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https://github.com/jkriege2/JKQtPlotter.git
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3050debd16
- added example for simple RGB math image plot with RGB/CMY-color mapping - fixed some of the OpenCV examples (improved QMake-project files)
114 lines
5.0 KiB
Markdown
114 lines
5.0 KiB
Markdown
# Example (JKQTPlotter): 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 shows an RGB image read from a BMP-file. The image is generated as an [OpenCV](https://opencv.org/) [`cv::Mat`](https://docs.opencv.org/4.0.0/d3/d63/classcv_1_1Mat.html) 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 (https://opencv.org/) [`cv::Mat`](https://docs.opencv.org/4.0.0/d3/d63/classcv_1_1Mat.html) 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`](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/simpletest_imageplot_opencv/jkqtplotter_simpletest_imageplot_opencv.cpp):
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```.cpp
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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.getPlotter()->setUseAntiAliasingForGraphs(true); // nicer (but slower) plotting
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plot.getPlotter()->setUseAntiAliasingForSystem(true); // nicer (but slower) plotting
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plot.getPlotter()->setUseAntiAliasingForText(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->setTitle("");
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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->setNx(picture.cols);
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graph->setNy(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->setX(0);
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graph->setY(0);
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// width and height of the image in plot-axis-coordinates
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graph->setWidth(picture.cols);
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graph->setHeight(picture.rows);
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// image column with the data
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graph->setImageRColumn(cPictureR);
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graph->setImageGColumn(cPictureG);
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graph->setImageBColumn(cPictureB);
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// determine min/max of each channel manually
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graph->setImageMinR(0);
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graph->setImageMaxR(255);
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graph->setImageMinG(0);
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graph->setImageMaxG(255);
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graph->setImageMinB(0);
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graph->setImageMaxB(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.getXAxis()->setAxisLabel("x [pixels]");
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plot.getYAxis()->setAxisLabel("y [pixels]");
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// 7. fix axis aspect ratio to width/height, so pixels are square
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plot.getPlotter()->setMaintainAspectRatio(true);
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plot.getPlotter()->setAspectRatio(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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You can modify the program above to display the image in the correct orientation, by adding the line
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```.cpp
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// 5.1 invert y-axis, so image is oriented correctly
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plot.getYAxis()->setInverted(true);
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```
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This will reorient the y-axis to point from top to bottom (for increasing positive coordinates):
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