Add libglitter_get_colour_space_conversion_matrix_{double,float}

Signed-off-by: Mattias Andrée <maandree@kth.se>

4 files changed, 159 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index e36b3fb..4731a2f 100644
--- a/Makefile
+++ b/Makefile
@@ -27,6 +27,8 @@ OBJ =\
 	libglitter_desaturate_float.o\
 	libglitter_create_render_context.o\
 	libglitter_free_render_context.o\
+	libglitter_get_colour_space_conversion_matrix_double.o\
+	libglitter_get_colour_space_conversion_matrix_float.o\
 	libglitter_update_render_context.o
 
 HDR =\
diff --git a/libglitter.h b/libglitter.h
index 0fc5888..4cd64bf 100644
--- a/libglitter.h
+++ b/libglitter.h
@@ -7,6 +7,14 @@
 
 
 /**
+ * The CIE xyY values of the D65 illuminant
+ */
+#define LIBGLITTER_ILLUMINANT_D65\
+	0.312726871026564878786047074755,\
+	0.329023206641284038376227272238, 1.0\
+
+
+/**
  * Rendering context for an input raster's specifications
  * 
  * Render context's are thread-safe, however updating them are not
@@ -183,4 +191,38 @@ void libglitter_desaturate_double(double **, size_t, size_t, size_t, size_t, siz
 void libglitter_desaturate_float(float **, size_t, size_t, size_t, size_t, size_t, float, const float *);
 
 
+/**
+ * Get the matrix each pixel shall be multiplied with
+ * to convert it from the output's colour space to sRGB
+ * 
+ * This is useful when the output does not use sRGB,
+ * but the application does
+ * 
+ * @param  matrix   Output buffer for the conversion matrix
+ * @param  c1x      The CIE x value (as in CIE xyY) of the output's first primary colour
+ * @param  c1y      The CIE y value (as in CIE xyY) of the output's first primary colour
+ * @param  c2x      The CIE x value (as in CIE xyY) of the output's second primary colour
+ * @param  c2y      The CIE y value (as in CIE xyY) of the output's second primary colour
+ * @param  c3x      The CIE x value (as in CIE xyY) of the output's third primary colour
+ * @param  c3y      The CIE y value (as in CIE xyY) of the output's third primary colour
+ * @param  white_x  The CIE x value (as in CIE xyY) of the output's white point
+ * @param  white_y  The CIE y value (as in CIE xyY) of the output's white point
+ * @param  white_Y  The CIE Y value (as in CIE xyY) of the output's white point
+ * 
+ * `LIBGLITTER_ILLUMINANT_D65` can be input in place of
+ * `white_x, white_y, white_Y` (it expands to three arguments)
+ * if the output's whitepoint is the D65 illuminant
+ */
+void libglitter_get_colour_space_conversion_matrix_double(double[3][3], double, double, double, double,
+                                                          double, double, double, double, double);
+
+/**
+ * This value is identical to `libglitter_get_colour_space_conversion_matrix_double`,
+ * apart from it parameter types, see `libglitter_get_colour_space_conversion_matrix_double`
+ * for details about this function
+ */
+void libglitter_get_colour_space_conversion_matrix_float(float[3][3], float, float, float, float,
+                                                         float, float, float, float, float);
+
+
 #endif
diff --git a/libglitter_get_colour_space_conversion_matrix_double.c b/libglitter_get_colour_space_conversion_matrix_double.c
new file mode 100644
index 0000000..fd3ecbc
--- /dev/null
+++ b/libglitter_get_colour_space_conversion_matrix_double.c
@@ -0,0 +1,90 @@
+/* See LICENSE file for copyright and license details. */
+#include "common.h"
+
+#define X(x, y) ((x) / (y))
+#define Z(x, y) ((1 - (x)) / (y) - 1)
+
+
+#if defined(__GNUC__) && !defined(__clang__)
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wunsuffixed-float-constants"
+#endif
+
+
+/**
+ * CIE XYZ-to-sRGB conversion matrix
+ */
+static const double srgb[3][3] = {
+	{ 3.240446254647737056586720427731, -1.537134761820080353089679192635, -0.498530193022728773666329971093},
+	{-0.969266606244679751469561779231,  1.876011959788370209167851498933,  0.041556042214430065351304932619},
+	{ 0.055643503564352832235773149705, -0.204026179735960239147729566866,  1.057226567722703292062647051353}};
+
+
+#if defined(__GNUC__) && !defined(__clang__)
+# pragma GCC diagnostic pop
+#endif
+
+
+static void
+invert(double m[3][4])
+{
+	double t;
+	size_t i;
+
+	/* Set m[0][0] = 1 */ for (t = m[0][0], i = 0; i < 4; i++)  m[0][i] /= t;
+	/* Set m[1][0] = 0 */ for (t = m[1][0], i = 0; i < 4; i++)  m[1][i] -= t * m[0][i];
+	/* Set m[2][0] = 0 */ for (t = m[2][0], i = 0; i < 4; i++)  m[2][i] -= t * m[0][i];
+
+	/* Set m[1][1] = 1 */ for (t = m[1][1], i = 1; i < 4; i++)  m[1][i] /= t;
+	/* Set m[2][1] = 0 */ for (t = m[2][1], i = 1; i < 4; i++)  m[2][i] -= t * m[1][i];
+	/* Set m[0][1] = 0 */ for (t = m[0][1], i = 1; i < 4; i++)  m[0][i] -= t * m[1][i];
+
+	/* Set m[2][2] = 1 */ for (t = m[2][2], i = 2; i < 4; i++)  m[2][i] /= t;
+	/* Set m[1][2] = 0 */ for (t = m[1][2], i = 2; i < 4; i++)  m[1][i] -= t * m[2][i];
+	/* Set m[0][2] = 0 */ for (t = m[0][2], i = 2; i < 4; i++)  m[0][i] -= t * m[2][i];
+}
+
+
+void
+libglitter_get_colour_space_conversion_matrix_double(double matrix[3][3], double c1x, double c1y,
+                                                     double c2x, double c2y, double c3x, double c3y,
+                                                     double white_x, double white_y, double white_Y)
+{
+	double mat[3][4];
+	double x1, x2, x3;
+	double y1, y2, y3;
+	double z1, z2, z3;
+
+	/* Get colour space in CIE XYZ */
+	mat[0][0] = x1 = X(c1x, c1y);
+	mat[0][1] = x2 = X(c2x, c2y);
+	mat[0][2] = x3 = X(c3x, c3y);
+	mat[1][3] = X(white_x, white_y) * white_Y;
+	mat[1][0] = 1;
+	mat[1][1] = 1;
+	mat[1][2] = 1;
+	mat[1][3] = white_Y;
+	mat[2][0] = z1 = Z(c1x, c1y);
+	mat[2][1] = z2 = Z(c2x, c2y);
+	mat[2][2] = z3 = Z(c3x, c3y);
+	mat[2][3] = Z(white_x, white_y) * white_Y;
+	invert(mat);
+	y1 = mat[0][3];
+	y2 = mat[1][3];
+	y3 = mat[2][3];
+
+	/* [[x1, x2, x3], [y1, y2, y3], [z1, z2, z3]] is
+	 * the output RGB-to-CIE XYZ conversion matrix. It
+	 * is multiplied by the CIE XYZ-to-sRGB conversion
+	 * matrix to get the output RGB-to-sRGB conversion
+	 * matrix. */
+	matrix[0][0] = x1 * srgb[0][0] + x2 * srgb[1][0] + x3 * srgb[2][0];
+	matrix[0][1] = x1 * srgb[0][1] + x2 * srgb[1][1] + x3 * srgb[2][1];
+	matrix[0][2] = x1 * srgb[0][2] + x2 * srgb[1][2] + x3 * srgb[2][2];
+	matrix[1][0] = y1 * srgb[0][0] + y2 * srgb[1][0] + y3 * srgb[2][0];
+	matrix[1][1] = y1 * srgb[0][1] + y2 * srgb[1][1] + y3 * srgb[2][1];
+	matrix[1][2] = y1 * srgb[0][2] + y2 * srgb[1][2] + y3 * srgb[2][2];
+	matrix[2][0] = z1 * srgb[0][0] + z2 * srgb[1][0] + z3 * srgb[2][0];
+	matrix[2][1] = z1 * srgb[0][1] + z2 * srgb[1][1] + z3 * srgb[2][1];
+	matrix[2][2] = z1 * srgb[0][2] + z2 * srgb[1][2] + z3 * srgb[2][2];
+}
diff --git a/libglitter_get_colour_space_conversion_matrix_float.c b/libglitter_get_colour_space_conversion_matrix_float.c
new file mode 100644
index 0000000..022c2a4
--- /dev/null
+++ b/libglitter_get_colour_space_conversion_matrix_float.c
@@ -0,0 +1,25 @@
+/* See LICENSE file for copyright and license details. */
+#include "common.h"
+
+
+void
+libglitter_get_colour_space_conversion_matrix_float(float matrix[3][3], float c1x, float c1y,
+                                                    float c2x, float c2y, float c3x, float c3y,
+                                                    float white_x, float white_y, float white_Y)
+{
+	double double_matrix[3][3];
+	libglitter_get_colour_space_conversion_matrix_double(double_matrix,
+	                                                     (double)c1x, (double)c1y,
+	                                                     (double)c2x, (double)c2y,
+	                                                     (double)c3x, (double)c3y,
+	                                                     (double)white_x, (double)white_y, (double)white_Y);
+	matrix[0][0] = (float)double_matrix[0][0];
+	matrix[0][1] = (float)double_matrix[0][1];
+	matrix[0][2] = (float)double_matrix[0][2];
+	matrix[1][0] = (float)double_matrix[1][0];
+	matrix[1][1] = (float)double_matrix[1][1];
+	matrix[1][2] = (float)double_matrix[1][2];
+	matrix[2][0] = (float)double_matrix[2][0];
+	matrix[2][1] = (float)double_matrix[2][1];
+	matrix[2][2] = (float)double_matrix[2][2];
+}