htpp

commit 2b15a44864f5e10c61d96c5aea498d0282d3f4a2
parent 0508bdc98c9d4e91a606c93aa0f0604f5cfbd1e9
Author: Vincent Forest <vincent.forest@meso-star.com>
Date:   Tue,  2 Jul 2019 15:17:20 +0200

Merge branch 'release_0.2'

Diffstat:
M
README.md
 | 
6
++++++
M
cmake/CMakeLists.txt
 | 
2
+-
M
doc/htpp.1.txt
 | 
12
++++++------
M
src/htpp.c
 | 
34
+++++++++++++++++++---------------

4 files changed, 32 insertions(+), 22 deletions(-)
diff --git a/README.md b/README.md
@@ -29,6 +29,12 @@ informations on CMake.
 
 ## Release notes
 
+### Version 0.2
+
+- Fix the XYZ to sRGB conversion: the reference white was not correctly set.
+- Fix the gamma correction of the linear sRGB color: there was an issue in the
+used formulae.
+
 ### Version 0.1
 
 - Handle the update of the htrdr-image file format introduced by
diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
@@ -35,7 +35,7 @@ include_directories(${RSys_INCLUDE_DIR} ${CMAKE_CURRENT_BINARY_DIR})
 # Configure and define targets
 ################################################################################
 set(VERSION_MAJOR 0)
-set(VERSION_MINOR 1)
+set(VERSION_MINOR 2)
 set(VERSION_PATCH 0)
 set(VERSION ${VERSION_MAJOR}.${VERSION_MINOR}.${VERSION_PATCH})
 
diff --git a/doc/htpp.1.txt b/doc/htpp.1.txt
@@ -54,9 +54,9 @@ either defined by the user through the *-w* option or automatically computed
 as the luminance from which roughly all image pixels have a luminance less
 than _white-scale_. Currently, *htpp* empirically defines _white-scale_ as the
 luminance greater than the luminance of 99.5% of the pixels. Once tone mapped,
-the pixels are transformed from the CIE 1931 XYZ color space to the sRGB color
-space.  Finally, the resulting pixel components are clamped to [0, 1] and
-encoded on 8-bits.
+the pixels are transformed from the CIE 1931 XYZ color space to the sRGB
+linear color space before to be gamma corrected. Finally, the resulting pixel
+components are clamped to [0, 1] and encoded on 8-bits.
 
 OPTIONS
 -------
@@ -125,9 +125,9 @@ NOTES
 
 COPYRIGHT
 ---------
-Copyright &copy; 2018 CNRS, |Meso|Star> <contact@meso-star.com>, Université
-Paul Sabatier <contact-edstar@laplace.univ-tlse.fr>. *htpp* is free software
-released under the GPLv3+ license: GNU GPL version 3 or later
+Copyright &copy; 2018-2019 CNRS, |Meso|Star> <contact@meso-star.com>,
+Université Paul Sabatier <contact-edstar@laplace.univ-tlse.fr>. *htpp* is free
+software released under the GPLv3+ license: GNU GPL version 3 or later
 <https://gnu.org/licenses/gpl.html>. You are free to change and redistribute
 it. There is NO WARRANTY, to the extent permitted by law.
 
diff --git a/src/htpp.c b/src/htpp.c
@@ -285,32 +285,36 @@ filmic_tone_mapping(double pixel[3], const double exposure, const double Ymax)
 }
 
 static double*
-XYZ_to_RGB(double XYZ[3])
+XYZ_to_sRGB(double XYZ[3])
 {
-  const double mat[9] = { /* D65 */
+  #define D65_x 0.31271
+  #define D65_y 0.32902
+  const double D65[3] = {D65_x / D65_y, 1.0, (1 - D65_x - D65_y) / D65_y};
+  const double mat[9] = { /* XYZ to sRGB matrix */
      3.2404542, -0.9692660,  0.0556434,
     -1.5371385,  1.8760108, -0.2040259,
     -0.4985314,  0.0415560,  1.0572252
   };
-  double* RGB = XYZ;
+  double* sRGB = XYZ;
+  double* XYZ_D65 = XYZ;
   ASSERT(XYZ);
-  d33_muld3(RGB, mat, XYZ);
-  RGB[0] = MMAX(RGB[0], 0);
-  RGB[1] = MMAX(RGB[1], 0);
-  RGB[2] = MMAX(RGB[2], 0);
-  return RGB;
+  d3_mul(XYZ_D65, XYZ, D65);
+  d33_muld3(sRGB, mat, XYZ_D65);
+  sRGB[0] = MMAX(sRGB[0], 0);
+  sRGB[1] = MMAX(sRGB[1], 0);
+  sRGB[2] = MMAX(sRGB[2], 0);
+  return sRGB;
 }
 
 static double*
-RGB_to_sRGB(double RGB[3])
+sRGB_gamma_correct(double sRGB[3])
 {
-  double* sRGB = RGB;
   int i;
   FOR_EACH(i, 0, 3) {
-    if(RGB[i] <= 0.0031308) {
-      sRGB[i] = RGB[i] * 12.92;
+    if(sRGB[i] <= 0.0031308) {
+      sRGB[i] = sRGB[i] * 12.92;
     } else {
-      sRGB[i] = 1.055 * pow(RGB[i], 1.0/2.4);
+      sRGB[i] = 1.055 * pow(sRGB[i], 1.0/2.4) - 0.055;
     }
   }
   return sRGB;
@@ -566,8 +570,8 @@ main(int argc, char** argv)
 
     filmic_tone_mapping(pixel, args.exposure, Ymax); /* Tone map the RGB pixel */
     if(args.pixdata == PIXEL_RADIANCE) {
-      XYZ_to_RGB(pixel); /* Convert in RGB color space */
-      RGB_to_sRGB(pixel); /* Convert in sRGB color space (i.e. gamma correction) */
+      XYZ_to_sRGB(pixel); /* Convert in RGB color space */
+      sRGB_gamma_correct(pixel); /* Convert in sRGB color space (i.e. gamma correction) */
     }
   }