Thresholding Tutorial using inRange function on a video

doc/tutorials/imgproc/table_of_content_imgproc.markdown

@@ -51,6 +51,14 @@ In this section you will learn about the image processing (manipulation) functio
 
     After so much processing, it is time to decide which pixels stay!
 
+-   @subpage tutorial_threshold_inRange
+
+    *Compatibility:* \> OpenCV 2.0
+
+    *Author:* Rishiraj Surti
+
+    Thresholding operations using inRange function.
+
 -   @subpage tutorial_filter_2d
 
     *Compatibility:* \> OpenCV 2.0

doc/tutorials/imgproc/threshold_inRange/threshold_inRange.markdown

+Thresholding Operations using inRange {#tutorial_threshold_inRange}
+=============================
+
+Goal
+----
+
+In this tutorial you will learn how to:
+
+-   Perform basic thresholding operations using OpenCV function @ref cv::inRange
+-   Detect an object based on the range of pixel values it has
+
+Theory
+-----------
+-   In the previous tutorial, we learnt how perform thresholding using @ref cv::threshold function.
+-   In this tutorial, we will learn how to do it using @ref cv::inRange function.
+-   The concept remains same, but now we add a range of pixel values we need.
+
+Code
+----
+
+The tutorial code's is shown lines below. You can also download it from
+[here](https://github.com/Itseez/opencv/tree/master/samples/cpp/tutorial_code/ImgProc/Threshold_inRange.cpp)
+@include samples/cpp/tutorial_code/ImgProc/Threshold_inRange.cpp
+
+Explanation
+-----------
+
+-#  Let's check the general structure of the program:
+    -   Create two Matrix elements to store the frames
+        @snippet samples/cpp/tutorial_code/ImgProc/Threshold_inRange.cpp mat
+    -   Capture the video stream from default capturing device.
+        @snippet samples/cpp/tutorial_code/ImgProc/Threshold_inRange.cpp cap
+    -   Create a window to display the default frame and the threshold frame.
+        @snippet samples/cpp/tutorial_code/ImgProc/Threshold_inRange.cpp window
+    -   Create trackbars to set the range of RGB values
+        @snippet samples/cpp/tutorial_code/ImgProc/Threshold_inRange.cpp trackbar
+    -   Until the user want the program to exit do the following
+        @snippet samples/cpp/tutorial_code/ImgProc/Threshold_inRange.cpp while
+    -   Show the images
+        @snippet samples/cpp/tutorial_code/ImgProc/Threshold_inRange.cpp show
+    -   For a trackbar which controls the lower range, say for example Red value:
+        @snippet samples/cpp/tutorial_code/ImgProc/Threshold_inRange.cpp low
+    -   For a trackbar which controls the upper range, say for example Red value:
+        @snippet samples/cpp/tutorial_code/ImgProc/Threshold_inRange.cpp high
+    -   It is necessary to find the maximum and minimum value to avoid discrepancies such as
+        the high value of threshold becoming less the low value.
+
+Results
+-------
+
+-#  After compiling this program, run it. The program will open two windows
+
+-#  As you set the RGB range values from the trackbar, the resulting frame will be visible in the other window.
+
+    ![](images/Threshold_inRange_Tutorial_Result_input.jpeg)
+    ![](images/Threshold_inRange_Tutorial_Result_output.jpeg)

samples/cpp/tutorial_code/ImgProc/Threshold_inRange.cpp

+#include "opencv2/imgproc.hpp"
+#include "opencv2/highgui.hpp"
+
+#include <iostream>
+#include <stdlib.h>
+
+using namespace std;
+using namespace cv;
+
+/** Function Headers */
+void on_low_r_thresh_trackbar(int, void *);
+void on_high_r_thresh_trackbar(int, void *);
+void on_low_g_thresh_trackbar(int, void *);
+void on_high_g_thresh_trackbar(int, void *);
+void on_low_b_thresh_trackbar(int, void *);
+void on_high_b_thresh_trackbar(int, void *);
+
+/** Global Variables */
+int low_r=30, low_g=30, low_b=30;
+int high_r=100, high_g=100, high_b=100;
+
+/** @function main */
+int main()
+{
+    //! [mat]
+    Mat frame, frame_threshold;
+    //! [mat]
+    //! [cap]
+    VideoCapture cap(0);
+    //! [cap]
+    //! [window]
+    namedWindow("Video Capture", WINDOW_NORMAL);
+    namedWindow("Object Detection", WINDOW_NORMAL);
+    //! [window]
+    //! [trackbar]
+    //-- Trackbars to set thresholds for RGB values
+    createTrackbar("Low R","Object Detection", &low_r, 255, on_low_r_thresh_trackbar);
+    createTrackbar("High R","Object Detection", &high_r, 255, on_high_r_thresh_trackbar);
+    createTrackbar("Low G","Object Detection", &low_g, 255, on_low_g_thresh_trackbar);
+    createTrackbar("High G","Object Detection", &high_g, 255, on_high_g_thresh_trackbar);
+    createTrackbar("Low B","Object Detection", &low_b, 255, on_low_b_thresh_trackbar);
+    createTrackbar("High B","Object Detection", &high_b, 255, on_high_b_thresh_trackbar);
+    //! [trackbar]
+    while(char(waitKey(1))!='q'){
+        //! [while]
+        cap>>frame;
+        if(frame.empty())
+            break;
+        //-- Detect the object based on RGB Range Values
+        inRange(frame,Scalar(low_b,low_g,low_r), Scalar(high_b,high_g,high_r),frame_threshold);
+        //! [while]
+        //! [show]
+        //-- Show the frames
+        imshow("Video Capture",frame);
+        imshow("Object Detection",frame_threshold);
+        //! [show]
+    }
+    return 0;
+}
+//! [low]
+/** @function on_low_r_thresh_trackbar */
+void on_low_r_thresh_trackbar(int, void *)
+{
+    low_r = min(high_r-1, low_r);
+    setTrackbarPos("Low R","Object Detection", low_r);
+}
+//! [low]
+//! [high]
+/** @function on_high_r_thresh_trackbar */
+void on_high_r_thresh_trackbar(int, void *)
+{
+    high_r = max(high_r, low_r+1);
+    setTrackbarPos("High R", "Object Detection", high_r);
+}
+//![high]
+/** @function on_low_g_thresh_trackbar */
+void on_low_g_thresh_trackbar(int, void *)
+{
+    low_g = min(high_g-1, low_g);
+    setTrackbarPos("Low G","Object Detection", low_g);
+}
+
+/** @function on_high_g_thresh_trackbar */
+void on_high_g_thresh_trackbar(int, void *)
+{
+    high_g = max(high_g, low_g+1);
+    setTrackbarPos("High G", "Object Detection", high_g);
+}
+
+/** @function on_low_b_thresh_trackbar */
+void on_low_b_thresh_trackbar(int, void *)
+{
+    low_b= min(high_b-1, low_b);
+    setTrackbarPos("Low B","Object Detection", low_b);
+}
+
+/** @function on_high_b_thresh_trackbar */
+void on_high_b_thresh_trackbar(int, void *)
+{
+    high_b = max(high_b, low_b+1);
+    setTrackbarPos("High B", "Object Detection", high_b);
+}