color-util

A header-only C++11 library for handling colors, including color space converters between RGB, XYZ, Lab, etc. and color difference calculators such as CIEDE2000.

Color Space Convertors

• Conversion between RGB and HSL
  • color-util/RGB_to_HSL.hpp
  • color-util/HSL_to_RGB.hpp
• Conversion between sRGB and CIEXYZ (D65)
  • color-util/RGB_to_XYZ.hpp
  • color-util/XYZ_to_RGB.hpp
• Conversion between CIEXYZ (D65) and CIELAB (a.k.a. CIE L*a*b*) (D65)
  • color-util/XYZ_to_Lab.hpp
  • color-util/Lab_to_XYZ.hpp

Color Difference Calculators

CIE76

Given two CIELAB colors, calculate_CIE76 calculates a perceptual difference between these two colors based on a metric called CIE76. This function is defined in color-util/CIE76.hpp.

It is known that this metric is not perceptually uniform especially with saturated colors. In general, CIEDE2000 is considered as a better choice.

CIEDE2000

Given two CIELAB colors, calculate_CIEDE2000 calculates a perceptual difference between these two colors based on a metric called CIEDE2000. This function is defined in color-util/CIEDE2000.hpp.

The correctness of the implementation is verified through the test dataset provided by Gaurav Sharma https://hajim.rochester.edu/ece/sites/gsharma/ciede2000/.

Dependency

• Eigen http://eigen.tuxfamily.org/

Installation

color-util is a header-only library, so it can be used by just copying the directory named color-util to the include directory of the target project. No need to build it in advance.

For CMake https://cmake.org/ users, this repository includes CMakeLists.txt; it can be installed by

cmake [PATH_TO_THIS_REPOSITORY] -DCMAKE_INSTALL_PREFIX=[PATH_TO_INSTALL_DIRECTORY]
make install

Alternatively, if the target project is also managed by CMake, the ExternalProject_Add command is also useful.

Example

Here is an example code for calculating a perceptual distance of two sRGB colors. First, include necessary headers:

#include <color-util/RGB_to_XYZ.hpp>
#include <color-util/XYZ_to_Lab.hpp>
#include <color-util/CIEDE2000.hpp>

Define the target colors in sRGB:

colorutil::RGB rgb_color_1(200.0 / 255.0, 100.0 / 255.0, 20.0 / 200.0);
colorutil::RGB rgb_color_2(100.0 / 255.0, 200.0 / 255.0, 50.0 / 200.0);

CIEDE2000 requires CIELAB colors as input, so convert them to CIELAB via CIEXYZ:

colorutil::XYZ xyz_color_1 = colorutil::convert_RGB_to_XYZ(rgb_color_1);
colorutil::XYZ xyz_color_2 = colorutil::convert_RGB_to_XYZ(rgb_color_2);
colorutil::Lab lab_color_1 = colorutil::convert_XYZ_to_Lab(xyz_color_1);
colorutil::Lab lab_color_2 = colorutil::convert_XYZ_to_Lab(xyz_color_2);

Finally, calculate the perceptual distance of the two colors:

double difference = colorutil::calculate_CIEDE2000(lab_color_1, lab_color_2);

In this case, it returns 53.8646 as the perceptual distance between the two colors.

License

MIT License.

Contribute

Pull requests are welcome.