rgb2spec is a small utility that converts an RGB color to a spectral distribution (SD). # Building and Installation ## Building rgb2spec is built by default when building Malia Rendering Framework. To build/rebuild only rgb2spec, use the dedicated Cmake target: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ bash cd /your/build/directory/ cmake /path/to/MRF/root/ make rgb2spec ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ !!! WARNING [Eigen3](https://gitlab.com/libeigen/eigen) is a required to build the rgb2spec tool. ## Installation As usual, installation is done by a simple: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ bash cd /your/build/directory/ make install ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ # Input Data Input can be either : - a triple (r,g,b) passed on the command line - an HDR image - a LDR image # Output data When passing a single color on the command line rgb2spec will save a text file that contains the spectral distribution. When passing an image, the output will be a spectral image (.hdr/.raw format), Any output of rgb2spec can be visualized in [SpectralViewer](https://adufay.gitlabpages.inria.fr/SpectralViewer/index.html). # Command line Options * -h or -help : prints a help message * -in_color {float,float, float} : Red Green Blue values * -in_file {string} : filename to a LDR or HDR image * -out {string} : filename where the spectrum will be saved. When not set, the default output is out.spd for a color input and out.hdr|raw for an image input. * -xyz_curves : allows to specify which CIE-XYZ sensitivity curves will be used. Possible values are : + CIE_1931_2DEG : the two degrees CIE standard observer curves from 1931 + CIE_XYZ_1964_10DEG : the 10 degrees CIE standard observer curves from 1964 by default the curves from 1931 are used. * -reflectivity : the color is assumed to represent a value associated with BRDF or reflectivity. Therefore, the spectral curve values should be in the range of [0,1] * -nbw {uint value} : number of wavelengths for the spectral image. The range 360 to 830 nm will be discreetized with the given number. # Caveats Remember that converting an hdr image to a spectral image can produce huge file. For example a 2K HDR image converted at 1nm resolution will generate a 3.7 GB file! # Performance Input Image | Conversion Timing | Wavelength Resolution | Architecture -------------|--------------------|-------------------------|----------------------------- [Pool 2K](https://hdrihaven.com/hdri/?h=pool) HDR | 0.584 seconds | 48 values equiv. 10nm | Intel i7-3770K CPU @ 3.50GHz [Pool 2K](https://hdrihaven.com/hdri/?h=pool) HDR | 7.12 seconds | 471 values equiv. 1nm | Intel i7-3770K CPU @ 3.50GHz # The Maths behind RGB2SPEC ********************************************************************************************* * .-------------. .-------------. .-------------. * | Non-Linear | | Linear | | CIE | .---------------. * | RGB +--+->| RGB +----+--+->| XYZ +------>+ Spectral | * | Color Space | | Color Space | | | SPACE | | Distribution | * '-------------' '-------------' | '-------------' '---------------' * Color Space * Illuminant * * *********************************************************************************************