.. | ||
.gitignore | ||
example.bmp | ||
jkqtplotter_simpletest_rgbimageplot_opencv_and_lib.pro | ||
jkqtplotter_simpletest_rgbimageplot_opencv.cpp | ||
jkqtplotter_simpletest_rgbimageplot_opencv.pro | ||
README.md |
Example (JKQTPlotter): Simple RGB image plot, showing a 3-channel OpenCV cv::Mat
This project (see ./examples/simpletest_imageplot_opencv/
) 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 OpenCV cv::Mat
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 OpenCV Interface function JKQTPCopyCvMatToColumn()
is used, that copies the data from a (https://opencv.org/) cv::Mat
directly into a column.
The function JKQTPCopyCvMatToColumn()
is available from the (non-default) header-only extension from jkqtplotter/jkqtpopencvinterface.h
. This header provides facilities to interface JKQTPlotter with OpenCV.
The source code of the main application is (see jkqtplotter_simpletest_imageplot_opencv.cpp
:
#include <QApplication>
#include <cmath>
#include "jkqtplotter/jkqtplotter.h"
#include "jkqtplotter/graphs/jkqtpimage.h"
#include "jkqtplotter/jkqtpopencvinterface.h"
#include <opencv2/core.hpp>
#include <opencv2/imgcodecs.hpp>
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 OpenCV cv::Mat
cv::Mat picture = cv::imread("example.bmp");
// 3. make data available to JKQTPlotter by adding it to the internal datastore.
// In this step the contents of each channel of the openCV cv::Mat is copied into a column
// of the datastore in row-major order
size_t cPictureR=JKQTPCopyCvMatToColumn(ds, picture, "R-channel", 2);
size_t cPictureG=JKQTPCopyCvMatToColumn(ds, picture, "G-channel", 1);
size_t cPictureB=JKQTPCopyCvMatToColumn(ds, picture, "B-channel", 0);
// 4. create a graph (JKQTPColumnRGBMathImage) with the columns created above as data
JKQTPColumnRGBMathImage* graph=new JKQTPColumnRGBMathImage(&plot);
graph->setTitle("");
// set size of the data (the datastore does not contain this info, as it only manages 1D columns of data and this is used to assume a row-major ordering
graph->setNx(picture.cols);
graph->setNy(picture.rows);
// 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.cols);
graph->setHeight(picture.rows);
// image column with the data
graph->setImageRColumn(cPictureR);
graph->setImageGColumn(cPictureG);
graph->setImageBColumn(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]");
// 7. fix axis aspect ratio to width/height, so pixels are square
plot.getPlotter()->setMaintainAspectRatio(true);
plot.getPlotter()->setAspectRatio(double(picture.cols)/double(picture.rows));
// 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("JKQTPColumnMathImage");
return app.exec();
}
The result looks like this:
The image is 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).
You can modify the program above to display the image in the correct orientation, by adding the line
// 5.1 invert y-axis, so image is oriented correctly
plot.getYAxis()->setInverted(true);
This will reorient the y-axis to point from top to bottom (for increasing positive coordinates):