X-Git-Url: https://git.sesse.net/?p=movit;a=blobdiff_plain;f=white_balance_effect.cpp;fp=white_balance_effect.cpp;h=4c24cd210c9d098c8b549f5cd85b7e70cc12b698;hp=0000000000000000000000000000000000000000;hb=cfe0bc4fa1e2a56eeb12c33e596f79c1292292c8;hpb=24660d2111d0ee97228016a7072304ff657d297b diff --git a/white_balance_effect.cpp b/white_balance_effect.cpp new file mode 100644 index 0000000..4c24cd2 --- /dev/null +++ b/white_balance_effect.cpp @@ -0,0 +1,153 @@ +#include +#include + +#include "white_balance_effect.h" +#include "util.h" +#include "opengl.h" + +namespace { + +// Temperature is in Kelvin. Formula from http://en.wikipedia.org/wiki/Planckian_locus#Approximation . +void convert_color_temperature_to_xyz(float T, float *x, float *y, float *z) +{ + double invT = 1.0 / T; + double xc, yc; + + assert(T >= 1000.0f); + assert(T <= 15000.0f); + + if (T <= 4000.0f) { + xc = ((-0.2661239e9 * invT - 0.2343580e6) * invT + 0.8776956e3) * invT + 0.179910; + } else { + xc = ((-3.0258469e9 * invT + 2.1070379e6) * invT + 0.2226347e3) * invT + 0.240390; + } + + if (T <= 2222.0f) { + yc = ((-1.1063814 * xc - 1.34811020) * xc + 2.18555832) * xc - 0.20219683; + } else if (T <= 4000.0f) { + yc = ((-0.9549476 * xc - 1.37418593) * xc + 2.09137015) * xc - 0.16748867; + } else { + yc = (( 3.0817580 * xc - 5.87338670) * xc + 3.75112997) * xc - 0.37001483; + } + + *x = xc; + *y = yc; + *z = 1.0 - xc - yc; +} + +// Assuming sRGB primaries, from Wikipedia. +static const Matrix3x3 rgb_to_xyz_matrix = { + 0.4124, 0.2126, 0.0193, + 0.3576, 0.7152, 0.1192, + 0.1805, 0.0722, 0.9505, +}; + +/* + * There are several different LMS spaces, at least according to Wikipedia. + * Through practical testing, I've found most of them (like the CIECAM02 model) + * to yield a result that is too reddish in practice, possibly because they + * are intended for different illuminants than what sRGB assumes. + * + * This is the RLAB space, normalized to D65, which means that the standard + * D65 illuminant (x=0.31271, y=0.32902, z=1-y-x) gives L=M=S under this transformation. + * This makes sense because sRGB (which is used to derive those XYZ values + * in the first place) assumes the D65 illuminant, and so the D65 illuminant + * also gives R=G=B in sRGB. + */ +static const Matrix3x3 xyz_to_lms_matrix = { + 0.4002, -0.2263, 0.0, + 0.7076, 1.1653, 0.0, + -0.0808, 0.0457, 0.9182, +}; + +/* + * For a given reference color (given in XYZ space), + * compute scaling factors for L, M and S. What we want at the output is equal L, M and S + * for the reference color (making it a neutral illuminant), or sL ref_L = sM ref_M = sS ref_S. + * This removes two degrees of freedom for our system, and we only need to find fL. + * + * A reasonable last constraint would be to preserve Y, approximately the brightness, + * for the reference color. Since L'=M'=S' and the Y row of the LMS-to-XYZ matrix + * sums to unity, we know that Y'=L', and it's easy to find the fL that sets Y'=Y. + */ +static void compute_lms_scaling_factors(float x, float y, float z, float *scale_l, float *scale_m, float *scale_s) +{ + Matrix3x3 xyz_to_rgb_matrix; + invert_3x3_matrix(rgb_to_xyz_matrix, xyz_to_rgb_matrix); + + float l, m, s; + multiply_3x3_matrix_float3(xyz_to_rgb_matrix, x, y, z, &l, &m, &s); + + *scale_l = y / l; + *scale_m = *scale_l * (l / m); + *scale_s = *scale_l * (l / s); +} + +} // namespace + +WhiteBalanceEffect::WhiteBalanceEffect() + : neutral_color(0.5f, 0.5f, 0.5f), + output_color_temperature(6500.0f) +{ + register_vec3("neutral_color", (float *)&neutral_color); + register_float("output_color_temperature", &output_color_temperature); +} + +std::string WhiteBalanceEffect::output_fragment_shader() +{ + return read_file("white_balance_effect.frag"); +} + +void WhiteBalanceEffect::set_gl_state(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num) +{ + float x, y, z; + multiply_3x3_matrix_float3(rgb_to_xyz_matrix, neutral_color.r, neutral_color.g, neutral_color.b, &x, &y, &z); + + float l, m, s; + multiply_3x3_matrix_float3(xyz_to_lms_matrix, x, y, z, &l, &m, &s); + + float l_scale, m_scale, s_scale; + compute_lms_scaling_factors(x, y, z, &l_scale, &m_scale, &s_scale); + + /* + * Now apply the color balance. Simply put, we find the chromacity point + * for the desired white temperature, see what LMS scaling factors they + * would have given us, and then reverse that transform. For T=6500K, + * the default, this gives us nearly an identity transform (but only nearly, + * since the D65 illuminant does not exactly match the results of T=6500K); + * we normalize so that T=6500K really is a no-op. + */ + float white_x, white_y, white_z, l_scale_white, m_scale_white, s_scale_white; + convert_color_temperature_to_xyz(output_color_temperature, &white_x, &white_y, &white_z); + compute_lms_scaling_factors(white_x, white_y, white_z, &l_scale_white, &m_scale_white, &s_scale_white); + + float ref_x, ref_y, ref_z, l_scale_ref, m_scale_ref, s_scale_ref; + convert_color_temperature_to_xyz(6500.0f, &ref_x, &ref_y, &ref_z); + compute_lms_scaling_factors(ref_x, ref_y, ref_z, &l_scale_ref, &m_scale_ref, &s_scale_ref); + + l_scale *= l_scale_ref / l_scale_white; + m_scale *= m_scale_ref / m_scale_white; + s_scale *= s_scale_ref / s_scale_white; + + /* + * Concatenate all the different linear operations into a single 3x3 matrix. + * Note that since we postmultiply our vectors, the order of the matrices + * has to be the opposite of the execution order. + */ + Matrix3x3 lms_to_xyz_matrix, xyz_to_rgb_matrix; + invert_3x3_matrix(xyz_to_lms_matrix, lms_to_xyz_matrix); + invert_3x3_matrix(rgb_to_xyz_matrix, xyz_to_rgb_matrix); + + Matrix3x3 temp, temp2, corr_matrix; + Matrix3x3 lms_scale_matrix = { + l_scale, 0.0f, 0.0f, + 0.0f, m_scale, 0.0f, + 0.0f, 0.0f, s_scale, + }; + multiply_3x3_matrices(xyz_to_rgb_matrix, lms_to_xyz_matrix, temp); + multiply_3x3_matrices(temp, lms_scale_matrix, temp2); + multiply_3x3_matrices(temp2, xyz_to_lms_matrix, temp); + multiply_3x3_matrices(temp, rgb_to_xyz_matrix, corr_matrix); + + set_uniform_mat3(glsl_program_num, prefix, "correction_matrix", corr_matrix); +}