SciColorMaps

Simple and convenient library providing custom .NET color maps (user-defined or imported from matplotlib) for scientific visualization.

Library comes in two versions (also available as NuGet packages):

• SciColorMaps.Portable.dll does not rely on any framework-dependent color structure (like System.Drawing.Color or System.Windows.Media.Color). It operates with pure byte arrays, so it can be used in any .NET project.

• SciColorMaps.dll provides some additional functions that handle GDI+ colors, so it can be used in WinForms and WPF projects.

NuGet packages contain binaries with all 75 matplotlib colormaps included. In most cases only a small subset of them is what is really needed. Luckily, SciColorMaps can be customized and recompiled quite easily. This repo includes special helper script for making your own SciColorMaps dll. Please read instructions here how to use it.

Base ColorMap class

Usage example:

// create 'viridis' colormap with 256 colors, mapping values from range [0, 1]
var cmap1 = new ColorMap();

// create 'rainbow' colormap with 256 colors, mapping values from range [0, 1]
var cmap2 = new ColorMap("rainbow");

// create 'gnuplot' colormap with 256 colors, mapping values from range [-7.5, 7.5]
var cmap3 = new ColorMap("gnuplot", -7.5, 7.5);

// create 'coolwarm' colormap with 64 colors, mapping values from range [10, 100]
var cmap = new ColorMap("coolwarm", 10, 100, 64);

// get color corresponding to value 25
var color = cmap[25];

// print names of all available predefined palettes
foreach (var palette in ColorMap.Palettes)
{
    Console.WriteLine(palette);
}

// prints full set of 75 matplotlib colormaps:
// accent
// afmhot
// autumn
// ...
// ylorbr
// ylorrd

User-defined colormaps

Users can create their own color palettes, like this:

// === works for both versions of SciColorMaps ===

var rgbs = new [] { 
                    new byte[] {0, 0, 0},
                    new byte[] {192, 0, 0},
                    new byte[] {255, 224, 255}
                  };
var positions = new float[] { 0, 0.4f, 1 };

// 1) static factory method with default colormap parameters:
var cmap1 = ColorMap.CreateFromColors(rgbs, positions);

// 2) static factory method, full set of parameters:
var cmap2 = ColorMap.CreateFromColors(rgbs, positions, 10, 100, 32);

// 3) ColorMap constructor:
var cmap3 = new ColorMap("my_own_colormap", -2, 2, 128, rgbs, positions);


// === won't compile for SciColorMaps.Portable ===

var colors = new Color[] { Color.Black, Color.Blue, Color.White };

// 4) static factory method with default colormap parameters:
var cmap4 = ColorMap.CreateFromColors(colors, positions);

// 5) static factory method, full set of parameters:
var cmap5 = ColorMap.CreateFromColors(colors, positions, 10, 100, 32);

// 6) ColorMap constructor:
var cmap6 = new ColorMap("fancy_colormap", 10, 100, 32, colors, positions);

Options 3 and 6 allow user setting the name of the custom colormap. Otherwise the name is set by default: "user".

Note also, the first color position should be 0.0f and last position should be 1.0f (otherwise an ArgumentException will be thrown).

Byte arrays can be easily converted to any framework-specific color structures/classes.

For example, in WPF the following extension method can be used:

using SciColorMaps.Portable;

public static class ColorUtils
{
    public static Color ToMediaColor(this byte[] rgb)
    {
        return Color.FromRgb(rgb[0], rgb[1], rgb[2]);
    }
}

...

var cmap = new ColorMap("ocean");
var color = cmap[0.3].ToMediaColor();

Grayscale colormaps

SciColorMaps provides the GrayColorMap decorator class. This class replaces base palette with its grayscale analog during construction.

Usage example:

// upper sreenshot
var cmap1 = new GrayColorMap(new ColorMap("gnuplot2", min, max));

// lower screenshot
var cmap2 = new GrayColorMap(new ColorMap("gnuplot2", min, max), GrayScaleOptions.Lightness);


// the three simple algorithms for conversion are implemented
// (as in GIMP: https://docs.gimp.org/2.6/en/gimp-tool-desaturate.html)

// public enum GrayScaleOptions
// {
//     Luminosity,      // gray = 0.21*R + 0.72*G + 0.07*B
//     Lightness,       // gray = (max(R, G, B) + min(R, G, B)) / 2
//     Average          // gray = (R + G + B) / 3
// }

// GrayScaleOptions.Luminosity is used by default

Mirrored colormaps

SciColorMaps also provides the MirrorColorMap decorator class. This class replaces base palette with its mirrored analog during construction.

Usage example:

// mirrored colors
var cmap = new MirrorColorMap(new ColorMap("ocean"));

WinForms demo app

Left button click on surface 2d area -> change colormap to its mirrored version.

Right button click on surface 2d area -> change colormap to its grayscale version.

Left button click on colormap strip -> open dialog for constructing your own palette.

WPF demo app

Shows how to use SciColorMaps.Portable.

UWP demo app

Shows how to use SciColorMaps.Portable in UWP projects.

The app allows loading sound from wav/mp3/mp4 files as well as recording sound from any input device (most likely, the microphone). When the audio signal is loaded, the app evaluates and visualizes its spectrogram in 2D and 3D. The visualization is based on the colormap selected in the left panel of a main page. Check it out: 3D-spectrogram with 'blues' colormap looks just like mountains in the fog ))

Compiling SciColorMaps

All customizable parameters are contained in Palette.cs file. So there's a helper script that can generate this file according to particular needs. Here's how to use it:

1. Download or clone this repo

2. Go to matplotlib folder and edit colormaps.txt text file, e.g.:

ocean
hot
coolwarm

Basically you include here only colormaps you really need. You can view all available colormap names in colormaps subfolder. If you specify non-existing colormap it'll be simply ignored.

Note also that 'viridis' will be included to the list anyway since it's the default modern colormap.

3. run generate_cs.py script:

python generate_cs.py [-r 16] [-p] [-a]

-r - colormap resolution (number of base colors; should be 8, 16, 32, 64, 128 or 256)

-p - if specified then generate cs file for portable SciColorMaps version

-a - if specified then generate cs file with all palettes found in colormaps folder (ignoring colormaps.txt input file)

Examples:

// generate cs file with all palettes found in colormaps folder 
// (ignore colormaps.txt) and resolution = 8 base colors

python generate_cs.py -r 8 -a


// generate cs file for portable version 
// (with default resolution = 16 base colors)

python generate_cs.py -p

4. go to cs subfolder and copy generated Palette.cs file to SciColorMaps or SciColorMaps.Portable project folder.

5. open SciColorMaps.sln in Visual Studio and compile new dll.

RECTANGULAR conditional compilation symbol

Accessing elements in jagged arrays is significantly faster (up to 40%) compared to rectangular arrays, hence the jagged arrays are used and compiled by default. If an efficient memory management is of more importance then compile SciColorMaps with the 'RECTANGULAR' conditional compilation symbol.

compilation	dll size
default	~95kb
RECTANGULAR	~29kb

Also, if you are worried about the memory usage, please note that palette arrays are instantiated lazily in the calling code, e.g.:

var palette = Palette.GnuPlot.Value;