Learn Threshold Operation

double threshold(InputArray src, OutputArray dst, double thresh, double maxval, int type)

Applies a fixed-level threshold to each array element

Parameters:

• src – input array (single-channel, 8-bit or 32-bit floating point).
• dst – output array of the same size as well as type every bit src.
• thresh – threshold value.
• maxval – maximum value to role amongst the THRESH_BINARY as well as THRESH_BINARY_INV thresholding types.
• type – thresholding type

• THRESH_BINARY

  

• THRESH_BINARY_INV

  

• THRESH_TRUNC

  

• THRESH_TOZERO

  

• THRESH_TOZERO_INV

  

Find an instance inwards OpenCV documentaion.

Steps:

1. Load an image
2. Create a window to display results
3. Create Trackbar to conduct type of Threshold
4. Call the component "Threshold_Demo" to perform threshold operation.

Functions:

threshold, createTrackbar, imread, cvtColor, namedWindow, waitKey.

Example:

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#include "opencv2/imgproc/imgproc.hpp" #include "opencv2/highgui/highgui.hpp" #include <stdlib.h> #include <stdio.h>  using namespace cv;  int threshold_value = 0; int threshold_type = 3;; int const max_value = 255; int const max_type = 4; int const max_BINARY_value = 255;  Mat src, src_gray, dst; char* window_name = "Threshold Demo";  char* trackbar_type = "Type: \n 0: Binary \n 1: Binary Inverted \n 2: Truncate \n 3: To Zero \n 4: To Zero Inverted"; char* trackbar_value = "Value";  void Threshold_Demo( int, void* );  int main( int argc, char** argv ) {   /// Load an icon   src = imread( "shape.jpg", i );    /// Convert the icon to Gray   cvtColor( src, src_gray, CV_RGB2GRAY );    /// Create a window to display results   namedWindow( window_name, CV_WINDOW_AUTOSIZE );    /// Create Trackbar to conduct type of Threshold   createTrackbar( trackbar_type,                   window_name, &threshold_type,                   max_type, Threshold_Demo );    createTrackbar( trackbar_value,                   window_name, &threshold_value,                   max_value, Threshold_Demo );    /// Call the component to initialize   Threshold_Demo( 0, 0 );    /// Wait until user finishes plan   while(true)   {     int c;     c = waitKey( xx );     if( (char)c == 27 )       { break; }    } }   void Threshold_Demo( int, void* ) {   /* 0: Binary      1: Binary Inverted      2: Threshold Truncated      3: Threshold to Zero      4: Threshold to Zero Inverted    */    threshold( src_gray, dst, threshold_value, max_BINARY_value,threshold_type );    imshow( window_name, dst ); } 

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Result:

Sources:
http://docs.opencv.org/doc/tutorials/imgproc/threshold/threshold.html