Is there a way to plot graphs in OpenCV?

Question

To begin with: I am working on image processing in OpenCV C++.

The Requirement is to plot a graph out of the Vector values of a 1D image. I referred http://answers.opencv.org/question/73233/how-do-you-plot-graphs-in-opencv-projects/ and found a solution for it. It is a brilliant one that one could make in OpenCV but, the plot is not recognized by the OpenCV original libraries.

To find a solution for this, I went through all the library files and came to a conclusion that the header file
#include opencv2/plot.hpp is not in the original OpenCV library(latest version). It must be implemented in some additional library but hasn't been on live I suppose.

Here is my CODE for your reference:

#include <opencv2/plot.hpp>

int PlotGraph(Mat & data) {


Mat plot_result;

Ptr<plot::Plot2d> plot = plot::createPlot2d(data);

//Set Background color
plot->setPlotBackgroundColor(Scalar(50, 50, 50)); 

//Set plot line color
plot->setPlotLineColor(Scalar(50, 50, 255));
plot->render(plot_result);

imshow("plot", plot_result);
waitKey();

plot->setPlotLineColor(Scalar(50, 255, 255));
data = data / 3;
plot->render(plot_result);

imshow("plot", plot_result);
waitKey();

plot->setPlotGridColor(Scalar(255, 0, 255));
data = data * 4;
plot->render(IMREAD_UNCHANGEDplot_result);

imshow("plot", plot_result);
waitKey();

plot->setPlotTextColor(Scalar(255, 0, 0));
randu(data, 100, 400);
plot->render(plot_result);

imshow("plot", plot_result);
waitKey();

return 0;

}

There are many ways in C++ and other libraries such as GNU to plot graphs but, I am being bit curious and not want to give up on this.

I would appreciate if anyone gives me a solution to this or suggest a way to plot graphs in OpenCV C++.

Solution 1

I have found a way to plot graphs in OpenCV. Here it goes,

From the https://raw.githubusercontent.com/sturkmen72/opencv_samples/master/plot-test.cpp link provided by Sturkmen, I took the codes and made it as my header file.

plot.h

#pragma once
#include <opencv2/core.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/highgui.hpp>

namespace cv
{
namespace plot
{
    //! @addtogroup plot
    //! @{

    class CV_EXPORTS_W Plot2d : public Algorithm
    {
    public:

        CV_WRAP virtual void setMinX(double _plotMinX) = 0;
        CV_WRAP virtual void setMinY(double _plotMinY) = 0;
        CV_WRAP virtual void setMaxX(double _plotMaxX) = 0;
        CV_WRAP virtual void setMaxY(double _plotMaxY) = 0;
        CV_WRAP virtual void setPlotLineWidth(int _plotLineWidth) = 0;
        /**
        * @brief Switches data visualization mode
        *
        * @param _needPlotLine if true then neighbour plot points will be connected by lines.
        * In other case data will be plotted as a set of standalone points.
        */
        CV_WRAP virtual void setNeedPlotLine(bool _needPlotLine) = 0;
        CV_WRAP virtual void setPlotLineColor(Scalar _plotLineColor) = 0;
        CV_WRAP virtual void setPlotBackgroundColor(Scalar _plotBackgroundColor) = 0;
        CV_WRAP virtual void setPlotAxisColor(Scalar _plotAxisColor) = 0;
        CV_WRAP virtual void setPlotGridColor(Scalar _plotGridColor) = 0;
        CV_WRAP virtual void setPlotTextColor(Scalar _plotTextColor) = 0;
        CV_WRAP virtual void setPlotSize(int _plotSizeWidth, int _plotSizeHeight) = 0;
        CV_WRAP virtual void setShowGrid(bool needShowGrid) = 0;
        CV_WRAP virtual void setShowText(bool needShowText) = 0;
        CV_WRAP virtual void setGridLinesNumber(int gridLinesNumber) = 0;
        /**
        * @brief Sets the index of a point which coordinates will be printed on the top left corner of the plot (if ShowText flag is true).
        *
        * @param pointIdx index of the required point in data array.
        */
        CV_WRAP virtual void setPointIdxToPrint(int pointIdx) = 0;
        CV_WRAP virtual void render(OutputArray _plotResult) = 0;

        /**
        * @brief Creates Plot2d object
        *
        * @param data \f$1xN\f$ or \f$Nx1\f$ matrix containing \f$Y\f$ values of points to plot. \f$X\f$ values
        * will be equal to indexes of correspondind elements in data matrix.
        */
        CV_WRAP static Ptr<Plot2d> create(InputArray data);

        /**
        * @brief Creates Plot2d object
        *
        * @param dataX \f$1xN\f$ or \f$Nx1\f$ matrix \f$X\f$ values of points to plot.
        * @param dataY \f$1xN\f$ or \f$Nx1\f$ matrix containing \f$Y\f$ values of points to plot.
        */
        CV_WRAP static Ptr<Plot2d> create(InputArray dataX, InputArray dataY);
    };
    //! @}
}
}

namespace cv
{
namespace plot
{
    using namespace std;

    class Plot2dImpl : public Plot2d
    {
    public:

        Plot2dImpl(InputArray plotData)
        {
            Mat _plotData = plotData.getMat();
            //if the matrix is not Nx1 or 1xN
            if (_plotData.cols > 1 && _plotData.rows > 1)
                CV_Error(Error::StsBadArg, "ERROR: Plot data must be a 1xN or Nx1 matrix.\n");

            CV_Assert(_plotData.type() == CV_64F);

            //in case we have a row matrix than needs to be transposed
            if (_plotData.cols > _plotData.rows)
            {
                _plotData = _plotData.t();
            }

            plotDataY = _plotData;
            plotDataX = plotDataY * 0;
            for (int i = 0; i<plotDataY.rows; i++)
            {
                plotDataX.at<double>(i, 0) = i;
            }

            //calling the main constructor
            plotHelper(plotDataX, plotDataY);

        }

        Plot2dImpl(InputArray plotDataX_, InputArray plotDataY_)
        {
            Mat _plotDataX = plotDataX_.getMat();
            Mat _plotDataY = plotDataY_.getMat();
            //f the matrix is not Nx1 or 1xN
            if ((_plotDataX.cols > 1 && _plotDataX.rows > 1) || (_plotDataY.cols > 1 && _plotDataY.rows > 1))
                CV_Error(Error::StsBadArg, "ERROR: Plot data must be a 1xN or Nx1 matrix.\n");

            CV_Assert(_plotDataX.type() == CV_64F && _plotDataY.type() == CV_64F);

            //in case we have a row matrix than needs to be transposed
            if (_plotDataX.cols > _plotDataX.rows)
            {
                _plotDataX = _plotDataX.t();
            }
            if (_plotDataY.cols > _plotDataY.rows)
            {
                _plotDataY = _plotDataY.t();
            }

            plotHelper(_plotDataX, _plotDataY);
        }

        //set functions
        void setMinX(double _plotMinX)
        {
            plotMinX = _plotMinX;
            plotMinX_plusZero = _plotMinX;
        }
        void setMaxX(double _plotMaxX)
        {
            plotMaxX = _plotMaxX;
            plotMaxX_plusZero = _plotMaxX;
        }
        void setMinY(double _plotMinY)
        {
            plotMinY = _plotMinY;
            plotMinY_plusZero = _plotMinY;
        }
        void setMaxY(double _plotMaxY)
        {
            plotMaxY = _plotMaxY;
            plotMaxY_plusZero = _plotMaxY;
        }
        void setPlotLineWidth(int _plotLineWidth)
        {
            plotLineWidth = _plotLineWidth;
        }
        void setNeedPlotLine(bool _needPlotLine)
        {
            needPlotLine = _needPlotLine;
        }
        void setPlotLineColor(Scalar _plotLineColor)
        {
            plotLineColor = _plotLineColor;
        }
        void setPlotBackgroundColor(Scalar _plotBackgroundColor)
        {
            plotBackgroundColor = _plotBackgroundColor;
        }
        void setPlotAxisColor(Scalar _plotAxisColor)
        {
            plotAxisColor = _plotAxisColor;
        }
        void setPlotGridColor(Scalar _plotGridColor)
        {
            plotGridColor = _plotGridColor;
        }
        void setPlotTextColor(Scalar _plotTextColor)
        {
            plotTextColor = _plotTextColor;
        }
        void setPlotSize(int _plotSizeWidth, int _plotSizeHeight)
        {
            if (_plotSizeWidth > 400)
                plotSizeWidth = _plotSizeWidth;
            else
                plotSizeWidth = 400;

            if (_plotSizeHeight > 300)
                plotSizeHeight = _plotSizeHeight;
            else
                plotSizeHeight = 300;
        }
        void setShowGrid(bool _needShowGrid)
        {
            needShowGrid = _needShowGrid;
        }
        void setShowText(bool _needShowText)
        {
            needShowText = _needShowText;
        }
        void setGridLinesNumber(int _gridLinesNumber)
        {
            if (_gridLinesNumber <= 0)
                _gridLinesNumber = 1;
            gridLinesNumber = _gridLinesNumber;
        }
        void setPointIdxToPrint(int _cursorPos)
        {
            if (_cursorPos >= plotDataX.rows || _cursorPos < 0)
                _cursorPos = plotDataX.rows - 1;
            cursorPos = _cursorPos;
        }
        //render the plotResult to a Mat
        void render(OutputArray _plotResult)
        {
            //create the plot result
            _plotResult.create(plotSizeHeight, plotSizeWidth, CV_8UC3);
            plotResult = _plotResult.getMat();
            plotResult.setTo(plotBackgroundColor);

            int NumVecElements = plotDataX.rows;

            Mat InterpXdata = linearInterpolation(plotMinX, plotMaxX, 0, plotSizeWidth, plotDataX);
            Mat InterpYdata = linearInterpolation(plotMinY, plotMaxY, 0, plotSizeHeight, plotDataY);

            //Find the zeros in image coordinates
            Mat InterpXdataFindZero = linearInterpolation(plotMinX_plusZero, plotMaxX_plusZero, 0, plotSizeWidth, plotDataX_plusZero);
            Mat InterpYdataFindZero = linearInterpolation(plotMinY_plusZero, plotMaxY_plusZero, 0, plotSizeHeight, plotDataY_plusZero);

            int ImageXzero = (int)InterpXdataFindZero.at<double>(NumVecElements, 0);
            int ImageYzero = (int)InterpYdataFindZero.at<double>(NumVecElements, 0);

            double CurrentX = plotDataX.at<double>(cursorPos, 0);
            double CurrentY = plotDataY.at<double>(cursorPos, 0);

            drawAxis(ImageXzero, ImageYzero, CurrentX, CurrentY, plotAxisColor, plotGridColor);

            if (needPlotLine)
            {
                //Draw the plot by connecting lines between the points
                Point p1;
                p1.x = (int)InterpXdata.at<double>(0, 0);
                p1.y = (int)InterpYdata.at<double>(0, 0);

                for (int r = 1; r<InterpXdata.rows; r++)
                {
                    Point p2;
                    p2.x = (int)InterpXdata.at<double>(r, 0);
                    p2.y = (int)InterpYdata.at<double>(r, 0);

                    line(plotResult, p1, p2, plotLineColor, plotLineWidth, 8, 0);

                    p1 = p2;
                }
            }
            else
            {
                for (int r = 0; r<InterpXdata.rows; r++)
                {
                    Point p;
                    p.x = (int)InterpXdata.at<double>(r, 0);
                    p.y = (int)InterpYdata.at<double>(r, 0);

                    circle(plotResult, p, 1, plotLineColor, plotLineWidth, 8, 0);
                }
            }
        }

    protected:

        Mat plotDataX;
        Mat plotDataY;
        Mat plotDataX_plusZero;
        Mat plotDataY_plusZero;
        const char * plotName;

        //dimensions and limits of the plot
        int plotSizeWidth;
        int plotSizeHeight;
        double plotMinX;
        double plotMaxX;
        double plotMinY;
        double plotMaxY;
        double plotMinX_plusZero;
        double plotMaxX_plusZero;
        double plotMinY_plusZero;
        double plotMaxY_plusZero;
        int plotLineWidth;
        bool needShowGrid;
        bool needShowText;
        int gridLinesNumber;
        int cursorPos;

        //colors of each plot element
        Scalar plotLineColor;
        Scalar plotBackgroundColor;
        Scalar plotAxisColor;
        Scalar plotGridColor;
        Scalar plotTextColor;

        //the final plot result
        Mat plotResult;

        //flag which enables/disables connection of plotted points by lines
        bool needPlotLine;

        void plotHelper(Mat _plotDataX, Mat _plotDataY)
        {
            plotDataX = _plotDataX;
            plotDataY = _plotDataY;

            int NumVecElements = plotDataX.rows;

            plotDataX_plusZero = Mat::zeros(NumVecElements + 1, 1, CV_64F);
            plotDataY_plusZero = Mat::zeros(NumVecElements + 1, 1, CV_64F);

            for (int i = 0; i<NumVecElements; i++)
            {
                plotDataX_plusZero.at<double>(i, 0) = plotDataX.at<double>(i, 0);
                plotDataY_plusZero.at<double>(i, 0) = plotDataY.at<double>(i, 0);
            }

            double MinX;
            double MaxX;
            double MinY;
            double MaxY;
            double MinX_plusZero;
            double MaxX_plusZero;
            double MinY_plusZero;
            double MaxY_plusZero;

            needPlotLine = true;

            //Obtain the minimum and maximum values of Xdata
            minMaxLoc(plotDataX, &MinX, &MaxX);

            //Obtain the minimum and maximum values of Ydata
            minMaxLoc(plotDataY, &MinY, &MaxY);

            //Obtain the minimum and maximum values of Xdata plus zero
            minMaxLoc(plotDataX_plusZero, &MinX_plusZero, &MaxX_plusZero);

            //Obtain the minimum and maximum values of Ydata plus zero
            minMaxLoc(plotDataY_plusZero, &MinY_plusZero, &MaxY_plusZero);

            //setting the min and max values for each axis
            plotMinX = MinX;
            plotMaxX = MaxX;
            plotMinY = MinY;
            plotMaxY = MaxY;
            plotMinX_plusZero = MinX_plusZero;
            plotMaxX_plusZero = MaxX_plusZero;
            plotMinY_plusZero = MinY_plusZero;
            plotMaxY_plusZero = MaxY_plusZero;

            //setting the default size of a plot figure
            setPlotSize(600, 400);

            //setting the default plot line size
            setPlotLineWidth(1);

            //setting default colors for the different elements of the plot
            setPlotAxisColor(Scalar(0, 0, 255));
            setPlotGridColor(Scalar(255, 255, 255));
            setPlotBackgroundColor(Scalar(0, 0, 0));
            setPlotLineColor(Scalar(0, 255, 255));
            setPlotTextColor(Scalar(255, 255, 255));
            setShowGrid(true);
            setShowText(true);
            setGridLinesNumber(10);
            setPointIdxToPrint(-1);
        }

        void drawAxis(int ImageXzero, int ImageYzero, double CurrentX, double CurrentY, Scalar axisColor, Scalar gridColor)
        {
            if (needShowText)
            {
                drawValuesAsText(0, ImageXzero, ImageYzero, 10, 20);
                drawValuesAsText(0, ImageXzero, ImageYzero, -20, 20);
                drawValuesAsText(0, ImageXzero, ImageYzero, 10, -10);
                drawValuesAsText(0, ImageXzero, ImageYzero, -20, -10);
                drawValuesAsText((format("X_%d = ", cursorPos) + "%g").c_str(), CurrentX, 0, 0, 40, 20);
                drawValuesAsText((format("Y_%d = ", cursorPos) + "%g").c_str(), CurrentY, 0, 20, 40, 20);
            }

            //Horizontal X axis and equispaced horizontal lines
            int LineSpace = cvRound(plotSizeHeight / (float)gridLinesNumber);
            int TraceSize = 5;
            drawLine(0, plotSizeWidth, ImageYzero, ImageYzero, axisColor);

            if (needShowGrid)
                for (int i = -plotSizeHeight; i<plotSizeHeight; i = i + LineSpace)
                {

                    if (i != 0)
                    {
                        int Trace = 0;
                        while (Trace<plotSizeWidth)
                        {
                            drawLine(Trace, Trace + TraceSize, ImageYzero + i, ImageYzero + i, gridColor);
                            Trace = Trace + 2 * TraceSize;
                        }
                    }
                }


            //Vertical Y axis
            drawLine(ImageXzero, ImageXzero, 0, plotSizeHeight, axisColor);
            LineSpace = cvRound(LineSpace * (float)plotSizeWidth / plotSizeHeight);

            if (needShowGrid)
                for (int i = -plotSizeWidth; i<plotSizeWidth; i = i + LineSpace)
                {

                    if (i != 0)
                    {
                        int Trace = 0;
                        while (Trace<plotSizeHeight)
                        {
                            drawLine(ImageXzero + i, ImageXzero + i, Trace, Trace + TraceSize, gridColor);
                            Trace = Trace + 2 * TraceSize;
                        }
                    }
                }
        }

        Mat linearInterpolation(double Xa, double Xb, double Ya, double Yb, Mat Xdata)
        {

            Mat Ydata = Xdata * 0;

            for (int i = 0; i<Xdata.rows; i++)
            {

                double X = Xdata.at<double>(i, 0);
                Ydata.at<double>(i, 0) = int(Ya + (Yb - Ya)*(X - Xa) / (Xb - Xa));

                if (Ydata.at<double>(i, 0)<0)
                    Ydata.at<double>(i, 0) = 0;

            }

            return Ydata;
        }

        void drawValuesAsText(double Value, int Xloc, int Yloc, int XMargin, int YMargin)
        {

            char AxisX_Min_Text[20];
            double TextSize = 1;

            sprintf(AxisX_Min_Text, "%g", Value);
            Point AxisX_Min_Loc;
            AxisX_Min_Loc.x = Xloc + XMargin;
            AxisX_Min_Loc.y = Yloc + YMargin;

            putText(plotResult, AxisX_Min_Text, AxisX_Min_Loc, FONT_HERSHEY_COMPLEX_SMALL, TextSize, plotTextColor, 1, 8);
        }

        void drawValuesAsText(const char *Text, double Value, int Xloc, int Yloc, int XMargin, int YMargin)
        {

            char AxisX_Min_Text[20];
            int TextSize = 1;

            sprintf(AxisX_Min_Text, Text, Value);
            Point AxisX_Min_Loc;
            AxisX_Min_Loc.x = Xloc + XMargin;
            AxisX_Min_Loc.y = Yloc + YMargin;

            putText(plotResult, AxisX_Min_Text, AxisX_Min_Loc, FONT_HERSHEY_COMPLEX_SMALL, TextSize, plotTextColor, 1, 8);
        }


        void drawLine(int Xstart, int Xend, int Ystart, int Yend, Scalar lineColor)
        {

            Point Axis_start;
            Point Axis_end;
            Axis_start.x = Xstart;
            Axis_start.y = Ystart;
            Axis_end.x = Xend;
            Axis_end.y = Yend;

            line(plotResult, Axis_start, Axis_end, lineColor, plotLineWidth, 8, 0);
        }

    };

    Ptr<Plot2d> Plot2d::create(InputArray _plotData)
    {
        return Ptr<Plot2dImpl>(new Plot2dImpl(_plotData));

    }

    Ptr<Plot2d> Plot2d::create(InputArray _plotDataX, InputArray _plotDataY)
    {
        return Ptr<Plot2dImpl>(new Plot2dImpl(_plotDataX, _plotDataY));
    }
}
}

Now, the header file is ready. I added this plot.h to my cpp file.

Here is my Graph plotting function in OpenCV C++:

Plot.cpp

#include <iostream>
#include <opencv2/opencv.hpp>
#include "plot.h"


int PlotGraph(Mat & data) {

//converting the Mat to CV_64F
data.convertTo(data, CV_64F);
Mat plot_result;

Ptr<plot::Plot2d> plot = plot::Plot2d::create(data);
plot->setPlotBackgroundColor(Scalar(50, 50, 50)); 
plot->setPlotLineColor(Scalar(50, 50, 255));
plot->render(plot_result);          

imshow("Graph", plot_result);
waitKey();

return 0;
}

so, we can create our own plot.h header file and plot graphs in OpenCV without using external libraries.

Solution 2

There is no plot support in OpenCV. You can use the plot contrib module, but it is very basic.

You could try Profactor CvPlot https://github.com/Profactor/cv-plot. (I am the developer). It is very easy to integrate, purely opencv based and can be extended with custom controls. This is how you can plot to a cv::Mat or show a diagram with an interactive viewer:

#include <CvPlot/cvplot.h>
std::vector<double> x(20*1000), y1(x.size()), y2(x.size()), y3(x.size());
for (size_t i = 0; i < x.size(); i++) {
    x[i] = i * CV_2PI / x.size();
    y1[i] = std::sin(x[i]);
    y2[i] = y1[i] * std::sin(x[i]*50);
    y3[i] = y2[i] * std::sin(x[i]*500);
}
auto axes = CvPlot::makePlotAxes();
axes.create<CvPlot::Series>(x, y3, "-g");
axes.create<CvPlot::Series>(x, y2, "-b");
axes.create<CvPlot::Series>(x, y1, "-r");

//plot to a cv::Mat
cv::Mat mat = axes.render(300, 400);

//or show with interactive viewer
CvPlot::show("mywindow", axes);

You may also want to try Leonardvandriel's cvplot. It works similar but cannot be extended with custom drawables.

Comments

[Miki]

The plot module is in the contrib modules. You need to rebuild OpenCV to use it

[api55]

this plot library is in opencv contrib library, other than that one, there is no direct way of doing it, manually you can do it, if you see the examples of histogram calculation, you will see line plot there... Nevertheless, I would recommend to use any other library for this purpose, since OpenCV alternatives usually look pretty bad

[DivyaMaheswaran]

Alright guys, thank you. Looks like there is a additional setup process to add the contributing modules. I will try doing that and also take into account that there are better libraries to plot graphs.

[sturkmen]

you can test it without compiling contrib module. here is the test code

[DivyaMaheswaran]

@sturkmen please have a look at my answer below. Thanks for your awesome solution.

[DivyaMaheswaran]

@sturkmen Is there a way to scale the graph?

[sturkmen]

you can use setMinX,setMinY,setMaxX,setMaxY i think change of these values works to scale the graph.

[DivyaMaheswaran]

Ptr<plot::Plot2d> plot = plot::Plot2d::create(data); plot->setPlotBackgroundColor(Scalar(50, 50, 50)); plot->setPlotLineColor(Scalar(50, 50, 255)); plot->setMinX(0); plot->setMinY(0); plot->setMaxX(4000); plot->setMaxY(1000); plot->render(plot_result); imshow("Graph", plot_result); waitKey(); return 0; }

[DivyaMaheswaran]

@sturkmen including the above codes doesn't scale the graph. Is this what you meant?

[sturkmen]

could you post screenshots of graph before adding this code and after

[DivyaMaheswaran]

All it does is it sets the value for X and Y axis but I wanted the axis numbering on the graph. Anyway, I used GNUPlot to plot a graph. Now, I am trying to LOG the graphical data using BOOST C++. I have posted a question stackoverflow.com/questions/46282226/… on this. Please have a look and give me your valuable suggestion genius.

[sturkmen]

plot module still needs some improvements. you can share your remarks about using it in the related issue page

[mereth]

really helpful for plotting graphs using only opencv, thanks

[KansaiRobot]

Can it be used to put plots inside an image or a video? ( I mean inside each frame)

[palfi]

@KansaiRobot yes. e.g. video.read(frame); axes.render(frame(someRect)); github.com/Profactor/cv-plot/blob/master/CvPlot/inc/CvPlot/c‌​ore/…