JKQtPlotter/examples/rgbimageplot_cimg

Example (JKQTPlotter): Simple math image plot, showing a 3-channel CImg image

This project (see ./examples/rgbimageplot_cimg/) simply creates a JKQTPlotter widget (as a new window) and shows an RGB image read from a BMP-file. The image is generated as an cimg cimg_library::CImg<uint8_t> image and then copied into a single column of the internal datasdtore (JKQTPMathImage could be directly used without the internal datastore). To copy the data a special cimg Interface function JKQTPCopyCImgToColumn() is used, that copies the data from a CImg cimg_library::CImg<uint8_t> directly into a column.

The function JKQTPCopyCImgToColumn() is available from the (non-default) header-only extension from jkqtplotter/jkqtpinterfacecimg.h. This header provides facilities to interface JKQTPlotter with cimg. The cimg-binding itself is header-only, and NOT compiled into the JKQtPlotter libraries. Therefore you can simply include the header and use the facilities provided by it.

The CMake-build system of JKQtPlotter (and its examples) is compatible with both cimg 3.4.x and 4.x and uses the standard find_package(cimg) facilities provided by cimg to compile and bind against that library. If you want to build the cimg-based JKQtPlotter examples (see list above), you either have to ensure that CMake finds cimg by itself (i.e. somewhere in the default search paths), or you can set the CMake variable cimg_DIR so it points to the cimg directory before configuring JKQtPlotter.

The source code of the main application is (see rgbimageplot_cimg.cpp:

#include <QApplication>
#include <cmath>
#include "jkqtplotter/jkqtplotter.h"
#include "jkqtplotter/graphs/jkqtpscatter.h"
#include "jkqtplotter/graphs/jkqtpimagergb.h"
#include "jkqtplotter/jkqtpinterfacecimg.h"
#include "CImg.h"

int main(int argc, char* argv[])
{
    QApplication app(argc, argv);

    JKQTPlotter plot;


    // 1. create a plotter window and get a pointer to the internal datastore (for convenience)
    plot.getPlotter()->setUseAntiAliasingForGraphs(true); // nicer (but slower) plotting
    plot.getPlotter()->setUseAntiAliasingForSystem(true); // nicer (but slower) plotting
    plot.getPlotter()->setUseAntiAliasingForText(true); // nicer (but slower) text rendering
    JKQTPDatastore* ds=plot.getDatastore();


    // 2. now we open a BMP-file and load it into an cimg cv::Mat
    cimg_library::CImg<uint8_t> picture; // CImg<T>-Image for the data
    picture.load_bmp("rgbimageplot_cimg_example.bmp");
    qDebug()<<picture.width()<<"x"<<picture.height()<<"x"<<picture.spectrum();



    // 3. make data available to JKQTPlotter by adding it to the internal datastore.
    //    In this step the contents of each channel of the cimg cv::Mat is copied into a column
    //    of the datastore in row-major order
    size_t cPictureR=JKQTPCopyCImgToColumn(ds, picture, "R-channel", 0);
    size_t cPictureG=JKQTPCopyCImgToColumn(ds, picture, "G-channel", 1);
    size_t cPictureB=JKQTPCopyCImgToColumn(ds, picture, "B-channel", 2);


    // 4. create a graph (JKQTPColumnRGBMathImage) with the columns created above as data
    JKQTPColumnRGBMathImage* graph=new JKQTPColumnRGBMathImage(&plot);
    graph->setTitle("");
    // where does the image start in the plot, given in plot-axis-coordinates (bottom-left corner)
    graph->setX(0);
    graph->setY(0);
    // width and height of the image in plot-axis-coordinates
    graph->setWidth(picture.width());
    graph->setHeight(picture.height());
    // image column with the data
    graph->setImageRColumn(static_cast<int>(cPictureR));
    graph->setImageGColumn(static_cast<int>(cPictureG));
    graph->setImageBColumn(static_cast<int>(cPictureB));
    // determine min/max of each channel manually
    graph->setImageMinR(0);
    graph->setImageMaxR(255);
    graph->setImageMinG(0);
    graph->setImageMaxG(255);
    graph->setImageMinB(0);
    graph->setImageMaxB(255);



    // 5. add the graphs to the plot, so it is actually displayed
    plot.addGraph(graph);

    // 6. set axis labels
    plot.getXAxis()->setAxisLabel("x [pixels]");
    plot.getYAxis()->setAxisLabel("y [pixels]");
    // 6.1 invert y-axis, so image is oriented correctly
    plot.getYAxis()->setInverted(true);

    // 7. fix axis aspect ratio to width/height, so pixels are square
    plot.getPlotter()->setMaintainAspectRatio(true);
    plot.getPlotter()->setAspectRatio(double(picture.width())/double(picture.height()));

    // 8. autoscale the plot so the graph is contained
    plot.zoomToFit();

    // show plotter and make it a decent size
    plot.show();
    plot.resize(800,600);
    plot.setWindowTitle("JKQTPColumnRGBMathImage");



    return app.exec();
}

The result looks like this:

Note the step

    // 5.1 invert y-axis, so image is oriented correctly
    plot.getYAxis()->setInverted(true);

above, which ensures that the image is not draw upside-down! This will reorient the y-axis to point from top to bottom (for increasing positive coordinates). The image would be upside-down, because computer images use a coordinate system with 0 at the top-left (left-handed coordinate system) and the JKQTPlotter has its 0 at the bottom-left (right-handed coordinate system).

See examples/rgbimageplot for a detailed description of the other possibilities that the class JKQTPColumnRGBMathImage offer with respect to determining how an image is plotted.