Hi, On 11:09, Sat 26 Apr 08, Øyvind Kolås wrote: > On Fri, Apr 25, 2008 at 6:52 PM, Jan Heller <jan.heller@xxxxxxxxx> wrote: > > > I wrote it to better familiarize myself with > > Gegl and I am posting it here in hope it will be useful for > > others. > > I think it is a good operation to have, so I have commited a slightly > modified version to svn. Nice, thanks! > > GEGL and babl deals with the out of gamut handling themselves at a > later stage, during processing we preserve headroom and footroom. This > allows us to change the contrast of the image to bring details back in > later. The implemented gamut handling also seemed to introduce banding > that the conversions in babl does not. Good to know. > > It would also be nice to replace the planckian locus lookup table with > a function that approximates it. I played with MATLAB for a while and came up with rational functions of degree 5 that approximate the Planckian locus dataset reasonably well. Attached is a modified version of the operation using these approximations. Regards, Jan
/* This file is an image processing operation for GEGL * * GEGL is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 3 of the License, or (at your option) any later version. * * GEGL is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with GEGL; if not, see <http://www.gnu.org/licenses/>. * * Copyright 2008 Jan Heller <jan.heller (at) matfyz.cz> */ #ifdef GEGL_CHANT_PROPERTIES gegl_chant_double (original_temp, "Original temperature", 1000, 12000, 6500, "Estimated temperature of the light source in K the image was taken with.") gegl_chant_double (intended_temp, "Intended temperature", 1000, 12000, 6500, "Corrected estimation of the temperature of the light source in K.") #else #define GEGL_CHANT_TYPE_POINT_FILTER #define GEGL_CHANT_C_FILE "color-temperature.c" #include "gegl-chant.h" #define LOWEST_TEMPERATURE 1000 #define HIGHEST_TEMPERATURE 12000 gfloat rgb_r55[][12]; static void convert_k_to_rgb (gfloat temperature, gfloat *rgb) { gfloat nomin, denom; int channel, deg; if (temperature < LOWEST_TEMPERATURE) temperature = LOWEST_TEMPERATURE; if (temperature > HIGHEST_TEMPERATURE) temperature = HIGHEST_TEMPERATURE; /* Evaluation of an approximation of the Planckian locus in linear RGB space * by rational functions of degree 5 using Horner's scheme * f(x) = (p1*x^5 + p2*x^4 + p3*x^3 + p4*x^2 + p5*x + p6) / * (x^5 + q1*x^4 + q2*x^3 + q3*x^2 + q4*x + q5) */ for (channel = 0; channel < 3; channel++) { nomin = rgb_r55[channel][0]; for (deg = 1; deg < 6; deg++) nomin = nomin * temperature + rgb_r55[channel][deg]; denom = rgb_r55[channel][6]; for (deg = 1; deg < 6; deg++) denom = denom * temperature + rgb_r55[channel][6 + deg]; rgb[channel] = nomin / denom; } } static void prepare (GeglOperation *operation) { Babl *format = babl_format ("RGBA float"); gegl_operation_set_format (operation, "input", format); gegl_operation_set_format (operation, "output", format); } /* GeglOperationPointFilter gives us a linear buffer to operate on * in our requested pixel format */ static gboolean process (GeglOperation *op, void *in_buf, void *out_buf, glong n_pixels) { GeglChantO *o = GEGL_CHANT_PROPERTIES (op); gfloat *in_pixel; gfloat *out_pixel; gfloat original_temp, original_temp_rgb[3]; gfloat intended_temp, intended_temp_rgb[3]; gfloat coefs[3]; glong i; in_pixel = in_buf; out_pixel = out_buf; original_temp = o->original_temp; intended_temp = o->intended_temp; convert_k_to_rgb (original_temp, original_temp_rgb); convert_k_to_rgb (intended_temp, intended_temp_rgb); coefs[0] = original_temp_rgb[0] / intended_temp_rgb[0]; coefs[1] = original_temp_rgb[1] / intended_temp_rgb[1]; coefs[2] = original_temp_rgb[2] / intended_temp_rgb[2]; for (i = 0; i < n_pixels; i++) { out_pixel[0] = in_pixel[0] * coefs[0]; out_pixel[1] = in_pixel[1] * coefs[1]; out_pixel[2] = in_pixel[2] * coefs[2]; in_pixel += 4; out_pixel += 4; } return TRUE; } static void gegl_chant_class_init (GeglChantClass *klass) { GeglOperationClass *operation_class; GeglOperationPointFilterClass *point_filter_class; operation_class = GEGL_OPERATION_CLASS (klass); point_filter_class = GEGL_OPERATION_POINT_FILTER_CLASS (klass); point_filter_class->process = process; operation_class->prepare = prepare; operation_class->name = "color-temperature"; operation_class->categories = "color"; operation_class->description = "Allows changing the color temperature of an image."; } /* Coefficients of rational functions of degree 5 fitted per color channel to * the linear RGB coordinates of the range 1000K-12000K of the Planckian locus * with the 20K step. Original CIE-xy data from * * http://www.aim-dtp.net/aim/technology/cie_xyz/k2xy.txt * * converted to the linear RGB space assuming the ITU-R BT.709-5/sRGB primaries */ gfloat rgb_r55[][12] = {{ 6.9389923563552169e-01, 2.7719388100974670e+03, 2.0999316761104289e+07,-4.8889434162208414e+09, -1.1899785506796783e+07,-4.7418427686099203e+04, 1.0000000000000000e+00, 3.5434394338546258e+03, -5.6159353379127791e+05, 2.7369467137870544e+08, 1.6295814912940913e+08, 4.3975072422421846e+05 },{ 9.5417426141210926e-01, 2.2041043287098860e+03, -3.0142332673634286e+06,-3.5111986367681120e+03, -5.7030969525354260e+00, 6.1810926909962016e-01, 1.0000000000000000e+00, 1.3728609973644000e+03, 1.3099184987576159e+06,-2.1757404458816318e+03, -2.3892456292510311e+00, 8.1079012401293249e-01 },{ -7.1151622540856201e+10, 3.3728185802339764e+16, -7.9396187338868539e+19, 2.9699115135330123e+22, -9.7520399221734228e+22,-2.9250107732225114e+20, 1.0000000000000000e+00, 1.3888666482167408e+16, 2.3899765140914549e+19, 1.4583606312383295e+23, 1.9766018324502894e+22, 2.9395068478016189e+18 }}; #endif
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