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3D histogram
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‎doc/tutorials/viz/histo3D/histo3D.markdown

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Creating a 3D histogram {#tutorial_histo3D}
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================
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Goal
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----
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In this tutorial you will learn how to
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- Create your own callback keyboard function for viz window.
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- Show your 3D histogram in a viz window.
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Code
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----
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You can download the code from [here ](https://github.com/opencv/opencv/tree/master/samples/cpp/tutorial_code/viz/histo3D.cpp).
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@include samples/cpp/tutorial_code/viz/histo3D.cpp
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Explanation
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-----------
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Here is the general structure of the program:
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- You can give full path to an image in command line
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@code{.cpp}
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CommandLineParser parser(argc, argv, keys);
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if (parser.has("help"))
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{
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parser.printMessage();
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return 0;
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}
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String nomFic = parser.get<String>(0);
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Mat img;
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if (nomFic.length() != 0)
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{
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img = imread(nomFic, IMREAD_COLOR);
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if (img.empty())
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{
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cout << "Image does not exist!";
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return 0;
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}
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}
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@endcode
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or without path, a synthetic image is generated with pixel values are a gaussian distribution center(60+/-10,40+/-5,50+/-20) in first quadrant,
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(160+/-20,10+/-5,50+/-10) in second quadrant, (90+/-10,100+/-20,50+/-20) in third quadrant, (100+/-10,10+/-5,150+/-40) in last quadrant.
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@code{.cpp}
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else
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{
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img = Mat(512,512,CV_8UC3);
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parser.printMessage();
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RNG r;
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r.fill(img(Rect(0, 0, 256, 256)), RNG::NORMAL, Vec3b(60, 40, 50), Vec3b(10, 5, 20));
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r.fill(img(Rect(256, 0, 256, 256)), RNG::NORMAL, Vec3b(160, 10, 50), Vec3b(20, 5, 10));
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r.fill(img(Rect(0, 256, 256, 256)), RNG::NORMAL, Vec3b(90, 100, 50), Vec3b(10, 20, 20));
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r.fill(img(Rect(256, 256, 256, 256)), RNG::NORMAL, Vec3b(100, 10, 150), Vec3b(10, 5, 40));
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}
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@endcode
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Image tridimensional histogram is calculated using opencv calcHist and normalize between 0 and 100.
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@code{.cpp}
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float hRange[] = { 0, 256 };
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const float* etendu[] = { hRange, hRange,hRange };
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int hBins = 32;
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int tailleHist[] = { hBins, hBins , hBins };
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int canaux[] = { 2, 1,0 };
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calcHist(&img, 1, canaux, Mat(), h.histogram, 3, tailleHist, etendu, true, false);
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normalize(h.histogram, h.histogram, 100.0/(img.total()), 0, cv::NormTypes::NORM_MINMAX, -1, cv::Mat());
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minMaxIdx(h.histogram,NULL,&h.maxH,NULL,NULL);
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@endcode
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channel are 2, 1 and 0 to synchronise color with Viz axis color in objetc viz::WCoordinateSystem.
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A slidebar is inserted in image window. Init slidebar value is 90, it means that only histogram cell greater than 9/100000.0 (23 pixels for an 512X512 pixels) will be display.
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@code{.cpp}
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namedWindow("Image");
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imshow("Image",img);
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AddSlidebar("threshold","Image",0,100,h.seuil,&h.seuil, UpdateThreshold,&h);
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waitKey(30);
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@endcode
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We are ready to open a viz window with a callback function to capture keyboard event in viz window. Using Viz::spinonce enable keyboard event to be capture in imshow window too.
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@code{.cpp}
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h.fen3D = new viz::Viz3d("3D Histogram");
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h.nbWidget=0;
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h.fen3D->registerKeyboardCallback(KeyboardViz3d,&h);
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DrawHistogram3D(h);
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while (h.code!=27)
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{
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h.fen3D->spinOnce(1);
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if (h.status)
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DrawHistogram3D(h);
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if (h.code!=27)
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h.code= waitKey(30);
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}
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@endcode
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The function DrawHistogram3D processes histogram Mat to display it in a Viz window. Number of plan, row and column in three dimensional Mat ca be found using this code :
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@code{.cpp}
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int planSize = h.histogram.step1(0);
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int cols = h.histogram.step1(1);
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int rows = planSize / cols;
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int plans = h.histogram.total() / planSize;
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h.fen3D->removeAllWidgets();
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h.nbWidget=0;
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if (h.nbWidget==0)
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h.fen3D->showWidget("Axis", viz::WCoordinateSystem(10));
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@endcode
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To get histogram value at a specific location we use at method with three arguments k, i and j where k is plane number, i row number and j column number.
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@code{.cpp}
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for (int k = 0; k < plans; k++)
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{
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for (int i = 0; i < rows; i++)
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{
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for (int j = 0; j < cols; j++)
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{
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double x = h.histogram.at<float>(k, i, j);
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if (x >= h.threshold)
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{
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double r=std::max(x/h.maxH,0.1);
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viz::WCube s(Point3d(k - r / 2, i - r / 2, j - r / 2), Point3d(k + r / 2, i + r / 2, j + r / 2), false, viz::Color(j / double(plans) * 255, i / double(rows) * 255, k / double(cols) * 255));
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h.fen3D->showWidget(format("I3d%d", h.nbWidget++), s);
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}
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}
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}
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}
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@endcode
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- Callback function
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Principle are as mouse callback function. Key code pressed is in field code of class viz::KeyboardEvent.
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@code{.cpp}
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void KeyboardViz3d(const viz::KeyboardEvent &w, void *t)
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{
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Histo3DData *x=(Histo3DData *)t;
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if (w.action)
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cout << "you pressed "<< w.symbol<< " in viz window "<<x->fen3D->getWindowName()<<"\n";
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x->code= w.code;
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switch (w.code) {
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case '/':
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x->status=true;
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x->threshold *= 0.9;
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break;
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case '*':
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x->status = true;
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x->threshold *= 1.1;
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break;
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}
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if (x->status)
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{
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cout << x->threshold << "\n";
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DrawHistogram3D(*x);
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}
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}
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@endcode
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Results
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-------
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Here is the result of the program with no argument and threshold equal to 50.
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![](images/histo50.png)

‎doc/tutorials/viz/histo3D/images/histo50.png

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‎doc/tutorials/viz/table_of_content_viz.markdown

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*Author:* Ozan Tonkal
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You will learn how to create your own widgets.
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- @subpage tutorial_histo3D
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*Compatibility:* \> OpenCV 3.0.0
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*Author:* Laurent Berger
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You will learn how to plot a 3D histogram.

‎samples/cpp/tutorial_code/viz/histo3D.cpp

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#include <opencv2/opencv.hpp>
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#include <iostream>
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using namespace std;
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using namespace cv;
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#ifdef HAVE_OPENCV_VIZ
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const String keys =
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"{Aide h usage ? help | | print this message }"
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"{@arg1 | | Full path to color imag (3 channels)}"
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;
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struct Histo3DData {
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Mat histogram;
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int seuil;
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double threshold;
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Ptr<viz::Viz3d> fen3D;
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int nbWidget;
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bool status;
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double maxH;
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int code;
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};
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void DrawHistogram3D(Histo3DData &);
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void AddSlidebar(String sliderName, String windowName, int sliderMin, int sliderMax, int valeurDefaut, int *sliderVal, void(*f)(int, void *), void *r);
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void UpdateThreshold(int , void * r);
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void KeyboardViz3d(const viz::KeyboardEvent &w, void *t);
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void DrawHistogram3D(Histo3DData &h)
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{
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int planSize = h.histogram.step1(0);
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int cols = h.histogram.step1(1);
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int rows = planSize / cols;
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int plans = h.histogram.total() / planSize;
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h.fen3D->removeAllWidgets();
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h.nbWidget=0;
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if (h.nbWidget==0)
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h.fen3D->showWidget("Axis", viz::WCoordinateSystem(10));
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for (int k = 0; k < plans; k++)
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{
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for (int i = 0; i < rows; i++)
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{
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for (int j = 0; j < cols; j++)
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{
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double x = h.histogram.at<float>(k, i, j);
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if (x >= h.threshold)
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{
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double r=std::max(x/h.maxH,0.1);
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viz::WCube s(Point3d(k - r / 2, i - r / 2, j - r / 2), Point3d(k + r / 2, i + r / 2, j + r / 2), false, viz::Color(j / double(plans) * 255, i / double(rows) * 255, k / double(cols) * 255));
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h.fen3D->showWidget(format("I3d%d", h.nbWidget++), s);
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}
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}
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}
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}
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h.status = false;
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}
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void KeyboardViz3d(const viz::KeyboardEvent &w, void *t)
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{
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Histo3DData *x=(Histo3DData *)t;
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if (w.action)
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cout << "you pressed "<< w.symbol<< " in viz window "<<x->fen3D->getWindowName()<<"\n";
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x->code= w.code;
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switch (w.code) {
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case '/':
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x->status=true;
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x->threshold *= 0.9;
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break;
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case '*':
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x->status = true;
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x->threshold *= 1.1;
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break;
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}
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if (x->status)
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{
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cout << x->threshold << "\n";
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DrawHistogram3D(*x);
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}
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}
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void AddSlidebar(String sliderName, String windowName, int sliderMin, int sliderMax, int defaultSlider, int *sliderVal, void(*f)(int, void *), void *r)
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{
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createTrackbar(sliderName, windowName, sliderVal, 1, f, r);
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setTrackbarMin(sliderName, windowName, sliderMin);
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setTrackbarMax(sliderName, windowName, sliderMax);
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setTrackbarPos(sliderName, windowName, defaultSlider);
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}
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void UpdateThreshold(int , void * r)
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{
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Histo3DData *h = (Histo3DData *)r;
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h->status=true;
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h->threshold = h->seuil/1000000.0;
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cout<<"Widget : "<<h->nbWidget<<","<< h->threshold<<"\n";
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}
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int main (int argc,char **argv)
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{
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CommandLineParser parser(argc, argv, keys);
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if (parser.has("help"))
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{
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parser.printMessage();
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return 0;
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}
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String nomFic = parser.get<String>(0);
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Mat img;
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if (nomFic.length() != 0)
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{
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img = imread(nomFic, IMREAD_COLOR);
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if (img.empty())
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{
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cout << "Image does not exist!";
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return 0;
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}
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}
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else
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{
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img = Mat(512,512,CV_8UC3);
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parser.printMessage();
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RNG r;
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r.fill(img(Rect(0, 0, 256, 256)), RNG::NORMAL, Vec3b(60, 40, 50), Vec3b(10, 5, 20));
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r.fill(img(Rect(256, 0, 256, 256)), RNG::NORMAL, Vec3b(160, 10, 50), Vec3b(20, 5, 10));
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r.fill(img(Rect(0, 256, 256, 256)), RNG::NORMAL, Vec3b(90, 100, 50), Vec3b(10, 20, 20));
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r.fill(img(Rect(256, 256, 256, 256)), RNG::NORMAL, Vec3b(100, 10, 150), Vec3b(10, 5, 40));
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}
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Histo3DData h;
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h.status=true;
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h.seuil=90;
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h.threshold= h.seuil/1000000.0;
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float hRange[] = { 0, 256 };
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const float* etendu[] = { hRange, hRange,hRange };
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int hBins = 32;
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int histSize[] = { hBins, hBins , hBins };
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int channel[] = { 2, 1,0 };
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calcHist(&img, 1, channel, Mat(), h.histogram, 3, histSize, etendu, true, false);
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normalize(h.histogram, h.histogram, 100.0/(img.total()), 0, NORM_MINMAX, -1, Mat());
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minMaxIdx(h.histogram,NULL,&h.maxH,NULL,NULL);
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namedWindow("Image");
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imshow("Image",img);
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AddSlidebar("threshold","Image",0,100,h.seuil,&h.seuil, UpdateThreshold,&h);
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waitKey(30);
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h.fen3D = new viz::Viz3d("3D Histogram");
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h.nbWidget=0;
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h.fen3D->registerKeyboardCallback(KeyboardViz3d,&h);
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DrawHistogram3D(h);
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while (h.code!=27)
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{
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h.fen3D->spinOnce(1);
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if (h.status)
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DrawHistogram3D(h);
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if (h.code!=27)
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h.code= waitKey(30);
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}
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return 0;
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}
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#else
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int main(int argc, char **argv)
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{
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cout << " you need VIZ module\n";
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return 0;
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}
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#endif

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