea(int maxArea) = 0;
    CV_WRAP virtual int getMaxArea() const = 0;

    CV_WRAP virtual void setPass2Only(bool f) = 0;
    CV_WRAP virtual bool getPass2Only() const = 0;
};

• OpenCV uses Macros to identify symbols to binding generators

Binding code for MSER Class

emscripten::class_<cv::MSER ,base<Feature2D>>("MSER")
    
    .function("getPass2Only", select_overload<bool(cv::MSER&)>(&Wrappers::MSER_getPass2Only_wrap),pure_virtual() )
    .function("setMinArea", select_overload<void(cv::MSER&,int)>(&Wrappers::MSER_setMinArea_wrap),pure_virtual() )
    .function("getDelta", select_overload<int(cv::MSER&)>(&Wrappers::MSER_getDelta_wrap),pure_virtual() )
    .class_function("create",select_overload<Ptr<MSER>(int,int,int,double,double,int,double,double,int)>(&Wrappers::create_MSER_wrapper))
    .function("getMaxArea", select_overload<int(cv::MSER&)>(&Wrappers::MSER_getMaxArea_wrap),pure_virtual() )
    .function("setMaxArea", select_overload<void(cv::MSER&,int)>(&Wrappers::MSER_setMaxArea_wrap),pure_virtual() )
    .function("setPass2Only", select_overload<void(cv::MSER&,bool)>(&Wrappers::MSER_setPass2Only_wrap),pure_virtual() )
    .function("getMinArea", select_overload<int(cv::MSER&)>(&Wrappers::MSER_getMinArea_wrap),pure_virtual() )
    .function("detectRegions", select_overload<void(cv::MSER&,const cv::Mat&, std::vector<std::vector<Point> >&,std::vector<Rect>&)>(&Wrappers::MSER_detectRegions_wrap),pure_virtual() )
    .function("setDelta", select_overload<void(cv::MSER&,int)>(&Wrappers::MSER_setDelta_wrap),pure_virtual() )
;

Binding Generator Script

• parses all OpenCV headers
  • extracts all the symbols with OpenCV Wrap macros
    • classes
    • functions
    • class functions
    • properties
    • enumerations and constants
  • generates appropriate binding for each type

Results

• We have covered six modules so far

  • core
  • image processing
  • object detection
  • features_2d
  • image codecs
  • machine learning

60 classes

800 functions(including class methods)

80 Enums

• Function overloading
• Default parameters

C++ code

JS code

void erode(){

   Mat image,dst;
   image = imread("image.jpg", CV_LOAD_IMAGE_COLOR);  
 
   // Create a structuring element
   int erosion_size = 6;  
   Mat element = getStructuringElement(cv::MORPH_RECT,
   cv::Size(2 * erosion_size + 1, 2 * erosion_size + 1),
   cv::Point(erosion_size, erosion_size) );
 
   // Apply erosion or dilation on the image
   erode(image,dst,element);  
   
   namedWindow( "Display window", CV_WINDOW_AUTOSIZE );  
   imshow( "Display window", image );                 
 
   namedWindow( "Result window", CV_WINDOW_AUTOSIZE );   
   imshow( "Result window", dst );
}

function erode(){
    var src = cv.matFromArray( getInput() , cv.CV_8UC4 ); 
    var dst = new cv.Mat();
    cv.cvtColor(src, src , 
        cv.cv_ColorConversionCodes.COLOR_RGBA2RGB.value,0);

    // Create a structuring element
    var erosion_type = cv.cv_MorphShapes.MORPH_RECT.value;

    var erosion_size=new cv.Size(2*Control.erosion_size+1,
         2*Control.erosion_size+1 );

    var element = cv.getStructuringElement( erosion_type 
        ,erosion_size  ) ;

    
    // Apply erosion or dilation on the image   
    cv.erode(src, dst, element) ;

    show_image( dst , "canvas2");
    
    // Clean up   
    src.delete();
    dst.delete();
    erosion_size.delete();
				
}

Erode Function

Core and image processing modules

Feature Extraction module

HAAR object detection - Working with HTML5 video element

Performance

• Sources of penalty

  • how well browsers supports asm.js

  • Data should be copied into/from ASM.js heap

    • before computation

    • after computation

      • saved on this by returning a pointer to the heap

  • Wrapper functions overhead

  • Image format conversion

    • RGBA -> RGB and vice versa

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