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211 lines
10 KiB
Markdown
211 lines
10 KiB
Markdown
# Example (JKQTPlotter): Image Plots with Custom Palettes {#JKQTPlotterImagePlotUserPalette}
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This project (see `./examples/imageplot_userpal/`) demonstrates how to use user-defined color-palettes for image plots.
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The source code of the main application is (see [`imageplot_userpal.cpp`](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/imageplot_userpal/imageplot_userpal.cpp)).
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# Build Palettes Programmatically
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JKQTPlotter comes with a large set of predefined color palettes, which are enumerated in `JKQTPMathImageColorPalette`.
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In addition you can build your own palettes as simple lookup-tables of type `JKQTPImageTools::LUTType` (which is a `QVector<QRgb>`) and register them in the system (using `JKQTPImageTools::registerPalette()`). There are several options available for building such a palette:
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1. you can simply define a palette from single colors:
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```.cpp
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JKQTPImageTools::LUTType pal{
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QColor("blue").rgb(),
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QColor("green").rgb(),
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QColor("white").rgb(),
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QColor("yellow").rgb(),
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QColor("red").rgb(),
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QColor("red").rgb()
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};
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```
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Such a palette will have exactly as many entries, as you specified: 
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2. Alternatively you can build a palette from a set of colors with assocziated positions on the values axis (typically 0..1 as these are in any way later mapped to the actual data range):
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```.cpp
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QList<QPair<double, QRgb> > palsteps2;
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palsteps2<<qMakePair<double, QRgb>(0.00, QColor("blue").rgba());
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palsteps2<<qMakePair<double, QRgb>(0.05, QColor("green").rgba());
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palsteps2<<qMakePair<double, QRgb>(0.45, QColor("white").rgba());
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palsteps2<<qMakePair<double, QRgb>(0.55, QColor("yellow").rgba());
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palsteps2<<qMakePair<double, QRgb>(0.95, QColor("red").rgba());
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palsteps2<<qMakePair<double, QRgb>(1.00, QColor("red").rgba());
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pal=JKQTPBuildColorPaletteLUT(palsteps2, JKQTPImageTools::LUTSIZE);
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```
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Such a palette will have `JKQTPImageTools::LUTSIZE (=255)` entries and the colors are not spaced equally: 
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3. The palettes so far had steps, but you can also give a series of nodes with positions (on the value axis) and RGB-colors there (e.g. `palsteps2` above) but then linearly interpolate between these by calling:
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```.cpp
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pal=JKQTPBuildColorPaletteLUTLinInterpolate(palsteps2, JKQTPImageTools::LUTSIZE);
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```
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The resulting LUT is then: 
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4. Finally there is a second way of linear interpolation, where linear segments are given for the three color channels separately. To use such a definition, call `JKQTPBuildColorPaletteLUTLinSegments` instead (see documenttaion there).
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For each of these options, you finally call `JKQTPImageTools::registerPalette()` to make them known to the system:
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```.cpp
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int userpalette_id=JKQTPImageTools::registerPalette("userpal_computer_readable_name", pal, QObject::tr("User Palette Human-Readable Name"));
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```
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This function returns an integer, which you can cast to a `JKQTPMathImageColorPalette` to use your new palette:
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```.cpp
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JKQTPColumnMathImage* graph=new JKQTPColumnMathImage(plot);
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// ...
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graph->setColorPalette(static_cast<JKQTPMathImageColorPalette>(userpalette_id));
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```
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# Load Palettes from Files
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In addition to building palettes/LUTs programmatically, as shown above, you can simply load palettes from files using:
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```.cpp
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JKQTPImageTools::registerPalettesFromFile(":/usercolorpalettes/palettes/All_idl_cmaps.xml");
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```
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This function may load different file formats (discriminated by the extension):
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1. XML-files (extension `.xml`) may contain one or more color palettes and should be formatted as follows:
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```.xml
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<ColorMap name="PALETTENAME" space="RGB">
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<Point x="scalar" r="RED" g="GREEN" b="BLUE"/>
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<Point x="scalar" r="RED" g="GREEN" b="BLUE"/>
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...
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</ColorMap>
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```
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or with several palettes in one file:
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```.xml
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<ColorMaps>
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<ColorMap name="PALETTENAME" space="RGB">
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<Point x="scalar" r="RED" g="GREEN" b="BLUE"/>
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<Point x="scalar" r="RED" g="GREEN" b="BLUE"/>
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...
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</ColorMap>
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<ColorMap name="PALETTENAME" space="RGB">
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<Point x="scalar" r="RED" g="GREEN" b="BLUE"/>
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<Point x="scalar" r="RED" g="GREEN" b="BLUE"/>
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...
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</ColorMap>
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...
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</ColorMaps>
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```
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2. CSV-files (extensions `.csv`, `.rgb`, `.pal`) are simply a list of 3 or 4 comma-separated values:
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```
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red, green, blue
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red, green, blue
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...
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```
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or:
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```
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scalar, red, green, blue
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scalar, red, green, blue
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...
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```
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By default the palettes are simply read from the files as raw data. Alternatively you can linearly interpolate between the nodes in the file by calling
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```.cpp
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JKQTPImageTools::registerPalettesFromFile(":/usercolorpalettes/palettes/All_idl_cmaps.xml", true);
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```
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Examples for such palette files can be found here: [/examples/imageplot_userpal/palettes/](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/imageplot_userpal/palettes/)
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# Main Program of the Example (GUI)
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The rest of the example program [`imageplot_userpal.cpp`](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/imageplot_userpal/imageplot_userpal.cpp) just generates a 2D function plot as a color-map and displays it ...
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```.cpp
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// 1. create a window containing a plotter and a combobox to select the color palette
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// ... and get a pointer to the internal datastore (for convenience)
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QWidget win;
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QVBoxLayout* lay=new QVBoxLayout();
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win.setLayout(lay);
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JKQTPMathImageColorPaletteComboBox* cmbPalette=new JKQTPMathImageColorPaletteComboBox(&win);
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lay->addWidget(cmbPalette);
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JKQTPlotter* plot=new JKQTPlotter(&win);
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lay->addWidget(plot);
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JKQTPDatastore* ds=plot->getDatastore();
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// 2. now we create data for the charts (taken from https://commons.wikimedia.org/wiki/File:Energiemix_Deutschland.svg)
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const int NX=100; // image dimension in x-direction [pixels]
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const int NY=NX; // image dimension in x-direction [pixels]
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const double dx=0.6e-2; // size of a pixel in x-direction [micrometers]
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const double dy=0.6e-2; // size of a pixel in x-direction [micrometers]
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// 2.1 Parameters for airy disk plot (see https://en.wikipedia.org/wiki/Airy_disk)
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double NA=1.1; // numerical aperture of lens
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double wavelength=488e-3; // wavelength of the light [micrometers]
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// 2.2 calculate image of airy disk in a row-major array and immediately store the values
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// in a new image column cAiryDisk
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size_t cAiryDisk=ds->addCalculatedImageColumn(NX, NY, [&](size_t ix, size_t iy)->double {
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double x=static_cast<double>(static_cast<int>(ix)-NX/2)*dx;
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double y=static_cast<double>(static_cast<int>(iy)-NY/2)*dy;
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const double r=sqrt(x*x+y*y);
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const double v=2.0*M_PI*NA*r/wavelength;
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if (ix==NX/2 && iy==NY/2) return 1.0;
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else return pow(2.0*j1(v)/v, 2);
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}, "imagedata");
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// 3. create a graph (JKQTPColumnMathImage) with the column created above as data
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// The data is color-coded with the color-palette JKQTPMathImageMATLAB
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// the converted range of data is determined automatically because setAutoImageRange(true)
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JKQTPColumnMathImage* graph=new JKQTPColumnMathImage(plot);
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graph->setTitle("default MATLAB palette");
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// set the image column with the data
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graph->setImageColumn(cAiryDisk);
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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(1);
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graph->setHeight(1);
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// color-map is taken from cmbPalette
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plot->connect(cmbPalette, &JKQTPMathImageColorPaletteComboBox::currentPaletteChanged,[&](JKQTPMathImageColorPalette p) { graph->setColorPalette(p); plot->redrawPlot(); });
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cmbPalette->setCurrentColorPalette(graph->getPalette());
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// 4. add the graphs to the plot, so it is actually displayed
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plot->addGraph(graph);
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// 5. fix axis and plot aspect ratio to 1
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plot->getPlotter()->setMaintainAspectRatio(true);
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plot->getPlotter()->setMaintainAxisAspectRatio(true);
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// 6. autoscale the plot so the graph is contained
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plot->zoomToFit();
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// 8. show plotter and make it a decent size
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win.show();
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win.resize(500,550);
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win.setWindowTitle("JKQTPColumnMathImage, User Palettes");
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```
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...along with a `JKQTPMathImageColorPaletteComboBox` to select a colormap and redraw the plot:
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```.cpp
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JKQTPMathImageColorPaletteComboBox* cmbPalette=new JKQTPMathImageColorPaletteComboBox(&win);
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// ...
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plot->connect(cmbPalette, &JKQTPMathImageColorPaletteComboBox::currentPaletteChanged,[&](JKQTPMathImageColorPalette p) { graph->setColorPalette(p); plot->redrawPlot(); });
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cmbPalette->setCurrentColorPalette(graph->getPalette());
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```
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It also adds two `QPushButton`s that allow to save the current or all registered color-palettes to small PNG-Files:
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```.cpp
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QPushButton* btnSavePal=new QPushButton(QObject::tr("save current palette"), &win);
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btnSavePal->connect(btnSavePal, &QPushButton::clicked, [&]() {
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auto img=JKQTPImageTools::GetPaletteImage(cmbPalette->currentColorPalette(), JKQTPImageTools::LUTSIZE, 16);
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img.save(JKQTPImageTools::JKQTPMathImageColorPalette2String(cmbPalette->currentColorPalette())+".png");
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});
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lay->addWidget(btnSavePal);
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QPushButton* btnSaveAllPal=new QPushButton(QObject::tr("save all palettes"), &win);
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btnSavePal->connect(btnSaveAllPal, &QPushButton::clicked, [&]() {
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for (auto pn: JKQTPImageTools::getPredefinedPalettes()) {
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auto p=JKQTPImageTools::String2JKQTPMathImageColorPalette(pn);
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auto img=JKQTPImageTools::GetPaletteImage(p, JKQTPImageTools::LUTSIZE, 16);
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img.save("palette_"+JKQTPImageTools::JKQTPMathImageColorPalette2String(p)+".png");
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}
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});
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lay->addWidget(btnSaveAllPal);
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```
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The whole program looks like this:
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