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103 lines
4.4 KiB
Markdown
103 lines
4.4 KiB
Markdown
# JKQtPlotter: Examples: Simple RGB image plot, showing a 3-channel OpenCV cv::Mat {#JKQtPlotterImagePlotRGBOpenCV}
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This project (see `./examples/simpletest_imageplot_opencv/`) simply creates a JKQtPlotter widget (as a new window) and adds a color-coded image plot of a mathematical function (here the Airy disk). 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).
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To copy the data a special OpenCV Interface function `JKQTPcopyCvMatToColumn()` is used, that copies the data from a cv::Mat directly into a column.
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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.
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The source code of the main application is (see [`jkqtplotter_simpletest_imageplot_opencv.cpp`](../simpletest_imageplot_opencv/jkqtplotter_simpletest_imageplot_opencv.cpp):
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```c++
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#include <QApplication>
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#include <cmath>
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#include "jkqtplotter/jkqtplotter.h"
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#include "jkqtplotter/jkqtpgraphsimage.h"
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#include "jkqtplotter/jkqtpopencvinterface.h"
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#include <opencv2/core.hpp>
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#include <opencv2/imgcodecs.hpp>
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int main(int argc, char* argv[])
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{
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QApplication app(argc, argv);
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JKQtPlotter plot;
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// 1. create a plotter window and get a pointer to the internal datastore (for convenience)
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plot.get_plotter()->set_useAntiAliasingForGraphs(true); // nicer (but slower) plotting
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plot.get_plotter()->set_useAntiAliasingForSystem(true); // nicer (but slower) plotting
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plot.get_plotter()->set_useAntiAliasingForText(true); // nicer (but slower) text rendering
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JKQTPdatastore* ds=plot.getDatastore();
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// 2. now we open a BMP-file and load it into an OpenCV cv::Mat
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cv::Mat picture = cv::imread("example.bmp");
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// 3. make data available to JKQtPlotter by adding it to the internal datastore.
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// In this step the contents of each channel of the openCV cv::Mat is copied into a column
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// of the datastore in row-major order
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size_t cPictureR=JKQTPcopyCvMatToColumn(ds, picture, "R-channel", 2);
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size_t cPictureG=JKQTPcopyCvMatToColumn(ds, picture, "G-channel", 1);
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size_t cPictureB=JKQTPcopyCvMatToColumn(ds, picture, "B-channel", 0);
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// 4. create a graph (JKQTPColumnRGBMathImage) with the columns created above as data
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JKQTPColumnRGBMathImage* graph=new JKQTPColumnRGBMathImage(&plot);
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graph->set_title("");
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// 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
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graph->set_Nx(picture.cols);
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graph->set_Ny(picture.rows);
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// where does the image start in the plot, given in plot-axis-coordinates (bottom-left corner)
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graph->set_x(0);
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graph->set_y(0);
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// width and height of the image in plot-axis-coordinates
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graph->set_width(picture.cols);
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graph->set_height(picture.rows);
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// image column with the data
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graph->set_imageRColumn(cPictureR);
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graph->set_imageGColumn(cPictureG);
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graph->set_imageBColumn(cPictureB);
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// determine min/max of each channel manually
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graph->set_imageMinR(0);
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graph->set_imageMaxR(255);
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graph->set_imageMinG(0);
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graph->set_imageMaxG(255);
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graph->set_imageMinB(0);
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graph->set_imageMaxB(255);
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// 5. add the graphs to the plot, so it is actually displayed
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plot.addGraph(graph);
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// 6. set axis labels
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plot.get_xAxis()->set_axisLabel("x [pixels]");
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plot.get_yAxis()->set_axisLabel("y [pixels]");
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// 7. fix axis aspect ratio to width/height, so pixels are square
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plot.get_plotter()->set_maintainAspectRatio(true);
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plot.get_plotter()->set_aspectRatio(double(picture.cols)/double(picture.rows));
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// 8. autoscale the plot so the graph is contained
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plot.zoomToFit();
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// show plotter and make it a decent size
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plot.show();
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plot.resize(800,600);
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plot.setWindowTitle("JKQTPColumnMathImage");
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return app.exec();
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}
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```
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The result looks like this:
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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).
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